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U.S. DEPARTMENT OF COMMENCE • W. Aveiell Harriman, Secretary

NATIONAL BUREAU OF STANDARDS E. U. Condon, Director

STRENGTH OF HOUSES

APPLICATION OF ENGINEERING PRINCIPLES

TO STRUCTURAL DESIGN

hy

Herbert L. Whittemore, John B. Cotter,

Ambrose H. Stang, and Vincent B. Phelan

Building Materials and Structures Report BMS109

Issued April 1, 1948

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 194S For Sale by the Superintendent of Documents, L'. S. Government Pruitinsj Offioe, Wasliington 25, D. C. Price S1V50
Foreword

strength of houses in the past has been made adequate by patterning

them after those which have withstood the test of service conditions.

Architects and builders of small structures have followed closely traditional methods handed down from the craftsmen of medieval England.

From these traditions, cities have crystallized building codes now enforced

under the police power of the community.

The trend for the immediate future seems to indicate houses so con- structed as to contribute in greater measure to the welfare of the occupants

by bringing more of the out-of-doors into the house. Wider windows to give more sunlight and allow stimulating vistas of garden, trees, and

flowing water; larger rooms and movable partitions; and walls, floors,

and roofs fabricated from plastics and from aluminum and magnesium

alloys are some of the improvements anticipated.

Library research failed to disclose rational methods for determining

the strength of present-day houses and little in that respect that could be

applied to house design for the future. This report is an attempt to apply

engineering methods to the design of houses for strength. Fundamental

data for wind, snow, and floor loads have been reviewed and convenient

methods developed for computing applied loads.

The engineering approach to strength of houses described in this report,

it is thought, will open the way for designers to introduce unconventional

materials and unusual methods of fabrication by determining in the

laboratory whether constructions have the n>jcessary strengths, thus

greatly shoi'tening the time required to develop and obtain acceptance of

new constructions for houses.

Some approach along rational lines is necessaiy if houses are to benefit

from the fund of technical infoiTnation now available on materials and

methods of manufacture being utilized for other commodities.

It is time that the strength of houses be given careful engineering scru- tiny — not because houses need be stronger, for few fail — but to judge

how much material is superfluous. Material is costly as is the labor

required to shape and fit it into place.

E. U. Condon, Director.

II
CONTENTS

Page

Foreword Il

I. Introduction 1

II. Outline of method for determining

strength of houses 3

1. Load 8

2. Design load 3

3. Racking load 3

4. Allowable load 3

III. Dead load 4 IV. Floor load 4 V. Wind load 5

1. General 5

2. Velocity pressure 5

3. Relation between velocity pressure and wind load 9

(a) Subcommittee No. 31, American Society of Civil Engineers 9 (b) External loads on buildings

with plane surfaces normal

to wind 10

(c) External loads on plane sur- faces inclined to wind 10

(1) Windward slope 10

(2) Leeward slope 10

(d) External loads on rounded

roof surfaces 10

(e) External loads on a flat roof 11

(f) External loads on walls parallel to wind 11 (g) Angle of wind to walls 11

(h) Internal wind loads 11

(i) Design wind load for building surfaces 14

(j) Elements which are subject

to external wind loads on

both faces 14

4. Discussion 15

5. Precise wind load 15

6. Approximate wind load 15

7. Comparison with authorities 22

8. Combined and design wind load .... 24

i. Snow load 24

1. Basic snow load 24

2. Comparison with authorities 26

3. Snow load on sloping roof 26

I. Water load 27

.1. Assumptions ; 28

•X. Conventions 28

1. Definitions 28

2. General 29

(a) Dimensions 29

(b) Weight 29

(c) Structural properties 29

3. Elements 29

(a) Wall and partition 29

(1) Height 29

(2) Width 30

(3) Thickness 30

(4) Weight 31

(5) Closures 32

(b) Floor 32

(1) Bearing 32

(2) Dimensions and weight 32

(c) Roof 32

(1) Bearing 32

(2) Dimensions and weight 32

Page X. Reactions on elements of house 32

XI. Roof 33

1. Sloping roof with no horizontal re- action from gable 33

(a) House with unsymmetrical

sloping roof 33

(b) Dimensions 33

(c) Wind load on roof 33

(d) Snow load on roof 34

(e) Loading conditions 34

, (f) Compionents of loads 35

(g) Reactions at ridge 35

(h) Reactions at wall 35

(i) Design loads at ridge and

wall 35

(j) Effect of attic floor on reactions at wall 35

2. Sloping roof with horizontal reactions from gable 38

(a) Wind load on gable 38. (b) Distribution on roof of gable

reactions 39

(e) Racking load on roof 39

(1) Racking modulus 39

(2) Reactions due to rack- ing load 40

(d) Deformation under distrib- uted racking load 41

(e) Racking load transferred at ridge in unsymmetrical

sloping roof 41

(f ) Reactions at wall due to rack- ing load 42

(g) Projection method for deter- mining vertical and horizontal reactions at wall 43

3. Projecting roof 44

(a) Noncontinuous projection ... 44

(b) Continuous projection 45

XII. Hip and valley rafters 47

1. Auxiliary roof members 47

2. House with hip roof 47

3. Loads on south roof 48

4. Loads on hip roof 48

5. Reactions on hip roof 48

6. Loads on wall 50

7. Loads on hip rafter 50

8. Loads on fastenings 52

9. Combined loads on hip rafter 52

10. Total loads on hip rafter 52

XIII. Walls 53

1. Design Loads 53

2. Walls which have no openings 53

(a) Compressive load 53

(b) Transverse load 53

(c) Racking load 53

3. Walls which have openings 53

(a) Structural properties of walls which have openings 53

(b) Compressive load 53

(1) Bi'essummers 53

(2) Illustration of Adams'

method 54

(3) Recommended method

for distributing vertical reactions on wall 54

(4) Illustration of recom- mended method 55

III
Page

(5) Vertical reaction at bottom of wall 58

(c) Transverse load 58

(1) Illustration of recom- mended method 58

(d) Racking load 59

(1) Racking modulus 59

(2) Method for determining racking load on

wall 59

(3) Method for determining righting reaction on wall 63 XIV. Partitions 64

1. Load-bearing partitions 64

(a) Compressive load 64

(b) Transverse load 64

(c) Racking load 64

2. Nonload-bearing partitions 64 XV. Floors 64

1. Design load 64

(a) Transverse load 64

2. No partition above floor 64

3. Partition above floor 64

(a) Partition normal to floor members 65

(b) Partition parallel to floor

members 65

4. Floor with opening 65

5. Floor with stair opening 66 XVI. Weights of house constructions 67

1. Description of constructions 67

2. Weight 70

3. Walls 70

(a) Wood 70

(b) Steel 70

(c) Masonry 71

4. Load-bearing partitions 72

5. Nonload-bearing partitions 72

(a) Wood 72

(b) Steel 72

6. Floors 72

(a) Wood 72

(b) Steel 72

(c) Masonry 73

7. Roofs 73

(a) Wood 73

(b) Steel 73 XVII. Variations in strength of house constructions 73

1. General 73

2. Comparison of variations in strength 73

3. Relation of materials to variations. . 74

(a) Walls 74

(1) Wood 74

(2) Steel 74

(3) Masonry 75

(b) Load-bearing partitions 75

(1) Wood 75

(c) Floors 75

(1) Wood 75

(2) Steel 75

(3) Masonry 75

(d) Roofs 75

4. Relation of workmanship to variations 75

(a) Walls 75

(1) Wood 75

(2) Steel 76

(3) Masonry 76

(b) Load-bearing partitions,

floors and roofs 76

Page XVIII. Allowable loads on house constructions .. . 77 i, 1. General 77 I (a) New materials 77 I (b) Fastenings 77 I (c) Unusual structural members 77 i (d) Stressed-skin constructions. . 77

2. Efficient use of material 78

3. Criteria for allowable loads 78

(a) Design loads 78

(b) Design of walls 78

(c) Construction 79

(d) Least maximum load 79

(e) Criterion a, percentage of

least maximum load 79

(1) Wood 80

(2) Steel 81

(3) Reinforced brick and

concrete 81

(4) Masoni-y 81

(f) Criterion b, damage 82

(g) Criterion c, slope of curve for both deformation and set. . . 82

(h) Criterion d, structurally sig- nificant deformation 84

(i) Criterion e, deformation

affecting the utility of a house 84

4. Loads 85

5. Distribution of criteria 87

6. Cracks in plaster 89

7. Graphs of allowable loads 90

8. Relation of materials and design to allowable load 90

(a) Walls 90

(1) Wood 90

(2) Steel 95

(3) Reinforced brick and

concrete 96

(4) Masonry 96

(b) Load-bearing partitions 97

(1) Wood 97

(c) Nonload-bearing partitions. . 98

(1) Wood 98

(2) Steel 98

(d) Floors 98

(1) Wood 98

(2) Steel 98

(3) Reinforced concrete . . 99

(e) Roofs 99

(1) Wood 99

(2) Steel 100

9. Relation of materials and design to allowable load-weight ratio 100

(a) Walls 100

(1) Wood 100

(2) Steel 104

(3) Reinforced brick and

concrete 105

(4) Masonry 105

(b) Load-bearing partitions 106

(1) Wood 106

(c) Nonload-bearing partitions.. 106

(1) Wood 106

(2) Steel 107

(d) Floors 107

(1) Wood 107

(2) Steel 107

(3) Reinforced concrete . . 107

(e) Roofs 108

(1) Wood 108

(2) Steel 108

10. Allowable loads for constructions not having standard height or span 108

(a) Compressive load 108

IV
Page

(b) Transverse load 108

(c) Concentrated load 109

(d) Impact load 109

(e) Racking load 109 XIX. Comparison of allowable loads with design

loads for typical houses 109

1. Objective 109

2. Typical houses 109

(a) Constructions 109

(b) Locations 115

3. Utility factor 115

4. Direction for design loads and

fastenings 115

5. Relation of allowable transverse

load to span 115

6. Roof 115

(a) Strength 116

(b) Roof fastenings 116

(1) Fastening A 116

(2) Fastening B 116

(3) Computed strength of fastenings 116

(c) Utility factor for all roofs. . . 117

7. Gables 117

(a) Strength 117

(b) Fastenings 118

8. Attic floor 118

(a) House 22-D 118

(1) Vertical loads 118

(2) Horizontal loads 118

(b) House E 119

(1) Vertical loads 119

(2) Horizontal loads 119

(3) Framing around openings 119

9. House 22-D, one story 119

(a) Wall 119

(1) Compressive load 119

(2) Transverse load 121

(3) Racking load 121

Page

(b) Partition 124

(1) Compressive load 124

(2) Racking load 124

(c) Floor 124

(1) Transverse load 124

10. House E, second story 126

(a) Wall 126

(1) Compressive load 126

(2) Transverse load 126

(3) Racking load 127

(b) Partition 127

(1) Compressive load 127

(2) Racking load 127

(c) Floor 127

(1) Transverse load 127

11. House E, first story 128

(a) Wall 128

(1) Compressive load 128

(2) Transverse load 128

(3) Racking load 129

(b) Partition 129

(1) Compressive load 129

(2) Racking load 129

(c) Floor 129

(1) Transverse load 129 XX. Conclusions 180

1. Wind map 130

2. Velocity pressure vs. wind load 130

3. Snow map 130

4. Engineering principles 130

5. Design load 130

6. Typical design load 130

7. Fastenings 130

8. Tests for strength 131

9. Allowable load 131

10. Loads for 100 constructions 131

11. Allowable load vs. design load 131

12. New approach to house design 131 XXI. Selected references 132

List of BMS Reports (facing p'. 132)

V

STRENGTH OF HOUSES

APPLICATION OF ENGINEERING PRINCIPLES

TO STRUCTURAL DESIGN

ABSTRACT

Methods for designing small houses to have adequate strength without waste of material are described and illustrated in this report. For each element of a house,

compressive, transverse, and racking loads were computed by the accepted principles of mechanics for typical one- and two-story frame houses in several locations representative of extreme wind and snow loads in the United States. Allowable loads for the 100 wall, partition, floor, and roof constructions included in the "structural properties" Building Materials and Structures Reports are compared

with design loads for two houses in three locations. The comparison shows that some

had insufficient strength, while others were much stronger than is necessary. The application of engineering principles to the design of houses presents a complete

and logical method for determining allowable loads for walls, floors, and roofs, and

makes it practicable to develop house constructions that have sufficient strength and

require the least amount of material.

I. INTRODUCTION

Substantial shelter has been a contributing

factor in the advancement of civilization down

through the ages, particularly where it has furnished an environment conducive to creative

work in the realm of invention and culture.

Although intensive study has resulted in unmistakable improvements in many lines, the evolution of structural design for houses has not kept

pace with the advance in engineering requirements for other types of construction, with the

progress attained in the development of safer

and more rapid methods of transportation, or with the achievements in speedier and more

efficient means of communication.

In an effort to improve the structural design

of houses and impelled by the results of studies

of substandard dwellings and their demoralizing effect on the community, the National

Bureau of Standards, by quantitative evaluation of technical construction aspects, has investigated by scientific method the structural

characteristics of a house which are measurable

and to which engineering principles can be

applied. Social and economical aspects of housing are not treated in this discussion. Some of

the properties of a house which can be measured

are strength, heat transmission, moisture penetration, sound insulation, and fire resistance.

Although methods for measuring these properties have been known for years, their application to house constructions has been limited.

Among the engineering requirements neces- sary for a satisfactory house, undoubtedly, the

most important is strength. Low heat transmission or high sound insulation would be of no value if the structure were not sufficiently

strong to withstand severe winds, heavy rains or snows, and other service loads.

With the strength of a house made adequate

for the conditions to which it is to be subjected over a period of years, other desirable features

may be considered and minor modifications

added to make the construction satisfactory in

all essential respects.

From a cost standpoint, it is desirable to use

material more efficiently than is done at present. There is a well-defined trend in other engineering fields to decrease weight and increase

strength by using less but stronger material.

For example, the weight of a structure may be

decreased by employing improved material such

as heat-treated steel, by the careful design of

each member for the actual load, and by more

efficient methods of fabrication, such as welding. Although economies resulting from advantageous utilization of material in stationary

structures may not be as great as in the manufacture of movable equipment, such as automobiles and aiiTilanes, where this principle is strictly adhered to, still, its application to the

construction of houses will effect noticeable

savings in their cost. More efficient fabrication

should result in benefits similar to those that

have made possible the general use of motor

cars and other products formerly not within

reach of the average citizen.

In the past, engineering methods have been

applied to the manufacture of new materials.

1
2 Building Materials and Structures Reports

but not to the house as a complete unit. This is evident by the lack of structural-test results.

Loads under service conditions can be determined as accurately for houses as for bridges or office buildings.

Allowable loads are the loads which can

safely be applied to a particular construction in a house under service conditions. Methods for

computing allowable compressive, transverse,

racking, concentrated, and impact loads are

described in this paper, and by these methods

the allowable loads were determined for each

of the 100 house constructions described in

individual EMS reports of the "structural properties" series.

Although it is customary for engineers to compute the allowable load which can safely be

applied to a construction, it is believed that for

house construction, loading tests in a laboratory

are much more satisfactory. Laboratory tests provide a quick and economical means for developing a floor, wall, or roof construction to have the necessaiy strength at the lowest practicable construction cost. Both the materials

and the design can be changed repeatedly until

the most satisfactory construction is obtained.

Materials and mode of fabrication favorable

to high strength and other factors are discussed

for each group of building material: wood,

steel, and masoniy. To cite just one example,

there is an indication that for wood-framed

walls the allowable load is greater when the

facing material (plywood or fiberboard) is glued to the studs than when it is nailed.

Whether to glue or nail the faces is an economic

problem which the builder can solve only after

making tests and studying costs. Some of the wall and floor specimens covered

by the "structural properties" BMS reports

have been considered stronger than the same

constructions in houses. Judging from the

meager information available, it seems probable

that there is no significant difference in

strength between such a specimen and the same

construction in a house. However, this conclusion should receive further study and consideration to definitely settle the matter.

When designing a house for strength, it is essential to know the greatest loads which may

be applied to elements of the house during its service life. These are the design loads for

compression, transverse, and racking on walls

and partitions, and the design transverse loads on roof and floors. Architects compute design

transverse loads on floors and sometimes other

design loads, but do not compute all the design

loads on each wall, partition, roof, and floor. In

fact, there has been no accepted method for

computing these loads.

In addition to the weight of the construction,

design loads for the house depend upon the

plans for the house and the wind, snow, and

floor loads. The methods described for computing the design compressive, transverse, and

racking loads on walls and partitions, also the

transverse loads on roofs and floors, should present no diflficulties to an engineer because they

are an application of the fundamental principles

of engineering mechanics, especially the principle of static equilibrium, parallel and con- current coplanar forces.

Design loads for a typical one-story and a

typical two-stoiy house were computed for

three locations, Los Angeles, Calif. ; Miami,

Fla. ; and Portland, Maine, through the use of a wind map based on Weather Bureau data

giving the velocity pressure of the wind. Upon

this velocity pressure the wind and snow loads on roof and walls depend. The wind and snow map indicates that the strength of house constructions should be different for different parts

of the counti'y. Therefore, the three locations were selected as representative of extremes in

wind and snow load.

The ratio of the allowable load to the design

load for each of the 100 constructions is given

in this report for one- and two-story houses in

the three locations. In general, the picture

presented by the ratios is that constructions

which have given satisfactory service over a

period of years usually have enough strength

for severe conditions. However, many constructions are too strong for some locations,

indicating economic waste, and others are not

strong enough, indicating structural weakness.

One important feature of the proposed

method for obtaining design loads is that design loads for the fastenings, such as roof to wall, are easily obtained. Consideration of a number of usual fastenings shows that they

have only a fraction of the strength necessary

for some locations.

Inadequate fastenings probably account for

much damage resulting from severe storms. If the strength of all fastenings were ample for

any load to be expected, the increase in cost of

the house would be small and many failures of

houses would be prevented. Tests of fastenings

to determine strength about which there is doubt seems desirable and the cost of testing

justified.

It is believed that for the first time, this

application of engineering principles to struc- tural design presents a complete and logical

method for designing houses and, more important, ways for determining the allowable load

of walls, floors, and roofs. This approach makes

it practicable to develop house constructions

that have sufficient strength with the least
Strength of Houses 3

amount of material at the lowest cost of fabrication.

II. OUTLINE OF METHOD FOR DETERMINING STRENGTH OF HOUSES

1. Load

Each of the factors affecting the strength of

a house was studied and the most reliable fundamental data selected. The applied loads on a

house include the weight of furniture and occu- pants applied to floors, the pressure of wind on

roof and walls, and the weight of snow on roof.

These loads with the weight of the construction are carried by supporting elements and eventually by the earth under the foundation. Although for some of the loads the magnitude

changes from time to time from an engineering

viewpoint, all, except impact loads, are static

loads.

The floor loads are those recommended by

competent authorities after surveys to determine actual loads for different occupancy.

The greatest velocity pressure of wind and

greatest snow load for each station were computed from data furnished by the Weather

Bureau and are presented herein for ready use by house designers. For a given house, the wind

load on roof depends upon the slope and on both

walls and roof; upon the air pressure inside

the house; which, in turn, depends upon the area of openings and their location with respect

to direction of wind. For a given house, values

may be taken directly from graphs based on

these relationships.

The weight of construction may be computed

or, more accurately, determined by weighing

large specimens of the wall or roof.

2. Design Load

From the dimensions given on the plans for

the house, also the applied loads and weights of

constructions, it should be practicable to compute the design load for each floor, wall, and

roof. It is convenient to consider each roof or

story separately, beginning at the top of the

house. The work is greatly simplified if each

element and also the entire house is considered

statically determinate, i.e., the loads and reactions on an element do not depend upon the

deformation under load of either the loaded

element or adjacent elements.

Actually, some houses are statically indeterminate, but, if the design loads are based on assumptions that they are statically determinate, there is reason to believe the the design

is safe although it may be somewhat uneconomical.

Typical assumptions are : each floor is a rigid

diaphragm insofar as loads in the plane of

the floor are concerned, portions of wall in each

story between doors and windows are simple

vertical beams under horizontal wind loads, and

they are supported laterally only at the floor

above and below. Wind load on portions of wall

having openings is transmitted laterally half to each of the adjacent walls ; floors and roofs are simple beams having only two supports.

3. Racking Load

It was found that this approach could be applied satisfactorily except for racking loads on

walls and load-bearing partitions. If the floor

is a rigid diaphragm and the house has more

than one room, the house is statically indeterminate under the racking load because the load on an intersecting wall or partition depends

upon the load on the other elements and, in

turn, on their racking moduli.

The conventional engineering solution involves simultaneous equations and for this case

the solution is very tedious. This method does

not appear suitable for designing houses.

After some study, it was found that if the

stoiy above was assumed to move to leeward,

parallel to its original position, until the total

racking resistance equalled the wind load, in

most cases the floor was not in equilibrium

under these forces. It was evident that the

story above must rotate about the center of

rotation of the racked story until equilbrium is established.

For translation, only walls and partitions

parallel to the wind are loaded but, for rotation,

all the walls and partitions are loaded except

those intersecting the axis of rotation.

Racking loads, determined by considering

translation as an approximate solution only,

may be either very much less or very much

greater than the correct values. In the latter

case, the design is not safe.

The computation of racking loads by steps is simple and direct and should present no diffi- culties to an engineer. Heretofore, little or no

attention has been paid to racking loads; cer- tainly no method of making sure that a house

would not collapse under wind loads has been

available, although this subject ha^ received

much attention for steel-frame buildings.

It is quite evident that engineering training

is essential for the application of these methods

for obtaining the design loads on a particular

house. These methods apply particularly if many houses are to be built from the same plans — as for prefabricated houses.

4. Allowable Load

Perhaps the reason adequate methods have

not been developed heretofore for finding all the

design loads for each element of a house is be- cause there have been no very satisfactory
4 Building Materials and Structures Reports

methods for determining the allowable (working) loads on a particular construction. Of

course, allowable transverse loads on woodframe floors and roofs are computed frequently,

but these methods cannot be applied with confidence to prefabricated sheet-steel floors nor

to other unusual constructions. In particular,

there are no accepted methods for computing

allowable impact or racking loads on any construction.

To determine the strength of any house construction under all the loads to which it is subjected in a house, a systematized program

of laboratory tests on large portions of a wall,

floor, or roof was worked out. Previous reports

in this series give the structural properties for

100 house constructions of wood, steel, and

masonry. Some are conventional constructions

and others are newer developments, as yet not

extensively used.

The Building Materials and Structures

(BMS) reports give the results of the National

Bureau of Standards investigations of the properties and suitability of unusual building materials and methods of construction.

A list of BMS reports, with prices and

method of purchasing, may be obtained without

cost from the National Bureau of Standards,

Washington 25, D. C. The structural reports are those having "structural properties of" in

the title. This report discusses the basic considerations

for selecting an allowable load from the laboratory data, based on strength and safety considerations only. It should be a simple matter for

anyone to modify the criteria to comply with

other essential requirements but, in general, the

cost of the house will be increased.

Allowable loads for each of the constructions

for which the structural properties have been

deteiTnined are given in this report. Because

the values are not based on experience with

actual houses, they should be considered as engineering estimates to be confirmed by

experience.

If the design loads for each element of a given house are known, suitable constructions can be selected, or can be developed, that will

provide adequate strength without the use of

unnecessary material or workmanship. It seems

evident that only in some such way as this can

houses be designed with the assurance that they

will not fail under loads for which they have

been designed and also that materials will be

used efficiently.

III. DEAD LOAD

The force exerted by gravity on an element

of a house may be considered a dead load. It is, therefore, the weight of the construction, which

may be expressed in pounds per square foot of

face area. For a particular construction, the

weight may be taken as the nominal value

which has found acceptance in the building

industiy, or, it may be computed from the description and dimensions of the materials given

in the specifications : or, it may be obtained

much more accurately by weighing the completed construction. The BMS reports on the

structural properties of house constructions

give the weight of each construction which was

obtained by dividing the weight of the specimens by the actual face area.

IV. FLOOR LOAD

The force exerted by gravity on objects or persons on the floor of a house may be considered the floor load, usually given in pounds per

square foot of the face area of the floor. When a house is being built, and also when

it is being repaired or altered, floor loads are exerted by staging, equipment, piles of material, and workmen. For conventional constructions erected and repaired by the usual

methods, these loads are not considered by the

architect when designing the house because

experience indicates that they do not exceed

safe values. For any building, whether of con- ventional or of unusual construction, the con- tractor should prevent overloading by shoring

and bracing, erecting falsework, and judiciously scheduling the sequence of the operations.

The contractor alone is responsible for the

satisfactory completion of the building.

When a house is occupied as a dwelling, furniture and occupants exert loads on the floors. When designing a house, it is impracticable to determine for each room either the amount of

furniture or the number of occupants because

they vary with the occupancy. Likewise, it is not practicable to determine the weight and

location of each piece of furniture. Therefore,

it is customaiy to consider the load on a floor as uniformly distributed. Experience indicates

that floors designed in this way are safe, i.e., they do not collapse under the load for which

they were designed, perhaps because heavy furniture, such as pianos and bookcases, is usually

placed near a wall and covers only a small portion of the floor area. Floor loads are discussed in Minimum Live

Loads Allowable for Use in Design of Buildings

[1].* A survey showed that the heaviest furniture loads for residential occupancy were

pianos weighing up to 55 lb/ft- and bookcases

weighing up to 170 lb/ft-. The equivalent uniform load was much less than 30 lb/ft-.

After careful study, several competent archi-

* Figures in brackets indicate the literature references at the end of this paper.
Strength of Houses

tects and builders stated that for residential

occupancy the funiiture loads seldom exceed 15

lb/ft- uniformly distributed, but that the load

caused by a crowd of people averaged 40 Ib/ftand might occur in any room at any time. It is evident, therefore, that the floor of a house

should be designed for a uniformly distributed

load of 40 lb/ft-.

For persons moving in unison, as when dancing, the load should be considered an impact

load. The stresses in a floor under an impact

load are much greater than those under static

load. However, movement in unison is practically impossible in a crowd that loads the floor to 40 lb/ft-.

A load of 20 lb/ft- on an attic floor used for

light storage only is recommended in Light

Frame House Construction [2]

V. WIND LOAD

1. General

Wind loads are the forces exerted upon sur- faces in the path of the wind. These loads depend upon velocity of wind, size and shape of

surface, and angle between surface and direction of wind. Wind loads on walls and roof of a building are normal to the surface on which

they act because air is an almost perfect fluid. Experience indicates that the direction of

the wind is horizontal, i.e., parallel to the

ground in flat country. If the building is on a

steep slope or in rough, broken country, this

assumption may not be justified. Experience

also indicates that the actual wind loads on a

building depend considerably upon the sur- roundings, such as hills, trees, and adjacent

buildings.

Many houses in New England were damaged

or destroyed during the hurricane in 1938. The

reports of this disaster indicate that high

water, storm waves along the coast, and uprooted and broken trees caused most of the

damage.

If the roof was lifted bodily from the building or the building moved from the foundation,

probably there were no anchors. Too often

these anchors are omitted.

It does not appear feasible to design houses

to withstand the impact of large trees nor storm waves along the coast.

2. Velocity Pressure

The pressure exerted by the wind is q=V2mv'^, (1)

in which

9= velocity pressure

m=mass of unit volume of air, i.e., weight per unit volume divided by

acceleration due to gravity

t;= velocity of wind.

5

Kent [3] gives the weight of dry air as W=1.325ZB/T, (2)

in which

17= weight of air, pounds per cubic foot

5=height of barometer, inches of mercury

r=absolute temperature, 459.6-f t being temperature, degrees Fahrenheit.

The value 1.3253 is the weight, in pounds, of

4,596 ft^ of air at 0° F and 1-in. barometric

pressure.

The United States Weather Bureau furnished

values up to December 31, 1939, of the "maximum wind velocity" observed at 188 stations in

this country. Each value is the greatest velocity,

for a time interval of 5 minutes, ever recorded

at the station. The records at individual sta- tions range from 5 to 70 years ; the average is 52 years.

The data include the highest barometer reading and lowest temperature ever recorded at each station, also, the height of the anemometer

cups above the ground.

To obtain the greatest velocity pressure that

might occur at each station, the weight of air was computed for the greatest pressure

(highest barometer) and lowest temperature,

although these conditions might never occur

simultaneously with the "maximum wind

velocity."

The ratios of B/T range from 0.0577 for 21

stations to 0.0730 for Canton, N. Y. and average

0.0661. For standard conditions —temperature

59° F and barometric pressure 29.92 in. of

mercury — the ratio is 0.0577. This average

ratio of B/T is 14.6 percent greater than for

standard conditions. The ratios of B/T range

from 12.7 percent less than the average to 10.4

percent more (spread 23.1 percent). For the same velocity of wind, the velocity pressures

have the same range as the ratios B/T.

The effect of water vapor in air upon the

weight is very small and is neglected because

the greater the amount of water vapor the less the weight.

Humphreys [4] says:

From careful theoretical considerations, in which

the individual eddies or parcels are supposed continu- ously to exchange momentum with the surrounding

air, 0. G. Sutton, following Ertel, derives the simple

expression, n

for moderate heights, a few feet to 200, say, in which

f and Vi are the mean wind velocities at the heights

h and respectively, and w is a number, 0 to 1, though

commonly about 0.25, that varies with the vigor of the
6 Building Materials and Structures Reports

vertical interchange that, in turn, depends on the

intensity of the insulation, mainly, and the condition and nature of the surface. Taking n=0.25, this expression becomes

Vi \ hi I

1/7

Knowing the height of anemometer, the

"maximum wind velocity" at the height of 30 ft may be computed. This height was selected as about the height of the roof for three-story

houses. Both the velocity and the velocity pres- sure decreases with a decrease in height, therefore, the observed velocity, v, was multiplied by

(SO/H) in which H is the height of anemometer in feet. The relation of velocity of wind

and velocity pressure to height above the

ground are shown in figure 1, as ratios of the

values for 30 ft. Mattice found [5] — using a Dines pressuretube anemometer —that during gusts, the wind

velocity is considerably greater than the "extreme wind velocity" (fastest single mile)

recorded by a Robinson anemometer. Mattice

draws no conclusions but, after considering his

data, the greatest velocity of wind for this re- b 0

50

40

30

20

10

0

0.5

wind velocity

1.0 ratio

port was taken as 50 percent greater than the

"maximum wind velocity." Therefore, the

velocity, v, was multiplied by 1.50/1.00.

The greatest velocity pressure, at 30 ft above

ground, for each Weather Bureau station was

computed by using the equation

^30 = 1.3253 B/T

32.2

^30=0.0996 B/T

r/30V"'' 1.50^ / 5280 \

-1^' [\h) ^TM^Km^r]

in which

^30= velocity pressure at 30 ft above

ground, pounds per square foot

5=barometric pressure, inches of mercuiy

r= absolute temperature, 459. t being temperature, degrees Fahrenheit

H=')ne\sh.i of anemometer, feet

'y=wind velocity, miles per hour.

1.5 0.5 1.0 velocity pressure ratio

1.5

Figure 1.Relation of tuind velocity and velocity pressare to height above the ground

[ The values are ratios of value at 30 ft. ] From the velocity pressures for each station,

figure 2 was plotted.

The isograms connect points having the same

velocity pressure, and the value at any location

is termed the "basic velocity pressure."

Assuming the velocity pressure varies line- arly between isograms, the value for any location may be found by interpolation along the

shortest line through the location between

isograms or an isogram and a point having
Strength of Houses
8 Building Materials and Structures Reports

different values. The line may have any direction and may cross intermediate regions within

closed isograms, as around Reading, Pa., and

Knoxville, Tenn.

Erie, Pa., is 6/11 the shortest distance between the 10 and 15 lb/ft- isograms or 12.7

lb/ft-. Milwaukee, Wis., is half the distance

from the 15 lb/ft- isogram to the point 20

lb/ft2 (Madison) or 17.5 Ib/ft^.

The errors in velocity pressures taken from

the map, were estimated by comparing the map

values for Weather Bureau stations with the

computed values. For 52 percent of the stations, the map values are too great, average

difference 1.6 lb/ft-, and for 48 percent they are

too small, average difference 0.8 lb/ft". Of

those too great, the differences do not exceed

5 lb/ft", except Charles City, Iowa, 5.8 ; Milwaukee, Wis., 7.5 ; Minneapolis, Minn., 8.6

;

Philadelphia, Pa., 5.9 ; and Topeka, Kan., 6.4

lb/ft-. Of those too small, the differences do not

exceed 2 lb/ft-, except Parkersburg, W. Va.,

3.0 lb/ft2.

It is a remarkable coincidence that in regions

where there are the most houses, there also are

the most stations, and there probably the errors

in the velocity pressure are small. This reflects credit on the judgment of the Weather Bureau

when selecting sites for stations, although the use of the wind data for determining wind loads on houses was not contemplated.

The wind load on a house is a function of the

velocity pressure which increases continuously

from zero at the ground to the value at the

top of the house as shown by velocity pressure curve in figure 1. Therefore, it does not appear

practicable to compute the theoretical wind

load on a given house nor the height of the

resultant above ground.

To facilitate the computation of wind loads on houses, consideration was given to the simplifying assumption that the wind load on each

story is a function of the velocity pressure at midheight of the story and that this load is uniformly distributed vertically. This velocity

pressure is termed the "nominal velocity pressure" for the story.

Actually, the wind load is greater than the

nominal value above midheight and less below

midheight and the resultant of the wind load

is above midheight of the story.

The nominal velocity pressure is safe for designing houses, provided the racking load and

the overturning moment on story and trans- verse load on wall are not less than the corre- sponding theoretical values. At infinite height,

the nominal and theoretical racking, overturning, and transverse loads are the same and the

difference increases the nearer the ground.

The racking load is the resultant horizontal

force on the story and the overturning moment

is the racking load times the vertical distance

from the bottom of story to the action line of

the resultant racking load. For design, the

effect of different transverse loads on walls may

be judged by comparing the maximum bending

moments (where shear is zero) due to the

transverse wind loads, considering the wall a simple (vertical) beam supported along the

bottom and top.

To determine whether nominal windloads

gave safe values for design, both nominal and

theoretical loads were computed and compared

for stories that should give the greatest differ- ences. For a story 9 ft high, between 2 and 11 ft above ground, having a wall 8 ft high (platform construction), the nominal racking load is 3.2 percent greater than the theoretical load

and the transverse moment on wall 7.8 percent

greater.

It is believed that for any story not over 25 ft high, the nominal racking load and nominal

transverse moment on a wall are greater than

the theoretical values. Thus, for a story 17 ft high, between 2 and 19 ft above ground and a

wall 16 ft high, the nominal racking load is 5.0

percent greater and the transverse moment 4.4

percent greater than the theoretical values.

For racking and transverse loads, therefore,

nominal wind loads are safe values for design.

However, the nominal overturning moment

of a story, about the bottom of the story, is a

little less than the theoretical moment. Thus,

for the 9-ft story, the nominal overturning

moment is 4.2 percent less than the theoretical

value and for the 17-foot story, 4.4 percent less. If the overturning moment is taken either at the ground level or the level of the footings

for the foundation, the nominal again is less than the theoretical, but the difference in percent is smaller.

Ferrington [6] says:

The resistance of the surface of the ground, fences,

hedges, shrubs, etc., all help to reduce the energy of the wind in the lower levels. . . . From the comparison

of a long series of geostrophic and observed winds we

conclude that over the open sea, or on an exposed spit of flat sand like Spurn Head, the wind loses one-third

of its velocity from "friction" and at other well-exposed

stations the loss is, on the average, as much as 60

percent. . .

.

It should be remembered that theoretical

values apply to houses on bare, smooth, horizontal surfaces. Actually, when a house is built, this condition may be approximated for a few locations only because the house, as soon

as occupied, is inevitably surrounded by windbreaks unless erected on an exposed beach. If
Strength of Houses 9

it is a farmhouse, barns, haystacks, and fences

immediately become necessities, and soon trees and shrubs add more shelter.

If the house is in a settled community, the

surrounding buildings and trees decrease the

wind load considerably. These considerations

justify taking the nominal wind load for all design wind loads.

To find the nominal wind load value, take the

velocity pressure for the building site from the

* wind map, multiply it by the height factor, h,

in table 1 for midheight of each story or roof.

Table 1.

Height factor for velocity pressure

[The height factor, A, is the ratio of velocity pressure at given height to velocity pressure at 30 ft above ground]

Factors for height Factors for height Factors for height Factors for height Factors for height Factors for height from 0 to 10 ft from 10 to 20 ft from 20 to 30 ft from 30 to 40 ft from 40 to 50 ft from 50 to 60 ft

Height Height Height Height

Height

Height Height

Height factor Height factor Height factor Height factor factor Height factor

ft A ft A ft A ft A ft A ft A

0.0 0 10. 5 0. 7408 20.5 0. 8969 30.5 1. 0047 40. 5 1. 0895 50. 5 1. 1604

1. 0 0. 37.S4 11.0 .7508 21.0 .9031 31. 0 1.0094 41.0 1. 0934 51. 0 1. 1637

1. 5 . 4249 11. 5 .7604 21. 5 .9092 31. 5 1. 0140 41. 5 1.0971 51. 5 1. 1670

2. 0 .4614 12.0 .7697 22.0 .9152 32.0 1.0186 42.0 1. 1009 52. 0 1. 1702

2. 5 .4917 12.5 .7787 22.5 .9211 32.5 1. 0231 42.5 1. 1046 52. 5 1. 1734

3.0 .5179 13.0 .7875 23.0 .9269 33.0 1. 0276 43.0 1. 1083 53.0 1. 1766

3.5 .5413 13.5 .7960 23. 5 . 9326 33. 5 1. 0320 43.5 1. 1120 53. 5 1. 1797 4.0 . 5623 14.0 .8043 24.0 . 9382 34,0 1. 0364 44. 0 1. 1156 54. 0 1. 1829

4.5 .5816 14. 5 .8124 24. 5 . 9438 34. 5 1. 0407 44. 5 1. 1192 54. 5 1. 1860

5.0 . 5993 15,0 .8203 25.0 .9492 35. 0 1. 0450 45.0 1. 1228 55. 0 1. 1891

5.5 . 6159 15. 5 .8281 25. 5 .9546 35. 5 1. 0493 45. 5 1. 1264 55. 5 1. 1922

6.0 .6314 16. 0 .8356 26. 0 . 9599 36.0 1.0535 46. 0 1. 1299 56. 0 1. 1952

6. 5 . 6460 16. 5 .8430 26. 5 .9652 36. 5 1.0576 46. 5 1. 1334 56. 5 1. 1983

7.0 . 6598 17.0 . 8502 27.0 .9704 37. 0 1. 0618 47. 0 1. 1369 57.0 1. 2013

7. 5 .6730 17. 5 .8573 27. 5 . 9754 37. 5 1. 0658 47. 5 1. 1403 57. 5 1. 2043

8.0 .6855 18.0 .8642 28.0 .9805 38.0 1.0699 48.0 1. 1437 58.0 1. 2073

8.5 .6974 18. 5 .8710 28. 5 . 9855 38.5 1. 0739 48. 5 1. 1471 58. 5 1. 2102

9.0 .7089 19.0 .8776 29. 0 . 9904 39.0 1. 0778 49.0 1. 1505 59. 0 1. 2132

9. 5 . 7200 19. 5 .8842 29. 5 .9952 39. 5 1. 0818 49. 5 1. 15.38 59. 5 1. 2161

10.0 . 7306 20.0 .8906 30.0 1.0000 40.0 1. 0857 50.0 1. 1571 60.0 1. 2190

In general, houses having unnecessary

strength cost more than those having little more than sufficient strength to withstand

service conditions. The economic importance of

designing houses for wind loads based on the

velocity pressure at midheight of each story for

the building site is obvious because most of

the houses in this country are one-story.

3. Relation Between Velocity Pressure

AND Wind Load

(a) Subcommittee No. 31, American

Society of Civil Engineers

All available information on wind loads,

including wind-tunnel data, was studied carefully over a period of ten years by Subcommittee No. 31, and is covered in the report Wind

Bracing in Steel Buildings issued by the American Society of Civil Engineers. The Final

Report (1940) [7] recommends a minimum

standard wind load, in pounds per square foot,

for the design of buildings, including tall buildings, anywhere in the United States and

Canada, with the qualification that

"Special windforce specifications should be

formulated locally for areas that are defi- nitely known to be subject to hurricanes

and tornadoes."

The Subcommittee makes many definite rec- ommendations for wind load depending on

position with respect to direction of wind, slope

of roof, and size and position of openings with

respect to direction of wind. Sufficient allow- ance has been made in the prescribed wind load

for the effect of air currents striking vertical

faces obliquely, either in a lateral or vertical

sense. All these values are in pounds per square foot

for a velocity pressure of 15.5 Ib/ft^, the velocity pressure resulting from the adoption of 20

\h/ft~ by the Subcommittee as the minimum

standard wind load.

For some locations in this countiy the greatest velocity pressure is less and for other locations more than 15.5 lb/ft-.

For this report, since the wind load is directly

proportional to the velocity pressure, the rec- ommendations of the Subcommittee are given in

terms of velocity pressure.

The following recommendations are those of

the Subcommittee with reasonable deductions

therefrom. Much of the wording is that of the

Subcommittee report. Only the recommendations applicable to houses are given here.

To obtain the coefficient of velocity pressure
10 Building Materials and Structures Reports

given here, divide the wind load recommended

by the Subcommittee by 15.5.

(6) External Loads on Buildings With

Plane Surfaces Normal to Wind

For buildings having vertical plane faces

normal to the wind, the load to be considered is a pressure of 20 lb/ft" corresponding to a wind

velocity of only 77.8 mi/hr and a velocity pres- sure of 15.5 Ib/ft^. Consequently, a substantial

amount of shielding is tacitly assumed to exist.

This load is the combined wind force of an

external pressure (inward) of 0.8 q on the

windward wall of buildings having an average

ratio of height to width, with an external suction (outward) of 0.5 q on the leeward wall.

Therefore, the total combined load on the outside of the windward and leeward vertical faces

of an average building may be 1.3 q.

(c) External Loads on Plane Surfaces

Inclined to Wind

For both symmetrical and unsymmetrical

gable roofs, where oc is the slope of the roof to the horizontal, in degrees, the recommended

wind loads are as follows

(i) Windward Slope

For ex not greater than 20°, a suction (12

Ib/ft^) of 0.774 q out. For oc between 20° and 30°, a load of /=

(0.0774 oc —2.322) q out, the negative value in- dicating suction.

For oc equals 30°, the external load is zero. For oz between 30° and 60°, a load of f—

(0.01937 oc— 0.581) q in, the positive value in- dicating pressure.

For o: greater than 60°, a pressure (9 Ib/ft^)

of 0.581 q in.

(2) Leeward Slope

For all values of cc in excess of zero, a suction

(9 lb/ft-') of 0.581 q out should be considered.

The external wind loads are indicated graphically in figure 3.

p/fc/) of roof

1.0

0.8

^ 0.6

o

O

0.4

O.l

0

O.Z

0.4

0.6

0.8

1.0

1 i 3 ±

5 3 4 5

^ rooi leeward slopi

— roof , windward slofoe 1

ro//e/

) / 0 I 0 30 4

slope of

0 5

roof, a0 6

'. , degre

0

es 7 0 8 0 9

iward

/,

wine

Figure 3.External wind loads on Jwuse.

(d) External Loads on Rounded Roof

Surfaces

The Subcommittee report includes values for

the external wind loads on rounded roofs but

they are not given here because very few houses

have rounded roofs.
Strength of Houses 11

(e) External Loads on a Flat Roof

For a flat roof, a noiTnal suction of not less than (12 lb/ft-) 0.774 q out should be considered as applied to the entire roof surface.

(/) External Loads on Walls Parallel

to Wind

On walls parallel to wind, an external suction

(9 lb/ft-) of 0.581 q out should be considered.

(g) Angle of Wind to Walls

These values of wind load are for rectangular

houses and for the direction of the wind normal

to any one of the outside walls. Using the wind

loads for roofs of any slope, the greatest wind

loads on the walls and the racking loads on the

intersecting walls and partitions were esti- mated for other wind directions. It was evident

that the wind loads and racking loads were

greater for wind directions normal to the faces

of the house than for any intermediate direction.

(/i) Internal Wind Loads

The wind load to be assumed in design, is to be taken as the applicable external wind load

given in paragraphs (b) to (/) only in case the

building is airtight. Such a condition will rarely

arise. Normally, air leakage due to the usual

small openings around windows, doors, skylights, and eaves will give rise to an internal

pressure or suction of from 0.25 q to 0.35 q, depending on whether the openings are chiefly

in the windward or in the leeward surfaces. In

the rapid building up of gust velocities, the air

transfer may be so slow that the internal load

is less than this. In Standard N-790 of the

Netherlands, the external wind loads all have

been adjusted to take account of an internal

suction of 0.2 q. Where openings are of substantial size, the

internal wind load may be of considerable magnitude. It may be pressure or it may be suction,

depending on whether the openings are in windward surfaces, in leeward surfaces, or in surfaces parallel to the wind. Vei-y large internal

pressures have been and may be built up be- cause of the breaking of windows on the windward side of buildings by reason of flying

gravel from the roof or other objects carried

by the wind. The Subcommittee is of the opinion

that the only buildings for which the internal

wind load should be restricted to the amounts

mentioned in the preceding paragraph are those

for which the construction is such that the

doors and windows cannot be broken in, or that

have very small areas taken up by windows and

doors.

Particularly large internal loads may arise

when the windward or leeward side of a build743712°—48—

ing is completely open. The German regulations, effective since June 18, 1938, provide

that, for structures which are entirely open on

one or more sides, or which can be opened, or which by reason of one or more openings in one

or more sides are at least one-third open, or can be opened to this extent, a normal internal

load of 1.2 q acting out is to be assumed as applied to the under side of the roof. This is an

addition to the external suction of 0.4 q on the

leeward side of plane roofs, and is specified

with a view to insuring proper anchorage of

the roof as well as of the attachment of roofing

sheets.

It appears that reasonable allowances for in- ternal wind load would be as follows:

(1) For buildings that, although nominally

airtight with closed doors and windows and un- broken glass, are nevertheless, more or less "air

leaky" by reason of numerous distributed small

openings, an internal pressure or suction (4.5

lb/ft- ) or 0.2903 q out or in, acting normal

to walls and roof;

(2) For buildings with 30 percent or more

of the wall surface open, or subject to being

opened or broken open, an internal pressure

(12 Ib/ft^) of 0.774 q out or an internal suction

(9 lb/ft2) of 0.581 q in;

1

1.0

0.8

0.6

OA ^ 0.2

0

% O.l

.c: 0.4

0.6

0.8

1.0 Figure 4

winaward operlings

\

0 1M 0 I

^all Of.

0 30 40 50

'>ening, n , percent

leen pan'ord c

7//e/ cand

-)pen/rigs

90

-Internal ivind loads on house.
12 Building Materials and Structures Reports

14

(3) For buildings that may have percentages n of openings varying from 0 to 30 percent of the wall space, an internal pressure of

/= (0.2903+0.01612 n) gout,

or an internal suction of

/=(—0.2903—0.00969 n) q in. These proposals are indicated graphically in

figure 4.

(i) Design Wind Load for Building Surfaces

On the basis of the foregoing, the Subcommittee would recommend that the design wind

load applied to any surface of a building be

the combination of:

(1) The appropriate external wind load in- dicated in paragraphs (6) to (/) and

(2) The appropriate internal wind load from

paragi-aph {h)

.

Building Materials and Structures Reports

(j) Elements Which are Subject to External

Wind Loads on Both Faces

The Subcommittee discusses only wind loads on walls and roofs which have external wind

loads on the outside face and internal wind

loads on the inside face, but many houses have

elements such as overhanging eaves and porch

roofs which are subject to external wind loads on both faces.

The design wind load on plane elements was | estimated by considering the external wind load ' on both faces giving the greatest design load.

With the element attached along one edge to one of the walls of a house, the wind load was

taken as that on the adjacent wall unless for some other assumption the combined load was

greater. It seems probable that the wind load on the wall extends some distance outward presumably to the outer edge of an intersecting

element on a house.

The design wind loads on projections are given in table 2 and shown in figure 5.

p/fch of roof

Figure 5.Design wind loads for projecting elements on house.
Strength of Houses 15

4. Discussion

Wind-tunnel tests on models of buildings

show that the external wind loads are far from

uniform over a plane wall or roof. Therefore,

the values given above are not the actual loads.

Evidently the Subcommittee believes that if the building is designed for these uniformly

distributed loads, it will withstand the actual

wind loads.

Wind loads are given as accurately as justified

by the experimental data if the coefficient of q

is carried to the nearest tenth, i.e., to one

decimal place. The Subcommittee gives wind

loads in pounds per square foot in round

numbers ; therefore, the coefficients of q derived

from them are carried to several decimal places, so that there will be no apparent discrepancies,

particularly in values computed from the equations for coefficients depending on the slope, ex

or percentage of openings, n. Insofar as accu- racy is concerned, all these coefficients might

well be rounded off to the nearest tenth.

For external wind loads, no value is given by

the Subcommittee for wind load on gable roof

if wind is parallel to ridge. For this report,

each slope is considered a flat roof, slope zero

degrees, and wind load taken as 0.774 q out.

5. Precise Wind Load

The computation of the exteimal wind loads on each story of a house presents no difficulties,

j each face in turn being considered the windi ward face, but the combined load on each eleI ment depends upon the internal wind load,

j Because of open stairways in houses and the

fact that inside doors are open much of the

time and do not fit closely when closed, it must

be assumed that the internal load is the same

on all walls and roof. Apparently this load can

be determined by considering the percentage

of openings, n, in each face of each story and

for each direction of wind. For a given di- rection of wind only two internal wind loads

need be considered ; the greatest for windward

openings in windward face and the greatest for

leeward openings in either side face or in lee- ward face.

The external wind load on windward face

always acts inward. If there are windward

openings, the internal load acts outward and

the combined wind load is less than the external. However, if the openings are in either

side face or in leeward face, the internal load

acts inward and the combined load is the sum

of the external and internal loads.

Therefore, for each direction of wind, the

combined wind load on windward face is the

external wind load for the story (in) plus the

greatest internal wind load (in) for any lee- ward face in any story.

For each of the three leeward faces, the ex- ternal wind load acts outward and the greatest

combined wind load occurs only when there are windward openings and the internal load

also acts outward.

Therefore, for each direction of wind, the

combined wind load on each of the three lee- ward faces is the external wind load for the

story (out) plus the greatest internal wind load

(out) for openings in the windward face in

any story.

The pi'ecise method is best explained by an

example. The Federal Housing Administration

cooperated in this work by supplying the plans

for house E, a typical two-story frame dwelling. The location is Madison, Wis., where the

velocity pressure at 30 ft is 20 lb/ft-.

The precise external wind loads are given in

table 3 and precise internal wind loads in table

4. For computing the percentage of openings, it is assumed that doors and window sash are re- moved, leaving the greatest possible opening

in the wall.

The precise combined wind loads and precise

design wind loads are given in table 5. The greatest combined loads, acting in and

acting out, for each face of house and for each

story (in bold-faced type) are the only ones

considered when selecting the design wind

loads.

Athough for this demonstration of the precise

method each value is given, it is obvious that

only those giving the greater values need be

computed. They can be selected by inspection.

6, Approximate Wind Load

Architects, when deteiTnining the design

wind loads on a house, may feel that the re- commended method is too cumbersome and may

compute the loads more quickly and easily by an

approximate method in general accordance

with Subcommitte recommendations. The approximate method might be somewhat as

follows

(1) The external wind load for the entire

wall or face of the house and the roof is found

by multiplying the velocity pressure (height 30

ft) for the location, from the map, by the coefi^cient recommended by the Subcommittee

(2) The internal wind load is found by computing the percentage of openings, n, in each

face and by detennining the greatest outward

and greatest inward load for that face

(3) The combined wind load is found by

adding the extenial and internal wind loads

algebraically. The design wind loads for each

wall and roof are the greatest value inward

and the greatest value outward.
16 Building Materials and Structures Reports

Table 3.

Precise external un'nd loads on House E in Madison, Wis.

(Velocity pressure 20 Ib/ft^ at 30 ft]

18.0 21. Z16.2 1^.4-

12.6 6.2-

7.6 0.9-

SOUTH FACE

SOUTH WIND

NORTH FACE WEST FACE

Element

Velocity

pressure, q Windward Parallel to wind Leeward Parallel to wind

IblfP coef Iblfn Acts coef IblfP Acts coef Ib/ft'- Acts coef Iblffi .ids Gable or roof - 18.0 0. 8 14.4 In 0. 774 13. 9 Out 0.5 9.0 Out 0.774 13. 9 Out

Second story 16.2 .8 13.0 do .581 9.4 do . 5 8.1 do .581 9.4 do

First story 12.6 . 8 10.

do .581 7.3 do . 5 6.3 do .581 7.3 do

Cellar 7. 6 .8 6. 1 do .581 4. 4 do . 5 .3. 8' do .581 4.4 do EAST WIND

Gable or roof- Second story.

First story

Cellar

Parallel to wind Windward Parallel to wind Leeward

18.0 0. 581 10. 4 Out 0.0 0.0 0. 581 10.4 Out 0. 581 10.4 Out

16. 2 .581 9. 4 do .8 13.0 In . 581 9.4 do . 5 8.1 do

12.6 .581 7.3 do .8 10.

do .581 7.3 do . 5 6.3 do

7.6 . 581 4. 4 do .8 6.

do .581 4. 4 do . 5 3.8 do NORTH WIND

Leeward Parallel to wind Windward Parallel to wind

Gable or roof _ _ - 18.0 0. 5 9.0 Out 0. 774 13. 9 Out 0.8 14. 4 In 0. 774 13.9 Out

Second story 16. 2 .5 8. 1 do .581 9.4 do .8 13.0 do .581 9.4 do

First story, _ -- 12.6 . 5 6.3 do .581 7.3 do .8 10.

do .581 7.3 do

Cellar 7.6 . 5 3.8 do . 581 4.4 do .8 6.1 do .581 4.4 do WEST WIND

Parallel to wind Leeward Parallel to wind Windward

Gable or roof 18.0 0. 581 10.4 Out 0. 581 10.4 Out 0. 581 10.4 Out 0.0 0.0 Second story 16. 2 .581 9. 4 do . 5 8. 1 do .581 9.4 do .8 13.0 In

First story 12.6 .581 7.3 do .5 6.3 do .581 7.3 do .8 10.1 do

Cellar.-- 7.6 . 581 4. 4 do .5 3.8 do .581 4. 4 do .8 6.1 do
Strength of Houses 17

Table 4.

Precise internal wind loads on House E in Madison, Wis.

[Velocity pressure 20 lb/ft= at 30 ft. Numbers on house are wall openings in percent. Values in bold-faced type are the greatest loads acting in and acting out

for each face of house]

18.0 21.2-

I6.Z 14.4-

12.6 6.2-

1.6 0.9-

6.2 15.3

XL

13.6

11.4

-Id. 3

2.1

15.3

13.1

-ZO.l

0

13.6

13.9

9.1

Wall opening, n, percent

SOUTH WIND

Element

Velocity

pressure,? Windward Parallel to wind Leeward Parallel to wind

IhlfP coef Ib/fP Acts coef Ihlff Acts coef ibim ylcts coef Ihlft'- Acts Gable or roof - _-_ 18.0 0. 390 7.0 Out 0. 290 5. 2 In 0.310 .5.6 In 0. 290 5. 2 In Second story . . . 16. 2 . 537 8.7 Do .422 6.8 Do .439 7.1 Do .422 6.8 Do

First story _. 12. 6 . 581 7.3 Do .401 5. 0 Do .417 5.3 Do .425 5.4 Do

Cellar 7. 6 . 290 2. 2 Do .468 3.6 Do .490 3. 7 Do .379 2.9 Do KAST WIND

Parallel to wind Windward Parallel to wind Leeward

Gable or roof._ . ... . 18.0 0. 330 6.3 In 0. 290 5.2 Out 0.310 5.6 In 0.290 5.2 In Second story 16. 2 .439 7 1 Do .509 8.2 Do .439 7. 1 Do .422 6.8 Do

First story .... . 12. 6 .465 5. 9 Do .474 6. 0 Do .417 5.3 Do .425 5.4 Do

Cellar...... 7.6 . 290 2, 2 Do . 585 4.4 Do .490 3. 7 Do .379 2.9 Do NORTH WIND

Leeward Parallel to wind Windward Parallel to wind

• Gable or roof _ 18. 0 0. 350 6.3 In 0. 290 5. 2 In 0. 324 5.8 Out 0.290 5.2 In Second story 16. 2 .4.39 7.

Do .422 6.8 Do . 537 8.7 Do .422 6.8 Do

First story. .. ... 12. 6 .465 5.9 Do .401 5. 0 Do . 500 6.3 Do .425 5. 4 Do

Cellar 7.6 . 290 2.2 Do .468 3.6 Do . 623 4. 7 Do .379 2. 9 Do WEST WIND

Parallel to wind Leeward Parallel to wind Windward

Gable or roof . 18.0 0. 350 6.3 In 0.290 5.2 In 0.310 5.6 In 0. 290 5.2 Out

Second story ........ 16. 2 .439 7.Do .422 6.8 Do .439 7. 1 Do .509 8.2 Do

First story 12.6 .465 5.9 Do .401 5.0 Do .417 5.3 Do .514 6.5 Do

Cellar 7.6 .290 2. 2 Do .468 3.6 Do .490 3. 7 Do .438 3.3 Do
18 Building Materials and Structures Reports

Table 5.

Precise combined wind loads and precise design wind loads for House E in Madison, Wis.

IVelocity pressure 20 Ib/ft^ at 30 ft. Values in bold-faced type are the greatest loads acting in and acting out for each face of house and for each story].

18.0 ZI.Z16. Z 14.4-

11.6 6.Z-

.7.6 0.9-

SOUTH FACE EAST FACE NORTH FACE WEST FACE

PRECISE COMBINED WIND LOAD—SOUTH WIND

Element Windward Parallel to wind Leeward Parallel to wind

Acts Acts Acts Acts Acts lb/ft' Acts lb/ft' Acts lb/ft' Acts Gable or roof 21.5 In 0.0 Out 0.0 In 22.6 Out 0.0 In 17.7 Out 0.0 In 22.6 Out

Second story 20. 1 Do .0 Do .0 Do 18.

1

Do .0 Do 16. 8 Do .0 Do 18.1 Do

First story 17.2 Do .0 Do .0 Do 16 0 Do .8 Do 15. 0 Do .0 Do 16.0 Do

Cellar 13.2 Do 2.6 Do 2.7 Do 13.1 Do 3.3 Do 12. 5 Do 2.7 Do 13.1 Do PRECISE COMBINED WIND LOAD—EAST WIND

Parallel to wind Windward Parallel to wind Leeward

Gable or roof . 0.0 In 18.6 Out 7. 1 In 8.2 Out 0.0 In 18.6 Out 0.0 In 18.6 Out

Second story .0 Do 17.6 Do 20.

1

Do 0.0 Do .0 Do 17.6 Do .0 Do 16.3 Do

First story .0 Do 15.5 Do 17.2 Do .0 Do .0 Do 15. 5 Do .8 Do 14.5 Do

Cellar 2. 7 Do 12.6 Do 13. 2 Do 2.

1

Do 2.7 Do 12.6 Do 3.3 Do 12.0 Do PRECISE COMBINED WIND LOADS—NORTH WIND

Leeward Parallel to wind Windward Parallel to wind

Gable or roof 0.0 In 17. 7 Out 0.0 In 22.6 Out 21. 5 In 0.0 Out 0.0 In 22.6 Out

Second story .0 Do 16.8 Do .0 Do 18.

1

Do 20.1 Do .0 Do .0 Do 18.

1

Do

First story .8 Do 15.0 Do .0 Do 16.0 Do 17.2 Do .0 Do .0 Do 16.0 Do

Cellar 3. 3 Do 12.5 Do 2.7 Do 13.1 Do 13.2 Do 2.6 Do 2.7 Do 13.

1

Do PRECISE COMBINED WIND LOAD—WEST WIND

Parallel to wind Leeward Parallel to wind Windward

Gable or roof 0.0 In 18.6 Out 0.0 In 18.6 Out 0.0 In 18. 6 Out 7.1 In 8.2 Out

Second story. .0 Do 17.6 Do .0 Do 16.3 Do .0 Do 17.6 Do 20.

1

Do 0.0 Do

First story .0 Do 15.6 Do .8 Do 14.5 Do . 0 Do 15. 5 Do 17.2 Do .0 Do

Cellar 2.7 Do 12.6 Do 3.3 Do 12.0 Do 2.7 Do 12.6 Do 13.2 Do 2.1 Do PRECISE DESIGN WIND LOADS—ANY WIND DIRECTION

Gable or roof. Second story _ First story

Cellar.

21. 5 In 18. 6 Out 7.

1

In 22.6 Out 21. 5 In 18.6 Out 7. 1 In 22.6 Out

20. 1 Do 17.6 Do 20.

1

Do 18. 1 Do 20. 1 Do 17.6 Do 20. 1 Do 18.1 Do

17. 2 Do 15. 5 Do 17. 2 Do 16.0 Do 17. 2 Do 15.5 Do 17. 2 Do 16.0 Do

13.2 Do 12. 6 Do 13. 2 Do 13. 1 Do 13. 2 Do 12. 6 Do 13.2 Do 13.

1

Do
Strength of Houses

In order to obtain some idea of how loads

determined in this way compare with loads

computed by the precise method; the approximate external, internal, and combined wind

19

loads ; together with approximate design wind

loads and ratio of approximate to precise design

wind loads were computed. The values are given in tables 6, 7, and 8.

Table 6.Approximate external wind loads on House E in Madison, Wis.

n w

h

SOUTH FACE EAST FACE NORTH FACE WEST FACE

SOUTH WIND

Element

Velocity

pressure, ? Windward Parallel to wind Leeward Parallel to wind

Roof

lb/ft'20

20

coef MP Ac's coef

0. 774

. 581

Ib/fP

I.5. 5

II. 6

Acts Out

do

coef Ib/fl' Acts coef

0. 774

.581

Ib/fti 15. 5 11.6

Act

Out

Wall 0.8 16.0 In 0. 5 10.0 but do EAST WIND

Roof_ __ ___ 20

20

Parallel to wind Windward Parallel to wind Leeward

0.0

.8 0.016.0

0. 581

.5 11.6 10.0 OutWall 0. 581 11.6 but In 0.581 11. 6 Out do NORTH WIND

Roof 20

20

Leeward Parallel to wind Windward Parallel to wind

0. 774

.581

15. 5 11.6 Out

do

0. 774

.581

15. 5 11.6 Out

Wall 0.5 10.0 Out 0. 8 16.0 In do WEST WIND

Roof 20

20

Parallel to wind Leeward Parallel to wind Windward

0. 581

. 5 11.6 10.0 Outdo

0.0

.8 0.0 Wall 0.581 11.6 Out 0. 5B1 11.6 Out 16. 0 In
20 Building Materials and Structures Reports

Table 7.Approximate internal wind loads on House E in Madison, Wis.

[Numbers on house are wall openings in percent. Values in bold-faced type are the greatest loads acting in and acting out for each face of house].

13.9 IZ.9

Wall opening, n, percent

EAST FACE NORTH FACE WEST FACE

SOUTH WIND

Element

Velocity

pressure, q Windward Parallel to wind Leeward Parallel to wind

Roof __

lb/ft' 20

20

coef Ib/fP Acts coef 0.290 .416

mt^

5.8 8.3

Acts In Do

coef Ib/ft^ 1 Acts coef

0. 290 .419

mt'

5.8 8.4

Acts

In Wall 0. 514 10.3 Out 0.415 8.3 I In Do EAST WIND

Roof 20

20

Parallel to wind Windward Parallel to wind Leeward

0.290

.500

5.8 10.0 Out Do

0.290

.419

5.8 8.4 In Wall 0. 425 8.5 In 0.415 8.4 In Do NORTH WIND

Leeward Parallel to wind Windward Parallel to wind

Roof _ 20 0. 290 5.8 In 0. 290 5.8 In Wall 20 0.425 j 8.5 In .416 8.4 Do 0. 498 io.o 1 Out .419 8.4 Do WEST WIND

Roof 2020

Parallel to wind Leeward Parallel to wind Windward

0. 290 .416

5.8

8.3 InDo

0. 290 .5045.8 10.1 Out

Wall 0. 425 8.5 In 0. 415 8.4 In Do
Strength of Houses 21

ESI

COO

K a

3

00

1

[

[

[

CO o^ c

o

allel t

CI o

(-< c3 Q

Ah o o

^ o

Acts 1

Out

20.3

c

c

o

§3 °

CO 0^

ind

o

Paral u C Do

o o

o"

3o

o

o

Acts In

i -*

ici in

50

rH O

O CD

go So

00 ^

'3

ad

o, o

|2L( '5

Q. o

2 o >,

J2 Otn^

a 8 - I
22 Building Materials and Structures Reports

The approximate design wind loads on roof

range from 14 to 20 percent more than the

precise values ; those on the second-story walls

from 21 to 23 percent more; and on first-stoiy

walls from 37 to 42 percent more.

7. Comparison With Authorities

A review of literature on wind loads indicates

that, until recently, the engineering basis for

computing them was not as sound as for other

phases of the theoiy of structures, perhaps

because of the lack of experimental data, in

particular, results of wind-tunnel tests. Recommended wind loads on surfaces inclined to the wind are not reviewed here. For

information on this subject, the six reports of

Subcommittee No. 31 may be consulted.

It is interesting, however, to summarize the

recommended wind pressures (pounds per

square foot) for plane surfaces normal to the

wind in chronological order.

1900, Bovey [8]. Wind pressure is the maximum force which has been estimated to vary

from 40 to 50 lb/ft- of surface perpendicular to the direction of blow. Ordinary gales blow with

a force of from 20 to 25 lb, which may sometimes rise to 34 to 35 lb, and even to upward of

50 lb during storms of great severity. Pressures much greater than 50 lb have been re- corded but they are wholly untrustworthy.

Up to the present time, indeed, all windpressure data are most unreliable, and to this

fact may be attributed the frequent wide divergence of opinion as to the necessary wind

allowance in any particular case.

It would be practically absurd to base calculations upon the violence of a wind gust, a

tornado, or other similar phenomena, as it is almost absolutely certain that a structure would

not lie within its range. In fact, it may be

assumed that a wind pressure of 40 lb/ft- upon

a surface perpendicular to the direction of blow

is an ample and perfectly safe allowance, es- pecially when it is remembered that a greater

pressure than this would cause the overthrow

of nearly all the existing towers, chimneys, etc. 1908, Burr and Falk [9]. A design pressure

of 30 lb/ft- is usual.

1910, Johnson, Bryan, and Turneaure [10].

A pressure exceeding 30 lb/ft- is very improbable over a space as wide as 150 or 200 ft and generally a greater pressure than this

does not extend over a path wider than 60 ft. A maximum pressure of 30 lb/ft- would appear

ample for areas of any considerable size ; and

in localities not subject to tornadoes or hurricanes, or in protected locations, a maximum

pressure of 20 to 25 lb/ft- is sufficient. The

usual assumption for roofs and exposed buildings is 30 lb.

1911, Marburg [11]. In good practice the

usual allowance for pressures on surfaces

normal to the direction of the wind is 30 Ib/ft^

which is about the strength of ordinary windows. This allowance may be regarded as amply sufficient for small roofs and buildings

except in very exposed situations, for which

40 lb/ft- may be assumed. In built-up districts

and for buildings which present very large sur- faces to the wind the assumed pressure may be

safely reduced to 25 lb or even less. 1912, Hool [12]. For all inclinations greater

than 60° the noraaal pressure is practically 30

lb/ft-. Some engineers, however, consider 40

lb/ft- a suitable figure to use in practice.

1914, Ketchum [13]. It would seem that 30

lb/ft- on the side and the normal component of a horizontal pressure of 30 lb/ft- on the roof

would be sufficient for all except exposed locations. If the building is somewhat protected, a horizontal pressure of 20 lb/ft- on the sides is certainly ample for heights less than 30 ft. 1914, Morris [14]. Thirty pounds per square

foot has come to be recognized pretty generally

as a safe value for the wind pressure on

vertical walls of ordinary height.

1914, Schneider's Specifications for wind

in Ketchum's Structural Engineers' Handbook

[13]. The wind pressure shall be assumed as acting in any direction horizontally. First—At

20 Ib/ft^ on the sides and ends of buildings and

on the actually exposed surface, or the vertical

projection of roofs. Second—At 30 lb/ft- on

the totally exposed surfaces of all parts composing the metal frame work. The frame work

shall be considered an independent structure

without walls, partitions, or floors. 1914, Thayer [15]. For office buildings 30

lb/ft- in any direction.

1921, Ketchum [16]. A pressure of 30 Ib/ft- on vertical face of buildings seems to be sufficient for all except the most exposed positions.

1924, Hool and Kinne [17]. A maximum

pressure of 30 lb/ft- is ample for structures in

exposed positions. For structures in a protected

position, 20 to 25 Ib/ft^ is ample.

1927, Swain [18]. For buildings in cities,

partially sheltered, 30 lb/ft- is probably ample

or excessive, while in exposed situations it may

be desirable to assume as high as 50 Ib/ft^.

1930, Merriman and Wiggin [19]. For buildings not more than 25 ft to the eave line, a horizontal wind pressure should be assumed not less than 15 lb/ft- on the sides and the corresponding normal component on the roof according to the Duchemin formula for wind pressure on

inclined surfaces. For buildings more than 25

ft to the eave line, the horizontal pressure

should be taken at not less than 15 lb/ft- for

the lower 25 ft, and 20 lb/ft- for the side sur-
Strength of Houses 23

face above 25 ft and the normal component on

the roof.

1932, Urquhart and O'Rourke [20]. The wind

is assumed to blow horizontally with a velocity

sufficient to cause a pressure of 30 to 40 Ib/ft- on a vertical surface.

1939, Spofford [21]. Pressure on vertical

surfaces may be taken normal to surface and

equal to the assumed wind pressure ; for bridges

30 Ib/ft^ in any direction.

1940, Subcommittee No. 31, ASCE [7], rec- ommends a wind force of 20 Ib/ft^ for buildings not exceeding 300 ft in height.

1945, ASA American Standard [22].

The following are the requirements for buildings less than 50 ft high

Design wind pressure 20 lb/ft- in any direction. Every exterior wall shall be capable of

withstanding this load acting either inward or outward.

The roofs of all buildings shall be capable of

withstanding a load equal to 25 Ib/ft^ applied over the entire roof and acting outward normal

to the surface.

The windward slope only of roofs or sections

of roofs with slopes greater than 30° shall be

capable of withstanding a load of 20 lb/ftacting inward normal to the surface.

Overhanging eaves and cornices shall be capable of withstanding outward loads equal to 40

lb/ft2.

Many texts, very properly, refer to the building code for the location of the building for the

design wind load; some give values for the

larger cities. None of the authorities call attention to the

fact that wind loads have different values in some regions from those in others; therefore,

the values they give apply to a building anywhere in the United States. It is a reasonable

assumption that many buildings have been dej signed for the values given by each authority

; and that damage or failure due to wind has been

infrequent. Otherwise, the values would have

been discredited and greater values substituted.

On the other hand, if the values were much too great there would not be the same incentive to change them and, as years rolled by, they would

j tend to be above criticism.

I Presumably, all of the recommended wind

I pressures given in the literature are a combinaJ tion of the force inward on the windward wall

j (0.8 q) and that outward on the leeward wall

(0.5 q) or 1.3 q, in accordance with the view-

' point of the Subcommittee, although the

authors do not discuss the actual load distribuj tion.

It is evident that the velocity pressure corre- sponding to a given design wind pressure may

be obtained by dividing the pressure by 1.3 and

the result can be compared with the velocity

pressures shown on the wind map. The velocity

pressures corresponding to the recommended

wind pressures are Wind Velocity- pressure pressux-e

lb/It' it^/li' 15 11.5 20 15.5 25 19.2 30 23.1 34 26.2 35 26.9 40 30.8 50 38.5 Of the 16 authorities, 12 give pressures ranging from 20 to 30 lb/ft- for ordinary conditions.

Considering first the ASA American Standard, the design wind pressure in any direction

is equivalent to a velocity pressure of 15.4 lb/

ft2.For racking and overturning, the ASA value

is correct. For transverse wind load on wall, there are two conditions to be investigated, an airtight

building and a building with openings.

If the building is airtight, the wind load for

windward wall is (0.8 q) 12.4 Vo/ii~ acting in; on leeward wall (0.5 q) 1.15 lb/ft- acting out; on wall parallel to wind (0.581 q) 9 lb/ft- act- ing out. All these loads are much less than 20

lb/ft-. But, as usually constructed, houses are not airtighf:.

If the building has 30 percent or more of

openings in each wall, the intenial wind load

for windward openings is (0.7739 q) 12 Ib/fV

acting out and for leeward openings (0.581 q)

9 Ib/ft^ acting in. The design loads for each wall are 21.4 lb/ftacting in and 21.0 lb/ft- acting out, only slightly

greater than the ASA value.

Taking House E as a typical dwelling, the

approximate loads for a velocity pressure of

15.5 lb/ft2 are 0.775 of those for Madison. The

greatest transverse wind load on walls inward

is 19.0 and outward, 17.0 Ib/ft^, a little less than

the ASA value of 20 \h/ft-. The greatest wind

load inward on roof is 6.6 and outward 20

lb/ft-, the latter the ASA value.

The velocity pressures corresponding to the

design wind pressures recommended by authorities were compared with the wind map.

The value of 20 Ib/ft^ (velocity pressure of

15.5 Ib/ft^) is not exceeded except near the

Atlantic and Gulf Coasts, westeim VeiTnont,

northern New York, eastern Pennsylvania,

Florida, eastern and western Tennessee, west- ern Kentucky, southern and northwestern Wisconsin, northern and southern Illinois, eastern

and northwestern Missouri, northeni Arkansas,

Minnesota, western Iowa, southern North Dakota, South Dakota, Nebraska, western Kansas,
24 Building Materials and Structures Reports

Oklahoma, northern Texas, northern and east- ern Montana, southeastern Wyoming, eastern

Colorado, northeastern New Mexico, southwest- ern Utah, northern Idaho, southern and western

Nevada, southeastern and western Washington,

and northwestern Oregon.

The value of 25 Ib/ft^ (velocity pressure of

19.2 Ib/ft^) is not exceeded except close to the

Atlantic and Gulf Coasts and in Washington

and Oregon on the Pacific Coast. Other regions

having greater values are northern New York,

southern Florida, northwestern Wisconsin,

southern Illinois, southwestern Minnesota,

western Iowa, southeastern North Dakota, east- ern South Dakota, eastern Nebraska, western

Kansas, western Oklahoma, and northern Montana. The value of 30 Ib/ft^ (velocity pressure of

23.1 lb/ft-) is not exceeded except intermittently along the Atlantic and Gulf Coasts and in

Washington and Oregon along the Pacific Coast.

A few other regions having gi'eater values are southern Florida, southwestern Minnesota,

eastern South Dakota, and eastern Nebraska.

The value of 40 lb/ft- (velocity pressure of

30.8 lb/ft-) is exceeded only in Rhode Island,

eastern Massachusetts, Charleston, S. C, south- ern tip of Florida, around Pensacola, Fla.,

northeastern Nebraska, western Washington,

and northwestern Oregon.

The value of 50 lb/ft- (velocity pressure of

38.5 lb/ft-) is exceeded only in southern Rhode

Island, Cape Hatteras, N. C, and very near the

Pacific Coast in Washington and Oregon.

It should be remembered, that when recom- mending design wind pressures most of the

authorities, perhaps unconsciously, were thinking only of regions with which they were familiar and of the larger cities. Most of the regions for which 20 Ib/ft^ appear to be inadequate are not thickly populated,

therefore the authorities and ASA American

Standard are justified provided these regions

prepare local codes.

For 30 Ib/ft^, the same comment applies

except that the regions are much smaller, which

confirms the judgment and experience of the

authorities giving this value.

It may be pointed out that the wind map

gives velocity pressures for very exposed building sites although a somewhat smaller value

may be justified if the building is sheltered, but

necessarily any decrease in the value must be

left to the designer. For this report, velocity

pressures are taken from the map.

8. Combined and Design Wind Load

It is recommended that houses be designed

for all loads—dead load, floor load, wind load,

snow load, and water load, if any—applied

simultaneously although actually the occurrence

of any one of them is unlikely and the occur- rence of all of them at the same time highly improbable. It is very diflflcult to believe that

when the wind is blowing a gale there can be

the greatest depth of snow on the roof or that

during a record-breaking blizzard there will be

standing room only in each room. Experience may show that a house is safe

if designed for combinations of loads somewhat

less than the greatest load.

Combined loading conditions at all likely to occur may be floor load 10 lb/ft- with: first,

the greatest wind load and half the greatest snow load; or second, half the greatest wind

load and the greatest snow load.

Combined wind and snow loads on roofs have

been discussed at length by structural engineers, apparently without general agreement.

Designing houses for the greatest value of

each load is suggested tentatively and is the

method followed in this report.

VI. SNOW LOAD

1. Basic Snow Load

The weight of snow accumulated on the roof

constitutes the snow load on a house. It varies

with the altitude of the building site, the geographical location of the building, and the slope

of the roof.

The United States Weather Bureau (1939)

furnished data on the greatest depth of snow

in sheltered areas (such as clearings in a

forest) at 166 stations. The data cover periods

of 15 to 67 years; the average was 44 years.

That Bureau gave the average density of snow

soon after it had fallen as 0.10 that of water.

Two inches of snow weigh about one (1.04)

\h/ft~. Later, the depth decreases and the density increases. The snow load for each station was computed and figure 6 drawn. The isograms

connect points having the same snow load, and

the value at any location is termed the "basic snow load."

Assuming the snow load to vary linearly between isograms, the value for any location may

be found by interpolation along the shortest

line through the location between isograms or an isogram and a point having different values.

It may cross intermediate regions within closed

(or nearly closed) isograms. For locations

south of the Great Lakes and north of the

regions of 10 lb/ft- or more, the line may cross these regions from the 5 lb/ft- isogram along

the Gulf to the 10 Ib/ft^ isogram along the

Great Lakes. Columbus, Ohio, is 4/5 this distance, 4 lb/ft- greater than 5 Ib/ft^ or 9 Ib/ft^.

26 Building Materials and Structures Reports

The errors in snow loads taken from the map

were estimated by comparing the map values

for Weather Bureau Stations with the value

computed from the observed depth of snow. For 63 percent of the stations, the map

values are too great, average 1.1 lb/ft-, and for

37 percent they are too small, average differ- ence 1 lb/ft-. Of those too great, the differences

do not exceed 3 lb/ft-, except for Sandusky,

Ohio, Providence, R.I., Sheridan, Wyo., and

Trenton, N.J., for which the differences range

from 4 to 5.1 lb/ft-. Of those too small, the

differences do not exceed 2.0 lb/ft-, except

Albany, N.Y., for which the value is 3.0 lb/ft-.

2. Comparison with Authorities

Although the snow load on a flat roof un- doubtedly is less than on the ground in sheltered

areas, the only way to compare the values

recommended by authorities with those from

the map is to consider the values recommended

for flat roofs. The snow loads recommended by

Ketchum [23] for latitude 35° and KidderParker [24] for the Southern and Pacific states agree closely with those on the map. For more

northern locations their values are about twice

those on the map, implying an average snow

density of 0.2 that of water.

The values recommended by Hool [12] agree

closely with those on the map but MerrimanWiggin [19] are slightly greater, except those

for Baltimore, Cincinnati, and St. Louis which

are about the same as the map values.

For houses, it is believed that the values on

the map are justified. The snow load on a roof

is somewhat less than on the ground around the

house because wind blows snow from the roof.

The depth of snow on the roof of an occupied

house decreases with time after a snow storm

more rapidly than on a storage building because

the house is heated. If there is thermal insulation in the roof, snow will remain on the roof

longer than if there is no insulation, but, even

in northern states, snow disappears from the

roofs of houses in a short time.

3. Snow Load on Sloping Roof

Apparently structural engineers agree that

the snow load on the horizontal projection of a

sloping roof is less than on a flat roof because

wind blows more snow from the sloping roof

and snow slides off ; the greater the slope the

less the snow load. The ration of snow load on

horizontal projection of roof to basic snow load

is the "stay-on" factor k.

After consideration of the recommendations

in the literature, for this report, values of k were taken as follows.

For slopes of 20° or less 1.00. For slopes of 20° to 60° 1.50—0.025 ex . For slopes greater than 60° . . .0. For any slope, the factor k may be taken

from figure 7.

p/fc/i of roof ± 11 1 A 1 J. A 1 4

0 10 20 30 40 50 60 90

slope of roof , a.^ degrees

Figure 7.

Relation beticeen slojje of roof and stay-on

factor k. For slopes from 20° to 60°, these values of k

are somewhat greater than those computed from

the snow loads for sloping roofs recommended

by Ketchum [23], Kidder-Parker [24], Marburg

[11], and Schneider in Ketchum's Structural

Engineers' Handbook [23].

All authorities agree that all snow slides off a roof if the slope is 45° to 60°, provided there are no snow guards. The slope causing the snow to slide depends upon the roughness of

the roof covering; the rougher the surface the

greater the slope.

Because sleet may freeze to the roof as it falls, Ketchum [23] and Kidder-Parker [24]

recommend a snow load not less than 5 to 10

lb/ft- (horizontal projection) for all slopes

except in Southern and Pacific States. i
Streti'^th of Houses 27

Hool [12] says on roofs inclined 60°, snow

load is often neglected if there are no snow

guards as it is naturally expected that snow

will slide off. Merriman-Wiggin [19] say there

is no snow on 45° roofs if there are no snow

guards and Schneider's formula [23] gives no snow load for slopes 45° and greater.

the roof; and C, snow on the roof having the

slope oc . The dimensions of the bases are a, b, and c, and the Weights Wa, Wb and WcThe snow load on ground is SB=WA/iaxb);

that on horizontal projection,

SH=W,/iaxb) ; and on roof,

Sj,=Wc/(aXc),

but Wc=W]i=kWA, and c—b / cos oc because b

is the horizontal projection of c. Then

SR=kW,.i cos cc /{axb),

but Wa / (axb) is the basic snow load. Therefore, the snow load on a sloping roof is SR=kSn cos oc. If the snow-load factor is k

743712°~48—

If the slope is 60° or more, it is very improbable that there is any sleet load on the roof

because houses are heated.

Knowing the basic snow load and the factor

k, the snow load on the surface of the roof may

be computed. In figure 8, let A be snow on the

ground ; B, snow on the horizontal projection of

cos oc then Si{=zKSii. The value of K for any

roof may be taken from figure 9.

VII. WATER LOAD

Water accumulated on a roof constitutes a water load. Obviously, water can accumulate

only on a conventional flat roof if it is entirely

surrounded, as by a parapet wall and only

when the drains, if any, are clogged. The maximum water load depends upon the depth of

water. As water weighs 62.4 Ib/ft-^, the water

load, w, lb/ft-, at any place on the roof is iv=62Ad \h/it-,

in which d is the depth of water, feet. Unconventional houses may be designed for

maintaining water on the roof for aquatic

gardens, swimming pools, thermal insulation, or other purposes.

hor/zonfol pr ojecfion

of roof

sloping roof

gro und

Figure 8.

Snow loud on ground and on sloping roof.
28 Building Materials and Structures Reports

pitch of roof ± ± 1 1 A 1 1^34

8 54 3 S Z 5 3 4 5

0 10 10 30 40 50 60 90

slope of roof, a .degrees

Figure 9.

Relation between slope of roof and

snoiv-load factor- K.

VIII. ASSUMPTIONS

The structural analysis of a house is greatlysimplified if, except under racking load, it is considered a statically determinate structure;

then four assumptions are justified.

Floor and roof rigid diaphragm.—Each floor

and roof is considered a rigid diaphragm under

forces acting in its plane. These forces cause

neither failure nor appreciable deformation of

the floor or roof.

It is reasonable to assume that if a floor or

roof is satisfactoiy under design transverse

loads it, also, is satisfactoiy under the coplanar

loads such as tensile, compressive, and racking

loads applied under service conditions. If, for a particular floor or roof construction, the

validity of this assumption is doubted, then the

construction should be tested and the structural

properties under these loads determined.

Wall connected to floor.—Each wall and

load-bearing partition is so connected to adjoining floor or roof at bottom and top that all horizontal reactions are transmitted. These re- actions may be either normal to wall (wind

load) or parallel to wall (racking load).

If floor and roofs are to be supported, obviously, in addition at least some of the walls

must be so connected to floors and roofs that

vertical reactions are transmitted.

Floor and roof simple beam.—Each floor and

roof is a simple beam between adjacent supports such as walls and load-bearing partitions. In most cases, no bending moment is transmitted past a support but moment may be

transmitted, as past a wall, by a balcony or by

overhanging eaves.

It is believed that there is very little economic

justification for a continuous floor or roof in a house. The safety of the design depends greatly

upon the actual elevation of supports being the

design elevation and any change in elevation

with time may cause failure, particularly

changes resulting from unequal settling of

foundations. If for economical erection of the

house, joists and rafters are continous over more than two supports, they should be designed as simple beams between adjacent supports; then, in all probability, the house will

be safe although somewhat uneconomical in use of material.

Wall simple beam.—Each wall and loadbearing partition is a simple beam supported

laterally at bottom and top to floor or roof.

In most cases no bending moment is trans- mitted past a floor but moment may be trans- mitted as past attic floor by a gable end which

is not supported laterally by roof.

IX. CONVENTIONS

When designing structures it is customary

for engineers to follow well-established conventions for drawings and computations that

simplify and expedite the work, especially if it

is to be verified by other engineers. The con- ventions in general use for wood, steel, and concrete structures are not very helpful for designing houses because few are applicable.

The following conventions are suggested and

followed in this report with the expectation

that, in the future, they will be replaced by more useful suggestions when available.

1. Definitions

Anchor.—A fastening for elements or members resisting forces acting to cause separation of the contacting surfaces.

Beaiing, Floor and Roof.—Horizontal line

parallel to supporting wall through action lines

of supporting reactions.

Closure.—Part of house closing an opening

in wall or partition, i.e., door or window.

Construction.—Materials, dimensions, and

methods of fabricating an element of a house.

Elements are of diff'erent constructions if there
Strength of Houses 29

is a significant difference in materials, dimensions, or method of fabrication.

Element.—Portion of completed' house ready

for occupancy, having one primary function, for

example, a floor or wall.

Fastening.—Any device resisting relative

displacement of two elements or members.

Height Factor, h.—Ratio of velocity pressure

at given height to velocity pressure at 30 ft above ground.

Height, Story.—Vertical distance from the

surface of a floor to surface of the next floor

above.

Height, Story-Wall—WaW not continuous

past floor (platform construction), vertical distance from wall bearing at bottom to wall bearing at top of wall.

Wall continuous past floor (solid masonry),

vertical distance from floor bearing at bottom

of wall to floor or roof bearing next above.

Key.—A fastening for elements or members

in contact resisting forces acting to cause displacement parallel to the contacting surfaces.

Load, Allowable.—Greatest applied load for

which a construction functions satisfactorily in a house.

Load, Applied.—Load on an element in addition to the weight of the construction.

Load, Design.—For a particular house, greatest load on an element that may occur under

service conditions.

Opening.—An aperture in wall or roof that

may be closed by a door or window.

Portion.—An undivided section of an element

having uniform width.

Reaction.—Load exerted by a support.

Stay-on Factor, k.—Ratio of snow load on

horizontal projection of roof to basic snow load.

Snoiv Load, Basic.—Greatest snow load on

ground ever recorded at a given location.

Snow-load Factor, K.—Ratio of snow load on roof surface to basic snow load.

Support.—Member of a house in contact with

and exerting a load on another member or

element.

Velocity Pressure, Basic.—Greatest velocity

pressure at height 30 ft above ground ever re- corded at a given location.

Velocity Pressure, Nominal.—Value at given

location at midheight of given story or roof.

Weight.—Of a construction, the weight in

pounds per square foot based on the face area.

2. General

(a) Dimensions

The dimensions for a house may be obtained

from the plans. If they are drawn to scale, a dimension not given numerically may be

measured.

For walls and roofs the dimensions are those

measured on the outside of the house. An error

of one percent (1 in. in 10 ft) is negligible

when computing design loads. The difference

between the longer dimensions of a completed

house and the dimensions shown on the plans

may exceed one percent because of differences

between actual and nominal dimensions of

materials and building units and, also, because

of unavoidable errors in workmanship.

(&) Weight

The weight of elements of the house may be

taken as the value accepted by the building in- dustry, may be computed from information in

specifications, or may be determined more ac- curately by weighing the element. Each BMS

report on structural properties gives the weight

based on the face area. Because of variations

in the density, moisture content, and dimensions of commercial materials, the weight may

vaiy as much as 10 percent.

(c) Structural Properties

The properties of a construction, including

allowable load, may be computed by the usual

engineering methods or they may be determined,

much more accurately, by testing specimens of

the construction representative of portions of a completed house.

The properties of over 100 constructions, deteiTnined by testing large specimens, are given

in the BMS reports on structural properties.

For some of these constructions, the properties

also were computed by engineering methods

but they did not agree, even approximately,

with the test values. This indicates, quite definitely, that the structural properties of house

constructions cannot be satisfactorily computed from average properties of the materials

because the strength and other properties of

many kinds of fastening are unknown and, for

frame constructions, there is no accepted

method for computing the effect of the faces

such as sheathing and plaster on the strength

of the construction.

3. Elements

(a) Wall and Partition

(1) Height

For any house suitable for human occupancy,

the ceiling height (vertical distance from surface of floor to ceiling above) must allow the

occupants to stand upright, a minimum of

about 6 ft 6 in. It also should comply with

health requirements, in some building codes at

least 7 ft 6 in. From an economic viewpoint.
30 Buhfting Materials and Structures Reports

if the ceiling height exceeds 9 ft, the cost of

the house and of heating may be considered excessive. If the wall is not continuous past the

floor (platform construction) the story-wall

height is the ceiling height. If the wall is con- tinous past the floor (solid masonry) the storywall height is the ceiling height plus the thick- ness of floor. Therefore, the least wall height

for a house should be 7 ft 6 in. The nominal

height of walls and partitions in BMS structural reports is 8 ft.

(2) Width

The width of each portion of wall may be

obtained from the plans. It is the distance between adjacent openings or edges of the wall.

Likewise, the width of each portion of a partition may be obtained, being the distance between a door and the opposite face of intersecting wall or partition.

(5) Thickness

For design, the thickness of wall or partition

is the distance between the inside and outside

surfaces of the structural members. For frame

walls, the studs are the structural members.

For masonry walls, stucco, furring, lath and

plaster, if any, are disregarded. For cavity

walls, if floor and roof bear only on the backing, the wall thickness is the thickness of the

backing; if they bear on both backing and

facing, the wall thickness is the distance from

inside surface of backing to outside surface of

facing. For brick veneer walls, if floor and

roof bear only on the wood frame, the wall

thickness is the distance from inside surface

of studs to outside surface ; if they bear on

both, the thickness is the distance from surface

of stud nearer inside of house to outside sur- face of brick veneer.

F floor loac/

3 sr?opv load

W wind load

*o- no load

S—^ wind direction

Figure 10.

Reactions on each element of a simple house (south and east wind).
Strength of Houses 31

U) Weight

The weight of a wall is the outside face area

times the weight of construction.

Although weight computed in this way closely approximates the actual weight of walls between openings, it is somewhat too great for

walls intersecting at a comer projecting out- ward because the material in the corner is considered twice.

For frame walls, it is customary to place

additional studs in comers, therefore, the computed weight approximates the actual weight.

For masonry walls, the error is greater the

greater the wall thickness. For an 8-in. solid

wall, the computed weight of a wall 3 ft wide

having a comer along one edge is 11.1 percent

too great, provided the error is equally divided

between the intersecting walls. If the wall is

6 in. thick, the error is 8.3 percent, and if 3 in., only 4.2 percent.

If a comer projects inward, the computed

weight of an intersecting wall is too small be- cause none of the material in the comer is considered. The number of corners projecting out- ward is four more than the number projecting

inward, and, most houses have few comers

projecting inward.

If the weight of an 8-ft specimen is used for

computing the weight of a wall having greater

height, the value is a little too small, provided

there are horizontal structural members in the

construction such as sills, plates, or girts but

the error is negligible for most constructions.

On the other hand, for masonry constmctions,

the weight of the wall is proportional to the

face area and the height ; thus, the computed

weight is correct.

B—^ w/naf direcfTon

Figure 11.

Reactions on each element of a simple house (north and ivest wind).
32 Building Materials and Structures Reports

In most houses, the structural members of

the floor extend into the wall. In frame walls,

they project into the spaces between studs,

therefore, the weight of the wall is not aifected

appreciably. In solid masonry walls, there are spaces lor the joists that decrease the weight

of the wall at the floor but the effect on the

weight of the wall is negligible, for an 8-in.

wall only about 1.5 percent. This method of

computing the weight of the wall probably is satisfactory, particularly as most of the errors

are on the side of safety.

(5) Closures

The dimensions of doors and windows are

the nominal height and width used commercially to designate the size. The weight may be

obtained by placing the doors and sash on a platform scale or it may be taken from publications such as Building Material Data [25].

The frame for closure and additional

members around the opening such as braces

above the opening are disregarded because, to some extent, they replace wall materials and to estimate their effect on the weight of the wall

presents complications that do not appear

worth the effort. For this report, the weight of all doors is taken as 4 lb/ft- and of all windows as 7 Ib/ft^.

(b) Floor

(1) Bearing

If the floor bearing is in a wall (or partition)

it is taken as being one-third the thickness of

the structural wall from the inside surface.

Most floors do not extend through the wall and

deflection of the floor under service loads causes the floor bearing to approach the inside

surface of the wall.

If the floor is supported on a projection, as by a steel angle, the floor bearing is taken as being one-third the width of the projection

from the inner edge.

(2) Dimensions and Weight

The span of a floor is the distance between

floor bearings and the width is the distance

between the structural walls on which the floor

does not bear. The face area is the span times

the width, and the weight of floor, the face area

times the weight of construction.

The ceiling (if any), subfloor, and finish

floor do not extend to the floor bearing in supporting walls and usually they do not extend to the other walls, so the computed weight is too

great. However, the weight of the joists beyond the floor bearing is not included ; therefore, it is probable that the computed weight

approximates the actual weight.

(c) Roof

(1) Bearing

The roof bearing, as for a floor, is taken as being one-third the thickness of the structural

wall from the inside surface.

(2) Dimensions and Weight

For a flat roof not extending beyond the

walls, the dimensions and weight may be

obtained as for a floor. If a flat roof extends

beyond the walls, the length is the distance

from end to end parallel to the structural

members; the width is the distance from edge

to edge normal to the members and the weight

is the face area times the weight of construction.

For a sloping roof, the length is the distance

from ridge to eaves parallel to the structural

members, the width is the distance from edge

to edge of the roof. The weight of each slope

is the face area times the weight of construction.

X. REACTIONS ON ELEMENTS OF HOUSE

The reactions on each element of a simple

house are shown in figures 10 and 11. To simplify the presentation, the house is one-story 12 by 16 ft, walls 8 ft high, and the

roof 30° slope. There is one door and one window. The dashed lines indicate the direction

of the studs, joists, and rafters.

The weights of construction are taken as roof

and attic floor 5 Ib/ft^; walls, gables, and floor 10 \h/fV-. The velocity pressure is 30 Ib/ft^ on

both wall and roof, basic snow load 25 Ib/ft^

and floor load 40 Ib/ft^.

The direction of wind is taken normal to each

face in turn and, for each direction of wind,

the window is closed and the door open; percentage of opening taken as 30 percent.

The assembled house with applied loads is shown for each direction of wind. They are

the resultants of the uniformly distributed surface loads acting at the center of the surface.

Around the assembled house is each element

with the weight, vertical and horizontal components of the wind load, if any, and all the

reactions. The weight is the total weight of

the element acting at the center of the face.

The reactions at the midwidth of an edge are

resultants of forces uniformly distributed along

the edge. Horizontal racking forces along the

top and bottom edges of walls cause a redistribution of the vertical forces along the bottom

edge. After redistribution, they vary linearly

from maximum at one vertical edge to minimum at the opposite vertical edge. In effect,

the resultant at midwidth is combined with a couple of opposite sense to the racking couple
Strength of Houses 33

and the resultant forces of this couple act at two-thirds the distance from midwidth to the

vertical edge.

XI. ROOF

For both symmetrical and unsymmetrical

sloping roofs of any slope, the design load and

reactions at ridge and wall may be deteraiined

by the methods described here. The methods

are best explained by computations for a particular house. Although analytical methods are

described, it is obvious that graphical methods

also are suitable and save time. Although it should be expected that errors in graphical

results will be somewhat greater than those in

analytical results, they are less than the errors

in the assumed loads ; therefore, entirely satisfactory for house design.

1. Sloping Roof With no Horizontal

Reaction From Gable

If the gable is continuous with wall below, so that all wind load on gable is transmitted as

reaction on attic floor and bending moment on

wall below, the gable exerts no horizontal re- action on roof.

(a) House With Unsymmetrical Sloping Roof

For this explanation, house E in Madison,

Wis., was selected, but the symmetrical roof

is replaced by an unsymmetrical roof having

slopes 25° and 50°, as shown in figure 12.

It is assumed that walls are conventional

wood-frame construction QA having 2- by

4-in. studs. The roof is construction QC having

2- by 6-in. rafters and weighs 4.6 lb/ft-.

(b) Dimensions

For design, the dimensions of all structural

members are taken as the nominal size. The roof bearings on walls are one-third the

distance from inside surface of stud to outside

surface; therefore, the distance between bearings is 19.64 ft. From the equation

sm oc sm p sm y

ji the slope spans are left slope 15.57 ft, right

slope 8.59 ft. It is believed that spans computed in this way closely approximate the

actual spans.

The dimensions measured on the plans or on

a scale drawing are

ft

T

, , . , ( left 16.3 Length of slope

^ g g Width of slope 23.5 Height, roof bearing to ridge 7.25 Midheight of roof, above ground 21.8

(c) Wind Load on Roof

The height factor, h, is 0.9152 and velocity

pressure on roof 18.3 \h/ft-. The wind loads

for each direction of wind and for windward

and leeward openings are given in table 9.
34 Building Materials and Structures Reports •

Table 9.Wind loads on umymmeirical sloping roof on House E in Madison, Wis.

I (Velocity pressure at niidheight of roof 18.3 \b/ft-. Leeward openings include openings in walls parallel to wind. Internal wind loads taken from table 4]

1

Roof

Left-hand slope, 25° Right-hand slope, 50°

Velocity- pressure. Q External wind load OpeningInternal wind load Combined

wind load

Velocity

pressure, ? External wind load Opening

Internal wind load Combined

wind load SOUTH WIND

Both slopes

parallel to wind. Docoef

0. 774

. 774

14. 2

14. 2

Acts Out Do

Windward

Leeward

8. 7

7. 1

Acts Out

In

lb/ft' 22.9

7. 1

Acts Out

In

coef

0. 774

. 774

Ib/ft^ 14. 2

14. 2

Acts Out Do

Windward

Leeward

Ib/ft^ 8.7

7. 1

Acts Out

In

Ib/fP 22.9

7. 1

Acts Out

In EAST WIND

L H slope, leeward 0. 581 10.6 Out Windward 8. 2 Out 18.8 Out 0. 387 7. 1 In Windward 8.2 Out 1. 1 Out R H slope, windward_ . 581 10.6 Do Leeward 7. 1 In 3.5 Do .387 7.

1

Do Leeward 7.

1

In 14. 2 In NORTH WIND

Both slopes.

parallel to wind. Do _

0. 774

. 774

14. 2

14. 2

Out DoWindward

Leeward

8. 7

7. 1

Out

In

22. 9

7. 1

Out

In

0. 774

. 774

14.2

14.2

Out DoWindward

Leeward

8. 7

7.1

Out

In

22. 9

7. 1

Out

In WEST WIND

L H slope, windward. 0. 392 7.2 Out Windward 8. 2 Out 16.4 Out 0. 581 10.6 Out Windward 8. 2 Out 18.8 Out R H slope, leeward .392 7. 2 Do Leeward 7. 1 In 0.1 Do .581 10.6 Do Leeward 7.1 In 3.5 Do

(d) Snow Load on Roof

The snow loads are (basic snow load 13.0

lb/ft-)

Left slope (A' = 0.79) 10.3 lb/ft2. Right slope . . . (A' = 0.16) 2.1 Ib/ft^. For this explanation, if there is snow, it is assumed that both slopes are loaded. However,

actually there may be snow on one slope but none on the other. The transverse load on a slope computed for snow on both slopes is correct if there is no snow on the other slope,

but the longitudinal (tension or compression)

load on loaded slope, and more important, the

load on fastenings at ridge and wall may be

much greater.

Obviously the condition for snow load on one

slope and none on the other slope should be

considered ; otherwise the roof may fail under

service conditions.

(e) Loading Conditions

All possible loading conditions are shown in

the first columns of figures 13 and 14.
Strength of Houses 35

The factors are direction of wind, windward

or leeward openings, and snow. For any unsymmetrical sloping roof such as

this, there are 12 conditions, including wind

parallel to ridge and, from both directions,

normal to ridge.

For any symmetrical sloping roof there are

eight conditions, including wind parallel to ridge and from one direction normal to ridge.

j| If there is no snow, there are only four condiI tions.

(/) Components of Loads

The vertical loads (weight and snow) are independent of the direction of wind. The sum

of these loads for snow and no snow are re- solved into components normal and parallel to

slope. The values for this roof are shown on

figure 15. The normal component is combined with the

wind load, also normal. The components for

this roof under all conditions are shown in the

second column, figures 13 and 14. The greatest outward normal component is one of the design transverse loads for the

f slope and the greatest inward is the other

j design transverse load.

Each component is multiplied by length of

slope, giving the total load per foot width of

slope parallel to ridge. For the first condition

these loads are:

Left slope : w/ft Normal load 304.9 Parallel load 31.0 Right slope

Normal load 191.0 Parallel load 33.6 The normal reactions at ridge and wall are

half the normal total load but the parallel re- actions must be determined.

(g) Reactions at Ridge

The four concurrent reactions at ridge are shown on figure 16 for the first condition, wind

parallel to ridge, windward openings, no snow.

It is convenient to choose axes normal to

slopes.

F^=0=b' cos 15°—89.55 sin 15°—152.45 b'= +181.9 lb/ft upward to left. Fj,= 0= 89.55—152.45 sin 15°+6 cos 15°

6 = + 133.5 lb/ft upward to right.

_ Negative values for these reactions would indicate that the assumed directions should be

reversed.

(h) Reactions at Wall

The parallel reaction at wall is the combination of the parallel reaction at ridge and parallel load ; in this case

lb/It Left slope 108.9 downward to left Right slope 149.9 downward to right

Obviously all parallel reactions are tensile or compressive loads on the slope and the value

varies linearly along the slope from the value

at one end to the value at the other end. If

there is a tensile reaction at ridge less than the

parallel load the longitudinal stress in the roof

is zero somewhere between ridge and wall.

The greatest tensile reaction at either ridge or wall for any condition is the design tensile

load and the greatest compressive reaction is the design compressive load for the slope of

roof.

When designing bearing surfaces and fastenings, such as anchors or keys, it is convenient

to know the vertical and horizontal reactions

at ridge and wall. They may be computed

from the normal and parallel reactions by the

usual methods.

The values for this roof under all loading

conditions are shown in the third column, fig- ures 13 and 14.

(i) Design Loads at Ridge and Wall

At ridge, the greatest horizontal reaction act- ing outward is the design load in compression

for the vertical bearing surface between slopes

and the greatest value acting inward is the

design load for anchors. The greatest vertical

reaction, either upward or downward, is the

design load for keys.

At wall, the greatest vertical reaction upward is the design load in compression for

the wall and the greatest value downward is the

design tensile load for wall and also the design

load for anchors. The greatest horizontal re- action either inward or outward is the design

load for keys.

(j) Effect of Attic Floor on Reactions at Wall

If there is no attic floor, the horizontal re- actions on each slope of roof are exerted by the

walls through keys.

If there is an attic floor and the horizontal

reactions act in opposite dii*ections, the floor

is under a longitudinal load equal to the smaller

of the reactions, tension if the reactions act outward, compression if they act inward. The

difference (if any) between the reactions is transmitted by the floor as racking load to all the walls and load-bearing partitions normal

to ridge.
Building Materials and Structures Reports

Lb/ff

South or North

Windward open.

No snow

22.9 22.9

4.6 4.6

1-9 3.3 1

1 84.. I

Lb/ ft of width

79.0

\2d.2

19.0

\ 176.2

22.9

10.3 2.t

Snow

4.6 4.6

9.4- 18.6

^3 3.1 21.3 21.3 \ 73.6 96.3

Leeward open.

No snow

lO.l

I 9.1

5not

10.3 2.1

4.6 4.6

ll.l

90.1

— 22.1 —

41.2

i\74.2

47.2

I 67.5

East wind

Windward open.

No snow

18.6

4.6 4.6

70.9

96.3

\62.8

98.3^

61.1

10.3 2.1

Sno^v

4.6 4.6

6.3

1 13.1

6.0

— 14.3

41.0 41.0

j /6.6

Figure 13.Loading conditions for unsymmetrical sloping roof on House E (north or south wind and

part of east wind).
Strength of Houses 37

^(75/ wind

Leeward open.

No snow

Lblff Lb Iff of width

I05.O

60.8 —

31.7

\ 100.

Snow

10. J 2.1

4.6 4.6

6.3 \ 165.3

^^137.5

25.9

\\33.Z

25.9

\ 1778

Wesf wind

Windward open.

No snow

15.4 18.6

4.6 4.6

—132.2—

26.1 \\6^

^1 393 39.3

\

1 13.1 I II. I

Snow

10.3 2.1

4.6 4.6

14.5

30.6

I8.Z

75.5 —

2.7

\62.7

162 1^

334

Leeward open.

No snow

3.5

4.6 4.6.

10.3 2.1

20.3

46.1

77.0

1 9.6

27.4

\\45.4

274 I 50.0

76.3-

102.0

Snow

4.6 4.6

65.0 85.0 6-^ 51

156.4 12 7.

Figure 14.

Loading conditions for iinsymmetrical sloping roof on House E (part of east ivind and west ivind).
38 Building Materials and Structures Reports

4.6

3.0.

-25

3.6

4.6^

No Snow

Figure 15.

Normal mid parallel components of weight

and snow on xinsymmetrical sloping roof.

If the horizontal reactions act in the same

direction, their sum is transmitted as racking

load to walls and partitions.

2. Sloping Roof with Horizontal

Reactions from Gable

If the gable is not continuous with wall

below, the wind load on each gable is transmitted horizontally, half to the roof and half

to attic floor, provided the structural members

in the gable are vertical.

(a) Wind Load on Gable

The internal wind loads on gables are the same as those on roof given in table 4. All

the wind loads on gables of this roof are given

in table 10.

Figure 16.

Reactions at ridge in unsyni metrical

sloping roof.

Table 10.

Wind load on gables of House E in Madison, Wis.

[Velocity pressure at midheight of roof 18.3 lh/!t-. Leeward openings include openings in walls parallel to wind. Internal wind loads taken from table 4]

Gable Velocity I pressure, g \ External wind load Opening Internal wind load Combined wind load SOUTH WIND

Windward- Do

Leeward Do

coef0.8 14.64

14. 64

9. 16

9. 15

Acts

In Do

Out Do

WindwardLeeward Windward

-

Leeward

lb/ft'

7. 1 8. 7

7.

1

Acts Out

In Out

In

lb/ft'5.94

21. 74

17. 85

2.05

Acts

In Do

Out Do EAST WIND

Parallel to wind (both gables)- Do0. 581

. 581

10. 63

10. 63 Out Do

Windward

-

Leeward

8. 2 Out 18. 83

7. 1 In 3. 53 Out Do NORTH WIND

Windward

-

Do

Leeward Do

0.8 14. 64 In Windward 8.7 Out 5. 94

.8 14.64 Do Leeward 7,

1

In 21.74

. 5 9. 15 Out Windward . 8. 7 Out 17. 85

. 5 9. 15 Do Leeward - . 7.

1

In 2. 05

In Do

Out Do WEST WIND

0. 581 10.63 Out Windward 8.2 Out 18. 83 Out

.581 10. 63 Do Leeward - _ _ _ 7.

1

In 3. 53 Do

Parallel to wind (both gables) _ Do
Strength of Houses 39

The greatest combined wind load acting out

is one of the design transverse wind loads on

gable and the greatest acting inward is the

other design transverse load.

For wind parallel to ridge, both gables exert

horizontal reactions on roof, windward gable

inward and leeward gable outward, both to leeward, whether openings are in windward or leeward walls. The resultant of wind loads on

both gables for any roof is independent of

openings and always equal to 0.8 g-|-0.5 q, or

1.3 q. For this roof, it is 23.8 lb/ft-, which is 1.3 q. When designing a roof, the resultant of the

gable reactions may be taken as applied at either the windward or leeward edge of the

roof. If the roof is symmetrical and openings

are in windward wall, probably there is tension

in the roof along the ridge ; if in leeward wall,

there is compression. For this discussion, it will be assumed that half the resultant wind

load on both gables is applied along windward

edge of roof.

For wind normal to ridge (see table 9, east and west wind) , it is evident that the wind loads on gables are always equal and both act out- ward; therefore, the only effect on roof is tension parallel to ridge, more for windward

openings than for leeward.

(b) Distribution on Roof of Gable Reactions

For wind parallel to ridge, gable reactions on

this roof are shown on figure 17. Along the veilical line through ridge, wind

load on gable is 23.8x6.58=156.6 lb/ft of

width, on attic floor 78.3 lb/ft, on left slope

78.3 Xcos 25° =71 lb/ft, on right slope 78.3 Xcos 50° =50.35 lb/ft. The reactions on roof and

floor decrease linearly from these values to zero at wall. The resultants for each slope and

each portion of floor act at two-thirds the distance from wall. They are the average re- action times the span. The sum of these four

resultants equals area of gable (64.6 ft-) times

the wind load.

(c) Racking Load on Roof

The gable exerts racking loads on each slope

of roof. In EMS structural reports are results

for racking loads on walls but none on roofs.

For determining design loads on roof, numerical

values of deformation of roof under racking

load are unnecessary if both slopes are the same construction, i.e., both slopes have the same racking modulus. The racking modulus

for the construction must be known if the

racking deformation is to be determined.

{1) Racking Modulus

Let acde, figure 18, be any house construction

having length I and width b fixed along edge

Figure 17.Distribution of racking load on roof. Figure 18. -Racking load along free edge of hoiise construction.
40 Building Materials and Structures Reports

ae and loaded along the opposite edge cd by

the racking (shearing) force F.

The racking deformation r is directly proportional to force F and length I but inversely

proportional to width b. For / and b equal 1 foot the racking ynodulus

R is the force, either in pounds or in kips, caus- ing a deformation r of 1 foot computed from

the inital rate of deformation.

For any values of / and b

r= -y—^ andAT?R=—,

b R b r The slope of ac' is r/l=F/b R.

If the racking force is applied anywhere between ae and cd as along fg, figure 19, the deformation of portion afge is bR'

Figure 19.Racking load betiveen fixed and free edge

of house construction. There is no racking deformation of portion

fcdg because there is no racking force on this

portion. Therefore, the deformation at c is the same as the deformation at /.

(2) Reactions Due to Racking Load

If racking load is applied to a sloping roof

there must be an equal and parallel reaction

in the opposite direction. If the roof is symmetrical, this reaction cannot be applied at ridge by the other slope because the racking

load on both slopes is the same and the racking

defoiTnations are the same. It is evident that

this reaction must be exerted by the wall, the

only other element in contact with the slope.

The racking load and wall reaction are a couple in the plane of the slope; therefore,

there must be a couple having the same moment

but opposite sign in the plane of the slope. If the angle between the slopes is 90°, this opposLoad

Figure 20.

Deformation of Jioiise construction under

racking load linearly distribiited along edge

normal to direction of load.
Strength of Houses 41

ing couple could be exerted by the other slope

only if it is warped, i.e., the ridge edge were

forced out of parallel with the wall edge in

plane normal to slope. But for i-oof constructions, the resistance to warping is negligible, even if the angle between slopes is not 90°

therefore, the opposing couple must be exerted

by the wall.

For designing houses, it is assumed that the

couple opposing the racking couple is in the

plane of the slope and exerted by the wall.

For symmetrical sloping roofs having the same racking modulus for each slope, there is no longitudinal racking reaction between slopes

at ridge, but for unsymmetrical sloping roofs,

particularly if the slopes have different racking

moduli, thei'e may be a racking reaction at ridge

because in a house the racking deformation of

the slopes must be the same.

(d) Deformation Under Distributed

Rackirig Load

Theorem : The racking deformation under a

racking load distributed linearly along an edge

normal to direction of load is the same as the

deformation under the residtant of the distributed load.

Proof: Let ac, a construction 1 foot wide,

fixed along the left edge, as shown in figure 20,

have the racking modulus R.

The racking load at c is w pounds per foot of

length and on any plane between a and c, such

as X, is-^iv. The shearing forces on plane c are

zero ; on plane a, ; on plane x, —2fil —^ ) The slope at x of the deformation curve is F w

-r^ = (/-

X-) but this is the first derivaOK ^IK

tive of the curve through the deformations. In- tegrating with respect to x, the defonnation

to

IS {M-x—x^) , in feet. It follows that the

deformation at a is zero, at c,

If the distributed racking load is replaced by

the resultant Galso at c is

I, the deformation at g and

Fl

bR

^ 2 , wl 21

bR R SR

Therefore, the racking deformation under

any linearly distributed racking load may be

computed by replacing the distributed load by

the resultant racking load. Q. E. D.

If structural members in gable are horizontal, none of the wind load on gable is ti*ansmitted to attic floor (if any). The reaction on

each slope is distributed linearly along the edge

of roof from zero at ridge to maximum at wall.

Half the wind load is transmitted to each slope

whether the roof is symmetrical or unsymmetrical and the resultant reaction on each

slope acts at two-thirds the span slope from

ridge.

For symmetrical sloping roof, the racking

deformation at resultant and at ridge is tvP/GR,

half the deformation for gables having vertical

structural members.

(e) Racking Load Transferred at Ridge in

Unsymmetrical Sloping Roof

For a symmetrical sloping roof, if the racking modulus is the same for both slopes, it is evident that the distributed racking loads and

therefore deformations at ridge are the same

for both slopes so there can be no longitudinal

reaction at ridge. If the roof is unsymmetrical

or the moduli difi'erent, there may be a longitudinal reaction necessaiy to make the deformations the same for both slopes.

552.Q

ZI6.U

Figure 21.

Transfer of racking load aloxi/ i idge in xinsy mmetrical sloping roof.
42 Building Materials and Structures Report

Both slopes of this roof are shown in the

plane of the paper on figure 21.

Let m be the total longitudinal reaction at ridge.

The racking deformations at ridge are

Left slope, = +

Right slope,

552.8 X 10.38 15.57m

23.5R

, 216.1X5.727

23.572 +

23.5R

8.59m

23.5i2

Because in a house r^, must equal Vu

552.8 X 10.38—15.57w = 216.1 X 5.7274-8.59m. m= 186.4 lb, or 7.93 lb/ft along ridge.

(/) Reactions at Wall due to Racking Load

The longitudinal reactions at walls are

Left wall. . .366.4 lb, or 16.18 lb/ft along wall

Right wall . .402.5 lb, or 17.76 lb/ft along wall Because the right slope is shorter, therefore

stiffer under racking load, it transmits to right

wall some of the racking load on the left slope.

The racking couples are

Left slope : +552.8 X 10.38—186.4 X 15.57= +2838.0 ft-lb. Right slope : —216.1 X 5.727—186.4 X 8.59 = —2838.0 ft-lb. Assuming that the forces of these couples are nonnal to edge of slope along wall and are the resultants of the linearly distributed re- actions shown on figure 21, the arm of both

couples is 15.113 ft (two-thirds width of wall) ; therefore the resultants are

lb Left wall 187.8 Right wall 187.8 The average reactions are

Left wall 16.57 along wall. Right wall 16.57 along wall.

At the windward and leeward edges of wall

the greatest reactions (twice the average) are

lb/ft Left wall 33.14 in plane of slope

Right wall 33.14 in plane of slope

Combining these reactions due to racking load

with parallel reaction due to weight of roof and

wind load on roof gives

Left wall

:

Windward edge of wall. Leeward edge of wall.

.

lb/It 108.9+33.14 = 142.04. 108.9—33.14= 75.76.

Right ivall

:

Windward edge of wall. . 149.9+33.14= 183.04. Leeward edge of wall. . . 149.9—33.14 = 116.76.

The normal reactions have no components in

plane of slope.

The vertical and horizontal reactions in plane

normal to ridge are

Left wall: Vertical Horizontal

lb /It lb/it Windward edge . . .198.08 down 64.24 out. Midwidth 184.1 down 34.2 out. Leeward edge 170.17 down 4.16 out.

Right wall: Windward edge . . .201.56 down 44.5 out. Midwidth 176.2 down 23.2 out. Leeward edge 150.84 down 1.90 out.

For all conditions of loading with wind parallel to ridge (north or south wind), all the re- actions at ridge and wall are shown on figure

22. All values are in pounds per foot along the

edge of roof or wall.
Strength of Houses 43

Leeward open

No snow

Reactions in Ibjff of width

"-^^ Leeward open.

Snow

Figure 22.

Reactions along ridge and ivall in unsymmetrical sloping roof for ridge parallel to vind.

(g) Projection Method for Determining

Vertical and Horizontal Reactions at Wall

The vertical reactions at wall may readily be

computed by considering the projection on a

743712°—48—

vertical plane through ridge of the resultant

racking load due to wind on gable and longitudinal racking reaction at ridge (if any)

These reactions are shown in figure 23.
44 Building Materinls and Structures Reports

552.8

Left wall

Z16.1

Righf wall

Figure 23.Raching loads in xmsymmetrical sloping roof projected on vei'ticul plane.

The moment of racking couples are

It-lb Left slope —1199.0

Right slope —2174.0

The resultant forces of opposing couple ex- erted by walls are

lb Left wall 79.26 Right wall 143.9 The greatest distributed reactions are

Ib/lt Left wall 13.98 along wall. Right wall 25.36 along wall. These reactions due to wind load on gable

may be combined with vertical reactions due to other loads.

The vertical reactions in plane normal to ridge due to all loads are

Left wall : i^/ft Windward edge 198.08 down.

Midwidth 184.1 down.

Leeward edge 170.12 down.

Righ t tuall : Windward edge 201.56 down.

Midwidth 176.2 down.

Leeward edge 150.84 down.

The horizontal reactions due to wind load on

gable may be determined by projecting the re- sultant racking loads on a horizontal plane ; for

this roof left wall 30.04 lb/ft, right wall 21.3

lb/ft.

For all loads, the horizontal reactions in

plane normal to ridge are

Left ivall : n, Windward edge 64.24 out. Midwidth 34.2 out. Leeward edge 4.I6 out. Right ivall: Windward edge 44.50 cut. Midwidth . . . ; 23^2 out.

'

Leeward edge 1.90 out. The projection method is convenient particularly if only the vertical reactions at wall are

desired.

3. Projecting Roof

If there are projections from the house, such

as the roof of a porch, suppoi-ted along the wall

and at outer edge, as by posts, the projection

is designed in the same way as a roof, assuming

that no bending moment is transmitted over

wall.

(a) Noncontinuous Projection

If the projection is supported only along the

wall, as for overhanging eaves, the design loads

may be determined as described here. Consider

House E having the unsymmetrical sloping roof

but with eaves extending 6 ft from wall for both

slopes. The velocity pressure on these over- hanging eaves is taken as 16.2 lb/ft-', the value

at midheight of the second story. The wind

loads on these projections are Windward side of house—

-

Slope 25° : ih/ft^ Upper face (—0.387 q) —6.27 up. Lower face (—0.8 q) —12.96 up. Combined load (—1.187 q) .—19.23 up. Slope 50°

:

Upper face ( +0.387 q) +6.27 down.

Lower face (—0.8 q) —12.96 up. Combined load (—0.413 q) . .—6.69 up. Leeward side of house—

Both slopes

:

Combined load (—0.081 q) . .—1.312 up. Side of house parallel to wind—

Both slopes : Combined load (—0.193 q) . .—3.127 up. For all directions of wind, the wind loads on

these eaves act upward. The greatest values
Strength of Houses

Wind — No snow

Loads and reactions in Ibjff of width

/\/foments in ft- lb /ft of width

No wind — Snow

Loads and reactions in lb Ift of width

Moments in ft— lb /ft of width

Figure 24.Some loads and reactions on noyi-continuous

projecting roof.

45

are for the projection on windward side of

house. For design, the greatest load acting upward is the wind load on projection on windward side of house combined with the weight of

projection. The greatest load acting downward

is the snow load combined with the weight, no wind load. These conditions are shown on fig- ure 24.

The reactions at wall are:

Vertical Hoiizontal Moment

Lb/It Ib/ii jt-lh/lt Wind, no snow : Slope 25° . . 76.7 down 48.4 in 270.0 counterclockwise

Slope 50° . . 1.8 up 30.5 in 66.6 clockwise

S^iou', no wind:

Slope 25°. . 89.4 up 0.03 in 243.0 clockwise

Slope 50° . . 40.0 up 0.1 out 77.4 counterclockwise

The moment decreases linearly from the

value at wall to zero at outer edge of eave. The greatest value in any direction is the

design load, in that direction, for eave construction at wall and also for fastenings.

(&) Continuous Projection

In this roof the rafters in eaves are continuations of those in roof, notched over the outer

edge of top plate in wall. The allowable bending

moment at smallest section should be determined either by tests or by computation and

compared with the design moments.

Provided the eave construction is a continuation of the roof construction and bending

moment is transmitted past the wall, the effect of eave load on design transverse loads of roof

between ridge and wall must be considered.

An interesting illustration of conditions that

may occur in service is shown in figure 25.

These are combinations of eave loads shown in

figure 24 and corresponding roof load for windward openings on 25° slope, and leeward openings on 50° slope. Insofar as transverse loads are concerned, each slope is a simple beam

overhanging one support having a uniformly

distributed load between supports and a different unifoiTnly distributed load on overhang.

For convenience, the left slope is shown upside down so that the distributed loads act downward. On right slope, the load between

supports acts downward but that on overhang

upward.
46 Building Materials and Structures Reports

Windward open.

No snow

Leeward open.

No snow

CP

8 o 50

Loads in Ib/fi

Shear and rnomenf diagrams

Left slope Riglif slope

90.0

114.4.

14-1.1

1 1 M

15.0

-

1 1 1 1 y/.z

^

15.5

1'—

I

I II /IZ MM

-8.59

6-

I 1 1 1 1I

194.5 69.

Q

3.1

t Rc Rd 22.2

6/. 6 43.

9

Loads and reactions in lb ff of width

104.5

4.144-

90.0 69.8

81.6

66./

2/7.4 /93.

6

Ik.

V\^/Z.46'— 1^9.49 A

210.0

Moments in ff—lbjff of width

Figure 25.Some transverse loads and reactions on

continuous jirojecting roof. For left slope, there are two design bending

moments on roof between ridge and wall and

they have opposite signs. One, the reverse moment over wall, is equal to the design mo- ment for eave, and the other moment, that

caused by the design transverse load between

ridge and wall on an effective span equal to the

distance from ridge to point of contraflexure.

This effective span is shorter than the actual

span.

For left slope the point of contraflexure between supports is where the moment is zero. Let X be distance from ridge to point of

contraflexure, then

M^=0=+69.8.r— 11.2x {x/2)

rc=12.46 ft. The second design transverse load therefore is 11.2 lb/ft on span 12.46 ft. For right slope the moment is maximum

vi^here shear is zero. Let ij be distance from

ridge to point of maximum moment, then

7^=0=81.6—17.27/

y=4.144: ft. and maximum moment between supports is M,=-S1.6y+n.2y iy/2) M^=193.6 ft-lb.

If there were no eave on right slope, the reactions at each support would be 73.88 lb and

maximum moment 158.7 ft-lb, only 82 percent

of maximum moment with eaves. It is evident

that a roof construction between ridge and wall,

safe under the transverse load 17.2 lb/ft- on span 8.59 ft, would be unsafe if there were an

overhanging eave, provided for some condition

of wind load the transverse load on roof acts in

opposite direction to load on eave. For this condition, the design transverse load on roof between ridge and wall should be determined by

finding the maximum moment, and the span

producing this moment under the given trans- verse load.

For this roof, the design transverse load for

roof between ridge and wall is 17.2 lb/ft- on a span of 9.49 ft, not on a span of 8.59 ft. To summarize, if the construction in a projection is a continuation of the roof between

ridge and eaves and the design transverse load on roof and projection act in the same direction,

the design span for the roof is from ridge to point of contraflexure. If the design span is taken as the actual span, the roof will be safe

but uneconomical.

If the design load on roof and projection act

in opposite directions, the design span is greater

than the actual span. It may be computed as the

span causing the same maximum bending mo- ment in a simple beam without projection as the maximum bending moment in the roof with

projection. If the design span is taken as the

actual span, the roof will be unsafe.
Strength of Houses 47

XII. HIP AND VALLEY RAFTERS

1. Auxiliary Roof Members

If the roof on a house slopes from three adjacent walls or if a house with sloping roofs has

an ell, auxiliary members are required along the

intersection of the two slopes to support the

edges of the roofs. These members may be loadbearing partitions or other portions of the

house. Usually, however, they are rafters

(beams) extending from ridge to wall. If, at the rafter, the roof projects outward, the member is termed a "hip" rafter, if inward, a

"valley" rafter. The method for computing the

design load on either a hip or valley rafter is the same.

2. House With Hip Roof

To illustrate the method of determining design loads for hip rafters consider House E at Madison, Wis., which has the unsymmetrical

roof shown in figure 12 combined with a roof

sloping 40° on the south face only. This roof,

S.

South EAST

Figure 26.

Roof of House E ivith unsymmetrical slopiyig roof and also sloping roof on south face.
48 Building Materials and Structures Reports

with dimensions, is shown in figure 26. The

design loads for hip rafters fb and db, also

design loads for fastenings, will be computed.

For the condition where there is no racking

load on the east slope and west slope, due to wind load on gable ends, the horizontal and

vertical reactions on the roof north of c in east wall and a in west wall may be taken from fig- ures 13 and 14. These reactions are affected by

the reaction at ridge of one slope upon the other

slope.

The wall reactions south of points c and a must be detei'mined from the reactions normal

and parallel to the slope of roof ; assuming, as for any sloping roof, that the parallel reaction

is taken at the wall not at the hip rafter.

The loads and therefore the reactions are proportional to length of roof. For portion of

roof a/6, the length is greatest along ab and

decreases linearly to zero at /. The reactions

exerted by wall are greatest at a and decrease

to zero at /. The reactions exerted by hip

rafter are greatest at b and decrease to zero at

/. Similarly the reactions on roof fedb are

greatest at e on wall and b on hip rafter and

decrease to zero at / and d. The reactions on

portion of roof deb are greatest at c on wall

and b on hip rafter and decrease to zero at d. For plane roofs, therefore, a hip rafter is a

straight simple beam supported at ridge and

wall and under zero load at wall with load increasing uniformly to ridge. A valley rafter

also is a straight simple beam supported at ridge and wall but under zero load at ridge with

load increasing uniformly to wall.

For both hip and valley rafters, the total load

is the average load (half the greatest load)

times the span of rafter. The reactions are

one-third the total load at end where load is zero and two-thirds the total load where load

is greatest.

3. Loads on South Roof

The south roof is construction QC, 2- by 6-in.

rafters, weight 4.6 lb /ft^ ; the same as east and

west slopes.

The wind loads on south slope are given in

table 11. The snow load is 5.0 lb/ft- (basic snow load

13.0 1b/ft2).

Table 11.

Wind loads on south slope of roof on House E, Madison, Wis.

(Slope of roof, 4n''-. velocity pressure at midheight of roof, 18.3 Ib/ft^; internal wind loads taken from table 4]

Direction of wind External wind load Internal wind load Combined wind load Windward opening Leeward open ins Windward opening Leeward opening

Ib/fP Acts IblfP Acts lb/ft' Acts lb/ft' Acts Mt' Acts South 3. 5 In 8.7 Out 7.1 In 5.2 Out 10. 6 In East 14. 2 Out 8. 2 Do 7.

1

Do 22. 4 Do 7. 1 Out

Nortli 10. 6 Do 8.7 Do 7.

1

Do 19.3 Do 3. 5 Do

West . 14. 2 Do 8. 2 Do 7.

1

Do 22.4 Do 7.1 Do

4. Loads on Hip Roof

For each loading condition (direction of

wind, opening, and snow) the load on each of

the three roofs is given in table 12. The loads (weight, wind, and snow) are re- solved into components normal and parallel to roof slope and the combined components given

under "unit load." The total loads, along lines

ab, eb, and cb, are the unit loads times the

length of roof and the values are in pounds per

foot width of roof.

5. Reactions on Hip Roof

At wall, the normal reaction is half the total

normal load and the parallel reaction all of

parallel total load. At hip rafter, there is no

parallel reaction and the normal reaction along

the rafter is less than corresponding value for

wall because length of rafter is greater than

width of wall. The normal reaction at hip rafter

is the normal reaction at wall times cosine of

angle between rafter and wall ; for this hip roof

the angles are as follows:

Roof Rafter Angle

afb fb a/6 = 63° 16' feb fb efb = S5° 57' edb db edb = 61° 40' deb db cdb = iT' 36' The reactions are given in table 13.
Strength of Houses 49

allel

Acts Down Do 0 0 0 0 QQ

0 0 QQ0 0 QQ

0 0 QQ0 0 QQ0 0

load

1:1. 0 fo

?o

33.6 49.0 33.6 49.0 33.6 49. 0

33.6 49.0 33.6 49.0 33.6 49.0 33.6 49.0

Total "5c 5S

0 0 QQ0 0 QQ a <=> o« i-iQ a ° oQ Q>=i

a

Norr

191.0 178.6 97.0

109.4 18.2 307165.1 177.6 191.0 178. 6

97.0

109. 4

151.7 139.2 ^ 1^

Slo

•allel Ads Down Do 0 0

fifl 0 0 QQ

0 0 QQ

0 0 QQ0 0 QQ

0 0 QQ

c ST' CC "0 CC id CO lO CO ui CO »d CO "d CO

Unit

mal I

c 0 0 0 QP

0 0 QQ a ° oO 3

° oQ q5

Nor Oi to ^ ai 00 10.1 11.4 OS

--H CO 17.2 18.5 1

19.9 18.6 10.1 11.4 15.8 14.5 iC 00 d

Ads Down Do 0 0 QQ QQ

0 0 QQ

0 0 QQ QQ

0 0 QQ0 0

1

load On 33.8 69,9 33. S

69.9 33.8 69.9 33.8 69.9 33.8 69.9 33.8 69.9 69.9

Tota: £ bad 0 0 QG 3

° oO q5 a° oQ

1 3 a ° oQ

D.

Nori

lb/ft 19.2

24.8

159.0 203.0 213.2 169.2 40.6 3.4178.2 134. 2 0.0

44.0

213.2 169.2 40.6 3.4

Slo

Acts Down Do 0 0 0 0 QQ

0 0 QQ0 0 QQ0 0 QQ0 0 QQ

0 0 QQ

load

Si 0 IN 0 <N CO to 0

CC to 0CC CO 0

CO cd 0 CQCO CO 0

CO to O CQ 00 CO

Unit

mal 1

§ 3 C qQ oO 3 ° oQ I a ° a q5

Nor

. . 14. 1

18.0 18.9 15. 0 CD CC

CC d 15.8 11.9 0 OS 0 CO 18.9 15. 0 to COCO 0'

Acts Down Do 0 0 GC

0 0 OQ

0 0 0 0 QQ0 0 QQ0 0 QQ QQ

Total

load

Para

Iblft

31.0

102.7 31.0

102.7 31.0102.7 31.0

102. 7

31.0

102.7 31.0102.7 31.0

102.7 31.0

102, 7

'dc

Si's 0 ^oQ °G 3 ° oQ Sq 3

° oQ

a ° oC c =

Slope

ab

Norn

lb/ft 304. 8

153.2

OS

CO

238.0 86.4 11.4

163.0

304.8

153.2 184.2 335.8

182.6 31.0 66.8218.4

Acts Down Do 0 0 QQ

0 0 QQ0 0 QQ0 0 QQ0 0 QQ0 0 QQ0 0 QQ

;

load

Par ^ 01 CC 01 CC 05 CO

1.9 6.3

CT> CC OS CO 01 CC Oi CO

Unit

-mal 1

3

° oO wQ oQ Sq oQ

Noi ^00 OS 11.3 20.6 (O CO TP U2 0

0 0 00 OS 11.3 20.6 OS

CO

Conditions

Windward

openings:

No

snow

Snnw

'

! e ;

1 S 1 1

&

(

Windward

openings:

No

snow

.

...

Leeward

openings:

1

No

snow

.

f

Windward

openings:

1

No

snow

Leeward

openings:

1

No

snow

1^

Snow.. f

Windward

openings:

1

No

snow

.

Snow Leeward

openings:

1

No

snow

.

I,

Snow

1

Wind

South.

._

East

North...

05 S

a

nH

Cv| OS ^Tj; o CO O CO CO CO

J a. o 00 ipQ QQ

cj o go t"Q oQ

CO

^ a o 00

00 ^ 00 OS

QQ

CO

a o 00

?PQ QQ

Of O !>•

i"Q

00 00

QQ QQ

00 00

QQ QQ

CD O

CO o>

00 00

QQ QQ

--H CO CO

OS id CO

^^Q Qc

1^ CD 00 d d d d

00 00

QQ QQ

00 0> 00 o

>^a Q

\0 CD CO

^' d

^Q

ic "Tji CD r>.

00 00

QQ QQ

^Q

o

d CO

^Q 8a

00 00

QQ QQ

CD O CD O

«Q ^Q

10 CO lO

^Q

CO O

c4 dd

r-l CO O 00 d t-^

00 00

QQ QQ

00 Oi 00 OJ

^Q

r-<-~t 00

OS d

Sa

00 00

QQ QQ

o ^- o

"Q ^Q

Tt" CD ^ ON

o

a

•« o ^ ;^2m

8

a

.88

= 1 2io2 -OoSgoS -SoSg

;:rZcQ5sZai ;~Zcci

8

§.o

3.° L

SSZcQ
50 Building Materials and Structures Reports

6. Loads on Wall

The load on wall is equal to reaction on roof

but in opposite direction. The horizontal and

vertical wall loads for south wind, windward

opening, no snow are shown in figure 27.

14.4

d

)

' c

35.6

125.0

Vertical loads

Loads In lb/ft of width of wall

Figure 27.

Loads on walls.

The design loads for a wall are the greatest

values for any condition of loading: out and in,

also, up and down.

The normal and parallel loads on wall do not

have the same ratio for all loading conditions

but the design loads on a wall may be determined by selecting a few loading conditions for

which the normal and parallel loads are large

and computing the vertical and horizontal loads

for each. The greatest of these values are the

design loads for the wall.

7. Loads on Hip Rafter

The loads exerted on a hip rafter by the roofs on both sides through the fastenings are the

only loads on the hip rafter. For designing the

rafter, either by the usual engineering methods

or from the results of laboratory tests, it is essential that the roof load normal to the plane

of the roof be resolved into components along

the three principal axes of the rafter—the longitudinal axis, P, and two axes normal to this

axis ; one, the axis for greatest section modulus,

A^T-, and the other, the axis for least section modulus, Nh.

The determination of roof loads on a hip

rafter is greatly simplified by the fact that

rafters always are placed with the plane for

greatest section modulus vertical. If the hip

rafter is wood, 2 by 8 inches, the 8-inch faces

always are in a vertical plane.

The method for resolving the normal roof

load into components along the principal axes

of the hip rafter will be illustrated for west roof

afb on rafter fb for south wind, windward

openings, no snow. This roof is shown in figure

28.
Strength of Houses 51

Vertical plane through hip rafter fb

Figure 28.—T'Fesf rooj afb, south wind, windivar-d openings, no snow.

Consider the load exerted by roof on hip

rafter as shown in the elevation. From table 13,

the load on rafter fb at b is 68.6 lb/ft along the

rafter acting out and it lies in plane ahb. The

vertical component is 62.2 lb/ft acting up and

the horizontal component is 29.0 lb/ft acting

to the west.

In the plan, for a horizontal plane through

the ridge, take axis Ph in the vertical plane

through the longitudinal axis of the rafter and

Nh normal to Ph- Nh is the axis for least

section modulus. The components of 29.0 lb/ft

are, Pu, 25.3 lb/ft acting to southwest and Nh,

14.1 lb/ft acting to northwest.

In the vertical plane through the hip rafter,

the components are P, 0.0, 67.1 lb/ft acting

out.

For this loading condition, therefore, the

loads exerted on rafter fb at b by roof afb are

parallel to longitudinal axis of rafter, P, 0.0;

along axis for greatest section modulus, Ny,

67.1 lb /ft acting out, normal to rafter; along

axis for least section modulus, Nh, 14.1 lb/ft

acting to northwest, normal to rafter. WTiether

the longitudinal, P, component of the roof load

is zero for all hip roofs is not known.

For roofs afb, fdb, and deb the components of

the roof loads along the principal axes of the

hip rafters for all loading conditions are given

in table 14. The values in bold-faced type are the greatest

values acting in opposite directions. If the roof

loads are computed for one loading condition,

the loads for any other condition are in the same ratio to the computed loads as the ratio

of the normal reactions on the rafter. The

direction of the load can be determined by

inspection. A table similar to table 14 can be

made readily by computing the rafter loads for one loading condition for each roof, then using

the ratios of the reactions to obtain the loads

for all the other loading conditions.
52 Building Materials and Structures Reports

Table 14.

Roof loads on hip rafters The loads are along principal axes of rafter. See figure 28. P, longitudinal axis of rafter (for all conditions, loads along this axis are zero). NV, axis for greatest section modulus. N'ff, axis for least section modulus. Values in bold-faced type are the greatest roof loads acting in opposite directions]

Roof afb: rafter fb R oof fdb Roof deb: rafter db Wind Conditions Rafter fb Rafter dh NV N T/

y Nv NV Nh

, mndivard openings:

\ No snow -

101} t

67.1

A.cts Out

lb/ft

14.1

Acts NW

lb/ft

6. 5

Acts Out

lb/ft

4.4

Acts SE

lb/ft

4.3

Acts Out

lb/ft

1. 7

Acts SWlb/ft 50.2

A.cts Out

lb/ft 40.3

Acts NE

/ Snow - 33. 7 Do 7. 1 NW 8.3 In 5. 6 NW 5. 5 In 2. 2 NE 46. 9 Do 37. 7 NE

South 1 Leeward openings:

1 No snow 40. 5 In 8.5 SE 53.3 Do 36.2 NW 35.0 Do 13. 9 NE 25.5 In 20. 5 SW

\ Snow. 73.9 Do 15. 5 SE 68.0 Do 46.2 NW 44.8 Do 17. 8 NE 28.8 Do 23.

1

SW

. Windward openings:

\ No snow 52.3 Out 11. 0 NW 71.4 Out 48. 5 SE 47.0 Out 18. 7 SW 4.8 Do 3.8 SW

/ Snow 19. 0 LJO 4.0 NW 56. 7 Do 38.5 SE 37.4 Do 14. 8 SW 8.

1

uo 6.5 SW

East \Leeward openings:

1 No snow . 2. 5 In 0. 5 SE 1.3.6 Do 9. 2 SE 8.9 Do 3. 5 SW 43. 4 Do 34.9 SW

I Snow ... 35.9 Do 7. 5 SE 1.2 In 0.8 NW 0. 7 In 0.3 NE 46.7 Do 37.5 SW

, Windward openings:

\ No snow 67.x Out 14.

1

NW 59.6 Out 40. 5 SE 39.3 Out 15. 6 SW 50.2 Out 40.3 NE

/ Snow.. 33.7 Do 7. 1 NW 44.9 Do 30.5 SE 29. 6 Do 11.7 SW 46.9 Do 37. 7 NE

North.... \ Leeward openings:

1 No snow __ 40. 5 In 8.5 SE 0.0 0.0 0.0 0.0 25.5 In 20. 5 SW

\ Snow.. 73.9 Do 15. 5 SE 14. 7 In 10.0 NW 9.7 In 3.8 NE 28.8 Do 23.

1

SW

. Windward openings:

\ No snow 40. 2 Out 8.4 NW 71.4 Out 48.5 SE 47.0 Out 18.7 SW 39.8 Out 32.0 NE

/ Snow 6.8 Do 1. 4 NW 56.7 Do 38.5 SE 37.4

8.9

Do 14.8 SW 36.6 Do 29.3 NE

West \Leeiuard openings:

1 No snow .. . 14. 7 In 3.1 SE 13.6 Do 9.2 SE Do 3.5 SW 1,2 Do 1.0 NE

V Snow - - 48. 0 Do 10. 1 SE 1.2 In 0.8 NW 0. 7 In 0.3 NE 2.0 In 1. 6 SW

8. Loads on Fastenings

The loads exerted on the fastenings, whether

anchors or keys, are the same as the loads

exerted by the roof on the v^^alls and hip rafters.

The design loads, then, for fastenings will be

the same as the design loads for walls and hip

rafters.

9. Combined Loads on Hip Rafter

For each loading condition, the combined

load on rafter at ridge in pounds per foot along

the rafter is the resultant along each of the

principal axes of the rafter of the loads exerted

by the roof on each side.

The greatest combined loads on hip rafter fb are Ny, 126.7 lb/ft acting out and 141.9 lb/ft

acting in; Nh, 30.7 lb/ft acting toward the

northwest and 40.1 lb/ft toward the southeast.

Those on rafter db are Ny, 89.5 lb/ft acting out

and 73.6 lb/ft acting in; Nh, 39.9 lb/ft acting

toward the northeast and 38.4 lb/ft toward the

southwest.

10. Total Loads on Hip Rafter

Rectangular wood rafters usually have the same strength out as in and the same strength

laterally either way; therefore, it is necessary

to consider only the greatest load edgewise and

the greatest flatwise. For both these hip

rafters, the axial load is zero for all loading conditions.

The design loads for these hip rafters are: Rafter fb, length 17.44 ft, edgewise (Ny)

total load 1237.4 lb acting inward, reaction at wall 412.5 lb acting outward, reaction at ridge

824.9 lb acting outward ; flatwise (Nh) total load

349.7 lb (SE), reaction at wall 116.6 lb (NW),

reaction at ridge 233.1 lb (NW).

Rafter db, length 11.63 ft, edgewise (Ny)

total load 520.4 lb acting outward, reaction at wall 173.5 lb acting inward, reaction at ridge

346.9 lb acting inward ; flatwise (Nti) total load

232.0 lb (NE), reaction at wall 77,3 lb (SW),

reaction at ridge 154.7 lb (SW).

These reactions are normal to rafter. The

load on wall exerted by a hip rafter is the same

magnitude as wall reaction on rafter but in

opposite direction and is a "point" load. For

designing the wall, this load may be resolved

into components vertical and along the width

of each of the two walls intersecting at the corner of the house.

Likewise, the load exerted by a hip rafter on

the ridge is the same magnitude as ridge reaction on rafter but in opposite direction and is a point load. For designing the roof, the loads

exerted by the two hip rafters may be resolved

into components along the ridge and normal to ridge horizontally and vertically.

The total load exerted by the two hip rafters,

then, is the combined components along the

three axes. The load along the ridge, combined

with any other loads on the roof acting parallel
Strength of Houses 53

to ridge is a racking load on each slope intersecting at ridge.

The combined loads normal to ridge, horizontally and vertically, cause either tensile or compressive loads in the roofs along lines ab and cb

because the roofs along these lines are two-force

elements. Practically, these axial loads in the

roof may be so small that no special members

need be put in the roof to carry them. However,

consideration should be given to special rafters

to take the point loads at ridge (b) and the

point reactions at wall (a and c)

For this assumed distribution of the ridge

reactions on the hip rafters, there can be no

racking in the triangular portions of the east

slope (deb) and west slope (a/6).

XIII. WALLS

1. Design Loads

For compressive load and for racking load,

the design load is in kips per linear foot along

top of wall ; for transverse load, in pounds per

square foot uniformly distributed on a span

equal to story height of wall.

For concentrated load, the design load is in

pounds on the disk, one inch in diameter; for

impact load, in feet height-of-drop of the 60-

pound sand bag.

The dimensions of the house and the geographical location have no bearing on the design

concentrated load nor on the design impact load.

They depend only upon the occupancy and are

the values which, in the opinion of the designer,

provide reasonable insurance against local

damage.

2. Walls Which Have no Openings

If a wall has neither doors nor windows the

design loads are:

(a) Co7npressive Load

The design compressive load is the greatest

vertical reaction along top of wall exerted by

construction above. The reactions may be either

uniformly distributed along wall or vary lineai*- ly from value at one edge to a different value at other edge.

(b) Transverse Load

The greatest wind load on span equal to story

height of wall is the design transverse load.

There are two transverse loads, one acting out- ward and the other inward.

(c) Rackifig Load

The design racking load on wall is the greatest reaction exerted by construction above ; it may act in either direction.

3. Walls Which Have Openings

(a) Structural Properties of Walls

Which Have Opeyiings

The design loads for walls that have openings

depend upon the structural properties of the

walls at doors and windows. These properties

may be determined in the laboratory by testing

specimens similar to those for walls which have

no openings, preferably specimens composed

entirely of doors and entirely of windows with

the surrounding framework and portion of wall

above or below.

No specimens which have openings were in- cluded in the program for house constructions,

therefore no properties are given in the BMS

reports.

With the exception of concentrated and impact loads, it appears probable that door and

window constructions can be designed and fabricated which have properties equal to those for

continuous walls.

For most wall constructions, it appears probable that the strength at openings is much less than elsewhere. Therefore, it is assumed for

this report that portions of wall at doors and

windows carry none of the compressive, transverse, or racking load. Any error then, is on

the side of safety.

(6) Compressive Load

If the compressive load over an opening is carried by the portions of wall adjacent to the

opening, it is necessary to select a load distribution approximating the actual distribution.

The only discussion of this subject found in

the literature is Adams' [26] treatments of

bressummers for dividing the weight of a brick

wall over a doorway.

(1) Bressummers

Adams says

The next case to be taken is to find the sec- tion required to carry a brick partition with a 4-

ft door opening 3 ft from one side over a clear span of 15 ft, as shown in Fig. 110. [Fig. 29

in this report]. The load over the doorway is transmitted down the two sides, but the exact

disti'ibution of the loading is somewhat doubtful. There are two possible views: the simpler one is that half the load goes each way, and

that it is divided over the intervening space in regular proportion from maximum to nothing.

Thus, load over door = 4 X 5 X .75x 1 = 15 cwts.,
54 Building Materials and Structures Reports

1

1

1

1

1 ^ 1

Brick wa/l 9 thick

weighing 1 cwf per cub. ft

T

1

1

1

1 * -1 -

*

I II -60 *

^ 1

1

1 ' " * -40 - *

V

1 II < -5 0->

FIG. 110

FIG. Ill 15CO

•1^

FIG. 112

Fig. 110- E-levafion ofBrick Partition to be carried

by Girder.

Figs. Ill and III.— /Methods ofdividing Load over doorway onto the sides.

Figure 29.

Adams' brick wall with doorivay.

[Adams' fig. 110, elevation of brick partition to be carried by

girder. Figs. Ill and 112, metliods of dividing load over door- way on to the sides]

half each way=7.5 cwts.; then for left side 7.5/8 = . 9375 per foot run, and .9375 x2 = 1.875 cwts. increase of load at door jamb as shown in Fig. 111. In a similar manner the extra load on the right will be 7.5x2/3 = 5 cwts. at door

jamb. The other view is that the load over doorway is transmitted to each abutment in inverse proportion to the distance from its center of gravity, and divided over the inter- vening space as before, viz., on the left 2+3 2

-j^g X 15 X -g- = 1.25 cwts., and on the right

2+8

15 15x^ = 6.6 cwts., as shown in Fig. 112.

As the former view gives the greater bending

moment on the girder, it will be best to adopt

it; the weight of the wall is 12 x.75x1 = 9 cwts. per foot run, then the load diagram will be as shown in fig. 113. [Fig. 30 in this report].

It is evident that only the first "view" applies

to distribution of reactions along top of wall.

Fig. 113.— Load diagram for Fig. 110. Figure 30.

Adams' load diagram for brick wall.

[Adams' fig. 113, load diagram for fig. 110]

(2) Illustration of Adams' Method

To apply Adams' method to a numerical ex- ample of reactions at top of wall, consider the

wall shown on figure 31, 22 ft 8 in. wide, with one door and two windows, one at right edge

of wall. There is an attic floor, the joists

supported on wall and load-bearing partition,

span 10 ft. If weight of this floor is 5 lb/ftand load is 20 Ib/ft^, the reactions on wall

are 25 lb/ft from weight and 100 lb/ft from

load ; combined reaction 125 lb/ft width of wall.

Taking the reactions from roof as windward

edge 191.9 lb/ft and leeward edge 242.7 lb/ft,

both acting downward, the combined reactions

along top of wall are 316.9 lb/ft at windward

edge and 367.7 lb/ft at leeward edge of wall.

The values of all reactions are shown and also

the total at each edge of opening. The greatest,

737.7 lb/ft, is the design compressive load for

this wall, provided a greater value does not occur for some other direction of wind.

It is evident that by Adams' method the load

at edge of opening is inversely proportional to width of adjacent wall and may be much greater on one edge than on the other, as is shown by

reactions at edges of door. Probably the load over an opening is carried mostly by portion of

walls quite near the opening and is more uniformly distributed than Adams shows.

(3) Recomynended Method for Distributing

Vertical Reactions on Wall

For this report, therefore, the vertical reaction over half the opening is rotated back over

the adjacent wall. The combined reaction on

adjacent wall is, then, a uniformly distributed

load equal to twice the original value at edge of

opening. Unlike Adams' method which requires some computing, this recommended method, in

general, involves only doubling the reaction at each edge of opening.
Strengih of Houses 55

191.9 321.2 339.5

316.9 321.4 332.6

126.0

_i

137,1

Ibp of wall

316.9

Reactions downward in lb /ft of width

134.1

663.4

440.1

321.4 3212 332.6 339.5

242.1

3619 361.7

125.0

_J_

550.0

361.9

Figure 31.

Adams' method for distributing vertical reactions on wall.

(^) Illustration of Recommended Method

To apply the recommended method to a numerical example, consider the same wall and

loading, as shown in figure 32. The original

reaction at edges of openings is shown, also

the rotation over adjacent wall of reactions over

openings. In general, the final reaction adjacent

to openings is twice the original reaction.

The width / between window and door is less

than the sum of the half openings, therefore a

strip of the reaction from door must be added

to the reaction from window for the overlapping distance giving a load of 990.2 lb/ft for

0.29 ft. It is ridiculous to believe that the reactions over openings are distributed in any such

way. An engineer certainly would expect the

load to be greater at edges of opening than at intermediate points.
56 Building Materials and Structures Reports

191.9 3Z1.Z 339.5

316.9 321.4

125.0

332.8

Top of wall

3611

316.9

Reactions downward in Ibjff of width

990.2

642.8

123.8 Design compressive

load

FlGURE 32.Recommended method for distributing vertical reactions on tvall.

If the width of wall between openings is less and on right,

than the sum of the half openings, it appears

reasonable to take the sum of the loads over the

half openings, divide by width of intervening

wall and add to the average original reaction.

On left of width /, the load on half opening is

332.8+336.2 3.0 „ X-^=501.81b.

The sum is 420.2+501.8=922.0 lb. Dividing by

width /, 324.3+327.2 2.58

X =420.2 lb, 922.0

2.5 :368.8 lb/ft.
Strength of Houses 57

Average original reaction on width /, 327^^^332^ =330.0 lb/ft.

Final reaction on width /, 368.8+330.0=698.8 lb/ft.

This value is slightly greater than if there were

no overlap.

For the window at leeward edge of wall, it may be assumed that there is no adjacent wall on the right, particularly because edge windows

usually are in pairs, one in each of the intersecting walls. For an edge door or window, it seems

reasonable to double the reaction at edge and

apply for a distance equal to width of opening.

The greatest reaction, 723.8 lb/ft, is the

design compressive load for this wall provided

a greater value does not occur for some other

direction of wind.

It is evident that the less the width of wall

between openings the greater the load and it may be more economical to provide a special

member (column) between openings than to

make the entire wall of a construction adequate

for this localized load. Most houses appear to have ample wall between openings to avoid

overlapping of reactions.

For this particular illustration, there is no

great numerical difference between the design

compressive loads obtained by the Adams'

method and the recommended method. Adams'

value, however, is close to the windward edge

of the wall and the recommended value close to the leeward edge.

It seems evident that, in general, as the distance between openings increases the values

obtained by Adams' method decrease, but the

recommended values remain the same. Because

houses have many openings, probably there is

little difference in the design loads obtained by

the two methods.

If the wind load on roof is outward, the

reaction on wall may act upward and the design

"compi-essive" load on wall is a tensile load, the

value of which may be determined by the

method just described.

If the reaction along top of wall is upward.

Bottom of wall

60.0

Z. ~?

66.J

JL _ 1^

80.0

316.9

66.5

- ± J

388.3 392.8

80.0

3d.O

T

404.2

11.4 average

361.1

433.3

398.6 410.9 439.1

Reactions upward in lb/ft of width

Figure 33.

Reactions at bottom of wall.
58 Building Materials and Structures Reports

anchors are necessary and the design load for

anchors is the greatest upward reaction for any

direction of wind.

(5) Vertical Reaction at Bottom of Wall

The weight of the wall causes a vertical reac- tion at bottom of wall as shown in figure 33. The weight of walls included in this program is given in the BMS reports on structural properties.If this wall is conventional wood-frame construction QA, the weight is 10.0 Ib/ft^. The

door weighs 4 lb/ft- and the windows 7 lb/ft-.

The upward reaction where there are no openings is 80 lb/ft, at the door 38 lb /ft, and at the

window 66.5 lb/ft. These nominal reactions are shown although probably the actual weight distribution will be less near midopenmg and

greater at edge of opening, particularly the

edge of doorway on which the dooV is hung.

Probably, because of the stiffness of wall and

supporting elements, the actual reactions vary

linearly from the value at one edge of wall to a different value at the other edge, but because

openings in houses are rather uniformly spaced,

it appears adequate to take the average reaction

uniformly distributed along the wall.

The vertical reaction at bottom of wall due to the reaction along top of wall is the same magnitude but opposite in direction. For this wall,

the combined upward reaction at bottom of wall

is 388.3 lb/ft at windward edge of wall and

439.1 lb/ft at leeward edge.

If the reaction along bottom of wall is downward, anchors in the foundation are necessary

and the design load for anchors is the greatest

downward reaction for any direction of wind.

(c) Transverse Load

As for compressive load, there are no laboratory data on the transverse properties of walls

having openings.

Assuming that wind load at openings is carried by adjacent walls, it is recommended that

wind load at openings be distributed in the same way as compressive load and for the same reasons.

(1) Illustration of Recommended Method

As a numerical illustration, take the same

wall as for the compressive load and assume

that the wind load on this second story is the

value shown in table 5 for the greatest outward

wind load of 18.1 Ib/ft^ acting out. The distribution of load is shown on figure 34.

f^c/pe of face of wolf

18.1

36.Z

,18.1

36.1 3Q.3 36.2

L oads in

Figure 34.

Recommended method for distributing wind load on ivall. The design transverse load acting out is 38.3

lb/ft- on the span of 8 ft unless a greater value

acting out occurs for some other direction of

wind. The design transverse load acting in is ' obtained by the same method.

The transverse reactions at top and bottom
Strength of Houses 59

of wall are each the design transverse load

times half the story height, acting normal to wall and opposing the transverse load. Keys

are necessary along the wall at top and bottom.

The design load for key is the greatest reaction,

either outward or inward, for any direction of

wind.

If, where the greatest transverse reaction is exerted on the wall, there is also compressive

load on the wall, the resulting frictional resistance may be subtracted from the design load

for key. The frictional resistance at bottom of

wall is always greater than that at top of wall.

The friction may be determined in the laboratory or may be estimated from the compressive

load and a coefficient of friction selected by the

designer. If the frictional resistance exceeds

the transverse reaction, theoretically no key is necessary.

If, where the greatest tranverse reaction is exerted, there is a tensile load on the wall, there

is, in general, no friction. There may be friction, provided the anchors exert compressive

forces on the top or on the bottom of wall and

the adjacent elements under all service conditions, particularly when wood plates and sills have shrunk.

(d) Racking Load

The racking load on walls and load-bearing

partitions is a statically indeterminate problem

because these loads depend upon the racking

deformations of the elements.

(1) Racking Modulus

If a house construction one-foot square is fixed along one edge and a racking (shearing)

force applied along the opposite edge, the

racking modulus is the force causing a racking

deformation of one foot computed from the

initial rate of deformation.

The racking modulus for each wall and loadbearing partition in the program was computed

from the graph in the BMS report. The allowable racking load, obtained by methods described later, was marked on the graph and the

racking deformation noted. This deformation

divided by 12 to give the deformation in feet

and by 8 ft, the nominal height of specimen,

gave the deformation of a specimen one foot

high. The allowable load divided by this deformation is the racking modulus in kips per foot. For some constructions, particularly highstrength masonry, the deformation is so small

at allowable load that it is impossible to obtain a value from the graph. In such cases a deformation of 0.0001 inch is taken.

The racking modulus for each wall and loadbearing partition is given in table 15., 743712°—48—5

Table 15.

Racking w.odulus for walls and load-hearing

'partitions

Construction symbol BMS Element Allowable

load

Deflection —in 8 ft -

Hacking?

mo'luliis AA 5 Wall f1 not ft

2. 50+

IHCllCS

0. 0001 KipHlft

2, 403, 000

6. 850

6, 850

y± ij Do 2 5Q [ 0.35 A O 7J-'O In A.D 1 )o 1 42^

L:i7 02 6, 825

13, 170

7, 690

125. 4 AE 5 Do +)l

.rli' Do

A l-I Do 0 94 72^ A.L 1

Do 41 59 66. 7 rxt A P J J fin A f? 20 Do 4 41 ^- Ol 7*1 oinnn 24, 200

jL T 24 Do

/IC A TJ 24 Do 2 01 01 ino-jA

19, O'iO

1 03 7 V, no bi'ciCHS Vy brscBS

27

27 DoDo

0 40

81 2475

21 Do 2 36 01 25 18 160 A.Z 18 Do 0 60 28 205 5 BD 23 Do 1 98 015 12 690 BE 22 Do 0. 79 0125 6 OHO BF 32 Do 2 08 010 90 Olio BG 31 Do 0 87 30 280 8 BH 31 Do 1. 00 . 39 246. 3 BI 31 Do 0'88 !40 21l'6 ByJ 31 Do 1 oO . 36 400 0

iJxV 31 Do 4 50 76 56H 0 BL 31 Do 1 04 . 38 262 7

I3\J . 32 Do 2 20 0041 51 500 BP 32 Do 0. 64 . 0025 24 620

J=>H RO - 36 Do 60 10 576. 0 B JJ 30 Do 88 40 211 7 B\' 2fi Do 3 QQ 0305 9 440

40 Do 1 50 05 2 885. 0

ISA. R V 42 Do 0 97 39 239. 0 R V 42 Do . 78 . 61 122. S CB 37 Do . 13 . 10 125 0 CF 38 Do !72 !0035 19, 720' 38 J-)o . 80 . 0008 96, 200

Kjjn - 39 Do . 23 . 20 ' 110. 6 OJ 47 Do . 80 . 52 147. 8

\jj - 47 Partition . 48 . 25 184. 6

^ - 48 Wall . 34 . 127 257. 5 OiV 48 r)o 47 . 15 301. 3

KjKJ 48 PSiFt it ion . 47 . 081 557. 0

\j± - 53 Wall 2. 40+ . 0008 288, 500 C V 46 Do 0 30 . 13

' 222. 2 ex.. 67 Do L50 !285 505^ 0 CZ 61 Do 1 5()-|- . 0025 96, 200 DA 61 Do 2. 50+ .002 120. 200 UdT\ R _ 78 Do 1. 00 . 002 48. 100 UKj 78 Do 1. 00 . 007 13, 700 DD 78 Do i. 50+ '. 0006 400.' 000 BE 78 Do 1.92+ .0001 1.845. 000 DF 78 Do 0. 65 . 0033 18. 900 OG 74 Do . 33 .072 440.0 DH. 74 Do .25 .04 601.0 DK -.- 72 Do .69 . 106 624. 0 DL, no braces DLa, braces

9090 Do

Do

.03

. 16

. 10 .80

28. 84

19. 2 DP.. 86 Do 1. 29 .0028 44, 200 qA 25 Do 0. 50 .185 259.0 Q7) 25 Partition .38 .21 173.5

{2) Method for Determining Racking Load

on Wall

The method for computing the racking load on walls and load-bearing partitions is most

clearly explained by a numerical case. Consider

the plan shown on figure 35 for the first stoiy

of a two-stoiy house.

The outside dimensions are 16 by 30 ft and

the walls are 8 ft high. The south wall (front

door) and east wall are construction AB,

medium-strength brick, modulus 6,850 kips/ft;

the north wall and west wall are construction

QA, conventional wood frame, gypsum plaster

inside and bevel siding outside, modulus 259.0

kips/ft; both the partitions are construction
60 Building Materials and Structures Reports

Norfh Wall

Construction QA

y Net width = io'-/l"(10. 91 7

')

West Wall

Construction QA

Net width = Z4-I0"

(24.833')

T

~-

1

Construction CO

Net width =n'-0"

ClI.O')

^

Const. CO

Net width = l2-0"

4.

-

1

T

O

o

J.

South Wall

Construction AB , Net width = 10- 5"(10.411 )

Figure 35.

Plan of first story of txvo-story house.

East Wall

Construe Net wid\

(19.667')

- ' Construction AB ^ Net width =19-6"

3L X

CO, wood frame, both faces fiberboard glued to frame, modulus 557.0 kips/ft.

The west wind acting on the story above and

the upper half of this story exerts a wind load,

taken as 7.0 kips to leeward on the floor at top

of this story. This floor is in equilibrium under

the wind load and reactions due to racking

forces on the walls below the floor. The reactions on floor, due to racking forces on walls, are equal and act in opposite directions to racking forces on walls. For conveni- ence in this discussion, these reactions on floor are term.ed "racking reactions."

Provided all openings have closures and roof

and all stories above are symmetrical, the re- sultant wind load may be considered as acting

on the floor at midwidth of the windward edge.

If these conditions are not fulfilled, the resultant may not act at midwidth.

In the BMS reports there are no racking

properties for walls having openings, therefore, it is assumed that only portions of wall

between openings resist racking load ; moreover; it is assumed that resistance is proportional to width.

The net width of each wall is given on the

plan, being the outside width minus the width

of each opening.

For a given racking deformation, the force on net width of wall may be computed. The deformation divided by height of wall is deformation at height of one foot. This value times
Strength of Houses 61

racking modulus is the force on wall one foot

wide, which when multiplied by net width of

wall is racking force on the wall.

Translation.—Assume, for the time being,

that the floor moves to leeward, parallel to position before wind load is applied, a distance r^, — the racking deformation of walls and partitions parallel to wind.

The magnitude of racking reactions on floor

due to translation are found by computing the

racking load on each wall and partition parallel

to wind for the deformation These reactions are

North ivall: (rj^/8)X 259.0X 10.917 = -353.4

East-irest partition:

(/i/8) X 557.0 X 11.0= —765.9 r^. South wall: (rj/8)X 6850 X 10.417= —8919.5 n

K 7^,^ := 0 = 7.0—353.4

r-^ =0.0006973 ft.

Substituting this value of rj gives

North wall —0.2464 kip. East-west partition —.5341 kip.

South wall —6.2190 kip.

5 F^ = 0 = 7.0—0.2464—0.5341—6.2190

7.0 = 6.9995 (check)

2Fj^ = 0 (check)

M„= 0= (—7.0 X 15)-|-(0.2464 X 30) -f- (0.5341 x 12) =—105+7.392+6.409 =—105 +13.801 = —91.199 ft-kips clockwise.

Rotation.—The resultant clockwise moment

of 91.199 ft-kips rotates the floor clockwise

about the center of rotation causing an increase

in the racking deformation of north wall and

racking reaction on floor, and a decrease in deformation of south wall and reaction on floor. The center of rotation for this stoiy is a

fixed point in the floor and is at the intersection

of the action lines of the resultant of racking

rates for east-west walls and resultant of racking rates for north-south walls. The center of

rotation lies within the boundaries of the floor. The racking rate for a wall, i.e., the rate of

increase in racking load with increase in racking deformation, is the racking modulus

divided by height of wall times net width of

wall.

The center of rotation is computed as follows

East-west coordinate, x Racking rate: West wall

259.0 X 24.833 =

North-south

partition . . 557.0X12.0 =

804.0

835.5

6850 East wall —g—X 19.667 = 16839.0

Resultant = 18478.5 Moments, origin at 0:

West wall 804.0 x 0 = 0 North-south

partition 835.5 X 5.0 = 4177.5 East wall 16839.0 X 16.0 = 269400.0 Total = 273577.5 273577 5 ^ = ^78^ =1^-805 ft. North-south coordinate, y Racking rate

XT , „ 259.0 North wall —g— Xl0.917= 353.4

557.0 East-west partition. . . —

g— X 11.0 = 765.9

o „ 6850

South wall —g— X10.417= 8919.5 Resultant= 10038.8 Moments, origin at O:

North wall 353.4 x30.0 =10600.0

East-west partition .. . 765.9 x12.0 = 9191.0 South wall 8919.5 X 0=0 Total = 19791.0

19791.0 ^=30038:8 =1-972 ft.

Y

W

Deformations not fo scale

Figure 36.Racking deformation of ivalls due to rotation of floor.
62 Building Materials and Structures Reports

The racking deformation of each wall due

to rotation of floor is proportional to the

moment arm of wall about center of rotation

as shown on figure 36.

If the rotation causes deformation Vn of north

wall, the deformation of each wall is

West wall -0.528 14.805^ 28.028

North-south partition

.

9.805^ 28.028

1.195^ 28.028

North wall 28.028

J 28.028

East-west pai'tition 10.028^ 28.028

South wall 1.972

,

28.028

: +0.3495 r^.

--0.04265 }-2

+ r,.

- +0.3578 r^.

0.07036 r„

Each defoi'mation times the racking rate for

the wall gives the racking force and this times

the moment arm to center of rotation gives the

moment on wall due to rotation of floor. These

moments are West wall . . North-south

partition. East wall .

.

North wall . East-west

partition

.

South wall .

0.528 , X 804.0 x 1-1.805= —6280.0 r„

0.3495 n X 835.5 X 9.805== —2863.0

. 0.04265 raX 16839.0 X 1.195= —857.5 r^. rlx 353.4X28.028= —9905.1 r!",.

0.3578 0.07036 ,X 765.9X10.028= —2748.1

'. X 8919.5 X 1.972= —1237.6 rg. Total=—23891.3 r„.

The moments of the racking reactions on

floor are equal and of opposite sense. Then for floor after rotation, the sum of the

moments of racking reactions equals the re- sultant moment due to translation.

23891.3/2 = 91.199 ft-kips.

7-.,= 0.003817 ft. This is 28.08 seconds of arc.

Substituting this value for Vn into expressions

for the deformation for each wall for rotation

gives the defonnation in feet. The racking deformation of walls due to translation and rotation are

Translation, Rotation, Vo Tot«l, r^+r.

It It It West wall 0.0 0.002016 0.002016 North-south

partition 0 .0i01334 .001334 East wall 0 — .0001628 — .0001628 North wall 0006973 .003817 .004514 East-west

partition 0006973 .001365 .002062 South wall 0006973 — .0002684 .0004289

The deformation for each wall times the

racking rate for the wall gives the following

racking force:

West wall 0.002016 X 804.0= 1.620 kips.

North-south

partition 001334 X 835.5= 1.114 kips. East wall 0001628 X 16839.0 = —2.740 kips.

North wall 004514 X 353.4= 1.595 kips. East-west

partition 002062 X 765.9= 1.580 kips.

South wall 0004289 X 8919.5= 3.825 kips.

The racking reactions on floor are equal and

opposite to these racking forces on walls. The

floor is in equilibrium under the wind load and

these racking reactions. These reactions on

floor are shown on figure 37.

y

l.Okips^

W

o

A/

/. 595 kips —S:— 1—

-5.0

1.580 kips

«; -

3.825 kips

oCD

o

1 1.0' 16.0'

J

Figure 37.Reactions on floor due to wind load and

racking of walls. 2 =0 =—1.595—1.580—3.825+7.0

7.0 = 7.0 (check)

2F,^ =0=—1.620—1.114+2.740

2.734 = 2.740 (check)

2 M^= 0= +1.595 X 30.0+1.580 X12.0+2.740 X 16.0 —1.114X5.0—7.0X15.0

110.650=110.570 (check).

The designer should check each floor of house

for equilibrium. It is evident that in this illus- tration the racking forces for translation only

are inadequate for design as shown by the

following camparison.
Strength of Houses 63

Translation

Translation and Ratio,

only, A Rotation, B AJB

Kips Kips West wall 0 1.62 0 North-south

partition 0 1.114 0 East wall 0 2.740 0 North wall 0.2464 1.595 0.1545 East-west

partition 5341 1.580 0.3381 South wall 6.219 3.825 1.625

Manifestly, if the forces for translation only

are taken as approximations, both partitions

and all walls except south wall may be unsafe

because the estimate racking forces are much

too small. On the other hand, the south wall

may be about twice the necessary strength.

The racking load is the racking force divided

by the net width of wall. These loads are:

West wall 2i^||^ = 0.0652 kip /ft.

1.114 North-south partition. . . ^2 o

" =0.0928 kip/ft.

2 740 East wall 19.667 = 0.1393 kip/ft.

1 595 North wall 10 dll = 0.1460 kip/ft.

East-west partition = 0.1437 kip/ft.

3 825 South wall 10^417 =Q-3670 kip/ft.

For each wall and load-bearing partition the

greatest racking load for any direction of wind

is the design racking load. It may act in either

direction along wall.

(3) Method for Determining Righting

Reaction on Wall

The racking loads at top and bottom of wall

exert an overturning couple on wall equal to the racking load times the story-wall height.

For the wall to be in equilibrium, there also

must be a righting couple of the same magnitude. The vertical reactions of the righting

couple act downward on windward portion of

wall and upward on leeward portion.

Because roof or floor at top of wall cannot

exert the righting couple, it must be applied at bottom of wall. If the wall is supported by

posts or piers and there are more than two supports, for deteiTnining righting reactions, it is divided into portions each of which is a simple

beam having only two supports. The righting

reactions are point loads and the moment arm

is the distance between supports. The reactions are readily computed by dividing the overturning moment by the moment arm. Posts may be

designed to carry upward reactions (anchors)

as well as downward reactions but they can

carry no racking load. Even if the supports

have a large cross section, as for brick piers two

or three feet square, there are no laboratory

reports on their racking resistance and assigning a design racking load presents difficulties. Certainly an engineer would hesitate to assign a design racking load for a pipe 4 inches

in diameter functioning as a post in the cellar

of a house.

The racking load at bottom of wall, therefore, must be transferred laterally by a floor to walls parallel to the racked wall inversely proportional to the distance between the racked

wall and the parallel wall.

If, on the other hand, the wall is in contact

along the bottom with supporting walls or other

members, the righting reactions are line loads.

The greatest downward righting reaction is at the windward end of the line of contact and

the reaction decreases linearly to zero at the

middle of the line. The reaction, similarly, in- creases upward from middle of line to the

greatest upward reaction at leeward end of

line.Let d be the length of line of contact in feet

and take origin of moments at middle of line. Let Q be the righting reaction in pounds per

foot at windward and leeward end of line of

contact. For the half contact between end of line and

origin, the total righting reaction is Q ^ 2

and righting moment X g X "f" »

Qd^

-j2~ ' ^^^^ contact. The total righting

reaction for the wall is ^j! foot-pounds.

D The value of Q is obtained by equating this

expression to the oveilurning moment and

solving for Q.

Some walls and load-bearing partitions bear on floors between the supports for the floor. If the wall is normal to the joists in the floor,

the righting reaction on windward portion of

wall tends to lift the floor and on leeward

portion to depress the floor. These vertical

righting reactions are transferred by the floor to the adjacent floor supports inversely proportional to the distance from racked wall to the support.

The effect of righting reactions is to either

increase or decrease the resultant of all vertical

loads on wall or other element due to weight of

roof, wall, and floor above and also to wind

load and snow load on roof and surface load
64 Building Materials and Structures Reports

on floor. By this means, the design compressive

load on each wall is determined and also the

design loads for fastenings.

When combining the resultant of the vertical

loads and the righting reactions, it is helpful

to make diagrams to scale for each story of

each wall showing the location of openings.

There should be a diagram for each direction

of wind, south, east, north, and west, and for

house occupied and unoccupied. Plot the re- sultant of vertical loads and add or subtract the

righting reaction.

XIV. PARTITIONS

1. Load-bearing Partitions

The discussion of walls also applies to loadbearing partitions and the design loads are determined by the same methods.

(a) Compressive Load

The compressive load is the vertical reaction

from floor above only, therefore always uniformly distributed along the partition. If there are floors adjacent to both faces of a partition,

the compressive load is the sum of the reactions

from each floor. There can be no upward "compressive" load on a partition. The bearing of a

floor on a partition is one-third the thickness of

structural members from the face toward the

floor.

(6) Transverse Load

There is no transverse load on a load-bearing

partition because it is assumed that the barometric pressure is the same everywhere within

the house.

(c) Racking Load

The racking load on a load-bearing partition

is obtained at the same time that racking loads on walls are computed.

2. NONLOAD-BEARING PARTITIONS

The only design loads on nonload-bearing

partitions are concentrated and impact loads.

These depend only upon the occupancy.

Care must be taken that there is sufficient

clearance between top of a nonload-bearing

partition and floor above so that none of the

floor load is transmitted to the partition.

XV. FLOORS

1. Design Load

As the floor is considered a rigid diaphragm,

loads in the plane of the floor may be neglected

when computing design loads. The design

loads, then, are transverse, concentrated, and

impact. Concentrated and impact loads depend

only upon the occupancy, and the selection of

the design values will depend upon the judgment and experience of the architect,

(a) Transverse Load

The design transverse load is expressed in

pounds per square foot, uniformly distributed over the floor span.

For any floor, the span is the distance between bearings on adjacent supports, such as walls or load-bearing partitions.

2. No Partition Above Floor

If there is no partition above the floor and

between the supports, the applied surface load on floor is the design transverse load on the

floor.

3. Partition Above Floor

If there is a partition above the floor and between supports, the reaction on floor is a line

load taken as acting at midthickness of partition. This line load is the sum of the average

weight of partition plus reactions, if any, from

floor above. The average weight is the sum of

the net weight of partition plus weight of

closures divided by width of partition.

Because there can be no surface load on the

floor in the area occupied by the partition, the

line load equivalent to the surface load should

be subtracted from the line load for the partition.

There are two cases to be considered; partition nonnal to structural members in floor and

partition parallel to members.

Figure 38.

Partition normal to floor members.
Strength of Houses 65

(a) Partition Normal to Floor Members

The floor is a simple beam under the appHed

surface load and line load exerted by partition.

From the maximum bending moment under

this loading, an equivalent surface load is obtained. This is the design transverse load for

the floor. Illustration of method for determining design

transverse load.—The floor shown on figure 38

is supported by walls or load-bearing partitions,

span 13 ft, surface load 40 lb/ft-. The partition

above is construction CJ, height 8 ft, width 10

ft, thickness 4 5/8 in., weight 5.42 Ib/ft^. The

door is 2 ft 6 in. by 7 ft. The line load on partition from floor above is 182.0 lb/ft of width.

The applied loads on floor are From partition

Weight : Gross area of partition ....10x8= 80.0 ft^. Area of door 2.5x7= 17.5 ft-'. Net area of partition 62.5 ft^. Net weight

of partition 62.5x 5.42 = 338.8 lb. Weight of door 17.5x4= 70.8 lb. Total weight of partition 408.8 lb. Average weight of partition . . 408.8 =40.88 lb/ft of width.

Reactions from

floor above 182.0 lb/ft of width.

Deducting the equivalent of the applied surI face load, the partition reaction is

' (40.88+182.0)— (0.385 X 40.0) = 207.48 lb/ft of width.

1 The applied surface load is 40.0 lb/ft-. These

i loads on the floor are shown on figure 39.

207.46 Iblff

O

40 Ibiff

^

J I li L 9.0 -4.0

13.0

0

Figure 39.Loads on floor, partition normal to floor members.

The reactions may be found separately for

the surface load and the line load and the total

reaction at each support is the sum of the values

for the separate loads. The reactions are

For surface load—

T'otal surface load. .40.0x13.0 = -- 520.0 lb/ft of width.

260.0 lb/ft of width.

For line load

5 M„ = 0= {Rj^ X 13.0) — (207.48 X 9.0)

22 = 143.64 lb/ft of width.

2M„' = 0=(207.48X4.0) —(72^.^^ X13.0) Rr 63.84 lb/ft of width.

J?i = 260.0+ 63.84 = 323.84 lb/ft of width.

7?^ = 260.0+143.64 = 403.64 lb/ft of width. 2 F,^ = 0 = 323.84+403.64—520.0—207.48 (check)

The moment is a maximum where the shear

is zero.

5 Fj, = 0 = 323.84—40a;

a; = 8.096 ft. The maximum moment is

-72,a + [40...(:)] 1310.0 ft-lb/ft of width.

The surface load which gives the same maximum bending moment is M= 1V12 M= 1310.0 ft-lb/ft of width.

H' = 62.0 lb/ft2.

Therefore, the design transverse load is 62.0

lb/ft- on a 13.0-ft span.

If there is no partition above floor, the design

transverse load is 40.0 lb/ft- on a 13.0-ft span.

(b) Partition Parallel to Floor Members

The line load on floor is determined in the same way as for partition normal to members.

The line load equivalent to applied surface load

is deducted. The floor must be reinforced under

the partition to support the line load exerted

by the partition.

4. Floor With Opening

The method of determining the design trans- verse load for floor with opening is illustrated

by the attic floor shown on figure 40. The floor,

span 13.0 ft, has a 2.0- by 3.0-ft scuttle opening.

The surface load is 20 Ib/ft^.

Inner bearing of portions cdgh and efij is taken at inner edge of opening.

Design transverse load on each portion is

abcf. 20.0 lb/ft2, span 13.0 ft.

cd,(7^, 20.0 lb/ft2, span 8.0 ft. efij, 20.0 lb/ft2, span 3.0 ft. gjkm, 20.0 lb/ft2, span 13.0 ft. The weight of the floor is taken as 10.6 lb/ft-.

I
66 Building Materials and Structures Reports

Figure 40.

Floor with opening.

The inner end of portion cdgh bears on header dh. The design transverse load for

header dh is 122.4 lb/ft on 3.0-ft span. Reaction on each of joists cf and gj is 183.6 lb. These reactions are design loads for attaching

header to joists.

The inner end of portion efij bears on header

ei. The design transverse load on header ei is 45.9 lb/ft on 3.0-ft span. Reaction on each of

joists cf and gj is 68.8 lb. These reactions are design loads for attaching header to joists.

Along line cf and gj the floor must be either

reinforced or additional joists provided 'to support the header reactions.

The design load for fastening portion cdgh

to header dh is 122.4 lb/ft and for fastening

portion efij to header ei 45.9 lb/ft. These design loads may be tension, compression, or

shear, depending upon the method of attaching

floor to header.

5. Floor With Stair Opening

The first-story floor of two-story house

shown in figure 41 has a span of 22.0 ft, and a

3.17- by 9.33-ft opening for cellar stairs. Top

of stairs is fastened to header eg; bottom rests on the cellar floor. Total rise of stairs is 7.83

ft; total run is 7.5 ft. The stairs to second story consist of two

parts; a straight portion having 8 treads and

a 90°-tumed portion having three treads. If one carriage is fastened to the wall and the

other to a partition, the stairs are statically

indeterminate. When computing the design

loads on wall and partition, it is safe to assume

that all of the load on stairs is carried by

these walls. The outer end of each tread of the

tuni is fastened either to wall or to the header

in second floor; the inner end of each riser of

the turn is fastened to a post. Straight portion

of stairs has a total rise of 6.0 ft and a total run of 6.67 ft.

Second floor

Section through stairs

b c d

-1.33 9.33' -S.33

' h

oS First floor

22.0

bearing to bearing

Figure 41.

Floor with stair opening.

For this report, the applied load on each

tread is taken as 150 lb and the weight of stairs as 25 lb per tread.

The total applied load on ceflar stairs is 1,500 lb, total weight of stairs 250 lb. Vertical

reaction upward on each end of stair carriage

is 437.5 lb. For straight portion of stairs to second

story, the load on supporting wall and parti-
Strenglh of Houses 67

tion, due to applied load per tread and weight

per tread, is 105 lb/ft of width. The load on

wall and header due to total load of each tread

of the turn (applied load per tread plus weight

per tread) is 39.4 lb/ft. Half the total load of

turn is carried by the post, total 262.5 lb compression.

The surface load on floor is 40 lb/ft-. Inner

bearing of portion abef and cdgh are taken at inner edge of opening.

The design transverse load on each portion

of floor is

abef, 40 \h/it-, span 7.33 ft. cdgh, 40 Ib/f span 5.33 ft. ehij, 40 lb/ft2, span 22.0 ft.

The inner end of portion abef bears on header bf. The design transverse load on header bf

is 146.6 lb/ft on 3.17-ft span. Reaction on each

of joists ad and eh is 232.4 lb. These reactions are design loads for attaching header to joists.

The inner end of portion cdgh bears on header eg. The design transverse loads on header eg are; 106.6 lb/ft on 3.17-ft span, and

two symmetrically spaced loads of 437.5 lb from cellar stairs. Reaction on each of joists

ad and eh is 606.5 lb. These reactions are design loads for attaching header to joists.

In addition to header reactions, joist eh

carries a load of 105 lb/ft for a distance of 6.67

ft, the weight of the partition, and a load from

post of 262.5 lb. Along line eh the floor must be either re- inforced or an additional joist provided.

The design load for fastening portion abef

to header bf is 146.6 lb/ft, and for fastening

portion edgh to header eg, 106.6 lb/ft. These

design loads may be tension, compression, or

shear, depending upon the method of attaching

floor to header.

XVI. WEIGHTS OF HOUSE

CONSTRUCTIONS

1. Description of Constructions

A brief description of each of the constructions covered by the BMS repoi-ts on structural

properties is given in table 16.

Table 16.Sutiumtrij of hn)ise conftlriictiom from BMS

structural properties reports

ConWeight,

actual.

struc- BMS Sponsor, trade name, and based on

tion report Element description face symbol area.

MASONRY CONSTRUCTION SECTION, NB.S

AA 5 Wall AB 5 Do AC 5 Do AD 5, Do AE 5 Do AF 5 Do

Units, hish-strenKth brick; ce- ment mortar; excellent workmanship.

Units, medium-strength brick: cement-lime mortar; commerv\:\\ work niunship.

llniK. inrdium-strength brick;

cciiicni-linie mortar; excellent workmanship.

Units, structural clay tile on

end: cement-lime mortar; excellent workmanship.

Units, structural clay tile on

side; cement-lime mortar; excellent workmanship.

Units, stone-concrete block; ce- ment-lime mortar; excellent workmanship.

H. H. ROBERTSON CO., "KEYSTONE BEAM STEEL FLOOR" AG 10 Floor Frame and lower face, sheet

steel; upper face, concrete fill and composition finish floor.

55. 60

INSULATED STEEL CONSTRUCTION CO., "FRAMELESS-STEEL" AH

AI

9

9

9

9

Wall Frame, sheet-steel; both faces, sheet steel. Frame, sheet-steel; both faces, gypsum board. Frame and deck, sheet-steel; upper face, wood sleepers and wood finish floor; lower face, sheet Steel. Frame and deck, sheet-steel; upper face, insulation and

built-up roofing: lower face, sheet steel.

7. 47

4. 04

9. 52

10. 7:3

Partition, nonloadbearinf,'. AJ Floor

AK Roof

STEEL BUILDINGS, INC., "STEELOX" AL 12

12

12

12

Wall Frame and outside face, sheet

steel; inside face, wood furring

strips and insulatmg fiber- board. Frame, wood; both faces, insulating fiberboard. Frame and lower face, sheet

steel; upper face, wood sleepers and wood finish floor. Frame and lower face, sheet

steel; upper face, wood furring

Strips, insulation, and built- up roofing.

4. %

3. 04

8. 08

6. 99

AM

AN

AO

Partition, nonloadbeai'ing. Floor

Roof

CtlRREN FABRIHOHE CORPORATION, "FABRIHOME" AP 11

11

Wall Frame, sheet steel; inside face, gypsum board; outside face, plywood. Frame, sheet steel; both faces, gypsum board.4. 17 AQ Partition, 5. 10 nouloadbearing. CONNECTICUT PRE-CAST BUILDINGS CORPORATION, "TWACHTM.VX" AR 20

20 WalL Slab, reinforced concrete.

M. 80 AS Floor. Do 37. 70 STRUCTURAL CLAY PRODUCTS INSTITUTE AT

AU

24

24

WaU.

Do

Units, clay brick; cement mortar; deformed steel bars (verti- cal and horizontal). Units, facing, brick, and backins, striictural-clay tileonside; Cement mortar; air space and

steel wall ties.

88. 70

62. 30

BENDER BODY CO., "BENDER STEEL HOME"

A\- 27 Wall Frame, sheet steel; inside face, insulating fiberboard; outside

face, insulating fiberboard and

sheet steel.

7. 24
68 Building Materials and Structures Reports

Construc- tion symbol

BMS

report Element

Sponsor, trade name, and

description

Weight,

actual, based on

face

area.

TILECRBTE FLOORS, INC., "TILECRETE" A W 16 Floor Joists, rolled steel; fillers, struc- tural clay tile; fill, concrete; upper face, wood parquetry

finish floor.

51.50

NATIONAL CONCRETE MASONRY ASSOCUTION

,4.Y 21 Wall- TJnits, facing and baclcing, concrete block; cement mortar;

air space and steel wall ties.

44. 10

WHEELING CORRUGATING CO., "WHEELING LONG-SPAN STEEL FLOOR" AY 15 Floor Frame and deck, sheet steel; upper face, asphalt roofing, wood sleepers, and wood finish

floor; lower face, metal lath and plaster.

16. 10

Construction symbol

BMS

report Element

Sponsor, trade name, and

description

Weight,

actual, based on

face area.

NATIONAL CONCRETE MASONRY ASSOCIATION BO 32

32

Wall Units, facing, shale brick, and

backing, concrete block; ce- ment-lime mortar.

Units, concrete block; cementlime mortar.

60.80 BP Do 30. 70

WESTON PAPER & M ANUFACTtJBINQ CO., "RED STRIPE"

HARNISCHFEGER CORPORATION, "PRE-FAB"

BQ..

BR.

BS.. AZ.

BA

BB

BC

WallPartition, nonloadbearing. Floor

DoFrame, sheet steel; inside face, furring strips, paper, gypsumboard lath, and plaster; outside face, insulating fiber- board, furring strips, plywood,

paper, and wood shingles. Frame, sheet steel; both faces, furring strips, gypsum-board

lath, and plaster. Frame, sheet steel; upper face, wood nailing strips, wood subfloor, paper, and wood finish

floor. Frame, sheet steel; upper face, wood nailing strips, wood subfloor, paper, and wood finish

floor; lower face, wood nailing

strips, paper, gypsum-board

lath, and plaster.

10. 60

12.10

7. 59

14. 10

BT.

36 WallPartition, nonloadbearing. Floor

Roof.

Frame, wood; inside face, corru- gated double wall fiberboard

lath and plaster; outside face, wood sheathing, paper, and

wood-bevel siding. Frame, wood; both faces, corru- gated double wall fiberboard

lath and plaster. Frame, wood; upper face, wood

subfloor, paper and wood fin- ish floor; lower face, corru- gated double-wall fiberboard

lath and plaster. Frame, wood; upper face, wood

sheathing and built-up roof- ing; lower face, corrugated double-wall fiberboard lath and pla.ster.

8. 94

8. 16

13. 00

DOUGLAS FIR PLYWOOD ASSOCIATION

BRICK MANUFACTURERS ASSOCIATION OF NEW YORK, INC. BD 23 Wall Units, clay brick; cement-lime

mortar; air space and steel wall ties.

67.60

W. E. DUNN MANUFACTURING CO., "DUNN-TI-STONE" BE 22 Wall Units, concrete slabs; cementlime mortar; air space and

steel tie bars.

49. 50

NATIONAL CONCRETE MASONRY ASSOCIATION BF 32 Wall Units, facing, shale brick, and

backing, concrete block; ce- ment-lime mortar.

00.90

INSULITE CO., "INSULITE"

BU 30 Wall Frame, wood; inside face, ply- wood; outside face, plywood

and wood shingles.

4. 2.3

NELSON CEMENT STONE CO., INC., "NELSON PEE-CAST CONCRETE FOUNDATION" BV 26 Wall --| Slab, reinforced concrete 51. 70

KNAP AMERICA INC., "KNAP CONCRETE WALL UNITS" BW 40 Wall Units, flanged reinforccd-concrete slabs; wood splines (vertical); steel pins.

32. 30

CELOTEX CORPORATION, "CELOTEX"

BG.

BH.

BI.

BJ.

BK.

BL.

BM..

BN..

Wall

DoDo.

Do

Do

Do

Partition, nonloadbearing. Do

Frame, wood; inside face, insu- latiug-fiberboard lath and

plaster; outside face, insulat- ing fiberboard and wood-bevel

siding. Frame, wood; inside face, in- terior fiberboard; outside face, insulating fiberboard and

wood-bevel siding. Frame, wood; inside face, in- terior fiberboard; outside face, insulating fiberboard and

wood-bevel siding. Frame, wood; inside face, insu- lating-fiberboard lath and

plaster; outside face, insulat- ing fiberboard, paper, metal

lath, and stucco. Frame, wood; inside face, insu- lating -fiberboard lath and

plaster; outside face, insulat- ing fiberboard and brick veneer. Frame, wood; inside face, insu- lating-fiberboard lath and

plaster; outside face, insulat- ing fiberboard, wood furring

strips, and wood shingles. Frame, wood; both faces, insu- lating-board lath and plaster. Frame, wood; both faces, in- terior fiberboard.

Frame, wood; inside face, insu- lating-fiberboard lath and

plaster; outside face, insulat- ing fiberboard and wood-bevel

siding. Frame, wood; inside face, rigid fiberboard; outside face, insulating fiberboard and woodbevel siding. Frame, wood; both faces, insu- lating-fiberboard lath and

plaster. Frame, wood; both faces, rigid fiberboard. .

9. 10

4. 70

11.10

3.03

5. 02

4.51

20.00

50. 50

10.60

11.20

PALISADE HOMES, "PALISADE HOMES" CB

CC.

CD

CE

37 Wall Frame and outside face, wood 5. 24 plank (vertical); inside face, plywood.

37 Partition, Frame, wood plank (vertical); 4. 20 nonload- both faces, plywood.

bearing.

37 Do-- Frame, wood; both faces, ply- 2. 10 wood.

37 Floor Frame and deck, wood pla.nk; 7. 80 upper face, wood-finish floor.

W. E. DUNN MANUFACTURING CO., "DUNSTONE" CF 38 Wall Units, concrete block; cement- 52. 60 lime mortar. CG 38 Do Do 54. 80

WISCONSIN UNITS CO., "PFEIFER UNITS" CH 39 Wall Units, flanged reinforced-concrete slabs; steel plates (vertical); steel bolts.

15. 00

3.12
Strength of Houses 69

Woifrht, Wcipht, Con- ac( ijiil, Con- actual.

struc- BMS Sponsor, trade name, and based on struc- BMS Sponsor, trade name, and based on

tion report Element description face tion report Element description face symbol area. !^ymboI area.

AMERICAN HOUSES, INC., "AMERICAN HOUSES" OFFICE OF INDIAN AFFAIRS AND NATIONAL YOUTH AD.VIINISTRATION

47 Wall.

Partition, load- bearing.

Partition, nonloadbearing. Floor

Frame, wood: inside face, gyp- sum wallboard; outside face, plywood, paper, and wood

shingles. Frame, wood; both faces, gyp- sum wallboard. Do

Frame, wood; upper face, ply- wood, paper, and wood finish

floor.

5. 46

5. 42

5. .33

7.16

HOMASOTE CO., "PRECISION-BUILT"

WalL.

Do..

Partition,

load- bearing.

Frame, wood; both faces, fiber- board. Frame, wood; inside face, fiber- board; outside face, fiberboard and wood-bevel siding. Frame, wood; both faces, fiber- board.

Ih/frUnits, plain adobe (earth) block, molded by hand; cement-lime

mortar.

Units, bitudobe (earth with ad- mixture of bituminous stabilizer) block; cement-lime mortar. Monolithic terracrete (earth with admixture of Portland

cement), rammed by hand.

Units, terracrete (earth with ad- mixture of Portland cement)

block, machine pressed; ce- ment-lime mortar. Monolithic earth, rammed by

hand.

3. 60

4. 38

3.62

TENNESSEE COAL, IRON <t RAILROAD CO., "U.S.S. PANELBILT"

MU NLOCK ENGINI;ERING CO., "MUNLOCK DRY WALL IiRICK" CP 53 Wall Units, brick; cement mortar 76. 70

GLOBE-WERNICKE CO., "SCOT-BILT" Frame and outside face, sheet

steel; inside face, wood nailing

strips and sheet-steel panels. Frame and lower face, sheet

steel; upper face, wood nailing

strips, wood subfloor, and wood finish floor. Frame and deck, sheet steel; upper face, insulating fiber- board and asphalt roofing; lower face, wood nailing strips and gypsum wallboard.

9. 91

11. 90

DG 74 Wall Frame, sheetsteel. No. 14BWG;

inside face, insulating fiber- board; outside face, galvanized

sheet-steel bo.x-rib siding and

batten strips. Frame, sheetsteel, No. 11 BWG;

inside face, insulating fiber- board; outside face, galvanized

sheet-steel box-rib siding and

batten strips. Frame (similar to DG), sheet

steel; both faces, insulating

fiberboard. Frame, sheet steel; upper face, galvanized sheet-steel box-rib

roofing and batten strips.

3. 99

DH 74 Do 4.47

DI 74 Partition, nonloadbearing. Roof

4. 01

DJ 74 2. 68

HOMASOTE CO., "PRECISION BUILT, JR." DK 72 Wall Frame, wood; both faces, insulating fiberboard. 1 3. 13

PIIC HOUSING CORPORATION, "PHC"

TILECRETE CO., "TILECRETE TYPE A

Joists, rolled steel; fillers, asbes- tos-cement board; fill, concrete; upper face, wood finish

floor.

44. 20

HERMAN A. MUGLER, "MU-STEEL"

Wall_

Partition, nonloadbearing. Floor

Roof_

Frame and inside face, sheet

steel; outside face, insulating fiberboard and wood-bevel

siding. Frame and "inside" face, sheet

steel; one "outside" face, sheet

steel. Frame and lower face, sheet

steel; upper face, wood subfloor and wood finish floor. Frame and lower face, sheet

steel; upper face, insulating

fiberboard, wood sheathing, and built-up roofing.

6. 81

DL 90 Wall with- out braces, Frame, wood; inside face, ply- wood; outside face, insulating6. 63 demount- fiberboard and plywood.

able. 90 Wall, with Frame, wood; inside face, ply- 6. 98 braces, de- mountable. wood; outside face, insulating fiberboard and plywood. DM 90 Floor, de- mountable. Frame, wood; both faces, ply- wood.

5.93 DN 90 Roof, de- mountable. Frame, wood, rafters 5% in. deep; upper face, insulating

fiberIjoard and plywood.

5. 36

DO 90 Do Frame, wood, rafters 7% in. deep; upper face, insulating5. 97

fiberboard and plywood.

GENERAL SHALE PRODUCTS CORPORATION, SPEEDBRIK

9.16 DP

j 86 Wall Units, shale (cellular); cementlime mortar. 41.37

HOMASOTE CO., "PRECISION-BUILT, JR." (SECOND CONSTRUCTION) DQ.

PORTLAND CEMENT ASSOCIATION

Frame, wood; inside face, insulating fiberlDoard; outside face, paper and wood-bevel siding. CY 62 Floor _. Joists and bridging, precast rein- forced concrete; upper face, reinforced concrete.

36. 60 LEON H. WITTNER, MULTIPLE BOX-GIRDER PLYWOOD PANELS DR 99 Wall Frames, two, wood, plywood be- tween frames; both faces, ply4. 3S MASONRY CONSTRUCTION SECTION, NBS DS 99 Floor wood.

Frames, two, wood, plywood be- tween frames; both faces, ply- wood.

Frames, two, wood, plywood be- tween frames; both faces, ply- wood.

Frames, two, wood, plywood be- tween frames; both "faces, ply- wood .

8. 15 CZ 61 Wall Nonreinforced concrete, 1 part of Portland cement, 2.71 parts of sand, and 5.31 parts gravel, by

dry weight. Nonreinforced concrete, 1 part Portland cement, 2.53 parts sand, and 3.41 parts gravel, by

dry weight.

74. 90 DT 99 Roof 7. 96 DA 61 Do 75. 10 DU 99 Roof de- mountable.

8.38
70 Suilding Materials and Siruclures Reports

Weight, Con- actual. struc- BMS Sponsor, trade name, and based on

tion report Element description face symbol area.

FOREST PRODUCTS LABORATORY

Frame, wood; inside face, wood

lath and plaster; outside face, wood sheathing, paper, and wood bevel siding. Frame, wood; upper face, wood

subfloor, paper, and wood fin- ish floor; lower face, wood lath and plaster. Frame, wood; upper face, wood

sheathing, paper, and wood

shingles. Frame, wood; both faces, wood

lath and plaster.

10.00

13. 20

4. 60

12. 80

2. Weight

Specimens were weighed and values obtained were divided by the measured face areas. For the discussion of structural properties,

it was found helpful to group the constructions

as wood, steel, or masonry according to material

in the principal structural members.

Weights of the constructions in each group,

arranged in order beginning with the lowest, are shown in figure 42.

In designing a house, weight of the construction is important because the compressive load on a wall depends upon the weight of walls,

floors, and roof above. For the most economical

design, therefore, other factors being equal, the

construction weighing the least should be

selected.

Weight has an important effect on the price

of prefabricated constructions. The expense of

shipping raw material to the manufacturing

plant and of transporting the processed unit to the house site is a large portion of the total

cost. These transportation charges limit the

marketing area for prefabricated constructions.

If the processed sections of the house are very

large, the marketing area to be served will be

smaller than it would be for the customary un- assembled building materials such as lumber,

brick, and cement. In many cases, prefabricated constructions have to be transported by

special conveyances because they cannot safely

be shipped by common carrier. For large prefabricated constructions where the weight is low the marketing- area is increased if the

sections are so fabricated that processed vmits can be assembled at the site without hoisting

equipment. In general, decreasing the weight

of a prefabricated construction increases its marketing area. By enlarging the marketing

area, greater investment in the fabricating

plant is justified and uniform production at reasonable cost is made possible by the use of

highly specialized automatic equipment.

Figure 42 shows the types of construction

with low weights which deserve serious consideration, especially for prefabricated houses.

It, also, indicates trends which should be helpful

in the development of new constructions.

3. Walls

(a) Wood

Two constructions weigh much more than

other wood walls

BJ stucco and BK brick

veneer. Therefore, they were not included in

this study.

Weight of the other walls ranged from 3 to 11 lb/ft", averaging 6.04. Except for constructions CB, DL, and DR,

all wood walls have conventional frames of

studs and plates, some with girts under trans- verse joints in the fiberboard or plywood faces.

In all these framed walls, except for DK and

DQ, the studs are 2 by 4 in., spaced 1 ft 4 in. In DK, the studs are 2 by 2 in. and in DQ, 2 by

3 in., both spaced 1 ft. These two constructions

are lightest of all the wood wall constructions

(about 3 lb/ft2).

Of walls weighing less than the average, the

lighter ones (3 to 5 lb/ft-) are charcterized by

faces of fiberboard or plywood. Walls with

fiberboard, overlaid with either wood shingles or wood siding outside, Aveigh more than walls

with fiberboard only on the outside. The weight

of CB (planks vertical) and CI (gypsum board

inside) is less than 5.5 Ib/ft^.

Of the walls weighing more than the

average, DL is demountable in small pieces and

has many steel fastenings. It has plywood

inside and insulating fiberboard overlaid with

plywood outside, and the weight is only 6.6

\h/ft~. All the others have plaster inside, the

weights ranging from 9 to 11 lb/ft-, although

most of them have fiberboard lath inside and

fiberboard sheathing outside, overlaid with

either shingles or wood-bevel siding.

Conventional wood wall QA, which has wood

lath with plaster inside and wood sheathing

with wood-bevel siding outside, weighs 66 percent more than the average. Stucco wall BJ

and brick-veneer wall BK also have fiberboard

lath with plaster inside.

(b) Steel

All the steel walls have sheet-steel channelshaped structural members. Of the nine constructions, the three lightest and the three

heaviest have a steel frame to which the faces are fastened. In the three intermediate constructions, the structural members are steel sheets flanged to form a one-piece face with

studs. For two of these constructions, this face

is outside and for the other, it is inside.

Weights range from 4 to 11 lb/ft-, averaging

6.28 lb/ft2.
Strength of Houses 71

O

O

\

.0)

90

80

70

60

50

40

30

20

10

0

AC

CP

DA

CZ

AB

BD

A U

Avg 70.4 BF

OF BO

BV CG

BE AF

AX

AD

DP

AE

AR

BW

BK

BJ

BP

CH

W BY DL

BL QA

BX

CM Bl CI BQ

DK DR CB BG

DQ CN BHDLa

Avg_6._04_

Wood

AL

AZ

AH

DH AV

AP CQ

DG CU

6.28

in

D

A A

A f

i

DF

C

Steel

Walls

Masonry

O

O

I

Wood Wood Steel

Load Nonload-bearing

bearing

Partitions

Wood Steel Masonry Wood Steel

Floors Roofs

Figure 42.Weight of constructions.

Inside faces are fiberboard on four constructions, sheet steel on three, and gypsum board

on two, one of the latter being plastered.

Outside faces are sheet steel on five constructions, fiberboard overlaid with either sheet

steel or wood (shingles or siding) on three,

and plywood on one.

(c) Masonry

Weights of the masonry walls range from 15

to 157 Vo/ii-, averaging 70.4. Of the 29 constructions, 17 weigh less than

the average, the thickness ranging from 4 to 10 in. All except BV and CH have air spaces in

the wall. Of these walls, four (AC/. AX, BD,
72 Building Materials and Structures Reports

BE) are cavity walls; four {AF, BF, BP, BO)

are hollow concrete block; three {AD, AE, DP)

are structural clay tile; two {CF, CG) are

solid concrete block laid to leave air spaces; one (BW) is solid concrete units connected to vertical wood splines; and one (AR) is a concrete slab enclosing air spaces. Of the constructions weighing less than the average,

among the lighter are CH and BW (solid concrete units connected to vertical splines) and

structural clay tile; among the heavier are

cavity walls, hollow block, and solid block laid

to leave air spaces.

The 12 constructions weighing more than the

average, are all solid walls. (There are perforations through the clay units in wall CP.) Thickness ranges from 6 to 14 in. Among the lighter

of these solid walls are monolithic concrete

(6 1/16 in. thick) and brick (8 1/16 to 8 1/2 in. thick), with weights ranging from 74 to 96

lb/ft-. The heavier solid walls are all earth

constructions (11 3/4 to 14 in. thick) with

weights ranging from 117 to 157 lb/ft-.

4. Load-bearing Partitions

All load-bearing pai-titions have conventional

wood frames of studs and plates, studs being

2 by 4 in., spaced 1 ft 4 in. Weights range

from 4 to 13 lb/ft-, averaging 7.28 Ib/ft^.

The lightest partition has fiberboard faces,

the next heavier has gypsum-board faces, and

the heaviest has wood lath with plaster faces.

5. Nonload-bearing Partitions

All nonload-bearing partitions have either

wood or sheet-steel structural members.

(a) Wood

All wood nonload-bearing partitions, except

CC, have conventional wood frames of studs

and plates. With the exception of those used

in CD and CK, studs are 2 by 4 in., spaced 1 ft 4 in. Weights range from 2 to 11 lb/ft-, averaging 5.81 lb/ft2.

Of partitions weighing less than the average,

the lightest, CD, has a wood frame (studs 1 3/8 by 1% in., spaced 1 ft) with ply^vood faces,

and the next three have fiberboard faces. Plank

partition CC has plywood faces and weighs

about 1.5 lb/ft- less than the average. Partition, CK, (studs 2 by 3 in., spaced 1 ft 4 in.)

weighs a little less than the average.

Of the partitions weighing more than the

average, all have faces of fiberboard lath with

plaster and weigh from 9 to 11 Ib/ft^.

(6) Steel

All the steel nonload-bearing partitions have

sheet-steel structural members. Except for CV,

these members are channels having the webs

perpendicular to the faces. For CV, the structural members are steel sheets flanged to form a

one-piece "inside" face with studs. The weights

range from 4 to 12 lb/ft-, averaging 6.47 Ib/ft^.

Of the partitions weighing less than the

average, (4 to 5 lb/ft-), the lightest has fiberboard faces and the other two have gypsumboard faces.

Of the partitions weighing more than the

average, CV has sheet steel on the "outside"

face and the heaviest construction, BA, has

gypsum-board lath with plaster face.

6. Floors

(a) Wood

The wood floors BS, CL, and QB have conventional frames of joists and headers, the joists

being 2 by 8 in., spaced 1 ft 4 in. The other

floors have unusual wood frames.

The weights of the floors range from 6 to 13

lb/ft-, averaging 9.21 \h/it-.

Of the wood floors weighing less than the

average, the lightest, DM, is demountable in

pieces and has plyv/ood panels on both faces.

The next heavier, CL, has plywood subfloor and

wood finish floor. The plank floor CE has a wood finish floor on the deck and DS has plywood on both faces.

Both floors weighing more than the average

have plaster on the lower face and weigh 13

lb/ft-. One, BS, has a wood subfloor with wood

finish floor on the upper face and fiberboard

lath with plaster on the lower face. The other,

QB (conventional), has wood subfloor with

wood finish floor on the upper face and wood

lath with plaster on the lower face.

(b) Steel

All the steel floors have sheet-steel structural

members. In six of the eight constructions these

members are steel sheets formed into a onepiece deck or lower face with either one or two

joists.

The two heaviest floors are AG and AY. Floor

AG has a concrete fill on the cellular sheet-steel

lower face and weighs more than three times

AY. Therefore, AG was not included in this

study. The weights of the other floors range

from 8 to 16 Ib/ft^, averaging 10.64 Ib/ft^.

All the steel floors have upper faces of nailing

'

strips, sleepers, or wood subfloor overlaid with

wood finish flooring. Of the floors weighing less than the average, all except BB have sheet-steel

lower faces. Floor BB, the lightest, has no

lower face.

Of the floors weighing more than the average,

all have lower faces of plaster on either gypsum

or metal lath.
Strength of Houses

(c) Masonry

All the masonry floors are reinforced concrete

and the weight ranges from 37 to 52 Ib/ft^,

averaging 42.50.

Of the floors weighing less than the average,

one, CY, has precast concrete joists on which a

slab is poured and the other, AS, is a precast

concrete slab having enclosed air spaces. For

both, the concrete is the upper face.

Of the floors weighing more than the average,

both (AW, CT) have joists of expanded rolled

I-beams, fillers resting on the lower flanges of

the joists, concrete fill, and wood finish floor.

7. Roofs

(a) Wood

The lightest and the heaviest wood roofs have

conventional frames of rafters and headers

(QC, rafters 2 by 6 in., spaced 2 ft) {BT,

rafters 2 by 8 in., spaced 1 ft 4 in.). All the

others have unusual frames. The weights range

1 from 5 to 12 lb/ft-, averaging 7.30 Ib/ft^.

The lightest roof, QC (conventional), has

wood sheathing with wood shingles on the upper

face and no lower face. Heavier roofs, DN and

DO, are similar and demountable in pieces but

have different depths of rafters. The upper

face is fiberboard overlaid with plywood. The

next heavier roofs, DT and DJJ, are similar

(one demountable in panels). Both faces are plywood. The heaviest roof, BT, has wood

sheathing with built-up asphalt roofing on the

upper face and fiberboard lath with plaster on

the lower face.

(&) Steel

All the steel roofs have sheet-metal structural

members. In four of the five constructions,

these members are steel sheets formed into a one-piece deck or lower face with rafters. The

weights range from 3 to 12 lb/ft-, averaging

8.27 lb/ft-'. The lightest roof has a sheet-steel upper face

and the others have fiberboard sheathing overlaid with built-up roofing. Roof CX has wood

sheathing between the insulating fiberboard

and the built-up roofing.

The lightest roof has no lower face and the

heaviest has nailing strips with gypsum-board

lower face. The other roofs have sheet-steel

lower faces.

XVII. VARIATIONS IN STRENGTH OF

HOUSE CONSTRUCTION

1. General

It is generally believed that for a given house

construction there are differences in strength

73

caused by differences in the materials and workmanship. While the consti'uctions were being

tested, visitors to the laboratory frequently

commented that obviously the specimens were much better in materials and workmanship and

therefore stronger than the same constructions

in houses. Because all the specimens for a construction were built at the same time by the same workmen and from the same lots of material, it seemed probable that the differences in

strength of the specimens were less than the

differences in strength of the same constructions in houses.

The BMS reports on structural properties were studied to determine whether they would

throw any light on this question. The methods

for determining the compressive, transverse,

concentrated, impact, and racking strengths are described in BMS2. For each construction and

for compressive, transverse, and racking loads

the difference between the greatest and the least

maximum load was divided by the average max- imum load and taken as the variation in

strength.

Many constructions did not fail under the

concentrated or the impact loads. For the con- centrated load, the test was discontinued if the

specimen did not fail under a load of 1,000 lb and for the impact load under a height-of-drop

of 10 ft ; therefore, no variations were computed for either concentrated or impact loads.

Only concentrated and impact loads were applied to nonload-bearing partitions.

For the racking load, the test was discontinued if the specimen did not fail under a load

of 50,000 lb; therefore, no racking-load variations were obtained for some constructions,

mostly masonry walls.

The variations for wood, steel, and masoniy

constructions are given in table 17.

2. Comparison of Variations in Strength

For wood walls under transverse loading, the

variation when loaded on the outside face is almost twice the variation when loaded on the

inside face, probably because there were different materials in the faces. Under the racking

load, the structural members (studs) do not

fail, only the faces or the fastenings fail, but

the variation is about one-half the variation for

compressive and transverse loadings.

For steel walls, the variations are about the same for all loadings and about one-half the

variation of the wood walls under compressive

and transverse loadings.

For masonry walls, the variations are about

the same for all loadings. Almost one-half the

masonry walls are not included in the variation

for racking load because they did not fail. Apparently, the variations for masonry walls
74 Building Materials and Structures Reports

Table 17.Variations in strength of house constructions

Element

Structural members

Compressive-load

variation

Transverse-load variation Racking-load

variation

All-loads Loaded inside face Loaded outside variation face

Range Average Range Average Range Average Range Average Average

Wall Wood

Percent

9 to 72

3 to 24

1 to 53

18 to 28

Percent

29

13

2022

Percent

0 to 39

2 to 25

5 to 92

15 to 33

10 to 53

2 to 7

2 to 20

6 to 43 2 to 14

Percent

19

926

22

37

51228

8

Percent

8 to 63

3 to 13

5 to 92

15 to 33

Percent

34

72322

Percent

1 to 44

4 to 24

5 to 60

4 to 15

Percent

14

14

19

8

Percent

24

1122

18

Do Steel Do Masonry

Partition, load-bearing. Floor... Wood

Do

Do Steel Do Masonry

Roof Wood

Do Steel

are about the same as the variations for wood

walls.

All the load-bearing partitions were wood.

The difference in the variations of wood partitions and wood walls probably is due to the fact

that there were nineteen walls and only three

partitions. For compressive and transverse

loadings, the variations of the partitions and

walls are about the same. The variation under

racking load is about one-third the variations

for these partitions under compressive and

transverse loading and about one-half the variations for any of the walls under racking load.

For wood floors, the variation (transverse

loading only) is greater than the variation of

wood walls under transverse loading and

greater than the variation of any other house

element under any loading. Because of the in- herent characteristics of wood the variation

under transverse loading may increase as the

span increases. For walls, the span is 7 ft 6 in.,

for floors 12 ft, and for roofs 14 ft. For steel floors, on the other hand, the variation is less than the variations for steel walls

under transverse loading and less than the variation for any other element under any loading.

For masonry floors, the variation is greater

than for steel floors but less than the variations

for masonry walls under transverse loading,

probably because all the masonry floors are re- inforced concrete and very few of the masonry

walls were reinforced.

For wood roofs, the variation is about the same as the variations for wood walls under

transverse loading although the span is 14 ft (not 7 ft 6 in.).

For steel roofs, the variation is about twice

the variation for steel floors and a little greater

than the variations for steel walls under trans- verse loading.

The weighted average variation for all the

wood construction is 26 percent ; for all the steel constructions, 8 percent ; and for all the masonry constructions, 21 percent. Whether or not

the variations for houses is greater or less than

the variations for laboratory specimens, it seems probable that the variations for walls,

load-bearing partitions, floors, and roofs in

houses are about the ratio : steel 8, masoni'y 21,

and wood 26.

3. Relation of Materials to Variations

The variations in strength depend upon the

materials in the structural members (studs,

joists, and rafters) and also the materials in

the faces. For many masonry constructions,

the same material is both a structural member

and a face. The relations between materials

and variations were studied to find the relation

for structural members and for each face separately, although they are so interrelated that

the results indicate little more than trends,

which in some cases may be misleading.

(a) Walls

(1) Wood

Studs.—Except wall CB (plank, variation 13

percent) , all wood walls have studs. Assuming

that variations in strengths depend upon diifer- ences in size and species of wood of studs, the

variations range from 17 to 36 percent. In

order, they are Douglas fir studs less than 2 by

4 in., then all other red pine, Douglas fir, and

southern pine 2- by 4-in. studs.

Inside face.—For the materials in inside face,

the variations range from 10 to 32 percent. In

order, the materials are wood lath with plaster,

fiberboard, plywood, fiberboard wath plaster,

and gypsum board.

Outside face.—For the materials in the outside face, average variations range from 13 to 36 percent. In order, the materials are plank,

wood siding, plywood, wood sheathing with

wood siding, fiberboard with stucco, fiberboard

with wood siding, fiberboard with wood shingles, fiberboard with brick veneer, fiberboard,

plywood with wood shingles, and fiberboard

with plywood.

(2) Steel

Studs.—For all the steel walls, the average
Strength of Houses 75

variations are small, ranging from 8 to 12 percent depending upon the studs. The variations are least for channel-shaped members having

the studs and a face in one piece (8 percent)

and greatest for channel-shaped studs to which

the faces are fastened (12 percent) . Inside face.—For the materials in the inside

face, average variations range from 9 to 12

percent. In order, the materials are sheet steel,

fiberboard, gypsum-board lath with plaster, and

gypsum board.

Outside face.—For the materials in the outside face, average variations range from 8 to 18

percent. In order, the materials are fiberboard

with wood siding, sheet steel, fiberboard with

plywood and wood shingles, plywood, and fiberboard with sheet steel.

(5) Masonry

For all the masonry walls, average variations are nearly the same for the solid walls and those

having air spaces in the wall. For those having

air spaces, the materials in order are brick,

structural tile on end, brick with structural tile on side, concrete block, reinforced concrete,

structural tile on side, brick with concrete

block, averaging 21 percent. For solid walls,

the materials in order are reinforced brick,

brick, earth, reinforced concrete, plain concrete, averaging 24 percent.

Inside face.—For the materials in the inside

face, average variations range from 17 to 27

percent. In order, the materials are structural

tile on end, brick, tile on side, reinforced brick,

concrete block, reinforced concrete, earth, and

plain concrete. Outside face.—For the materials in the outside face, average variations range from 17 to 27 percent. In order, the materials are struc- tural tile on end, concrete block, reinforced

brick, brick, reinforced concrete, tile on side,

earth, and plain concrete. Apparently, the variations for earth are more

than for many masonry materials widely used

at present. Therefore, the average variation

for each construction was obtained, and ranged

from 6 to 65 percent. Adobe walls DB and bitudobe walls DC had very small variation ; monolithic earth wall DF and terracrete block wall

DE were very near the middle of the range ; and

monolithic terracrete wall DD had the greatest

variation. Whether the differences in variations were due to differences in material or to differences in workmanship is not known.

(b) Load-bearing Partitions

(1) Wood

Studs.—The three load-bearing partitions all 743712°—48—

had 2- by 4-in. Douglas fir studs, spaced 1 ft 4 in., and average variations ranged from 16

to 22 percent.

Faces.—For the materials in the faces, the

variations ranged from 16 to 22 percent, plaster

with wood lath having the least variation,

fiberboard next, and gypsum board the greatest.

(c) Floors

(1) Wood

Joists.—There does not appear to be any

relation between the size and species of wood

in the joists and the variations.

Upper face.—For materials in the upper face,

average variations range from 10 to 53 percent.

In order, the materials are smallest, plank subfloor with wood-finish floor; near the middle of

the range, plywood and wood subfloor with

wood-finish floor; the greatest, plywood subfloor with wood-finish floor. Loiver face.—For materials in the lower face,

average variations range from 32 to 46 percent.

In order, the materials are no lower face, plywood, wood lath with plaster, and fiberboard

lath with plaster.

(2) Steel

There is no significant difference in the aver- age variations due either to the shape of the

cross-section of the joists or the materials in

the faces. The greatest variation is 6 percent.

(J) Masonry

There is no significant difference in average

variations attributable to the kind of reinforcement or to the materials in the faces.

(d) Roofs

For both wood and steel roofs, there is no

significant difference in the average variations

due to the rafters or the materials in the faces.

4. Relation of Workmanship to Variations

(a) Walls

(1) Wood

For wood walls, the average variation for all prefabricated constructions is nearly the same

as the average variation for all the constructions having the pieces assembled on the house

site.To members of the laboratoiy staff, it appeared that there were great differences in the

care and skill with which the sponsors built the

specimens, but there is no relation between the

average variation and the care and skill with
76 Building Materials and Structures Reports

which the specimens were built. There is some

indication that constructions having the smaller

variations were built with the least care and

skill. The conventional wood-frame constructions,

wall QA, partition QD, floor QB, and roof QC, were built and tested at the Forest Products

Laboratoiy, Madison, Wis. It is reasonable to believe that they were built with more care and

skill than is commercially available for the construction of wood houses.

For wall QA, the average variation is 10 percent, and the average variation for all wood

walls 24 percent ; for load-bearing partition QD,

16 percent and for all load-bearing partitions 18

percent; for floor QB, 40 percent, and for all wood floors 37 percent ; and for roof QC, 43 percent, and for all wood roofs 28 percent. There were many wood walls in the program, but

few partitions, floors, and roofs.

It seems reasonable to suppose that the variation in the strength of like specimens depends

upon the workmanship ; the better the workmanship, i.e., the greater the care and skill with

which the construction is built, the less the variation in strength. Skilled workmen make better

joints and sort the material to some extent,

placing each piece to the best advantage.

For wall QA, the variation is about half the

average for all the wood walls. To determine

whether there was any relation between the

variation and the strength of QA under compressive, transverse, and racking loads, these

strengths were compared with the average of

the strengths of all the other wood walls having

2- by 4-in. studs of Douglas fir, No. 1, common,

spaced 1 ft 4 in. For compressive load, QA is 27

percent greater; for transvei'se load, inside 8

percent and outside 19 percent less; and for

racking load, 68 percent greater. Probably the

great racking strength of QA may be attributed

to the wood sheathing laid diagonally outside

and the wood lath with plaster inside. Many of

the wood walls did not have wood sheathing and

QA is the only wall having plaster on wood lath. Because the racking strength depended more on

the materials in the faces than upon the workmanship, only the compressive and transverse

strengths should be compared. If good workmanship accounts for the greater compressive

strength of QA, why is the transverse strength

considerably less than for the other walls ? For partition QD, the variation is a little less than average, but the average strength is about

24 percent greater than averages of the

strengths for all the other load-bearing partitions.

For floor QB, the variation is about the same

and the strength only 70 percent of average

strength for the similar floors having 2- by 8-in.

joists of Douglas fir or longleaf Southern pine,

spaced 1 ft 4 in. The one other roof with which roof QC can be

compared for strength has deeper rafters more

closely spaced and of a difiierent species of

wood, therefore roofs are not included in this

study.

It seems evident that for the wood constructions tested, which were built with unusual care and skill, there is no veiy definite relation between the variations and the strength of the

constructions.

(2) Steel

Some steel constructions were submitted by

large companies presumably having wellequipped plants skillfully managed and others

by small companies having much less experience

with steel-house construction. No relation was

found between the experience of the sponsor

and the variations in strength.

(3) Masonry

The specimens for some masonry constructions (reinforced concrete) were made in the

sponsor's plant, but most of the specimens were

built in the laboratory by local workmen.

Of the 29 masoniy constructions, 13 were

built under the direct supervision of the

Bureau's Masonry Construction Section. For

some constructions, the workmanship was purposely poor and for others it was purposely

good. The weighted average (22 percent) of

the variations for the constructions built by this j Section is almost the same (24 percent) as the

weighted average of the variations for all the

other masonry constructions.

Because none of the constructions supervised

by the Masonry Construction Section (masonry

units and mortar) duplicated any of those su- pervised by the other sponsors, it is impossible

to compare strengths.

Because with workmen from the building in- dustry it has been found extremely difficult even under direct supervision to change the workmanship (such as filling all joints with mortar)

,

it seems probable that the laboratory specimens

quite accurately duplicate the workmanship of

masoniy houses in the District of Columbia.

If it is desired to know the strength of masonry built in other localities by other workmen,

specimens should be made and tested.

(b) Load-bearing Partitions, Floors, and Roofs

Consideration of the load-bearing partitions,

floors, and roofs did not result in anything

which would be an addition to this discussion

of workmanship.
Strength of Houses 77

XVIII. ALLOWABLE LOADS ON

HOUSE CONSTRUCTIONS

1. General

When designing a house, the architect must

know not only the loads that will be applied in

service but, also, the allowable loads that the

constructions will carry safely. These loads serve the same purpose as allowable or working

stresses for wood, concrete, and steel in building codes.

Houses have never been designed like engineering structures. Since prehistoric times,

safe house constructions have been found by the

tedious and wasteful method of trial and error.

If the modem research that has proved so successful in the solution of other problems had

been applied to houses, not only would homes be

more satisfactory as dwellings but, much more

important, the cost would be much less. This

would be an outstanding contribution to the

problem of providing acceptable houses for the

low-income groups in this country.

Any attempt to apply conventional design

methods for engineering structures (tall

buildings, bridges) encounters perplexing

difficulties.

(a) New Materials

Strength and other properties are known for

common building materials such as wood, concrete, steel, etc., but for many of the new materials advocated for house construction there is

little reliable information as to strength and

performance. In use for such a short time, the

deterioration of these new materials under service conditions has not been definitely determined and, therefore, an architect is justified

in hesitating to use them until necessary basic

data are available.

The BMS reports on structural properties do

give data on the strength properties of constructions built with some of these newer materials but give nothing on deterioration in

service.

(6) Fastenings

The pieces of material in a house are fastened

in many ways. Mortar is used for masonry

units ; wood constructions are fastened by nails,

drive screws, and glue ; sheet materials, including sheet steel and plastics, may be fastened by

devices like spot welds, self-tapping screws,

special rivets, and interlocking connections.

(c) Unusual Structural Members

Of late years, new and unusual structural

members for houses have been advocated although little is known of their behavior under

load.

An outstanding example is sheet-steel members (studs, joists) having a channel, I-beam,

or other cross section. The behavior under load

of rolled-steel sections (thickness 1/8 in. or more) has been established by long experience,

but their use in houses is uneconomical because

the loads are light. As yet there is no assurance

that the methods for computing the strength of

rolled sections can be applied safely to sheetsteel sections. Experience with structures of

thin metal for aircraft shows that too often

they fail under loads less than the computed

loads by buckling where there is compressive

stress. If a house wall consists of sheet-steel

studs 2 in. deep and a sheet-steel face is spotwelded to the stud, the face may be considered

the flanges of a tee beam when computing the

transverse strength. However, under load, the

face, if on the compression side, may buckle and

the actual strength be much less than the computed strength. If the face is attached by drive screws or self-tapping screws, the strength may

be much less than if it was attached by spot

welds because under load the face and the stud

do not behave as a unit.

Members built up of pieces of wood fastened

by nails or glue have been suggested for floor

joists. Although they can be so designed and

fabricated that they are satisfactory, they have

not come into general use because solid (onepiece) joists are cheaper for the spans usually

required for houses.

(d) Stressed-skin Constructions

When designing large structures, it is cus- tomary to assume that walls, floors, and roof

contribute nothing to the strength and stiffness

of the building. All the loads, including the

weight of these portions of the structure, are

carried by the frame. For airplanes, on the

other hand, the weight of the completed struc- ture can be reduced greatly if the covering of

the fuselage, wings, and control surfaces contribute to the strength and stiffness, that is, if they are stressed-skin construction.

Automobiles and especially streamlined

trains of stressed-skin construction weigh much

less than constructions of previous design and

have proved satisfactory in service. Although

it is probably uneconomical to carry the

stressed-skin principle as far in houses as in

mobile equipment because of the high cost of

fabrication, this principle should receive serious

consideration.

In a brick house, the walls not only exclude

the weather but contribute to the strength; in

fact, they are structural members.
78 Building Materials and Structures Reports

Although it long has been recognized that, in a wood-frame house, the sheathing nailed to the

studs resists most of the racking load, it was

assumed that the studs carry all the compressive and transverse (wind) load and that under

these loads the sheathing and siding outside

and lath and plaster inside function only to exclude the weather and to provide a satisfactory appearance architecturally.

The fallacy of this assumption was shown by

the Forest Products Laboratory in BMS25.

Specimens with conventional faces both inside

and out had about twice the compressive and

transverse strength of specimens consisting

only of studs with top and bottom plates.

Consideration of other structural reports

leads to the belief that, in many of the constructions, the faces necessarily must function as stressed members, although inefficiently.

2. Efficient Use of Material

Wood was wastefully used from an engineering standpoint by early settlers in building

cabins of logs cut from trees which had to be

removed to clear the farm. When power-driven

sawmills became available, wood frames having

lighter members were developed and less wood

was required. Because houses having joists,

studs, and rafters spaced 16 inches were satisfactory, this spacing became a rigid trade practice. It exerted a paralyzing influence on frame

house construction by fixing the commercial

sizes of sheets of fiber, gypsum, and plywood.

There appears to be a great need for the application of sound engineering principles to the

development of new construction having just

the necessary strength with which to use material efficiently. Undoubtedly, the trend in the

future will be less material and more fabrication

which may result in prefabrication in wellequipped factories. In the past, abundance of

raw material has made it seem unnecessary

to carry on extensive laboratory research on

structures and houses or to spend the time and

money to design them as carefully as they could

be designed.

3. Criteria for Allowable Loads

The BMS structural reports give strength

data on about 100 house constructions, both

conventional and unconventional, and are an

adequate sampling of the constructions available at present. The requirements for specimens

and the methods of testing are described in

BMS2.

A study of these data led to the following cri- teria for determining the allowable load. If, in the future, experience shows that other

criteria are more useful, they should replace

these criteria. The allowable load for each

criterion should be determined and the lowest

value used when designing a house.

The selection of working stresses (allowable

loads) has been discussed from time to time but no entirely logical method has been developed.

Salmon, in a long discussion of this subject,

concludes, "What then is the real basis which

should detei-mine the working stress in a material? The answer is successful practice."

To avoid misunderstandings, it is necessary

to emphasize that these criteria apply only if the other portions of this report are followed.

(a) Design Loads

If the maximum load on a house is definitely

known, the allowable load on the construction

should be greater than if the maximum load is uncertain or if the assumed maximum load may

be exceeded greatly under conditions which

may occur in the life of the structure. The following criteria, particularly criterion a for the allowable load on a construction, are

only justified if the design loads on the house

are the greatest which in any likelihood will occur. The design live load on a fioor (40 lb/ft-) may

be approached at a large gathering if the room

is filled with people most of whom are standing.

A greater load is very unlikely because it would

automatically be prevented by lack of floor

space.

If the design wind load and the snow load obtained in accordance with sections IV and V of

this publication are not the greatest which occur

in the life of the house, then the observed | Weather Bureau data should be extended by

more recent values at existing and additional

stations.

The house is designed for all loads to be

applied at the same time when, actually, the occurrence of the design value for any one of

them is unlikely and the occurrence of all design

loads simultaneously is highly improbable. It is very difficult to conceive of the greatest snow

load on the roof occurring when the wind is blowing a gale or of there being no standing room on any of the floors during a record

breaking blizzard.

Experience may show that a house is safe if designed for a value less than the sum of all the

design loads. The law of probability may indi- cate that one-half or two-thirds of the sum is a

suitable value.

(b) Design of Walls

For design, the compressive, transverse, and

racking loads are carried by the portions of the
Strength of Houses 79

wall between openings ; that is, by the net width

of the wall, not the gross width.

(c) Construction

Allowable loads apply only to constructions

for which the strength has been detennined by

test and then only if the construction in the

house is as strong as the specimens.

Because the specimens each have several

structural members, the test results are necessarily averages and more representative of the

strength in a house than the results of tests on

individual members or other pieces.

In the manufacture of automobiles, guns, and

electrical equipment, methods have been developed for determining the dimensions of each

part so that they are interchangeable. The

strength and wear are controlled through chemical composition and heat treatment. Often

defective parts are eliminated by nondestructive

tests such as magnaflux and X-ray.

In the house building industry, on the contrary, it is customary to rely on plans and specifications. Often the latter describe in rather

general terms the materials and workmanship,

leaving to the builder considerable latitude for

the exercise of independent judgment.

Sometimes the specifications for the house

state that the material shall comply with ASTM

or other specifications, but the material delivered is seldom tested for compliance. Practically

all specifications require first-class workmanship or workmanship acceptable to the inspector

but, with the exception of dimensions, there are no quantitative measures of workmanship. This

is particularly true for constructions of masonry units and mortar.

It is evident that for houses there are diffi- culties in determining whether or not a construction in a house has the strength of laboratory specimens. If a house is built commercially

in accordance with the description in a BMS

report, there are some uncertainties about the

strength. If the wood is graded visually by a competent inspector and masonry units and

mortar tested for compliance with the values in

the BMS report, there is less uncertainty, but

this leaves the workmanship in doubt, particularly because the reports give almost no information about the workmanship.

If, on the other hand, specimens of the construction made under the same conditions as the

house are tested in a laboratory, the strength is known. Obviously, it is unnecessary to test specimens for each house ; for constructions

built frequently, several tests a year should be

sufficient. For this report, when determining allowable

loads, it was assumed that the constructions in

the house are as like the specimens as is commercially practicable and that the strength is very nearly the strength of the specimens.

If specimens of the actual construction are

tested, the percentages for criterion a may be

increased and if on the other hand, there is no

inspection and the owner or the building official believes that the contractor either cannot or will

not exercise the care and skill characteristic of

the best commercial practice, he is perfectly

justified in fixing a lower percentage. How

much lower, must necessarily be detennined by

individual judgment based on a knowledge of

the conditions.

During discussions of specifications and codes

for structural steel in buildings, it has been

emphasized repeatedly that no design stress,

however low, can be set up which will assure

the safety of a building designed and erected by

ignorant, careless, and unskilled contractors.

Obviously, this also applies to houses.

The same allowable load applies, despite

minor changes in the construction, unless there

is reason to believe that the change decreases

the strength. The application of plaster to the

inside face of a masonry wall should not de- crease the strength, but the use of thin fiberboard sheathing instead of wood sheathing on

a wood-frame wall might decrease the racking

strength and there is no way to estimate how

much except by testing the wall.

(d) Least Maximum Load

It is obvious that the working load cannot ex- ceed the maximum load on the specimens. The

maximum loads for the three specimens loaded

in the same way were not exactly the same. It may be assumed that the differences were

caused by differences in both materials and

workmanship. Therefore, the working load for

the construction should not exceed the least of

the three maximum loads.

Either greater or smaller least maximum

loads should be substituted for the values in the

reports if and when other values are determined

by tests.

(e) Criterion a, Percentage of Least

Maximum Load

In accordance with good engineering practice, the allowable load should be somewhat less than the least maximum load and this ratio

may be expressed in percent. For a particular

construction, the greater the ratio of the allowable load to the maximum test load the more

eflScient the use of material and the less the cost of the house, but only provided the allowable

load is not appreciably greater than the design
80 Building Materials and Structures Reports

load. It is uneconomical to use a 2-in. bolt if a

V2-in. bolt is strong enough.

Logically, there should be a ratio for each

construction based on experience, but, for convenience, it is customary in the building industry to group similar constructions for design

purposes and when applying building code

regulations. Therefore, the ratios recommended

here are estimates applying to all the constructions in the groups wood, steel, and masonry.

They are values selected by engineering judgment based on experience with the constructions

which have been widely used for years.

The values for criterion a are given in table

18.

Table 18.

Values for criterion a

Load Wood

Steel, reinforced bnck, or reinforced concrete Masonry

WALLS AND LOAD-BEARING PARTITIONS

Compressive

Transverse _ Concentrated Impact.

Racking: Faces- Wood (sheathing) Other materials

Percent

60

90

90

90

90

60

Percent

75

7590

90

75

Percent

40

40

90

90

40 NONLOAD-BEARING PARTITIONS

Impact.

Concentrated. .. . . _ 90

90 90

90

90

90 FLOORS

Transverse - Concentrated __ Impact ---

60

90

90

7590

90

40

90

90 ROOFS

Transverse Concentrated . . . 65

90

75904090

(1) Wood

When selecting the criteria for wood, con- sideration was given to the observed behavior

of wood constructions, that under heavy service

load minor adjustments or movements occur between the parts, particularly the structural

members, but that the effect on the strength of

the construction is negligible. This behavior is very marked at bearings if the forces are perpendicular to the grain of the wood as in plates over and under the ends of studs and at the ends

of joists and rafters where they bear on walls.

The strength of wood increases as the moisture content decreases while the wood seasons. The relation for small clear specimens is given

in Forest Products Laboratory Report No. 1313

[27]. When computing the strength of wood

structures, it is customary to take the strength

of unseasoned material. The moisture content

of structural members of the wood house constructions averaged 12 percent. Therefore, the

actual strength was greater than for unsea- soned material and greater than the strength

computed by the usual methods.

Peck [28] found for six cities, widely scat- tered in this country that, over a period of 16

months, the moisture content of interior woodwork did not exceed 12 percent and of exterior

woodwork 14 percent. The only exception was New Orleans where the values were 13 and 16

percent.

The moisture content of the wood in a house

varies somewhat with the season of the year but

the greater values are only for a few months

and for the season when the wind loads and snow loads, if any, are small.

The moisture content of the BMS constructions average 12 percent which is the value

recommended in Wood Handbook [29] for most

of this countiy when designing wood buildings.

The strength of wood depends upon the length

of time the load is applied—the longer the time

the less the strength, as brought out by Markwardt and Wilson [30]. When selecting the

criteria, the ratio of the strength of walls,

floors, and roofs in a house to the strength

found in the laboratory can be estimated by

considering the time each of the loads is applied.

Wood ivalls and partitions.—For compressive

loads, the long-time loads (1 year or more) on

the first-story wall of a two-story house may be

as much as half the design load. The long-time

load is much less in a one-story house, but for

the criterion only the more severe condition was

considered.

The transverse load (wind only) is applied

to a wall for a few hours at most.

The conditions under which an impact load

is applied to a wall were closely simulated by

the impact tests in the laboratory ; therefore,

the duration of the load was not considered. A

large value is justified because any damage is local and cannot cause the house to collapse.

The eff'ect of the concentrated load is still less serious.

For the racking load, if the sheathing or other members resisting the load (wind only) are wood, the duration of the load is the same

as for transverse load and the criterion should

be the same. Many constructions having wood

structural members (studs) have faces of fiberboard or other materials and a smaller value seems desirable until more information is available.

Wood floors.—The long-time transverse loads on a floor may be as much as half the design

load ; therefore, the value is the same as that for

compressive load on walls.

If there are several heavy permanent loads in

line along the joists, such as heavy bookcases

and kitchen or bathroom fixtures, the increase

in ratio of long-time load may make it advisable

to provide additional joists under these loads.

The values for concentrated and impact loads
Strength of Houses 81

are the same as for these loads on walls and

partitions and for the same reasons. Wood roofs.—In the northern United States

there may be snow on the roof for months, but

the duration is shorter than for the long-time

compressive loads on walls or transverse loads on floors; therefore, the criterion should be

greater. If, on the other hand, the only appreciable transverse load applied on the roof is the

effective wind pressure, a still greater value is justified, for some locations as much as 85

percent.

(2) Steel

When selecting the a criteria for steel, consideration was given to the ductility of the steel sheets from which house constructions are fabricated. The sheets must be ductile to permit

cold forming of the members. It also permits

members that are slightly bent in handling to be straightened cold without injury. If one member is more heavily loaded than adjacent

members and the load reaches the yield point,

the member deforms plastically without a de- crease in the load and the load on adjacent

members increases, thus distributing the load more uniformly under subsequent loadings.

After being deformed slightly, the member behaves under load practically as it did before

the deformation occurred. However, local dents

in members reduce the compressive load at fail- ure. This load for these formed members, even

if undamaged, usually is much less than the

yield strength of the material ; therefore, the

ductility of the material has little effect on the

failure which occurs suddenly by buckling.

For steel house construction, the duration of

the load has no effect on the strength and there

is no fatigue effect. Corrosion may decrease the

strength by decreasing the thickness especially

because the members are very thin. Corrosion

sufficient to decrease the strength of the struc- ture has never been found in hotels or office buildings. Conditions in steel houses may be more severe, therefore, adequate protection is advisable to insure a satisfactory service life,

j Inspection of sheet-steel houses indicates that

in some cases the appearance had suffered

through lack of painting but there was little structural damage. If in the future, it is found

that these criteria do not provide a satisfactory

life, it may be necessary to take lower values

although this is an' inefficient way to solve the

problem. Greater protection of the steel against

corrosion and possibly improved maintenance

are more satisfactory solutions.

The strength properties of steel are more

uniform than those of any other material for

houses and the dimensions much nearer the

nominal size, particularly if prefabricated in a

well-equipped shop.

The National Emergency Specifications for

the Design, Fabrication, and Erection of Structural Steel for Buildings, [31] Section 10 re- quires that, in the calculations for the design,

the stress be 24 kips/in.^ for structural steel in

tension and, for some cases, in compression.

The structural steel shall comply with the re- quirements for A-7 Structural Steel [32] (yield

strength, minimum, 33 kips/in.^). The ratio of

the allowable stress to the yield strength, therefore, is 73 percent but this ratio applies to steel structures designed by the usual engineering

methods. That the actual stresses in the completed structure under load may be appreciably

greater or less than the computed stresses is recognized by engineers. Few complete steel structures have been tested by loading to fail- ur although many individual members have

been tested. It is true that the specimens of

house constructions were not completed houses

but they were large portions of a house. Because

the uncertainties in the strength of house constructions which have been tested are less than

the uncertainties in the strength of designed

steel structures, the criterion should be some- what greater for compressive, transvei'se, and

racking load.

The effect of an impact load is local and does

not endanger the house and that of a concentrated load is of negligible structural importance, therefore large values for these loads are justified.

(3) Reinforced Brick and Concrete

The strength of reinforced brick and concrete

constructions are not greatly affected by the

duration of the load ; also, the concrete protects

the steel reinforcement from corrosion. The

effect of local damage to the reinforcement is very much less than in steel constructions. On

the other hand, reinforced concrete constructions lack the unity of steel constructions. That

is, the concrete and the steel under the loads to which a house is subjected in service do not act together as completely as the members of a steel house.

Masonry

When selecting the a criteria for masoniy,

consideration was given to the inherent property of masonry (whether monolithic or built

of units) that the thickness is usually much

greater than for other constructions; that the

components are united in a monolithic mass

which acts as a unit under load, therefoi-e, the

loads are more uniformly distributed ; and that

the support of the foundation is uniformly dis-
82 Building Materials and Structures Reports

tributed. Masonry materials suitable for houses

are readily available in most localities and they

are very durable.

On the other hand, if a portion of masonry

structure is subjected to forces which approach

the strength of the materials, they do not deform plastically to any great extent and distribute the forces to adjacent material, but

failure occurs locally. Forces are applied locally

by temperature changes, settling of foundations, and settling around openings, such as doors and windows. These concentrated stresses may be twice the average sti'ess. Moreover, the

transverse, impact, and racking strength of

unit masonry depends greatly upon the rate of

absorption of the units and the mix and consistency of the mortar, and it has not been found

economically practicable to control these factors

closely even in the best commercial practice.

Likewise, the strength of concrete depends

greatly upon the proportions of aggregate, ce- ment, and water and upon the placing of the

concrete. No floor or roof of masonry without reinforcement was submitted for the programs on

structural properties. Presumably, a vaulted or barrel-arch floor or roof comes in this category,

but it is difficult to visualize the use of either in an ordinary house; therefore, the a criterion

for transverse load on masoniy floors and roofs

has no useful significance.

The effect of an impact load is local and does

not cause the house to collapse. Similarly, the

effect of a concentrated load has no structural

significance.

(/) Criterion b, Damage

For many constructions, damage was observed under loads considerably less than the

maximum, often less than one-half. Therefore,

the allowable load should not exceed the least

load damaging any one of the specimens.

Damage is taken as either cracking or breaking of any piece in the specimen also cracking

or breaking of fastenings or joints.

Damage may be classified as either structural

damage that affects the strength of the construction or utility damage that affects the appear- ance or usefulness of the house as a dwelling;

but, it is difficult, if not impossible, to determine

whether a particular damage is one or the other.

If, for the load at which the damage occurred,

there is a perceptible change in the slope of the

deformation or set curves in the graphs, it is reasonable to consider it structural damage.

Often there is no perceptible change.

For reinforced concrete, small cracks perpendicular to the reinforcement are not considered

structural damage by engineers and visible

buckling of faces (plywood or sheet steel),

which affects appearance only and probably disappears when the load is removed, should also

be disregarded.

However, a crack in a masonry wall either in

the units or in a mortar joint is structural damage as is splitting or breaking of wood members

(studs, joists, rafters) whether or not the effect

is visible on the load graph. Likewise, the fail- ure of a fastening (nail, screw, bolt, or spot

weld) is structural damage although the effect on the maximum load may be negligible.

For most of the constructions having plaster on a face, cracks were plainly visible under

loads very much less than the maximum, particularly if the transverse load was applied to the opposite face causing tensile stresses in the

plaster. For this report, cracks in plaster were

taken as damage and for many constructions

determined the allowable load particularly because, as shown in BMS25, the plaster contributed to the strength of the construction. The

fact that similar wood constructions, particularly floors with plaster on the ceiling, have

been used extensively for about 100 years and

have proved safe for much higher loads raises

the question of the structural significance of

cracks in plaster. Although deflection caused by

loading undoubtedly is one cause of cracks,

there are others, such as the settling of foundations and the shrinking and swelling of wood

members with variations in moisture content.

If, contrary to usual engineering practice, the

allowable load may safely exceed the load caus- ing damage, criterion b should be disregarded

and the allowable load based on the other

criteria.

(g) Criterion c. Slope of Curve

for Both Deformation and Set

In addition to the strength of a house construction, the deformation under load and the

set (permanent deformation) must be con- sidered when determining the allowable load.

Therefore, load-deformation and 1 o a d - s e t graphs are shown in all the BMS reports on

structural properties.

It is customary to obtain load-deformation

(or stress-deformation) graphs for engineering

materials and structural members by applying

the load in increments and measuring the deformation. For many metals, the set can be

determined with suflJicient precision from the

load-deformation graph; as, by the "off-set"

method for determining the yield strength of

metals [33]. Because the elastic behavior of

house constructions was unknown when the

BMS structural reports were prepared, it was

considered desirable to obtain the set by apply- > ing the load in increments, measuring the ' deformation, removing the load, and measuring |
Strength of Houses 83

the set. Although this procedure increased

somewhat the time required to make the tests,

it provided needed information on the elastic

behavior of the constructions. In addition, it subjected the specimens to cycles of loading and

unloading which simulated the cycles of loading

applied to a house. If the load had been in- creased continuously to the maximum, partial

failure of some of the members or of the fastenings might not have an appreciable effect on

the behavior of the specimens because of the

friction between the members caused by the

load. It is conceivable that the maximum load

might have been greater if the specimen had

been loaded continuously.

Because for most engineering structures the

set is negligible for loads less than the so-called

elastic limit, it seemed probable that this also was true for house constructions and that the

load-set graph would be helpful when determining the allowable load. These graphs show large

sets for many constructions, sometimes onehalf the deformation. This condition may have

been caused by plastic material such as rammed

earth, described in BMS78, to friction between

the faces and the structural members in a framed construction, or to permanent deformation (bending) of the fastenings. The signifi- cance of the set readings for wood-frame construction is discussed in BMS25.

If they serve no other purpose, the load-set

graphs show that many constructions that have

given satisfactory service are not elastic,

however violently this jolts our engineering

concepts.

For most engineering structures, the loaddeformation curve is a straight line below the

elastic limit, then the deformations increase

much more rapidly than the load. The allowable

load is taken somewhere on the straight portion

of the curve. On the contrary, the curves for

many house constructions have no straight

portion, even approximately. No straight portion should be expected for the impact load

because, theoretically, the curves should be

parabolas.

However, the criterion can be applied that

the allowable load should not exceed the value

I for which the deformation and the set increase

greatly for a small increase in load,

j Johnson [34] says the French Commission

defined the "apparent elastic limit" as "the load

I per square millimeter of the original section,

where the deformation begins to increase sen-

' sibly with no increase in the external force

j applied (corresponding to the dropping of the

! beam in testing machinery)." He points out

that for most materials there is no such point

other than the ultimate strength and since for

these materials an elastic limit corresponding

to sensible deformations is required for practical purposes he proposed for all elastic materials and to be universally used in all kinds of

practical tests the following: 'The apparent

elastic limit is the point on the stress-diagram

of any material, in any kind of test, at which

the rate of deformation is fifty percent greater

than it is at the origin."

Johnson states that for certain stones and

concretes the stress graphs are reverse curves and no kind of "elastic limit" can be attributed

to them.

Some of the load-deformation graphs for

house constructions are also reverse curves (BMS30, 31, 47, 48, and 67), particularly the

graphs for load-shortening under compressive

load. It is probable that the rate of deformation

(shortening) near the origin was great because

the members (studs and plates) were not in

intimate contact; then, as the load increased,

the rate was less until as the maximum load was approached the rate of deformation again

increased. Undue consideration should not be

given to the portion of the curve for small loads.

Instead of considering the rate of deformation

at the origin, it is suggested that the least rate be taken.

Johnson's "apparent elastic limit" applies to engineering materials and gives a value for

which the deformation is very small. For

house constructions, on the contrary, the deforaiation under the allowable load may be considerable without impairing the usefulness of

the house; therefore, the allowable load may

be taken as the load at which the rate of deformation is three times the least rate. This

criterion, also, may be applied to the set curve and the lower of the values obtained from the

deformation curve and the set curve taken as the allowable load. The deformation curve and the set curve are so related that a load

which causes a marked increase in the rate of

deformation also causes a marked increase in

the rate of set. If the rate for either curve has

increased to three times the least rate, engineering judgment leads to the conclusion that material is being rapidly deformed plastically, and

that failure is approaching.

Difficulty was found, however, in applying

this criterion to the set curves, perhaps because

they were close to the axis of the loads. Most

of the allowable loads determined from the set curves were very much greater (average 40

percent) than those determined from the deformation curves. Therefore, this criterion was applied only to the deformation curves. The most convenient method of measuring

the rate of deformation from a graph is to consider the angle which the tangent to the curve at a given point makes with the load (vertical)
84 Building Materials and Structures Reports

axis. The rate of deformation is the tangent of

this angle.

(h) Criterion d, Structurally Significant

Deformation

The strength of walls was determined separately under compressive and transverse loading. In a house, these loads are applied simultaneously and the deflection of a thin wall

caused by the transverse load might result in

failure. Specimens of thin walls should be

tested under combined loading.

Until such tests are made, it appears advisable to take an allowable transverse load which

does not deflect the wall more than one-sixth

the actual thickness of the structural members

nor cause a set of half this distance.

The deflection caused by an impact load is instantaneous, therefore, it is unnecessary to limit the deflection but the set should not exceed

one-twelfth this thickness because if applied re- peatedly the sets may become great. Unlike

compressive and transverse loads, an impact

load affects only a small portion of the wall

which is supported laterally by adjacent portions.

For ivalls the d criteria are Transverse load

dl lateral deflection, one-sixth the actual

thickness of the structural members

d2 set, one-twelfth the thickness

Impact load

d2 set, one-twelfth the thickness

{i) Criterion e, Deformation Affecting

the Utility of a House

In addition to the deformation affecting the

structural integrity of a house there are deflec- tions and sets affecting the utility of the house

as a dwelling. Recommended values are given

in table 19. Table 19.

Values of criteria e

Element Compressive load

Transverse loadConcentrated load

Impact

load

Racking load Walls and load-bearing partitions: el, deflection ... _ _ _ ._ in. 1.00

0. 50 .50 .25

in. 1.00

0. 60

in. in. 1.00in. 18 ft 1.00

e2, set... 0. 10 0. 50

e3, shortening

e4, set . Nonload-bearing partitions: el, deflection .. 1.00

e2, set . 10 Floors:

el, deflection 2. 00 1.00

4. 00

2. 00

2. 00

e2, set „. .10 1.00 Roofs:

el, deflection _ e2, set .50 Deformations.—There are doors and windows

in the walls and doors in the partitions. Although the house is subjected to the allowable

loads very infrequently, the resulting deformations should not break windows, especially the

glass, nor damage either doors or windows so that they do not function reasonably well when

load returns to normal.

Ordinarily these closures do not fit the

frames closely, therefore a wall or partition

may deform considerably before appreciable

load is applied to the closure. As the deformation increases, the closures deform elastically

before appreciable permanent damage occurs. Until more definite information is available, it is recommended that the permissible lateral

deflection of walls and partitions be taken as

1.0 in. for compressive, transverse, and impact

loading. Under racking load, the openings in

walls and load-bearing partitions deform in

their plane, the top being displaced horizontally

with respect to the bottom, and may exert compressive forces in the plane of the windows and

doors ; the permissible deformation should be

taken as 1.0 in. The shortening of walls and partitions under

compressive loading should be taken as 0.5 in. Usually the height of doors and windows is less than the story height, therefore the deflection

and shortening at the opening is proportionally

less than for the wall or partition. Also, the

walls and partitions are subjected to considerable compressive load before the doors and

windows are fitted to the frames, therefore,

under the allowable compressive load the

shortening of the openings is considerably less than the total shortening of the walls and partitions. Because there is no impact load and very

little wind load when the closures are fitted, this

is not the case for deflections under transverse

and impact loads nor for deformation under

racking load.

If for a particular construction the deformation under the allowable load damages conventional doors and windows, the architect is at

liberty to design closures which are not

damaged either by the deformations suggested

here or by greater deformations.

For floors under transverse and impact loading, the deflection under the allowable load does

not affect the strength, provided the shortening

of the floor due to the deflection does not de- crease the bearing area on the walls enough to cause crushing failure or enough to cause the

floor to drop off the supports. For a wood floor

12-ft span, a deflection of 2 in. shortens the

floor about 1/16 in., which is a movement of

1/32 in. at each end. This is less than toler- ances customary in the building trades for

many constructions. It has been customary in

engineering design to limit the deflection to 1/360 the span, not only for houses but also for

other buildings. If this value is not exceeded. [ it is assumed that plaster will not crack.
Strength of Houses 85

Although this value for the permissible deflection of plastered constructions has given

reasonably satisfactory results, it appears to be a rule-of-thumb requirement unsupported

by convincing technical data. If a construction

tested for structural properties has plaster in

the faces, it is unnecessary to limit the deflec- tion to 1/360 the span because the test load

causing the plaster to crack is reported.

The limit for deflection which does not crack

plaster should not be applied generally to shop

and mill buildings in which there is no plaster

because of the mistaken impression that the

building is unsafe if this deflection is exceeded.

Insofar as utility is concerned, if there is no

plaster in a house, the deflection is limited only

by the value having a definite detrimental

effect, physical or mental, on the occupants.

The deflection of floors in boats and summer

camps is often much greater than is customary

in houses. Because foundations settle, floors in

older houses are sometimes out of level an inch

or more. There is however no record of any

relation between the deflection or sagging of

floors and the well-being of the occupants. It

is evident that permissible deflection is a matter of personal opinion. Therefore, for

economy in construction, permissible deflec- tions should be large. Almost never is a floor

actually loaded to 40 lb/ft- over its entire area and if, under this load, the deflection is 2.0 in., when the load returns to normal (perhaps 8

Ib/ft^) the deflection is much less. For most conventional floors, the deflection

under the allowable load determined by these

criteria is much less than 2.0 in. Many people do not distinguish between the

deflection of a floor and the vibration under

moving or impact loads. From an engineering

viewpoint, however, there is no direct relation

between the deflection under a static load and

either the period or amplitude of vibration

under dynamic load. At present, there is no

information to guide the architect on the permissible vibration of floors. In general, both

the deflection and the vibration can be decreased, but only at an increase in price.

The problem can be solved practically by

making houses available with floors having

widely different depth of joists to sell or rent at amounts proportional to construction costs.

I The occupants could then appraise the floor in

terms of dollars and cents and might conclude

that it was not worth the price to prevent the

I tinkling of crockery on the pantry shelf. Under repeated applications of the increasing test loads, the permanent set should not

exceed 1.0 in,, which amount is hardly noticeable. This is evidenced by the fact that the

floors of many summer cottages and old houses

are out of level this much, probably because the

foundations have settled slightly. This does

not, however, indicate that the building is unsafe for occupancy.

If the partitions are transverse to the floor

joists, it is unlikely that the doors will be

damaged by deflection of the floor; but if the

partitions are parallel to the joists, doors may

be damaged if the deflection of the floor is excessive, particularly if the partitions are loadbearing. A door frame at midspan of the floor

is not deformed by the deflection, but, as the

distance between the door and midspan in- creases, the racking deformation of the door

frame increases. The location of doors should

be considered when designing the house and

the doors fitted with clearances above and below

which prevent damage.

For roofs, the transverse loads are wind and

snow (short-time loads) and, unless leaks occur, the deflection may be great without affecting

the utility of the house provided the roof is draining. The deflection causing leaks depends

upon the construction and materials but there

is almost no information on this subject.

The set for deflections, deformations, and

shortening has an indirect relation to the

utility. If the sets are great, they are additive

under repeated applications of the allowable

load and the house may fail. For many satisfactory house constructions, the sets are great

therefore, the permissible set is taken as onehalf the corresponding deformation except for

concentrated loads.

The effect of the concentrated load on a disk

1.0 in. diameter is local and only decreases the

utility of the house if the disk punches a hole or the depression after the load is removed

(set) retains dust and disease germs detrimental to health. For all constructions except

roofs, the permissible set for concentrated load

is taken as 0.1 in. For roofs, the set should not cause leaks and is taken as 0.5 in. This value

is too great for clay tile and perhaps for tin

roofing and there is a need for tests to determine for each kind of roof the set which causes

leaks.

4. Loads

The values for the allowable loads on walls are given in table 20, on load-bearing partitions in table 21, on nonload-bearing partitions

in table 22, on floors in table 23, and on roofs

in table 24.
86 Building Materials and Structures Reports

Table 20.Alloivable loads on walls

[Values for criterion a, percentage of least load, are given in table 18. Values for criterion b are the loads at which damage occurs (See p. 82). Values for criterion c, slope of curve for both deformation and set, are three times the least slope (See p. 82 ) . Values for criterion d, structurally significant deformations,

are given on page 84. .Values for criterion e, deformation affecting utility of a house, are given in table 19]

Construction symbol

Compressive load; height, 8 ft Transverse load; span, 7 ft 6 in. Concentrated load; diameter of disk, 1 in.

Impact load; span, 7 ft 6 in.; weight of sandbag, 60 lb Racking load

Inside face Outside face Inside face Outside face Inside face Outside face

Load

Crite- rion LoadCrite- rion Load

Crite- rion Load

Crite- rion Load

Crite- rion Drop

Crite- rion Drop

Crite- rion Load

Crite- rion WOOD

Kips/ft lb/ft' Ib/fft lb lb ft /' Kips/ft BO 6.84 a 75 b 75 b 191 a 210 b 1. 0 b 1.0 b 0. 87 c BH.. 3. 00 b 120 dl 115 dl 215 e2 558 a 2.6 el 3.2 el 1.00 c BJ 2. 50 b 100 dl 115 dl 127 a 558 a 2. 2 el 2. 5 b&el 0. 88 c BJ-... 3. 50 b 97 b 70 b 248 a 900+ a 2. 0 b 1.0 b 1. 50 c BK 3. 30 a 50 b 64 b 202 a 900+ a 2. 5 b 7,0 b 4. 50 c BL 3. 71 a 75 b 60 b 225 a 650 b I. 0 b 2.5 b 1.04 c BQ---- 4. 00 b 90 b 50 b 248 a 400 b 1. 5 b 0. 5 b 0. 60 c BU 2. 90 a 80 dl 90 dl 575 e2 680 e2 2. 0 el 2. 1 el .88 b BX 4. 77 a 90 b 50 b 277 a 300 b 1.0 b 1. 0 b .97 a BY 1. 90 b 106 dl 100 dl 91 a 450 a 2.0 b &el 1. 5 b .78 a CB 3. 50 c 50 dl 50 dl 459 a 900+ a 1.8 el 1.6 el .13 c CI. 2. 53 a 115 dl 108 dl 167 a 450 e2 1. 0 b 1. 5 b .80 b CM 2. 00 c 100 b 120 dl 202 a 225 a 1.3 el f '1.3 el a

I ''2.0 b } CN 2. 95 a 135 dl 125 dl 180 e2 200 b 2.0 el 2. 0 b .47 a DK 1. 62 a 20 dl 20 dl 207 e2 207 0.8 el 0.8 el .69 a DL 2. 16 a 40 b 70 b & dl 495 a 700 e2 3. 5 b&el 2.8 el f «.03 c DQ 3. 27 a 50 dl 45 dl 202 a 357 a 1. 5 b 1. 8 el

\ d. 16 .49 c

a DR 6. 61 a 55 dl 55 dl 900+ a 900+ a 4. 5 el 4. 5 el 4. 20 c QA 2. 75 b 96 dl 26 b . 100 b 900+ a 2. 5 b 1. 5 b 0. 50 b STEEL

AH 5. 75 a 166 a 166 a 520 e2 520 e2 2. 0 2. 0 b 0. 94 a AL.. 4. 74 a 108 a 100 a 225 a 178 e2 3. 6 d2 & el 2. 7 d2 . 41 a AP 71 a 82 a 130 a 720 a 0. 4 d2 2.0 b AV 11.30 a 200 dl 220 dl 138 a 850 e2 1.0 b 2.

1

el /

=. 40 c

I

<>. 81 e2 XZ.. 6. 47 a 126 a 110 b 295 a 760 e2 2.0 b 2.0 b .60 c CQ 2. 30 c 120 b 110 dl 320 e2 220 e2 1.8 d2 & el 1. 7 el .30 b CU 4. 50 b 254 a 202 a 485 e2 512 b 6. 5 el 3. 2 c 1. 54 a DG 3. 58 a 60 dl 52 dl 87 a &e2 430 e2 2. 0 b 2. 5 el 0. 33 c DH 3. 42 a 69 dl 59 dl 86 a &e2 510 e2 2. 0 b 2.8 el .25 b REINFORCED BRICK AND CONCRETE

AR

AT

54.0

106.0

18.0

aab82

100

289

a

ca

240

100

170

b

cb

900+

900+

900+

a

a

a

900+ 900+

900+

a

a

a

3.0

9.0

4. 0

b & c c b & c5. 0 9.0

3. 0

b

cb

4.41 + a BV 3. 00 b MASONRY

AA 99.6 a 46 a 46 a 900+ a 900+ a 4.7 c 4.7 c 2. 50+ a AB 21.0 a 16 a 16 a 900+ a 900+ a 1.9 c 1. 9 c 2. 50+ a AC 36. 2 a 32 a 32 a 900+ a 900+ a 3.0 c 3.0 c 2. 50+ a AD.. - 18.0 a 14 a 14 a 900+ a 900+ a 0. 6 c 0. 6 c 1. 42 a AE 9. 5 a 23 a 23 a 900+ a 900+ a 1. 1 e 1. 1 c 1.37 a AF 15.3 a 12 a 12 a 900+ a 900+ a 0. 5 c 0. 6 c 1. 20 a AU 10.6 a 7 a 10 a 900+ a 900+ a 2.0 b 1.3 c 2, 01 a AX 14.4 a 19 a 19 a 900+ a 900+ a 1. 5 b & c 1. 5 b & c 2.36 a BD / «24.

7

a a 9 a 581 a 581 a 1.5 b 1.5 b 1. 98 a

\ '19.

3

a } ' BE 16. 9 a 8 a 7 a 900+ a 900+ a 0. 6 c 0.5 b 0. 79 a BF 13. 6 a 18 a 16 a 900+ a 900+ a 1. 5 c 1.5 c 2. 08 a BO... 13.0 a 22 a 14 a 900+ a 900+ a 1.6 c 1.

1

c 2. 20 a BP.. _-- 7.8 a 3 a 3 a 900+ a 900+ a 0. 5 b 0.6 b 0. 64 a BW. 7.9 a 77 a 77 a 900+ a 900+ a 1.0 b 1. 0 b 1. 50 b CF 15.6 a 10 a 10 a 900+ a 900+ a 0.8 c 0.8 c 0. 72 a CG 14.4 a 10 a 10 a 900+ a 900+ a 0.5 c 0. 6 c .80 a CH.. 2. 6 a 18 a 37 a 900+ a 540 e2 1.0 d2 1. 5 d2 . 23 b CP 23. 5 a « 28 a 28 a 900+ a 900+ a 3.0 c 3.0 c 2. 40+ a CZ 43. 6 a 101 a 101 a 900+ a 900+ a 9. 0+ a 9. 0+ a 2. 50+ a DA.. 59.6 a 86 a 86 a 900+ a 900+ a 9. 0+ a 9. 0+ a 2. 50+ a DB 5. 4 a 23 a 23 a 900+ a 900+ a 1. 5 b 1. 5 b 1.00 a DC 4. 4 a 27 c 27 c 554 a 554 a 2.0 b 2. 0 b 1.00 c DD 38. 8 a 26 a 26 a 900+ a 900+ a 1.0 b 1. 0 b 2. 50+ a DE.. 43. 2 a 40 a 40 a 900+ a 900+ a 2. 0 b & c 2. 0 b & c 1. 92+ a DF 4. 9 a 20 c 20 c 900+ a 900+ a 1. 5 b 1. 5 b 0. 65 a DP 15. 9 a 9 a 9 a 900+ a 900+ a 0. 5 b 0. 5 b 1. 29 a

" Sandbag struck over a stud. Sandbag struck between studs. Without braces. With braces.

' Cavity wall, loaded on facing and backing.

' Cavity wall, load centered on backing only.
Strength of Houses 87

Table 21.

Allowable loads on load-bearing partitions

[Loads which may be applied to partitions over and above the weight of partition]

Construction symbol

Compressive load; height, 8 ft Transverse load; span, 7 ft 6 in. Concentrated load: diameter of disk, 1 in.

Impact load; span, 7 ft fi in.; weight of sandbag, 60 lb Rackiiiu load

Load Crite- rion

Inside face Outside face Inside face Outside face Inside face Outside face Load

CriteCrite- rion Load rion

Crite- Load rionCrite- Load rionCrite- Load rion

Crite- Drop rionCrite- Drop rion WOOD

Kips/ft Iblft- Ib/fP lb lb ft ft Kips/ft CJ 1.50 c 84 <11 84 (11 158 a 158 a 1.5 b 1. 5 b 0. 48 a CO 3. 30 a 120 dl 120 dl 219 a 219 a ' «1.0 b "1.0 b 1 .47 a

1 bl.5 b 1>1. 5 1. / QD 0. 96 b 48 b 48 b 162 a 162 a 2. 5 b 2. 5 b .38 b

» Sandbag struck over a stud.

i> Sandbag struck between studs.

Table 22.

Allowable loads on nonload-bearing partitions

[Loads which may be applied to partitions over and above

the weight of partition]

Construction symbol

Concentrated load; diameter of disk, 1 in. Impact load; span, 7 ft 6 in.; weight of sandbag, 60 lb Load Criterion Drop 1 Criterion woon

lb ft AM 130 a I.O b BM 150 a 1.0 b BN 134 a 1. 2 el BR --- 171 a 0. 5 b BZ 166 a 1.0 b CA 90 a 1.

el cc 900+ a 0.5 el CD 330 e2 . 2 el CK 165 a 1.

el STEEL

AI 98 a 0.8 el AQ 127 a 1.0 b BA 280 a 1.0 b CV 300 e2 2.5 b Dl 87 a 1. 5 el

Table 24.Allowable loads on roofs

[Loads which may be applied to roofs over and above the weight of roof]

Construction symbol

Transverse load; span, 14 ft Load CriterionConcentrated load; diameter of disk, 1 in. Load Criterion WOOD

Iblff lb BT 23 b 900+ a DN 24 b 753 a DO 67 b 750 b DT. _ 123 b 900+ a DU 200 b 900+ a QC 48 a 900+ a STEEL

AK 134 a 414 a AO 42 a 382 a CS 112 a 660 e2 cx 1.35 a & b 900 b DJ 25 a 900+ a

5. Distribution of Criteria

The distribution of the criteria are given in

table 25.

Table 25.Distribution of criteria for allowable loads

Table 23.Allowable loads on floors

[Loads which may be applied to floors over and above the weight of floor]

Transverse load; Concentrated load; Impact load; Construction span, 12 ft diameter of disk, span, 12ft; weight

symbol 1 in. of sandbag, 60 lb Load Criterion Load

1 Criterion Drop Criterion WOOD

Ib/fP lb ft BS 35 b 900+ a 1. 5 b CE 124 e 900+ a 9. 0+ a CL 192 a 900+ a 9. 0+ a DM 97 a 900+ a 2.5 b DS 100 b 900+ a 9. 0+ a QB 29 b 900+ a 4. 0 b STEEL

AG 379 b 900+ a 9. 0+ a

A.J 195 a 296 a 7.0 b AN 141 a 900+ a 9. 0+ a AY 90 b 900+ 4. 0 b BB 108 a 900+ a 9. 0+ BC. _ 80 b 900+ a 1.0 b CR 282 a 900+ a 9. 0+ a CW 210 a 900+ a 9. 0+ a REINFORCED CONCRETE

AS 60 b 900+ a 5. 5 b AW_. 326 a 900+ a 9. 0+ a CT 244 a 900+ a 9. 0+ a cy._. 246 c 900+ a 9. 0+ a

Criterion Allowable load a b c d e WALLS

Compressive: Wood -

Percent

58

7567

100

Percent32

1233

Percent

1012

Percent Percent

Steel Reinforced brick and concrete... Masonry _ . ... Transverse: Wood; inside face _ 42

39

1111

dl,58 Wood; outside face 61

Steel; inside face 56

44

67

dl,33

Steel; outside face dl, 44 Reinforced brick and concrete;

inside face... 33

33

8

8

Reinforced brick and concrete; outside face --. 67 Masonry; inside face 9292

74

5356

11

100

100

10096

Masonry; outside face. _ _ Concentrated: Wood; inside face. 526 e2, 21 c2, 21 e2, 44 e2, 78

Wood; outside face _ __ Steel; inside face

Steel; outside face.. - _ 11 Reinforced brick and concrete;

inside face Reinforced brick and concrete; outside face Masonry; inside face.. Masonry; outside face e2.4
88 Building Materials and Structures Reports

Table 25Distribution of criteria for allowable loads—Cont.

Criterion Allowable load a b c d e

WALLS—Continued

Impact: Wood; inside face . 5358

56

33

33

6738

38

1522

50

8

el, 47 el, 42 el, 22 el, 44

Wood; outside face..

Steel; inside face d2, 22

Steel; outside face 11 d2, 11

67

33

50

50

5533

Reinforced brick and concrete; inside face. . ._. ... .. Reinforced brick and concrete; outside face . Masonry; inside face 88

30

33

5088

d2, 4 Masonry; outside face . . d2, 4 Macking: Wood

Steel e2, 11 Reinforced brick and concrete... Masonry . 4 LOAD-BEARING PARTITIONS

Compressive: Wood . 33 33 33

Traitsverse: Wood... _ _. 33 <I1, 67 Concentrated: Wood.. 100 Impact: AVood.... 100 Racking: Wood. _ - -- - 67 33 NONLOAD-BEARINO PARTITIONS

Concentrated: Wood 89 e2, 11 e2, 20

el, 56 el, 40

Steel --- 80 Impact: Wood 44 Steel 60 FLOORS

Tra nsiierse: Wood. ... - - 33 50 17 Steel 62 38 Reinforced concrete 50 25 25 Concentrated: Wood 100

Steel 100 Reinforced concrete 100 Impact: Wood 50 33 17 Steel 62 38 Reinforced concrete. .. .. 75 25

ROOFS

Transverse: Wood..-. 17 . 83 Steel 90 10 Concentrated: Wood 83 17

Steel 60 20 e2, 20

ALL CONSTRUCTIONS

All loads: Wood .. 33 35 7 dl, 12 el, 10

Steel - 47 21 4 dl, 6 e2, 4 el, 7

Reinforced brick and concrete. Masonry..

57 26 17 d2, 3 e2, 12

73 10 15 d2, 1 e2, 1 Compressive:

All materials _ .. .- 78 15 7 Transverse: All materials.. 49 23 5 dl, 23 Concentrated:

80 6 e2, 14 Impact:

All materials.. - 10 48 19 d2, 3 cl, 20 Racking:

All materials 58 15 25 e2, 2 All loads: All materials 51 23 10 dl, 6 cl, 5 d2, 1 e2, 4

Evidently many more allowable loads are

fixed by some criteria than by others. For many

constructions, particularly masonry, if there were no criterion a (whatever the percentage

selected), the least maximum load would have

to be taken as the allowable load because no

other criterion fixes a smaller value. For all kinds of loading, this criterion sets the allowable load for three-fourths of the masonry constructions and for fewer of the others, down to a third of the wood constructions.

If it is conceded that the allowable load

should not exceed the load causing damage,

criterion b is necessary because it determines

the allowable loads for a third of the wood constructions and for a smaller proportion of the

others, down to a tenth of the masonry constructions.

Some kind of allowable load (or working

stress), depending on the slope of the loaddeformation curve, is generally accepted in

engineering practice. For the house constructions tested, criterion c, (slope of curve) fixes

less than a fifth of the allowable loads for the

reinforced and masonry constructions, less than one-tenth for the wood and for a few of

the steel constructions.

The strength deformation criteria dl (de- [ flection) and d2 (set) apply only to the lateral

deflection of walls and load-bearing partitions ' as a safeguard against collapse under combined

compressive and transverse loading. This

criterion is unnecessary if the results ol)tained

under combined loading are available. However for the present, criterion dl does serve to

limit the allowable transverse load on many

wood and steel walls also on load-bearing partitions. Criterion d2 only limits the transverse

loads and impact loads on a few steel walls and

also a very few masonry walls.

The utility deformation criteria el (deflection) and e2 (set) also e3 (shortening) and e4

(set) are unnecessary to insure the structural

safety of the house; they affect only the utility

of the house to the occupants. Many engineers are convinced that the values for these criteria are too great. They can be decreased to any

desired value, provided they are the controlling

criteria, by increasing the cost of the house.

Of the loadings to which these criteria apply,

the concentrated load is probably the least important, but criterion e2 (identation 0.1 in.)

fixes the allowable load for about half the steel walls, a quarter the wood walls, a few nonloadbearing partitions and steel roofs, and none of

the load-bearing partitions and floors. The reader is reminded that the allowable

concentrated load is a matter of opinion and in

any case depends upon the materials in the face

of the construction and not at all upon the

materials in the principal structural members.
Strength of Houses 89

Criteria e3 and e4 apply only to the shortening of walls and load-bearing partitions but no

allowable compressive loads are fixed by these

criteria because other ci'iteria gave smaller

loads.

If the setting of smaller values for criteria el

and e2 is contemplated, consideration should

be given to the fact that, although these criteria

do not fix the allowable compressive or trans- verse loads for walls or load-bearing partitions and do determine the racking load on

only a few steel walls, el controls the allowable

impact load for half the wood and steel walls

and also for nonload-bearing partitions. For

i the constructions in this group, the lowest al1 lowable height-of-drop (60-lb sandbag) for the

j wood walls, both inside and outside, is 0.8 ft and most of them are 2.5 ft or less. For the

steel walls, the lowest value is 1.8 ft for loading

' on the inside, all the other values being above

3.5 ft. For loading on the outside, the lowest

value is 1.7 ft. All the nonload-bearing partitions are much less stiff than the walls, the lowest value being 0.2 ft and the highest 1.2 ft for

wood constructions. For steel constructions,

the lowest value is 0.8 ft and the highest 1.5 ft. Insofar as criterion el is concerned, the al- lowable height-of-drop for the impact load

depends upon two factors, the impact which is likely to be applied to the walls and the deflection which does not damage doors or windows.

Records show that trucks and street cars have

1 crashed into houses or buildings, but it is unI economical to design houses to withstand such

I impacts. However, the impacts of smaller

objects such as bricks and baseballs are likely to occur and should be considered in the design.

I Impacts likely to occur on the walls inside the rooms depend greatly upon the habits of the

occupants.

6. Cracks in Plaster

If cracks in a plaster face are not considered

damage, then the next greater critical load may

I be taken as the allowable load. Apparently the

allowable load is determined more often by

cracks in the plaster under transverse loading

than under the other loadings. For walls, if the transverse load is applied to the outside

I face (plaster in tension) the cracks occur at

I somewhat smaller loads than if the load is apI plied to the inside face.

i The behavior under transverse load of all

11 constructions with plaster faces was studied.

I Each construction is listed in table 26 with the

critical loads in order.

Critical loads are taken as the load determined

by each of the criteria (if obtainable) and the

least maximum load. There may be several

kinds of damage, first in one portion of the construction and then in another portion at a greater load. The load for each kind of damage mentioned in the BMS reports is considered

a critical load.

If the allowable load given previously for any

constructions that have plaster faces is equal

to or greater than the design load for the house,

then to disregard the cracks in the plaster, and

take the next greater critical load as the allowable load serves no useful purpose. Many walls

that have plaster fulfill this requirement.

When wall AZ, which has a sheet-steel frame,

is loaded on the inside face, the allowable load is not limited by cracks in the plaster, but, when

loaded on the outside face, cracks do fix the

load. If the cracks are disregarded, a slightly

greater allowable load may be taken.

All the other walls have wood frames. If the

cracks in wall BJ, which has stucco on metal

lath in the outside face, are disregarded, the

allowable load would be about twice as great as

it is. For wall BK, which has brick veneer outside,

the allowable load is limited by cracks in the

brick work for both inside and outside loading.

Disregarding cracks in the veneer, the allowable loads could be about twice as great as they

are because the loads causing cracks in the

plaster are much greater than those causing

cracks in the brick veneer. Except, for wall QA, which has wood lath,

all the wood walls have fiberboard lath. When

loaded on the outside face, all the plaster on

fiberboard lath cracked at much greater loads

than did the plaster on the one wall having

wood lath. For the one load-bearing partition QD, provided cracks are disregarded, the allowable load

could be twice as great, but there are no usually

accepted design values for transverse load on

partitions.

For all the floors, the allowable loads are

limited by cracks in the plaster ceiling. The

allowable load for floors BS and QB which have

wood frames is less than the usually accepted

design load for floors in houses (40 lb/ft-) and

at least twice as great for floors AY and BC

with steel frames. Depending upon the kind of

lath, the allowable loads increase in the order,

wood lath (QB), fiberboard lath (BS), gypsumboard lath (BC), and expanded metal lath

(AY).

For the floors with plaster ceiling, the least

allowable load is for conventional w^ood floor

QB. If cracks in the plaster are disregarded,

the allowable load jumps from 29 to 145 lb/ft-, a value greater than the design load for floors

in houses.

The one roof BT has a wood frame and fiberboard lath. If cracks are disregai'ded, the al- lowable load jumps from 23 to 142 lb/ft-.
90 Building Materials and Structures Reports

Table 26.

Critical transverse loads on constructions with plaster faces Table 2Q'.—Critical transverse loads on constructions with plaster faces—Continued

[Im =least maximum load]

Transverse load

Construction symbol Inside face Outside face Load 1 Criterion Load 1 Criterion WALLS

AZ

BO.

BJ..

BK.

BL.

BQ.

BX.

QA.

Ib/fP ib/fr- 126 a 110 bl

136 dl 131 dl

162 c 132

168 Im 162

176 Im

75 b' 75 bl

135 dl 100 dl

180 el 160 el

274 a 194 305 Im 215 fm

320 d2

330 d2 370 e2

385

97 b' 70 bl 145 dl 150 dl

195- el 210 el

205 d2 255 c, d2

310 e2 258 315 a 275 e2

350 287 Im

50 b^ 64 b2

108 dl 100 bl 160 b> 125 dl

157 el 170 el

215 d2 200 c, d2

248 a 225 e2

255 e2 265

275 294 fm

276 Im

75 b' 60 bl

130 <ll 120 dl

195 el 160 el

314 230 d2

325 d2 232 350 258 Im

260 e2

275 c

90 b' 50 bl 100 dl 92 dl

135 b\ el 132 el

184 a 150 a

205 Im 155 c

220 d2

232 c 157 b3

240 e2 167 Im

90 bl 50 bl

120 dl 110 dl

175 el 160 el

232 a 237 a

250 c 263 Im

258 Im 283 b*

272 b» 350 d2

325 d2

96 dl 26 bl

150 el 80 dl

236 a 116 el

262 Im 194 a

215 Im LOAD-BEARING PARTITIONS

QD

( 48

106

216

L 240

bldl

aIm FLOORS

AY... __-

f 90

250

< 280 320

I 334

( 80

J 105

S 140

I 151

f 35 247

<^ 350

375

I, 412

[ 29 145 242

bla

c

b«Im

blaIm

c

bla

b'elIm

blaIm

BC

BS. _._

QB.... ...

BT .*.

f 23 142

<^ 204

210

L 218

bla

c

bsIm

1 Piaster cracked.

2 Bricli veneer craclced.

5 One outer stud ruptured.

* One outer stud partially ruptui-ed.

* One outer stud craclied.

' Rupture of weld holding the flange of a joist to the end member.

' One outer joist cracked.

' One outer rafter ruptured.

7. Graphs of Allowable Loads

The allowable loads for walls arranged in

order, beginning with the greatest, are shown

in figures 43 (compressive, transverse, and

racking loads) and 44 (concentrated and impact loads) . Those for partitions, floors, and

roofs are shown in figure 45. In designing a house, low weight is a desirable characteristic of the construction ; therefore, the values in figure 42 (weight) are arranged in order, beginning with the lowest.

On the other hand, an allowable load equal

to the design load is necessary ; therefore, in the

graphs showing allowable load, the constructions are arranged in decreasing order beginning with the greatest. In selecting the construction for a particular house for which the

design loads are known, start at the left of the

graph and move to the right until a construction is found having the requisite allowable

load. If it is unsuitable because of weight,

price, or other characteristics, a construction

with somewhat greater allowable load may be

preferable.

8. Relation of Materials and Design

TO Allowable Load

(a) Walls

The allowable loads are shown on figures 43

and 44.

(1) Wood

Compressive load.—It is evident from figure

43 that, of the wood walls under compressive

loading, wall DR is at the top and has the greatest allowable load. The other walls with unconventional frames are CB (planks) which is above the middle and DL (demountable) which

is near the bottom of the group.

Two of the walls have light conventional

frames, DQ which is above the middle and DK

which is at the bottom of the group.

All the other walls have conventional frames

and are scattered through the group from next
Strength of Houses 91

o

&

O

/OO

80

60

40

20

0

BO BK BU PL AVAL CO^BV

\yczDA

BX CB CN BI DK AH DH AR

\-BG —BJ—BH—CI BY—AZ—DG—A TDR BL DQ QA CM ^ CU

AC

-DD

DE AB

CP

BD DP—CG—AE

BE AX AU DE

AD AF BO DB

CF—BF BP—CH. BW DC

Wood

300

Steel

AH

Reinforced

Masonry

Masonry

200

100

0

o

§ ^ 100

CI AV AP

BH BJ 19 AL

CN CM BU CU CO BW

DR BI BX BK DK

BY BQ BL DL

QA BG DQ

200

DA AC

CZ DE AE AX AD BD BP

AR AA DD DF AB CG AU

BH

CM BU

CH BY BK

CU

AV AZ DH

AH AP

DR CI DL CB

BI BJ BX DK

BG BQ QA

0

BV

^AT

DC BO CH CF BE

n CP DB BF AF DP

lilil!lnnnnnnHnnnnnnnr.n.r.»,.

AA

AL

CQ

BW CP

DA AC DB AB AU DP

CZ CH AE BF AF BD

DG DE DD AX BO CG BP

DC DF AD CF BE

I «l « » —

Wood Steel Reinforced

Masonry

Masonry

o

-J

o

CD

^ BL

BJ

DR BU DK CN AH DG

0

BI BY DQ CU AL

BX CI QA CI n AZ

H BG BQ DL AV

DH

CZ AX BD

AC CP AU

AB DD BF AF

DA BO AD DC

BW DB

DE AF DF

DP CF

BE

CG CH

Wood

With braces

I Without braces

Steel Reinforced

Masonry

Masonry

Figure 43.Alloiuable compressive, transverse, and racking loads for walls.

743712°—48—
92 Building Materials and Structures Reports

<alOOO o ^ DL CQ

BU BJ CU

DR BX DK BG AH AV

CB BH DO BI AL

BL CM CI

BQ BK CN BY

OA

BV

AR S

y AD

AC

AX |i BP

AU BO

y CH

CG

DB

DA

DP

DF

AB AF BF CF CZ DF

AA t] AF f] BE tl BiV t] CP f] DD li BO

CI

Y BX

DQ DK

BO BG

AH A, ill DH

AZ CU

Wood

AD

AC AU

HAX^ BP^ cpn

BO CG

AR AB AE

AA AE BE fl BW 1^ [Vl

DD DP CH

DB

CF DA DF DC^

CZt\DE BD t 1

Steel Reinforced

Masonry

Masonry

10

tf_

BH n C

\aa

DA

Z AU

DL ^ AH \] AR f h CP

4

2

0

DR BJ

BI CB BG

AL

CU CO

BV

A T OA CN CM DK

BK BY DO CI

U 80 BX

AC AB

DE BO BW

DC BF AF AD

BD DF CF CG

AX DB DD BP

BH AC

4

2

0

DR BU

BK BL BY

BI CB BG

AL

DH AP

CU AH

DE

DC BF AU

DL DO CM BQ

CN QA DK

CI BX

CP BD DF DD BF

A^ DB BW AF

AB CH BO AD DP

nn^AE CF CG

Wood $fee/ Reinforced

Masonry

Masonry

Figure 44.

Alloivable concentrated and impact loads for walls.
Strength of Houses 93

I

QD 20 rCJ-i ^ CO

'X3o

o

I

oo

o

oI

0

400

300

200

100

Wood Load-bearing Partitions

QD

DS

CE

CL

AJ

CW

cr AW

BC n AS

AY

CR BB

AG ^AN

CJ

CO

0

CT DO AK

DT CX DJ

DU BT AO

.a

O

Wood Load-bearing Wood Steel

QP Partitions Floors

I rCJCO

0

Masonry Wood Steel

Roofs

Wood Load-bearing Partitions

1000

^500

o

CJ

QD

^ BR BN BA DI

CD BM CV AI CL OB AY CRAJ

m

CT

DO

DU

AO

AK

CLO

I.

0

10

8

6

4

Z

0

CO CC CK CA AO CE DS^ AN fftCW AW DT DN^ CA f? BZ AM M BS DM^AG BB ^AS CY BT DJCS

Wood Wood Steel Load Nonload-bearing

bearing

Partitions

Wood Steel Masonry

Floors

Wood Steel

Roofs

^ QB

DS

AN^AJ CY

AG CIV BC AW

Wood

Load

bearing

Wood Sfeei

Nonload-bearing

Partitions

Figure 45.Allowable loads for partitions, floors, and roofs.

Wood Steel Masonry

Floors
94 Building Materials and Structures Reports

to the top to next to the bottom. The studs are 2 by 4 in., spaced 1 ft 4 in., of Douglas fir or Norway pine with no indication that the kind

of wood affects the allowable load.

Depending upon materials on the inside face,

plywood is scattered through the group, but

all walls with fiberboard lath and plaster are

well above the middle, and are above those with

fiberboard only. The walls with gypsum board,

CI, and wood lath with plaster, QA (conventional), are below the middle and are lower

than the three walls with fiberboard only.

Depending upon the materials in the outside

face, walls of plywood and wood sheathing laid

diagonally are scattered through the upper

three-quarters of the group; fiberboard with

brick veneer, BK, is above the middle ; and

fiberboard with stucco, BJ, is still higher.

Fiberboard only or fiberboard overlaid with

plywood, siding, or shingles is scattered from

next to the top to the bottom of the group.

Transverse load, inside.—As for compressive

loading, wall DR is at the top and has the

greatest transverse allowable load.

The four walls not having 2- by 4-in. studs are grouped together at the bottom: CB

(plank), DQ (2- by 3-in. studs), DL (demountable), and DK (2- by 2-in. studs). Conventional frame walls with 2- by 4-in. studs are intermediate with no indication that the kind of

wood in the studs affects the allowable load.

Depending upon the materials on the inside

face, walls of plywood ai*e scattered through

the group, gypsum-board walls are near the

top, but walls having fiberboard lath with

plaster are slightly below the middle, and walls

of wood lath with plaster are next to the top of

the plaster group.

Most of the fiberboard only are above the

middle, but the two walls on light conventional

frames are near the bottom of the group.

Depending upon the materials in the outside

face, walls of plywood are scattered through

the group, wood sheathing laid diagonally is at the middle, and fiberboard with stucco is higher. Fiberboard with brick veneer is well

below the middle. Fiberboard only, CM, is above the middle, and DK is at the bottom.

Walls of fiberboard overlaid with plywood,

siding, or shingles are scattered through the

group.

Transverse load, outside.—Again, wall DR,

which has the greatest allowable load, is at the

top. Of the four walls not having 2- by 4-in.

studs, DL (demountable) is just below the

middle, and the others, CB, DQ, and DK are near the bottom. Wall QA (conventional) is next to the bottom. The other walls are intermediate.

Depending upon the materials on the inside

face, walls of plywood are scattered through

the group, gypsum board is above the middle,

and fiberboard lath with plaster is lower. Wood

lath with plaster is next to the bottom. Most of

the fiberboard only are above the middle but

two walls on light conventional frames are near the bottom of the group.

Depending upon the materials on the outside face, walls of plywood are above the

middle and wood sheathing laid diagonally is near the bottom. Fiberboard with brick veneer

is higher, and fiberboard with stucco is still higher at the middle of the group. Fiberboard

only is near the top, except the one wall on a

light frame, which is at the bottom. Overlaid

fiberboard walls are scattered through the

group.

Racking load.—Except wall DL (demountable), the wood frame walls have no braces and

the racking load depends more on the materials

in the faces and the fastenings than on the

frame.

Wall BK, having brick veneer is at the top

;

DR having plywood faces is next. Of the other

four walls not having 2- by 4-in. studs, DK (2-

by 2-in. studs) is just below the middle; DQ I (2- by 3-in. studs) in considerably lower; DL

(demountable, with braces) is next to the

bottom; and CB (plank) is at the bottom of the

group.

Depending upon the materials on the inside

face, walls of fiberboard lath with plaster are scattered through the group, mostly above ! the middle, followed closely by walls of wood

lath with plaster. Gypsum-board walls are

at the middle of the group, and walls of fiberboard only are scattered from near the top to near the bottom. Plywood is scattered from

next to the top to the bottom.

Depending upon the materials on the outside

face, fiberboard with brick veneer is at the top

and fiberboard with stucco is very near the top.

Plywood is above the middle, but wood sheathing laid diagonally is considerably below the

middle. Fiberboard only and fiberboard overlaid with siding or shingles is scattered from

near the top to next to the bottom of the group.

Conce7itrated load.—The concentrated load is applied to the face at what is judged to be the

weakest place—midway between studs. The ! allowable load depends to a great extent upon I the materials in the face. The test was discontinued when the applied load was 1,000 lb. Inside face.—As shown in figure 44, the four

walls having plywood inside faces are at the

top of the group. They are followed immediately by four walls having fiberboard lath with

plaster and two others below the middle.

Gypsum board is near the bottom and wood

lath with plaster is next to the bottom. Fiberboard only ranges from the middle to the

bottom of the group.
Strength of Houses 95

Outside face.—The concentrated load test was discontinued for brick veneer, plank, plywood, stucco, and one wall of wood sheathing

with siding. All have an allowable load of

900+ lb. Plywood overlaid with shingles is above and below the middle of the group and

one wall of wood sheathing with siding is below

the middle. Fiberboard only and fiberboard

overlaid with siding are scattered from above

the middle to the bottom.

Impact load, inside.—Wall DR is at the top,

having the greatest allowable load. Wall DL

(demountable) is next. Of the other walls not

having 2- by 4-in. studs, CB (plank) is just

below the middle and DQ (2- by 3-in. studs) is

still lower. Wall DK (2- by 2-in. studs) is at the bottom of the group. All the walls having

2- by 4-in. studs are scattered through the

?roup.

Depending upon the materials on the inside

face, plywood is scattered above the middle,

fiberboard lath with plaster is scattered from

near the top to near the bottom. Wood lath

with plaster is next to the top of the plaster

group and gypsum board is next to the bottom.

Walls of fiberboard only are scattered through

the entire group from near the top to the

bottom.

Depending upon the materials in the outside

face, plywood ranges from the top to next to the bottom. Fiberboard with brick veneer and

fiberboard with stucco are well above the

middle, while one wall of wood sheathing with

siding is above the. middle and one is below.

Fiberboard only and fiberboard overlaid with

siding or shingles are scattered from near

the top to the bottom of the group.

Impact load, outside.—The brick veneer wall

BK is at the top and DR is next. Of the other

walls not having 2- by 4-in. studs, DL (demountable) is near the top, DQ (2- by 3-in.

studs) and CB (plank) are at the middle, and

DK (2- by 2-in. studs) is next to the bottom.

The walls having 2- by 4-in. studs are scattered

through the group.

Depending upon the materials on the inside

face, one fiberboard lath with plaster is at the

top, another is above the middle, and the rest are at or near the bottom. Gypsum board is below the middle followed by wood lath with

plaster. Plywood walls are scattered above the

middle and walls of fiberboard only range from

near the top to next to the bottom.

Depending upon the materials in the outside

face, brick veneer is at the top and stucco is near the bottom. One wall of wood sheathing

with siding is below the middle and one is at the bottom.

Plywood walls are scattered, mostly above

the middle, and plank is at the middle. Fiberboard only and fiberboard overlaid with siding or shingles are scattered from near the top to next to the bottom.

(2) Steel

Compressive load. — Wall AV is at the top

and has the greatest allowable load in compression. Except that, for this wall, the yield

strength and tensile strength of the sheet steel are appreciably greater than those for the other

steel walls, there is no indication that the properties of the steel afi'ect the allowable load. The

width of the studs (perpendicular to the wall)

ranges from 2 3/8 to 4 in., the spacing from

9 13/16 in. to 4 ft 0 in., and the thickness of

the sheet steel from No. 20 United States

Standard Gage (0.0368 in.) to No. 11 BWG

(0.120 in.), but apparently there is no relation

between these variables and the allowable load.

For some walls, a face and studs were fomied

from the sheet and for these the allowable loads are near the middle and at the bottom of the

group. The studs in DH were No. 11 BWG

(0.120 in.) but the allowable load is less than

for DG. These two walls were identical except

that the studs in wall DG were No. 14 BWG

(0.083 in.) ; therefore, the greater strength for

DH was not realized.

Depending upon the materials on the inside

face, fiberboard only is at the top of the group.

It is followed by gypsum-board lath and

plaster; sheet steel and fiberboard then alter- nate. Depending upon the materials in the outside

face, fiberboard overlaid with sheet steel is at the top followed by fiberboard overlaid with plywood (1/2 in.) and shingles. Fiberboard overlaid with siding is at the middle of the group.

All the others are sheet steel. Transverse load, inside. —Wall CU is at the

top, and the width of the studs is the greatest

except one. There is an indication that as the width of

the studs decreases and the spacing increases

the allowable load decreases.

Depending upon the materials on the inside

face, sheet steel and fiberboard are scattered

through the group ; but, steel is higher; gypsumboard lath with plaster is about the middle;

and gypsum board is lower.

Depending upon the materials in the outside

face, fiberboard overlaid with siding is at the

top. Plywood and fiberboard, either alone or

overlaid with siding or shingles, are scattered

through the group. Sheet steel only is near the

middle and sheet steel box siding (0.0245 in.)

is at the bottom.

Transverse load, outside.—Except that wall

AV is at the top and CU is next, the order is
96 Building Materials and Structures Reports

the same for outside loading as for inside loading.

Racking load.—The braces in wall AV in- crease the allowable load. There is little relation between the design of the wall and the al- lowable load.

Co7icentrated load, inside.—Depending upon

the material on the inside face, the walls above

the middle of the group are sheet steel and

gypsum-board lath with plaster, and those

below are fiberboard only and gypsum board.

Concentrated load, outside.—Depending upon

the material in the outside face, sheet steel is scattered through the group from top to bottom.

Plywood only and plywood overlaid with

shingles is above the middle, and fiberboard

overlaid with siding is at the middle.

Impact load, inside.—Comparing the order

of the walls for transverse load inside, three

walls above the middle are in the same relative

position for impact load inside. Of the others,

two are considerably higher and three are con- siderably lower. Tv/o of the walls having the

steel sheet formed into a face with studs are at the top of the group.

Depending upon the material on the inside

face, steel followed by gypsum-board lath with

plaster are above the middle and fiberboard is below the middle. Gypsum board is at the

bottom.

Depending upon the material in the outside

face, there is no definite trend ; but, apparently,

the order is fiberboard, steel, and plywood.

Impact load, outside.—Comparing the order

of the walls for transverse load applied to the

outside face, most of the walls above the middle

for transverse load are below the middle for

impact load outside and in the same order;

walls below the middle of the transverse group

are above the middle of the impact group. Of

the walls having a one-piece face with studs, one is at the top and one is at the bottom.

Depending upon the material on the inside

face, steel is scattered from the top to the

bottom of the group, fiberboard is above the

middle and near the bottom, gypsum board

followed by gypsum-board lath with plaster, are next to the bottom.

Depending upon the material in the outside

face, steel is scattered through the group, the

steel box siding (0.0245 in.) is above the middle,

as is also fiberboard. Plywood is below the

middle.

(3) Reinforced Brick and Concrete

Compressive load.—Wall AT, brick reinforced longitudinally and transversely, is at the

top, having the greatest allowable load in compression. Next is a hollow concrete slab and at the bottom is a conci-ete slab having flanges.

Transverse load, inside.—The slab having

flanges is at the top, the reinforced brick wall

is next, and at the bottom is the hollow slab. Transverse load, outside.—The hollow slab

now is at the top, followed by the slab having

flanges, and the reinforced brick wall which is at the bottom.

Racking load.—No racking load was applied

to the reinforced brick wall. The hollow slab is at the top followed by the flanged slab. Concentrated load.—Both inside and outside faces are either brick or concrete and for

each of the walls the allowable load is 900+ lb. Impact load, inside.—The reinforced brick

wall is at the top. This is followed by the slab

having flanges and then the slab enclosing air

spaces.

Impact load, outside.—The reinforced brick

wall again is at the top, followed by the flanged

slab, and the slab enclosing air spaces.

As determined by the order in the group,

the reinforced brick wall has a greater allowable load under impact than under transverse

loading but both slabs have smaller allowable

loads.

(J^) Masonry

Compressive load.—Wall AA, high-strength

brick, is at the top and has the greatest allowable load in compression. It is followed by

plain concrete, terracrete (earth), and mediumstrength brick, all near the top. Cavity walls

of brick are high in the group and those of

concrete blocks are near the middle. Tile on

end is above the middle and tile on side is near

the bottom. Near the middle are concrete slabs

laid to leave air spaces, concrete blocks only,

and concrete blocks with brick facing.

Near the bottom are solid concrete blocks,

laid to leave air spaces; and the earth walls:

adobe, rammed earth, and bitudobe.

There is no relation between the thickness

of the wall and the allowable load. There is no very definite relation between the allowable

load and the compressive strength of the materials such as masonry units and mortar.

Transverse load, inside.—Walls CZ and DA,

plain concrete, are at the top, and have the

greatest allowable load for transverse loading

inside.

Wall BW, solid concrete units connected to

vertical splines, follows plain concrete but CH

is below the middle of the group.

Walls of brick are scattered from near the

top, AA (high-strength brick), to near the

bottom, DP.

All earth walls are above the middle, in

order, terracrete, bitudobe, adobe, and rammed

earth.

Structural clay tile on side, AE, is above the

middle and on end, AD is below.
Strength of Houses 97

All concrete block walls scatter from just

above the middle, BO, to the bottom, BP. Of

the solid concrete block walls, those having

brick facing are the higher. Of the cavity

walls, AX, concrete block, is at the middle ; BD,

brick, is near the bottom ; and A U, tile on side,

is next to the bottom. The walls CF and CG,

solid concrete blocks laid to leave air spaces, are midway between the middle and the bottom.

Except that the earth walls are much thicker

than the other walls and have great allowable

loads, there is no indication that the thickness

of the walls is related to the load.

Transverse load, outside.—With a few exceptions, the order for outside loading is the same as for inside loading and the discussion is the same. Wall CH is much higher in the group,

perhaps because the flanges extend inward, also

AU is higher loaded on the brick facing than on

the tile, but BO is lower in the group when

loaded on the brick facing than on the concrete

block.

Racking load.—The seven walls at the top,

AA to CP, did not fail under a racking load of

50 kips, therefore the test was discontinued.

Most of the brick walls are scattered above the

middle. The earth walls are scattered from

well above the middle to near the bottom in the

order: terracrete, DD, and DE; adobe, DB;

bitudobe, DC ; and rammed earth, DF.

One cavity wall, AX (concrete block), is well

above the middle and the others, AU (tile on

side, brick facing) and BD (brick) are to- gether just above the middle.

The concrete block walls BO and BF, having

a brick facing, are well above the middle of the

group and those without brick facing are from

below the middle to next to the bottom.

Of the solid concrete units connected to vertical splices, BW is at the middle and CH is at the bottom of the group.

Structural clay tile on end and on side are together just below the middle and the solid

concrete block CG and CF, laid to enclose air

spaces, are near the bottom.

Concentrated load, inside and outside.—Except for three walls, the concentrated loading was discontinued and the allowable load is 900-|- lb. The exceptions are BD, brick cavity

wall; DC, bitudobe (cavity in the earth) ; and

CH, concrete units flanged inward (unit

cracked when loaded outside between flanges).

The least allowable load for any of the

masonry walls is 540 lb. Impact load, inside.—The plain concrete

walls CZ and DA are at the top having the

greatest allowable load under impact. The test was discontinued at a drop of 10 ft, therefore,

the actual strength was not determined. Highstrength brick wall AA follows. The other

brick walls are all well above the middle of

the group, except DP which is at the bottom.

The cavity walls all are above the middle,

AU, tile and brick, are higher than AX, concrete block, and BD, brick.

The earth walls are scattered through the

group. Well above the middle are DC, bitudobe,

and DE, terracrete block; at the middle are DB, adobe, and DF, rammed earth; and lower

is DD, monolithic terracrete. Concrete block walls with brick facing are at

the middle and walls of block only are near the

bottom.

Structural clay tile on side, AE, is just below

the middle and on end, AD is lower.

Walls BW and CH, concrete units connected

to vertical splines, are below the middle. Still lower is CF, concrete blocks laid to enclose air

spaces, and next to the bottom is CG.

Impact load, outside.—Except for a few

walls, the order for outside loading is the same

as for inside loading. CH is much higher in the

outside group, perhaps, because the flanges ex- tend inward. AU is much lower under impact

when loaded on the brick facing, although it was higher under transverse loading. As for

transverse loading, BO is lower in the group

when loaded on the outside brick facing than

when loaded on the concrete block.

(b) Load-heay^ing Partitions

The allowable loads are shown in figure 45.

(i) Wood

Compressive load.—The three load-bearing

partitions all have 2- by 4-in. studs and single

plates of Douglas fir. No. 1, common. All studs

are spaced 1 ft 4 in. Evidently the difi'erences

in the allowable loads are not due to differences

in the frames.

Depending upon the materials in the faces,

partition CO, fiberboard glued to the frame, is at the top, followed by gypsum board, then by

wood lath with plaster.

Transverse and racking loads.—For trans- verse and racking loads, the order is the same

as for compressive load with CO at the top.

Concentrated load.—Depending upon the material in the faces, fiberboard is at the top

followed by wood lath with plaster, then by

gypsum board.

Impact load.—Depending upon the material

in the faces, wood lath with plaster now is at the top, followed by gypsum board, then by

fiberboard.
98 Building Materials and Structures Reports

(c) Nonload-bearing Partitions

The allowable loads are shown on figure 45.

{!) Wood

Concentrated load.—The allowable load under

concentrated loading depends principally upon

the material in the faces and also upon the

spacing of the structural members (studs).

In general, the greater the spacing (span)

the less the allowable load. Depending on the

spacing, partition CC (5 3/8 in.) is at the top

having the greatest allowable load for concentrated loading and CD (1 ft 0 in.) next. For

all the other partitions the spacing is 1 ft 4 in. Depending upon the material in the faces,

plywood (14 in.) is at the top followed by

fiberboard lath with plaster, also, gypsum board

and, at the bottom, fiberboard only (I/2 in.).

hnpact load.—Partition BN is at the top,

having the greatest allowable load under impact.

Most of the partitions have 2- by 4-in. studs,

spaced 1 ft 4 in., but, in CK the studs are 2 by 3

in. The allowable load under impact for this

partition is too great, because there are four

studs in each specimen, not three, to represent

portions of the partitions in a completed house.

Estimating the probable allowable load of representative specimens is impracticable.

The two partitions at the bottom are CC,

plank, and CD, 2- by 2-in. studs, spaced 1 ft 0

in. There is no indication that the allowable

load depends on the kind of wood.

Depending upon the material in the faces,

fiberboard (14 in.), CK (extra stud), and gypsum board (V2 in.) are above the middle of the

group ; fiberboard lath with plaster is below

the middle and plywood (14 in.) is at the

bottom.

(2) Steel

Concentrated load.—Partition CV is at the

top, having the greatest allowable load. For

all the partitions, the spacing of the structural

members did not vary greatly.

Depending upon the material in the faces,

sheet steel is at the top, followed by gypsumboard lath with plaster and gypsum board only.

Fiberboard is at the bottom.

Impact load.—Partition CV is at the top,

having the greatest allowable load under impact. In general, the allowable load decreases as the width (perpendicular to faces) of the

studs decreases.

Depending upon the material in the faces,

sheet steel is at the top, then fiberboard, gypsum board, and gypsum-board lath with plaster.

(d) Floors

The allowable loads on floors are shown in

figure 45.

(1) Wood

Transverse load.—Floor CL is at the top and

has the gi'eatest allowable load applied transversely. This floor and the two at the bottom

of the group have 2- by 8-in. joists, spaced 1 ft 4 in., of Douglas fir and long-leaf southern

pine. The other three floors have unconventional frames and are at or above the middle of the

group. There is no indication that the allowable load depends upon the kind of wood.

Depending upon the material in the lower

face (ceiling), the two floors that have no ceil- ings are at the top of the group. They are followed by two floors with plywood (% in.)

ceilings; at the bottom are the two floors that

have ceilings of lath with plaster. Of these,

BS, fiberboard lath with plaster, is above QB

(conventional), which has wood lath with

plaster, and the allowable load is taken as the

load causing cracks in the plaster.

Depending upon the material in the upper

face, CL, plywood with oak finish floor, is at the top. Floors DS and DM, plywood only, are at the middle and the others are scattered.

Concentrated load.—For all the wood floors,

the concentrated loading was discontinued and

the allowable load is 900-|- lb. hnpact load.—For the floors above the

middle, the impact loading was discontinued

and the allowable load is 9.0-|- ft drop.

Below the middle are QB (conventional)

which has a plaster ceiling and DM (demountable) which has a plywood ceiling. BS with a

plaster ceiling is at the bottom.

Under transverse loading, the load causing

cracks in the plaster is nearly the same for

wood lath and fiberboard lath, but, under impact loading, the plaster on wood lath cracked

at nearly three times the height-of-drop of

that for plaster on fiberboard lath.

(2) Steel

Transverse load.—Floor AG, cellular sheetsteel panel with concrete fill, is at the top and

has the greatest allowable load. The next four

floors have a lower face (ceiling) of sheet steel,

one-piece deck with the joists. The two floors

BB and BC at and near the bottom, have channel-shaped sheet-steel frames. There is no re- lation between the depth of the joists and the

allowable load. There is a slight indication that

as the thickness of the sheet steel increases the

allowable load decreases.
Strength of Houses 99

Depending upon the material in the lower

face (ceiling), all the floors at and above the

middle have sheet-steel ceilings and BB, below

the middle, has no ceiling. The two floors, AY

and BC, at the bottom of the group have plaster

ceilings but there is little diff'erence in the al- lowable loads for metal lath and gypsum-board

lath. Depending upon the material in the upper

face, concrete with composition finish flooring

is at the top. For all the other floors, the finish

flooring is either hard or soft wood on either

wood subflooring or wood sleepers with no indication that the materials in the upper face

have any effect on the allowable load.

Concentrated load.—The concentrated load was applied to the upper face only. For all the

floors except AJ, the loading was discontinued

and the allowable load is 900+ lb. For AJ the

load is 296 lb. Impact load.—For all the floors above the

middle, the impact loading was discontinued

and the allowable load is 900+ lb. Floors AJ

and AY, below the middle, have a one-piece

face with joists; and BC, at the bottom, has

channel-shaped joists.

Depending upon the material in the lower

face (ceiling), all except the two floors at the

bottom have either sheet-steel ceilings or no

ceiling. The two at the bottom of the group

have plaster ceilings and the allowable load is taken as the load causing cracks in the plaster.

For plaster on expanded metal lath (AY), the

height-of-drop is four times that for plaster on gypsum-board lath (BC).

Depending upon the material in the upper

face, concrete with composition flooring is at the top, whereas for the other floors there is no

indication that the materials affect the allowable load.

Comparing the order of the floors under

transverse loading with the order under impact

loading, AG (concrete fill) is at the top for

both, and AY and BC (plaster ceilings) are at the bottom for both. Under transverse loading,

the three floors CR, CW, and AJ, above the

middle, are each two places lower under impact.

They have one-piece face and joists. The two

floors AN and BB, below the middle under

transverse loading, are each three places higher

under impact. Floor AN has a one-piece face

and joists which interlock and BB has channelshaped sheet-steel joists.

(3) Reinforced Concrete

Transverse load.—Floor AW is at the top

and has the greatest allowable load. It has steel

joists, structural clay tile fillers on the lower

flanges, and a concrete fill. Floor CT, below

the middle, is similar except that the fillers are asbestos-cement, not clay tile. The steel joists

in CT are slightly higher in carbon content,

and the yield point and tensile strength are appreciably greater than the steel joists in AW.

However, the weight per foot of the joists in

CT is somewhat less than that of the joists in

AW. It appears probable that there is no appreciable difference in the strength of the joists. In addition, the compressive strength of the

concrete was the same in both floors ; therefore,

the lower allowable load for floor CT can only

be ascribed to the greater spacing of the joists,

2 ft 0 in., not 1 ft 5 i/o in. It is unlikely that

the substitution of asbestos-cement fillers for

the tile fillers has any appreciable effect on the

allowable load.

Floor CY, next the top, has precast re- inforced concrete joists and nearly the same

allowable load as CT.

Floor AS, at the bottom, is a hollow re- inforced concrete slab. Concentrated load.—For all the floors, the

concentrated loading was discontinued and the

allowable load is 900+ lb. Impact load.—For the three floors AW, CY,

and CT, at the top, the impact loading was discontinued and the allowable load is 9.0+ ft drop. For impact loading, the order is the same

as for transverse loading and the discussion is much the same except that AS has one-fourth

the transverse allowable load of CT but more

than half the height-of-drop.

(e) Roofs

The allowable loads are shown on figure 45.

(1) Wood

Transverse load.—Roof DU is at the top,

and has the greatest allowable load applied

transversely. For all the roofs except QC

(conventional), the allowable load was determined by damaged.

Roof DT, which has the upper rafters edgewise, should have a greater allowable load than

DU, with the upper rafters flatwise, but it has

only about half the load.

Roof DN is similar to DO except that the

rafters are 6 in. deep, not 8 in. The transverse

strength of 6-in. rafters is about half that of

8-in. and the allowable loads have about the same ratio.

Roof QC (conventional), at the middle of the

group, has 2- by 6-in. rafters, spaced 2 ft 0 in.,

but BT, at the bottom, has 2- by 8-in. rafters,

spaced 1 ft 4 in. Considering the rafters only,

the transverse strength of roof BT should be

two and a half times the strength of roof QC
100 Building Materials and Structures Reports

because longleaf pine has a slightly greater

modulus of rupture than Douglas fir. However,

the allowable load is less than half because

the plaster ceiling cracked.

Depending upon the mateiial in the lower

face, plywood is at the top and fiberboard lath

with plaster is at the bottom. The other roofs

have no ceiling.

Depending upon the material in the upper

face, %-in. plywood is at the top and %-in.

plywood is lower. Wood sheathing overlaid

with shingles or built-up roofing are below the

middle of the group.

Concentrated load.—For the roofs DT and

DU which have %-in. plywood in the upper

face, QC, which has wood sheathing with

shingles, or BT, which has built-up roofing, the

concentrated loading was discontinued and the

allowable load is 900+ lb. For roofs DN and DO, the upper faces are

alike and both are %-in. plywood. The allowable loads are nearly the same.

(2) Steel

Transverse load.—Roof CX is at the top, and

has the greatest allowable load applied transversely. All the roofs, except DJ. at the

bottom, have a one-piece face with rafters. DJ

has channel-shaped rafters. There is an indication that the thinner the sheet steel and the

greater the spacing of the rafters, the less the

allowable load.

Depending upon the material in the lower

face, sheet steel is high in the group and gypsum board is at the middle. Roof DJ, at the

bottom, has no ceiling.

Depending upon the material in the upper

face, all the roofs above the bottom have builtup roofing on wood sheathing or fiberboard.

The roof at the bottom has sheet-steel box-rib

roofing.

Concentrated load.—Roof DJ, which has boxrib roofing is at the top and is followed by

built-up roofing over wood sheathing (next

to the top) and fiberboard.

9. Relation of Materials and Design

TO Allowable Load-weight Ratio

For a house construction, efficient use of

material requires a high ratio of allowable

load to weight. Although this ratio is not of

first importance in house design it should be

considered—particularly for walls, load-bearing partitions, floors, and roofs above the first story—^because if the ratio is low, the load on

first-story walls and partitions may be greater

than is necessary, and constructions having

greater allowable loads are required for the

first story.

To assist the architect when selecting a construction, the ratio of allowable load to weight

was computed, for each construction. The

values for walls are shown in figures 46 (compressive, transverse, and racking loads) and 47

(concentrated and impact loads). Those for

partitions, floors, and roofs are shown in figure

48.

A study of these figures also should be helpful when developing new and unconventional

constructions because they indicate the designs

and materials having high load-weight ratios.

(a) Walls

The load-weight ratios for walls are shown

in figures 46 and 47.

(1) Wood

Compressive load.—Wall DR is at the top,

and has the greatest ratio of allowable load

to weight. Experts on plywood house construction believe that some changes in the design

would increase the allowable load and decrease i, the weight, thereby greatly increasing the load- i weight ratio. Presumably these changes are ' economically practicable.

Wall DR may be considered a "stressed-skin"

construction because the faces and frames are fastened by glue and, therefore, act together \ under load more completely than if fastened

by nails only.

Apparently, gluing the faces to the structural j members is conducive to high load-weight

j ratios because in walls CN and CM the fiber- \ board inside face is also glued to the studs and

they are above the middle and higher than

similar walls having the faces nailed to the

studs.

Wall CI, above the middle, has gypsumboard inside face glued and nailed to the ribbon

at midheight of the wall. Wall DQ, also above

the middle, has fiberboard inside face glued

to the fight 2- by 3-in. studs. Wall DK, near the

bottom, has fiberboard inside and outside

faces glued to the light 2- by 2-in. studs. Wall

DL, next below DK is demountable in pieces

and both faces are removably attached to the

studs by steel clips.

All the other walls have conventional frames

except CB, plank vertical, above the middle.

Depending upon the material on the inside

face, the load-weight ratio decreases in the

order: glued plywood, glued fiberboard, nailed

plywood, nailed fiberboard, and nailed fiberboard

lath with plaster.

Depending upon the material in the outside

face, nailed fiberboard either bare or overlaid
Strength of Houses 101

AZ BW AA AD DC CF AU BP

AR CH AE CP BO DP DD BF

AT DA AC BF AB CG BD

CZ AX DE AF DB OF

a nrini-i _ Wood Steel Reinforced

Masonry

Masonry

400

o

Oil

o

C3

I.

o

Q. <:

300

200

100

0

BU DO BG

BY CN BK

AH

CU

BX CM QA

BL BQ

BJ DL

DG

AL CQ BV AE AD CP AF

AV DH AR BO CZ AC A A CG DC

AZ H BtV AB AU BD DD CF

AX BF DA DP BE DE DF, nn^ ^ ^ X. BP CH DB \ Wood

With braces

Without braces

Steel Reinforced Masonry

Masonry

Figure 46.

Allowable compressive, transverse, and racking load-weight ratios for walls.
102 Building Materials and Structures Reports

AD AF AU

DP CF BO CP DB DC

AE BE BF DA BD DD

BW AX CG CZ AA DF

,^AB AC DE

AD AF AU

DP CF BO CP DB DC

AE BE BF DA BD DD

BW AX CG CZ AA DF

..^ AB AC DE

Wood steel Reinforced

Masonry

Masonry

1000

DH

DG

AL AH AV

AZ BV

CQ AR CH AX AB BP DB DF

AT DA AC AE BD DE DP DD

AP CZ CP BW BO DC BE CG

f\^AA AU BF CF AD AF

A A BV CH BW BD BO AD AF

AT DA AX BF CF DB DF

AR CZ AC AB BP DE DP DD

„ p,t[^CP AE AU DC BE CG

| Wood Steel Reinforced Masonry

Masonry

Figure 47.

Allowable concentrated and impact load-weight ratios for walls.
Strength of Houses 103

oI

O

o

o

/OOO

0

40

30

20

10

0

200

QD

CJ

CO

Wood Load-bearing Partitions

DM

CL cw

CR

AN

AJ

BBAG AS

AY CT

BC AW

CY

Wood Load-bearing Wood Steel Masonry

Partitions Floors

CJ

Wood Steel

Roofs

CO

J5 Wood Load-bearing Partitions

>3od

-4-

200

ICQ

CL as cw DT

QD

CJ

I BN

CD CK BZ AQ DI

DM DS AN AY

CE BB BC

QB CR

0

CO CC^ AM BR CV BA ||TMgC/1 BM ^AI

AS

AJ CY AW

i

-^G CT

DO 57" i CS

DU CX I DJ AK

AO

Wood

Load

bearing

O

o

1200

Wood Steel Nonload- bearing

Partitions

Wood Steel Masonry

Floors

Wood Steel

Roofs

.5)

900

600

JOG

CK

AM CV

QD

CO

CJ

CA DI BN CD BA AI

CC BR AQ

'i CW AY AW

AN AJ CT

BB CR AC CY

BC *i„ AS

Wood

Load

bearing

Wood Steel

Nonload-bearing

Partitions

Wood Steel Masonry

Floors

Figure 48.

Alloxvahle load-weight ratios for partitions, floors, and 7-oofs.
104 Building Materials and Structures Reports

with siding or shingles is scattered throughout

the group, glued plywood is at the top, nailed

plywood, shingles, and siding, are above the

middle, and nailed wood sheathing with siding

is at the middle, and, finally, stucco and brick veneer are at the bottom.

Transverse load, inside.—The architect is reminded that, when selecting a wall for trans- verse (wind) load, it is necessary only that the

allowable load be adequate for the particular

house. Therefore, he may select the wall for

compressive load and then check to make cer- tain that the transverse load is adequate.

Wall DR is at the top, and has the greatest

allowable load, DQ (light frame, glued inside

face) is above the middle, CB (plank) is below

the middle, DK (light frame, glued both faces)

is near the bottom, and DL (demountable in

pieces) is still lower.

Depending upon the materials on the inside

face, glued plywood and fiberboard are at the

top, nailed fiberboard is above the middle, and

nailed wood and fiberboard lath with plaster are below the middle.

Depending upon the materials in the outside

face, glued plywood is at the top and nailed

plywood is above the middle but nailed wood

sheathing with siding is just below the middle.

Fiberboard is scattered through the group

but stucco and brick veneer are at the bottom.

Transverse load, otitside.—As for inside loading, wall DR is at the top, DQ (light frame,

glued inside face) just above the middle, and

CB (plank) just below. However, DL (demountable in pieces) is now at the middle,

probably because the pieces of the outside face

are about 10 in. high, but the inside face is one

piece from top to bottom of the wall. DK (light

frame, glued both faces) is somewhat higher

in the group.

Depending upon the materials in the faces,

the order is the same as for inside transverse

loading, except that wood sheathing with

siding outside is next to the bottom.

Racking load.—Wall DR is at the top, having

the greatest load-weight ratio.

Depending upon the materials in the faces,

and disregarding overlays, outside, (siding,

shingles) plywood glued is at the top, then

fiberboard both faces glued (DK 2- by 2-in.

studs, spaced 1 ft 0 in.), nailed plywood, nailed

fiberboard, glued gypsum board and nailed plywood are all above the middle of the group.

They are followed by fiberboard with both

faces nailed and plaster inside; fiberboard on

both faces, one glued, the other nailed, at the

middle; fiberboard with both faces nailed, and

nailed fiberboard with plaster inside ; stucco or

brick veneer are well below the middle; and

lowest is nailed wood and nailed fiberboard

lath with plaster inside and nailed wood sheathing outside.

The plank wall CB is next to the bottom and

at the bottom is the demountable wall DL

braced and unbraced.

Concentrated load, inside.—The allowable

load-weight ratios are shown in figure 47.

Although the spacing of the structural

members is not of great importance for the

concentrated load, all the walls with less than

1 ft 4 in. spacing are well above the middle

of the group, as are those with glued inside

faces.

Depending upon the material on the inside

face, all the plywood is at the top; fiberboard

is next lower, most of which is above the

middle. Gypsum board is at the middle, followed by all walls with plaster.

Concentrated load, outside.—Depending upon

the material exposed on the outside face, plywood and plank are near the top, with wood

siding well scattered through the group. Fiberboard only and wood shingles are near the

middle but stucco is well below the middle and

brick veneer is at the bottom.

Impact load, inside.—Wall DR is at the top,

and has the greatest load-weight ratio. Next

is DL, demountable in pieces, faces attached

by steel clips. The plank wall, CB, is at the

middle and the walls with fiberboard glued to

light studs, DQ and DK, are above and at the

middle.

Depending upon the material on the inside

face, plywood, both glued or clipped to the

studs, is at the top followed by fiberboard either

glued or nailed and plywood nailed, most of

which is above the middle. Nailed gypsum

board, wood, and fiberboard lath with plaster, are all below the middle.

Depending upon the material in the outside

face, plywood, both glued or clipped, is at the

top. Sheathing of wood, fiberboard, and plywood, overlaid with wood siding or shingles, all nailed, are scattered from near the top to near

the bottom. Fiberboard only, glued, is at the

middle. Brick veneer and stucco are at and

near the bottom.

Impact load, outside.—Wall DR is at the top

and, with a few exceptions, the order is the same as for impact loading inside.

Wall DL, demountable, is nearer the middle,

and with the exception of the comments on

clipped faces, the discussion for impact inside

applies to impact outside.

(2) Steel

The load-weight ratios are shown in figure

46.Compressive load.—Wall AV is at the top,
Strength of Houses 105

having the greatest load-weight ratio. Apparently there is no relation between the loadweight ratio and the thickness of the sheetsteel in the studs or the yield strength. The

studs in AF are formed to a more intricate cross section than the others which may ac- count in part for the high ratio.

Depending upon the material on the inside

face, fiberboard and sheet steel alternate

through the group, except that AZ, next the

bottom, has gypsum-board lath with plaster on

the inside face.

Depending upon the material in the outside

face, sheet steel extends from the top to below

the middle of the group. Fiberboard overlaid

with siding or shingles is near the bottom.

Transverse load, inside and outside.—For

both inside and outside transverse loading, the

order is much the same. There is no very

obvious explanation for the differences in loadweight ratios. Gypsum board only and gypsum-board lath with plaster are below the

middle and at the bottom respectively.

Racking load.—There are many materials

in the faces and many kinds of fastenings. Apparently there is no consistent relation between

these factors and the load-weight ratios.

For wall AV, the ratio depends greatly upon

whether there are diagonal braces extending

from the top to the bottom of the wall.

Concentrated load, inside.—The load-weight

ratios are shown in figure 47.

It is evident that the load-weight ratio depends on the material on the inside face. There

is no relation between the ratio and the spacing

of the structural members.

Sheet steel is above the middle of the group,

gypsum board and gypsum-board lath with

plaster are at the middle and fiberboard only

is below the middle.

Concentrated load, outside.—Again there

is no relation between the spacing of the

structural members and the load-weight ratio.

Each of the materials in the outside face appear to be scattered through the group.

Impact load, inside.—Apparently there is no

consistent relation between the design of the

walls and the materials to the load-weight ratio.

Depending upon the material on the inside

face, in general, the order is sheet steel, fiberboard only, gypsum-board lath with plaster,

and gypsum board only.

Impact load, outside.—Depending upon the

materials on the inside face, in general the

order is fiberboard only, gypsum board, sheet

steel and, at the bottom is gypsum-board lath

with plaster.

Depending upon the materials in the outside

face, in general the order is box-rib sheet-steel

siding at the top, plywood next, sheet steel next

lowest and, at the bottom, plywood with

shingles.

(3) Reinforced Brick and Concrete

The load-weight ratios are shown in figure

46.

Compressive load.—Wall AR, which is at the

top, has the greatest load-weight ratio. This

wall, a reinforced hollow concrete slab, is fol- lowed by the reinforced brick wall, AT, and the

reinforced slab having flanges, BV.

Transverse load, inside.—Wall BV, flanged

slab, is at the top ; it is followed by AR, hollow

slab, and lowest is AT, solid wall.

Transverse load, outside.—Hollow slab AR

is at the top ; flanged slab 5F is next; and lowest is solid wall AT.

Racking load.—Racking loads were not applied to wall AT, reinforced brick. Wall AR,

hollow slab, is above BV, flanged slab. Conceyitrated load, inside and outside.—The

load-weight ratios are shown in figure 47.

For all these walls, the concentrated loading was applied to the concrete or brick face and

discontinued at 1,000 lb. Although the allowable loads are the same, the weights are different.Impact load, inside.—Wall AT, brick, is at the top; AR, hollow slab follows; and BV,

flanged slab is lowest.

Impact load, outside.—Wall AR, hollow slab,

is at the top; AT, brick follows; and lowest is BV, flanged slab.

(^) Masotiry

Compressive load.—The load-weight ratios are shown in figure 46.

Wall AA, solid, high-strength brick, is at the

top, and has the greatest load-weight ratio. It

is followed by plain concrete DA and CZ.

Medium-strength brick is scattered above

the middle.

Structural clay tile on end, AD, is above the

middle of the group and tile on side, AE, is below the middle. Cavity walls, BD. brick;

and AX, concrete block ; are above the middle

but AU, brick with tile on side, is near the

bottom. Walls of concrete block and solid concrete units laid to leave air spaces are scattered near the middle.

Of the earth walls, DE, terracrete block, is above the middle and DD, monolithic terracrete,

is below. The others : adobe, DB, bitudobe, DC,

and rammed earth, DE, are shown together at the bottom of the group.

Walls BW and CH, concrete slabs attached to vertical splines, are well below the middle, as are BE and BO, concrete block with brick

facing.
106 Building Materials find Structures Reports

Transverse load, inside.—Walls BW and CH,

concrete slabs attached to vertical splines,

which are at and near the top, have the greatest load-weight ratio. They are followed by

CZ and DA, plain concrete. Structural clay tile wall AE, on side, is near

the top and AD, on end, is near the middle of

the group.

Cavity wall, AX, concrete block, is well above

the middle, but AU, tile on side with brick,

and also BD, brick, are near the bottom.

AA, high-strength brick, is well above the

middle and around the middle are the mediumstrength brick walls.

Walls BO and BF, concrete block with brick

facing, are just above the middle.

Two earth walls, DE, terracrete block, and

DC, bitudobe, are near the middle but the

others are much lower.

The concrete block walls and the concrete

units laid to leave air spaces are all below the

middle.

Transverse load, outside.—Walls CH and

BW, concrete units attached to splines, are at the top. For outside loading, the order is about

the same as for inside loading and the discussion is the same. Racking load.—Cavity wall AX, concrete

block, which is at the top, has the greatest loadweight ratio. The other cavity walls are near

the middle of the group.

Wall BW, concrete units attached to vertical

splines, is next to the top but similar wall, CH,

is well below the middle.

Walls BO and BF, concrete block with brick

facing, are near the top and lower is structural

clay tile on side ; still lower is clay tile on end.

Plain concrete is above the middle. Mediumstrength brick is at or above the middle but

high-strength brick is below the middle.

Concrete block is below the middle, concrete

units laid to enclose air spaces are still lower.

Terracrete walls are near the bottom and

the three other earth walls are at the bottom.

Concentrated load, inside and outside.—The

load-weight ratios are shown in figure 47. For the concentrated load, the order is the same for loading inside and outside. With one

or two exceptions, the loading was discontinued, therefore the allowable loads are 900 -|- Ib. The differences in the load-weight ratios are due to differences in the weights of the

walls.

Almost all the walls above the middle of the

group have air spaces in the wall and most of

those below are solid walls. All the earth walls

are at the bottom.

Impact load, inside and outside.—With the

exception of walls AU and BO (different

materials in the two faces) which are several

places lower when loaded outside than when

loaded inside, the order is the same for both

loadings.

The plain concrete walls CZ and DA are at the top, having the greatest load-weight ratios.

Most of the brick walls are above the middle

of the group as are the cavity walls AX, BD,

and AU, also CH and BW, concrete units at- tached to vertical splines.

Structural clay tile on side, AE, is above the

middle and the same tile laid on end, AD, is below the middle.

Concrete block with brick facing, BF and BO,

are near the middle.

Concrete block is below the middle, as are

concrete units laid to enclose air spaces.

All the earth walls are below the middle.

(b) Load-bearing Partitions

The allowable load-weight ratios are shown

in figure 48.

(1) Wood

All the load-bearing partitions have con- ventional wood frames, therefore differences in

the ratios are due to differences in the faces.

Compressive, transverse, racking, and con- centrated load.—Partition CO is at the top,

having the greatest load-weight ratio. The

faces on this partition are fiberboard glued to the studs. Next is CJ, which has gypsum-board

faces glued and nailed to the ribbon at midheight and nailed to the other members of the

frame. Last is QD (conventional) which has

wood lath, nailed, with plaster faces.

Impact load.—Partition CJ is at the top,

followed by CO and QD (conventional).

(c) Nonload-bearing Partitions

The allowable load-weight ratios are shown

on figure 48.

(i) Wood

Concentrated load.—Partitions CC and CD,

plywood, 14 in., nailed, are at the top, and have

the greatest load-weight ratios.

Fiberboard, 14 in., nailed, is about the middle

of the group. At the middle is CK, gypsum

board, 1/2 in., glued and nailed to the ribbon at midheight, and also nailed to the frame. The

three partitions at the bottom have nailed fiberboard lath with plaster.

Impact load.—Partitions BN, CA, and AM,

fiberboard, 1/2 i^i-. nailed, are at the top, having

the greater load-weight ratios. CK, gypsum

board, Vo in., glued and nailed, is just above the

middle and CC, plank, is at the middle.
Strength of Houses 107

Partition CD, studs 2 by 2 in., spaced 1 ft 0 in., plywood V4. in-, is just below the middle,

followed by the three partitions having con- ventional frames and nailed fiberboard lath

with plaster.

(2) Steel

Concentrated load.—For the steel nonloadbearing partitions, there is an indication that

the load-weight ratio is less the greater the

spacing of the structural members.

Partition CV, which is at the top, has the

greatest load-weight ratio. On this partition

the faces are sheet steel. Next are AQ and AI,

gypsum board screwed, then BA, nailed gypsum-board lath with plaster and, finally, DI,

fiberboard clipped to the frame.

Impact load.—Partition BA, which is at the

top, has the greatest load-weight ratio. The

faces are nailed gypsum-board lath, with

plaster. The next, DI, has fiberboard fastened

by clips.

At the middle of the group is CV, which has

sheet-steel faces, followed by AI and AQ with

gypsum board fastened by screws.

(d) Floors

The load-weight ratios are shown in figure

48.

(1) Wood

Transverse load.—Floor CL, conventional

frame, which is at the top, has the greatest

load-weight ratio. The other floors having

conventional frames, BS and QB, are at the

bottom. Those having unconventional frames

are intermediate.

Depending upon the material in the lower

face (ceiling), the floors having no ceiling, CL

and CE, are at and near the top ; plywood, DM

and DS, follow.

Floor BS, fiberboard lath with plaster, and

QB (conventional), wood lath with plaster, are

at the bottom.

Depending upon the material in the upper

face, most of the plywood is above the middle

and all with wood subfloor and finish floor are

at the bottom.

Concentrated load.—Floor DM, demountable

in pieces, which is at the top, has the greatest

load-weight ratio. Depending upon the material in the upper face, most of the plywood is above the middle and most of the wood subflooring is below.

Impact load.—Floor CL, which is at the top,

has the greatest load-weight ratio. The frame

is conventional, 2- by 8-in. joists, spaced 1 ft 4

in. The other floors QB and BS, having con743712°—48—

ventional frames are at the bottom. Those

having unconventional frames are intermediate.Depending upon the material in the lower

face (ceiling), the two floors CL and CE, which

are at the top, have no ceiling; the next two,

DS and DM, plywood % in. and the two at the

bottom, QB and BS, have lath with plaster.

Depending upon the material in the upper

face, nearly all the plywood is above the middle

of the group and nearly all the wood subflooring is below.

(2) Steel

Transverse load.—Floor CR, w^hich is at the

top, has the greatest load-weight ratio. Floors

BB and BC, having channel-shaped joists, are below the middle of the group.

Depending upon the material in the lower

face (ceiling), sheet steel is above the middle,

except for AG, concrete fill. The floor having

no ceiling, BB, is at the middle. Floors BC

and AY, which are at the bottom, have lath

with plaster ceilings.

Depending upon the material in the upper

face, all the floors have wood finish flooring over either wood subflooring or wood sleepers,

except AG, which has a concrete fill and composition finish floor. Concentrated load.—Floor BB, which is at the top, has the greatest load-weight ratio.

Depending upon the material in the upper

face, all the floors have wood finish flooring over wood subfloor or wood sleepers, except

AG, which is at the bottom and has composition finish flooring over concrete. Impact load.—Floor BB, which is at the top,

has the greatest load-weight ratio.

Depending upon the material in the lower

face (ceiling), the floor having no ceiling is at the top, followed by sheet steel to well below

the middle. AY, which has metal lath with

plaster, is below the middle and BC, which is at the bottom, has gypsum-board lath with plaster.

(3) Reinforced Concrete

Transverse load.—Floor CY which is at the

top, has the greatest load-weight ratio. The

joists are precast reinforced conci'ete. Floors

AW and CT, which are next, have expanded

steel joists and floor AS, which is lowest, is hollow concrete slab. Concentrated load.—For all reinforced floors,

the concentrated allowable load is 900+ lb. Therefore, the differences in the load-weight

ratios are due to differences in the weights of

the floors. Floor CY with precast joists, which is at the top, is followed by AS, hollow slab ; below
108 Building Materials and Structures Reports

the middle of the group are CT and AW with

expanded steel joists.

Impact load.—Floor CY, which is at the

top, has the greatest load-weight ratio. This

precast-joist floor is followed by the two floors

having expanded steel joists, and the hollow

slab.

(e) Roofs

The load-weight ratios are shown in figure

48.

(1) Wood

Transverse load.—The cellular plywood roofs

DU and DT, which are at the top, have the

greatest load-weight ratios.

Floor DO, demountable in pieces, with 8-in.

joists, is just above the middle and DN. similar

except for 6-in. joists is next to the bottom.

Roof QC, conventional, is just below the

middle. The joists are 2 by 6 in., spaced 2 ft 0 in., and there is no ceiling. The other con- ventional frame roof, BT, which has joists 2 by

8 in., spaced 1 ft 4 in., and a plaster ceiling, is at the bottom.

Depending upon the material in the lower

face (ceiling), the two roofs, DU and DT,

which have plywood ceilings (stressed-skin)

,

are at the top. The next three have no ceiling

and the one at the bottom, BT, has a plaster

ceiling.

Depending upon the material in the upper

face, the two roofs, DT and DU, with %-in.

plywood (stressed-skin), are at the top and

DO and DN, fiberboard overlaid with -Ys-in. plywood (demountable in pieces), are lower in

the group.

Conventional roof QC, which has wood

sheathing with wood shingles, is at the middle

of the group and BT, which has sheathing with

built-up roofing, is at the bottom.

Concentrated load.—Except for roofs DN

and DO, upper face %-in. plywood, the con- centrated allowable load is 900 -f- lb. Therefore,

the differences in the load-weight ratios, to a

great extent, are due to differences in the

weights.

Roof QC (conventional), which is at the top,

has the greatest load-weight ratio. The upper

face is wood sheathing overlaid with shingles.

DN and DO, %-in. plywood, are next to the

top; DT and DU, %-in. plywood, follow; and

BT, wood sheathing overlaid with built-up

roofing, is lowest in the group.

(2) Steel

Transverse load.—In general, the less the

depth of the structural members the less the

load-weight ratio.

Roof CX, which is at the top, has the greatest strength-weight ratio.

Depending upon the material in the lower

face (ceiling), sheet steel is scattered from top

to bottom of the group ; CS, gypsum board, is at the middle; and DJ, which has no ceiling,

is next to the bottom.

Depending upon the material in the upper

face, all the roofs except DJ have built-up roofing over wood sheathing. CX, which is at the

top, has fiberboard. DJ, which is next to the

bottom, has box-rib sheet-steel roofing.

Concentrated load.—Roof DJ, which is at the top, has the greatest load-weight ratio.

The upper face is 0.0245-in. sheet-steel roofing.

Next is CX, which has built-up roofing over wood sheathing. All the other roofs have builtup roofing over fiberboard.

10. Allowable Loads for Constructions

NOT Having Standard Height or Span

(a) Compressive Load

Walls and load-bearing partitions are the

only elements of a house subjected to compressive loading. In general, the higher the wall the less the

allowable load and the greater the shortening

and lateral deflection because many of the walls

and partitions are "long columns."

A wall height of 10 ft may be taken as the

greatest for the average house. A study of the

walls and partitions indicated that, up to this

height, the allowable load in this report is safe except for wood walls DQ and DK, which

have light conventional frames.

For a wall or partition of any height, the

allowable load, also, the shortening and lateral

deflection, may be determined most satisfactorily by testing specimens having the height of

the walls in the building.

{h) Transverse Load

Walls, load-bearing partitions, floors, and

roofs are the elements subjected to transverse

loading. For walls and partitions, the height

determines the span.

In general, the greater the span the less the

allowable load and the greater the deflection.

If the span is less than the standard span, the

load is greater than the allowable load for the

standard span up to the load causing shear

failure. It is believed that under the maximum

transverse load, most of the constructions failed

by rupture of members under tensile and compressive stresses. No tests of short specimens were made to determine the shearing strength,

therefore, there is no way to compute the al- lowable load for spans less than the standard
Strength of Houses 109

span from the data in the Building Materials

and Structures reports. If it were not for the

possibility of shear failure, the greater allowable load for short spans could be computed by

the same method as for long spans.

Usually in a house, the span of the floor in a bath room or kitchen is much less than for

the other rooms but the loads are much greater.

If the floor construction is the same for all rooms, the price should be less than if a different construction is required for bath rooms and

kitchens. Tests of short span floors probably

are worth while.

For spans greater than standard, the allowable load should be computed by finding from

the standard span location of loads and allowable load, the bending moment at midspan,

then the load on the long span causing the same moment. The deflection, also, may be

computed.

For a wall or partition, this load is the allowable load because the weight of the construction has no effect on either the transverse load or the deflection.

For a floor or roof, the weight should be

added to the allowable load when computing the

bending moment and subtracted from the computed load on the long span to obtain the allowable load which may be applied over the long

span.

(c) Concentrated Load

Under concentrated loading, the allowable

load as well as the indentation and set are independent of the height of a wall or partition or the span of a floor or roof.

{d) Impact Load

The allowable impact load for walls, partitions, and floors having heights or spans either

greater or less than those tested, cannot be

determined by computation.

For a house construction not having the

standard height or span reported in the Building Materials and Structures series, specimens

should be tested and the allowable height-ofdrop determined by application of the criteria.

(e) Racking Load

Walls and load-bearing partitions are the

only elements subjected to racking loads.

The allowable load (shear) is independent

of the height of the wall, therefore the allowable load given in this report may be applied to a wall or partition of any height. However,

the racking deformation is greater the greater

the height. For any height, the deformation

should be taken as directly proportional to the

height.

XIX. Comparison of Allowable Loads

WITH Design Loads for

Typical Houses

1. Objective

How do design loads for a house compare

with the allowable loads? It is evident that, if the recommended methods give design loads

greater than the allowable loads for the usual

house constructions, there is something seriously wrong with the design loads, with the al- lowable loads, or with both.

Most of the houses in this country are con- ventional wood-frame construction. They have

successfully withstood the wind and snow loads

in most locations. Therefore, conventional woodframe houses were selected for this comparison. Comparisons were also made for other

constructions.

If the allowable load for a construction

greatly exceeds the design load, the construction is overdesigned for the particular house

and location. Some other construction which

has less material and will cost less is indicated.

2. Typical Houses

The Federal Housing Administration furnished architect's plans for House 22-D, one

story, and House E, two story, which were

believed to be typical of small houses which

had found wide acceptance. Both houses are conventional wood-frame construction.

House 22-D.—Elevations of this one-story

house are shown on flgure 49 and floor plans on flgures 50 and 51.

House E.—Elevations of this two-story house

are shown on figure 52 and floor plans on

figures 51 and 53. The values for elevation at midheight of

story, for House E, do not agree exactly with

those in tables 3, 4, and 5 because those in the

tables were scaled from the plans while those on figure 52 were computed from the story

heights given on the figure.

(a) Constructions

The dimensions and spacing of the studs and

joists on the plans are almost the same as those

for the conventional wood-frame constructions

for which the structural properties are re- ported in BMS25 and which are also described
110 Building Materials and Structures Repori

a= 16° 34 [16.561°)

Net mdfh 11.64

South Face

Net width Z3.I8

East Face

Scale = 1-0

Net width Z0.84

North Face

Areas

area ft'

a Door 16.68

b Do ZO.OI

Q) Louvre 2.5

Glass Size

@ Window 9\ll" 11.61 (D Do efx 6" 1.0

(i) Oo q\iz 1.5

33.5

Net width Z2.ll

West Face

Scale -s ~ 1-0

7771 |// /// .

Figure 49.

Elevations for one-story House 22-D.
Strength of Houses 111

North

6-0 I*— 14-0^ 6-0

t-t— //-//'H £y I "

IO-6^\

I ll\ I II

\ ' " I ' " 6-0 Vl-O^l-OA 6-0 - Z6'-0"-

South

Floor plan

- 1

o

^ I o

00

7T

YO.25'

to bearing

14.0

0.083

{ to bear,

f

0.083'

02

5

'-\ to bear.

12.0

26.0

ki

3- Load-bearing

- Non load- bearing

Door sizes

a, 2'-6\ 6-8"

b, 3-0"x6'-8" I II I It c, 2-0x6-6

i'-0"k6'-8"

r

0.333 walls

, ;^^| and partitions ^-^9.58 -^"X^ I o

^ /.67H h^l

CO

0.5 foundation

26.0

-10.5 \*]3.5

1.5 sq.

12.0-

15.67-

15.5-

\-\V-0.Z22

^•\\-a056\

0.056 ,

I 0.222 H

\^l02l'^\^ 15.22'-^

1 1 span n span fl \^I3.72'^\-IIJ2'-A^

D span D span D

\^ I3.6l'-*\\^ll.6l'-^ Scale r6 = l'-0

D span D span D first floor

H \-3.39' O

Attic floor

Figure 50.Floor 'plans for one-story House 22-D.
Building Materials and Structures Reports

b C

tv y

Firsf floor a b' c- Attic floor

d'

House 22-D, One Story a b c d

J \ Ai,

/77 ' ^

I

li _ JL.

1/7 / ;

I

1

I A m n

5 t a I u V wo

First floor Second floor

House E , Two Story

Figure 51.Floor plans for House 22-D and House E.

P 9

Attic floor
Strength of Houses 113

a= ZgUd' (29.8V

11

V-3.0'

b

2.58^ pr

CO

m5

20.08

Net width, 2nd sfory, 14.92

Net width. 1 5t storyJ4. 50

South Face

Areas

area

ft' Net width. 2nd story, 11.51

^ Net width, 1st story, 11.51'

East Face

Net width 2nd story, 14.92

Net width, Ist story, 14.0

North Face

1^

3 Z

7-7-7-7 3 t

I CO H

INet width. 2nd story, 11.51

^ Net width, Ist story, 11.59'

West Face

77 7 / / / 7/

Scale = 1-0

7777

FiGtJRE 52.Elevations for two-story House E.
114 Building Materials and Structures Reports

North

4-l\*-IO-ll~A4-

5-l0\-8-5-\5-10 ZO-I

South

First floor plan

1

1^

2.33 ^ ^

^ J.

-3.17

Z0.08

F'/rst floor

7.17 ^ 0 c'

-^5-\^^Y 0.056'

^9.67'-^ Ito bear — 4-0.056'

V 0.222' I 0.222^

to bear. I to bear.

00

' "I I II \ I II 5 -/0\^ 8-5 A 5 -10 20-1

1^ oo

Second floor plan

-7/7^ \-10.42-^

-If

II

-ii

\- 0.221

3./7 - ri

20.08

\-9.39'^

Scale Jo' 1-0 span

Second floor

20.08

\- 9.39^^10.14'-^

cr wCJ Attic floor

Load- bearing

Non load - bearing

Door sizes

a, l'-6"x6'-8" ' I II I II b, 3-0 X 1-0

c , 2-0 x6 -8

d, 2'-2"x6'-8"

i'-0"k6'-8"

0.5 foundation sill 0.333 walls and

partitions

P'iGURE 53.Floor plans for two-story House E.
Strength of Houses 115

briefly in table 16. Therefore, it was assumed

that these houses were the constructions in

BMS25 for which the allowable loads have

been determined.

Roofs.—Both roofs are taken as construction QC : 2- by 6-in. wood rafters spaced 24 in.

upper face, wood sheathing, paper, and wood

shingles; lower face, none; weight 4.6 lb/ft-.

Walls.—All the walls are taken as construction QA : 2- by 4-in. wood studs, spaced

16 in.; inside face, wood lath with plaster;

outside face, wood sheathing, paper, and woodbevel siding; weight 10.0 Ib/ft^.

Partitions.—All the partitions, both loadbearing and nonload-bearing, are taken as construction QD: 2- by 4-in. wood studs, spaced

16 in.; both faces, wood lath with plaster;

weight 12.8 \h/ff\

Floors.—According to the plans, the attic

floor (actually ceiling) in House 22-D is 2- by

6-in. wood joists, spaced 16 in. Presumably

there is no upper face and the lower face is lath with plaster. No floor of this construction was included in the program, therefore no

allowable load from laboratory data is available. For design, the weight is estimated as

8.0 Ib/ft^.

The attic floor in House E is also 2- by 6-in. wood joists, spaced 16 in. The upper face is matched flooring and the lower face is lath

with plaster. No floor of this construction was

included in the program, therefore no allowable load is available. For design, the weight

is estimated as 10.6 lb/ft-.

All the first- and second-story floors are taken

as floor QB, which was constructed of 2- by

8-in. wood joists, spaced 16 in. The upper face

consisted of wood subflooring, building paper,

and wood finish floor ; the lower face was wood

lath with plaster; weight 13.2 lb/ft-. Presumably the architect did not intend to have

plaster on the lower face of the first floor, but no conventional wood-frame floor without

plaster was included in the program.

(b) Locations

A few locations for the houses were selected

from the Wind Map and the Snow Map where

these loads are either about the greatest or

least in the United States. The locations are

Los Angeles Miami Portland

Calif. Fla. Maine

Basic velocity ib/ft^ ib/ft' ib/w pressure 5.0 33.0 11.9 Basic snow load. . .0.0 0.0 28.0

3. Utility Factor

The ratio of the allowable load for the construction to the design load for the particular

house and location is the utility factor. If it is less than one, the house is unsafe. If much

greater than one, the construction is inefficient

and other constructions having a smaller allowable load should be considered, taking into ac- count the price, weight, durability, thermal

conductivity, and fire resistance.

Because for economic reasons a given house

construction must be suitable for a range of

house design and locations, a construction may

by considered satisfactory provided the utility

factor is not less than one and does not exceed

two.

4. Direction for Design Loads

AND Fastenings

If a direction is stated with the numerical

value of a load, this direction is that in which

the load or the reaction acts on the floor, wall, or roof under consideration.

5. Relation of Allowable Transverse

Load to Span

An equivalent allowable transverse load for

the span in the house was computed from the

allowable loads in the tables which gave the same bending moment at midspan. These loads are inversely proportional to the squares of

the spans.

For spans less than the test span, the Building Materials and Structures report on the

construction was studied for indication of

shear failure. If shear failure is reported, the

computed load on the shorter span was decreased, if necessary, to a value for which the

shear does not exceed the shear in the specimens tested.

6. Roof

(a) Strength

The transverse strength of roofs under loads

applied to the lower face is not known because no roofs were tested under this loading. It is assumed that the transverse strength of roofs

is the same, whether loaded on the upper face or the lower face.

In addition, the racking strength of roofs is unknown because racking loads were not applied to roofs.

To the allowable transverse loads for roofs

given in table 24 was added the weight of the

roof because this weight also is included in

the design load.

The allowable transverse load for roof QC,

adjusted for span, is House 22-D, 50.5 Ib/ft^ on span 14.29 ft ; House E, 80.5 lb /ft- on span

11.32 ft. The design loads for roofs and fastenings, with utility factors, are given in table 27.
116 Building Materials and Structures Reports

Table 27.Design loads for roof and fastenings

[Loading condition A, south or north wind, windward openings, no snow; B, east or west wind, leeward openings, snow. TJ.F. =utility factor]

Design loads House 22-D, one-story House E, two-story Loading conditions Los Angeles | Miami | Portland Los Angeles | Miami | Portland LOADS ON ROOF

Transverse: Out.—

In Jb/ftl

Span

Parallel: Compression___ te//;*

Tension.

ft.

0.9

4.6

14. 29

92.3

13.8

U.F.

"ii.'o

29.

1

7.

14. 29

90.8

436. 3

U.F.

1.7 23.9

14. 29

513. 2

117.9

U.F.

"~2.l 1.65.7

11.32

81.0

18.0

U.F.

33.2

15.

1

11.32

130.8

362.4

U.F.

2.4 9.4 23.9

11.32

381.0

102.8

U.F. "3.4

A, with same load both slopes. B, with load acting on windward

slope. In Portland, snow on wind- ward or on both slopes.

B, with load acting on leeward slope adjacent to east or west wall. A, with load acting on both slopes adjacent to ridge. LOADS ON FASTENINGS

AT KIDCE Nor mal to ridge: Horizontal- Iblft Iblft Iblft Iblft Iblft Iblft Bearing 66.0 49.5 375.9 55. 1 82.8 262, B, with snow on both slopes in

1

Portland. Anchor.. 16.4 10.2 487.8 0.3 131.8 1. 2 20.7 7.6 417. 6 0.4 118.5 1.3 A.

Vertical

Key 5.3 21.8 35. 1 3.3 91.

1

1.3 9.3 18.6 61.1 2.8 79.4 2. 2 B.

Parallel to ridge: Key 0.0 0.0 0.0 0.0 0.0 0.0 Load always zero if symmetrical slop- ing roof. AT WALL

Normal to wall: Horizontal

Key, B, with snow on both slopes in Port- acts inward 71.5 5.6 85.3 4.7 388. 9 1.0 60. 7 6.6 119.4 3.4 275.3 1.5 land. Load acts to windward on

leeward slope. Key, acts outward 0.0 297. 2 1.4 63.

1

6.4 0.0 227.7 1.8 50. 1 8.0 A.

Vertical

B, with snow on both slopes in Port- Bearing, acts up 69.8 74.4 384.9 66.4 116.5 308. 1 land. Load acts on windward slope. Anchor, acts down... 0.9 386. 7 392. 5 0.9 97.4 3.6 7.2 48.3 369.6 0.9 96. 5 3.6 A, with same load on both slopes. Parallel to wall

Key 3.2 126. 0 21.0 19. 2 7. 6 53.0 3.6 112.0 23.8 16.9 8.6 46. 9 A, with same load on east and west

walls, acting to windward on both

slopes at wall.

Roof QC is safe for both houses in all three

locations. For Los Angeles and Portland, how^-

ever, the factor is so great that a less expensive

roof should be developed.

(6) Roof Fasteyiings

Because the rafters in roof QC are spaced

24 in., the values for load parallel to slope and

for fastenings must be doubled to obtain the

load on each rafter. The parallel loads are much less than allovi^able tensile and compressive loads on wood loaded parallel to the grain.

These 2- by 6-in. rafters have a nominal sectional area of 12 in-. In the past, many houses have been demolished by severe wind storms and hurricanes.

The opinion has been expressed from time to time that many of these failures would not

have occurred if the fastenings had been

stronger, particularly the roof fastenings.

The design loads for fastenings appear great.

Therefore, an attempt was made to determine

just how rafters usually are nailed at plate

and ridge in order that the strength of these

fastenings could be computed. This detail of

the construction is generally left to the contractor who follows trade practice.

{1) Fastening A

An unpublished survey of 100 houses in

different parts of the country showed that for

good practice (not the best practice) it is customary to toenail each rafter to the plate

with four 20-penny spikes (two on each side)

and toenail it to the ridge with two 10-penny

spikes through the upper edge into the ridge

board and opposite rafter.

{2) Fastening B

Another method of fastening is to toenail

rafters to plate with two 16-penny common

nails and two 10-penny nails, one large and

one small nail on each side. The ridge board

should be fastened to one rafter by two 8- or 10-penny nails through the board into the

rafter. The other rafter should be toenailed

with three 8- or 10-penny nails, one in the

upper edge and one in each side.

(3) Computed Strength of Fastenings

For each of these fastenings withdrawal re- sistance and lateral resistance was computed

in accordance with Design Specification for

Stress-Grade Lumber [35]. Fastenings A are
Strength of Houses 117

stronger than fastenings B, so the utility In Los Angeles, on the other hand, the fastenfactors were based on the B fastenings. The ings are excessively strong and other fastening

strengths of the B fastenings are at less cost is indicated. Laboratory tests on

specimens of a size simulating actual construcAt ridge, two-nail rafter: w .(.-^^ loaded just the way they are in a

Withdrawal resistance (anch^^^^^^ 312.9 ^ j^^^ development of cheapLateral resistance, acting either i i j j ^ j_ • j. i i, £

up or down (key) 231.2 er and better fastenings, not only for houses ot wood but, also for those of other materials.

"withdrawal resistance (anchor) 696.0 How thoroughly nailing is done in the field Lateral resistance, acting in, out, can only be ascertained by constant inspection.

or parallel to wall (key) 806.1

,. ^, „ i_i 1 J (c) utility Factor For All Roofs

In the specification, the allowable loads for ' ^ nails are less than one-fifth the load which For each of the roofs included in the program,

would be required to separate the pieces com- the allowable transverse load was computed, as

pletely. This allowable load was doubled to for roof QC, from the values in table 24, by in- obtain the design loads for these rafter fasten- eluding the weight and adjusting for the span

ings. in the houses. Also, the design transverse load

In Miami, for both houses, the anchors at for each house and location was computed.

ridge have only about one-third the required Finally, the utility factor for each roof was

strength. For fastenings A, also, the allowable obtained. The values are given in table 28.

load is less than half the design load for the Roof QC is included to facilitate comparison

fastening. with the other roofs.

Table 28.Utility factors for roofs

Allowable load House 22-D House E

Symbol Roof construction Span 14.29 ft Span 11.32 ft Los Angeles Miami Portland Los Angeles Miami Portland

BT Wood frame with plaster

lb/ft'».«. 1 IblfP52.8 U.F.

3.

U.F.

1. 4 U.F.1.

U.F.

4. 5 U.F.1.9 U.F.

1. 8 Do -- Hi7. 3 234.8 13.7 6.4 4. 9 20.

8.6 7. 9 DN Wood frame, no plaster 28. 2 44.9 5.4 1.0 1.

7. 1 1.4 1. 8 DO. - Do 70.0 111.6 12.

2. 5 2.8 16.3 3. 5 4. 4 DT. - Do ---- 125. 7 200.3 16. 6 4.8 4. 7 23.3 6. 6 7. 5 DU Do -- 200.0 318.7 25. 2 7.8 7.3 35.6 10.7 11. 7 QC. Do 50.5 80. 5 11.0 1. 7 2.

14.2 2. 4 3. 4 AK Sheet steel, no plaster . 138.9 221.4 13.8 5.9 4.7 20. 1 7.9 7. 6 AO - Do-._ 47.0 74.9 7.0 1.7 1.8 9. 7 2. 4 2. 9 CS Do- 118.9 189. 5 10. 7 5.3 3. 9 15. 8 7. 1 6. 3 cx Do 138.3 220. 4 16. 1 5. 5 5.0 23. 1 7. 5 7.9 DJ. Do 26. 6 42.3 9.3 0.9 1. 2 10. 6 1. 2 1.9

"Allowable load which does not crack the plaster on lower face. See table : ''Allowable load if cracks in plaster are acceptable.

7. Gables

(a.) Strength

The gables are wall QA although, presumably, it was not intended there should be plaster on the inside face. Taking the allowable trans- verse loads from table 26 if cracks in plaster are acceptable and adjusting for span (height

of gable at ridge), the allowable transverse

loads are: House 22-D House E

Ih/ft' lb/ft' Loaded, inside face 206.6 266.2 Loaded, outside face 110.2 142.0 For louvre in south gable of House E, two

studs are cut and the design wind load on this

gable is doubled adjacent to louvre. The louvre

in north gable of House E and both louvres of

House 22-D are inserted between studs and the

design wind load on these gables adjacent to louvre is not increased.

The design transverse loads on gables are given in table 29.

Table 29.

Design transverse load on gables

Gables

Design transverse load

Los Angeles Miami Portland HOUSE 22-D

South and north: Loaded, inside face.._ Loaded, outside face.

Iblft' 4.2

4.7

U.F.

49.2

23. 4

ibim

27.9

31.3

U.F.

7.4 3.5

lb/ft' 10.1 11.3

U.F.

20. 5 9.8 HOUSE E

South gable: Loaded, inside face,._ Loaded, outside face _ North gable: Loaded, inside face_.. Loaded, outside face _

9.4

10.8

4. 7 5.4

28.3

13.1

56.6

26.3

61.4

71.0

30.7

,35.5

4.3

2.0

8.7

4. 0

22.2

25. 6

11.

12. S

12.0

5.5

24.0

11.
118 Building Materials and Structures Reports

Except for south gable of House E, the total

transverse load decreases linearly from the

value below ridge to zero at east and west

walls. For constant transverse strength of

gable from east wall to west wall, the spacing

of studs should increase from ridge to wall.

Midway between ridge and wall the spacing of

studs should be four times the spacing at ridge

(16 in.) or 5 ft 4 in. Except for south gable of House E in Miami,

the gables have excessive strength as shown by

the utility factors which range up to 56.6 in

Los Angeles.

There is no compressive load or racking load on gables.

The reaction upward on bottom of gable vertically below ridge is: House 22-D, 63.9 lb/ft;

House E, 56.3 lb/ft. These reactions decrease

linearly to zero at east and west walls.

( b ) Fastenings

The design loads on fastenings for gables

are given in table 30.

Table 30.

Design loads on fastenings for gables

[Design loads for fastenings vertically below ridge, which decrease to zero at wall]

Gables Design loads on fastenings

Los Angeles Miami Portland HOUSE 22-D

South and north gables: Bearing

Key, acting normal to gable: At top . At bottom

Acting upActing inward

Acting outwardActing upActing inward

Acting outwardActing up

Acting inwardActing outward

Iblft63.9Iblft

12.0

13. 4

Iblft

13.4

15.0

Iblft63.9Iblft

79. 7

89. 1

Iblft

89,4

ino. 0

Iblft63.9Iblft

28.9

32.3

Iblft

32.3

36.

1

HOUSE E

South and north gables: Bearing

Key, acting normal to gable: South gable, at top . South gable, at bottom North gable, at top. . - . North gable, at bottom . .

56. 3

23.0 26.5

11. 5

13. 2

26.4 30.4

13. 2

15. 2

56.3

150.0

172.8

75.0

86. 4

173.4 199.9

86. 7 99.9

56.3

54. 2 62.5

27.

1

31. 2

62.5

72.

1

31.3 36.0

The louvre in south gable of House E is 2 ft 6 in. wide. According to the convention adopted

for transverse load on walls adjacent to openings, the design transverse load and design load on fastenings are zero for the width of the

louvre. The values for south gable apply from

edge of louvre outward for 1 ft 3 in. For the

remainder of the distance to wall, the design

loads for north gable apply.

8. Attic Floor

(a) House 22-D

(1 ) Vertical Loads

For House 22-D, the attic floor (figs. 50 and

51) has no applied floor load, therefore the

design loads for members and fastenings adjacent to scuttle, jkgf, and chimney, us, are not given here.

The reactions upward exerted by walls and

partitions below, due to weight of floor, are

East wall: ii./ft d'z 60.9 zd 46.9 East partition:

wq 60.4 qh 101.8

West partition:

c'v 101.8 vp 54.4 West wall:

a'n 40.9 na 54.9

These values, also, are the design loads for

fastenings (bearing) acting vertically.

{2) Horizontal Loads

The design loads acting horizontally are

Los Angeles Miami Portland

Tension

:

(East or west wind) 'h/lt ib/it Parallel to joists 63.0 29.3 a368.6 Normal to joists

At wall 15.4 101.7 36.7 Below ridge 28.9 190.9 68.8 Compression

:

(South or north wind)

Parallel to joists 0.0 194.9 26.2 Beam load: (East or west wind)

Along east or west wall 25.8 170.3 61.4 (South or north wind)

Along south or north wall At wall 17.2 113.2 40.8 Below ridge 50.0 330.0 119.0

* Snow both slopes.
Strength of Houses 119

The design tensile and compressive loads

parallel to joists, are also the design loads for

fastenings. These fastenings are keys acting

normal to both east and west walls. For tension, the keys act outward and for compression

inward.

For any direction of wind, the attic floor is a deep beam under horizontal loads applied to the windward edge, the leeward edge, or to both

edges. For east and west wind the floors in

both houses are simple beams under uniformly

distributed load supported by the racking re- sistance of south and north walls. For south

and north wind, these floors are continuous

beams over four supports in House 22-D and

three supports in House E. The supports are

the east and west walls and the partitions.

For south or north wind, the beam load is the same at east and west walls and increases linearly to a greater value vertically below ridge.

If the roof is a symmetrically sloping roof, the

greatest load is midway between walls.

Under beam load, the design loads for fastenings are those for roof and gable above and for

walls below.

(b) House E

(1) Vertical Loads

For House E, the attic floor (figs. 51 and 53)

has no applied load if the house is unoccupied

(empty) and has a floor load of 20 lb/ft- if occupied.

The reactions upward exerted by walls and

partitions below are

Unoccupied Occupied

Ih/lt lb/ft East wall, rd 53.7 155.1 Partition, qc 103.5 298.8 West wall, oa 49.8 143.7 The values if occupied are also the design

loads for bearing.

{2) Horizontal Loads

The design loads acting horizontally are

Los Angeles Miami Portland

Tension

(East or west wind) ib/H ib/ft ih/it Parallel to joists 44.7 14.0 "237.3 Normal to joists

At wall 18.3 120.8 43.6 Below ridge 31.4 207.8 74.7 Compression

(South or north wind)

Parallel to joists 0.0 104.0 5.5 Beam load: (East or west wind)

Along east or west wall 38.8 255.8 92.3 (South or north wind)

Along south or north wall At wall 22.2 146.6 52i.9 Below ridge 54.8 361.4 130.3

^ Snow both slopes.

(3) Framing Around Openings

If the house is occupied, there is an applied

load of 20 lb/ft- on the attic floor and the

design loads for the members and fastenings

adjacent to chimney and scuttle openings are

as follows:

Design load Span

Chimney: A

Floor, efba /6//f-'. . 20.0 6.95 Header,/?) lb /ft.. 106.3 2.33 Fastenings:

Header to joist, / and b lb.. 123.8 Scuttle

Floor, femi/i Ib/ff^.. 20.0 6.28 Floor, ni Ib/fV^.. 20.0 0.61 Header, mi lb/ft.. 96.1 2.50 Header,, nj lb/ft. . 9.3 2.50 Fastenings:

Header to joist, m and i lb. . 120.1 Header to joist, n and j lb . . 11.6 Each of the members ef and ha has a pointload of 123.8 lb at a distance of 2.44 ft from

bearing on partition ; each of members kn and

jh has two point-loads, one of 11.6 lb at a distance of 0.61 ft from bearing on partition and

the other of 120.1 lb at a distance of 3.11 ft from bearing.

Customarily, in house construction, header

nj would be the same size as header mi.

Probably that part of the point-loads carried

by the west wall and by the partition would be

distributed along the wall so that the effect of

the openings on the wall and partition would

be approximately the same as if there were no

opening.

9. House 22-D, One Story

(a) Wall

The design loads at top of wall are obtained

by combining the greatest reactions on roof,

gable, and attic floor above. On the wall these

loads act in the opposite direction.

{1) Compressive Load

East and west tvalls.—The design compressive load for east and west wall. House 22-D,

also for top edge of floor under these walls,

and top of east and west cellar walls are shown

in table 31.

Table 31.

Design compressive load for east and west walls, House 22-D

Los Angeles Miami Portland Acting Acting Acting Element down- Acting down- Acting down- Acting ward upward ward upward ward upward

(com- (ten- (com- (ten- (com- (ten- pression) sion) pression) sion) pression) sion1

East wall:

lb/ft lb/ft lb/ft lb/ft lb/ft Ibfff 261.

0.0 270.6 682.1 891.6 97.7 Top floor 208.2 .0 212.8 357.

523.3 5.

Top cellar wall. 518.6 .0 523.2 294.7 833.7 0.0 West wall: 249.4 .0 258.6 691. 5 879.6 108. S Top floor 200.0 .0 204.6 360. 7 515.1 11.6 Top cellar wall. 593. 5 .0 598.

270.7 90S. 6 0.0
120 Building Materials and Structures Reports

For walls, the values for loads acting downward are design loads in compression and for

loads acting upward are design loads in tension.

For top of floor and top of cellar wall, the

values for loads acting downward are design

loads for bearing and for loads acting upward,

they are design loads for anchors.

South and north tvalls.—The design compressive load for south and north walls, House

22-D, also for top edge of floor under these

walls, and top of south and north cellar walls are shown in table 32.

Table 32.

Design compressive load for south and north walls, House 22-D

Los Angeles Miami Portland

Element

Acting Acting Acting down- Acting down- Acting down- Acting ward upward ward upward ward upward

(com- (ten- (com- (ten- (com- (ten- pression) sion) pression) sion) pression) sion)

South wall:

lb/ft lb/ft lb/ft lb/ft lb/ft lb/ft 113.0 0.0 113.0 0.0 113.0 0.0 Top floor 141.3 .0 277.4 122.6 141.3 .0 Top cellar wall. 141.3 .0 309.5 154. 7 141.3 .0 North wall: 71.7 .0 71. 7 0.0 71.7 .0 Top floor 142.9 .0 292.4 134. 4 142.9 .0 Top cellar wall. 142.9 .0 325. 8 167.8 142. 9 .0 The design compressive load for south and

north walls is based only on weight of gable

above, therefore, it is the same for any location.

There never is any design tensile load on south

or north wall.

For each location, the design compressive

load downward for wall is greatest for east

wall.

The allowable compressive load for each wall

construction was taken from table 20 and,

making no adjustment for the actual story-wall

height, the utility factor was computed for the

greatest design load acting downward (east

wall). The utility factor for each wall construction for downward compressive load is given in table 33.

For east and west walls, construction QA has

sufficient compressive strength for the three

locations, but is overdesigned, the factor being

greater than ten for Los Angeles and Miami

and greater than three for Portland.

All the other wall constnictions have adequate compressive strength for House 22-D in

the three locations. Except for wall DK in

Portland, they all are overdesigned; the factor

ranging from 2.1 for wall BY in Portland to 405.5 for wall AT in Los Angeles.

The design compressive loads on south and

north walls are a small fraction of the loads on

east and west walls. Therefore, they have adequate strength, but the utility factors are very

much greater than the values in table 33. For

wall QA in any location, the factor for south

wall is 24.3 and for north wall 38.3. Insofar as compressive load only is concerned, an economical construction for south

and north walls should have a much smaller

allowable compressive load than that for east and west walls.

Tensile load on wall.—There are no tensile

design loads for south and north walls House

22-D. For Los Angeles, there are none for

east and west walls. For Portland, they are about one-eighth the design compressive loads

and for Miami, about two and one-half times

the design compressive load.

Because no tensile load was applied to walls,

the allowable tensile load is not known. It may

be estimated by the usual engineering methods.

For the wood and steel wall constructions, it seems probable that the allowable tensile load

is not less than the allowable compressive load,

but for masonry, the tensile properties of walls

should be investigated.

Attachment of plate to studs, wall QA.—In

wall QA (BMS25), two 16-penny common wire

nails passed through the lower member of the

double top plate into each stud and three 10-

penny nails per stud space passed through the

upper member of the plate into the lower

member.

The sheathing, applied diagonally, was at- tached to the upper member of top plate by two

8-penny nails per board, 8 inches wide (2.12

nails per foot width of wall) . Each board, also, was attached to lower member by one 8-penny

nail.All these nails are part of the wall construction and should not be confused with fastenings between roof and wall. The allowable

loads on these attachments are

lb /ft (a) Lower member of top plate to studs. .122.1

(b) Upper member to lower member 122.9

(c) Sheathing- to upper member . . .135.8

(d) Sheathing to lower member 67.9 Total allowable load, sum (b) and (c) . .258.7 The attachments in wall QA are ample for

Portland, factor 2.4, but very inadequate for

Miami, factor 0.4. Even if the allowable load is doubled, which sometimes is considered good

practice, these attachments still are inadequate

for Miami. Moreover, the load for (a) is computed for the nail penetrating the side grain,

not the end grain as in this wall. The Design

Specification [35] does not say that nails in

the end grain offer no resistance to withdrawal,

merely that, "800-D-l. The structural design

shall be such that nails are not loaded in withdrawal from end grain of wood."

Presumably the allowable load on these at- tachments should be (c)-|-(d), sheathing to members of plate, 203.7 lb/ft, which is adequate

for Portland, but not for Miami, factor 0.3. There would be no difficulty if the plate

could be attached to each stud by a four-foot
Strength of Houses 121

strip of box strapping over the plate, down each

edge of stud, and secured by a few strong nails,

(2) Transverse Load

The design transverse loads on wall House

22-D are

Los Angeles Miami Portland

Acting on: "'/I'' Inside face 7.59 50.09 18.06 Outside face 8.22 54.27 19.57

The allowable transverse load for each wall

construction was taken from table 20 and, after

adjusting for the actual span (story-wall

height), the utility factor was computed. The

factors are given in table 33.

For load on inside face, wall QA has enough

transverse strength for the three locations, but

not enough for load on outside face in Miami,

factor 0.4. For load on inside face, the utility

factor for each location is about four times the

factor for load on outside face, showing that

wall QA is an unbalanced design. For Los

Angeles and Portland, the factors for load on

inside face are excessive.

All wood walls, including wall QA, have

sufficient transverse strength for Los Angeles.

All wood walls, with the exception of wall DK,

have sufficient transverse strength for Portland. All wood walls, except BK, BL, BQ, BX,

and QA which had plaster on the inside faces

and walls CB, DK, DL, DQ, and DR, which had

no plaster have the necessary transverse

strength for Miami.

All the wood walls are greatly overdesigned

for Los Angeles, wall CN having a factor of

15.0. Except for walls DK, DL, DQ, and QA, all the wood walls are somewhat overdesigned for

Portland.

All the steel walls have enough transverse

strength, except DG and DH for Miami. Some

are overdesigned. The factor for wall CU for

Los Angeles is 28.2. All the reinforced brick and concrete walls

have sufficient transverse strength for each

location. The factor is 32.1 for wall BV in Los

Angeles.

Masonry walls BW, CZ, and DA have adequate transverse strength for the three locations, but other masonry walls tested are deficient in this respect, particularly for Miami.

Some engineers who have had wide experiience with small houses think many of these

masonry walls have withstood satisfactorily

the wind loads in most parts of this country.

Several explanations have been suggested for

this apparent discrepancy between the trans- verse strength found in the laboratory and that

found in service.

First: The transverse strength of masonry

walls may be greater if the load is uniformly

distributed than if it is applied at the quarter

points of the span.

Second: The transverse strength is greater,

the greater the compressive load on wall. There was no compressive load on wall when the

transverse load was applied in the laboratory.

For wood and steel walls, the transverse

strength does not depend greatly upon the compressive load on wall.

Third: Due to the sheltering effect of sur- rounding fences, trees, and buildings, the velocity pressure of the wind is much less than

the values for midheight of wall assumed in

this report.

A satisfactory explanation of this question can only be determined by further investigation.

Transverse fastenings.—The design loads

for fastenings are the same for top and bottom

of wall. They are keys acting normal to wall.

The design loads for transverse fastenings

are

Los Angeles Miami Portland

Fastenings: ib/jt ib/it ib/jt Acting inward 15.5 102.3 36.9 Acting outward. . .16.8 110.8 40.0

{3) Racking Load

The design racking loads for House 22-D

with wall QA and load-bearing partition QD

are

Los Angeles Miami Portland

South wall: w/ft u.F. ib/it vs. w/ft u.f. House wall 23.4 21.4 154.6 3.2 55.8 9.0 Cellar wall 29.2 ... 192.4 ... 69.4 ... East ivall: House wall 13.3 37.6 87.9 5.7 31.7 15.8 Cellar wall 20.9 ... 137.6 ... 49.6 ... North wall: House wall 21.4 23.4 141.2 3.6 50.9 9.8 Cellar wall 30.2 ... 199.5 ... 71.9 ... West luall

House wall 13.2 37.9 87.1 5.7 31.4 15.9 Cellar wall 21.0 ... 138.4 ... 49.9 ... The design racking load for house wall is also the design load for keys at top and bottom

of wall. The value for cellar wall is the design

load for keys. These keys act along the wall in

either direction.

The design racking load depends upon the

racking modulus, not only of the wall considered, but also the modulus of each of the other

walls and the load-bearing partitions.

The design racking loads for this house with

walls of other constructions were not computed,

therefore, the utility factors could not be obtained. It is thought that if the computations

had been made for the other constructions the

design racking load would not exceed 200 lb/ft.
122 Building Materials and Structures Reports

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124 Building Materials and Structures Reports

Except wood walls CB and DL, all the other

wall constructions have this strength, some

considerably more.

(&) Partition

(1) Compressive Load

For House 22-D in any location, the design

compressive load for both load-bearing partitions is 203.5 lb/ft acting downward. There

never is a tensile load on these partitions.

All the load-bearing partitions in the program are wood frame. The allowable compressive loads are given in table 21. The utility

factors are, partition CJ, gypsum-board faces,

7.4; CO, fiberboard faces, 16.2; QD, plaster

faces, 4.7. All these partitions have ample

strength but are overdesigned.

The design compressive loads (bearing) ex- erted by the two load-bearing partitions are

Los Angeles Miami Portland

Pwrtition: ib/ft ib/jt w/jt East 198.8 273.3 217.1 West 210.2 300.4 232.4

These partitions never exert upward loads.

The east partition exerts these loads on

south-north wood beam and the west partition

exerts them on floor below.

The east-west nonload-bearing partitions

exert design compressive loads on wood beam

and on east and west cellar walls. These are

point loads and are the same for any location.

On top of wood beam and east cellar wall

there are two point loads, each 650.1 lb, one

at 12 ft 6 in. from south wall and the other at 21 ft 5 in. On top of wood beam and west cellar wall

there are three point loads: 635.2 lb at 8 ft 7

in. from north wall, 713.0 lb at 14 ft 0 in., and

621. 2 lb at 20 ft 7 in.

{2) Racking Load

The design racking loads and utility factors

for partition QD in House 22-D (one-story) are

Los Angeles Miami Portland

Partition: ib/tt u.F. ib/jt u.f. ib/it u.f. East 8.9 42.7 58.6 6.5 21.1 18.0 West 8.9 42.7 58.9 6.5 21.2 17.9

Partition QD has ample racking strength for

House 22-D in any location but it wastes

material.

The allowable racking loads for the other

partitions are CJ, 480.0 and CO, 470.0 lb/ft. As

for the walls, it would be necessary to compute

the design racking loads to obtain the utility

factors. Probably they have sufficient racking

strength but are overdesigned.

Racking fastenings.—The values for design

racking load of partition are also the design

loads for fastenings at top and bottom of

partition.

(c) Floor

If required, the horizontal loads in the plane

of floor may be computed as illustrated for attic

floor. These loads are not given here.

{1) Transverse Load

When determining the transverse load on

floor, no account was taken of the weight of the

additional nonload-bearing partitions in walls

of closets. The weight of east-west nonload-bearing

partitions is transferred to east and west cellar

walls and to south-north wood beam. These

partitions are not loads on floor because they

are parallel to the joists in floor. If the weight of equipment in kitchen, utility

room, and bath exceeds 40 Ib/ft^, the excess is disregarded. In designing a house, these

weights should be included when computing

the design transverse load on floor. There are two south-north load-bearing partitions. The east partition is supported directly

by the south-north wood beam. The west partition exerts a line load on west floor normal to

joists in addition to the surface load. The

design transverse loads on portions of floor

shown in figure 51 are

Portion of floor Load Span

lb /ft' ft yzdc 40.0 11.67 imha 40.0 13.67 rumi 49.81 13.67 vwtir 53.64 13.67 The design transverse load on span 12 ft for

all floor constructions was obtained from table

23 and the allowable load for the two spans in

this house computed.

Four of the floors have plaster on the lower

face: AY and BC are sheet steel, and BS and

QB are wood frame. For these floors, the allowable load is taken from table 26 as value if cracks are pei-missible. The utility factors may

be taken from table 34. Floor QB has ample strength for each of the

floors but is stronger than necessary for the

east floor, yzdc.

If floor QB is satisfactory for west floor,

vivur, with the partition and its load from attic

floor, the question arises why a floor construction requiring less material would not be

acceptable for east floor, yzdc, having no partition load and on a shorter span? Certainly the

cost of the floor is a considerable portion of

the cost of a structure such as this house.
Strength of Houses 125

Table 34. —Utility factors for floors [The letters for portions of floor are shown on figure 51 for both houses]

House 22- D, one-story

First floor

House E, two-story Second floor First floor Portion of floor

Span (ft)

yzdc, east floor

11. 67

imba

13. 67

rumi

13. 67

vwur, west floor

13. 67

mnkj

3.36

tUST

6. 86

node

8. 70

Mca

9. 39

vwqn

13. 36

uvnin

13. 36

fl/ba

5. 34

strq

7.34

1 jneb

8. 58

iwjm

13. 25 Construction symbol WOOD

U.F. U.F. U.F. U.F. U.F. U.F. U.F. U.F. U.F. U.F. U.F. U.F. U.F. U.F. BS _ _ 6.5 4.7 3.8 3.5 15. 0 3.3 2. 0 1. 6 0. 6 0.6 32. 5 17. 0 12. 4 5. 0 CE 3.3 2.3 1.9 1. 7 41. 8 9. 9 6.

5. 2 2. 5 2.2 16.4 8. 6 6.3 2. 5 CL 5.

3. 7 2. 9 2. 7 63.3 15.9.3 8. 0 3.8 3. 4 25.0 13. 1 9.6 3. 9 DM 2. 6 1. 8 1. 5 1.4 32. 7 7.7 4. 7 4. 1 1. 9 1. 7 12.8 6.7 4.9 2. 0 DS.. 2. 7 1.9 1. 5 1. 4 34. 3 8.

4.9 4. 2 2. 1) 1.8 1.3. 4 7. 0 5. 1 2. 0 QB 9

- 3.9 2.7 2. 2 2.0 13. 1 2.9 1. 7 1.4 0.5 0.5 19. 6 10. 2 7.4 2. STEE L AG 10. 1 7.0 5. 6 6. 2 137. 2 31. 9 19.3 16. 4 7.4 6. 6 53. 5 27. 7 19. 9 7. 5 AJ 5. 2 3.7 3. 0 2.8 65.0 15. 4 9.5 8. 1 3.9 3.5 25. 6 13.4 9.8

9.8 4. 0 AN 9

3.7 2.7 2.

2.0 47.3 11. 2 6. 9 5. 9 2.8 2. 5 18.6 7. 1 2. AY 6.6 4. 7 3.8 3. 5 33. 4 7. 7 4. 6 3. 9 1. 7 1. 5 33. 2 17.4 12. 6 5. 1 BB 2.9 2. 0 1. 6 1. 5 36. 7 8.7 5.3 4. 5 2. 1 1. 9 14.4 7.5 5.5 2. 2 BC 2.8 I. 9 1. 6 1.4 29.7 6. 8 4.

3.5 1.5 1.4 14.7 7.6 5.5 2. 1 CR 7.5 5.4 4.3 4.0 92. 8 22. 1 13.6 11.7 5.6 5.0 36. 6 19.3 14.0 5. 7 CW 6.6 4.0 3.2 3.0 69. 7 16. 5 10. 2 8. 7 4. 2 3.7 27. 4 14.4 10. 5 4. 3

AS.. AW.

CT..

CY..

REINFORCED CONCRETE

1. 6 0.9 0. 8 0. 7 30. 2 6. 5 3.7 3.0 1.0 0.9 11. 4 5.6 3.8 1. 1 8.7 6.0 4.8 4. 5 119. 1 27.6 16.7 14. 1 6.3 5.6 46.4 23.9 17.2 6.4

6.5 4. 4 3.6 3.3 90. 8 20.9 12. 6 10.7 4. 7 4. 2 35.3 18. 2 13. 0 4. 8

6. 6 4. 5 3.6 3. 4 89. 2 20. 7 12. 5 10.6 4. 8 4.3 34.8 18.0 12. 9 4. 9 The architect made some provision for this

condition by specifying 2- by 8-in. joists for

both floors but spacing them 16 inches in east

floor and 12 inches in west floor. Of the other wood floors, all will safely support the occupants, but floor BS and CL are somewhat overdesigned for west floor. All the

wood floors have excessive strength for east

floor, the factor ranging from 2.6 for DM to

6.5 for BS.

The steel floors all have strength enough and

floors AN, BB, and BC have strength to spare.

For east floor, the factor ranges from 2.8 for

BC to 10.1 for AG.

Reinforced concrete floor, AS, is the only

floor that lacks the strength required for all floors. It has the strength for the east floor

but not for the other floors. The greatest

factor is 8.7 for east floor, AW.

In the ground floor of this house there are two openings, as shown on figure 51, "First

I floor," one for chimney (stvo) and the other for

access to cellar (jkgf) . The design loads for

members adjacent to these openings are

Floor ijfe.—Load along- ei and fj, 206.2 lb/ft. Header /.?', load 206.2 lb/ft, span 2.0 ft. Fastenings at / and j, 206.2 lb. Floor kmhg.—Load along gk and hm, 117.6 lb/ft. Header gk, load 117.6 lb/ft, span 2.0 ft. Fastenings at g and k, 117.6 lb. Beams eh and im.—Two point loads, 206.2 lb at 8.0 ft. from west wall and 117.6 lb at 9.5 ft, span 13.67 ft. Floor rson.—Load along nr and os, 228.2 lb/ft. Header os, load 228.2 lb/ft, span 1.5 ft. Fastenings at o and s, 171.2 lb. Floor tuqp.—Load along pt and qii, 95.5 lb/ft. Header pt, load 95,5 lb/ft from floor and 175.7

lb/ft from partition, total 271.2 lb/ft, span 1.5'ft. Fastenings at p and t, 203.4 lb.

Beams nq and ru.—Two point loads, 171.2 lb at 8.83

ft from west wall and 203.4 lb at 10.33 ft, span 13.67 ft. Where these members bear on west cellar

wall and on wood beam they exert point loads

acting downward.

Opposite openings, the load exerted by floor on wall and beam are redistributed locally between uniform and point loads without changing the magnitude appreciably. It does not seem necessary to consider the point loads due

to openings when designing cellar walls and

beams.

The south-north wood beam, 12 ft 0 in. from

east wall, is supported (as four simple beams)

on south and north cellar walls and on three

posts in cellar. Post A is 7 ft 9 in. from south

wall, post B is 16 ft 9 in., and post C is 25 ft 9 m. The design compressive (point) loads on

these walls and posts are

Los Angeles Miami Portland

lb lb lb South wall 3206.3 3423.7 3259 9 Post A 7371.2 7591.4 7425.4 Post B 9031.7 9062.3 9039.2 PostC 8146.5 8376.5 8203.2 North tvall 3347.0 3585.1 3405.7 There never are loads acting upward on

these supports. Neither is there anv racking

load.

This ends the evaluation and discussion of

design loads on the elements of House 22-D

in Los Angeles, Miami, and Portland.
126 Building Materials and Structures Reports

10. House E, Second Story

Much of the explanation and discussion for

House 22-D also applies to House E. This information is not repeated here.

(a) Wall

(1) Compressive Load

East and ivest walls.—The desi^ compressive load for east and west walls, second story

of House E are

Los Angeles Miami

Acting Acting downward Acting downward Acting (compres- upward (compres- upward

sion) (tension) sion) (tension)

lb/ft lb/ft lb/It Ib/tt East wall. .. .443.1 0.0 543.3 612.8 West wall .. .420.1 .0 520.3 624.2

Portland

Acting downward Acting

(compres- upward

sion) (tension)

Ib/tt lb /It 926.5 78.7 903.5 87.9

The design reactions at bottom of east and

west walls are

Los Angeles Miami Portland

Acting Acting Acting upward Acting upward Acting upward Acting (compres- downward (compres- downward (compres-downward

sion) (tension) sion) (tension) sion) (tension) lb/It Ib/tt East wall 301.8 0.0 West wall . . . 29^0.3 .0

lb/It lb/It 351.9 427.9

340.4 429.9

lb/It lb/It 543.5 31.9 532.0 18.1

These values are not the design loads for

fastenings because the wall is continuous past

the second floor. They are the design compressive and tensile loads in wall, particularly the

studs, just above the ribbon supporting the

second floor. South and north walls.—The design compressive loads for south and north walls are

Los Angeles Miami Portland

Acting Acting downward Acting downward

(compres- upward (compression) (tension) sion)

lb/It lb/It Ib/lt South wall.. . 80.0 0.0 80.0 North wall. . . 65.8 .0 65.8

Acting

Acting downward Acting upward (compres- upward

(tension) sion) (tension)

lb /It 0.0

.0

lb /It lb /It 80.0 0.0 65.8 .0 The design reactions at bottom of south and

north walls are

Los Angeles Miami Portland

Acting Acting Acting upward Acting upward Acting upward Acting (compres-downward (compres-downward (compres-downward

sion) (tension) sion) (tension) sion) (tension)

lb/It lb/It lb/It lb/It lb/It lb/It South wall. . .136.1 0.0 439.3 279.6 209.5 49.8 North wall. . .136.1 .0 439.3 279.6 209.5 49.8

These are design compressive and tensile

loads in wall above floor bearing.

The design compressive load on south and

north walls is the same for any location. It is about one-sixth the design compressive load

for east and west walls in Los Angeles and

only one-twelfth the value in Portland. Certainly, a less expensive construction for south

and north walls is indicated.

The east wall has the greatest design compressive load.

The utility factors for the greatest load act- ing downward are presented in table 33.

For wall QA, the factor ranges from 3.0 in

Portland to 6.2 in Los Angeles showing the construction is safe but much stronger than is desirable.

• All the walls of other constructions will

carry the compressive load but many of them

have much greater compressive strength than

is required for the second story of this house.

The factors show the trend

:

Smallest Largest

Type of wall utility Wall utility Wall

factor factor Wood 1.7 DK 14.9 DR

Sheet steel 2.5 CQ 25.5 AV

Reinforced brick and concrete 19.4 BV 239.2 AT

Masonry 2.8 CH 224.8 AA

All the smallest factors are for Portland and

the largest for Los Angeles.

{2) Transverse Load

For the second story walls of House E, the

design transverse loads are

Los Angeles Miami Portland

Acting on: w/it' ib/it' ib/ii' Inside face 9jO 59.4 21.4 Outside face 10.1 66.4 23.9

The utility factors for transverse load may

be taken from table 33.

Wall QA has the necessary transverse

strength for each location if loaded on the

inside face. If loaded on the outside face, the

strength is enough for Los Angeles but not

enough for Portland. For Miami, the strength

is about one-third the required value.

Of the 19 wood walls, six do not have the

necessary transverse strength if loaded on the

inside face and twelve if loaded on the outside

face.

The greatest factor is for wall CN, value

12.2. All the steel walls have enough transverse

strength except walls T>G and BH. For wall

CTJ, the factor is 22.9. None of the reinforced brick and concrete

walls are deficient in transverse strength. Wall

BY has the greatest factor, 26.0. Walls CZ and DA are the only masonry constructions complying with the requirements

for transverse strength.
Strength of Houses 127

Transverse fasteriings.—The design loads

for transverse fastenings are

Los Angeles Miami Portland

Fastenings: ib/fc ib/tc ib/jt Acting inward 18.7 123.7 44.6 Acting outward. .. .20.9 138.2 49.9

(5) Racking Load

For second story of House E, with wall QA

and partition QD, the design racking loads for

walls are

Los Angeles Miami Portland

House wall: w/ft u.f. w/it u.f. w/fc u.f. South wall. .. .29.4 17.0 194.4 2.6 70.1 7.1 East wall 17.1 29.2 112.9 4.4 40.7 12.3 North wall 29.4 17.0 194.4 2.6 70.1 7.1 West wall 16.9 29.6 111.7 4.5 40.3 12.4

These values are also design loads for keys.

If the design racking loads for the other

walls were computed and the greatest value

does not exceed 300 lb/ft, all the walls have

sufficient racking strength except wood walls

CB and DL, steel wall DH, and masonry wall

CH.

( b ) Partition

(1) Compressive Load

For second story of House E in any location,

the design compressive load for the one loadbearing partition is 597.6 lb/ft acting downward. The utility factors are, partition CJ 2.5,

CO 5.5, and QD 1.6. Partition QD has the necessary strength and

is economical for House E. The other partitions are also adequate as to strength but are uneconomical.

To determine the vertical loads at bottom of

partition, the south-north load-bearing partition in second story is taken as two independent partitions. The south portion of the partition extends from south wall of house to east- west wood beam 13 ft 8 in. from south wall.

The north portion of the partition extends from

wood beam to north wall of house.

Both partitions exert point loads acting

downward on house walls and wood beam.

These loads on first story are

Los Angeles Miami Portland

South pwrtition:

South wall, 9 ft 8 in. ib ib ib from west edge 2801.9 3236.4 2909.0 Wood beam 2801.9 3236.4 2909.0 North partition:

North wall, 10 ft 5 in. from east edge 3009.0 3264.8 3072.0 Wood beam 3009.0 3264.8 3072.0

{2) Racking Load

The design racking loads and utility factors

for second-story partition QD of House E are

Partition

Los Angeles

Ih/jc U.F. ..11.4 33.3

Miami

Ib/jt U.F. T5.2 5.1

Portland

U,/lt U.F. 27.1 14.0

(c) Floor

(1) Transverse Load

The design transverse loads on portions of

the second floor of House E shown in figure 51

are

Portion of floor Load Span

mnkj 40.0 3.36 tusr 40.0 6.86 node 40.0 8.70 hica 40.0 9.39 vwqn 40.0 13.36 uvnm 44.98 13.36 The portion uvnm has a line load exerted by

nonload-bearing partition normal to floor joists

in addition to the surface load.

For the floor constructions having plaster on the lower face, cracks are not permissible,

therefore, the allowable loads on a span of 12

ft are taken from table 23. For each floor construction, the allowable load was computed for

each of the five spans in this second floor. If the floors were tested on the 3.36- and

6.86-ft spans, it appears probable the floors

would fail by shear under transverse loads less than these computed values. However, no

results of tests are available.

The utility factors are available in table 34.

Floor QB has half the transverse strength

required for portion vtvqn and uvnm which have

the longest span. Also, floor BS has about half

the necessary strength.

All the other wood floors meet the strength

requirements. Floors DM and DS are eco- nomical in the use of material but for floor CL,

the factor is 3.8. On the shorter spans, all the wood floors

have excessive strength, the factor for floor

CL being 63.3. All the steel floors have enough transverse

strength. Floors AY, BB, and BC are eco- nomical for the longest spans. On the shortest

span, floor AG has a factor of 137.2.

Except reinforced concrete floor AS, all the

floors in this group have sufficient transverse

strength but are uneconomical on the shortest

span. The factor for floor AW is 119.1.
128 Building Materials and Structures Reports

11. House E, First Story

(a) Wall

(1) Compressive Load

The design compressive loads for first-story

walls, also for top of wall, top edge of first- story floor under walls, and top of cellar walls are given in table 35.

The values for top of first-story wall are the

design compressive and tensile loads in the

wall just below the ribbon supporting the

second floor. The utility factors for each wall construction appear in table 33. Wall QA has all the compressive strength

required for the first story and is economically

designed for Miami and Portland.

Table 35.—^Design compressive load for first-story walls of House E

Los Angeles Miami Portland Element Acting Acting Acting Acting Acting Acting downward upward downward upward downward upward

(compression) (tension) (compression) (tension) (compression) (tension)

Iblft Iblft Iblft Iblft Iblft Iblft South wall: 1015.4 0.0 1315. 2 234, 3 1099. 0 4,5 Top wall 507.7 .0 794, 7 234,3 564.8 4,5 Top floor 654.9 .0 1477. 6 771. 7 857. 6 151.7 Top cellar wall 1018. 2 .0 1901. 8 795.0 1236. 0 129.2 East wall: 603.6 .0 703. 7 682.9 1086.9 31.9 301.8 .0 351. 9 427.9 543. 5 31. 9

379. 5 .0 508. 1 776. 7 621. 2 90.9

379. 5 .0 558, 2 862.8 621. 2 109.0

Nortti wall: 732.0 .0 1142.7 325.8 833. 7 49.8

367. 6 .0 670, 7 279.6 440.9 49.8

530. 6 .0 1326, 2 780. 6 726, 7 181.0 Top cellar wall 769. 2 .0 1623. 2 814. 1 979, 7 170. 6 West wall: 1080.

1

.0 1180.3 682. 9 1563, 5 18.1 Top wall 540.

1

.0 590. 2 429.9 781.8 18,1 614.9 .0 665,0 787.9 856,6 116, 4

614. 9 . 0 665.0 838.6 856, 6 134, 7

All the other wood walls have adequate compressive strength. In general, the wood walls are not very greatly overdesigned. The greatest factor is 6.1 for wall DR in Los Angeles.

Steel walls have all the compressive strength

desired. Like the wood walls, they are not

greatly overdesigned. The factor for wall AV

is 10.5 in Los Angeles.

Reinforced brick and concrete walls, al- though adequate as to compressive strength,

tend to be overdesigned. Wall AT has a factor

of 98.1. The masonry walls have ample compressive

strength. The factors range from 1.7 for wall

CH in Portland to 92.2 for AA in Los Angeles.

Wall CH consists of flanged, reinforced-concrete slabs fastened to vertical steel plates with

steel bolts. There is an air space in the wall.

Wall AA is high-strength brick laid in cement

mortar with excellent workmanship. It is a

solid v/all. In addition to the distributed loads, there are point loads on top of first-story walls

exerted by partitions and floor joists in second

story.

On south wall at 9 ft 8 in. from west edge,

there is a design point load of 2801.9 lb for

Los Angeles, 3236.4 lb for Miami, and 2909.0

lb for Portland, all acting downward.

On north wall at 10 ft 5 in. from east edge,

there is a design point load of 3009.0 lb for

Los Angeles, 3264.8 lb for Miami, and 3072.0

lb for Portland, all acting downward.

Other point loads which are the same for any

location are : 423.7 lb on south wall at 3 ft 8 in. from west edge, 3186.0 lb on east wall at 13 ft 8 in. from south edge, 752.2 lb on west wall

at 5 ft 6 in. from north edge, and also 472.5 lb on the same wall at 15 ft 7 in. from north edge.

All these loads act downward.

Under all these point loads, there are additional compressive members (posts) in wall

extending from top of first-story wall through

first floor to top of cellar wall.

(2) Transverse Load

The design transverse loads on first-story

walls of House E are

Los Angeles Miami Portland

Acting on: ih/w ib/w ib/it' Inside face 7.9 52.2 18.8 Outside face 8.5 56.4 20.3

The utility factor for each wall construction

is listed in table 33. Wall QA is strong enough under transverse

loading except in Miami when loaded on outside face.

Of the other wood walls BK, BL, BQ, BX,

CB, DK, DL, DQ, and DR lack the strength re- quired for Miami. Wall DK is the only wall

lacking enough transverse strength for Portland. The factor is 13.4 for wall BH in Los

Angeles.

Each of the steel walls complies with the

transverse strength requirements except wall
Strength of Houses 129

DG (factor 0.8) and wall (factor 0.9) when

loaded on outside face in Miami.

The reinforced brick and concrete walls have

ample transverse strength, the factors ranging

from 1.4 for AR to 32.4 for BV.

Walls BW, CZ, and DA are the only masonry

walls which have the necessary transverse

strength and they are well designed from the

standpoint of efficient use of material because

the factor for each is less than two.

The design loads for transverse fastenings

are

Los Angeles Miami Portland

Fastenings: ib/ic ib/it ib/jt Acting inward 16.0 105.4 38.0 Acting outward 17.3 114.0 41.1

(6') Racking Load

For the first story of House E, with wall QA

and load-bearing partition QD, the design racking loads are:

Los Angeles Miami Portland

South ivall: Ib/tt V.F. lb/It U.F. lb/It U.F. House wall . . .53.0 9.4 349.9 1.4 126.2 4.0 Cellar wall . . .54.5 360.0 129.8 . . . East wall: House wall . . .39.1 12.8 258.2 1.9 93.1 5.4 Cellar wall . . .43.1 284.4 102.6 . . . North wall: House wall . . .52.0 9.6 343.5 1.5 123.9 4.0 Cellar wall . . .55.2 364.4 131.4 ... West %vall: House wall . .39.5 12.7 260.9 1.9 94.1 5.3 Cellar wall . . .42.8 282.2 101.8 . . . For Miami, wall QA is adequately and eco- nomically constructed for the first-story walls

of House E. For Portland, the racking

strength is five times the necessary strength,

and for Los Angeles, ten times.

(b) Partition

(1) Compressive Load

For the first story of House E, the design

compressive load on east-west load-bearing

partition is 1386.8 lb/ft acting downward.

The allowable compressive load on partition

QD is 960 lb/ft. The utility factor is 0.7 and

this partition is not strong enough.

For partition CJ, the factor is 1.1 and for

CO, 2.4, which indicates that these partitions

will carry the compressive load safely. In partition CJ, the material is efficiently used and

there is not much excess material in CO.

On the east-west load-bearing partition at 10 ft 5 in. from east wall, there is a design

point load on the top of partition of 5443.5 lb for Los Angeles, 5622.1 lb for Miami, and

5487.5 lb for Portland. At the intersection of

east-west and south-north partitions 9 ft 0 in. from east wall, there is a design point load of

3186.0 lb and at the edge of stair opening 16

ft 5 in. from east wall, the design point load is 811.4 lb. These point loads are the same for

any location.

Under all these point loads there are additional compressive members (posts) in the

partition extending from top of east-west partition to wood beam below.

On the south-north load-bearing partition,

first story of House E, there is no design compressive load.

(2) Racking Load ^ In House E, which has walls QA and loadbearing partitions QD, the design racking loads

for load-bearing partitions in first story are

Los Angeles Miami Portland

Partition: w/it u.f. ib/jt u.f. ib/ic u.f. East-west 35.1 10.8 231.8 1.6 83.6 4.5 South-north ...26.3 14.4 173.8 2.2 62.7 6.1

In Miami, partition QD has ample racking

strength for both east-west and south-north

first-story partitions. For House E in Portland, the strength is about five times the re- quired racking strength and in Los Angeles it is twelve times.

(c) Floor

(1) Transverse Load

For the first floor of House E in any location,

the design transverse loads on portions of floor

shown in figure 51 are

Portion of floor Load Span

Ib/h' It fgba 40.0 5.34 strq 40.0 7.34 jneb 40.0 8.58 tupo 40.0 13.25

For the utility factors, turn to table 34.

All the floor constructions have the transverse

strength for the first floor of House E. The

smaflest factor is 1.1 for floor AS, (reinforced

concrete) on 13.25-ft span and the largest is 53.5 for AG (steel) on 5.34-ft span.

Floor QB has twice the required transverse

strength on the longest span and 19.6 times on

the shortest span. Factors for other wood

floors run from 2.0 to 32.5, indicating excessive

material, particularly on the shorter spans.

For the steel and concrete floors, the over- design is more than for wood floors. Factors

are 2.1 to 53.5 for steel and 1.1 to 46.4 for concrete. On top of cellar wall, in addition to the point

loads from top of first-story walls, there are
130 Building Materials and Structures Reports

point loads from partitions and floor joists in

first story.

Point loads which are the same for any

location are 476.3 lb on south cellar wall 3 ft 8 in. from west edge, 2678.7 lb on east wall 13

ft 8 in. from south edge, 384.8 lb on north wall

at 16 ft 5 in. from east edge, and 820.4 lb and

364.4 lb on west wall at 5 ft 8 in. and 15 ft 0 in. from north edge. These loads all act downward.

On north wall (cellar), there is a design

point load at 9 ft 0 in. from east edge, the

magnitude of which depends upon the location.

The values are

^ Los Angeles Miami Portland

lb Uj lb Acting downward (bearing) .577.4 1517.7 809.2 Acting upward (anchor) 0.0 698.7 0.0 The east-west wood beam under first floor

13 ft 8 in. from south wall is supported as two

simple beams on east cellar wall and on two

posts in cellar. Post Z) is 9 ft 0 in. from east wall directly below intersection of the partitions in first story. Post £" is 16 ft 4 in. from

east wall at edge of stair opening.

The load on east cellar wall is given above.

It is the same value whatever the location of

the house.

The design point loads on posts are

Los Angeles Miami Portland

lb lb lb Post D 15520.5 16605.2 15787.8 Post E 6298.8 6333.0 6307.2

This ends the evaluation and discussion of

design loads on elements of House E in Los

Angeles, Calif. ; Miami, Fla. ; and Portland,

Maine.

XX. CONCLUSIONS

1. Wind Map

The wind map, showing the greatest velocity

pressure at each location, is an engineering

evaluation of Weather Bureau data. Further

study may show that changes are desirable but,

if the velocity pressures are increased greatly

for regions subject to severe storms, the

strength and consequently the cost of conventional houses will have to be increased over

present practice.

2. Velocity Pressure vs. Wind Load

The relation between velocity pressure and

wind load on roof and walls of a house are taken directly from the Final Report of Subcommittee 31, American Society of Civil Engineers [7]. This report gives the most reliable

data available at present.

There is need tor research on the relation of

observed velocity pressure to measured wind

load on walls and roof of typical houses.

3. Snow Map

The snow map, showing the greatest weight

of snow at each location, is an engineering deduction from Weather Bureau data.

Changes may be desirable but, if the values

for regions of heavy snowfall are increased

greatly, the strength of the usual house must

be increased. Experience seems to indicate

that many houses of conventional construction

have enough strength for the actual snow loads.

Research is needed to determine with

reasonable accuracy the relation between the

observed depth of snow on the ground and the

measured snow load on roofs of different slopes on both heated and unheated houses.

4. Engineering Principles

The assumptions on how load is transmitted

from one element of a house to another element

follow closely those for designing large steel- frame buildings. In the future, perhaps these

assumptions will be replaced by others more

acceptable to engineers and building officials. The application of an assumption is in

accordance with the well-established principles of engineering mechanics, especially the

essential principle of static equilibrium.

5. Design Load

Design loads for each element of a house

are very close estimates of the loads which it

is probable will be applied to the element

during the life of the house. The design loads

for each element of the two typical houses for

which plans are given can be compared with

the loads computed by the usual method. The

design loads given in this report are believed

to be less than the loads obtained by the usual

methods.

6. Typical Design Load

The design load of each element of a typical

one-story and a typical two-story house are given for three locations selected as representative of extreme wind and snow loads in

the United States.

7. Fastenings

The design loads include the design loads for

fastenings which in many houses appear far

from adequate. If more secure fastenings were

customary (at little increase in cost) fewer

houses would be damaged or wrecked by severe storms.
Strength of Houses 131

8. Tests for Strength

Methods for applying loads in the laboratory to house elements, simulating service loads, are described in BMS2. Tests on 100 house

constructions have been reported in the

Building Materials and Structui'es series. The

American Society for Testing Materials is preparing standards for testing building assemblies including the elements of houses. In

future, we may expect these methods to be

used by the housing industry when developing

constructions to have adequate strength at reasonable cost. Undoubtedly, building officials will require tests of new and unusual constructions.

9. Allowable Load

A very important question is the service load

which should be permitted on a given construction. At present, it is customary to compute the strength of the principal load-carrying members in the construction by the accepted

methods for structural design. This approach

is not entirely satisfactory for house constructions because tests show that the strength of

the completed wall or roof is at times much

greater than the strength of the structural

members.

For many of the newer constructions, such

as those of sheet metal and plywood, there

are no generally accepted methods for computing the strength. There is, however, no diffi- culty in loading them in the laboratory and

determining the strength.

10. Loads for 100 Constructions

Allowable load for 100 house constructions are given in this report. Experience may

indicate that some should be decreased and

others increased.

If the proposed allowable loads for conventional constructions are arbitrarily decreased

very much, the strength of the house, particularly in regions subject to severe storms,

would appear to be inadequate. However,

many conventional constructions have withstood successfully the loads in these regions.

11. Allowable Load vs. Design Load

The allowable load for each construction is compared with the design loads for the two

houses in the three locations. For some constructions, the allowable load is much less than the design load, showing that the house

is unsafe ; for other constructions, it is far too

great, indicating an unnecessary waste of

material and useless additional expense.

12. New Approach to House Design

General adoption of the approach to the

design of houses for strength discussed in this

publication, with such modifications as experi- ence shows are necessary, should result not

only in greater safety for occupants but through

economical use of materials should also result

in savings in cost of construction.

Appreciation is here expressed for the advice

and cooperation of the following specialists in

the preparation of this report

Wallace Ashby, U. S. Dept. of Agriculture, Washington, D. C. Dr. G. N. Brekke, National Bureau of Standards,

Washington, D. C. Ralph R. Britton, National Housing Agency, Washington, D. C. Prof. Charlee H. Buraside, (deceased) Columbia University, New York, N. Y. John H. Courtney, American Standards Association,

Washington, D. C. Dr. Hugh L. Dryden, National Bureau of Standards,

Washington, D. C. F. H. Frankland, consulting engineer, New York,

N. Y. (Formerly with American Institute of Steel Construction)

Frank J. Hanrahan, National Lumber Manufacturers

Association, Washington, D. C. Louis P. Harrison, U. S. Weather Bureau, Washingington, D. C. R. P. A. Johnson, Forest Products Laboratory, Madison, Wis.

Walter Junge, Federal Housing Administration,

Washington, D. C. Albert F. Magrum, U. S. Weather Bureau, Washington, D. C. William A. Mattice, U. S. Weather Bureau, Washington, D. C. Prof. Edward R. Maurer (retired), University of Wisconsin, Madison, Wis.

Frank W. Milliken, Federal Housing Administration,

Washington, D. C. Leon S. Moisseiff (deceased), consulting engineer,

New York, N. Y. Lewis E. Moore, consulting engineer, Boston, Mass. Herbert H. Moss (retired), Linde Air Products Co., New York, N. Y. Douglas E. Parsons, National Bureau of Standards,

Washington, D. C. Harry C. Plummer, Structural Clay Products Insti- tute, Washington, D. C. Chester L. Post, Public Buildings Administration,

Washington, D. C. James A. Schad, American Iron & Steel Institute,

New York, N. Y. Henry J. Schweim, Gypsum Association, Chicago, 111. Allen W. Stephens, (deceased), Public Buildings Administration, Washington, D. C. Lawrence M. Stevens, Green Lumber Company and

Prefabricated Home Manufacturers Institute Washington, D. C. George N. Thompson, National Bureau of Standards,

Washington, D. C. Clarence A. Willson, National Housing Agency,

Washington, D. C.
132 Building Materials and Structures Reports

Bert L. Wood, American Iron & Steel Institute, New

York, N. Y. H. B. Zachrison, Corps of Engineers, U. S. Army,

Washington, D. C.

Grateful acknowledg-ment is made to E. J. Schell and G. W. Shaw of the Building Practices and Specifications Section for their technical assistance in the preparation of drawings

and descriptions and to Louise D. C. Nobel and

Edith R. Meggers of the same section for their

painstaking efforts in reviewing editorially the

entire report.

XXI. SELECTED REFERENCES

[I] Minimum Live Loads Allowable for use in Design

of Buildings, Report of Building Code Committee, U. S. Dept. of Commerce, Elimination of Waste Series.

[2] Light Frame House Construction, Vocational Division Bull No. 145, Federal Security Agency,

U. S. Office of Education (1940).

[3] Robert Thurston Kent, Mechanical Engineers

Handbook, Power II, 11 ed. (1936).

[4] W. J. Humphreys, Physics of the Air, 3 ed. (1940)

.

[5] W. A. Mattice, A comparison between wind velocities as recorded by the Dines and Robinson

anemometers, Monthly Weather Review, 66, (August 1938).

[6] H. Ferrington, Wind loads on buildings, The

Structural Engineer, London, XXI, (December

1943), and XXII, (January 1944).

[7] Wind bracing in steel buildings, Final Report of Subcommittee No. 31, Committee on Steel of the Structural Division, Paper No. 2095, Trans. Am.

Soc. Civil Engineers, 105 (1940).

[8] Henry T. Bovey, Theory of Structures and

Strength of Materials (1900).

[9] William H. Burr and Myron S. Falk, Influence Lines for Bridges and Roofs (1908).

[10] J. B. Johnson, C. W. Bryan, and F. E. Turneaure,

The theory and practice of modern framed

structures, Stresses Pt. 1 (1910).

[II] Edgar Marburg, Framed structures and girders, Stresses, I, Pt. 1 (1911).

[12] George A. Hool, The Elements of Structures

(i9ia).

[13] Milo S. Ketchum, Structural Engineers' Handbook (1914).

[14] Clyde T. Morris, Designing and Detailing of Simple Steel Stnactures (1914).

[15] Horace R. Thayer, Structural Design, Simple

Structures II (1914).

[16] Milo S. Ketchum, The Design of Steel Mill Build- ings (1921).

[17] George A. Hool and W. S. Kinne, Steel and Timber Structures (1924).

[18] George Fillmore Swain, Structural Engineering

(1927).

[19] Thaddeus Merriman and Thos. H. Wiggin, Civil Engineers' Handbook, 5 ed. (1930).

[20] Leonard Church Urquhart and Charles Edward

O'Rourke, Stresses in Simple Structures

(1932).

[21] Charles M. SpofFord, The Story of Structures

(1939).

[22] American Standard Building Code Requirements

for Minimum Design Loads in Buildings and

Other Structures, A58.1-1945. Note—This draft is prepared for Committee consideration. It does not necessarily represent

the final conclusions of the committee.

[23] Milo S. Ketchum, Structural Engineers' Handbook 2 ed. (1918).

[24] Frank E. Kidder and Harry Parker, KidderParker Architects' and Builders' Handbook, 18

ed. (1936).

[25] Building Material Data, Bureau of Yards and

Docks, U. S. Navy Department (January 1, 1940) . [26] Henry Adams, Structural Design in Theory and

Practice, London, 2 ed. (1923).

[27] Forest Products Laboratory Report No. 1313,

Moisture content-strength adjustments for wood, U. S. Dept. of Agriculture, (December

1941) . [28] Edward C. Peck, Moisture content of wood in dwellings, U. S. Dept. of Agriculture, Circ. No.

239 (October 1932).

[29] Forest Products Laboratory Wood Handbook,

Basic information on wood as a material of construction with data for its use in design and

specifications, U. S. Dept. of Agriculture Publication (1935).

[30] L. J. Markwardt and T. R. C. Wilson, Strength

and related properties of ivoods grown in the United States, U. S. Dept. of Agriculture, Tech. Bull No. 479 (Sepetmber 1935).

[31] War Production Board National Emergency

Specifications for the Design, Fabrication and

Erection of Structural Steel for Buildings,

American Institute of Steel Construction, Inc. (Sept. 10, 1942).

[32] ASTM Standards 1944, Pt. 1, Metals, Designation: A7-42 Steel for bridges and buildings,

Am. Soc. for Testing Materials.

[33] ASTM Standards 1944, Pt. 1, Metals, Designation E6-36, Terms relating to methods of test- ting. Am. Soc. for Testing Materials.

[34] J. B. Johnson, Materials of Construction, John

Wiley & Sons, New York, N. Y., 3 ed. (1900).

[35] National Design Specification for Stress-Grade

Lumber and its Fastenings, National Lumber

Manufacturers Assn., Wa«hington, D. C. (1944).

Washington, April 30, 1947. a U. S. GOVERNMENT PRINTING OFFICE: 1948 743712
BUILDING MATERIALS AND STRUCTURES REPORTS

On request, the Superintendent of Documents, U. S. Government Printing Office, Washington 25, D.C., will place your name on a special mailing list to receive notices of new reports

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The following publications in this series are available by purchase from the

Superintendent of Documents at the prices indicated

BMSl Research on Building Materials and Structures for Use in Low-Cost Housing 10(* BMS2 Methods of Determining the Structural Properties of Low-Cost House Constructions lOc* BMS3 Suitability of Fiber Insulating Lath as a Plaster Base 15C BMS4 Accelerated Aging of Fiber Building Boards lOc' BMS5 Structural Properties of Six Masonry Wall Constructions * BMS6 Survey of Roofing Materials in the Southeastern States 15<t BMS7 Water Permeability of Masonry Walls* * BMS8 Methods of Investigation of Surface Treatment for Corrosion Protection of Steel . . lOt* BMS9 Structural Properties of the Insulated Steel Constmction Co.'s "Frameless-Steel"

Constructions for Walls, Partitions, Floors, and Roofs lOc* BMSlO Structural Properties of One of the "Keystone Beam Steel Floor" Constructions

Sponsored by the H. H. Robertson Co 10(^ BMSll Structural Properties of the Curren Fabrihome Corporation's "Fabrihome" Constructions for Walls and Partitions 10^ BMS12 Structural Properties of "Steelox" Constructions for Walls, Partitions, Floors, and

Roofs Sponsored by Steel Buildings, Inc 15(* BMS13 Properties of Some Fiber Building Boards of Current Manufacture lOt' BMS14 Indentation and Recovery of Low-Cost Floor Coverings 10^ BMS15 Structural Properties of "Wheeling Long-Span Steel Floor" Construction Sponsored

by the Wheeling Corrugating Co lOc* BMSl6 Structural Properties of a "Tilecrete" Floor Construction Sponsored by Tilecrete Floors, Inc 10(* BMS17 Sound Insulation of Wall and Floor Constructions 20(* Supplement to BMS17, Sound Insulation of Wall and Floor Constructions 5?^ Supplement No. 2 to BMS17, Sound Insulation of Wall and Floor Constructions 10^ BMS18 Structural Properties of "Pre-fab" Constructions for Walls, Partitions, and Floors,

Sponsored by the Harnischfeger Corporation 10(' BMS19 Preparation and Revision of Building Codes 15<^ BMS20 Structural Properties of "Twachtman" Constructions for Walls and Floors Sponsored by Connecticut Pre-Cast Buildings Corporation lOt* BMS21 Structural Properties of a Concrete-Block Cavity-Wall Construction Sponsored by

the National Concrete Masonry Association lOf* BMS22 Structural Properties of "Dun-Ti-Stone" Wall Construction Sponsored by the W. E. Dunn Manufacturing Co lOo* BMS23 Structural Properties of a Brick Cavity-Wall Construction Sponsored by the Brick

Manufacturers Association of New York, Inc lOc* BMS24 Structural Propei-ties of a Reinforced-Brick Wall Construction and a Brick-Tile Cavity-Wall Construction Sponsored by the Structural Clay Products Institute 15f* BMS25 Sti-uctural Properties of Conventional Wood-Frame Constructions for Walls, Partitions, Floors, and Roofs 15<' SMS26 Structural Properties of "Nelson Pre-Cast Concrete Foundation" Wall Construction

Sponsored by the Nelson Cement Stone Co., Inc 10(* BMS27 Structural Properties of "Bender Steel Home" Wall Construction Sponsored by the Bender Body Co

BMS28 Backflow Prevention in Over-Rim Water Supplies lOf* BMS29 Survey of Roofing Materials in the Northeastern States ISf* BMS30 Structural Properties of a Wood-Frame Wall Construction Sponsored by the Douglas Fir Plj'^vood Association 10c BMS31 Structural Properties of "Insulite" Wall and "Insulite" Partition Construction Sponsored by The Insulite Co *

* Out of print.
BUILDING MATERIALS AND STRUCTURES REPORTS

(Continued)

BMS32 Structural Properties of Two Brick-Concrete-Block "Wall Constructions and a Concrete-Block Wall Construction Sponsored by the National Concrete MasonryAssociation 15^ BMS33 Plastic Calking Materials 15(i( BMS34 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 1 15(^ BMS35 Stability of Sheathing Papers as Determined by Accelerated Aging * BMS36 Structural Properties of Wood-Frame Wall, Partition, Floor, and Roof Constructions

with "Red Stripe" Lath Sponsored by The Weston Paper and Manufacturing Co. 10<* BMS37 Sti-uctural Properties of "Palisade Homes" Constructions for Walls, Partitions, and

Floors, Sponsored by Palisade Homes * BMS38 Structural Properties of Two "Dunstone" Wall Constructions Sponsored by the W. E. Dunn Manufacturing Co 10^ BMS39 Structural Properties of a Wall Construction of "Pfeifer Units" Sponsored by the Wisconsin Units Co 10<J BMS40 Structural Properties of a Wall Construction of "Knap Concrete Wall Units" Sponsored by Knap America, Inc 10^ BMS41 Effect of Heating and Cooling on the Permeability of Masonry Walls * BMS42 Structural Properties of Wood-Frame Wall and Partition Constructions with

"Celotex" Insulating Boards Sponsored by The Celotex Corporation 15<* BMS43 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 2 15?^ BMS44 Surface Treatment of Steel Prior to Painting 10^ BMS45 Air Infiltration Through Windows 15^ BMS46 Structural Properties of "Scot-Bilt" Prefabricated Sheet-Steel Construction for Walls, Floors, and Roofs Sponsored by The Globe-Wernicke Co 10<}

BMS47 Structural Properties of Prefabricated Wood-Frame Construction for Walls, Partitions, and Floors Sponsored by American Houses, Inc 10<j; BMS48 Structural Properties of "Precision-Built" Frame Wall and Partition Constructions

Sponsored by the Homasote Co 15<f BMS49 Metallic Roofing for Low-Cost House Construction . 15^ BMS50 Stability of Fiber Building Boards as Determined by Accelerated Aging 10^ BMS51 Structural Properties of "Tilecrete Type A" Floor Construction Sponsored by the

Tilecrete Co 10^ BMS52 Effect of Ceiling Insulation Upon Summer Comfort 10«J BMS53 Structural Properties of a Masonry Wall Construction of "Munlock Dry Wall Brick"

Sponsored by the Munlock Engineering Co 10(? BMS54 Effect of Soot on the Rating of an Oil-Fired Heating Boiler 10<# BMS55 Effects of Wetting and Drying on the Permeability of Masonry Walls 10^ BMS56 A Survey of Humidities in Residences 10<t BMS57 Roofing in the United States—Results of a Questionnaire * BMS58 Strength of Soft-Soldered Joints in Copper Tubing 10^ BMS59 Properties of Adhesives for Floor Coverings 10^ BMS60 Strength, Absorption, and Resistance to Laboratory Freezing and Thawing of Build- ing Bricks Produced in the United States 15^ BMS61 Structural Properties of Two Nonreinforced Monolithic Concrete Wall Constructions 10^ BMS62 Structural Properties of a Precast Joist Concrete Floor Construction Sponsored by

the Portland Cement Association 10^ BMS63 Moisture Condensation in Building Walls 15^ BMS64 Solar Heating of Various Surfaces * BMS65 Methods of Estimating Loads in Plumbing Systems 15^ BMS66 Plumbing Manual * BMS67 Structural Properties of "Mu-Steel" Prefabricated Sheet-Steel Constructions for Walls, Partitions, Floor, and Roofs Sponsored by Herman A. Mugler 15^ BMS68 Performance Test for Floor Coverings for Use in Low-Cost Housing: Part 3 20«' BMS69 Stability of Fiber Sheathing Boards as Determined by Accelerated Aging 10^ BMS70 Asphalt-Prepared Roll Roofings and Shingles 20^* BMS71 Fire Tests of Wood- and Metal-Framed Partitions 204 BMS72 Sti'uctural Properties of "Precision-Built, Jr." Prefabricated Wood-Frame Wall

Construction Sponsored by the Homasote Co 104 BMS73 Indentation Characteristics of Floor Coverings 10^ BMS74 Structural and Heat-Transfer Properties of "U. S. S. Panelbilt" Prefabricated

Sheet-Steel Constructions for Walls, Partitions, and Roofs Sponsored by the Tennessee Coal, Iron & Railroad Co 154 BMS75 Survey of Roofing Materials in the North Central States 154 BMS76 Effect of Outdoor Exposure on the Water Permeability of Masonry Walls 15^ BMS77 Properties and Performance of Fiber Tile Boards 104 BMS78 Structural, Heat-Transfer, and Water-Permeability Properties of Five Earth-Wall

Constructions 254 BMS79 Water-Distributing Systems for Buildings 204 BMS80 Perforinance Test of Floor Coverings for Use in Low-Cost Housing: Part 4 154

* Out of print.
BUILDING MATERIALS AND STRUCTURES REPORTS

(Continued)

BMS81 Field Inspectors' Check List for Building Constructions (cloth cover, 5 x IV2 inches j 20<f BMS82 Water Permeability of Walls Built of Masonry Units 204 BMS83 Strength of Sleeve Joints in Copper Tubing Made With Various Lead-Base Solders 10<^ BMS84 Survey of Roofing Materials in the South Central States * BMS85 Dimensional Changes of Floor Coverings with Changes in Relative Humidity and

Temperature 104 BMS86 Structural, Heat-Transfer, and Water-Permeability Properties of "Speedbrik" Wall

Construction Sponsored by the General Shale Products Corporation 154 BMS87 A Method for Developing Specifications for Building Construction—Report of Subcommittee on Specifications of the Central Housing Committee on Research,

Design, and Construction 154 BMS88 Recommended Building Code Requirements for New Dwelling Construction With

Special Reference to War Housing * BMS89 Structural Properties of "Precision-Built, Jr." (Second Construction) Prefabricated

Wood-Frame Wall Construction Sponsored by the Homasote Co 154 BMS90 Structural Properties of "PHC" Prefabricated Wood-P'rame Constructions for Walls,

Floors, and Roofs Sponsored by the PHC Housing Corporation 154 BMS91 A Glossary of Housing Terms 154 BMS92 Fire-Resistance Classifications of Building Constructions 304

BMS93 Accumulation of Moisture in Walls of Frame Construction During Winter Exposure 10^ BMS94 Water Permeability and Weathering Resistance of Stucco-Faced, Gunite-Faced, and

"Knap Concrete-Unit" Walls 10^ BMS95 Tests of Cement-Water Paints and Other Waterproofings for Unit-Masonry Walls 154 BMS96 Pi'operties of a Porous Concrete of Cement and Uniform-Sized Gravel 104 BMS97 Experimental Dry-Wall Construction With Fiber Insulating Board 104 BMS98 Physical Properties of Terrazzo Aggregates 154 BMS99 Structural and Heat-Transfer Properties of "Multiple Box-Girder Plywood Panels"

for Walls, Floors, and Roofs 154 BMSlOO Relative Slipperiness of Floor and Deck Surfaces 104 BMSlOl Strength and Resistance to Corrosion of Ties for Cavity Walls 10^ BMS102 Painting Steel lO^f BMS103 Measurements of Heat Losses From Slab Floors 10^ BMS104 Structural Properties of Prefabricated Plywood Lightweight Construction for Walls, Partitions, Floors, and Roofs Sponsored by the Douglas Fir Plywood

Association 254

BMS105 Paint Manual $1.00

BMS106 Laboratory Observations of Condensation in Wall Specimens * BMS107 Building Code Requirements for New Dwelling Construction 204 BMS108 Temperature Distribution in a Test Bungalow With Various Heating Devices 10^ BMS109 Strength of Houses: Application of Engineering Principles to Structural Design. ..?1.50 BMSllO Paints for Exterior Masonry Walls 154

* Out of print.
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