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NBSIR 85-3143

Influence of Block and Mortar

Strength 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

April 1985

-QC

100

.056

85-3143

1985

DEPARTMENT OF COMMERCE

ONAL BUREAU OF STANDARDS

V.

NBSIR 85-3143

INFLUENCE OF BLOCK AND MORTAR

STRENGTH ON SHEAR RESISTANCE OF

CONCRETE BLOCK MASONRY WALLS

WATIONfll. BOTEflU OF STAND.y?DS

UBRAEY

MF -

dC. '00

' 1 ^

N :r'

Kyle Woodward

Frank Rankin

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Gaithersburg, MD 20899

April 1985

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

NATIONAL BUREAU OF STANDARDS. EmMt Ambtor. Director

ABSTRACT

Data from seventeen masonry wall panel tests are presented. All of the walls

are ungrouted, unreinforced, and constructed with hollow concrete block. The

primary variables in the test series are block and mortar strength, but the

applied vertical compressive stress and wall aspect ratio are also varied.

The walls are built with either a "high" strength block or a "low" strength

block having gross area unit strengths of approximately 1800 psi and 1300 psi,

respectively. The mortar is either a Type S or a Type N mortar and, for con- venience, is identified as high and low strength mortar, respectively. Thirteen

of the wall panels have nominal dimensions of 64 in. long x 64 in, high x 8 in.

thick, but two of the walls are 96 in. long and the remaining two walls are

48 in. long. The applied net area vertical compressive stress is constant for

a given test, but varies between 100 psi and 400 psi for tests in the series

reported herein. The walls are tested in the NBS Tri-directional Test Facility

using fixed-ended boundary conditions at the top and bottom of the walls, A

vertical compressive stress is applied and maintained while in-plane lateral

displacements are imposed at the top of the wall. The test results indicate

that for the lower levels of vertical compressive stress the effect of block

and mortar strength on maximum in-plane shear resistance is relatively small,

while with increased vertical compressive stress the effect of increasing

material strength becomes significant and results in increased shear resistance.

There is an interaction between the block and mortar strength such that the

wall behavior may not be adequately predicted by considering the two strengths

independently.

iii
TABLE OF CONTENTS

Page

ABSTRACT iii

LIST OF TABLES v LIST OF FIGURES vi

1. INTRODUCTION 1 2. TEST SPECIMENS 2 2.1 MATERIALS 2 2.2 WALL DETAILS 2 2.3 TEST SETUP AND INSTRUMENTATION 2 2.4 TEST PROCEDURE 6

3. DISCUSSION OF RESULTS 15

3.1 GENERAL BEHAVIOR 15

3.2 MAXIMUM IN-PLANE RESISTANCE 15

3.3 SHEAR STRESS-DISPLACEMENT RELATIONSHIP 23

3.4 DIAGONAL STRAIN 23

4. SUMMARY AND CONCLUSIONS 36

4.1 SUMMARY 36

4.2 CONCLUSIONS 36

5. ACKNOWLEDGEMENTS 37

6. REFERENCES 38

APPENDICES A-1

A. OVERVIEW OF MASONRY RESEARCH PROGRAM A-1

B. MATERIALS B-1

B.l CONCRETE MASONRY UNITS B-1

B. 2 MORTAR B-1

C. WALL PANEL DESCRIPTION C-1

C. l WALL PANEL FABRICATION C-1

C. 2 PRISM FABRICATION C-1

D. WALL PANEL TESTS: SETUP AND PLACEMENT D-1

D. l TEST SETUP D-1

D.2 WALL PANEL PLACEMENT D-1

E. WALL PANEL LOAD-DISPLACEMENT OTRVES E-1

iv
ABSTRACT

Data from seventeen masonry wall panel tests are presented. All of the walls

are ungrouted, unreinforced, and constructed with hollow concrete block. The

primary variables in the test series are block and mortar strength, but the

applied vertical compressive stress and wall aspect ratio are also varied.

The walls are built with either a "high" strength block or a "low" strength

block having gross area unit strengths of approximately 1800 psi and 1300 psi,

respectively. The mortar is either a Type S or a Type N mortar and, for con- venience, is identified as high and low strength mortar, respectively. Thirteen

of the wall panels have nominal dimensions of 6A in, long x 64 in, high x 8 in.

thick, but two of the walls are 96 in, long and the remaining two walls are

48 in. long. The applied net area vertical compressive stress is constant for

a given test, but varies between 100 psi and 400 psi for tests in the series

reported herein. The walls are tested in the NBS Tri-directional Test Facility

using flxed-ended boundary conditions at the top and bottom of the walls. A

vertical compressive stress is applied and maintained while in-plane lateral

displacements are imposed at the top of the wall. The test results indicate

that for the lower levels of vertical compressive stress the effect of block

and mortar strength on maximum in-plane shear resistance is relatively small,

while with increased vertical compressive stress the effect of increasing

material strength becomes significant and results in increased shear resistance.

There is an interaction between the block and mortar strength such that the

wall behavior may not be adequately predicted by considering the two strengths

independently.

iii
TABLE OF CONTENTS

Page

ABSTRACT ili

LIST OF TABLES v LIST OF FIGURES vi

1. INTRODUCTION 1 2. TEST SPECIMENS 2 2.1 MATERIALS 2 2.2 WALL DETAILS 2 2.3 TEST SETUP AND INSTRUMENTATION 2 2.4 TEST PROCEDURE 6

3. DISCUSSION OF RESULTS 15

3.1 GENERAL BEHAVIOR 15

3.2 MAXIMUM IN-PLANE RESISTANCE 15

3.3 SHEAR STRESS-DISPLACEMENT RELATIONSHIP 23

3.4 DIAGONAL STRAIN 23

4. SUMMARY AND CONCLUSIONS 36

4.1 SUMMARY 36

4.2 CONCLUSIONS 36

5. ACKNOWLEDGEMENTS 37

6. REFERENCES 38

APPENDICES A-1

A. OVERVIEW OF MASONRY RESEARCH PROGRAM A-1

B. MATERIALS B-1

B.l CONCRETE MASONRY UNITS B-1

B. 2 MORTAR B-1

C. WALL PANEL DESCRIPTION C-1

C. l WALL PANEL FABRICATION C-1

C. 2 PRISM FABRICATION C-1

D. WALL PANEL TESTS: SETUP AND PLACEMENT D-1

D. l TEST SETUP D-1

D.2 WALL PANEL PLACEMENT D-1

E. WALL PANEL LOAD-DISPLACEMENT QIRVES E-1

iv
LIST OF TABLES

Page

Table 2.1 Wall Panel Details 4

Table 2.2 Wall Panel Horizontal LVDT Location Dimensions 8

Table 3.1 Wall Panel Maximum In-plane Resistance 20

Table B.l Dimensions and Properties of Concrete Masonry Units B-3

Table B.2 Masonry Sand Sieve Analysis B-5

V
LIST OF FIGURES

Page

Figure 2.1 Typical wall panel 3

Figure 2.2 Test setup 5 Figure 2.3 Wall panel LVDT layout 7 Figure 2.4 Diagonal LVDT 9

Flguer 2.5 Leaf spring transducer 10

Figure 2.6 Wall panel instrumentation (48 in.) 11

Figure 2.7 Wall panel instrumentation (64 in.) 12

Figure 2.8 Wall panel instrumentation (96 in.) 13

Figure 2.9 Simplified description of test method 14

Figure 3.1 Typical crack pattern (64HL240) 16

Figure 3.2 Typical crack pattern (64LH340) 16

Figure 3.3 Flexural cracking (64LH105) 17

Figure 3.4 Crack pattern with high vertical stress (64HL320) 17

Figure 3.5 Crack pattern in low strength wall (64LL250) 18

Figure 3.6 Maximum shear stress versus vertical stress for

48 in. and 96 in. walls 21

Figure 3.7 Maximum shear stress versus vertical stress for

64 in. walls 21

Figure 3.8 Cracking in 96 in. wall panels 22

Figure 3.9 Regression analysis curves 22

Figure 3.10 Shear stress-displacement curves (64HH & 64LH) 24

Figure 3.11 Shear stress-displacement curves (64HL & 64LL) 25

Figure 3.12 Shear stress-displacement curves (64HH & 64HL) 26

Figure 3.13 Shear stress-displacement curves (64LH & 64LL) 27

Figure 3.14 Shear stress-displacement curves (48 in.) 28

Figure 3.15 Shear stress-displacement curves (96 in.) 29

Figure 3.16 Combined shear stress-diagonal strain curves 31

Figure 3.17 Shear stress-diagonal strain curves (64HH & 64LH) 32

Figure 3.18 Shear stress-diagonal strain curves (64HL & 64LL) 33

Figure 3.19 Shear stress-diagonal strain curves (64HH & 64HL) 34

Figure 3.20 Shear stress-diagonal strain curves (64LH & 64LL) 35

Figure B.l Concrete Masonry Units B-4

Figure D.l Wall panel transport harness D-2

Figure D. 2 Placement of a wall panel D-2

Figure E.l Crack pattern and load-displacement curve for

specimen 64HL160 E-2

Figure E.2 Crack pattern and load-displacement curve for

specimen 64HL240 E-3

Figure E.3 Crack pattern and load-displacement curve for

specimen 64HL320 E-4

Figure E.4 Crack pattern and load-displacement curve for

specimen 64HL400 E-5

Figure E.5 Crack pattern and load-displacement curve for

specimen 64LL170 E-6

Figure E.6 Crack pattern and load-displacement curve for

specimen 64LL250 E-7

VI
LIST OF FIGURES (CONT.)

Page

Figure E.7 Crack pattern and load-displacement curve for

Specimen 64LL340 E- 8

Figure E.8 Crack pattern and load-displacement curve for

specimen 64LL420 E- 9

Figure E.9 Crack pattern and load-displacement curve for

specimen 64LH105 E-10

Figure E.IO Crack pattern and load-displacement curve for

specimen 64LH170 E-11

Figure E.ll Crack pattern and load-displacement curve for

specimen 64LH250 E-12

Figure E.12 Crack pattern and load-displacement curve for

specimen 64LH340 E-13

Figure E.13 Crack pattern and load-displacement curve for

specimen 64LH420 E-14

Figure E.14 Crack pattern and load-displacement curve for

specimen 48LH170 E-13

Figure E.15 Crack pattern and load-displacement curve for

specimen 48LH430 E-16

Figure E.16 Crack pattern and load-displacement curve for

specimen 96LH220 E-17

Figure E.17 Crack pattern and load-displacement curve for

specimen 96LH320 E-18

vii
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1. INTRODUCTION

This report describes an experimental test series investigating the shear

behavior of unreinforced, hollow concrete block masonry walls. The test series

reported herein is part of a larger experimental research program which has as its main objective the determination of the in-plane shear (lateral load)

resistance of shear dominated masonry walls. The primary parameters discussed

in this report are block and mortar strength. The vertical (axial) compressive

stress and wall aspect ratio are also parameters in this test series, but only

secondarily, in order to observe the interaction of parameters.

Data from seventeen wall tests are presented in this report. The walls have

nominal heights and thicknesses of 64 in. and 8 in. , respectively. Thirteen

of the seventeen walls are 64 in. long, two of the walls are 48 in. and the

remaining two walls are 96 in. long. The vertical compressive stress varies

in the test series from a low of about 100 psi to a high of approximately 400

psi. These stresses are based on the net cross-sectional area of the walls.

The concrete block has a gross area unit strength of either 1300 psi or 1800

psi (approximate) and the mortar is proportioned either as a Type S or a Type N.

This report is the third in a series of reports documenting the overall research

program. Since the report is but one in a series, certain information common

to all of the reports has been placed in appendices. The intent of this organization is to reduce redundancy in the main body of the report without omitting

information necessary to the report's understanding if read independently of the

other reports in the series. The purpose of this report is to present in a timely manner a general description of the tests and a limited presentation of

key data. Detailed data analysis is left to summary reports which are issued

periodically and combine sufficient test information to fully address a particular topic.

A brief background description of the overall research program is in appendix

A. The materials and wall panel descriptions are discussed in chapter 2 along

with instrumentation and general test procedure. Further descriptions of

materials, fabrication techniques, and test setup may be found in appendices

B, C, and D. A brief, general discussion of the more obvious test results is

presented in chapter 3. The individual wall panel load-displacement curves

and crack pattern maps are in appendix E. The summary and conclusions are presented in chapter 4.

1
2. TEST SPECIMENS

This chapter presents a brief description of the materials used in constructing

the walls, the details of each wall (e.g., length, block strength), instrumenta

tion, and general test procedures. More complete descriptions may be found in

appendices B, C, and D.

2 .

I

MATERIALS

All materials used in the wall panels and companion prisms were commercially

available and were representative of those commonly used in building construction. The concrete block was hollow, two-core block and was from two lots.

One lot contained block having a gross area unit compressive strength of 1813

psi while the other lot had block whose gross area unit compressive strength

was 1304 psi. For the purposes of this report the block having the strength of

1813 psi was identified as "high" strength, while the other block was termed

"low" strength. These terms were relative indices and not a classification of

their absolute strengths. The mortar used in constructing the walls was propor

tinned as either a Type S and termed "high" strength or as a Type N and designated "low" strength.

2.2

WALL DETAILS

A typical wall panel is illustrated in fig. 2.1. The details of each wall are listed in table 2.1. The wall panel identifier is a two part label with

the two parts separated by a hyphen. That part of the identifier preceeding

the hyphen is the descriptive label and has the form mABn. In place of m there is a number representing the nominal length of the wall panel expressed

in inches. The n term is the approximate applied vertical compressive stress

on the wall panel. The stress is based on the net cross-sectional area of the

wall and is in units of psi. The positions represented by A and B designate

the strength of block and mortar, respectively. The letter H signifies "high"

while the letter L denotes "low". An example of the descriptive label is

64HL240 which is read to mean a 64 in. long wall constructed with "high"

strength block and "low" strength mortar which is tested with an applied vertical compressive stress of about 240 psi.

2.3

TEST SETUP AND INSTRUMENTATION

The walls are tested in the NBS Tri-directlonal Test Facility (fig. 2.2). The

facility is a structural test rig which can apply forces and/or displacements

in any or all of the six degrees of freedom at the top of the wall. The bottom

of the wall is held stationary by a restraining crosshead.

The instrumentation used to monitor the behavior of a wall panel during a test

can be divided into two main categories. The first category includes the load

and displacement transducers mounted on the hydraulic actuators which are part

of the test facility. The information from these transducers is used both for

the control system of the test facility and for measuring specimen response.

The global forces and displacements imposed on a test specimen are computed

from these data. The second category of instrumentation includes the

2
64' —Mortar

joint

head

(typ)

Mortar

bed (typ)

joint ^

Half

kerf Stretcher Stretcher Stretcher

Half

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Whole

kerf

Stretcher Stretcher Whole

kerf

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

Wall course: one block and

bed joint

48" and 96" walls are similar

except for length

64"

Figure 2,1 Typical wall panel

3
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5
transducers physically attached to the wall specimens. These Include

horizontally mounted linear variable differential transformers (LVDTs) which

are mounted to measure the in-plane displacement of the wall along the wall

height. The displacements are measured relative to a fixed reference. The

positions of the LVDTs are shown in fig. 2.3 and listed in table 2.2. The

other instrumentation attached to the test specimen measure displacements of one part of the wall relative to another part of the wall. These data are then used to compute wall strains by dividing the measured displacement by the

gage length of the transducers. Two general types of transducers are used,

the first being LVDTs mounted between swiveling posts attached to the wall

surface (fig. 2.4). These devices are used only for measuring displacement

along the wall diagonals, one on each side of the wall. The other type of

transducer is a leaf spring transducer also mounted on posts attached to the

wall surface (fig. 2.5). The general locations of the transducers mounted

on the wall panels are shown in figures 2.6, 2.7, and 2.8 for the 48 in., 64

in., and 96 in. long walls, respectively.

All of the analog instrumentation is connected to a high speed analog-todigital converter which is part of a general computer-based data acquisition

and load control system.

2.4 TEST PROCEDURE

The first step in a typical wall test was to check the data channels for unusual

variations in output and obtain a measure of the ambient voltage oscillation.

With the data channels in proper working order a set of data was acquired which

served as the "zero" condition of the test. The hydraulic actuators of the

test facility were then pressurized and another set of data readings were obtained. Compressive vertical (axial) load was applied to the wall until the

desired value was achieved. After stabilizing the vertical load, in-plane

lateral displacement was applied at the top of the wall panel. The lateral displacement was applied with the upper crosshead of the facility maintaining a "zero" rotation condition (fig. 2.9). The vertical load was automatically

maintained at the preset level by the facility's control system. The initial

direction of lateral displacement was always to the west, but the displacement

pattern varied slightly between tests. The lateral displacement was generally

increased in the initial direction until a diagonal crack was fully formed.

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

could not support the imposed vertical load. Data were acquired at regular

intervals during the test at lateral displacement intervals of about 0.005 in.

6
West East

n—1 «

,

* •—

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in-plane loading

C' TA'

B'

D'

(Note: upper crosshead not shown)

vr/ //////////////////

i Lower crosshead

Linear varying differential

transformer (LVDT), typ.

1

(t of wall

D

LVDT support

system (idealized)

Figure 2.3 Wall panel LVDT layout

7
Table 2.2 Wall Panel Horizontal LVDT Location Dimensions

(Refer to fig. 2.3 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.

)

64HL160 10.25 9.50 27.13 29.25 9.88 10.88 27.25 28.25

64HL240 9.88 9.88 26.75 29.50 10.0 10.38 27.50 27.75

64HL320 10.38 9.50 27.13 29.25 7.38 10.38 27.63 27.38

64HL400 10.25 9.38 27.0 29.13 7.38 10.38 27.75 27.38

64LL170 10.25 9.13 27.50 28.50 9.50 10.0 27.88 27.13

64LL250 10.38 9.13 27.38 28.63 9.25 10.0 27.63 27.38

64LL340 10.13 9.25 27.38 28.75 9.25 10.25 27.50 27.38

64LL420 10.13 9.25 27.38 28.75 9.25 10.25 27.50 27.38

64LH105 10.0 9.75 26.75 29.38 7.13 10.75 27.50 27.75

64LH170 9.75 9.75 26.88 29.25 8.75 10.75 27.0 27.88

64LH250 9.75 9.63 26.75 29.50 8.63 10.63 27.13 28.0

64LH340 10.0 9.63 26.75 29.50 8.63 10.75 26.88 28.0

64LH420 10.0 9.63 26.75 29.50 8.63 10.75 26.88 28.0

48LH170 10.13 9.25 27.88 28.50 9.38 10.0 27.88 27.38

48LH450 10.63 9.13 28.25 28.13 9.38 10.25 27.75 27.38

96LH220 10.50 9.0 28.50 27.75 9.38 10.13 27.75 27.25

96LH320 10.50 9.0 28.50 27.75 9.38 10.13 27.75 27.25

8
i
Figure 2.5 Leaf spring transducer

10
East

- 20 -

- 12 -

20 ^

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Swivel ended LVDT

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f JH

/

/ m V IX

West

Letters identify transducer

position for later reference

ITT12 20

12 -

20 -

north SIDE OF 48" WALL PANEL

West

- 20 -

20

12 _LiI

I*- SL

o

,

r

East

• Leaf spring transducer

Swivel ended LVDT

Letters identify transducer

position for later reference

12L12 20

Tl^12 -^J

20 -

SOUTH SIDE OF 48' WALL PANEL

Figure 2.6 Wall panel instrumentation (48 in.)

11
J Leaf spring transducer

«.—» Swivel ended LVDT

NORTH SIDE OF 64" WALL PANEL

J Leal spring transducer

Swivel ended LVDT

<fc SOUTH SIDE OF 64" WALL PANEL

Figure 2.7 Wall panel instrumentation (64 in.)

12
East

20 y12

- 36 -

inT-12—J

H

20 -

—• Leaf spring transducer — Swivel ended LVDT

,NL /

I" I'

West

Letters Identify transducer

position lor later relererKe

FT12 20

NORTH SIDE OF 96" WALL PANEL

West

20 f

12

.I. F

- 36 -

- 12 -

iTlTl

- 20 - - 12 -

Leal spring transducer

- - Swivel ended LVDT

JM

»SL

1 IS I« i

East

Letters IdentILy transducer

position lor later reference

FT-|12 I i

20

• 36 -

SOUTH SIDE OF 96' WALL PANEL

Figure 2.8 Wall panel instrumentation (96 in.)

13
Aq is the imposed in-plane lateral displacement

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

CL Upper

crosshead

CL Upper crosshead

Lower crosshead

SIMPLIFIED DESCRIPTION OF IMPOSED DISPLACEMENT

Figure 2.9 Simplified description of test method

14
3. DISCUSSION OF RESULTS

In addition to the seventeen wall panel tests reported herein, data from wall

panel tests reported previously [1, 2] are used in the discussion which

follows. The combination of wall tests include variations in applied vertical

compressive stress and wall panel aspect ratio. The focus of the discussion is on the Influence of block and mortar strength, but effects of the other parameters will be discussed when it appears that there is an interaction between

the parameters. The presentation is not intended to be a detailed analysis of

the data as that will appear in a subsequent summary report.

3.1 GENERAL BEHAVIOR

The typical mode of wall distress was a diagonal tension form of shear distress

as evidenced by the pronounced cracking along the diagonals of the wall panels

(figures 3.1 and 3.2). The exception to this mode of distress came only when

the level of vertical compressive stress was low, resulting in a flexurally

dominated initial mode of distress as shown in fig. 3.3 where the horizontal

flexure crack developed. However, even for the walls exhibiting flexural distress, it was possible to produce a local diagonal tension crack and, if the

vertical compressive stress was increased sufficiently, a general diagonal

tension mode of distress.

Given that the typical indication of distress was diagonal tension cracking,

there were observed differences in the form of the crack paths. It was previously observed [1, 2] that both the level of vertical compressive stress

and the aspect ratio influenced the orientation of the cracking. In general,

the trajectory of the crack pattern was rather constant along a roughly 45

degree line, especially for the square wall panels. The path that the diagonal

crack followed, however, was slightly more variable with most of the previously

reported walls exhibiting block cracking rather than a simple stair-step crack

along the mortar joints. The previous walls all had high strength block and

mortar. The influence of block and mortar strength seemed to be consistent

with the mortar strength having more effect. The degree of influence was a function of the level of vertical compressive stress and to a lesser degree

aspect ratio. Walls with high strength block and low strength mortar tended

to exhibit diagonal cracking of the stair-step fashion (fig. 3.1), but with

high levels of vertical stress some block cracking occurred (fig. 3.4).

Conversely, walls with low strength block and high strength mortar exhibited

much more through block cracking (fig. 3.2). The combination of low strength

block and mortar resulted in a definite combination of the two types of crack

path (fig. 3.5), though it appeared that the cracking began along the mortar

joints and then, shortly afterward, initiated in the block units.

3.2 MAXIMUM IN-PLANE RESISTANCE

The capacity of particular interest in these tests is the maximum In-plane

lateral load resistance. This load is referred to as the shear force capacity

and when the shear force is divided by a nominal value for the wall's net

cross-sectional area the resulting computed stress is termed the shear stres^^.

The advantage of using shear stress rather than force is in the normalization

15
A

B

C

East

Spalled area — Direction of initial displacement

West

Figure 3.1 Typical crack pattern (64HL240)

Spalled area — Direction of initial displacement

West

Crack pattern; 64LH340-6L04 (North face)

Figure 3,2 Typical crack pattern (64LH340)

16
Figure

East

A

B

C

D

Spalled area —Direction of initial displacement

West

Crack pattern: 64LH105-6L01 (North face)

Figure 3.3 Flexural cracking (64LH105)

East

A

B

C

Spalled area — Direction of initial displacement

West

Crack pattern: 64HL320-5L03 (North face)

3.4 Crack pattern with high vertical stress (64HL320)

17
East

Crack pattern; 64LL250-6L06 (North face)

Figure 3.5 Crack pattern in low strength wall (6ALL250)

18
of the capacity with respect to varying wall area as between a 96 in. wall

and a 64 in. wall. This may be an incomplete normalization, but for the purposes of this report it is considered an acceptable normalization. The maximum

shear resistance of each wall panel is listed in table 3.1 along with the

applied vertical compression stress and wall displacement coincident with the

achievement of maximum shear.

The maximum shear stresses are plotted versus the vertical compressive stresses

in figures 3.6 and 3.7 along with data from the previously reported tests

[1, 2]. Figure 3.6 contains the data for the 48 in. and 96 in. long wall

panels. It appears that the block strength does not affect the maximum shear

stress for the 96 in. walls and had only a minor impact for the 48 in. walls.

In the case of the 48 in. walls the trend is, as might be expected, lower

maximum shear resistance with the lower block strength. The trend, or more

appropriately, the lack of a trend, for the 96 in. walls is most probably the

result of the diagonal crack path. The diagonal cracking in the 96 in. walls

was almost exclusively along the mortar joints (fig. 3.8) making it unlikely

that the block strength would be a significant parameter for maximum shear

stress. The mortar strength is not an intentional variable for the 48 in. and

96 in. long walls and no observations can be made on the effect of mortar

strength.

The maximum shear stress versus vertical compressive stress comparisons for

the 64 in. long wall panels are plotted in fig. 3.7. The comparison for block

strength is made between the open and closed forms of each symbol and the

comparison for mortar strength is made between similar forms, open or closed,

of the different symbols. The most obvious general trend is the divergence of

maximum shear stresses as the vertical stress increases. The group of data

points at the 160 psi vertical compressive stress level reflect four different

parameters and yet there is little difference between the points. By contrast,

the spread in maximum shear stresses at the 400 psi vertical compressive stress

level is quite large. It is clear that the vertical compressive stress has an effect on the apparent interaction between block and mortar strength and the

maximum shear stress for the 64 in. long wall panels.

The trend of the data plotted in fig. 3.7 is more easily visualized by regression analyses (fig. 3.9). Four of the lines are linear while the remaining

line, labelled 64LH, is quadratic because the regression analyes showed a significant improvement in fit for the quadratic compared to the linear representation. The line labels indicate the data used in determining each line.

Label 64 XX means that all of the data for the 64 in. long wall panels are used

in the regression analysis for that line. A certain amount of caution should

be exercised in evaluating the trends especially outside the limits of the

data values. The bounds are indicated by vertical lines on the plot and describe

the limits of stresses generally contained in the actual data. The tendency

towards dispersion as the vertical stress increases is evident. Another clear

trend is that as the vertical stress increases there is a marked decrease in

maximum shear stress for the low strength block walls as compared to the high

strength walls. A similar trend for mortar strength exists for the high strength

block walls, but the trend is not as pronounced for the low strength block

walls. This observation suggests that the total wall behavior may be

19
Table

3.1

Wall

Panel

Maximum

In-plane

Resistance

4-> c • c

e •H

QJ B w

O 3

tC B OJ •H O

o. X c

W CO CO o ON NO LO NO ON m o 00 C3N I-H CO CO CM 'd' •H :s 4-1 o^ 00 NO NO NO CM CM 00 CM CM lO o CO o o o o o I-H o i-H o o o o f-H o ^H

4-1 -H

CO CO o o o o o o o o O o o o o o o o o

0)

CO Pi

(U-X c <D /-N

CO O -H CM f-H o m 'd* 00 00 CM NO NO CM CO CO C CO CM cn (ON <r m o CM u~l M3 NO NO o

a

1

CO a

4J

I-H f-H ^H ^H ^H ^H f-H ^H ^H ^H CM c CO M •H

CO 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 e (U 3 Pi B CO •H T) a o 00 CM o CO o r-^ o ^H CO CM X CO -H

CO o ^ o CM NO 00 CM f-H NO o CM C3N (Ti CO s l-J N-X CO cn 'sf CM CO CO <3’ CM CO CO <r <r CM CM m

0) -H

i-H > CO

CO •H ^

O CO w •H CO CO CO NO CM NO CM CO CO ^H 00 CO m O O m

U (U^C vO <3* o NO CO ^H o NO Nd* CM NO CO CM

Vj CO CM CO CM CO I-H ^H CM CO <r CM CO

CU a. CO > B OJ O I-I U 4Jc«

rH

COC

O /—

s

4J •iHCN

OJ u • o o o o NO NO NO NO nD NO NO NO NO CM CM 'd' <t 2 O c

0) -H vO M3 NO NO ^H I-H 1—

H

I-H CM CM

CO w <r <r <• <r <3* CO CO NO NO

1 CM CM CN CM CM CM CM CM CM CM CM CM CM •-H CO CO

CO CO CO s CO <D O U

CM CO <r NO 00 ON ^H CM CO 'd- m o ^H CM CO O o o o o o o o o o o o o ^H I-H ^H

i-t hJ l-J *-l K-l l-J 1-1 kJ 1-4 1-4 1-4 1-4 p-l 1-4 1-4 1-4 1-4 1-4 (U LO m m m NO NO NO M3 NO NO NO M3 NO NO NO NO NO

•H 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I-H <+-l o o o o o o o O m o o O o o o o o QJ *H M3 CM o lO CM o m CM m CM CM

rH C u CM CO <t CM cn >d* ^H ^H CM CO •<r f—

H

•<r CM CO

CO CO C P-J i-J kJ i-j 1-4 SC X X X X X X X X

St P-i QJ E E ix: X hJ hJ hJ 1-4 1-4 1-4 1-4 1-4 hJ 1-4 1-4 1-4 1-4 73 <1- <r <r <r <1* 'd' <r CO CO NO lO M NO NO NO NO NO NO NO NO NO NO NO NO <T C7N ON

20

Values

of

stress

are

based

on

the

net

cross-sectional

area

of

the

walls
MAXIMUM

SHEAR

STRESS

(psi)

MAXIMUM

SHEAR

STRESS

(psi)

300

250

200

150

100

50

0 50 100 150 200 250 300 350 400 450 500

VERTICAL COMPRESSIVE STRESS (psi)

Figure 3.6 Maximum shear stress versus vertical stress for

48 in, and 96 in. walls

300

250

200

150

100

50

° 50 100 150 200 250 300 350 400 450 500

VERTICAL COMPRESSIVE STRESS (psi)

o 64LH

• 64HH

A 64LL

A 64HL

d)A

a

A

^

^ ^ ^ ^

o 96LH

• 96HH

A 48LH

A 48HH %

Figure 3.7 Maximum shear stress versus vertical stress for

64 in, walls

21
MAXIMUM

SHEAR

STRESS

(psi)

A

BC

D

Spalled area — Direction of initial displacement

West

Crack pattern: 96LH320-6L13 (North face)

Figure 3.8 Cracking in 96 in. wall panels

Figure 3.9 Regression analysis curves

22
affected by the interaction of block and mortar strengths rather than simply by

each strength independently. The regression line for all of the 64 in. long

walls is plotted in fig. 3.9 and it is labelled 64XX. The equation of the

line is V = (70.8 + 0.321a) where v is the maximum shear stress and a is the

vertical compressive stress, both in units of psi. The standard error of the

regression analysis (e) is 17.4 psi and parallel lines 2e above and below the

regression line are also shown on the plot.

3.3 SHEAR STRESS-DISPLACEMENT RELATIONSHIP

The measured shear stress-displacement curves are shown in figures 3.10 through

3.15. The shear stress is the measured global in-plane lateral load divided by

the wall's net cross-sectional area and the displacement is the in-plane wall

displacement as measured by the top west LVDT (fig. 2.3). The curves include

only the data up to a displacement just past that corresponding to the maximum

shear stress.

The curves in figures 3.10 and 3.11 illustrate the effect of block strength

variation for the 64 in. long walls built with high and low strength mortar,

respectively. As the relationships in fig. 3.10 indicate, there is a noticeable

decrease in stiffness for the low strength block walls compared to high strength

block walls built with high strength mortar. However, the same trend is not

observed for the walls built with low strength mortar. There does not appear

to be any indication that the variation in block strength significantly affects

the wall displacement at which the maximum shear is achieved.

The curves in figures 3.12 and 3.13 show the effect of mortar strength variation

for the 64 in. long walls built with high and low strength block, respectively.

Based on the information presented in fig. 3.12, it appears that for the walls

built with high strength block a decrease in mortar strength causes a decrease

in wall stiffness. A similar trend is not apparent in the data for walls

built with low strength block. These relationships also do not exhibit a tendency for the mortar strength to affect the wall displacement at which the

maximum shear stress occurs.

Shear stress-displacement curves are shown in figures 3.14 and 3.15 for 48 in.

and 96 in. long walls, respectively. All of the wall panels whose data are shown in these two figures have high strength mortar, but have either low or high strength block. Based on the trends observed in the 64 in. wall panels, it

is expected that the low strength block walls will exhibit a marked lower stiffness, but the wall displacement coincident with the maximum shear stress will

be relatively unchanged. As the curves in figures 3.14 and 3.15 illustrate,

the trends observed for 64 in. walls do, in fact, exist for the 48 in. and 96 in.

long walls.

3.4 DIAGONAL STRAIN

The primary mode of distress in the walls is diagonal tension cracking. It seems reasonable that cracking is a function of the tensile component of the

diagonal stresses or strains. It is suggested by the previous reports (1, 2]

that diagonal tension strain is a reliable indicator of the onset of diagonal

23
SHEAR

STRESS

(psi)

Figure 3.10 Shear stress-displacement curves (64HH & 64LH)

24
SHEAR

STRESS

(psi)

Figure 3.11 Shear stress-displacement curves (64HL & 64LL)

25
300

240

180

120

60

0 0.02 0.04 0.06 0.08

WALL DISPLACEMENT (inches)

0.10

gure 3.12 Shear stress-displacement curves (64HH & 64HL)

26
300

240

180

120

60

0 0.02 0.04 0.06 0.08

WALL DISPLACEMENT (inches)

0.10

ure 3.13 Shear stress-displacement curves (64LH & 64LI.)

27
SHEAR

STRESS

(psi)

Figure 3.14 Shear stress-displacement curves (48 in.)

28
300

240

180

120

60

0

T

0.03 0.06 0.09 0.12

WALL DISPLACEMENT (inches)

0.15

Figure 3.15 Shear stress-displacement curves (96 in.)

29
tension cracking and that the threshold strain at cracking is relatively

unaffected by variations in vertical compressive stress and wall aspect ratio.

The data from the tests reported herein also tend to suggest that the threshold

strain is unaffected by variations of block and mortar strength.

The relationships between shear stress and the diagonal strain for all of the

64 in. wall panels are shown in fig. 3.16. These include data from wall panels

reported previously. The diagonal strain is that computed from the displacements measured by the NL diagonal LVDT shown in fig. 2.7. With four noticeable

exceptions, the curves show a definite tendency to exhibit unstable strain

growth, indicative of cracking, at a common threshold strain. The exceptions

are all from tests with relatively high vertical stress levels (>300 psi), but

not all wall panels subjected to such vertical stresses exhibited this atypical

behavior. Within the scope of this report, the exceptions will remain anomalies

and possible explanations for their behavior are not discussed.

The data shown in fig. 3.16 is divided into other figures (fig. 3.17-3.20)

which highlight the trends for changing block or mortar strength. The effect

of block strength is shown in figures 3.17 and 3.18 for high and low strength

mortar, respectively. The effect of mortar strength is shown in figures 3.19

and 3.20 for high and low strength block, respectively. The data in these

figures emphasize that within the variation of parameters actually tested the

threshold diagonal strain is independent of the varied parameters.

30
SHEAR

STRESS

(psi)

Figure 3.16 Combined shear stress-diagonal stress curves

31
SHEAR

STRESS

(psi)

Figure 3.17 Shear stress-diagonal strain curves (64HH & 64LH)

32
SHEAR

STRESS

(psi)

Figure 3.18 Shear stress-diagonal strain curves (64HL & hU\A.)

33
SHEAR

STRESS

(psi)

Figure 3.19 Shear stress-diagonal strain curves (64HH & 64HL)

34
SHEAR

STRESS

(psi)

DIAGONAL STRAIN (microstrain)

Figure 3.20 Shear stress-diagonal strain curves (64LH & 64LL)

35
4. SUMMARY AND CONCLUSIONS

4 . 1 SUMMARY

Data from seventeen wall tests were presented. The walls were built using

hollow concrete block having an approximate gross area unit strength of either

1800 psi or 1300 psi and mortar proportioned as either Type S or Type N. All

of the walls had a nominal height and thickness of 64 in. and 8 in., respectively. Thirteen of the walls had a length of 64 in. , two of the walls

were 48 in. long, and the remaining two walls were 96 in. long. The applied

vertical (axial) compressive stress was varied in the test series between the

approximate limits of 100 psi and 400 psi, based on the net cross-sectional

area of the wall. The walls were subjected to in-plane lateral displacement

in combination with a constant applied vertical compressive stress. The displacement was applied at the top of the wall while the bottom of the wall was held stationary. Rotation of the loading surface was restrained at the top

and bottom of the wall, simulating a fixed-fixed boundary condition. The data

indicated that for the lower levels of applied vertical stress used in the

test series the influence of both block and mortar strength on the maximum

shear resistance was negligible. However, as the vertical stress levels were

increased the influence became significant with the expected result that higher

strength block and/or mortar resulted in higher shear resistances. There also

appeared to be an interaction between the effects of block and mortar strength

on the shear resistance, suggesting that it may not be adequate to consider

their effects independently.

4.2 CONCLUSIONS

The conclusions stated below are based solely on the data reported herein and

data previously reported from this research program. The conclusions are only

valid for the ranges of parameters included in these tests.

® For the lower levels of applied vertical compressive stress the

influence of block and mortar strength on the maximum shear

resistance was negligible. The influence of the strengths became

more significant as the vertical stress was increased.

® Where block and mortar strengths influenced shear resistance, the

influence appeared to be a function of their interactive effects

and not solely due to one or the other.

® In general, the linear relationship between maximum shear resistance

and applied vertical compressive stress was unaffected by block or mortar strength. The high strength block-low strength mortar walls

were an exception and exhibited a quadratic relationship.

® The diagonal tension strain threshold at which diagonal cracking

occurred was unaffected by the variation in block and mortar

strength.

36
5. ACKNOWLEDGEMETNS

The concrete block and the mason who fabricated the walls were provided by the

National Concrete Masonry Association,

The authors wish to thank the reviewers, Dr. John Gross, Dr, Len Mordfin and

Dr. Spencer Wu, for their comments and suggestions.

37
6.

REFERENCES

1. Woodward, Kyle and Rankin, Frank, "Influence of Vertical Compressive Stress

on Shear Resistance of Concrete Block Masonry Walls," Report No. NBSIR 84-

2929, National Bureau of Standards, Gaithersburg, MD, October 1984, 53 pp.

2. Woodward, Kyle and Rankin, Frank, "Influence of Aspect Ratio on Shear

Resistance of Concrete Block Masonry Walls," Report No. NBSIR 84-2993,

National Bureau of Standards, Gaithersburg, MD, January 1985, 56 pp.

3. 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.

4. "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.

5. "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.

6. "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.

7. "Standard Specification for Mortar for Units Masonry," (ASTM C270-82), 1983

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

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

8. "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.

9. "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.

10. "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.

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

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

,

May 1984, 43 pp.

38
Appendix A. OVERVIEW OF MASONRY RESEARCH PROGRAM

The principal objective of the overall program of research is to define the

shear capacity 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 serious deficiency of supporting research. The NBS/BSSC review

committee for the ATC3-06 masonry design provisions [3] suggested that research

was 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.

A-1
W3i\jt-»vii ,a

K a

< • .4»

n*^;-..iKy*A -'T :*!' 4l'v<:.^^. fc»» t »»«»»>( iswi&l;

«*jRian ' •'^^ .«>, "(>t , «Kl ".l^ i;»‘'> oWt^^-'-ic' nirn'i^^fr ul »i«fl3 ifaiHig

; a. ^

,. ^ V¥-/ # •:*J'i.’^||ft3 '»e«rf8

ffl ,.

’ '^ ja -''J .v''i

ftv

' 3to

„ ,. wrtai-v

' ii'iw ' S3 .'3®»a.- ^ '''jt' Ji • '.

. . . »"... '-. t _ • . - -# ^ ^ V' ar^ . t>-«-Ai^h.4i»^w .^R-{Xe^ "S<>, V nilWJLWX V^^^
Appendix B. MATERIALS

All materials used in the wall panel construction and associated prisms were commercially available and were representative of those commonly used in building construction,

B. 1 CONCRETE MASONRY UNITS

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

panels and prisms:

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

2. 8 in. X 8 in. x 16 in., 2 core hollow kerfed corner block with a steel sash groove at one end.

The dimensions represent nominal sizes. Typical measured dimensions and physical characteristics of the units are presented in table B.l, The measurements

were made in accordance with the procedures set forth in ASTM C140 [4] . The

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

wall courses were made by sawing kerfed corner blocks in half through the

kerf. Both halves produced by this procedure were 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 units having ultimate gross area compressive

strengths of either 1000 psi or 2000 psi. The mixture proportions were:

1000 psi unit 2000 psi unit

1950 lbs

1250 lbs

200 lbs

190 lbs

1950 lbs

1250 lbs

260 lbs

190 lbs

lightweight expanded shale aggregate

sand

Portland cement

NEWCEM

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

furnance slag manufactured by Atlantic Cement Co., Inc. and is used as a partial

replacement for portland cement. It meets the requirements of ASTM C989 , grade

120 [5] and when blended within the range of 25 to 65 percent with portland

cement, meets the requirements of ASTM C595 [6]. 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 1000 psi

and 2000 psi units made 118 units with 3.3 lbs of cementitious materials per

unit and 115 units with 3,9 lbs of cementitious materials per unit, respectively.

R.2 MORTAR

Two types of mortar were used in constructing the wall panels and prisms. onc

type of mortar was a portland cement-lime mortar that was proportioned within

the limits of a Type S mortar according to the specifications of ASTM C?7o (71.

B-1
The other type of mortar was also a portland cement-lime mortar, but proportioned within the limits of a Type N mortar. 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

upon delivery. The analyses were done according to the specifications

in ASTM C144 [8] and the results appear in table B.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 [9].

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

Type S, identified as meeting the specifications of ASTM C207 [10],

The Type S mortar was 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 Type N mortar was proportioned 1:1:5 with 1 part by volume of cement, 1 part by volume of lime,

and 5 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 3 minutes after all cement, lime, sand, and most of the water were

added. Finally, small amounts of water were added to produce mortar of a consistency acceptable to the mason. Retempering of the mortar, if required,

was permitted only once per batch.

B-2
Table B.l Dimensions and Properties of Concrete Masonry Units

1000 psi Unit * 2000 psi Unit **

Hollow

Stretcher

Hollow

Corner/ Sash

Groove

Hollow

Stretcher

Hollow

Corner/ Sash

Groove

Width (in.) 7.65 7.64 7.63 7.63

Height (in.) 7.56 7.56 7.59

V

7.57

Length (in.) 15.66 15.66 15.62 15.64

Minimum Face

Shell Thickness (in.) 1.30 1.29 1.30 1.30

Gross Area (in.^) 119.8 119.6 119.2 119.3

Net Solid Area (in.^) 60.4 66.1 61.5 67.0

Gross Ultimate Compressive Strength (psi) 1304 1398 1813 1795

Density (Ib/ft^) 98.1 96.8 102.4 104.5

Absorption (Ib/ft^) 14.0 13.7 10.8 10.2

* Average of measurements from 9 units of each type.

** Average of measurements from 6 units of each type.

B-3
Figure B.l Concrete Masonry Units

B-4
Table B.2 Masonry Sand Sieve Analysis*

Screen Cumulative

Size

Number

Percent

Retained

4 0.1

8 0.6

16 2.0

30 11.0

50 59.9

100 86.6

100+ • • • •

Total 157 V 100 = 1.57 Fineness Modulus

*Average of three samples taken upon delivery of sand.

B-5

Appendix C. WALL PANEL DESCRIPTION

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.

C. 1 WALL PANEL FABRICATION

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

block in alternate wall courses. The wall panels had overall nominal

dimensions of 64 in, in height, 8 in, in thickness, and either 96 in., 64 in.,

or 48 in, in length. The wall panels (and prisms) were constructed 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 a least 30 days. The temperture 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 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 vertically

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.

C.2 PRISM FABRICATION

Prisms were made along with most of the wall panels using mortar from the same batch as was used for the wall panel. Each prism was made by stack bonding

three stretcher units. The mortar bedding between the blocks was either face

shell only or full area bedding. Within each group of prisms the bedding was

the same. The mason used a 4 foot level to maintain the level of each block

and to plumb the prism. The ultimate compressive strength of the prisms was determined by testing the prisms in uniaxial testing machine having a total

capacity of 400,000 pounds force. A spherically seated upper bearing block

covered the entire bearing surface of the prisms. The load on the prism was applied at any convenient rate for the first 40,000 pounds force while the

remaining load was applied at a rate of 40,000 pounds per minute until fallur*-

occurred. The maximum load sustained by the prism was used in computing the

ultimate compressive stress.

C-1
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Appendix D. WALL PANEL TESTS; SETUP AND PLACEMENT

D.l TEST SETUP

The test setup (fig. 2.2) is the NBS Trl-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

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

The NBS/TTF is a computer-controlled loading apparatus which can apply 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 shown in fig. 2.2. 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.

n.2 WALL PANEL PLACEMENT

The wall panels were handled by attaching a carrying harness to the panel (fig.

D.l). The harness had attachment points for lifting the wall and a clamping

arrangement which held the harness against the ends of the panel. The overhead

crane was used to place the wall panel in the NBS/TTF and a special device was fabricated which permitted the wall to be placed under the upper crosshead.

The special device was a large welded assembly in the shape of a "C" which

permitted the crane hook to be centered above the wall panel without interfering with the upper crosshead (fig. D.2).

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

their horizontal position. The walls were aligned vertically 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 crosshead 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.

D-1
Figure D.l Wall panel transport harness

Figure D.2 Placement of a wall panel

D-2
Appendix E. WALL PANEL LOAD-DISPLACEMENT CURVES

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

the wall (fig. 2.9). This displacement is referred to as the global in-plane

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

by the horizontal LVDT's mounted to the wall (fig. 2.3). The global in-plane

displacment (GID) is determined by the displacement transducers in the hydraulic actuators. The GID and the wall displacement measured directly by LVDT's

are not necessarily the same. The GID is affected by total apparatus displace

ment while the direct LVDT displacement more nearly measures an absolute inplane displacement of the wall. However, the direct LVDT displacment can be

strongly affected by the breakup of a wall after cracking. Spalling and split

ting in the region near a wall LVDT can produce large distortions in the appar

ent displacement. In general, the GID is a consistent measure of displacement

which is unaffected by a 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 reponse 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

load-displacment 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, points on the load-displacement curve identified by

the symbols are coincident with the crack pattern also associated with that

symbol. S 3nnbol A does not refer to the same point on every load-displacement

curve.

E-1
East

A

BC

D

Spalled area —» Direction of initial displacement

West

Crack pattern: 64HL160-5L01 (North face)

Figure E.l Crack pattern and load-displacement curve for

specimen 64HL160

E-2
Crack pattern: 64HL240-5L02 (North face)

Figure E.2 Crack pattern and load-displacement curve for

specimen 64HL240

E-3
Figure

East

Spalled area — Direction of Initial displacement

West

E.3 Crack pattern and load-displacement curve for

specimen 64HL320

E-4
GLOBAL

IN-PLANE

LOAD

(kips)

\\

NWn kW

A

B

\

\

' \

1

\ c

Spalled area

\ V Note: spalling began

after deflection exceeded 0.3 in. V \

\

\ — Direction of initial displacement

\w

> \\

\\\\ West

Crack pattern: 64HL400-5L04 (North face)

Figure E.4 Crack, pattern and load-displacement curve for

Specimen 64HL400

E-5
A

BC

D

E

FSpalled area — Direction of initiai dispiacement

West

Crack pattern: 64LL170-6L07 (North face)

Figure E.5 Crack pattern and load-displacement curve for

specimen 6ALL170

E-6
A

BC

D

E

Spalled area —

Direction of initial displacement

West

40

^ 24

(/) Q. Q

<o 8

liJ < 0

0. z

-8

<

mO

O -24

-40

-0.35 -0.21 -0.07 0 0.07 0.21 0.35 GLOBAL IN-PLANE DISPLACEMENT (inches)

Crack pattern; 64LL250-6L06 (North face)

Figure E.6 Crack pattern and load-displacement curve for

specimen 64LL250

E-7
Figure E.7 Crack pattern and load-displacement curve for

specimen 64LL340

E-8
A

BC

Figure

Spalled area — Direction of Initial displacement

West

E.8 Crack pattern and load-displacement curve for

specimen 64LL420

E-9
area

A

BC

D

Spalled —Direction of Initial displacement

West

Crack pattern: 64LH105-6L01 (North face)

0 0.06 0.12 0.18 0.24 0.30 GLOBAL IN-PLANE DISPLACEMENT (inches)

Figure E.9 Crack, pattern and load-displacement curve for

specimen 64LH105

E-10
A

BC

Note: This crack line practically

disappeared after the other cracks formed at 0.2in. deflection — Direction of Initial displacement

West

0 0.08 0.16 0.24 0.32 0 40 GLOBAL IN-PLANE DISPLACEMENT (inches)

Figure E.IO Crack pattern and load-displacement curve for

specimen 64LH170

E-11
Crack pattern: 64LH250-6L03 (North face)

Figure E.ll Crack pattern and load-displacement curve for

specimen 6ALH250

E-12
A

BC

East

Spalled area — Direction of Initial displacement

West

Fi§Dre E»12 Crack pattern and load~displacefnent curve for

specimen 64LH340

E-13
Crack pattern: 64LH420-6L05 (North face)

GLOBAL IN-PLANE DISPLACEMENT (inches)

Figure E.13 Crack pattern and load-displacement curve for

Specimen 64LH420

E-14
A

BC

East

V

1 \

1 >

\

\

\ MlV

'w i

Spalled area

Direction of initial displacement

west

Crack pattern: 48LH170-6L10 (North (ace)

Figure E.14 Crack pattern and load-displacement curve fr>r specimen 48LH170

E-15
Crack pattern; 48LH450-6L11 (North face)

Figure E.15 Crack pattern and load-displacement curve for

specimen 48LH450
-0.35 -0.21 -0.07 0 0.07 0.21 0 35 GLOBAL IN-PLANE DISPLACEMENT (inches)

Figure E.16 Crack pattern and load-displacement curve for

specimen 96LH220

E-17
ABC

D

Spalled area — Direction of Initial displacement

West

Crack pattern; 96LH320-6L13 (North face)

Figure E.17 Crack pattern and load-displacement curve for

specimen 96LH320

E-18
FORM NBS-1 14A (REV. 1 1-84)

U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA

SHEET (See instructions)

REPORT NO.

NBSIR 85-3143 April 1985

4. TITLE AND SUBTITLE

Influence of Block and Mortar Strength on Shear Resistance of Concrete Block

Masonry Walls

5. AUTHOR(S)

Kyle Woodward and Frank Rankin

6. PERFORMING ORGANIZATION (If joint or other than NBS, see in struction s) 7, Contract/Grant No.

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

GAITHERSBURG, MD 20899

9.

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

same as 6 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

bi blipgraphy or literature survey, mention it here) Data from seventeen masonry wall panel tests are presented. All of the walls are ungrouted, unreinforced, and constructed with hollow concrete block. The primary variables

in the test series are block and mortar strength, but the applied vertical compressive

stress and wall aspect ratio are also varied. The walls are built with either a "high"

strength block or a "low" strength block having gross area unit strengths of approximately 1800 psi and 1300 psi, respectively. The mortar is either a Type S or Type N

mortar and, for convenience, is identified as high and low strength mortar, respectively.

Thirteen of the wall panels have nominal dimensions of 64 in. long x 64 in. high x 8 in.

thick, but two of the walls are 96 in. long and the remaining two walls are 48 in. long.

The applied net area vertical compressive stress is constant for a given test, but

varies between 100 psi and 400 psi for tests in the series reported herein. The walls

are tested in the NBS Tri—directional Test Facility using fixed—ended boundary conditions at the top and bottom of the walls. A vertical compressive stress is applied and

maintained while in-plane lateral displacements are Imposed at the top of the wall. Thttest results indicate that for the lower levels of vertical compressive stress the effect of block and mortar strength on maximum in-plane shear resistance is relatively

small, while with increased vertical compressive stress the effect of increasing materia!

strength becomes significant and results in increased shear resistance. There is .m interaction between the block and mortar strength such that the wall behavior mav n- l Ftl adequately predicted by con sidering the two strengths independently. , 12. KEY WORDS fS/x to twelve entries; alphabetical order; capitalize only proper names; and separate key words by sr - Axial stress; block; concrete block; failure; masonry; mortar; shear; strength.

13. AVAILABILITY 14. *. 1 P t- ' i Uni imited For Official Distribution. Do Not Release to NTIS r 1 Order From Superintendent of Documents, U.S. Government Printing Office, Washington. DC

20402. IJ. 1 r

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