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NBS BUILDING SCIENCE SERIES 62

AU Of

Evaluation of

Structural Properties of Masonry

in Existing Buildings
The Building Science Series

The Building Science Series disseminates technical information developed at the National Bureau of Standards on

building materials, components, systems, and whole structures. The Series presents research results, test methods, and performance criteria related to the structural and environmental functions and the durability and safety characteristics of building elements and systems. These publications, similar in style and content to the NBS Building Materials and Structures Reports (1938-59),

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please contact the Program Planning and Liaison Unit, Center for Building Technology, Institute for Applied

Technology, National Bureau of Standards, Washington, D.C. 20234.

[See mailing list announcement on last page]
«JiUMv>»'

Evaluation of Structural Properties

of Masonry in Existing Buildings

S. G. Fattal and L. E. Cattaneo

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Prepared for the

Office of Construction Veterans Administration Washington, D.C. 20420

(Supersedes NBSIR 74-520)

* ^

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary
Library of Congress Cataloging in Publication Data

Fattal, S. G. Evaluation of Structural Properties of Masonry in Existing

Buildings.

(NBS Building Science Series; 62)

Supt. of Docs. No.: C 13.29:2/62

1. Masonry—-Testing. 2. Walls—Testing. I. Cattaneo, L E., joint author. II. United States. Veterans 'Administration. Office of Construction. III. Title. IV. Series: United States. National Bureau

of Standards. Building Science Series; 62. TA 435.U58 No. 62 [TA670] 690'08s [691] 74-30411

National Bureau of Standards Building Science Series 62

Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 62, 127 pages (March 1977) CODEN: BSSNBV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1977

For sale by the Superintendent of Documents, U.S. Governn>ent Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13.29/2:62>. Stock No. 003-003-01738-8 Price $1.90

(Add 25 percent additional for other than U.S. mailing).
Table of Contents

Page

List of Symbols v

SI Conversion Units y^jj

Abstract 1

1. Introduction and Objective 1

2. Scope 2

3. Properties of Masonry 3

3.1 Types of Masonry Constituents and Wall Systems 3

3.2 Evaluation of Mechanical Properties 7 3.2.1 Sources of Information 7 3.2.2 Available Test Data 8 3.2.3 Interpretation of Available Data 9 3.2.4 Strength Reduction Factors 13

3.3 Sectional Properties ..... 15

3.3.1 Introduction 15

3.3.2 Walls Without Openings, In-Plane Loads 15

3.3.3 Walls with Openings, In-Plane Loads 16

3.3.4 Walls Without Openings, Out-of -Plane Loads 17

3.3.5 Walls With Openings, Out-of-Plane Loads 18

3.3.6 Filler Walls, In-Plane Loads 18

3.3.7 Filler Walls, Out-of-Plane Loads • • • 19

4. Test Methods 2 6

4 . 1 Scope 26

4.2 Types of Tests and Specimen Dimensions 26

4.2.1 Compression Specimens 27

4.2.2 Shear Specimens 27

4.2.3 Flexure Specimens 2 8

4.3 Sampling and Transportation 30

4.3.1 General Considerations 30

4.3.2 Equipment and Cutting Procedures 31

4.3.3 Transportation 31

4.4 Preparation of Specimens 32

4.4.1 General Requirements 32

4.4.2 Compression Specimens 32

4.4.3 Shear Specimens 33

4.4.4 Transversely Loaded Flexure Specimens 34

4.4.5 Eccentrically Loaded Flexure Specimens. . 35

iii
Table of Contents (cont'd..)

Page

4.5 Test Apparatus 35

4.5.1 Testing Machine 35

4.5.2 Deformation Gages 36

4.6 Testing Procedure 37

4.6.1 Compression Tests 37

4.6.2 Shear Tests 38

4.6.3 Flexure Tests, Transverse Loading 39

4.6.4 Flexure Tests, Eccentric Loading 39

4.7 Interpretation 41

4.7.1 Compression 41

4.7.2 Shear 42

4.7.3 Flexure, Transverse Loading 44

4.7.4 Flexure, Eccentric Loading 44

4.7.5 Capacity Reduction 51

4.8 Implementation 51

4.8.1 Sampling and Testing 51

4.8.2 Field Inspection 53

5. Strength of Masonry Walls 53

5.1 Introduction 53

5.2 Flexure-Compression Interaction 54

5.3 Compression-Shear Interaction 59

5.4 Flexure-Shear-Compression Interaction 61

5.5 Load-Deflection Relationship for Shear Walls 61

6. Summary and Conclusions 62

7. Acknowledgements 68

8. Bibliography 69

Appendix A, Seismic Investigation of a Masonry Building 74

Appendix B, Approximate Methods for Evaluating Natural Period of

Vibration of a Building 104

Appendix C, Description of Specimens and Test Setup for Data Listed

in Tables 3 . 1 to 3 . 3 . . . 113

iv
List of Symbols

A Cross- sectional area Area of flanges (frame columns) of concrete infilled frame

A^ Total (vertical) area of wall openings

A^ Area of transformed section of wall of more than one material

A^ Area (vertical) of wall without openings

A Cross sectional area of web (masonry wall) of infilled frame assembly

, w

a Coefficient greater than unity reflecting apparent increase in

flexural compressive strength

C Numerical constant related to fixity conditions at top and base of

wall

C Coefficient in moment amplification equation to account for the

influence of loading configuration

c Distance from centroidal axis to outermost tensile surface

^l'^2 Distances from centroidal axis to outermost fibers in maximum

compression

E Modulus of elasticity in compression normal to bed joint

Ej^ Modulus of elasticity of brick masonry

E^ Modulus of elasticity of concrete block masonry

E^/E^ Modulus of elasticity in direction normal to bed joint of masonry

on sides 1 and 2, respectively, of the centroidal axis

^kl'^k2 Kern eccentricities from centroidal axis of cross section in

directions 1 and 2, respectively

f Form factor dependent on geometry of cross section

f Compressive stress in masonry (allowable or calculated) m

f Nominal uniform shear stress on cross section

V

f^ Calculated average compressive stress on masonry cross section

f^ Compressive strength of masonry

f^ Tensile strength of masonry in flexure

f^j^,f^2 Flexural tensile strength of masonry on sides 1 and 2, respectively,

of centroidal axis.

f^ Shear strength of masonry

G Modulus of rigidity (shear modulus)

Gj^ Modulus of rigidity of brick masonry

G Modulus of ridigity of concrete block masonry

c V
g Gage length, or, gravitational acceleration

^l'^2 Coefficients used in moment capacity equations for out-of -plane

flexure of masonry walls

h Height of masonry, or, incremental length of discretized cantilever

beam model of a building

I Moment of inertia about a major principal axis of cross section

Moment of inertia contributed by concrete columns of infilled frame

assembly

I Moment of inertia contributed by solid masonry filler wall of

infilled frame assembly

k Effective height coefficient dependent on wall top and bottom fixity

conditions

L Horizontal length of masonry wall, or, length of cantilever beam

model of a building

M Internal resultant moment on wall cross section

M^^ In-plane moment capacity of wall about major principal axis

M^^ Out-of-plane moment capacity of wall about minor principal axis

M 2 Out-of-plane moment capacity of masonry cross section producing

maximum compressive stress in outer fibers on sides 1 and 2,

respectively

'^kl''^k2 Out-of-plane moment capacity of masonry cross section under com- pressive kern loading, producing maximum compressive stress in

outer fibers on sides 1 and 2, respectively

M Internal moment on a section induced by transverse loads and/or

eccentrically applied compressive loads

M^ Internal resultant (in-plane) moment on wall cross section

My Internal resultant (out-of-plane) moment on wall cross section

Lesser of the two moments at the top and bottom of a wall

' Greater of the two moments at the top and bottom of a wall

m Distributed mass per unit of length, or, ratio of compressive elastic

moduli of two materials comprising a composite section

P Compressive force on cross section

^kl'^k2 Compressive load capacity of masonry wall under load applied at

kern eccentricities e^^-j^ and ^1^2' J^sspectively

Axial load capacity of masonry wall

P Test load at failure of masonry specimens

up Circular natural frequency of a beam

Q Ratio of maximum static deflection due to shearing deformation to

that due to flexural deformation in a beam

vi
Distributed load on a beam

Out-of-plane flexural stiffness of masonry wall

Strength reduction factor, or, ratio of net area of mortar contact

to gross area of concrete block masonry

Vertical (surface) area of wall openings

Vertical (surface) area of wall without openings

Fundamental period of vibration

Thickness

Coefficient indicative of the influence of compression on in-plane

shear strength of masonry

Shear force parallel to bed joints, in plane of wall

Coefficient of variation

Average racking shear strength of masonry in the presence of

axial compressive load

Total weight of a building

Weight of bracket assembly in eccentric flexure test

Weight of masonry specimen above cracking plane in eccentric

flexure test

Width of small test specimen

Distance from centroid of cross section to point of load application

in eccentric flexure test

Distance from centroid of cross section to center of gravity of

bracket assembly in eccentric flexure test

Factor which accounts for moment amplification produced by eccentric

compressive load acting on transverse displacement of wall section

Average shear strain

Change in gage length in small test specimen, or, in-plane horizontal

deflection of top of wall relative to its base

Maximum static deflection of beam due to flexural deformation

Maximum static deflection of beam due to shear deformation

Average compressive strain in masonry

Slope of deflected beam

vii
SI Conversion Units

In view of present accepted practice in this technological area, U. S.

customary units of measurement have been used throughout this report. It

should be noted that the U. S. is a signatory to the General Conference on Weights and Measures which gave official status to the metric SI system of

units in 1960. Readers interested in making use of the coherent system of

SI units will find conversion factors in ASTM Standard Metric Practice Guide,

ASTM Designation E 380-72 (available from American Society for Testing and

Materials, 1916 Race Street, Philadelphia, Pennsylvania 19103). Conversion

factors for units used in this paper are:

Length

1 in = 0.0254* meter

1 ft = 0,3048* meter

Area

1 in^ = 6.4516* x 10 ^ meter^

1 ft^ = 9.2903 X 10"^ meter^

Force

1 lb (Ibf) = 4.44 8 newton

1 kip = 4448 newton

Pressure , Stress

1 psi = 6895 pascal

1 psf = 47.88 pascal

Moment

1 Ibf-ft = 1.3558 newton-meter

1 Ibf-in = 0.1130 newton-meter

* Exact Value

viii
Evaluation of Structural

Properties of Masonry

In Existing Buildings*

S. G. Fattal and L. E. Cattaneo

The current state of knowledge on the structural behavior of masonry is

synthesized to develop a methodology for the evaluation of the load capacity

of masonry walls in existing buildings. A procedure is described for direct

sampling and testing of specimens removed from masonry walls of buildings to

determine their strength in shear, flexure and compression, and to measure

their load-deformation characteristics. A documentation of strength and stiffness properties obtained from available test data is included to provide an alternate source of information on masonry of comparable construction. Sample

calculations of masonry building analysis for seismic forces are given in

Appendices A and B.

Key Words ; Analysis; compressive strength; deflection; design; flexural

strength; masonry walls; racking strength; seismic loading; shear strength;

shear wall; stiffness.

1. Introduction and Objective

After the disastrous San Fernando earthquake 1970, the Veterans Administration began implementing a program for the evaluation of VA hospital

buildings in accordance with seismic design requirements developed by the VA

Earthquake and Wind Forces Committee. This report relates to that task by

prescribing procedures for evaluating the strength and stiffness of unreinforced

masonry walls in existing buildings.

An initial literature survey indicated a scarcity of technical documentation dealing with old masonry construction. Among possible methods of data

acquisition on masonry properties considered during the course of this investigation, the direct method of sampling and testing small specimens removed from

existing masonry construction was found to be the most feasible. Information

acquired in this manner will be more representative of the masonry in the actual

construction than that acquired from tests on new specimens of similar construction or test logs taken during construction. Other techniques such as nondestructive testing by ultra-^-sonic devices, are relatively recent developments

which have not found widespread commercial application.

*Research sponsored by the Office of Construction, Veterans Administration,

Washington, D. C, 2042Q

1
The direct test method recommends three types of prism tests as a means of

acquiring the basic strength parameters of the masonry which they represent.

Procedures are described for sample extraction in the field, transportation

and test set-up including appropriate instrumentation for deformation measurements and interpretation of results.

This report also compiles and interprets test data on specimens which

represent some of the common types of masonry construction, using, as its

source, the results from three different experimental studies conducted at

the National Bureau of Standards [4,50,65].* Since this information is derived from tests of new specimens built under controlled environmental conditions, it will be less representative of existing masonry properties than

that obtained from sampled test specimens.

2. Scope

The report is organized into three main sections. Section 3 begins

with an introductory background information on common types of masonry

constituents and wall systems which are classified according to type of

construction or function in a building. This is followed by a documentation

and discussion of available test data on masonry strength in shear, compression

and flexure. For comparison, the tables also include allowable stress

values recommended by seven different codes and standards, three of which

are foreign. The last part of Section 3 specifies sectional properties

of masonry walls to be used for stress and stiffness calculations.

Section 4 presents sampling and test methods of masonry specimens

removed from existing construction. The three types of tests pertain to

the evaluation of masonry strength in flexural tension, shear and compression.

Interpretation of test results is discussed in Section 4.7.

Section 5 describes limit states of masonry walls under combined loading

conditions. Interaction relationships are discussed for ultimate strength

under combined compression and flexure, compression and shear, and under

simultaneous compression, shear and flexure. The load-def lection relationships

of shear walls are giyen in Section 5.5.

Appendix A consists of a numerical example employing the methodology

for seismic investigation of typical masonry structures. Appendix B describes

approximate methods for the evaluation of the natural period of a building.

Appendix C describes the test setup for data listed in Section 3.

*Nurnbers in brackets indicate references listed in the Bibliography.

2
3. Properties of Masonry

3.1 Types of Masonry Constituents and Wall Systems

Coittmon types of units used in masonry construction are clay and sandlime brick, concrete block and structural clay tile. Other products

such as natural building stone and adobe block are also utilized, although to

a much lesser extent.

Building and facing bricks are available in a variety of rectangular

sizes. The units are classified as hollov/ if the core area exceeds 25

per cent of the gross cross-sectional area, otherwise they are considered

as solid. Detailed descriptions and classification of various brick units can be found in ASTM designations C55, C62, C73, C216 and C652.

Concrete block masonry units are made of standard or lightweight concrete

aggregate. The hollow units which have more than 25 per cent coring are used for load-bearing as well as nonload-bearing masonry application including

non-structural partition walls, while solid blocks, with less than 2 5 per

cent core area are used in load-bearing type construction.

Detailed classifications of concrete masonry are found in ASTM degignations C90, C129, C140^ C145, and C331. Illustrations of various common shapes

and sizes of units, reproduced from reference [24] , are shown in figure

3.1. Clay tile masonry units which are similar to brick in composition

are available in a variety of sizes and sectional configuration and are generally characterized by relatively thin webs. The hollow construction

offers savings in matej:ial and weight and provides good insulation. Classifications of structural clay tiles are found in ASTM designations C34, C56

,

and C112. Common shapes of clay tile units, reproduced from reference [26], are illustrated in figure 3,2.

In conventional practice, masonry units are identified by their nominal

diminsions. For instance,^ the actual dimensions of an 8x8xl6-in concrete

block are 7-5/8x7-5/8x15-5/8 in. Hollow tile masonry units are laid with

the cores, either horizontal (figure 3.2) or vertical. In the text of this

report, masonry units are identified by their nominal dimensions while calculation of sectional properties for strength and stiffness determination are based on the actual dimensions of the units.

Masonry units are laid in mortar which acts as their binding agent.

Full mortar bedding is usually employed between courses of masonry built

3
with solid units. For hollow units, use of face shell mortar bedding is a

coitimon practice. As strength properties of masonry walls are usually governed

by the type of mortar used, the latter is specified when strength values

are prescribed (see tables 3.1 to 3.3),

Prevailing types of mortar are cement-lime -sand and masonry cement-sand

mortar. Different proportions of the constituents in these types will

produce different strength properties. Standard mortar designations, namely,

types M, S, N, 0 and K are used for the appropriate mortar identification

according to the range of constituent proportions, by volume, specified

in ASTM designation C270. Types M, S, and N are commonly used for structural

masonry applications. Types M or S are specified for high flexural strength

requirements. Various other specifications for mortar and mortar ingredients

are found in ASTM designations C5, C91, C109, CllO, C144, C150, C157, and

C207.

Masonry walls are classified according to type of construction and

intended use in a building. A few of the common ones are identified here

for purposes of convenient reference. A single-wythe wall has one masonry

unit in its thickness. A multi-wythe wall has several masonry units in

its thickness. In a composite wall construction, at least one of the wythes

is built with masonry units and/or mortar dissimilar from those in the

neighboring wythes. Multi-wythe walls without cavity are laid contiguously

with the spaces between the wythes, called collar joints , filled with mortar

or grout. To insure monolithic action of the assembly, additional bonding

is effected by the use of header units or metal ties laid horizontally

in bed mortar across the wythes at periodic intervals throughout the height

of the wall. A cayity wall is identified by a continuous vertical air

space between any two adjacent wythes and by metal ties laid as in composite

wall construction and connecting the two wall sections flanking this space.

Reinforced masonry walls built with solid units are reinforced by placing

steel bars, vertically and/or longitudinally, as needed, in the space between

consecutive wythes and by grouting this space. In hollow block walls, vertical

reinforcement may be placed as needed, through the hollow cores which are then

grouted.

The following types of masonry walls are identified by their intended

function in a building. A load bearing wall supports the vertical loads

above it in addition to its own weight, with or without the aid of a vertical

load-carrying space frame. A non-load bearing wall supports no vertical

loads other than its own weight. A shear wall resists planar forces which

are primarily induced by exterior horizontal loads acting on a building.

A curtain wall is a non-load bearing wall, built outside the building frame

4
8x8x8 8x8x8 8x8x16

SASH LINTEL STANDARD LINTEL BOND BEAM

4x8x16 4x8x8 4x8x12

STANDARD HALF CORNER

Figwce 3.1 - Concrete masonry units

5
Figure S.2 - Clay tile masonry units.

6
and not entirely supported at each floor. A panel wall is a non-load bearing

exterior wall supported at each story level. A partition is a non-load

bearing interior space divider which will function as a shear wall unless

isolated along three edges from the rest of the structure. Veneer is the

exterior masonry layer of a two-layer wall system, connected to the interior

layer and/or to the primary load-supporting structure by horizontal ties.

Veneer is generally designed to be non-load bearing. A pier is a masonry

wall segment flanked by two adjacent openings or by an opening and the

vertical edge of the wall. A lintel is a wall segment above an opening.

A masonry filler wall or infill wall designates a wall fully enclosed

within a structural frame or bounded between two columns and wholly supported

at each story level. Filler walls are generally designed to be non-load

bearing although they may participate in supporting a portion of the gravity

loads depending on the construction sequence used in the field. Because

of their confinement and high in-plane lateral stiffness relative to the

surrounding frame, filler walls function as shear walls by absorbing the

major portion of the horizontal thrust on a building before cracking. The

presence of filler walls significantly alters the structural behavior and

response of the primary frame under earthquake loads

.

3.2 Evaluation of structural Properties

3.2.1 Sources of Information

To investigate the capacity of masonry elements in existing buildings

a knowledge about their structural properties must be acquired. The following

are possible sources of such information listed in the order of decreasing

reliability.

1. Data from samples of actual construction.

2. Test logs of samples taken during construction.

3. Available data from comparable construction.

4. Data from new specimens of the same material construction.

5. Assumed properties from code tables.

Information acquired fjrom source 1 would be much more desirable than information

from any of the other sources listed above since the masonry samples represent

actual conditions in the existing structures at the time of the survey.

However, the reliability of results will depend upon the method employed

in the removal of samples and the implementation of the appropriate specifications

for testing procedures. Consequently, Section 4 has been dedicated in its

7
entirety to the detailed discussion of a methodology describing field sampling

procedures from actual construction, test methods, and interpretation of

test results to evaluate strength and stiffness properties of masonry.

Infomation from test logs of samples taken during actual construction

will probably seldom be available. Likewise, available test data on old

masonry is too limited to be of practical significance for purposes of this

study. By contrast, a substantial amount of experimental research data on

new masonry construction exists to justify its consideration as a possible

source for predicting the structural behavior of masonry walls in existing

buildings. To assist the user in his search of documented test data on masonry, a comprehensive list of selected references has been included in

the Bibliography.

In Section 3.2.2 and 3.2.3, available data from recent masonry tests

conducted at the National Bureau of Standards have been compiled and interpreted in order to provide a supplementary source of information on the

procedure that can be used to reduce and synthesize experimental data on masonry from existing publications.

3.2.2 Available Test Data

This section is devoted to the documentation of strength and stiffness

properties obtained from available test data for masonry comparable in

construction to masonry in existing structures. The objective is to provide

an alternate source of information to assist in approximate and reasonably

conservative evaluation of properties. This information is compiled in

tables 3.1 to 3.5 which contain entries of the following masonry propertiies

derived from selected documents referenced in the text.

f^ = compressive strength

f^ = shear strength

v

^ f^ = tensile strength in flexure

E = modulus of elasticity

G = modulus of rigidity (shear modulus)

The format of the first three tables permits comparisons, in each case,

(Table 3.1: Compression; Table 3.2: Flexural Tension; Table 3.3: Racking

Shear) of the given property as determined by tests, both of small specimens

and large specimens (when available) of various types of masonry construction.

Other pertinent physical data are also tabulated together with values of

maximum allowable stresses as determined by seven different recognized design

8
recommendations or codes (listed under column headings J[45], K[46], L[13],

M[48] , N[47] , 0[25], and P[23] in the tables). Table 3.4 gives a summary of

allowable stresses in masonry recommended by the same codes and standards.

The source of strength properties listed in tables 3.1 to 3.3 is a bank

of data obtained from tests conducted at the National Bureau of Standards

and reported in three different publications [4, 50, 65], These data are interpreted in the following section.

A summary of background information on the specimens and testing

procedures is given in Appendix C for ready reference. For a thorough

description of the test setups the reader should consult the specified

references mentioned in the text.

3.2.3 Interpretation of Available Data

The entries in Tables 3.1 to 3.3 are samplings of experimentally

determined strengths of brick and concrete block masonry, together with

values of maximum allowable stresses included by various masonry standards

building codes. To assist in the judicious use of this data as an alternate

source of infonaation on masonry, some additional explanation is provided

in this and the next sections.

In the calculation of cross sectional area of hollow concrete block,

distinction is made between gross area, net solid area, and net area of

mortar contact. Representative values [4, 65] of net solid areas are

52% for 8x8xl6-in two-cell hollow concrete block and 72% for 4x8xl6-in

three-cell hollow concrete block. The same references indicate that mortar

contact area in the 8x8xl6-in block is in the range of 38 to 46% of the

gross area; and in the 4x8xl6'-in block, approximately 67% or more.

Note that in tables 3.1 to 3.3 the mortar used in the masonry specimens

was often classified as Type N or S , approximately, in order to limit tabulation

of mortar types to ASTM C270 designations. As indicated in ASTM C270, a given type of mortar includes different combinations of materials and their

proportions. This method of classification is herein adopted for simple

reference to various building codes which use the same classification.

a. Compressive Strength Properties CTable 3.1)

Determination of compressive strength (f^) is far from being a widely

standardized proceduj^e. Methods of test recommended by various organizations

9
[13, 23, 25, 45, 46, 47, 48] and ASTM Designation E447, differ for the same type of masonry as well as for different types. Methods employing

small specimens recommended by various sources prescribe different heightto-thickness ratios (h/t) of specimens as the standard parameter (correction

factor = 1.0) for correcting tested strength of specimens of other (h/t)

ratios. Compressive strengths in columns F and H are tabulated as recorded

by the referenced investigator for the size specimen shown in columns

E and G. Applications of any (h/t) correction factor to values in column

F are reflected, when applicable, in the values of columns J through P.

Allowable stresses in columns J through P are, in general, obtained from

the various sources (UBC , etc.) using recommended relationships between

allowable compressive stress (f^ ) , and ultimate compressive strength (fj^) • This relationship is usually given as a table or in mathematical form. In some instances tabular correlation is given directly between strength

of the masonry units used and allowable masonry compressive strength.

Such tabulations usually give separate values of allowable stress for

masonry containing different types of mortars, and for different conditions

of workmanship (i.e., with or without inspection).

Whenever small specimen compressive strength was available (listed in

column F) , allowable stresses were derived using the respective procedures

of each organization (columns J thorugh P) . It is to be noted that, in some

cases, values of allowable compressive stress recommended by a given

organization are intended for only one particular kind of masonry (e.g. brick

masonry only, coliimn K; or concrete block masonry only, column L) . When

small specimen strength was not available, derived allowable stresses were based on assumed masonry strength obtained from the particular organization's

table which correlated assumed compressive strengths with strength of units

and types of mortar.

Due to scatter in the data of Table 3.1 a detailed treatment of the values

appears impractical. However, an overall appraisal of the itemized strengths

and allowable stresses leads to some inferences. It appears that, whether

derived from available prism strengths or from tabular "assumed" strengths

based on a knowledge of masonry unit and mortar, the more conservative

allowable stresses (excluding U.B.C.) are about 1/4 to 1/5 of the masonry

wall strengths.

This fact is reflected in the often encountered (0.2f') used as an m

alternate expression for calculating the allowable compressive stress in

10
some of the cited codes and seems to strengthen the correlation of these

quantities. Lacking more specific values of ^^^) r Table 3.1 could provide

reasonably close values of compressive strength of types of masonry construction comparable to those being examined. Alternately, if some information

about the unit and the mortar is available, Ca conservative assumption could

be made of the mortar type) an "assumed" (f^) could be selected from a suitable

code tabulation as in BIA [45] ; or, if this procedure leads to an allowable

stress value, as in UBC I45J , it could be projected to (f^l^) by application

of a conservative factor Ca value of 4 is suggested)

.

b. Flexural Tensile Strength Properties (Table 3,2)

Flexural tensile strength normal to the bed joints is relatively low in

unreinforced masonry. It is dependent on the bond between mortar and units,

and easily affected by poor workmanship and other causes of bond disturbance

(cracks). Since the prescriptive codes and standards on masonry [13,23,25,

45,46,47,48] are based on working stress design, tensile strength values are generally specified by reference to commentaries or other supporting research

documentation [70,80J. Recommended maximum allowable tensile stresses' in

flexure are presented by all of the organizations named, usually as specific

values, dependent on types of mortar and workmanship.

Added to the features of tensile strength mentioned above (low value,

sensitivity of bond to workmanship, development of bond cracks) , the data

presented in Table 3.2 include anomalies which raise doubt: (a) wide range

of experimental strengths for equal specimens, (b) proximity of experimental

strengths to allowable stresses, and (c) experimental values less than

allowable values. These facts rule against putting too much reliance on the

limited tensile strength data. The cored brick in items 1 and 2 show a somewhat higher strength, although not conclusively. It is to be noted

that the Australian and British codes [23, 25] recommend that, in general,

no reliance be placed on masonry tensile strength. However, attention

is directed to other circumstances which affect the apparent tensile strength

of masonry, such as the influence of vertical loads on the transverse flexural

strength of walls.

c. Shear Strength Properties (Table 3.3)

Racking shear strength of masonry is also comparatively low and

frequently dependent on the bond between mortar and units. Test Method

ASTM E-72 includes a procedure for determining the racking shear strength

of an 8-ft square panel (a method which does not lend itself to economy or

11
production). Other methods which show promise are discussed in Section 4.

For allowable shear stresses, the same organizations make reference to

experimentally determined shear strength in recommending maximum allowable

shear stress values as a function of Cf) or as specific values dependent m

on types of masonry unit, mortar, and workmanship. Based on the background

data available so far CBIA Commentary [46] ) allowable shear stresses for

brick represent approximately a safety factor of 4.

To the extent to which it can be applied, lower experimental values

from Table 3.3 are proposed as shear strengths for comparable types of

masonry. For other brick masonry it is suggested that it be identified

conservatively by unit and mortar in the BIA Standard to establish an assumed

(f ') , and that the shear strength be taken as 2^. It is also suggested

that other concrete block masonry be likewise identified for selection of

an allowable shear stress in the NCMA. Standard (A.C.I. Standard and Canadian

Code are similar) ; a conservative assumption that these allowable shear

stresses also contain a safety factor of at least 2 would provide interim

shearing strengths taken as twice the allowable shear stress. As in flexure,

the apparent racking strength may be increased by superimposed vertical

loads

.

d. Modulus of Elasticity E, and Modulus of Rigidity G, CTable 3.5)

There are no standard procedures for the experimental evaluation of

elastic properties of masonry. The modulus of elasticity may be determined

from measurements obtained from compression tests of masonry prisms while the

modulus of rigidity Cor shear modulus) may be obtained from measurements of

diagonal deformations in racking test specimens. These and other test methods

and procedures are discussed in Section 4.

In the absence of sufficient data (in the references of tables 3.1 to 3.3)

to give a satisfactory indication of modulus values or, as a substitute of

tests of field samples (section 4), reference is made to the information in

table 3.5 of various organizations. With the exception of the Australian

values, consistency of the recommended relationships for E and for G is

noteworthy, particularly since their sources represent interests in different

types of masonry (brick only, concrete block only, and, brick or block).

Plummer [63J points out tha,t for a given group of brick data alone the equation E = 1000 f passes through a range bounded by E = 1200 f and E = 700 f '

;

the observed values of E varied from 2,652,000 psi to 473,000 psi and (f^)

values between 2800 psi and 600 psi Cnot respectively) . With such dispersion

and the desire to be conservative kept in mind, the equations E = 1000 f^

12
and G = 400 subject to the inspection limitations prescribed (Sect. 3.2.4),

are suggested for adoption.

3.2.4 Strength Reduction Factors

The strength reduction factors discussed in this section are applicable

to strength estimates obtained from sources other than direct tests of sampled

specimens removed from existing buildings. The strength reduction factors

for the latter case are specified in Section 4.7.5.

a. Workmanship

One of the major factors influencing the strength of masonry elements

in a structure is the quality of workmanship exercised at the time of

construction. In recognition of the importance of quality control in the

field, various codes (UBC, BIA, NCMA, etc.) make a clear distinction

between inspected and uninspected construction by prescribing different

allowable values for masonry design. Sometimes different values are also

prescribed for the elastic moduli, as in UBC and BIA (table 3.5) and for

lateral support requirements of walls, as in BIA. Values of compressive

stress reduction factors specified for masonry construction without inspection

range from about 0.67 by BIA to 0.50 by UBC and NCMA.

For the purpose of evaluating the strength of masonry walls in existing

structures it is proposed that a reduction factor of 2/3 be introduced for

construction without inspection, to be applied as a multiplier to the mean

values of the strength properties (f), Cf") and (f') obtained from sources m V t

other than tests of specimens directly obtained from the existing structure

under investigation. In cases where no information is available about inspection, the masonry should be assumed to have been constructed without inspection.

b. Variability

Another important factor inherent in masonry construction is the

variability of strength exhibited between test specimens of seemingly

"identical" construction. Depending on the type of test, type of masonry

and size of specimen used, the scatter of test results may be considerable

even for tests conducted under controlled laboratory conditions. In an actual construction where the controlled environmental conditions of a laboratory are absent, a wider scatter may reasonably be expected in the

strength of masonry walla built with the same constituents.

13
In the absence of any docixmentation for the quantitative prescription

of strength variability of masonry construction according to type, a variability factor of 2/3 is tentatively proposed for use as a reduction

factor to be applied as a multiplier to the mean values of strength properties

available from sources (e.g.: tables 3.1 to 3.3) other than direct tests

of specimens obtained from the existing structure under investigation,

to account for the effect of variability.

c. Size of Specimen

There is a difference in masonry strength attributable to size that

should be recognized when interpreting available test data as a source of such

information. Usually small prisms will develop greater strength than fullscale walls. Test experience indicates the difference may be as much as 50

per cent for flexure specimens and between 10 to 30 percent for shear and

compression specimens, depending primarily on the size of test prisms used.

In the absence of a better quantitative documentation of test strength

as a function of size, a reduction factor of 2/3 is proposed to be applied

as a multiplier to the mean values of strength properties derived from prism

tests available from sources other than direct tests of specimens obtained

from existing masonry contruction, to account for size effects. Data from

full-scale wall tests need not be so reduced. Attention is drawn to the

fact that tables 3.1 to 3.3 compile test data for prisms as well as large-seal

specimens

.

d. Peak Loading History

Exposure to cyclic or peak loads induced by earthquakes and other natural

disasters could adversely effect the masonry strength in existing buildings.

Site measurements recorded after an earthquake frequently show an increase

in the natural period of a building which tends to become more compliant as a result of internal structural damage. Such damage is not always obvious

enough to detect by visual means, nor is it possible to assess total

level of damage attributable to cumulative exposure to past disaster loads.

In recognition of the detrimental effect of disaster loads on masonry,

it is proposed that a reduction factor of 2/3 be applied as a multiplier

to the mean values of masonry strength data derived from sources other than

direct testing of specimens removed from existing construction.

14
The total reduction factor to be applied as a multiplier to mean masonry

strength property values, is the product of applicable reduction factors

specified in items (a) through (d) above.

3.3 Sectional Properties

3.3.1 Introduction

Sectional properties are used in combination with elastic constants to

determine the distribution of lateral and gravity loads to the appropriate

elements in a building and to convert element forces to stress values for

comparison with available capacity. The sectional properties of masonry

are specified in accordance with loading condition (in-plane or out-ofplane) , type of masonry units (hollow or solid) , type of construction (single

wythe , double wythe or cavity), confinement condition (with or without frame

enclosure), and configuration of openings.

3.3.2 Walls Without Openings, In-Plane Loads

Sectional properties will be specified by reference to the wall shown

in figure (3.3). For the specified in-plane loads the sectional properties

are defined in terms of length L and thickness t as follows

A = Lt

where

A = cross sectional area

I = moment of inertia

t = effective thickness of the wall as defined below

For single-wythe solid masonry unit construction, t is the actual wall

thickness. For two-wythe masonry construction consisting of solid units of

identical material composition, t is the sum of the thicknesses of the two

units plus the thickness of the collar joint. For single wythe hollow concrete

block construction t is governed by the net area of mortar bedding. Representative thickness values are: 40% of the gross thickness for 8x8x16-

in and 6x8xl6-in 2-cell hollow block, 67% of the gross thickness for

4x8xl6-in 3-cell hollow concrete block [4, 65, 75]. For two-wythe hollow

block construction of the same material composition, t is the sum of computed

thicknesses of the two blocks plus the thickness of the collar joint.

(3.1)

(3.2)

15
For two-wythe construction of masonry units of dissimilar composition the

principle of transformed section may be applied to obtain the equivalent

thickness t. For instance, the effective thickness t of a solid brick wall

equivalent to a wall consisting of a brick wythe and a hollow concrete block

wythe is obtained from the equations:

^ = ^b + ^VV (^-3)

^ = ^b ^ ^VS^ (^-^^

where

t, = thickness of brick unit b

t = gross thickness of concrete block unit

c r = ratio of net area of mortar contact to gross area

: of concrete block

E /E, = ratio of block-to-brick elastic moduli

c b

G /G, = ratio of block-to-brick shear moduli

c b

Equations (3.3) and (3.4) apply in calculations involving in-plane

flexural and shearing deformations, respectively. For cavity wall construction

of masonry units of dissimilar composition the effective thickness is determined according to the method used for two-wythe construction of masonry units

of dissimilar composition if loading and boundary conditions induce identical

deformations in both wythes . Otherwise the thickness of each wythe is determined separately assuming no interaction exists between the two wythes. Cavity

walls of identical material composition are treated in the same manner.

3.3.3 Walls With Openings, In-Plane Loads

A masonry wall with openings is characterized by different sectional

properties throughout its height. Depending on the type of calculation

involved, a distinction will be made in the method for determining the effective thickness t.

a. For calculations used in determining the distribution of seismic shear

forces on a building, the equivalent thickness of a wall without openings as described in section 3.3.2 is further reduced by a factor which is the ratio

of the net (area of openings deducted) to gross wall areas. In equation

form,

t = t^ (1 - ^) (3.5)

16
where

t = equivalent thickness of wall with openings

t^ = effective thickness of the same wall without openings

(s=solid)

= total (vertical) area of openings

A = gross (vertical) surface area of solid wall.

b. For stress and stiffness calculations of individual walls the equivalent

thickness is calculated according to the procedures described in section 3.3.2.

Depending on the geometry and arrangement of the openings , the wall is divided

into a number of piers (as illustrated in figure 3.5) . The wall is then

analyzed according to principles of equilibrium, deformation compatibility and

constitutive relations applied to the individual piers.

3.3.4 Walls Without Openings, Out-of -Plane Loads

Sectional properties will be specified by reference to figure 3.1. The

sectional properties of walls of single or multi-wythe integral construction

having the same material composition and built with solid masonry units

is determined according to the equations:

A = Lt (3.6)

(3.7)

where

;

A = area of horizontal cross section of wall

I = moment of inertia of horizontal cross section of wall

about minor principal axis

L = width of the wall cross-section

t = actual total thickness of wall

For single wythe construction of hollow sectional configuration equation

(3.6) applies except t designates the equivalent thickness as determined by

the net mortar bed area (Section 3.3.2) . The moment of inertia may

be conservatively (but closely) estimated by considering only the face shell

areas to be effective in flexure. In equation form,

I = ^ [t^ - (t - 2t^)^] (3.8)

where

t = out-to-out thickness of masonry unit

t^ = thickness of one face shell or flange.

17
For two-wythe construction of hollow masonry units of the same composition, the area is the sum of the areas of the individual wythes as specified

above. The centroid of the section and the moment of inertia about this

centroid may be conservatively estimated by considering only the face shell areas of the individual wythes to be effective in flexure.

For two-wythe construction of masonry units of dissimilar composition

the area may be determined according to the principles of transformed sections.

In equation form,

^t = ^ ^ ^ ^V^) (^-^^

where

:

- area of the transformed section of wall equivalent in

composition to material 1 = area of material 1 = area of material 2 E„/E = ratio of elastic moduli of material 2 to material 1

The moment of inertia is determined on the basis of the same transformed

section. However, care must be exercised to preserve the relative positions

of different sections within the actual (gross) thickness of the wall

(transformation applies to sectional widths) . For cavity walls the sectional

properties of each individual wythe is determined as above, on the basis of

uncoupled action.

3.3.5 Walls With Openings, Out-of -Plane Loads

Openings will change the net sectional configuration at various levels

through the height of the wall. The sectional properties are determined at

each such level in the manner specified for walls without openings. This will

allow the wall to be treated as a non-prismatic beam spanning in the vertical

direction and loaded transversely. The procedure for calculating critical

flexural stresses is used in the sample problem in Appendix A.

3.3.6 Filler Walls, In-Plane Loads

To assess the contribution of masonry filler walls to the sectional

properties of concrete infilled frames subjected to in-plane loads the

effective wall thickness obtained by the procedures described in subsections

3.3.2 and 3.3.3 is further modified by the ratio of masonry-to-concrete

elastic moduli if the infill wall is mechanically connected to the surrounding

18
frame in a manner that will insure integral action of the assembly. The

result is an I-shaped figure the sectional properties of which can be readily

obtained (figure 3,4).

To account for the influence of openings in filler walls, the sectional

properties of the transformed I-section are reduced as follows:

S

A = A„ + A^ (1 - (3.10)

t w Sw

S

I = + I (1 - ^) (3.11)

r w b

, w where

A^ = area of flanges (frame columns)

A = transformed area of solid web

w

= vertical (surface) area of wall openings

S = vertical (surface) area of solid wall w

= the portion of moment of inertia contributed by the

concrete columns

I = the portion of moment of inertia contributed by the w • transformed solid web

Equations (3.10) and (3.11) are considered to be sufficiently accurate

for calculating the distribution of lateral seismic forces in a structure.

For stress and stiffness calculations the frame-wall assembly is divided

into several piers according to its geometry and location of openings as shown in figure 3.6.

For the case where the infill wall is not mechanically attached to

the surrounding frame, sectional properties of the uncracked infill wall

are determined as in Sections 3.3.2 and 3.3.3, by treating it independently

of the frame

.

3.3.7 Filler Walls, Out-of-Plane Loads

The procedures prescribed in sections 3.3.4 and 3.3.5 are also applicabl

to filler walls. The need to transform the wall section into equivalent

concrete does not arise in this case since the only function of the frame is

to provide a certain amount of rotational constraint at the frame-wall interface.

19
20


Table 3.4 - Summary of code -veaormended allowable streaaes in masonry.

Source

Material

Re ferenced

Axial Compressive

psi

Flexural Tensile

psi

Shear

psi

UBC Brick

Block

250-100

175-50

20-7.5

12-5

20-7.5

12-5

BIA Brick 0.2 fm 36-19 80 - 0 . 5\/f^ ' m

NCMA Block 0.2 fm 39-16 34-23

ACI Block 0.2 £•m 39-16 34-23

TANADA Brick

Block

0.25 fm 0.2 fm

36-28

36-16

50 -yJP

34-23

BRITAIN Brick

Block

900-43

725-72

10-0 15

AUSTRALIA Brick 0.75 f

1 10-0 15

Table 3.5 - Code-reoommended values of modulus of elasticity (E) and

modulus of rigidity (G)

.

Source

Material

Referenced

E , psi G, psi

Inspection No Inspect

.

Inspection No Inspect.

UBC Brick

or Block

lOOOf

m

<3 X 10^

500£'

m <1.5 X 10^

400f

m <1.2 X 10^

200f

m <0.6 X 10^

BIA Brick

lOOOf

m

<3 X 10^

lOOOf

m

<2 X 10^

400f

m <1.2 X 10^

400f

m

<0 .8 X 10^

NCMA Block

lOOOf

m

<3 X 10^

400f

m

<1.2 X 10^

ACI Block

lOOOf

m

<2 X 10^

400f

m

<0 .8 X 10^

CANADA

Brick

or Block

lOOOf

m

<3 X 10^

400f

m

<1.2 X 10^

BRITAIN Brick

or Block

4000fj^ (allow.)*

AUSTRALIA Brick

562 fm

<2.4 X 10^

225f

m

<1 X 10^

*£, - code basic (i.e., allowable) compressive stress

23
ELEVATION

SECTION

Figure 3.3 - Masonry wall without openings.

M ^CONCRETE FRAME

V

MASONRY

INFILL

d

ELEVATION

•m 94

TRANSFORMED SECTION

= transformed wall thickness

t - masonry wall thickness

Figure 3.4 - Infilled frame without openings.
®

_4A

ELEVATION

B A_ ® —A B

U .1

SECTION A-A I 1 4

Xg

^

I ^^CENTROIDAL AXES

SECTION B-B C : I—

I

Figure 3.5 - Masonry wall with openings.

.M

ELEVATION

©

CONCRETE FRAME

MASONRY INFILL

® ®

®

®

-Ab

TRANSFORMED

SECTION A-A Qui

transformed

Section b-b LF

CENTROIDAL AXES

tfn > transformed wall thickness

t masonry wall thickness

Figure 3.6 - Infilled frame with openings.

25
4. Test Methods

4.1 Scope

The structural investigation of masonry buildings linder seismic loads

discussed in Appendix A makes use of the following properties of masonry wall

sections

:

f^ = strength under axial compression

f^ = shear strength under diagonal compression

f^ = tensile strength under out-of-plane flexure

E = modulus of elasticity

and G = modulus of rigidity

The direct manner of acquiring this information on masonry in existing

structures is to remove wall samples and to conduct appropriate laboratory

tests using specimens prepared from these samples.

In Sections 4.2 to 4.6, procedures are prescribed for sample extraction

and transportation, specimen preparation and execution of tests in a laboratory. Section 4.7 describes the interpretation of test results to determine

compressive, shear and flexural strength as well as load-deformation properties.

Guidelines for the implementation of the testing program are discussed in

Section 4.8. With regard to standard test methods which relate to the types

of tests herein prescribed, the following sources are cited: ASTM Designation

E44 7-72, Standard Methods of Tests for Compressive Strength of Masonry Assemblages, ASTM Designation E-518*, Standard Method of Test for Flexural Bond

Strength of Masonry, and ASTM Designation E-519*, Standard Method of Test

for Diagonal Tension (Shear) in Masonry Assemblages.

4.2 Types of Tests and Specimen Dimensions

In order to obtain representative test values of masonry properties,

some codes require that a test shall consist of not less than 5 specimens,

while others require a minimum of 3 specimens. It is recommended that at

least 3 specimens be used in each of the 3 different types of tests (compression, shear, flexure) for a given type of masonry in an existing building.

The optimum size of a test specimen is the smallest size that will yield

results representative of in-situ wall strength. The prescribed sizes of

Publication by ASTM pending.

26
test specimens are principally governed by considerations of the combined

effect of cutting, handling and actual specimen size on the masonry strength.

The follov/ing requirements are listed to assist in selecting dimensions of

specimens for use in the three types of tests.

4.2.1 Compression Specimens (Figure 4.1a)

The axial compression test is used to evaluate the compressive strength

(f) and the modulus of elasticity (E) of the masonry in the direction normal m

to the mortar bed. The tests should be conducted in triplicate for each type

of masonry comprising the wall cross section. For instance, a composite

wall section consisting of a 4-in brick wythe and an 8-in hollow block wythe

will require separate testing of specimens of each wythe prepared from the

composite samples by cutting through the collar joint and chiseling off excess surface mortar. In cases where header joints are unavoidable between

two adjacent wythes of the same composition, the assembly should be tested

as a unit. The general dimensional requirements for the test specimens

are as follows:

1. Width of specimen (w) should contain not less than one whole unit

in the bottom and top courses and should not be less than thickness

(t) of specimen.

2. Height of specimen (h) should be not less than 12 inches.

3. Height of specimen (h) should contain not less than 3 whole

courses plus the minimum whole number more to make h/t equal to or greater than 3.

4.2.2 Shear Specimens (Figure 4.1b)

Shear specimens should be tested by compression applied along a diagonal axis within the centroidal plane of the cross section. In order

to avoid fabricating specially fitted loading shoes for different specimens

of random height-to-width ratios, all specimens should be cut square. The

diagonal compression test will be used to evaluate the shearing strength

(f) and the modulus of rigidity (G) of the masonry. The criteria for

testing multi-wythe wall sections are those prescribed for the compression

specimens. However, a specimen of composite construction (dissimilar wythes)

in which header units are unavoidable, m.ay be tested as a unit if it conforms

to the sectional configuration and type of construction of the masonry which

it is intended to represent, and to the dimensional requirements herein
specified. The general dimensional requirements for the test specimen are

as follows;

1. Height of specimen (h) should contain a whole number of, but not

less than, 3 courses.

2. Height of specimen (h) should be not less than 12 inches.

3. The height-to-thickness ratio (h/t) should be not less than 2.

4. The width of specimen should be equal to not less than 2 masonry

units

.

5. The width should be established with respect to the vertical joint

pattern in such a way that one pair of diagonally opposite corners

of the specimen contain whole units or the largest possible fractions

thereof

.

4.2.3 Flexure Specimens

Since under seismic excitation walls may flex in either direction, a total of 6 tests will be necessary to evaluate flexure bond strength at the

two opposite outer fibers of the wall. As an alternate option, only 3 specimens may be tested by determining only the flexural strength at the

outer fibers corresponding to the exterior face of the wall in the structure

if it can be reasonably ascertained that the exterior face will develop

less tensile strength as a result of exposure to the generally more severe environmental condition.

For multi-wythe construction, test specimens of the two outermost

wythes can possibly be obtained from a single sample of the full wall cross section by further careful cutting through the collar joint mortar in the

laboratory. Since flexural strength is particularly sensitive to adverse

conditions in bed joints, special care must be exercised to obtain samples

free of any such defects. Visual probing of both surfaces of the wall,

preferably with the aid of a magnifying glass, helps detection of surface

cracks in bed mortar or at bonded interfaces.

Generally, the thickness of flexure test specimens should be limited

to the thickness of a single wythe. The two outermost wythes of a multiwythe sample should be detached and tested separately in a manner that

will induce tension in the fibers corresponding to the two surfaces of the

wall. This recommendation is prompted by the following considerations: (1)

flexural strength calculations of a single wythe specimen do not require

knowledge of an elastic modular ratio, otherwise needed to transform a section

of dissimilar masonry units, and (2) reduction of thickness permits the use

of considerably smaller test specimens without violating the minimum (h/t)

28
requirements, resulting in a corresponding reduction in the number of cutout samples and in the number of standard fixtures required for the tests.

Sometimes a situation is encountered that requires headers between two

adjacent wythes of the same composition to be included in the samples. In

such exceptional cases the two-wythe assembly may be tested as a unit to

avoid the necessity of cutting through the header units and causing possible

damage to the rest of the sample. Two types of loading options are provided

for the flexure tests; specimens may be tested as horizontal beams with the

transverse loads applied vertically, or, they may be tested in the vertical

position and loaded in a manner that will induce equal and opposite couples

at the ends. The general dimensional requirements for the flexure specimens

are given below according to loading type.

a. Transversely loaded specimens (Figure 4.1c)

1. Width of specimen (w) should contain not less than 2 whole units

in the bottom and top courses, plus the minimum whole number more needed to make width (w) equal to or greater than thickness (t) of

specimen.

2. Height (span length) of specimen (h) should contain not less than 2 whole courses plus the minimum whole number more to make (h/t) equal

to or greater than 4 (plus allowance for span overhang)

.

3. The specimen should extend at least 3/4 in beyond the simple supports

at each end.

b. Eccentrically loaded specimens (Figure 4. Id)

1. Brick masonry specimens should be at least five courses high and

preferably two units wide (figure 4.2). One-unit wide specimens having whole

units at the top and at the bottom may be used if it can be demonstrated

that test results are not significantly altered by such reduction in width.

This may be accomplished by comparison of results obtained from exploratory

tests using specimens of both sizes.

2. Concrete block and clay tile masonry specimens should be at least

one unit wide and three courses high having whole units at the top and at the

bottom.

29
4.3 Sampling and Transportation

4.3.1 General Considerations

Locations of samples for the preparation of replicate test specimens

should be well dispersed with the aim of achieving wide representation.

However, each set consisting of 3 specimens for the 3 different types of / tests should come from the same vicinity in order to correlate different

property values. The necessity for duplicate sets of test specimens of

seemingly identical types of masonry walls in different parts of a particular

structure should be governed by consideration of the significance of

differences in the types of mortar, units, and in the ages of the respective

walls. Consideration should be given to the structural safety of the building by confining sample extraction to regions of low stress intensity and by

using appropriate shoring of the voided portions of the wall. For a cluster

of buildings of approximately the same age, of comparable size and geometric

layout, and of the same type of masonry wall construction and sectional

configuration, the number of replicate sets of test specimens (1 set = 3 test types x 3 replicates = 9 specimens) should be comparable to the accepted

norm for new masonry construction, which is about one set per 5000 sq

.

ft. of vertical wall area.

Wall samples should be obtained from areas of sound masonry construction

without defects. By careful visual inspection of both surfaces it should be

ascertained that samples represent wall areas which are free of cracks and

of unduly deteriorated mortar. Other defects such as spalled masonry units

and broken out mortar should also be avoided. Because of their greater exposure

to weathering agents, parapets and other free-standing exterior walls should

be particularily suspect of such adverse conditions.

The dimensional requirements of samples taken from composite walls are usually governed by the economic necessity of obtaining the required number

of test specimens using the least niomber of cutout samples. Samples and test

specimens of walls need not necessarily be of the same size. Samples should

be of the same thickness as the walls from which they are extracted. Any

cutting through the collar joints of mult iple-wythe samples as called for in

the preparation of test specimens should be conducted in the laboratory.

Removal of larger samples for the purpose of providing multiple test

specimens will reduce the likelihood of possible damage caused by the cutting

operations at the site and will permit additional cutting to be conducted

in the laboratory under conditions of maximum control. Removal of samples

30
having twice the width Cand/or height) of test specimens will be generally

governed by handling and transportation requirements and considerations of

structural safety of the existing building.

4.3.2 Equipment and Cutting Procedures

Samples should be extracted from the wall with a saw having a diamond

or silicon-carbide cutting edge capable of cutting samples without excessive

heating or shock. Preferably, the saw should be capable of cutting completely

through the wall thickness from one surface. This may be accomplished by

using a circular saw mounted on a fixture which can be securely attached

to the wall. If cutting must be done from both surfaces of the wall, a positioning pilot hole, off to one side, should be drilled through the

wall for referencing the sample outline on both surfaces. As cutting

progresses, the sample should be stabilized with wedges or through-thewall clamps to prevent fracturing. Upon having cut the sample free of

the wall, it may be necessary to chisel away some of the surrounding wall

to facilitate removal of the sample. Field sampling equipment is available

from commercial sources which also provide instructional guidance in their

use

.

If the sample is to be used as a source for a specimen of smaller

thickness, such further extraction should be conducted at a suitably equipped

laboratory or stone cutting plant. Prior to cutting through a collar joint,

the masonry on both sides of the surface to be cut should be securely held by

clamps bearing against the vertical edges normal to the bed joints. Cut

surfaces should be trimmed of excess mortar so that specimen dimensions are determined by masonry unit surfaces.

4.3.3 Transportation

Transportation of samples from their source should be accomplished with

care to avoid damage by vibration or shock. Samples should be crated for

transportation in a vertical position (i.e., as they existed in the wall)

,

fully supported on their bases and clamped or wedged in a direction prependicular to their horizontal (bed) joints. Further aid can be derived by

effective use of vibration absorbent materials or devices used to cushion the

crates and by lashing the crates to the vehicle. Handling and transporting

a sample in a horizontal position should be avoided.

31
4.4 Preparation of Specimens

4.4.1 General Requirements

Specimens which were obtained from areas of sound masonry construction

might have been damaged in the cutting and transportation process. All

specimens should be examined visually as carefully as possible to detect

cracks, spalls, undercuts or other damage which might be detrimental to

test results. If a specimen is found to contain such impairments, it should

be replaced with an undamaged one.

Specimens which are considered acceptable for testing should have their

load bearing surfaces capped with high-strength gypsum plaster prior to

testing. This is done in order to distribute test loads uniformly and

to prevent load concentrations which might be caused by projections or by general lack of planeness of the load bearing surface. Guidance in

this procedure can be obtained from the following ASTM Designations: E447,

Compressive Strength of Masonry Assemblages; C67, Sampling and Testing

Brick and Structural Clay Tile; and C140, Sampling and Testing Concrete

Masonry Units, whichever relates most appropriately to the type of masonry

in the specimen at hand. Nevertheless the following general recommendations

are made for preparing all specimens.

Bearing surfaces of these specimens and portions adjoining them should

be brushed free of dust and loose particles, then coated with shellac (to

prevent absorption of water from plastic gypsum mortar) and be allowed to

dry. Casting surfaces to be placed against gypsum mortar should be lightly

coated with oil to facilitate their removal. The average thickness of the

hardened gypsum cap should not exceed 1/8 in. Since caps cannot be properly

patched after setting, imperfect caps should be removed and replaced with

new ones but without damaging the specimen. Caps should be made of special

high-strength gypsiom mixed with just enough water to form an easily troweled

paste. When ready for test, the capping gypsum should develop a compressive

strength of at least 5000 psi, tested as 2-in cubes aged in the same manner as the caps. Proper blending of gypsum with a minimal amount of water is more

easily achieved by slowly sprinkling the gypsum into water unaccompanied by

stirring

.

4.4.2 Compression Specimens (Figure 4.1a)

Compression specimens should be capped over their complete top and

bottom bearing surfaces. The bottom surface is capped by lifting the

32
specimen and pressing it down into plastic gypsum mortar spread on a level,

oiled casting surface. Removal of extruded mortar will assist in checking

thickness of the cap. The weight of the specimen may cause it to sink

instead of being pressed down. It is important that the vertical axis of

the specimen be kept perpendicular to the capping surface and that the

operation be done in a single motion. Tilting and rocking adjustments of

the specimen are likely to destroy full bearing of the cap on the specimen.

If the specimen is too heavy for lifting by hand, it can be clamped or bolted between two horizontal 2 by 4' s nominal, and handled mechanically

(e.g. by hoist or fork lift).

After the cap has hardened enough to permit separation of the casting

surface and capped specimen without damage to the cap, the capping operation

should be repeated for the top bearing surface. It is recommended that this

be done by overturning the specimen and capping the opposite bearing surface

in the same manner. If, however, it is impractical or hazardous to the

specimen to attempt overturning, the following alternative method is

recommended, without waiting for the bottom cap to be uncovered, plastic

gypsum mortar may be spread over the top bearing surface in excess of the

desired thickness. The second oiled capping plate can then be carefully

lowered onto the plastic gypsum with the aid of a carpenter's level. This

top capping plate should be sufficiently heavy to allow gravity to assist in

its placement; additional weight should be superimposed simultaneously if

necessary. The same precautions against any disturbing adjustments which

mi^t destroy the bearing contact between specimen, gypsum and plate must be

observed. Caps are to be formed approximately parallel to each other and

perpendicular to the specimen axis. After caps are sufficiently hardened to

permit handling of the specimen, capping plates should be removed and the

specimen temporarily supported in a way which permits circulation of air to

assist drying of the caps.

4.4.3 Shear Specimens (Figure 4.1b)

Shear specimens (which are cut square - cf. Section 4.2.2) should

be prepared for testing in diagonal compression. This requires preparation

of 2 diagonally opposite corners to serve as bearing points for the test

load. The compressive in -plane load is directed, through steel loading

shoes, along the diagonal of the specimen which joins the two prepared load

bearing corners. This ma,nner of loading eliminates the need for a separate

hold-down force to prevent rotation of the specimen (cf. ASTM Method E-72) .

33
The steel loading shoes may be one of the two types shown in Figure 4.3.

The open end type, (a), lends itself to use in laterally placed pairs at both

corners of a specimen to provide bearing over the entire thickness of larger

specimens without fabricating overly large shoes. Because of the wide range

of specimen sizes that might be encountered, no specific dimensions are given,

but the length of bearing of the shoe is especially important. The length of

shoe bearing along the perimeter of the specimen should be enough to prevent

excessive bearing stress. Experience indicates that a shoe bearing length,

on one side, equal to approximately 1/8-th the length of the side of the

specimen is satisfactory. If the shoes are longer than needed for the

specimen at hand, the recommended bearing length can be achieved by using

temporary steel liner plates of the shorter length. Shoes should be of

welded construction fabricated from 1/2-in (or heavier) steel plate, designed

with sufficient braces to prevent distortion under load.

The position of the specimen for capping the loading corners and for

testing, is obtained by rotating it (in-plane) through 45° from its natural

orientation in the building wall. With the diagonal which joins the loading

corners maintained perpendicular to a level surface, the loading corners

should be bedded in high-strength gypsum in the loading shoes. Hollow cores

of the loading corner masonry units which will rest within the shoes should

previously be filled solid with the capping gypsum. These operations generally

follow the manner described for capping compression specimens (Section 4.4.2)

using the steel shoes instead of the plane capping plates. Care should be

exercised to prevent the gypsum from constraining the face surfaces of the

corners in the loading shoes.

4.4.4 Transversely Loaded Flexure Specimens (Figure 4.1c)

Flexure specimens should be prepared for testing with the specimen's

vertical axis in a horizontal position. In order to reduce load concentrations

and to provide hard and smooth bearing surfaces for load and reaction rollers,

cold rolled steel bar stock should be embedded flatwise in high-strength

gypsum plaster on the specimen at the required locations. The length of the

bars should be equal to the specimen width and it is recommended that a bar

cross section of 1/2" x 1^1/2" be used (for adaptability to specimens of

most masonry unit sizes).

In order to avoid the necessity for specially fabricated articulated

loading equipment which compensates for lack of planeness in the specimen,

the following procedure is recommended: On a plane level surface place two

of the bars directly opposite and parallel to each other and spaced at a

34
center to center distance equal to the span length chosen for the specimen.

The upper surfaces of the bars should contain several keying recesses (e.g.

shallow, slightly inclined drill holes, approx. 1/2" diam.) to provide

mechanical bond between the bars and bedding plaster while assembling the

test. After oiling the upper surfaces and recesses of the bars (to

facilitate cleaning for re-use) place a suitable quantity of plastic gypsum

on top of the bars. Lower the specimen, centered over the bars in the

horizontal test position, and with a single motion imbed the specimen in

the gypsum firmly against the bars as nearly level as possible. It may be

necessary to gain more space (for manual or mechanical handling) by placing

the bars on separate supports above the level reference surface beforehand.

If this is done, it is important that the separate elevators maintain and

transfer the level reference surface reliably. Equal steel blocks are recommended for this purpose. When the gypsum has hardened sufficiently,

carefully overturn the specimen, with bars attached, for similar preparation

of the opposite surface.

The procedure to be followed is the same except that the bars are to

be spaced at a distance equal to 1/2 the span length of the specimen. This

will result in the bars being attached to the opposite surface at the 1/4-

point test loading positions of the specimen span length. The specimen

must be carefully turned over once more to its original horizontal position

to be made ready for test. Each pair of bars (and, by attachment, the

respective surface of the specimen) will then have bearing surfaces in

a single plane, thus compensating for any warpage in the specimen which

might be detrimental to test results. The upper and lower planes of bearing

are not necessarily parallel; this will be offset by a spherically seated

loading head discussed in Section 4.5.

4.4.5 Eccentrically Loaded Flexure Specimens (Figure 4 . Id)

Since loading is transmitted to these specimens through the side clampin

action of the brackets gypsum capping is not necessary.

4.5 Test Apparatus

4.5.1 Testing Machine

The testing machine used for exerting and measuring loads applied to

the specimens should be of sufficient load capacity and conform to the

requirements of Section 16, 17 and 18 of ASTM Designation E-4 , Verification o

35
Testing Machines. It must be power operated in order to apply load continuously,

rather than intermittently, and should have an adjustable loading rate control

which will provide the rate required in Section 4.6. The space provided in

the machine for specimens should be large enough to accommodate test assemblies

with attached displacement gages in a readable position if gages must be read

visually. Alternative remote observations are discussed in Section 4.5.2.

The upper crosshead of the testing machine must be equipped with a spherically seated bearing block which can be adjusted so that its contact

surface is made parallel to the upper load bearing surface of the test

assembly at the beginning of the test. The spherical seat should be lockable

to prevent slipping when used on unstable test assemblies (e.g., those

requiring the use of rollers) . Selection of diameter of the spherical bearing

block, and of size of auxiliary loading equipment, (such as bearing plates,

rollers, I-beams, etc.) should be made on the basis of accepted engineering

design. Undue deformation of loading equipment should be avoided to prevent

undesirable loading conditions which would be detrimental to test results.

4.5.2 Deformation Gages

Instruments for measuring deformation of masonry under load are used

in the compression and shear tests. These measurements are used in calculations

discussed in Section 4.7 to determine the elastic moduli of the masonry.

Contraction or extension of the masonry over a given gage length should be

measured with a dial micrometer having dial graduations of 0.001 inch or a Linear Variable Differential Transformer (LVDT) having an equivalent least

count. The spindle-actuated rack and pinion type dial micrometer is read

visually; the transformer coil, sliding core type of LVDT is used in

combination with auxiliary electronic equipment for read-out. LVDT readings

can be made remotely with a visually read voltmeter (preferably digital) or with automatic recording equipment if available. Gage length deformations

should be measured and recorded to the nearest estimated 0.001 inch (i.e.

1/10 the least count) .

Mounting of instruments on specimens is done expediently with supporting

brackets attached to the masonry units by hot-melt adhesive. Adhesive in

small cartridge form is dispensed easily by electrically heated pistol style

applicators. Mounting hardware of aluminum, rolled or extruded sections and

tubing are recommended for lightness of weight.

To illustrate, deformation in a given gage length can be measured by a dial micrometer gage attached to the specimen by a bracket at one end of the

36
gage length (Figures 4.1a and b) . The detecting spindle of the gage should

be parallel to and point toward the opposite end of the surface gage-line.

At this same opposite end, a light, stiff tube or rod is pin-mounted at one

end with the swivel pin perpendicular to the mounting surface. The tube is

positioned parallel to the surface gage line with the free end of the tube

in contact with the end of the gage spindle (connected if necessary; details

are discussed for particular tests in Section 4.6) . It is usually necessary

to provide a slide guide bracket for the tube at the end away from the swivel.

If, instead, an LVDT is used in the above illustration, it is recommended

that the transformer coil be mounted on the tube at the end away from the

swivel; and that one end of the sliding core be attached to a bracket mounted

at the location which had been occupied by the dial gage.

Loose fits between gage assembly parts can be overcome, and contact

maintained, by stretched rubber bands.

4.6 Testing Procedures

4.6.1 Compression Test (Figure 4.1a)

Specimens should be tested with the centroid of their bearing surfaces

aligned vertically with the center of thrust of the spherically seated bearing

block. If necessary, a top bearing plate and other hardware may be used to

uniformly distribute the load from the spherically seated loading head.

Four deformation gages of the type described in Section 4.5 should be

attached for measuring axial contraction of the specimen. These compressometers

are mounted over four corresponding vertical gage lengths which are each near

a different corner of the specimen on the faces that were parallel to the

wall surface. It is recommended that the four equal gage lengths be chosen to

extend between the midheights of the bottom and top courses of masonry units.

In this way deformations can be observed occurring over an equal whole number

of courses and joints.

When gage assemblies are mounted over vertical gage lengths as in this

test, it is recommended that the dial micrometer (or LVDT core) be bracketmounted at the lower end (Figure 4.1) . The tube (or rod) extension of the

gage, thus being suspended from the upper end, will tend to be more stable in

a hanging position.

37
The gage length and initial readings of the gages (with no load on the

specimen) should be recorded. As the spherically seated block is brought to

bear on the test assembly, the moving portion should be slightly rotated to

help obtain uniform seating.

Load should be applied to the specimen continuously at a uniform rate of

from 1/3 to 1/4 -th. the estimated expected maximum load per minute. Loading

may be stopped briefly at equal load increments to record load and gage

readings. Observation intervals should be at a convenient load increment

value of approximately, but no more than, 1/15 the expected maximum load.

This will provide approximately 10 sets of observations to derive 2/3 of

the load-deformation relationship. At 2/3 the expected maximum load (or sooner if sudden failure appears imminent) the deformation, gages should be

removed and the load continuously increased at the specified rate until the

maximum load that can be applied to the specimen is determined.

4.6.2 Shear Test (Figure 4.1b)

Since shear tests are to be conducted by application of compressive load

along a vertically positioned diagonal axis of the specimen, such tests should

follow the same loading procedure (where applicable) as described for the

compression test (Section 4.6.1).

With the specimen properly positioned in the testing machine, four

deformation gages, of the type described in Section 4.5.2, should be attached

(2 on each face) for measuring the average horizontal extension and vertical

contraction along the diagonals of the specim.en under load (cf . Figure 4.1b) . The four deformation gages are mounted over the gage lengths on the four face

diagonals of the specimen. These gage lengths should be equal and symmetrical

about the intersections of the face diagonals. Their length is determined by

the intersection of the diagonals with the mid-heights of the uppermost and

lowermost courses of the specimen; or, that same length reduced by a reasonable

clearance from the loading shoes to avoid local disturbance of the mounting

brackets.

If a composite specimen must be tested as a unit, the necessary transformed

area calculations for location of load application points at the centroid of

the section can be made using the values of elastic moduli obtained from preceeding compression tests and equation (3.9). Proper positioning of the

specimen in the testing machine will minimize the effect of out-of -plane

flexure on test results. Large differences in deformations recorded by the

38
two vertically-oriented diagonal gages at opposite faces of the specimen are

an indication of improper positioning.

4.6.3 Flexure Test, Transverse Loading (Figure 4.1c)

With the surface selected to receive tensile stress placed underneath

(Section 4.4.4), the specimen should be positioned horizontally in the

testing machine so that the center of thrust of the spherically seated

loading head is aligned with the centroid of the load bearing plates previously

attached to the specimen.

The specimen should be supported across its full width on two rollers, one placed under the mid-width of each bottom plate to establish the span length.

Temporary chocks may be necessary to prevent rolling. Similarly, a roller

should be placed on each plate over the 1/4-span loading positions, together

with any distributing hardware (e.g., I-beams) needed to transfer load applied

by the testing machine symmetrically and uniformly to the two 1/4-span loading

rollers. Since flexural test loads will be relatively small, weight of

equipment superimposed on the specimen should be measured for later addition

to observed applied loads.

By hand rotation, the spherically seated loading head should be adjusted

as nearly parallel as possible to the contact surface of the loading hardware.

Contact should be made gently by applying a small load with the testing machine

and locking the spherical block. The load should be continuously increased at

a uniform rate until the maximum load the specimen can withstand is determined.

Rate of loading should be sufficient to cause failure in 1 to 2 minutes. No

deformation gages are used in this test.

4.6.4 Flexure Test, Eccentric Loading (Figures 4.4, 4.5, 4.6)

This alternate test method to determine flexure bond strength of existing

masonry walls is essentially patterned after the testing procedure for concrete

masonry block assemblies described in ASTM Desingation E149-66, Standard

Method of Test for Bond Strength of Mortar to Masonry Units. The adaptation

of the ASTM procedure to test sampled specimens of concrete block, and brick

as well as other types of masonry construction requires the fabrication and xase of special apparatus consisting of brackets for clamping the specimens at top

and bottom and lever arm attachments for application of eccentric loads.

A test set-up, using the ASTM E149 apparatus for testing concrete block

masonry specimens is shown in figure 4.4 and shop drawings of the fixtures

39
appear in ASTM E149. This equipment is dimensioned to accommodate the size

of specimens made of large masonry units such as concrete block and clay

tile.

The primary intent of the test method is to induce equal and opposite

couples at the ends of the specimen, flexing it in single curvature. By

making the lever arms sufficiently long the effect of axial load is kept to

a minimum and a condition of pure flexure is closely simulated. For this

purpose, the length of the lever arm should be designed in a manner that would

keep the stress which is attributable to total axial load (applied load, plus

appropriate weight of hardware and specimen) within 30 percent of the maximum

calculated flexural stress attributable to the total end moment (the product

of applied load and lever arm, plus the product of the weight of upper hardware

attachment and the distance of its centroid from the centroidal axis of the cross section of the test specimen)

.

An apparatus similar to that used for ASTM E149 testing has been

introduced by the Brick Institute of America, BIA (previously Structural

Clay Products Institute, SCPI) , for testing small jDrick masonry specimens

in flexure. For background information reference is made to the following

publications

:

1. Research Report Number 9, Compressive, Transverse and Racking

Strength Tests of Four-Inch Brick Walls, Structural Clay Products

Research Foundation, Geneva, Illinois, August 1965.

2. Progress Report No. 1, Small Scale Testing, Structural Clay Products

Research Foundation, Geneva, Illinois, October 1964.

A typical test set-up using a six-course stacked bond brick specimen is

shown in figure 4.5. Figure 4.6 shows photographs of the top and bottom

bracket assemblies of the BIA equipment which was used in a recent experimental

program conducted at the National Bureau of Standards. This type of equipment

can be fabricated to accomodate one-unit-wide specimens as in figures 4.5

and 4.6, and two-unit-wide specimens as in figure 5.5 of Report No. 9 cited

above

.

In general, testing procedures for masonry specimens should be in

accordance with those described in ASTM E149. Load should be applied at a rate sufficient to cause failure in 1 to 2 minutes. No deformation gages are used in this test.

40
4.7 Interpretation

Sections 4.7.1 to 4.7.4 discuss procedures for deriving masonry strength

properties from individual test results, including use of load-deformation

histories to calculate the elastic constants. In section 4.7.4 these values

are further modified to account for variability and other inherent factors.

For the purpose of correlating calculations of sectional properties of test

specimens and of walls, frequent reference is made to Section 3.3 in which

length of wall (L) corresponds to width of specimen (w) . For single-wythe

specimens or for multi-wythe specimens of the same composition, (A) is the

horizontal cross sectional area of the specimen calculated on a gross or net basis as prescribed in Section 3.3.

4.7.1 Compression

For a specimen of single wythe construction, or multiple wythes of the

same material, tested with the load over the geometric centroid

P

m A

compressive strength

compressive load at failure

appropriate (gross or net) cross -sectional area

Intermediate values of stress (f ) , at observed test loads P < P , m u are calculated as

(4.2)

where

;

f = m

P = A =

Corresponding values of average compressive strain measured by 4 compressometers (cf. Section 4.6.1) are calculated as

A + A + A + A

e = -± 1 £ i (4.3)

4g

where

= average compressive strain

A^ = change in length of i-th gage

g = compressometer gage length

Values of compressive stress (f ) and corresponding strain (e ) are
plotted to develop a stress'-strain diagram (Figure 4.7) . At a level of

(f '/2) , a value of the tangent modulus of elasticity (E) is graphically

m

determined. This value of (E) , modified according to the provisions of

section 4.7.5, will be used in the transformed area calculations, where

necessary, and in seismic resistance evaluations.

4.7.2 Shear

Barring premature compressive crushing of the masonry at the diagonally

loaded corners, shear specimens will fail along the loaded diagonal by shear

cracking in the mortar joints, or by tensile cracking of the units, or by

a combination of both. These different types of cracking patterns will be

primarily governed by the relative strengths of the masonry constituents.

High-strength mortar used with low-strength masonry units will cause cracking

to occur through the masonry units while low-strength mortar with highstrength masonry units will produce cracking along the mortar joints.

For a shear specimen of single wythe construction, or multiple wythes of

the same material, tested with the diagonal compressive load in the centroidal

plane of the specimen thickness (t) , the shear strength of masonry corresponding to the mode of failure characterized by diagonal cracking through the mortar

is calculated as 0.707 P

f' = s Cl-u) (4.4) v A

masonry shear strength

diagonal compressive load at failure

appropriate (gross or net) cross sectional area parallel

to bed joints

coefficient representing influence of compression on shear

strength

The results of various racking tests conducted at NBS indicate a value

of coefficient (u) which varies between 0.3 and 0.5. The use of the lower

value in eq , (4.4) will give

p f;=0.5^ (4.5)

This simplified equation should be used to calculate the shear strength of

masonry from test results regardless of the observed failure mode. It is

noted that the use of the smaller frictional coefficient overestimates

shear capacity at zero axial load but conservatively predicts this capacity

where

f = V

A

u =

42
under a combination of axial load and diagonal compression; a situation

most frequently encountered in practice. It is further noted that in cases where specimens fail by diagonal cracking through the masonry units,

eq. (4.5) conservatively predicts a nominal shear capacity which is less

than the actual shear capacity by an indeterminate amount.

Intermediate values of average shear stress (f ) at observed test loads

(P) are calculated as

f^ = 0.707 I(4.6)

Values of average shear strain which correspond to the above stresses

and which are determined by means of the four diagonal deformation gages of

equal length (cf. Section 4.6.2) are calculated as

A + A + A + A Y = — — (4.7)

where

Y = average shear strain

A^= change (+ or -) in gage length no. i

g = length of one gage

It should be noted that the absolute values of length change are used

in the above expression although, under load, the two vertical gage lengths

(Figure 4.1b) are contracted and the two horizontal gage lengths are extended,

the 1/2 factor, is used in eq. (4.7) to obtain average strain on 2 opposite

faces of the specimen since approximate average shear strain on one face

is given by

Y = ^

(4.8)

g

where subscripts (V) and CH) designate vertical and horizontal directions,

respectively. It is also emphasized that the 4 gages must be of equal

length for these calculations. Values of shear stress (f^) and corresponding

strain (y) are plotted to obtain a stress-strain diagram (similar to that

for compression in Figure 4.7). At a level of (f^/2), a value of tangent

modulus of rigidity (G) is determined graphically. This value of (G)

,

modified in accordance with the provisions of section 4.7.5, will be used

in the seismic resistance evaluations. For composite specimens eqs . (4.5)

to (4.8) still apply except that (A) should be replaced by the area of the

transformed section (A ) given by eq. (3.9).

43
4.7.3 Flexure, Transverse Loading

Calculations for flexural tests involve only the determination of the

ultimate flexural (tensile) strength by the equation

f. = ^ • h • £ (4 9) ^t 2 4 1

where

:

f^ = flexural tensile strength

= total test load at failure, (Figure 4.1c)

h = flexural test span length

c = distance from centroidal axis to outermost tensile

surface

I = net moment of inertia of mortar bed joint about centroid

of cross section

As mentioned in section 3.3, it is to be emphasized that in flexure

of hollow masonry construction, only the net mortar contact area is to be

considered effective.

4.7.4 Flexure, Eccentric Loading

Taking all forces into account, the tensile strength in flexure should

be calculated from the following expression:

•

' (P + w + w ) f^ = (^^u ^ Vb^ • I - A

(^-1°^

where

;

f^ = tensile strength in flexure

P = applied load at failure

Wj^ = weight of top bracket assembly

= weight of the portion of masonry specimen above the

observed plane of cracking

X = distance from centroid of cross section to point of

application of load P

X, = distance from centroid of cross section to center of b

gravity of top bracket assembly

A = net cross-sectional area of mortar bed joint

I = net moment of inertia of mortar bed joint about centroid

of cross section

c = distance from centroid of cross section to extreme fiber.

44
(c) - Flexure test (transverse loading). (d) " Flexure test (eccentric loading).

Figure 4.1 - Methods of testing masonry specimens.

45
CO9

COo

o

c

(a) BRICK (b) BRICK

(c) CONCRETE BLOCK OR CLAY TILE

Figure 4.2 - Flexure test specimens for eooentvic loading.

Figure 4.3 - Shear test loading shoes.

46

Figure 4.5 - Eooentvioally loaded flexure test setup for brick prisms.

48
UPPER BRACKET

LOWER BRACKET

Figwce 4.6 - End hraokets for ecoentriaally loaded flexio'e test of brick

prisms.

49
STRAIN e

Figure 4.7 - Stress-strain diagram.

50
4.7.5 Capacity Reduction

All strength and stiffness values derived from direct tests of sampled

specimens in accordance with the procedures discussed in Section 4 should

be reduced to account for the aggregate effect on masonry properties of:

(1) variability, (2) specimen size and (3) past earthquake exposure. The

reductions should be made as follows

(a) Strength (f, f, or f!) ^ m V t

(0 < V < 0.50) : x' = ^3 (4.11)

(v > 0.50): ^' = J

[1-1. 5{v - 0.50)]

(b) Stiffness (E or G)

x- = |i (4.12)

where: x = arithmetic mean of a strength or stiffness property derived

from replicate tests

x'= maximum strength or stiffness property to be used in structural

investigation of masonry buildings

V - coefficient of variation expressed as a decimal fraction

(0 £ V < 1.00) and calculated from

1 ^ (X - X) / „ T \ V = — —i — (4.13)

X n - 1 where: x = an individual measurement

n = total number of replicate specimens or measurements of a property

4 . 8 Implementation

4.8.1 Sampling and Testing

The extent of implementation of the testing procedures discussed in the

foregoing sections will depend on the feasibility of preparing undamaged

specimens from existing masonry construction and on the relative importance

of a specific test information in the seismic analysis of a particular

building. In both instances, the course of action to be taken will depend

on prior knowledge about the structure at hand and the experience gained

while field sampling is in progress. Nonetheless, some general guidelines

are provided for situations that can be anticipated.

51
Compression, testing requirements may be relaxed on the basis of an initial seismic investigation which will indicate that the masonry in the

structure under consideration has an adequate margin of safety against

failure by compression under the incremental loads induced by lateral and/or

vertical acceleration. This situation is likely to be encountered in buildings

in which the ratio of height to least horizontal dimension is small.

The scope of compression tests may be relaxed by reducing the number of

replicate tests to that which will be required to make an independent

assessment of the modulus of elasticity (E) on the basis of load-deformation

measurements. Such a reduction will be justified because, in general, the

elastic constants need not be evaluated with the same degree of accuracy as the strength properties. It is noted, for instance, that the modulus

of elasticity prescribed by various masonry codes and standards CUBC, BIA

and NCMA) is derived from the compressive strength (f ' ) , rather than from m

independent test measurements.

The existence of tensile or bond strength in the bed joint mortar of

masonry wall elements of a building is the necessary precondition for the

flexure tests. In addition, the bond strength should be high enough to

permit the extraction of a sufficient number of undamaged test specimens

without too high an attrition rate. In existing masonry buildings, initial

bond, if any, might have been partially or wholly destroyed by exposure to

past disaster loads and as a result of a progressive deterioration of the

mortar caused by environmental agents. A typical example of the latter case

is the degradation of mortar types with high lime content (such as were commonly used in old masonry buildings) through exposure to moisture.

In some exceptional instances, it might be possible to detect poor mortar

condition by visual inspection or by manual probing in the field and thus

eliminate the need for flexure tests. It is more likely, however, that

such decisions will have to be deferred until field sampling indicates

a considerable level of damage in the samples extracted from the walls.

As an approximate guideline, it is suggested that an attrition rate of 50

percent or greater, precluding accidental attrition, be used as grounds

for suspension of further sampling. In such an event, no tensile strength

should be assigned to the masonry under consideration (f^ = 0)

.

These guidelines may also be used to determine the feasibility of

conducting the shear tests of the masonry of a particular structure. In

the event that such shear tests are eliminated, no base shear strength

should be assigned to the masonry under consideration (f^ = 0) . In this

52
case, the average shear strength (v'), of masonry under axial compression

is evaluated using the second term on the right-hand side of equation (5.18)

.

4.8.2 Field Inspection

A documentation of the actual condition of the masonry in an existing

building could provide useful and valuable information for seismic evaluation.

Such information may be conveniently compiled by the field crew assigned to

the tasks related to the removal of wall samples for testing. A check list

will provide guidance on the relevant items to be considered in the survey.

Description of cracks, spalls and other visually identifiable defects in the

masonry may be effectively related by appropriate sketches on elevation

profiles and a list of correspondingly numbered commentaries. The use of

contract drawings, whenever available, will be most expedient for such purposes.

The contract documents may also be helpful in identifying the types of mortar

and masonry used and other pertinent data on masonry specifications.

5, Strength of Masonry Walls

5.1 Introduction

The procedure for predicting the racking strength of masonry walls described in Section 5.3 is based primarily upon the findings of a series of

racking tests conducted at the National Bureau of Standards [50]. A major

objective of these experiments was to study the influence of compressive

loads on in-plane shear capacity of walls. A total of 73 full-scale walls

of 8-in hollow concrete block and 4-in brick masonry were tested. In

addition, a large number of small-scale specimens of similar construction

were tested to investigate the correlation between wall strength and small

specimen strength. The sizes of full-scale specimens and the types of

racking tests are displayed in Figure 5.3. The specimens and test setups

for some of the racking specimens are discussed in Sections C.5 and C.6 of

Appendix C.

In another series of tests conducted recently at the National Bureau of

Standards, a considerable amount of data was compiled on out-of -plane (vertical)

flexural strength of masonry walls of various types of construction in

the presence of vertical compressive loads. The test results were synthesized

to develop analytical procedures for the prediction of wall strength under

compression and flexure. These experimental findings and the analytical

formulations for the proposed methodology, related in a series of separate

53
publications [52, 64, 65, 75], constitute the basis of the flexure-compression

interaction relations discussed in Section 5.2.

5.2 Flexure-Compression Interaction

The moment capacity of short masonry walls under compression and out-ofplane bending can be reasonably predicted from equilibrium considerations of

the cracked or uncracked section assioming a linear stress distribution on the cross section at failure. Using this approach. Yokel et al . [65] proposed

approximate analytical procedures for evaluating masonry strength which was

found to be in good agreement with experimental results. The validity of this

approach was further verified by a substantial body of related data obtained

from subsequent tests [52, 64, 75]. The governing relationships are given

here without derivation as an aid to the investigation of masonry walls under

combined axial load and out-of-plane flexure.

Assuming masonry has no tensile strength, the approximate flexure-compression interaction relationships for the general case of an asymmetrical transformed section (masonry units of dissimilar composition) as shown in figure

5.1, are given by the following equations:

For a cracked section

\l = P^l ^1 - ^1

o M „ = Pc^ (1 -- g^^2

aP

^kl

^kl

^1

aP

^k2

^k2

^2

aP

o

""l 1 + —

^2

aP

o^2

1 + —^1

I

o e2

= CI - ^) (5.1)

\l

^k2

'kl AC2

k2 Ac^

P = rAf"

o m

54
where I = moment of inertia of net transformed section about its

centroidal axis

A = net area of transformed section

^1' ^2 ~ distances from centroidal axis of transformed

section to outermost fibers in maximum compression

= axial compressive strength of the weaker masonry element

in the composite section

= axial load capacity of masonry

P = compressive force on the cross section

^kl ' ^k2 ~ ^^^^ eccentricities from centroid of transformed

section in directions 1 and 2, respectively

^kl ' '^k2 ~ compressive load capacity of masonry applied at

kern eccentricities e^^^ and e^^ ' respectively

M ^, M 2 = moment capacity of masonry corresponding to maximum

^ compressive stress in outer fibers on sides 1 and

2 respectively

r = strength reduction factor (see Sections 3.2.4 and 4.7.5)

a = flexural strength coefficient defined below.

Flexural strength coefficient (a) is a factor greater than unity

to account for an experimentally observed increase in the apparent compressive

strength of masonry from (f") under axial compression to (af') under combined

ra m

flexure and compression. The expressions for and (Pj^2 ^ eqs

.

(5.1) are based on the simplifying assixmption that the ratio of the elastic

moduli of the two materials comprising the composite section is the same

as the ratio of the flexural compressive strengths. In addition, the

expressions for ^^id (M^2^ '-'^ eqs. (5.1) are approximate when the

load is applied at an eccentricity greater than the kern eccentricity.

However, for a solid rectangular section of non-composite masonry, the

(g^) terms appearing in eqs (5,1) reduce to the values of 4/3 and the

expression for (M^) is no longer approximate.

A note of explanation is needed with regard to the compressive strength

(f^) . For a composite construction, such as a brick-block wall assembly, the

axial compressive strengths of the two wythes may have different values.

The lower of these two values defines (f " ) to be used in these equations. m

For an uncracked section _ p

M , = P, -,e ° el kl kl aP - P, i ° (5.2)

aP - P

M ^ = P, ^e ° e2 k2 k2 aP - P, ^ o kz

55
The cracking line which separates the uncracked and cracked regions is

defined by the equations

M=M=Pe=Pe f5 3) ^kl k2 kl kl k2 k2

Equations (5.1) are applicable in the regions (P <_ P, , ) and (P < P, ^) and

equations (5.2) are applicable in the regions (P >^ ^j^i^ ^ ^k2^' Figure

(5.2) shows an interaction diagram reproduced from reference [65] for an asymmetrical composite section of 4-in brick and 4-in hollow block assuming

a = 1. Note that the (M ) curve for a cracked section obtained from eq . (5.1) e agrees reasonably well with the solid curve developed from cracked section

theory

.

Equations (5.1) were derived on the basis of zero tensile strength of

masonry. For large (M/P) ratios, failure occurs when the maximum flexural

tensile strength of the specimen is developed. Assuming a non-zero tensile

strength for masonry the expressions for the cracking lines become

rf ' I t2

^el = ^"^^

rf I \2 = -l^^^%2 (5-4)

m -- ^2

f^j^, f^2 ~ unreduced flexural tensile strength of masonry on sides 1 and 2, respectively.

E^, E2 = modulus of elasticity in direction normal to bed

joint of masonry on sides 1 and 2, respectively.

The moment capacity for the cracked section is the larger of the two

values determined from eqs. (5.1) and (5.4).

where

For a symmetrical section, the interaction equations become considerably

simpler. Thus, for a cracked section

56
M3 = PC (1 - g ^)

g = 2(1 - -i

Pi = aP

o k 2 (5.5)

I ®k Ac

P = rAf

e m

and, for an uncracked section,

e Ac o The cracking line is defined by

M = J— (aP - P) (5.6)

\ = Vk ^'-'^

ox, in the case where f ^ > 0 , by

rf 'I M = —— + Pe, (5.8)

e c k

The moment capacity for the cracked section is the larger of the two

values obtained from eqs . (5.5) and (5.8).

To evaluate masonry strength by means of eqs. (5.1) to (5.8) a value

should be assigned to coefficient (a) . The values derived from the test data

varied within a range of 1.25 to 1.65 depending on the type of masonry

construction. Significantly, it is noted that flexural compressive stress

allowed by several masonry codes for working stress design (BIA, NCMA, UBC)

,

is 60 to 65 percent greater than the allowable stress under axial compression.

For investigating the capacity of masonry walls in existing buildings an arbitrary but generally conservative value of a = 1.3 is suggested, together

with the necessary condition (because a > 1) that axial load P, existing

singly or in combination with a moment M on a given cross section, should not

exceed the axial load capacity (P^) of the masonry wall,

P < P (5.9) — o

Equation (5.9) must be satisfied before eqs. (5.1) to (5.8) can be used

to determine the moment capacity of the section associated with (P) . In the

case where (P > P^) , axial capacity of the section is exceeded, and no further

investigation is needed.

57
In the case of slender walls, (P) should not exceed the buckling load

capacity (P^) of the wall,

P < P (5.10) — c

Equations (5.9) and (5.10) must be independently satisfied if eqs . (5.1)

to (5.8) are to be used for moment capacity determination. The buckling load

is calculated as follows:

2 P = ^IL-R (5.11)

^ (kh)2

•

R = EI (0.20 + 1^) < 0.70 (5.12)

where (R) is the flexural stiffness, (k) is the effective height coefficient

dependent on top and bottom fixity conditions and (h) is the clear unsupported

height of the wall. A value of k = 2.0 for cantilever walls such as parapets

and k = 1.0 for all other cases may be conservatively assumed. Eq. (5.12) is

taken from Ref. [65] where it was used to correlate analytically predicted

strength of slender walls with test results.

Equations (5.1) to (5.8) do not take into account moment capacity reduction attributed to slenderness effects. Consequently, to determine the

adequacy of a section, the calculated moment capacity (M^) , should be compared

to the resultant internal moment (M) on that section. In the presence of an axial load (P) , the calculations of moment (M) become quite involved. In an effort to simplify these calculations the following approximate procedure

similar in concept to those used by concrete and steel building codes and

standards, is introduced.

M = aM (5 .13)

s

- - > 1.0 (5.14)

P

c where (M ) is the internal moment on the section induced by transverse

s loads and/or eccentrically applied compressive loads, and (a) is a factor

to account for the moment produced by the compressive load acting on the

transverse displacement of that section. Coefficient (C ) is taken as m

58
but not less than 0.4 for walls other than cantilevers in which the maximum

moment (designated by the positive symbol M^) occurs at one end. The moment

at the other end, (M^) , is taken as positive if the member is bent in single

curvature, negative if bent in double curvature. For all other cases (C^)

is taken as 1.0.

5.3 Compression-Shear Interaction

The results of the NBS racking tests [50] are shown in figures 5.4

and 5.5. Both graphs express the average shear stress at failure versus

the average compressive stress. The average shear strength (f M is obtained

by dividing the horizontal racking force component at failure by the net

horizontal cross-sectional area of the masonry wall. The average compressive

stress (f ) is obtained by dividing the vertical load by the same area, m

-J r The average measured compressive and tensile bond strengths were 4150 psi

and 79 psi, respectively, for the brick masonry, and 1200 psi and 30 psi,

respectively, for the concrete block masonry based on a net area assumed

equal to 52 percent of the gross area. The mortar used was of type N specif

i

in ASTM Designation C270 and consisted of one part of masonry cement and

three parts of masonry sand in the case of concrete block specimens, and

of one part of portland cement, one part of type S lime (ASTM Designation

C207) and four and one-half parts of masonry sand, in the case of brick

specimens, all contituents being proportioned by volume. The mortar cubes

developed an average compressive strength of 580 psi.

To interpret racking test results, the distinction is made between (a)

failure by shear cracking of the mortar joint along the loaded diagonal,

(b) failure by tensile cracking through the masonry units along the loaded

diagonal and, (c) compressive failure by crushing of the masonry near the toe

The different failure modes were observed to depend on wall geometry, loading

configuration and type of masonry. The 8x8-ft walls, tested in accordance

with the ASTM E72 method, as in figure 5.3(d), and the 16xl6-in prisms under

diagonal loading, failed by diagonal shear cracking. The diagonally loaded

4x4-ft brick walls, as shown in figure 5.3(e), failed in a like manner

under small or no edge loads. Greater edge loads produced diagonal tensile

cracking through the brick units. The 4x4-ft concrete block walls were

not tested in this manner. The horizontal driving force (H) in the NBS type

tests, as in figure 5.3(a) to (c) , induced failure by toe crushing

with the exception of 4x8-ft brick walls which failed in shear.

59
In the plots of figures 5.4 and 5.5, attention is drawn to the fact that

results of square specimens without edge loads fall on a 45-degree line through

the origin. In the presence of edge loading, the plotted results appear to

describe approximately a straight line failure envelope for both cracking

patterns: through the mortar or through the masonry units. The results of

tests conducted elsewhere [29, 56, 59] tend to corroborate this behavior.

Assuming a linear relationship between the average shear strength (f^)

and the average axial stress (f^ ) , the racking strength of a masonry wall as goverened by failure initiated by shear cracking may be reasonably approximated by a linear relationship of the type,

V' = f • + u f (5.16)

f. .. V m

in which (f) represents the average shearing strength of masonry without

axial load, and (u) is a coefficient representing the influence of compressive

load on shear strength (Section 4.7.2) and may be evaluated from curves fitted

to the results of compression-shear tests (figures 5.4 and 5.5). For the

4x8-ft horizontally loaded and 4x4-ft diagonally loaded brick specimens a value of u = .40 was observed. This compared with u = .55 for the 8x8-ft

diagonally tested hollow block walls (figure 5.4). In the absence of experimentally determined values of coefficient (u) for field samples removed from

actual construction the following expression should yield generally con- servative estimates of shear strength,

v' = f + 0.3 f (5.17) v m

where

,

v' = average shear strength of masonry in the presence of

axial load

With an appropriate reduction factor (r) , calculated as in Section (3.2.4) or Section (4.7.5), depending on the source of information on masonry strength,

the lower bound value of shear strength is given by

v' = r f" + 0.3f (5.18) v m

Equation (5.17) should give reasonably conservative estimates of shear

strength when failure is triggered by shear or tension cracking along the

diagonal. As noted earlier, the NBS type tests, displayed in figure 5.3(a)

to (c) , produced compressive cracking near the toe of the specimen under high

edge loads. In figures 5.4 and 5.5, these points are plotted below the shear

60
failure envelope which is approximately represented by equation (5.16). It

is therefore necessary to compare the maximum compressive stress in the

wall under high edge loading conditions against the compressive strength of

masonry under combined in-plane flexure and direct compression. The

interaction equations (5.5) to (5,9) may be used judiciously for this purpose

keeping in mind that the sectional properties now relate to the major principa

axis and that approximations introduced by linear stress distribution theory

are rapidly amplified with decreasing (h/L) ratio because of deep beam action

However, on the basis of studies on the behavior of deep beams [78] , the

equations in Section 5.2 are judged to be adequate within the practical

range of (h/L) ratios (0.5 < h/L < 2).

5.4 Flexure-Shear-Compression Interaction

Very little is known on the behavior of masonry walls under the action

of loads which produce simultaneous biaxial bending, axial compression and

in-plane shear. A simple rational (albeit conservative) approach for use in

the seismic investigation of low or medium rise buildings which are of concern to this study is given below.

Assuming the presence of out-of-plane flexure does not significantly

influence the racking shear strength, equation (5.18) is used independently

to determine whether the wall is capable of resisting the induced shearing

stresses without diagonal rupture. The wall is then checked for the con- dition of combined compression and biaxial bending by the following linear

interaction relationship,

M M ^ + K;f^ < 1 (5.19) M M —

ex ey

where subscripts (x) and (jf) designate major and minor principal axes. Thus, (M ) is the same moment as (M) given in eq. (5.13), (M ) is the internal

y ^ (in-plane) moment, (M ) is the moment capacity about the minor principal

ey

axis calculated by the equations in Section 5.2, and (M ) is the planar

moment capacity calculated as noted in Section 5.3. Attention is once more

drawn to the fact that, as in the case of out-of-plane bending, eqs. (5.9)

and (5.10) must also be satisfied.

5.5 Load-Deflection Relationships for Shear Walls

The load-deflection relationships used in the sample problem of Appendix

are based on principles of mechanics of materials assuming the constitutive

61
relationships of masonry to be linear. The distribution of earthquakeinduced story shears to the individual walls is in proportion to their

in-plane stiffnesses which are determined from the following equation,

A = f||.c|^ (5.20)

where

A = in-plane horizontal deflection at top of wall relative to

its base

V = horizontal shear force in plane of wall

h,L = height and length of wall, respectively

A = horizontal cross sectional area of wall

I = moment of inertia about major principal axis of horizontal

cross section of wall

E,G = elastic and shear moduli of masonry material, respectively

f = form factor related to geometry of wall cross section

' C = numerical constant related to fixity conditions at top and base

of wall

For the condition relevant to the problem of Appendix A, it is assumed

that G = 0.4E [13, 45, 46J , f = 1.2 [54], and C = 1/12 (rotational fixity

at top and base). Substitution in eq. (5.20) gives,

A^ = (-^ + -ill-) (5 21) Et Vt 12I/t^ ^i.^i;

from which stiffness (k) is calculated as,

V Et k =

A 3, ^3 (5.22)

A/t 12l/t

3 A plot of (k/Et) vs. (h/L) for a rectangular section (A=Lt , I=tL /12) is

given in figure 5.6.

6. Summary and Conclusions

Methods have been prescribed for the evaluation of the strength and

stiffness of masonry wall elements in existing buildings by removal and

testing of small rectangular segments. The procedures describe methods of

extraction and transportation of wall samples, preparation of specimens,

instrumentation for deformation measurements, execution of tests and interpretation of results. The basic properties sought are the compressive

62
SIDE I SIDE 2

y N EUTRAL ^

AXIS

Figure 5.1 - Asyrmetrioat section.

8-IN COMPOSITE BRICK AND

HOLLOW CONCRETE BLOCK

Figvo?e 5.2 - Cross sectional moment capacity of asymmetrical section.

63
64
8

CVJ

o OO <]D| <]

m U UJ o Q Q: UJ OS OS o <-> iZ^ r- itz

0= 2 ^ o = 2

uj !i- uj ui S 2 a q: Z uJ 2 Z

3 q: 3 3 w

!3 !3 - ^ <

^ ^ ^ ^ <e

00 "00 ^ 00 _»< X X -** _*< 00 "00 ^ * i5

!3 < <^ O © o

g

'

' o

S1S31

nvnaiAiQNi

S3Aano

o

o

o

lO 8

Tsd ' J SSaaiS HVSHS aOVHSAV

65
66
U pq <:

Figure 5.6 - Stiffness vs. h/L ratio for shear walls.

67
strength, racking shear strength, flexural bond strength and stress-strain

relationships in shear and axial compression.

The sectional capacity of a masonry wall has been specified by means

of interactive relationships among axial compression, shear and flexure,

using the basic strength and stiffness parameters derived from tests.

Supplementary information on the basic strength properties of brick and

concrete block specimens derived from available test data is compiled to provide an indication of strength of comparable masonry construction under con- trolled environmental conditions and good workmanship.

The direct test approach described in this report has been proposed

after having studied possible alternate methods of evaluating masonry properties

in buildings which have been in service for various periods of time, and

is believed to be both practical and comprehensive. Among the more radical

methods, the use of ultra-sonic devices for non-destructive testing appears

to have good potential for structural application. Other promising research

areas are the use of spectroscopic or x-ray analysis and hardness tests on mortars to develop criteria for predicting tensile and shear strength of

masonry

.

7 . Acknowledgements

The contributions made by the following persons are gratefully acknowledged by the authors

- Phillip T. Chen, Robert D. Dikkers, Morris Ojalvo and Norman F. Somes

critically reviewed the report.

- Robert A. Crist, Richard N. Wright and Felix Y. Yokel provided con- structive criticism and technical guidance.

- Rebecca Hocker typed the several drafts of the report manuscript.

68
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69
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70
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Research Report No. 10, Structural Clay Products Research Foundation,

Geneva, Illinois, October, 1966.

38. Compressive, Transverse and Racking Strength Tests of Four-Inch Structural Clay Facing Tile Walls, Research Report No. 11, Structural Clay

Products Research Foundation, Geneva, Illinois, February 1967.

39. Negoita, A., Bearing Walls in Earthquake Areas, BUILD International,

Vol 5., No. 1, Essex, England, January 1972.

40. Peck, M.F., Phelan, V.B., Dill, R.S., and Petersen, P.H., Structural,

Heat Transfer, and Water Permeability Properties of "Speedbrick" Wall

Construction, BMS86, National Bureau of Standards, Washington, D.C.,

July, 1972.

41. Mattison, E.N., and Churchward, G. , Some Tests on the Bending Strength

of Concrete Masonry in Running Bond, Construction Review, Australian

Commonwealth Industrial and Research Organization, February, 1969.

42. Dikkers, R. , and Saxer, E.L., Flexural Strength of Plain and Reinforced

Concrete Masonry Walls, National Concrete Masonry Association, Arlington,

Virginia , 1957

.

43. Livingston, A.R., Mangotich, E., and Dikkers, R. , Flexural Strength of

Hollow Unit Concrete Masonry Walls, in the Horizontal Span, National

Concrete Masonry Association, Arlington, Virginia, 1958.

44. Motteu, H., Lejeune, M. , Collet, Y. , and Dzulinski, M. , Studies of

Load-Bearing Masonry Report No. 12, Scientific and Technical Construction Center, Brussels, Belgium, 1970.

45. * Uniform Building Code, International Conference of Building Officials,

Pasadena, California, 1973.

46. * Building Code Requirements for Engineered Brick Masonry, Brick Institute

of America, McLean, Virginia, 1969.

47. * Canadian National Building Code, Supplement No. 4, Ottawa, Canada,

1970.

71
48. * Report on Concrete Masonry Structures - Design and Construction, ACI

Committee 531, American Concrete Institute Journal, May-June, 1970.

49. A Design Guide to Engineered Clay Masonry Bearing Wall Systems, Canadian

Structural Clay Association, Ontario, Canada.

50. * NBS Racking Test Report, National Bureau of Standards, Washington,

D.C. (in preparation).

51. Proceedings of U.S. -Japan Seminar on Earthquake Engineering, Sendai,

Japan, September, 1970.

52. * Yokel, F.Y., Dikkers, R.D., Strength of Load-Bearing Masonry Walls,

Journal of the Structural Division, ASCE, May, 1971.

53. Yokel, F.Y., Stability and Load Capacity of Members with No Tensile

Strength, Journal of the Structural Division, ASCE, July, 1971.

54. * Benjamin, J.R., Statically Indeterminate Structures, McGraw-Hill,

1959.

55. Smith, B.S., Behavior of Square Infilled Frames, Journal of the Structural Division, ASCE, February, 1966.

56. * Benjamin, J.R., Williams, H.A. , The Behavior of One-Story Brick Shear

Wails, Journal of the Structural Division, ASCE, July, 1958.

57. Sahlin, S., Structural Masonry, Prentice Hall, 1971.

58. Blume, J. A., Newmark, N.M., and Corning, L.H., Design of Multistory

Reinforced Concrete Buildings for Earthquake Motions, Portland Cement

Association, Chicago, Illinois, 1961.

59. * Fiorato, A.E. , Sozen, M.A. and Gamble, W.A. , An Investigation of the

Interaction of Reinforced Concrete Frames with Masonry Filler Walls,

Structural Research Series No. 370, University of Illinois, Urbana,

Illinois, November, 1970.

60. Wiggins, J.H., Moran, D.F., Earthquake Safety in the City of Long

Beach Based on the Concept of Balanced Risk, J.H. Wiggins Company,

Palos Verdes Estates, California, 1961.

61. Architectural Institute of Japan, Design Essentials in Earthquake

Resistant Buildings, Elsevier Publishing Company, 1970.

62. Wang, Ping-Chung, Numerical and Matrix Methods in Structural Mechanics,

John Wiley, 1966.

63. * Plummer, H.C., Brick and Tile Engineering, Brick Institute of America,

McLean, Virginia, 1962.

64. * Yokel, F.Y., Mathey, R.G., and Dikkers, R.D., Compressive Strength of

Slender Concrete Masonry Walls, Building Science Series 33, National

Bureau of Standards, Washington, D.C, December 1970.

65. * Yokel, F.Y., Mathey, R.G., and Dikkers, R.D., Strength of Masonry

Walls Under Compressive and Transverse Loads, Building Science Series

34, National Bureau of Standards, Washington, D.C, March, 1971.

66. Watstein, D. , and Allen, M.H., Compressive Strength of Brick Walls

with Large Eccentricities, Proceedings of the Structural Journal,

ASCE, April, 1971.

72
67. Johnson, F.B. , Designing, Engineering and Construction with Masonry

Products, Gulf Publishing Company, Houston, Texas, 1969.

68. Amrhein, J.E., Reinforced Masonry Engineering Handbook, Masonry Institute of America, Los Angeles, California, 1972.

69. Amrhein, J.E., Masonry Design Manual, Masonry Industry Advancement

Committee, 197 2.

70. * Research Data with Commentary in Support of Specification for the

Design and Construction of Load-Bearing Concrete Masonry, National

Concrete Masonry Association, Arlington, Virginia.

71. Jacobsen, L.S., and Ayre , R.S., Engineering Vibrations, McGraw Hill,

1958.

72. Newmark, N.M. , and Rosenbleuth, E. , Fundamentals of Earthquake Engineering, Prentice-Hall, 1971.

73. Lew, H.S., Leyendecker, E.V. , and Dikkers, R.D., Engineering Aspects

of the 1971 San Fernando Earthquake, Building Science Series 40,

National Bureau of Standards, Washington, D.C., December, 1971.

74. Leonhardt, F. , Walther, R. , Versuche an Wandartigen Taragern mit

Unterschiedlicher Belastung, Lagerung und Bewehrung mit Schlussfolgerungen, Wilhelm Ernst & Sohn, Berlin, 1966.

75. * Fattal, S.G., and Cattaneo, L.E., the Strength of Masonry Walls Under

Flexure and Compression, National Bureau of Standards, Building Science

Series (in preparation).

76. Meli, R. , Behaviour of Masonry Walls under Lateral Loads, Proceeding

No. 101a, Fifth World Conference on Earthquake Engineering, Rome,

Italy, 1973.

77. Salse, E.A.B., and Fintel, M. , Strength, Stiffness and Ductility

Properties of Slender Shear Walls, Proceeding No. 109, Fifth World

Conference on Earthquake Engineering, Rome, Italy, 1973.

78. * Corley, W.G., and Hanson, J.M, , Design of Earthquake-Resistant Structural Walls, Proceeding No. Ill, Fifth World Conference on Earthquake

Engineering, Rome, Italy, 197 3.

79. Alexander, CM. Heidebrecht, A.C. and Tso, W.K., Cyclic Load Tests of

Shear Wall Panels, Proceeding No. 135, Fifth World Conference on Earthquake Engineering, Rome, Italy, 1973.

80. * Gross, J.G., Dikkers, R.D., and Grogan, J.C., Recommended Practice for

Engineered Brick Masonry, Brick Institute of America, McLean, Virginia,

November, 196 9.

81. American Standard Building Code Requirements for Masonry, ANSI A41,

Miscellaneous Publication 211, National Bureau of Standards, Washington,

D.C. , July, 1954.

73
APPENDIX A

Seismic Investigation of a Masonry Building

A. 1 Three-Story Building with Brick Masonry Bearing Wall and Rigid Floor

The intent of the following calculations is to provide a numerical

demonstration of a procedure for the analysis of a masonry building of moderate height, under the action of lateral forces of seismic origin. The

criteria for calculating base and story seismic shear forces and the load

factors used in this analysis have been selected arbitrarily only for the

purpose of the stated objective. In practice, such criteria will need to be

specified in accordance with the seismic provisions of the appropriate building regulatory agencies.

Figure (A.l) shows a three-story building with 12-in exterior brick

masonry bearing walls and 8-in hollow concrete block interior walls as indicated. Interior concrete columns are at locations 6, 7, 10 and 11.

Concrete girders are located along 5-7 and 9-12. The concrete joist floor

spanning in the y-direction is treated as a rigid diaphragm. The distributed

dead loads are 80 psf for the roof and third floor, and 73 psf for the

second floor. For simplicity, a distributed live load equal to 75% of dead

load is assumed. Masonry weights are 120 psf and 55 psf of wall area for

exterior and interior walls, respectively. The estimated ultimate compressive strength is f ' = 1200 psi for concrete block and f' - 3600 psi for brick

masonry (table 3.1). The respective elastic moduli for brick and concrete

block masonry are assumed as Ej_^ - 3000 ksi and = 1200 ksi. The respective

shear moduli are assumed as G, = 1200 ksi and G = 480 ksi. In accordance b c with Section 3.2.3c, shear strength is calculated as 120 psi and 70 psi, for

the brick and concrete block masonry, respectively, assuming f^ = 0.2

The validity of the approach herein used to analyze the building itself,

is dependent on two primary assumptions: (a) the wall system is capable of

integral action in flexure induced by lateral forces, and (b) the floors are rigid in their own plane. Assumption (a) is analogous to the condition of

vertical continuity, through adequate connections, between intersecting wall

elements. If the connections between abutting wall elements in a particular

building cannot be relied upon to offer total continuity, the building may be

conservatively analyzed for the two limiting conditions; the first, assuming

complete continuity, the second, assuming no vertical continuity. The strength

of individual wall elements can then be compared to the most critical stress

condition resulting from either assumption.

74
S& 20' = 60'

io<P4l = 40'

5' 4' 5' 4'Z 8' 2' 6' 4' 34' S' 4' 4' ^11 k kk—kk kkk k k H k

PLAN

II

Roof

3/ F/.

6'

3'3'

6'

3'

3'

6' Fin. Qrd

ELEVATION

Figure A.l - Three-story brick masonry building of bearing wall oonstruation.

75
Nei area, 'Cetc'i<rr ( Scc4. 3,3, 3j /'s colcu/ciiec^ as

/^^ : 0.673

Wei^h is ( k'lp) '

f^oo4 : [(<io)C4o) - (zo)0&)] (.08) = Id!

E.k4> rn/ls (^c>c)(^)(.i2oX. 900) ^ I z&

M. Walls ; (^^) ((>) (' 0 5-0 = / ^

£^4.V^/alls: (Z)(/^a) = ^€C.

In-f, Wal/S'. (^)(/^) -

Tc-tcl 3' ficor = ^^5^

^CL^ floor C/<^7)(7^) /30 =r / ^2

Ba4, Walli : (i^a)Ci f 0878/.900)-] ^ z fa

ln4. WoUs :

Toial 2"-^ FIcor = 4 3 5^

ra4, 31 A//- = IZ4 6

76
Wall ^ ThicK, Gross

Thi'cK. Effeci,

Thic/e.

AArff<j /v

/- 5 I'O o.a 40 40

f- 6 -67 ZO Z /o 24

7-8 h 0 20 60 M

lo-i 7 .i(> '67 .101 e> 1 t4

ho '86 Co 30 0

\ 1 y 1 Iff / (.3/ ) (i.o) (,8I) ^ &0 ) ^48. ^ ) (0 )

1-15 • io /. 0 .90 40 0 20

lO'iA • CI • 107 l(> hi 70 a

5' 7 1-0 I'O /6 40 32

1,0 1.0 14

5^ S'forles

(lai. 3)

Ax Ay

1-3 c>4o 12800 42bl SI -zoo 20 zoo 67 45 lit'!

-7-8 /ooo fo 000 430 II 5Z0

t7C> 5 IG

475^0 ltQ4o 0 0

(13- /C) (4^ 140) (14^-30) (0) (0) ( -)

l'/3 0 0 720 14 400 4300

10'

M

34 6e>o 14 !/2 3C

3-1 C40 5/2 /6 334 341

1440 8G40Q Z33 5 4SQ 11^2

Zti or 5332 Z25 77 20 84L 335'S ^8 480

(zto 000) (18480)

11
(open/n cJec/uc-^e.c/) to ^rcss ye.ri^ic£i / arep ('sect $.5).

(1) hJ&-f eirea. /s 40 Z froJS- area ( 5<ic,f/o/-> 3.3. Z). Nei ! area/ /$ ma/i^/^//e^ tc /t^ = 1200/3000 ~ . 4-

j There Z<Fre, area re^^<^T^/oAt -factor /s = C4)C'4) = ./Cs . Cen-^roic/s .

Ce.yi'iro/'c/ci / moments of inerT'/a.

^s^Lf t ^8480 - I8^.^(l8.lf = 44 04.0 /{^ (z- or3^S^f^f)

3 2 f ^8430 - l&l. 3 (IB. 5)^ = 42, ICO .fi'^ (/it s/ary)

loH -f- Ay^- - z

l^^3^ -i- Z20 000 - 131.5 (Zl)^ = 81, I/O (('^ -5-/^^;

78
For cJc/y^o/os-fya-^/on pcjrpajes -fUe fu^^^^'j^' eJ^-Zcy / perio^f

u)'// he ca/cu/aieJ c/s/^^ -four c/t//'ere/)r'- o^ef^ oer/s : Ccc) pir/s ryya^J/c i>ea/9i &<^c/a '/^<r?7, C^) nat>ier/c<7/ / ^^ra /fo ^

^l^eor yV(St// areas: //i cocrc/z/ia/e oZ/yec-Z/c/^ s

. ^ 3% -h Z i- ZO ^ / ^ (52.8 cr '^e.^)

s 107.8 ^ 3^ S-f^y

= 3G 1.7 + U -i- 2 4 = 77.7 .-;/•• s-^o>'.'cy

^ Ay 77

2Jil4404O 1 ^ 1417 (7^cr3^sfay.)

'7.7 1427^0 / = /^7C -fe (/'J- s-l^u )

Ay 1 37I/O //J3 6/0 :l/o2 ^'i^ (I'-' ^^^y )

79
r A /£LL) - '^'^^ - U!£]}±II2^. 4,33

'

(36)'-

' 3

(JSC B%.(l^'^)'

40

7

80
hlui^ef/ca/ I/)'/e^rar'/cP^j C'^PP'^o^fx B>3) :

ir\ 'fer/i'is o-f m S-SQ/^ -fay mass (^et/ae. ai' roc/ ytoa^e )^

Y -DiRFcTloK (Fi^.A-O

I

func-fion 1

' 3h = 3(ii) ^ _j . . . * . . = 3(^'

1.0 1-21 1.2 Z

1

1 1 1

V. 3.0 1.0 0

^

{disk. Id.) 3. &I 1.27. V 5.7 f.s/ 7)) hp

IS. 11

• / 7 Iff . u ^ 11. /fo / 3 ^ -r "m 37.S5 ill/

0

104, 22

%

20f.l 104.3

.009/ ,003

8

. 0O87

-

I 32 (300OK /^'^) {^3 6/0)j ==

81
X- DiR£^T/oNi (rr^ . A. i)

t.O iO--) 1,72 o^h

toio tdlO %o-}o

4

3/'Sa 7€.77 (0,8^, ^i,y/£i^

^B.2l 3i.i3 /o,3(^ -^/^^f^y^I^

3&^3 U$^.2 /^/'^ ^hf>\'^el^

30l. 43i,i> IS/. 4

y^hy/fly

^2^%;-^^ ^^'^'^ ^'^^''^ '^'^'^ ^^J^Y^fl^j

f=^'/% '^^^^1 '^^^^^ >oo&U

o 1^ s C, sec,

82
l/.A. t/hnual [do] :

Tx = 7^ =r 0.0 5/^ = <CSC^) = OJSO sec,

Cafculaie. ccc^rre^f^j io V/i Ma/ic^a/^ H^-^l^ oc/ / [^<^]

Assume Amc*^ = O-^^l C'^i'^p^ s^'i'<^ *{/a/ej£i^/o/} siu<r/y)

DAF = 3 ^ ftf ^

5^£^JA r 1/^ X = cx Sa.W - (V^)6'7/J(/:?4a) /^^^

//e 5^3/^ <s i?/ c/ar/r't^ , a///Fere.A /- base she^>r \/a/c/&s

will be ofssuwcci "for x cif^^ y (p//rec^/o/is m sah seif^c^i-

/2)^ ^ 5(>/3S <3.0^ .. F^^ ^ 0

/Vy r 3^/0'2 <3.0j /. Fiy^ O

Ai a^f fei^c/ j\ Fjk = ^x^j^j /.'^^ ^^^c

Fj^ =. Vy ur.h,/J vf^-h,

( U&C cf. 14- f'

4 VA manc/O'/

)

Foo-f

F'aol

f^,^ = Ci33)(43S){/2) /z&^Sa = 24.'!''

F^^ = (i38)(43^)Cx4) /28'^3^ =: S/.3^

F3. = (I33)(3^^3){3CJ / = ^1.4^

= 138.1^ ^

= {143) {43SJ (iZ)/ %S9So =

Fz^ ^ (MB) (4^^) (^4)/ z&^So = iS>F^

. (148) (3S3)(3i>)/ zaiffO = j^^V^^

83
84
?'

A6/^ c £1

= 3.4) Xi. = 7f7 A

h4 = '^^/A4. =r £T^Af = S:{r

^ vV--

85
2k„, '708

4 0 I78VJ ^ ,-^38]/ = /.oooV {chec/<s)

Aa = -Jy- {4'f^-'lS3V) = 1.4/ ^ (chec^^)

Et ' ' ft

V

3

'

3'

©

(D ®

® @

i 5' \4' \ 5' \ 4 \ iZ'

V

0

(D ®

7S'

86
A = 1. flL ^ Chi ) {zt, 6^. s.z,)

Ei ^ A/i ' I/t

Tier L T/i 3 / (C.tCi)\/r, yn A /Et\

1 3 60 IS J

1 '//Z 10.4 1.73

t) 10.4 3. (a /. ZD . 114 V

4 12 144. /. s- 1,^3 V4 ,372/ . ioa

5 7

& 7/1 S 10.4 1.73 ^.33Vc

7 4 S,33 4.S 3,33 . &40

6- 3 30 '3 .60IV .180

3 1L4 '17£ .58 .151

Z' or 3 ' S-Zari/ Wall

1 3 ./S ./SV V .ISO

I s l^'4 1. 73 .4S0

3 '//z

5" 10.4 3.C> 1.75 ,4-8)0

4 '//a 1S07 '72 ^/ .4-30

S '//2 £ 10.4 2. i> /.73 3.3^ .070)/ , 430

(> c> 4 4.^ 3.33 1.33 V, .430

7 3 60 .It .1^ V V ./to

Laii 4:^0 Co/ii^r?n en4rjes are c/e "fer e •^'^rc.

87
A^.t-,, 2.2oVf^ lasVy , Vt = .4IV^ (4-)

1/ .- Cs)

y'leld 41) e eyify'ies '/r> ii^e V^, cofc.'>>>/i jail's ^ si^^yi-/ wa//

,

li ( re ,

/V/3 i

v/^ . ^'/{A,iA^^A,J = £-t/l35 = 1. oocyst

'!(, -

VJe<,^ Wall (I'I2) .

I L

3'

0

® ® ®

©

88
Fi'er

f V ' h C AA /a/i- ^ '/ / ^ EtAn = (d 4-Ci] Vn ^^('^)

/ 3 _ 40 .^25']/ Z25

z Vn IQ 1 4. 3>1D

3 'iVs .620

4 Vn 13 3 1 4.V4

5 3 4-^ ,225 V .22S

\hJall (3-7)

^ / ( A/i ^ cl/t J

i,.-^ = £t//AUl ^

1'^'

] = = '274 Et

/ ( 'z(!^yi^)J Ins + .421 i^ij70 f,pf

kj.s = Bi/r 3x /2 ^ ; ^

Bt_ ^ ,4^c^i=t

/ L ''^^ r;.'joy,^)j /.&^.'^/C .214 270

^-r .>z(24yj-^) \ !.6-h.f25 ^^^^

J 1.3 ^^IL 34J2S kp^

yJall (lo-nj ' —

Wa// (/o^,4) ^

,

, //- sxiz 7 - iOfs^ft

89
A, ^ ^ V/4.4f£i: = . 22 47 V/si

s - . 2247 V/S^

V 16 dish' ^uie ^ plen 2 is 6 ^ro^irrf;c>i -fo s-////^ess^

^/f = 4(1^7^) ^-372 = .832 V/£i^

1/^ ^ V = .422oy

90
is - 3,3 4 £^

91
Miuss Cenfra/ c/s

w %

an

FT /V

7-t Z (J ^^ nU

3-7 '24- (/<i) 4-0 act 7-8 « (xo

)

J Q 6 O

3 -/6 (2^J <i O

/-/3 7' (is> X. U o 1 f ^

J U 0 4- s z 0

• 0S> (40 x&o) / 7 4, i o

ir7x -' 08 C^ox Id ) Kn " CI II /fc Hal/ 1'^ 2 3.04 no 4(3 4(>o.i

3- 7 7Z Oc)0'^) 11-^2 yi / A Q

" {xo)Ci) l4>4 ^0 x4 72 O 34^' ^

" (i^) CO /7'2<9 (, o It 20 7.3i, " (&0){.&67j 20 0 o

1- /s 0 ^ o 0 618.4

.0f5(G)(70)C/) 10 ^4 /58.4-

10-17 •33 (&)(') z4 IL 61- 3G 42,24

" (/&)(!) & /OS- (, 42.24

Z - Id. 15

ih 'Factors "fo etccouti

5/ai> l-4-li-l5 same as 57^0 384-0

" 3-4-7-8 II '1-280

Wa// 1-3 Tv^ice as a bov£ 4(^.08 1643-2

3-7 II 23. 04 92/. i> 7 37.23

7-5 II ze.a l440

II 414. n

1/ 14.^=1 7247.2 0

1-15 1) ^1.84 O I03i. 8

n /32

lo-n 126. 72 84.48

i0'/4 ZII'Z

Z ^ 454.7 IS. 10 12554

92
W X 1- (ft'li)

lA/y

5led) l-4-/&'/3 Sa/ne as roo-f 67^o 3 840

" 3-4-7-8 II -I2SO

wa// /-3 Twice a$ roo-f ie43.Z

3' 7

II 23.04 737.28

7-8 ii 28.8 I440

e-i(> II 34.5C> 4i4'l2

iS-li, 1-13 Ti^'ice as roo-f

71./$

S/.84

30 o

0

a

5-^ II 12.2

/f-/7 // 5.28 /2&. 72 64.48

I0-/4 II 84'46

X 4-V 12443

93
, f /In^^/ifS/S oind 5hears /n yi/g/Zs

(units : A*// kips)

VII?. % J — y

A<rcld. Wall

V

Si0

\i A

1

I'I3 fir 0 - o — 28.8 t4.C. 31. 3-7 40 _ — 13,3 U.l II. ^ t .4 12.

.&lS GO - — 33.7 iaz. is.1 1 1.8 20.-}

\o-(4 01 — 3.1 2.1 o z./

2 1.114 ^1.4

%

I X

\-3 - 40 - US i4hl 14'(^ U tl.2 Ii>> 1-8 4% 24 II '9 42.4 IS.^ i£ 14.1

1.282 0 o -I4.1S V8.9 -7.0 + hi 2^.7

14 i.f ^25 i.& 7 J ' 1 t./ 2.2

lo-n .02 .32. 0

5" 0 o . r

% 7.m 20B1

= ^'^Yl.^U = 2&.73

'

8 13

94
Wa//

1 1 d

V

I

1-13 '^43 57.4

3-1 ' t .3 U2.

\

8-/6 " 3^.4

10 'i4 4. 0 0 4.0

2 0^

1-3 17 t 7.3

7-5 1 Ti'

A

-3.S

f- C . z t. . 1 4. 2

0 0 /. z as 3 - sifff^ 3 0 ^ 0^

r (>h4 f S-/. S = //3.Z'^ (r /.'i94 = fC^??)

t^^lrr *'^2inff\xC^^-%) = -^^3-?'SS.ff3.3ti^-4l0["(rzc:2^, ..:o3)

'Tety^ ty £> ^ ;

95
f/rs/ Sicrry W<a//s ayxsf Se<^«>e^ F/a^ 7)' <^ >'<^

1^^'

ili4^

fite.icr', y\ja//

iN>^

«J \iK\

/-/3 o (,4,8 70.

3-7 7 /i' — /1• 0

8'l{, t 4,2 4i'3 _

10' f4 1/5 1 4. ''*/ 5./ 4< 8 u T' O

/ '"T

>-

Vj «JV

1 •\

1-3 40 Xht> 'ill S, / 1-3 24 34'3 ' 9 t . 7

l3'/(, 0 0 -i(>.(>4 278, C -4J ^3,4

14 /.«? 7.56 4.3 1 i . /

10.

n

< i 0 /'4 0 0 1,4

i/.37 20Z0 148^ o ^ 0 *^

96
cenn^i/^ei^ s ^louju. Self eyi^o"/^!: ^//i^ ia/a-uu, Jt^ /-f TtcP

S<S/ S/y>/ 'e.

,

Forces J^ra^/e/ % X-tf y/S"

97
f^Ot/l / m

1 .7/2 .15/ I-03Z

2 041 .320

3. II /, / / OSO '39^

5/ //

/ 1 ,/40 . SCO 1.104

r

(, 1

'

1 1/ 8 3 /

9 2../ 'CI 6 • Ml i

ft

10

II //

It i/

/s '0/4 ,see />2/3

ft

^

L

/i- //3/

n \ , 2^1 '141 • Of ,02^

98
ort, /I) / h )

I^OO f .08 ( a

)

• '^

// '480

• o7i (a) 564

/_£:? . V8

.^84

IJb2 4.9^8 19 P'/ l,3S^ 54. 2.

. (t.3n)0iA) (.3)= t_i_rz_ %0'

1

P-*—

M -- t lll.97{^'/3}4l.72(^V3jl- t /5/.8 "<

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^ - r = Ins I kips

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So J

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103
APPENDIX B

Approximate Methods for Evaluating

Natural Period of Vibration of a Building

B . 1 General

Earthquake regulations prescribed by design codes make use of the natural

period of a structure for seismic force calculations. Two simple methods for

the approximate calculation of this period are described in the following

sections for expedient use by the analyst. The cantilever beam formula lends

itself to buildings of uniform stiffness, geometry and mass distribution. The

numerical integration method is more general and admits buildings of irregular

configuration

.

B.2 Cantilever Beam Method

The prismatic cantilever beam is the simplest model used for the idealization of multi-story structures. The fundamental period in this case is given

by the closed form equation.

where (L) is the length, (E) is the elastic modulus, (I) is the moment of

inertia, (m) is the distributed mass per unit length and (T) is the fundamental period of the beam. This idealization requires the determination of a uniformly distributed mass value for the building and the appropriate evaluation

of constants (E) , (G) , (I), and (A). In equation (B.l), (L) may be considered

to be the above-ground height of the structure. The uniform mass may be obtained from the total weight (W) of the structure as follows.

where (g) is the gravitational acceleration. The elastic modulus of the most

common material in the structure may be used as a base modulus (E) of the

system. The other materials are appropriately transformed at various floor

levels according to modular ratios to give moment of inertia values which are averaged out for use in equation (B.l). The calculation of sectional properties requires certain prior adjustments of individual wall dimensions to

account for the effect of openings in these walls. For the purpose of predicting the fundamental period it will be sufficiently accurate to smear in

the openings according to eqs . (3.10) and (3.11).

T = 1.79 (B.l)

104
Equation (B.l) only considers the effect of flexural deformations.

In a short beam (high -/I/A'/L ratio), the effect of shearing deformations and

rotatory inertia will be significant and should be considered when modelling

a building of small height-to-width ratio. To account for these effects

equation (B.l) is modified by introducing an approximate factor [71] as follows

,

T = 1.79 [(1 + Q) (B.3)

where (Q) is the ratio of the maximum static deflection due to shearing deform

ation to that due to flexural deformation at the end of a uniformly loaded

prismatic cantilever beam. Denoting the two deflections by (A^) and (A^) , the

distributed load by (q) , and the form factor by (f), (Section 5.5), the expres

sion for (Q) is derived as follows,

AV

= ^

2GA

4 A. =

f 8EI

then

,

In evaluating the above parameters it should be kept in mind that "immovable"

or "fixed" live loads and non-structural attachments contribute to the mass

of the system. In addition, non-structural elements such as partition walls,

contribute to the lateral stiffness of the system whenever they are supported

along more than one edge. Consideration of such refinements is subject to

judgment in view of the approximation inherent in the beam model.

B.3 Numerical Integration

Certain structures cannot be adequately idealized by prismatic beam model

Buildings of irregular shape or with setbacks fall in this category. For such

cases, the structure in question may be idealized by a non-prismatic beam

having a discrete number of segments with lumped (story) masses at its nodes,

and analyzed numerically. Among several good numerical techniques devised to

analyze a discretized beam, Newmark ' s numerical integration method readily

suggests itself [62] . The method lends itself to manual calculation (as

opposed to computer processing) and is applicable with almost equal ease to

problems in which segment lengths, sectional properties, elastic constants or

105
lumped mass can be treated as variables. It can also be used to calculate

higher natural frequencies. A concise treatment of the method follows.

According to ordinary beam theory, the relationships between distributed

load (q) , shear force (V), moment (M) , slope (0) and deflection (y) in a beam are given by the equations,

V = /qdx

M = /Vdx

0 = dx + qdx (B.5)

y = / 0 dx

The effect of shearing distortions is considered in the second term on

the right hand side of the third equation above.

For a beam divided into segments of finite length interval (h) , (as opposed to infinitesimal length dx) , the approximate relationships corresponding

to equations (B.5) are given by,

V = hZq

M ^ hEV

. I , •. - ,v ^ - - y - hZ0

where the quantities under the summation sign (E) represent either equivalent

nodal values (q , M/EI, fq/AG and y) , or constants between two consecutive

nodes (V and 0 )

.

For dissimilar segment lengths, equations (B.6) are modified by including

variable length (h) under the summation symbol. Thus,

V ^ Ehq

M ^ EhV

e-zg.Elfl (B.7,

1 y - Zh0

The deflection of a beam due to a distributed load (q) can be computed

by successive numerical integration using equation (B.6). To simplify

numerical calculations, another approximation is introduced whereby distributed functions (such as, q, or M/EI) are converted into their nodal equivalent

concentrated values (ch. 3, Ref. [62]). If the particular function is

106
designated by (s) , its nodal equivalent (s) , in the case of equal segments,

is given by the equation,

for interior node (i), and

^i = T2 (^i-1 ^ i°^i ^ ^i+i) (B-s:

^o = 14 (^^o - ^^1 - ^2^

and {B.9)

s_ = ^

(7s I- 6s T - s „) n 24 n n-1 n-2

for end nodes (o) and (n) , respectively.

Similarly, in the case of unequal segments,

i = (1/6) [h (2s + s ) + h (2s + s.,,)] (B.IO)

1 11 1—1 1+1 1 1+1

for interior node i, and ,•^1 ^o = 6- + ^1^

and ^

(B.ll)

S - 7^ (2s + s ,

)

n 6 n n-1

for end nodes (o) and (n) , respectively.

To determine the natural frequency by numerical integration, a deflected

shape is first assumed. For periodic motion, the inertial force (-ma) is

- 2 equal to (m^p y^) where (m^) and (y^^) are the lumped mass and the assumed

displacement at any node (i) , and (p) is the circular frequency. Using

niomerical integration, a new deflected shape expressed in terms of (p") is

2 obtained. Equating computed nodal deflections to the assumed values, (p ) is

determined at each node. If the assumed shape is close to the modal shape,

the computed frequencies at the various nodes will be in close agreement,

otherwise, a second cycle is used in which the assumed deflections are the

computed deflections of the first cycle. Due to rapid convergence of the

process, one or at most two cycles should yield sufficiently accurate results

if good judgement is exercised in selecting the initial displacements.

B . 4 Fundamental Period of a Beam by Numerical Integration

The fundamental period of a prismatic and of a non-prismatic beam are calculated below by the numerical integration procedure described in Section

B.3. Since notation form is retained for some of the parameters, units have

been omitted in these calculations.

107
Prismatic Beam.

Mass per unit length (m) , flexural rigidity (EI) and shear rigidity

(GA/f) are treated as constants along the length of the beam, with G = 0.4E,

f = 1.2 and EI = 36 (GA/f). The rectangular cross section has a width of 5 and a depth of 12. The four segments are of equal length h

(5) (12) =60, I = (5) (12)^/12 = 720.

60, Also, A =

The tables below indicate two cycles to yield sufficiently close values

2 of (p ) at the nodes. A linear least squares fit gives [62],

2 P

= __1_3

Zy,

^ 0432

mh

^

which yields, upon substitution of 4h = L, the fundamental period.

T = ^ 3Q^2h2

P

This is in good agreement with the closed-form solution (Eq. B.l), the

higher estimate being due to the inclusion of shearing distortion effects and

approximations involved in the numerical integration procedure. Neglecting

shearing distortions,

2 ll/2

T = 2tt m

2-'m = 1.83L' m_EI

Non-prismatic Beam.

In this beam the distributed mass (m) , flexural rigidity (EI) and shear

rigidity (GA/f) are assumed to vary along the beam, with the nodal values as indicated in the top three lines of the numerical integration tables below. A

least squares fit to the results of the second cycle gives the fundamental

period.

T = 2Tr ^Y-

^YoY2^3

1/2

= 1.54L' m_EI

The contribution of shear deformations turned out to be negligible due

to the slenderness of the beam selected for this example. In actual structures, shearing deformations are often more dominant as indicated by the

numerical example in Appendix A.

108
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112
APPENDIX C

Description of Specimens and

Test Setup for Data Listed in Tables (3.1) to (3.3)

C.l Small Compression Specimens (table 3.1)

Tests of small compression specimens described in reference [65] employed

prisms of the following description: Compression tests were conducted on 3-

block high and 5-brick high prisms. The block prisms were constructed in

stacked bond. The brick prisms were constructed in running bond with a whole unit in the first, third and fifth courses and two half units in the

second and fourth courses. The prisms constructed of 8x8xl6-in hollow

concrete units contained only face-shell mortar bedding. Full bed joints

were used in fabricating prisms made of 8x8xl6-in solid and 4x8xl6-in hollow

concrete block. The brick prisms were constructed with full head and bed

mortar joints. The height of the brick prisms was 12.8 in and their heightto-thickness ratio was 3.5.

The small compression prisms in reference [65] were subjected to axial

compressive loads in a universal testing machine. Most of the specimens

were capped at top and bottom with high-strength plaster but some were

tested with fiberboard instead of plaster to provide support constraints

similar to those of large wall specimens. Loads were applied through steel

bearing plates and a spherical loading head which allowed rotation at the

top (simulated pinned support condition).

C.2 Large Compression Specimens (table 3.1)

Wall panel compression specimens described in reference [65] were con- structed in running bond and were nominally 4 ft wide and 8 ft high. Thickness

and cross section of the panels depended on the type of masonry units and

type of construction used. The brick used in these walls were cored; for

such brick, gross cross sectional areas were used in stress calculations.

Bricks were laid with full bed and head mortar joints.

Hollow block walls consisted of 8x8xl6-in whole 2-cell units and half

units that were obtained by cutting kerf block; the bottom course contained

a half unit at each end. Bed and head joint mortar was applied only to the

face shells except, at the outside edges of the walls, bed mortar was applied

to the exposed webs

.

113
r

Solid concrete block walls were laid in the same manner as the 8-in

hollow block walls except that 8x8xl6-in 100% solid block were used. Full

bed and head mortar joints were used in constructing these walls.

The 4-2-4-in thick block-block cavity walls contained 4-in 3-cell

hollow concrete block in both wythes. Full bed and head mortar was applied,

and head joints of opposite wythes were staggered. The wythes were bonded

with metal ties in accordance with ANSI Standard A41.1 [81].

The cavity walls containing brick were made with a facing of brick and

a backing of 3-cell 4x8xl6-in hollow concrete block. Full bed and head

mortar was applied in the brick facing wythe and face shell mortar was applied in the concrete block backing wythe as described previously.

In the 8-in composite wall panels the facing was made of brick and the

backing of 4-in hollow block. Bonding consisted of a brick header course in

every seventh brick course. Full head and bed joints were used in the brick

facing and block backing. The collar joint between wythes was filled as nearly as possible by pargeting the back of the brick facing and slushfilling the remaining gap as each course of block was laid.

Compression testing of wall panels in reference [65] was accomplished

in a universal testing machine. The load was applied to the wall concentrically through a loading beam, a 1-in square steel bar centered along the

mid-thickness of the wall and a steel plate that covered the top area of the

wall

.

Fiberboard was used as bedment material at the top end of the wall and

under a steel carrying channel in which the bottom course of the wall was

laid in mortar during construction. Generally, the compression testing of

the large wall panels followed the method of ASTM E72.

Construction of the compression wall panels of reference [4] was essentially the same as that described above for corresponding types of construction

in reference [65]. However, materials used in the tests of these two references were from different sources and exhibited somewhat different properties.

ASTM Method E-72 was closely followed in the compression testing of

wall panels in reference [4]. Testing was performed in a hydraulic universal

testing machine. The steel carrying channel (in which the wall was built

with its bottom course bedded in mortar) was set in high-strength plaster on

the platen over the top of the wall and a 1-inch square steel bar trans114
mitted the load from a loading beam to the top bearing plate along a line

parallel to, and at a distance of 1/3 the wall thickness from the inside

face of the wall.

C.3 Small Flexure Specimens (table 3.2)

Flexure tests were carried out on various small prisms reported in

reference [65] to measure bond or tensile strength at bed joints. Two-block

high concrete block prisms, laid in stacked bond, were made of both hollow

and solid 8x8xl6-in block and 4x8xl6-in hollow block, and were constructed

in the same manner as the prisms used for the compression tests. Flexure

tests of concrete block prisms were conducted in accordance with ASTM E149-

66. The test setup is shown in figure 4.4 and described in Section 4.

Flexure tests were also conducted on 7-course brick prisms tested as beams with the 8-in dimension of the brick horizontal. These prisms were constructed in stacked bond with full bed mortar joints, and were test

loaded transversely at the third points over a 16-in clear span.

Flexure tests of 2-block high prisms reported in reference [4] were

also performed by the method described in ASTM E149. Composite assemblies

were tested in the same manner but were constructed differently. A prism

tested with the brick facing in tension was 16-in long, 16-in high and 8-in

thick. Such assemblies consisted of 6 courses of brick facing in running

bond and 2 units of backing block, in stacked bond. Assemblies tested with

the concrete backing in tension were 24 in high and contained three block courses in stacked bond and nine brick courses in running bond.

C.4 Large Flexure Specimens (table 3.2)

Wall panel specimens for flexure tests reported in reference [65] were

of the same nominal size (4x8 ft) and construction as the corresponding

types of wall panel compression specimens. Flexural testing of these wall

panels was similar to the method employing air bag loading described in ASTM

Method E72. However, these walls were tested in a normal vertical standing

position. The transverse load was applied uniformly by a polyvinyl air bag

covering the width and span of the panel. A steel reaction frame provided

support for the air bag on one side of the specimen. On the opposite side

of the wall, upper and lower horizontal reaction bars were spaced approximately 7 ft apart and attached to another supporting frame. The two frames were

115
bolted together and the air bag was inflated with compressed air. The

reaction bars were faced with teflon and leather.

Flexure test wall panel specimens reported in reference [4] were similar

in construction to the corresponding types of compression wall panels described

under C.2 above. However, the height of these flexure walls was actually

104 in to permit flexural loading over a 7 1/2-ft span. Flexural testing

procedures were patterned after those of ASTM Method E72. The flexural load

test apparatus consisted of a structural steel frame fitted with lateral

hydraulic loading ram and reaction rollers to flex the wall in an upright

vertical position. Walls were tested in flexure by application of lateral

live loads to the quarter points of a simply supported 90-in vertical span.

C.5 Small Racking Shear Specimens (table 3.3)

Small prisms tested in shear are reported in reference [50] . The 32 x 32-in hollow block prisms were built in running bond using face shell mortar

bedding. Two diagonally opposite end cores in the top and bottom course,

respectively, were filled with mortar to prevent crushing of the masonry by

concentrated test loads applied at these locations. The intermediate size

4x4-ft specimens used in reference [50] for racking shear tests, were built

in running bond using full bed and head mortar joints. Both of these types

of prisms were tested in the manner shown in figure 4, 1(b) and 5.3(e). The

steel shoes at two diagonally opposite loaded corners were set in plaster

and were of the type shown in figure 4.3(a). The vertical compressive load

was applied by a conventional testing machine.

C.6 Large Racking Shear Specimens (table 3.3)

Wall panels used for racking tests reported in reference [4] were 8 ft

high and 8 ft long. They were constructed in a manner similar to that used

for compression wall specimens of corresponding types of construction.

Cored spaces in the blocks, and other cavities in the masonry, at two diagonally opposite corners of the walls which received a concentrated load

during the racking tests were filled solidly with mortar to prevent local

failure of the masonry during the tests. The racking test apparatus was in

the form of a yoke consisting of two steel side bars, one on each side of

the wall, connected at the ends to steel shoes placed at diagonally opposite

corners of the wall. The upper end of the yoke was fitted with a hydraulic

ram to apply a compressive load along the wall diagonal between the shoes.

Shoes were set in mortar (at time of construction) or in plaster (at time of

yoke placement).

116
Wall panel racking specimens reported in reference [50] were laid in

running bond and were 8 ft high and 8 ft long. Hollow concrete block walls

contained 8x8xl6-in two-cell units. Half-unit kerf blocks were used at the

end of alternate courses. Face shell mortar was applied in the manner

described in Section C.2. Cores at loading corners of the test walls were

filled with mortar to prevent local crushing. Brick wall panel specimens

were constructed with full bed and head mortar joints. The racking tests of

these wall panels were performed essentially according to ASTM Method E72 as shown in figure 5.3(d). One main exception was the substitution of vertical

hold-down tie rods by a vertically positioned hydraulic ram at the loading

corner, reacting against a structural frame attached to the laboratory test

floor

.

117
NBS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS BSS-62

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Buildings

5. Publication Date March 1977

6. Performing Organization Code

7. AUTHOR(S)

S. G. Fattal and L. E. Cattaneo

8. Performing Qrgan. Reoort No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit JSIo. i+6l5137

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Office of Construction

Veterans Administration

Washington, D.C. 20U20

13. Type of Report & Period Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Number: 74-30411

16. ABSTRACT (A 200-word or less factual summary of most si^ificant information. If document includes a significant

bibliography or literature survey, mention it here.)

The current state of knowledge on the structiiral behavior of masonry is synthesized to

develop a methodology for the evaluation of the load capacity of masonry walls in

existing buildings. A procedure is described for direct sampling and testing of

specimens removed from masonry walls of buildings to determine their strength in

shear, flexure and compression, and to measure their load-deformation characteristics.

A documentation of strength and stiffness properties obtained from available test data

is included to provide an alternate source of information on masonry of comparable

construction. Sample calculations of masonry building analysis for seismic forces

are given in Appendices A and B.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

Analysis; compressive strength; deflection; design; flexural strength; masonry walls;

racking strength; seismic loading; shear strength; shear wall; stiffness

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D.C. 20402. Order following NBS publications—NBSIR's and FIPS

from the National Technical Information Services,

Springfield, Va. 22161. Federal Information Processing Standards Publications

(FIPS PUBS)—Publications in this series collectively constitute the Federal Information Processing Standards Register. Register serves as the official source of information in the Federal Government regarding stand- ards issued by NBS pursuant to the Federal Property

and Administrative Services Act of 1949 as amended,

Public Law 89-306 (79 Stat. 1127), and as implemented

by Executive Order 11717 (38 FR 12315, dated May 11, 1973) and Part 6 of Title 15 CFR (Code of Federal

Regulations).

NBS Interagency Reports (NBSIR)—A special series of interim or final reports on work performed by NBS for outside sponsors (both government and non-government). In general, initial distribution is handled by the sponsor; public distribution is by the National Technical Information Services (Springfield, Va. 22161) in paper copy or microfiche form.

BIBLIOGRAPHIC SUBSCRIPTION SERVICES

The following current-awareness and literature-survey

bibliographies are issued periodically by the Bureau:

Cryogenic Data Center Current Awareness Service. A

literature survey issued biweekly. Annual subscription: Domestic, $20.00; Foreign, $25.00.

Liquified Natural Gas. A literature survey issued quarterly. Annual subscription: $20.00.

Superconducting Devices and Materials. A literature survey issued quarterly. Annual subscription: $20.00.

Send subscription orders and remittances for the pre- ceding bibliographic services to National Bureau of Standards, Cryogenic Data Center (275.02) Boulder,

Colorado 80302.
U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Washington, D.C. 20234

OFFICIAL BUSINESS

Penalty for Private Use, $300

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