NATL (NST. OF STAND & TECH

A11107 B'iDTSl

NBSIR 84-2929 ;<r -

vV'-r'.v

' 'r Influence of Vertical Compressive

Stress on Shear Resistance of

Concrete Block Masonry Walls

Kyle Woodward

Frank Rankin

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Gaithersburg, MD 20899

October 1984

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U S. DEPARTMENT OF COMMERCE

HATlOWUt

NBSIR 84-2929 C^ClOO

* » • INFLUENCE OF VERTICAL COMPRESSIVE t STRESS ON SHEAR RESISTANCE OF

CONCRETE BLOCK MASONRY WALLS / q

Kyle Woodward

Frank Rankin

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Gaithersburg, MD 20899

October 1984

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige. Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director

ABSTRACT

The results from tests on eight ungrouted and unreinforced concrete block

masonry walls are presented. The emphasis of the research program is on the

influence of vertical in-plane compressive stress on the lateral In-plane load

resistance of shear-dominated walls. Each wall has nominal dimensions of 64

in. X 64 in. x 8 in. and is fabricated from similar materials by the same experienced mason. The masonry units are hollow concrete block having a nominal

compressive strength of 1800 psi based on the gross area. The mortar is proportioned as a Type S. The walls are tested in the NBS Tri-directional Testing

Facility using fixed ended boundary conditions at the top and bottom of the

wall. Lateral in-plane displacements are applied at the top of the wall while

maintaining a constant compressive vertical stress. The vertical compressive

stress varies between 120 and 500 psi (based on net cross-sectional area) in

the test program. The test data indicate that the maximum in-plane lateral

load resistance exhibited by the walls increases with increased vertical com- pressive stress. The relationship between increasing vertical compressive

stress and the resulting increasing maximum lateral load resistance appears to

be linear within the range of vertical stresses used in the test program.

iii
TABLE OF CONTENTS

Page

ABSTRACT Ill

LIST OF TABLES vl

LIST OF FIGURES vll

1. INTRODUCTION 1 1.1 BACKGROUND 1 1.2 OVERVIEW OF MASONRY RESEARCH PROGRAM 1 1.3 SCOPE 1

2. MATERIALS 3

2.1 CONCRETE MASONRY UNITS 3

2.2 MORTAR 3

3. WALL PANEL DESCRIPTIONS 8

3.1 WALL PANEL FABRICATION 8

3.2 PRISM FABRICATION 8

3.3 WALL PANEL DETAILS 8

4. WALL PANEL TESTS: SETUP, INSTRUMENTATION, PROCEDURES 13

4.1 TEST SETUP 13

4.2 INSTRUMENTATION 13

4.3 TEST PROCEDURE 19

4.3.1 Placing a Wall Panel 19

4.3.2 Testing a Wall Panel 19

5. WALL PANEL TEST DESCRIPTION 26

5.1 64HH120 - 2L04 27

5.2 64HH160 - 3L01 29

5.3 64HH240 - 3L04 31

5.4 64HH300 - 2L05 33

5.5 64HH320 - 3L03 35

5.6 64HH400 - 3L02 37

5.7 64HH400 - 2L03 39

5.8 64HH500 - 2L06 41

6. DISCUSSION OF RESULTS 43

6.1 GENERAL BEHAVIOR 43

6.2 LOAD-DISPLACEMENT RELATIONSHIPS 43

6.3 DIAGONAL TENSION STRAIN 45

6.4 MAXIMUM LATERAL LOAD RESISTANCE 47

7. SUMMARY AND CONCLUSIONS 51

7.1 SUMMARY 51

7.2 CONCLUSIONS 51

Iv
TABLE OF CONTENTS (Continued)

Page

8. ACKNOWLEDGEMENTS 52

9. REFERENCES 53

V
LIST OF TABLES

Page

Table 2.1 Dimensions and Properties of Concrete Masonry Units 5

Table 2.2 Masonry Sand Sieve Analysis 7

Table 3.1 Wall Panel Details H

Table 4.1 Wall Panel Horizontal LVDT Location Dimensions 16

Table 6.1 Wall Panel Maximum Lateral Loads 49

Vi
LIST OF FIGURES

Page

Figure 2.1. Concrete block units 4

Figure 3.1. Typical wall panel 9

Figure 3.2. Typical prism 10

Figure 4.1. Test setup 14

Figure 4.2. Wall Panel LVDT layout 15

Figure 4.3. Wall panel instrumentation 17

Figure 4.4. Diagonal LVDT 18

Figure 4.5. Leaf spring transducer 20

Figure 4.6. Wall panel transport harness 21

Figure 4.7. Wall panel lifting hook 22

Figure 4.8. Placing a wall panel 23

Figure 4.9. In-plane displacement method 24

Figure 5.1. Specimen 64HH120-2L04 load-displacement curve 28

Figure 5.2. Specimen 64HH120-2L04 crack pattern 28

Figure 5.3. Specimen 64HH160-3L01 load-displacement curve 30

Figure 5.4. Specimen 64HH160-3L01 crack pattern 30

Figure 5.5. Specimen 64HH240-3L04 load-displacement curve 32

Figure 5.6. Specimen 64HH240-3L04 crack pattern 32

Figure 5.7. Specimen 64HH300-2L05 load-displacement curve 34

Figure 5.8. Specimen 64HH300-2L05 crack pattern 34

Figure 5.9. Specimen 64HH320-3L03 load-displacement curve 36

Figure 5.10. Specimen 64HH320-3L03 crack pattern 36

Figure 5.11. Specimen 64HH400-3L02 load-displacement curve 38

Figure 5.12. Specimen 64HM00-3L02 crack pattern 38

Figure 5.13. Specimen 64HH400-2L03 load-displacement curve 40

Figure 5.14. Specimen 64HH400-2L03 crack pattern 40

Figure 5.15. Specimen 64HH500-2L06 load-displacement curve 42

Figure 5.16. Specimen 64HH500-2L06 crack pattern 42

Figure 6.1. Combined load-displacement curves 44

Figure 6.2. Combined diagonal strain-displacement curves 46

Figure 6.3. Combined load-diagonal strain curves 48

Figure 6.4. Maximum shear resistance versus axial stress 50

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1 . INTRODUCTION

1.1 BACKGROUND

This interim report is the first in a series of reports which document an experimental investigation undertaken as part of an overall program of research

on masonry walls. The purpose of this and other reports in the series is to

present the results to researchers, designers, and code writers in a timely

manner. Detailed data analysis and interpretation are omitted from this report.

Instead, the analysis and interpretation of the data are presented in summary

reports. The summary reports are issued periodically as sufficient data become

available to more fully address a particular issue. Generally, summary reports

are based on the results presented in several interim reports since several

test series are required to fully explore a parameter and its relation to other

parameters .

1 .2 OVERVIEW OF MASONRY RESEARCH PROGRAM

The principal thrust of the overall program of research is directed towards

defining the shear capacity (in-plane lateral load resistance) and behavior of

shear-dominated masonry walls. The prediction of shear capacity and behavior

of masonry has been identified as an area in which there is a serious deficiency

of supporting research. The NBS/BSSC review committee for the ATC3-06 masonry

design provisions [1] suggest that research is needed to substantiate and

improve the current design recommendations for shear capacity.

The main variables which are to be investigated in the NBS masonry research

program are axial compressive stress, aspect ratio (wall length-to-height) , masonry type, mortar type, grout, vertical and horizontal reinforcement, outof-plane loadings, and loading history. Analytical studies are coordinated

with the experimental investigations so that a predictive model can be developed

for defining the shear capacity and behavior of a masonry wall. The predictive

model will lead to improved design standards, but in the interim the experimental

test results will aid in substantiating and improving the current design

provisions for shear in masonry walls.

1.3 SCOPE

This report presents data from tests of eight masonry walls subjected to inplane lateral displacements in combination with various vertical (axial) com- pressive stress levels. All eight walls were square, of the same size, and

made from similar concrete block and mortar. The only parameter intentionally

varied between tests was the axial compressive stress maintained on the wall

during in-plane loading. The wall panels had nominal dimensions of 64 in. x 64 in. X 8 in. The concrete block used in the wall panels was hollow block

having a unit compressive strength of approximately 1800 psi based on the

gross area. The mortar was proportioned as Type S mortar.

The materials and their properties are described in chapter 2. The wall panels

and accompanying prisms are described in chapter 3. The wall panel test setup,

instrumentation, and test procedure are discussed in chapter 4. Representative

1
test results are presented In chapter 5 while limited data Interpretation Is

discussed In chapter 6. A summary Is presented In chapter 7 along with

conclusions based on the data presented In this report.

2
2. MATERIALS

All materials used in constructing the wall panels and associated prisms were

commercially available and were representative of those commonly used in building

construction.

2.1 CONCRETE MASONRY UNITS

Two concrete masonry unit shapes were used in the construction of the wall

panels

1. 8 in. X 8 in. x 16 in., 2 core hollow strecher block.

2. 8 in. X 8 in. x 16 in., 2 core hollow kerfed corner block with a steel

sash groove in one end.

The dimensions represent nominal sizes. Typical measured dimensions and physical

characteristics of the units are presented in table 2.1. The measurements

are made in accordance with the procedures set forth in ASTM C140 [2]. The

units are illustrated in fig. 2.1. The half blocks at each end of alternating

wall courses are made by sawing kerfed corner blocks in half through the kerf.

Both halves produced by this procedure are used in the wall panels.

All of the concrete masonry units used in the wall panels and prisms were manufactured on the same day by a commercial block manufacturer. The mixture proportions were set to produce a unit having an ultimate compressive strength

of 2000 psi measured over the gross area of the unit. The mixture proportions

were

;

1950 lbs lightweight expanded shale aggregate

1250 lbs sand

260 lbs Portland cement

190 lbs NewCem

NewCem is the proprietary name for a very finely ground water granulated blast

furnace slag manufactured by Atlantic Cement Co., Inc. and is a partial replacement

for Portland cement. It meets the requirements of ASTM C989, grade 120 [3] and

when blended within the range of 25 to 65 percent with portland cement, meets

the requirements of ASTM C595 [4]. The preceeding description of NewCem is

presented only for purposes of information and is not an endorsement of the

proprietary product. The mixture used in producing the units makes 115 units

with 3.91 lbs of cementitious materials per unit.

2 . 2 MORTAR

One type of mortar was used in constructing all of the wall panels and prisms.

The mortar was a portland cement-lime mortar that was proportioned within the

limits of a Type S mortar according to the specifications of ASTM C270 (5).

The materials used in the mortar were:

1. Sand - a natural bank sand that was dug locally with its primary use being for masonry mortar. Sieve analyses were performed on the sand

3
Figure 2,1 Concrete block units

4
Table 2,1 Dimensions and Properties of Concrete Masonry Units

Hollow*

Stretcher

Hollow*

Corner/ Sash

Groove

Width (in.) 7.63 7.63

Height (in.) 7.59 7.57

Length (in.) 15.62 15.64

Minimum Face Shell

Thickness (in.) 1.30 1.30

Gross Area (in,^) 119.2 119.3

Net Solid Area (in.^) 61.5 67.1

Gross Ultimate

Compressive Strength (psi) 1813 1795

Density (Ib/ft^) 102.4 104.5

Absorption (Ib/ft^) 10.8 10.2

Average of measurements from 6 units.

5
upon delivery. The analyses were done according to the specifications

in ASTM C144 [6] and the results appear in table 2,2, The fineness

modulus was 1,57,

2, Portland cement - a commercially available, bagged, 94 lbs per bag.

Type I Portland cement identified as meeting the specifications of

ASTM C150 [7],

3, Lime - a commercially available, bagged, 50 lbs per bag, hydrated lime.

Type S, identified as meeting the specifications of ASTM C207 [8],

These materials were proportioned 1:3/8:

4

with 1 part by volume of cement, 3/8

part by volume of lime, and 4 parts by volume of sand. The parts were mixed in

a typical motorized mortar mixer (fixed horizontal drum with rotating blades)

for a period of not less than three minutes after all cement, lime, sand, and most

of the water was added. Finally, small amounts of water were added to produce

mortar of a consistency acceptable to the mason.

Immediately upon leaving the mixer, the time was recorded and a sample was

taken for determining the initial flow rate. The air content of the mortar was measured for selected mortar batches. Six mortar cubes (2 in, x 2 in, x 2 in,) were made during the early part of the wall panel construction. After completing

the wall panel, the mason constructed three prisms. Thus, each batch of mortar

produced a wall panel, six mortar cubes, and three prisms. Retempering of the

mortar, if required, was permitted only once per batch.

6
Table 2,2 Masonry Sand Sieve Analysis*

Screen | Cumulative

Size

Number

Percent

Retained

4 0,1

8 0,6

16 2,0

30 11,0

50 56,9

100 86,6

100+ • • • •

Total 157,2 100 = 1,57 Fineness Modulus

Average of three samples taken upon delivery of sand.

7
3. WALL PANEL DESCRIPTION

Eight wall panels were fabricated using concrete block taken from the same lot

and mortar having the same proportions of cement, lime, and sand. As companions

to each wall six mortar cubes (2 In. x 2 In. x 2 In.) were made and three prisms

were fabricated. The companion specimens were tested to provide Information on mortar compressive strength and wall panel compressive strength.

3.1 WALL PANEL FABRICATION

The wall panels were constructed In running bond with 50 percent overlap of

block in alternate wall courses (fig. 3.1). The wall panels had overall nominal

dimensions of 64 in. x 64 in. x 8 in. The wall panels (and prisms) were con- structed by an experienced mason using techniques representative of good workmanship. The wall panels were fabricated in a controlled environment laboratory

from materials stored in the same environment for at least 30 days. The temperature and relative humidity of the laboratory were maintained at approximately

73°F and 50 percent, respectively.

The bottom course of block was laid on a steel beam (channel) section without

bedding mortar. The steel beam and first course were then leveled using shims

as necessary. The first block laid in the bottom course was a whole kerf unit

with no head joint mortar. Head joints were subsequently formed by buttering

the end of the next block to be laid with mortar. The head joint mortar was only placed as deep as the face shell thickness. All head joints were "shoved"

joints with no closure units or backfilling of head joints. The mortar bed

joints were formed by placing mortar along the face shells of the previously

laid course of blocks. No mortar was placed on the cross-webs except for the

end cross-webs. Each course was laid to maintain a course height of 8 in. The

level of each course was fixed by a level string spanning between two plumb

posts. The end blocks were plumbed using a 4-foot level to maintain plumb end

surfaces of the wall panel. All joints were struck flush with a trowel, but

not tooled.

3.2 PRISM FABRICATION

Three prisms were made along with each wall panel using mortar from the same batch as was used for the wall panel. Each prism was made by stack bonding

three stretcher units (figure 3.2). The mortar bedding between the blocks was either face shell only or full area bedding. Within each group of three prisms

the bedding was the same. The prisms constructed with seven walls had face

shell bedding while the other prisms had full area bedding. The mason used a 4-foot level to maintain the level of each block and to plumb the prism.

3.3 WALL PANEL DETAILS

The details of each wall panel are listed in table 3.1. The wall panel identifier is a two part mnemonic with the two parts separated by a hyphen. That

part of the identifier preceding the hyphen has the form mHHn where m and n are numbers and HH signifies that a high strength block and a high strength mortar

are used. The term high is used only in a relative sense and does not imply

8
64' —Mortar

joint

head

(typ)

Mortar

bed (typ)

joint *

Half

kerf Stretcher Stretcher Stretcher

Half

kerf

Whole

kerf

Stretcher Stretcher Whole

kerf

/

64'

Shaded area identifies typical

horizontal mortar joint (bed joint)

mortar bedding - face shell

bedding except for end cross- webs

Running bond construction

NOTE; All dimensions are nominal dimensions

X

Wall course: /

one block and

bed joint

Figure 3.1 Typical wall panel

9
3 unit high

stretcher units

CONCRETE BLOCK PRISM

Figure 3.2 Typical prism

10
WALL

PANEL

WALL

AGE

MORTAR

CUBE

ULTIMATE

PRISM

PRISM

ULTIMATE

IDENTIFIER

AT

TEST

COMPRESSIVE

STRENGTH*

BEDDING

COMPRESSIVE

STRENGTH**

(DAYS)

28

DAY-

(PSI)

[DAYS]

(PSI)

[DAYS]

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11
a specific strength. The value of m is the nominal length of the wall panel

in Inches and for these wall panels is always 64. The value of n is the approximate axial (vertical) compressive stress (psl-net area) applied to the wall

panel in combination with the lateral displacement. That part of the identifier

following the hypen is a unique sequence number assigned to the wall panel

during construction. The first part of the identifier serves as a guide to the

characteristics of the wall test, but may not be unique (e.g., 64HH400). The

other entries in table 3.1 are self-explanatory. The ultimate compressive

strength of the prisms is determined by testing the prisms in a uniaxial

testing machine having a total capacity of 400,000 pounds force. A spherically

seated upper bearing block covers the entire bearing surface of the prisms.

The load on the prism is applied at any convenient rate for the first 40,000

pounds force while the remaining load is applied at a rate of 40,000 pounds

per minute until failure occurrs. The maximum load sustained by the prism

is used in computing the ultimate compressive stress.

12
4. WALL PANEL TESTS; SETUP, INSTRUMENTATION, PROCEDURES

4.1 TEST SETUP

The test setup (fig. 4.1) is the NBS Tri-directional Test Facility (NBS/TTF), a permanent loading apparatus designed to test building components using threedimensional loading histories. The NBS/TTF is described in a separate report

[9], but for purposes of completeness a brief summary is presented in this section.

The NBS/TTF is a computer-controlled loading apparatus which applies forces/displacements in all six degrees of freedom at one end of a test specimen. The

other end of the specimen is fixed. The six degrees of freedom are the translations and rotations in and about three orthogonal axes. The application of

such actions is accomplished by seven closed-loop, servo-controlled hydraulic

actuators which receive their instructions by means of computer generated

commands. The major components of the NBS/TTF are illustrated in fig. 4.1.

The reaction system is composed of the structural tie-down floor and two vertical

buttresses. The load distribution system consists of the two x-shaped steel

crossheads, one at the bottom and the other at the top of the test specimen.

The load application system is made up of the seven hydraulic actuators. The

control system is not visible in the figure, but includes the servo-control

electronics, the data acquisition equipment, and a minicomputer.

4.2 INSTRUMENTATION

The instrumentation used to monitor the test of a wall panel can be divided

into two groups. The first group consists of load and displacement tranducers

mounted on the hydraulic actuators. These devices measure the overall forces

applied to the upper crosshead by the hydraulic actuators and the displacements

of the actuator pistons as they move the upper crosshead. The second group of

instrumentation directly measures the behavior of the wall panel as it is

loaded. All of the instrumentation is connected to a computer-based analog-todigital-converter which has a sample rate of 50,000 data readings per second.

The In-plane displacement of a wall panel is measured by linear varying

differential transformers (LVDTs) which are displacement transducers. The LVDTs

are placed as shown in fig. 4.2 with four LVDTs located on each end surface of

the wall. The actual positions of the LVDTs are listed in table 4.1. The

LVDTs are mounted such that they measure the displacement of the wall relative

to a fixed reference (tie-down floor).

In addition to the overall measurement of the wall displacement, local measurements of displacement are made on each of the wall panel face shells. These

displacement measurements are taken between points on the wall and not referenced

to a fixed position. The local displacement measurements are made at the

locations shown in fig. 4.3 using specified gage lengths so that strain can

be computed. The displacement over the two long gage lengths is measured by

LVDTs mounted on swivels between two posts glued to the wall surface (fig.

4,4). The displacement over the short gage lengths is measured by specially

13
rwr"

Figure 4.1 Test setup

14
West

in-plane loading

C' TA'

B' jL

D'

(Note: upper crosshead not shown)

r Lower crosshead

East

1* c—1-^n

1

—Linear varying differential

transformer (LVDT), typ.

_L

of wall

LVDT support

system (idealized)

Figure 4,2 Wall panel LVDT layout

15
Table 4.1 Wall Panel Horizontal LVDT Location Dimensions

Refer to fig. 4.2 for identification of dimension locations A,B,C,D,A’ ,B' ,C'

,

and D'

.

Wall Panel A B C D A' B' C D’

Identifier (in.) (in.) (in.) (in.) (in.) (in.) (in.) (in.)

64HH120 11.25 10.50 27.75 27.50 10.75 10.38 27.50 27.00

64HH160 9.75 10.50 28.00 27.50 10.75 10.50 27.50 27.25

64HH240 10.00 10.75 28.00 27.50 10.75 10.63 27.50 27.25

64HH300 11.00 10.50 27.75 27.25 10.88 10.25 27.38 26.75

64HH320 10.13 10.38 28.38 27.50 10.88 10.38 27.50 27.25

64HH400-3L02 10.13 10.63 28.13 27.50 11.13 10.50 27.38 27.25

64HH400-2L03 10.63 10.50 27.50 27.50 11.00 10.25 27.50 27.00

64HH500 10.75 10.50 27.63 27.50 10.88 10.38 27.50 27.00

16
J Leaf spring transducer

Swivel ended LVDT

<t

1

NORTH SIDE OF WALL PANEL

I Leaf spring transducer »—-» Swivel ended LVDT

SOUTH SIDE OF WALL PANEL

Figure 4,3 Wall panel Instrumentation

17
A

'1 Figure 4.4 Diagonal LVDT

18
designed leaf spring transducers (LSTs) (fig. 4.5). The LSTs are strips of

metal (titanium) with strain gages mounted on each side (temperature compensated)

such that the output signal from the strain gages is proportional to the tip

displacement of the leaf spring. Each LST is calibrated to determine the

relationship between leaf spring tip displacement and the strain gage output.

A typical estimate of standard error for the regression analysis of displacement

versus LST output is 15 microinches. The LSTs are mounted on posts glued to

the wall (fig. 4.5) with a gage length of 1 in. The LSTs are mounted only

on block, units and their gage lengths do not cross mortar joints.

4.3 TEST PROCEDURES

4.3.1 Placing a Wall Panel

Each of the wall panels was handled by attaching a carrying harness to the panel

(fig. 4.6). The harness had attachment points for lifting the wall and a clamping arrangement which held the harness against the ends of the panel. An

overhead crane and specially fabricated device was used to place the wall

panel in the NBS/TTF. The special device was a large welded assembly in the

shape of a "C" (fig. 4.7). The shape permitted the crane hook to be centered

above the wall panel without interfering with the upper crosshead during placement

(fig. 4.8).

The walls were set in place using mechanical stops which fixed the walls in

their horizontal position. The walls were plumbed using small wedges set at

four places under the face shells of the walls. The walls were fastened to

the lower crosshead first, using an epoxy mortar along the bottom face shells

and end cross-webs. The upper crossshead was then lowered onto the wall whose

top face shell and end cross-webs were also mortared with the epoxy mortar. A

small vertical compressive load (1,000 to 2,000 pounds) was applied to the wall

to ensure contact between the wall and epoxy mortar. The upper crosshead was

locked in position and the epoxy mortar was allowed to cure at least 16 hours

before testing the wall.

4.3.2 Testing a Wall Panel

A typical test proceeded in the following steps. The data channels were checked

for unusual variations in output and a measure of the ambient voltage oscillation

was obtained. A first set of data was acquired to use as the "zero" condition of

the test. The hydraulic actuators were pressurized and another set of data was acquired. The desired vertical compressive load was applied to the specimen

with data acquired at regular intervals. After reaching the desired compressive

vertical load, in-plane lateral displacements were applied to the wall panel.

The lateral displacement was applied with the upper crosshead maintaining a "zero" rotation condition. The vertical displacement of the upper crosshead

varied to maintain the desired axial load. The initial direction of lateral

in-plane displacement was always to the west (fig. 4.9). The displacement

pattern varied slightly between tests but, generally, displacement was increased

in the initial direction (west) until a diagonal crack was fully formed.

Afterwards, the displacement was either reversed or increased until the wall

19
i ‘ i.t

Figure 4,5 Leaf spring tranducer

20
Figure 4.6 Wall panel transport harness

21
Figure 4.7 Wall panel lifting hook

22
Figure 4»8 Placing a wall panel

23
Aq Is the Imposed In-plane lateral displacement

Ai, A 2 are the vertical dimensions required to achieve desired vertical load. A-j need not equal A2-

0. Upper

crosshead

<1 Upper crosshead

Lower crosshead

SIMPLIFIED DESCRIPTION OF IMPOSED DISPLACEMENT

Figure 4.9 In-plane displacement method
could not support the Imposed vertical load. Data were acquired at regular

Intervals during the test. The Intervals coincided with lateral displacement

increments of approximately 0.005 In.
5. WALL PANEL TEST DESCRIPTIONS

In this chapter, a brief description of each wall test and its observed behavior is

presented. All of the descriptions share a common format consisting of a loaddisplacement curve, a crack pattern map, and a short narrative highlighting the

information contained in the two figures. In general, the combination of the

load-displacement curve and crack pattern map provides sufficient Information

to broadly describe the behavior exhibited by a test specimen. Other information

such as data from the LSTs is not presented since for the purposes of this

report the wall behaviors are adequately described by their load-displacement

relationships

.

The load-displacement curves describe the complete loading (displacement) history

for each wall test and provide a primary Indicator of wall behavior. The load

used in developing the curves is the horizontal load acting in the plane of the

wall as measured by the hydraulic actuator load transducers. The load is

referred to as the global In-plane load. The displacement used in the curves

is the horizontal displacement of the upper crosshead in the plane of the wall

(fig. 4.9). This displacement is referred to as the global in-plane displacement

to differentiate it from the in-plane wall displacement measured by the horizontal

LVDTs mounted to the wall (fig. 4.2). The global in-plane displacement (GID)

is determined by the displacement transducers in the hydraulic actuators. The

GID and the wall displacement measured directly by LVDTs are not necessarily

the same. The GID is affected by total apparatus displacement while the direct

LVDT displacement more nearly measures an absolute in-plane displacement of

the wall. However, the direct LVDT displacement can be strongly affected by

the breakup of a wall after cracking. Spalling and splitting in the region

near a wall LVDT can produce large distortions in the apparent displacement.

In general, the GID is a consistent measure of displacement which is unaffected

by local wall distortions and, as a result, is best for general comparisons

between tests.

The crack pattern maps reflect the observations of wall cracking at selected

points during the tests. The crack patterns provide useful information on the

physical response of a wall to an imposed loading history. The patterns serve

as a guide to identifying regions of high stress, general stress flow, and

physical load resisting mechanisms. It is, of course, desirable that the points

during a test at which crack patterns are recorded be identified on the loaddisplacement curves. This is accomplished by using an identifying symbol which

marks a location on the load-displacement curve corresponding to an associated

crack pattern on the map. The symbols are capital letters starting with the

letter A. Thus, in the narrative of each description reference will be made to

specific points on the load-displacement curve identified by the symbols and by

Implication the crack pattern also associated with that S 3nnbol. The sjrmbols are unique within a description, but not between tests. S3nnbol A does not

refer to the same point on every load-displacement curve.

26
5.1 64HH120 - 2L04

The loading history of this wall included displacements with several different

compressive axial stress levels (fig. 5,1). The purpose of this test was to

find the minimum level of compressive axial stress required to produce a "shear"

failure (diagonal cracking) rather than a "flexure" failure (horizontal cracking)

.

The initial axial stress of 60 psi did not suppress the flexural mode as shown

by the crack pattern (fig. 5.2) which exhibited a pronounced horizontal flexure

crack at the first course mortar joint. The lateral displacement was returned

to zero and the axial stress was Increased to 120 psi. The lateral displacement

was then increased until the bottom west block developed a diagonal crack

extending from the previous flexure crack in the mortar joint to the bottom

corner of the block. The displacement was denoted by the S 3nnbol A in fig.

5.1. The decrease in lateral load resistance coinciding with the formation of

the block diagonal crack was very pronounced. At this point in the test it was decided to increase the axial stress and repeat the lateral movement until

a complete wall diagonal crack could be formed. The lateral displacement was decreased until the lateral force was approximately zero. The axial stress

was increased to 200 psi and the lateral displacement was then increased. It

appeared that the cracking was confined to the existing cracks so the axial

stress was increased again. The previous steps were repeated except that the

axial stress was increased to 300 psi, A complete wall diagonal crack occurred

at this axial stress level with an accompanying reduction in lateral load

resistance. The wall diagonal crack passed mostly through the blocks rather

than the mortar joints. The displacement was denoted by symbol B in fig. 5.1,

The displacement was then reversed until a diagonal crack formed along the

other diagonal. The displacement at which this occured was denoted by symbol

C in fig, 5.1.

27
Figure 5,1 Specimen 64HH120-2L0A load-displacement curve

East

CracKs observed

at -^0.1 In with 60 psi axial stress A (refer Fig. 6.1) BC

Initial — displacement

direction

West CRACK PATTERNS; 64HH120-2L04 (north face)

Figure 5.2 Specimen 64HH120-2L04 crack pattern

28
5.2 64HH160 - 3L01

The compressive axial stress was initially set at 160 psi. The lateral displacement was eventually increased to a displacement equal to about three times

that at which diagonal cracking actually occurred in the wall (fig. 5.3). The

diagonal cracking which occurred with the 160 psi axial stress was primarily

confined to the mortar joints in a stair-step fashion (fig. 5,4). The axial

stress was subsequently increased to observe the effect, if any, of increasing

the axial stress after cracking had occurred. As seen in the load-displacement

curve the maximum lateral load resistance for higher axial stress was significantly greater than the resistance observed at the same displacement for lower

axial stresses, but the overall maximums were not significantly different.

For example, the maximum lateral load resistance observed for the case of 240

psi axial stress was approximately 30 kips and occurred at a displacement of

about 0.31 in. The resistance observed at about the same displacement for the case of 160 psi axial stress was 21 kips. However, the maximum lateral load

resistance for the case of 160 psi axial stress was 30 kips. Thus, the maximum

load resistance was about the same regardless of axial stress when the wall

was already cracked before increasing axial stress. The limiting resistance

seemed to involve that associated with slippage along the crack since relatively

few new cracks formed, but crushing zones were observed along certain portions

of the primary diagonal crack. Lateral load resistance was stable within the

lateral displacement imposed on the wall at the higher compressive axial stress.

29
Figure 5.3 Specimen 64HH160~3L01 load“displacement curve

East

A (rafar to Fig. BC

0

(!>:'<'((! Spallad irai

Initial — displacement

direction

West

6.3)

CRACK PATTERNS; 64HH160-3L01 (north face)

Figure 5»4 Specimen 64HH160—3L01 crack pattern

30
5.3 64HH240 - 3L04

The compressive axial stress was maintained at 240 psi throughout the test. The

diagonal cracking began in the center portion of the wall diagonal and extended to

each corner. A sharp drop in lateral load resistance (fig. 5.5) occurred as the

diagonal crack reached its full length. The diagonal crack passed through

both block units and mortar joints (fig. 5.6). As the displacement was increased

past the displacement at which diagonal cracking first occurred the lateral

resistance decreased slowly. However, a point in the loading history was reached (denoted by the symbol B in fig. 5.5) where two loud bangs were heard

from the wall and the resistance decreased at a higher rate. No new cracks

were observed to form with the noises and based on later examination of the

wall it was suggested that the noises were caused by the splitting of cross-webs

in the compression zones of the wall. The displacement was cycled several

times with a small displacement amplitude near the extreme displacement limit

to observe the rate of degradation of resistance with non-reversed cycling.

The displacement was then fully reversed until a diagonal crack formed along

the other diagonal of the wall panel. The final failure was primarily crushing

along the diagonal crack in the lower west corner compression zone.

31
Figure 5.5 Specimen 64HH240~3L04 load-displacement curve

—— A (refer to Fig. 5.5) C

D

E

Spalled area

Initial — displacement

direction

West

Figure 5.6 Specimen 64HH240-3L04 crack pattern

32
5.4 64HH300 - 2L05

The compressive axial stress was maintained at 300 psi throughout the test. The

loading history was basically one cycle with fully reversed displacements

(fig. 5.7). The diagonal crack which formed during the initial lateral

displacement of the wall panel initiated in the central region of the wall and

extended along the diagonal to the opposite corners (fig. 5.8). The cracking

occurred primarily through the block units and not the mortar joints. The

small flexure crack which was observed in the lower east bed joint occurred at

a displacement very near the occurrence of diagonal cracking. As the displacement was increased past the displacement at which the first full diagonal

crack formed the lateral resistance was initially stable (remained constant)

but, with increasing displacement, a parallel diagonal crack formed and the

resistance decreased. The displacement was increased until noticeable crushing

occurred in the lower west corner of the wall. As the crushing occurred the

lateral resistance decreased sharply. The displacement was then fully reversed.

Diagonal cracks formed along the other diagonal, but this time the diagonal

cracking passed through both block units and mortar joints. The angle of the

crack was also different.

33
Figure 5.7 Specimen 6AHH300-2L05 load-displacement curve

East

A (rater to Fig. 5.7) BC

D

The crack length denoted

by arrows was the first observed. The crack then extended to the corners

Initial —^ displacement

direction

West CRACK PATTERNS; 64HH300-2L06 (north face)

Figure 5.8 Specimen 64HH300-2L05 crack pattern

34
5.5 64HH320 - 3L03

A compressive axial stress of 320 psi was maintained on the wall panel throughout

the lateral displacement. The wall was first displaced 0.2 in. to the west

(fig. 5.9). The diagonal crack which formed (fig. 5.10) during this displacement

was accompanied by a loud bang and a sudden drop in lateral load resistance.

Displacement of the wall between the displacement at first cracking and 0.2

in. produced several more loud bangs, but no new visible cracking. The load

resistance decreased with increasing displacements. The displacement was fully reversed and then cycled three times between the two reversed displacement

limits. The first reversal to 0.2 in. (denoted by symbol C in fig. 5.9) in

the east direction caused two diagonal cracks to form, one after the other.

The first crack did not extend to the two corners (lower east and upper west),

but the second crack included extensions to the corners. The second cycle to

0.2 in. to the west (denoted by symbol D in fig. 5.9) produced a vertical

crack along the face shells of the west end with an accompanying large reduction

in lateral load resistance. The second cycle to 0.2 in. to the east (denoted

by symbol E in fig. 5.9) produced vertical cracking on the east side, but no drop in resistance was observed. The third cycle produced some reduction in

resistance and stiffness, but no new cracks were visible. The attempt at a fourth cycle was terminated when the wall panel could not sustain the 320 psi

axial stress and crushing occurred.

35
Figure 5.9 Specimen 64HH320-3L03 load-displacement curve

CRACK PATTERNS: 64HH320-3L03 (north taco)

Figure 5.10 Specimen 64HH320-3L03 crack pattern

36
5.6 64HH400 - 3L02

The compressive axial stress was maintained at 400 psi. The loading history

was basically one cycle between reversed displacement limits (fig. 5.11), but

the displacement limits were unequal. The first diagonal crack due to displacement in the west direction occurred at 0,125 in (fig. 5,12), The cracking

Initiated in the central region of the wall and then propogated along a line

below the true wall diagonal. A second diagonal crack formed at 0,175 in.

which propagated along and above the true wall diagonal. The lateral load

resistance was essentially constant during the formations of both cracks. The

lateral load resistance remained constant until a displacement of about 0.3

in, was reached at which point a loud bang was heard followed by extensions

of the previous cracks and a sudden decrease in lateral load resistance.

During the reversal of displacement diagonal cracks formed along the other

diagonal, but the test was terminated when the wall could no longer sustain

the 400 kip axial stress.

37
Figure 5.11 Specimen 6AHH400~3L02 load~displacement curve

CRACK PATTERNS: 84HH400-3L02 (north face)

Figure 5.12 Specimen 64HH400-3L02 crack pattern

38
5.7 64HH400 - 2L03

A compressive axial stress of 400 psi was maintained on the wall. This test was

a monotonic test to failure (fig. 5.13). The final failure was an inability to

sustain the 400 psi axial stress. The first diagonal crack to form Included

the upper east corner, but did not extend to the lower west corner (fig. 5.14).

The crack was visible only after the lateral load resistance dropped. Just

prior to the drop in resistance a loud bang was heard. The second, roughly

parallel, crack included the lower west corner. The second crack occurred

only after a significant increase in displacement past the displacement coinciding with the formation of the first crack. The lateral load resistance

increased as the displacement was increased until a displacement was reached

where a complete diagonal crack formed. Increasing the displacement further

led to a zone of crushing in the lower west corner followed by a sudden loss

in vertical load (stress) resistance.

39
Figure 5.13 Specimen 64HH400~2L03 load“displacement curve

CRACK PATTERNS: 64HH400-2L03 (north (aca)

Figure 5.14 Specimen 64HH400~2L03 crack, pattern

40
5.8 64HH500 - 2L06

The axial stress was maintained at 500 psi during most of the test. The loading

history was basically a single cycle, reversed displacement pattern (fig. 5.15),

but an unexpected problem modified the loading history. The first attempt

at applying a lateral displacement was terminated by the control software

because preset load limits were exceeded. Preset load limits restrict the

range of loads which can be applied to the specimen as a precaution against

unintentional overloading of the specimen. The axial stress was reduced and

the lateral displacement returned to zero. The preset load limits were increased

so that the error indication would not occur and the axial stress was again

increased to 500 psi. The lateral displacement was then applied with no further

difficulties. The initial diagonal cracking occurred in the center region of

the wall (fig. 5.16) accompanied by a reduction in lateral load resistance.

With increasing displacement, the crack propagated to the corners and a second

crack formed roughly parallel to the first crack, A displacement level was

reached, however, which resulted in crushing of certain regions of the wall

followed by a sharp drop in lateral load resistance and the inability of the

wall to sustain the 500 psi axial stress (denoted by sjnnbol C in fig. 5,15).

The axial stress was reduced and the displacement reversed until zero lateral

load was achieved. The axial stress was then increased to 500 psi and the

displacement Increased in the opposite or east direction. Diagonal cracking

occurred in the opposite direction, but the cracks were not continuous. The

test was terminated because the vertical displacement required to maintain the

vertical 500 psi stress was considered excessive.

41
Figure 5.15 Specimen 64HH500-2L06 load'-dlsplacement curve

East

—A (refer to Fig. 5.18) BC

D

Spalled area

Initial — displacement

direction

West CRACK PATTERNS; e4HHS00-2L05 (north face)

Figure 5.16 Specimen 64HH500-2L06 crack pattern

42
6. DISCUSSION OF RESULTS

The discussion which follows is limited to the wall panels described in this

report. Detailed data analysis is not presented, but it is left to a future

report when other test results will be available. A general overview of the

apparent behavior is presented with trends noted where evident.

6.1 GENERAL BEHAVIOR

The crack patterns exhibited by each wall panel indicate a diagonal-tension

type of failure when a flexural mode of failure is suppressed by the presence

of sufficient axial (vertical) compression. There are variations in the crack

patterns which point to a change in the actual critical region with Increasing

axial compression. The wall panel with 120 psi axial compression (64HH120)

fails with a localized diagonal-tension failure in the compression zone of the

panel (fig. 5.2). However, the same panel fails with a complete diagonal

crack when the axial compression is increased to 300 psi with a resulting

higher lateral load resistance. Such behavior indicates that the failure

criterion is dependent on the complete state of stress and not just one particular component of the stress. Just as importantly, however, is the recognition

that state of stress computations can not be based solely on the overall panel

average stresses, but must also include the local conditions which may be

radically different. An example is the compression zone of a cracked section.

The compression stresses and shear stresses may be quite high in this zone with the result being a local diagonal-tension failure.

At the other end of the spectrum, relatively high axial compression alters the

diagonal crack pattern such that instead of a single complete diagonal crack

which splits the panel, multiple diagonal cracks form. The cracks radiate from

opposite corners at angles which cause the cracks to bound a region of the wall

along the true diagonal. An example is the crack pattern of 64HH400 shown in

fig. 5.14. The final failure seems to be a crushing type of failure in the

bounded region. It should be pointed out that the axial stress level required

to produce banded diagonal cracking is high in comparison to typical design

levels of axial stress.

Between the two extreme behaviors the crack pattern is a relatively straightforward diagonal crack which generally follows the wall panel diagonal. In the

wall panels tested, the cracks generally passed through the block units or at

least included portions which passed through block units. It would appear

reasonable that since the cracking passed primarily through the block units

the general susceptibility to cracking for these wall panels is determined by

material properties of the block units and not the mortar.

6.2 LOAD-DISPLACEMENT RELATIONSHIPS

The load-displacement curves for all eight wall panels are shown in fig. 6.1.

The load is the in-plane global lateral load and the displacement is the movement of the wall at the top course of the wall as measured by the top west

LVDT (fig. 4.2). The curves are only shown to a point slightly beyond achieving

the peak lateral load resistance. The curves for 64HH120 and 64HH500 have

been adjusted to eliminate their initial loading cycles. It is clear that

43
Figure 6.1. Combined load-displacement curves

44
wall 64HH120 is heavily influenced by flexure which accounts for the general

rounding of the curve and the large displacement required to achieve diagonaltension failure. The wall 64HH160 demonstrates much less influence of flexure,

with only a small Increase in maximum lateral load resistance. The remaining

walls show the same general trend, less rounding of the curve and a sudden

drop in lateral load resistance. The wall 64HH400 - 3L02 is an interesting

anomaly in that its behavior is not like its companion 64HM00 - 2L03. At

present, it is not known why 64HH400 - 3L02 exhibited such behavior.

The walls 64HH400 - 3L02, 64HH400 - 2L03, and 64HH500 exhibited a markedly more

stable maximum lateral load resistance as compared to the other five walls.

The complete load-displacement curves are not shown in fig. 6.1, but the curve for wall 64HH400 - 2L03 in fig. 6.1 can be used as a guide to their

general behavior. The lateral load resistance is maintained at a high level

for a much larger displacement than was possible for the other five walls.

The relationship for 64HH400 - 2L03 suggests that the load resisting mechanism

changed during the test. The first peak resistance coincides with the formation

of the initial diagonal cracks while the gradual increase in resistance after

that is associated with the development of the banded crack pattern. Final

failure results from the crushing of the material within the banded region.

The effect of displacement reversals is observed in walls 64HH240 and 64HH320.

The load-displacement curve for wall 64HH240 shown in fig. 5.5 suggests that for

partial reversals of displacements such as a half-cycle pattern the effect of

reversals on stiffness and lateral load resistance is small. However, the loaddeflection curve for wall 64HH320 (fig. 5.9) indicates that the effect of complete

displacement reversals is significant with large reductions in stiffness

and lateral load resistance.

6.3 DIAGONAL TENSION STRAIN

Numerous strain measurements are available for each wall panel test. The

strain measurements are from a variety of locations on each wall panel

(fig. 4.3). For this report the data from only one of the locations is presented.

The strain measured by an LVDT mounted parallel to the diagonals provide an excellent general indication of overall wall diagonal strain. Since the cracking

appears to form as a result of diagonal tension the displacement measured by

the north side LVDT (denoted as NL in fig. 4.3) provides a measure of the diagonal

tensile strain in the wall. The local displacements measured by the diagonally

mounted wall LVDTs are divided by the initial gage length to arrive at a strain

value. The gage length used in all computations for the diagonally mounted

LVDT strain is 33.941 in. which is the diagonal length of a 24 in. square

(fig. 4.3).

In fig. 6.2, the computed strains from the north LVDT measurements are plotted

versus the same wall displacement used in fig. 6.1. The strain-displacement

curves exhibit a definite breakpoint at which the curves become asymptotic with

large increases in strain for small increases in displacement. This is, of

course, indicative of the formation of physical cracks in the wall. The curve

for 64HH120 is an exception to the general trend, but it may be discounted since

the wall is strongly influenced by flexure rather than by shear as is the case

45
DIAGONAL

STRAIN

(microstrain)

Figure 6.2. Combined diagonal strain-displacement curves

46
in the other walls. More interestingly, however, is that for the walls having

moderate amounts of axial stress (160-320 psi) the strain at which the straindisplacement relation changes is approximately the same for all the walls and

has a value of about 150 microstrain. This common value certainly suggests

that the limiting criterion for the formation of diagonal cracking and con- sequently maximum lateral load resistance is determined by a critical tensile

strain. The critical or threshold value of strain is more clearly shown in

fig. 6.3 which is a plot of global in-plane load versus the same strain as in

fig. 6.2. The wall panels 64HH400-3L02 and 64HH500 are exceptions to the

common threshold tensile strain of 150 raicrostrain, but the two walls do

exhibit a similar strain threshold. That fact may eventually provide a clue

as to why they behave differently, but the information currently available

does not provide an answer.

6.4 MAXIMUM LATERAL LOAD RESISTANCE

Typically, the single most important aspect of behavior to a designer is the

maximum resistance. As a result, the factors which influence the maximum

resistance need to be accounted for in design. Based on eight wall panel tests

the influence of axial compressive stress on the diagonal-tension capacity of a wall follows a definite trend. A list of the maximum lateral load resistances

for the wall panels is presented in table 6.1. Clearly, for changes in axial

compressive stress between 120 and 500 psi, increasing the axial stress increases

the maximum lateral load resistance. The trend of the relationship is shown

in fig. 6.4 which is a plot of maximum shear stress versus the axial compressive

stress. The maximum shear stress is computed by dividing the maximum lateral

load resistance by the net cross sectional area of the wall (246 sq. in.).

The axial stress is the total axial load divided the same net cross sectional

area of the wall. The relationship is strongly linear as evidenced by the

"best-fit" line developed by a linear regression analysis and its resulting

correlation coefficient (0.98).

47
Figure 6»3» Combined load-diagonal strain curves

48
Wall

Panel

Axial

Compressive

Maximum

Lateral

Load

Wall

Displacement

at

Identifier

Stress

(psi)*

Resistance

(kips-psi)*

Maximum

Resistance

(in.)**

K*

4CvOO

»—< I—I

p'.

m

m o ^ o o o • • • • o o o o o •

CJ^ CJ^ 00

CDa

\o CO o •H o o o • • • • o o o o CMm

in

vO

CM

CM

C3

M-iO

<U3

iH

CO>

CO X4J •H

m c3 CO CO \0 vO m P'* o

CM vO 00

O o CM vO vD p'v 1—1

CM CM CM CM M> 1 1 1 1 I X O 1 1 1 1 1 >0- O

00 CO CM r>. in o^ o^ • • • • • • • • M-l 4J o •—H in o o in CO O CO CM CO 'cr in m m M3

CO •

OJ

H <U

(-1

O

CO > Md I—i

CJ

CO I—I o C CO o O 4J •H c CU o CJ o to c

0) •H CO CO i-> 4J O CO

CO

X •H

CO CO o 0) u CO S-l o <u CM CM CO m m vO M3 & T3 CM vO •sT o CM o o O u CO CM CO CO 'O' '0- m (U a O c o rH

4J

CO iH

(U CO c X tu o XJ <U

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X IM CO

9) o I—1

CO

CO

X

X c CO

0> <V

CO e cx

'd' in CO CM CO M5 •H (U o o O o o O o o o 4.) J I-] X iJ h4 X CO CO CO CM CO CO CM CO CO CM CM CO I'H M 1 1 1 1 1 1 1 1 (U Cl. t4 o o o O o o o o CO CM CM vO vf o CM o o o 4.) •H a a a a a a a

c/3

O c X X X Ed Ed Ed Ed Ed * ^C *

'O' 'O' * *

vO \a vO vO vO M3 M3 M3 * 49
MAXIMUM

SHEAR

STRESS,

v

(psi)

Figure 6*4. Maxlmuin shear resistance versus axial stress

50
7. SUMMARY AND CONCLUSIONS

7.1 SUMMARY

Experimental data were presented from eight wall panel tests. Each wall panel

was approximately 64 in. long by 64 in. high by 8 in. thick and constructed of

similar hollow concrete block masonry units. Each wall panel was subjected to a lateral in-plane displacement at its top surface while the bottom surface was

fixed. The primary variable was the magnitude of vertical in-plane compressive

stress maintained on the wall during the lateral displacement. The acquired data

included forces and displacements imposed on the wall panels and local strain

measurements on each of the two face shell surfaces of the walls. A limited

presentation of data interpretation demonstrated the strong, nearly linear

relationship between increasing levels of vertical compression and the maximum

lateral force resistance achieved by the wall panels.

7.2 CONCLUSIONS

The conclusions presented below are based on eight wall panel tests. The wall

panels have similar geometry and are built using similar materials by the same mason

.

• A nearly linear relationship existed between increased amounts of axial

compression and the resulting maximum lateral (in-plane) load resistance

of the wall panel.

• The lateral displacement at which maximum lateral load resistance was achieved was not significantly influenced by the amount of vertical

compression for failures of a similar type.

• Tensile strain across the wall panel diagonal was the critical determinant

of diagonal cracking and there appeared to exist a threshold strain of

about 150 microstrain above which diagonal cracking occurs.

• The effect of fully reversed displacement cycling on load resistance

after diagonal cracking was significant with large amounts of degradation

of both load resistance and stiffness. The effect of partial reversals

such as half-cycle repetitions was apparently not significant to either

the load resistance or stiffness for a small number of repetitions.

51
8. ACKNOWLEDGEMENTS

The concrete block units and the mason who fabricated the wall panels and prisms

were provided by the National Concrete Masonry Association*

The authors wish to thank Dr. Spencer Wu, Dr. John Gross, and Dr. Len Mordfln

for their thorough review of this report. The authors also acknowledge the

help of Frank Davis and Allan DeLorme during the physical testing of the

specimens

.

52
9. REtERENCES

1. Leyendecker , Edgar V. and Cattaneo, Louis E. , "Review and Refinement of

ATC3-06 Tentative Seismic Provisions - Report of Technical Committee 5:

Masonry," Report No. NBSIR 80-211-5, National Bureau of Standards, Washington, D.C., October 1980, 421 pp.

2. "Sampling and Testing Concrete Masonry Units," (ASTM C140-75), 1983 Annual

Book of ASTM Standards, Vol. 4.05, American Society for Testing and Materials,

Philadelphia, PA, pp. 117-120.

3. "Standard Specification for Ground Iron Blast- Furnance Slag for Use in

Concrete and Mortar," (ASTM C989-82), 1983 Annual Book of ASTM Standards,

Vol. 4.02, American Society for Testing and Materials, Philadelphia, PA,

pp. 629-633.

4. "Standard Specification for Blended Hydraulic Cements," (ASTM C595-83),

1983 Annual Book of ASTM Standards, Vol. 4.02, American Society for Testing

and Materials, Philadelphia, PA, pp. 359-366.

5. "Standard Specification for Mortar for Unit Masonry," (ASTM C270-82), 1983

Annual Book of ASTM Standards, Vol. 4.01, American Society for Testing and

Materials, Philadelphia, PA, pp. 250-254.

6. "Standard Specification for Aggregrate for Masonry Mortar," (ASTM C144-81),

1983 Annual Book of ASTM Standards, Vol. 4.02, American Society for

Testing and Materials, Philadelphia, PA, pp. 107-108.

7. "Standard Specification for Portland Cement," (ASTM C150-83), 1983 Annual

Book of ASTM Standards, Vol. 4.01, American Society for Testing and Materials,

Philadelphia, PA, pp. 156-162.

8. "Standard Specification for Hydrated Lime for Masonry Purposes," (ASTM

C207-79), 1983 Annual Book of ASTM Standards, Vol. 4.01, American Society

for Testing and Materials, Philadelphia, PA, pp. 221-224.

9. Woodward, Kyle and Rankin Frank, "The NBS Tri-directional Test Facility,"

Report No. NBSIR 84-2879, National Bureau of Standards, Washington, D.C.,

April 1984, 43 pp.

53
NBS.114A (REV. 2. 80 ) U.S. DEPT. OF COMM. 2. Performlnf Orsan. Report NoJ Publication Date BIBLIOGRAPHIC DATA

SHEET (See Instructions)

1. PUBLICATION OR

REPORT NO.

NBSIR 84-2929

4. TITLE AND SUBTITLE

Influence of Vertical Ccrtpressive Stress on Shear Resistance of Concrete Block

Masoncy Walls

5. AUTHOR(S)

Kyle Woodward and Frank Rankin

6. PERFORMING ORGANIZATION (If Joint or other than NBS, see Instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contraet/Grant No.

I. Type of Report & Period Covered

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, State, ZIP)

Sams as above

10.

SUPPLEMENTARY NOTES

Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant Information. If document Includes a significant

bibliography or literature survey, mention It here)

The results frcm tests on eight ungrouted and unreinforced concrete block

masonry walls are presented. The eirphasis of the research program is the

influence of vertical inrplane coirpressive stress on the lateral in-plane

load resistance of the walls. Each wall has noninal dimensions of

64 in. X 64 in. X 8 in. and is fabricated fron similar materials by the

same experienced mason. The masonry units are hollcw concrete block having

a ncminal compressive strength of 1800 psi based on the gross area. The mortar

was proportioned as a Type S. The walls are tested in the NBS Tri-directional

Testing Facility using fixed ended boundary conditions at the top and bottom

of the wall. Lateral inrplane displacements were applied at the top of the wall

vMle maintaining a constant compressive axial load. The vertical compressive

stress varies between 120 and 500 psi (based on net cross-sectional area) in

the test program. The test results indicate that there is a linear relationship between increasing amounts of vertical coitpressive stress and the resulting increased in-plane maximum lateral load resistance.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

Axial load; concrete block; masonry ; shear; structural testing; walls.

13.

AVAILABILITY

Unlimited

I I For Official Distribution. Do Not Release to NTIS

Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

61

15. Price

$10.00

USCOMM'OC e043.P80