Behavior of Concrete Block Masonry Walls

Subjected to Repeated Cyclic Displacements

U.S. Department of Commerce

National Bureau of Standards

Washington, D.C. 20234

October 1983

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BEHAVIOR OF CONCRETE BLOCK MASONRY WALLS

SUBJECTED TO REPEATED CYCLIC DISPLACEMENTS

Kyie Woodward

Frank Rankin

U.S. Department of Commerce

National Bureau of Standards

Washington, D C. 20234

October 1983

Sponsored by

Bureau of Mines

Department of the Interior

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director

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ABSTRACT

An experimental investigation into the behavior of unreinforced, ungrouted

concrete block masonry walls subjected to repeated in-plane lateral cyclic

displacements indicated a pronounced effect of loading history on the wall

performance, but only at load/displacements nearing the load capacity failure

point. A total of 15 walls were tested of which 10 were 64 in. x 64 in. planar

walls and 5 were 64 in. high corner walls having equal leg lengths of 48 in.

The primary parameter varied in the investigation was loading history. The

cyclic tests included fully reversed displacement patterns and reversed displacement patterns superimposed on static displacement offsets. Monotonic

tests at both slow and rapid strain rates were done. The cyclic tests included

at least 100,000 repetitions.

iii
TABLE OF CONTENTS

Page

ABSTRACT iii

LIST OF TABLES vi

LIST OF FIGURES vii

ACKNOWLEDGMENTS xvi

1. INTRODUCTION 1-1

1.1 SCOPE 1-1

2. TEST SETUP 2-1

2.1 TRI-DIRECTI ONAL TEST FACILITY ( TTF) 2-1

2.1.1 Reaction System 2-1

2.1.2 Load Distribution System 2-2

2.1.3 Load Application System 2-2

2.1.4 Control System 2-3

2.2 USE OF THE TRI-DIRECTIONAL TEST FACILITY 2-3

2.2.1 Load Application Technique 2-3

2.2.2 Data Acquistion and Display 2-4

3. MATERIALS 3-1

3.1 CONCRETE MASONRY UNITS 3-1

3.2 MORTAR 3-1

4. TEST SPECIMENS 4-1

4.1 DESCRIPTION OF WALLS AND PRISMS 4-1

4.2 FABRICATION OF WALLS AND PRISMS 4-1

5. TEST PROCEDURES 5-1

5.1 PRISM TESTING PROCEDURES 5-1

5.2 WALL TESTING PROCEDURES 5-1

5.3 INSTRUMENTATION 5-2

6. TESTING PROGRAM 6-1

6.1 LOADING HISTORIES 6-1

6.2 TEST DATA' DESCRIPTION 6-2

6.2.1 Load Versus Displacement Curves 6-2

6.2.2 Strain Histories 6-3

6.2.3 Crack Patterns 6-3

6.3 TEST DESCRIPTIONS 6-4

6.3.1 Wall P10 6-4

6.3.2 Wall P7 6-4

6.3.3 Wall P9 6-4

6.3.4 Wall P6 6-5

6.3.5 Wall P8 6-5

6.3.6 Wall P4 6-6

6.3.7 Wall P2 6-6

6.3.8 Wall P5 6-6

6.3.9 Wall P3 6-7

iv
TABLE OF CONTENTS

Page

6.3.10 Wall PI . 6-7

6.3.11 Wall C5 6-8

6.3.12 Wall C4 6-8

6.3.13 Wall C3 6-8

6.3.14 Wall C2 6-9

6.3.15 Wall Cl 6-9

7. ANALYSIS AND INTERPRETATION 7-1

7.1 FAILURE MODE AND CRACKING 7-1

7.2 EFFECT OF LOADING HISTORY 7-1

7.3 CORNER WALL VERSUS PLANAR WALL BEHAVIOR 7-3

7.4 EFFECT OF Z-AXIS DISPLACEMENT 7-4

7.5 LOCALLY MEASURED STRAINS 7-4

7.6 DAMAGE THRESHOLD 7-5

7.7 APPLICABILITY OF TEST RESULTS 7-5

8. SUMMARY AND CONCLUSIONS 8-1

8.1 SUMMARY 8-1

8.2 CONCLUSIONS 8-1

v
LIST OF TABLES

Page

Table 3.1 Dimensions and Properties of Concrete Masonry Units 3-3

Table 3.2 Masonry Sand Sieve Analysis 3-4

Table 5.1 Average Mortar and Prism Data 5-3

Table 7.1 Wall Test Parameters 7-8

Table 7.2 Axial Load - Moment Interaction Values 7-9

vi
LIST OF FIGURES

Page

Figure 2.1. Overall view of test setup (looking to the north) ..... 2-5

Figure 2.2. Schematic of crosshead, buttress, and actuator

arrangement 2-6

Figure 3.1. Concrete masonry units 3-5

« Figure 4.1. Typical walls and prisms 4-3

Figure 5.1. Planar wall lifting rig 5-4

Figure 5.2. View of typical wall placement (looking to the west) .. 5-5

Figure 5.3. C-hook 5-6

Figure 5.4. Corner wall pickup 5-7

Figure 5.5. Typical planar wall instrumentation 5-8

Figure 5.6. Strain measuring device 5-9

Figure 5.7. Corner wall instrumentation 5-10

Figure 6.1. Wall displacement directions 6-11

Figure 6.2. Lateral load versus piston displacement for

wall P10 6-12

Figure 6.3. Lateral load versus wall displacement for

wall P10 6-12

Figure 6.4. Post-test crack observations for wall P10 6-13

Figure 6.5. Post-test crack observations for wall P7 6-14

Figure 6.6. Lateral load versus piston displacement for wall P9 ... 6-15

Figure 6.7. Lateral load versus wall displacement for wall P9 6-15

Figure 6.8. Strain measuring locations for wall P9 6-16

Figure 6.9. Strain history of SML 9 for wall P9 6-17

Figure 6.10. Strain history of SML 17 for wall P9 6-17

Figure 6.11. Pre-test crack observations for wall P9 6-18

vii
LIST OF FIGURES

Page

Figure 6.12. Post-test crack observations for wall P9 6-18

Figure 6.13. Lateral load versus piston displacement for wall P6 .. 6-19

Figure 6.14. Lateral load versus wall displacement for wall P6 .... 6-19

Figure 6.15. Strain measuring locations for wall P6 6-20

Figure 6.16. Strain history of SML 1 for wall P6 6-21

Figure 6.17. Strain history of SML 6 for wall P6 6-21

Figure 6.18. Strain history of SML 10 for wall P6 6-22

Figure 6.19. Strain history of SML 11 for wall P6 6-22

Figure 6.20. Strain history of SML 18 for wall P6 6-23

Figure 6.21. Strain history of SML 19 for wall P6 6-23

Figure 6.22. Piston displacement history for wall P6 6-24

Figure 6.23. Lateral load history for wall P6 6-24

Figure 6.24. Pre-test crack observations for wall P6 6-25

Figure 6.25. Post-test crack observations for wall P6 6-25

Figure 6.26. Lateral load versus piston displacement for wall P8 .. 6-26

Figure 6.27. Lateral load versus wall displacement for wall P8 .... 6-26

Figure 6.28. Strain measuring locations for wall P8 6-27

Figure 6.29. Strain history of SML 1 for wall P8 6-28

Figure 6.30. Strain history of SML 4 for wall P8 6-28

Figure 6.31. Strain history of SML 6 for wall P8 6-29

Figure 6.32. Strain history of SML 11 for wall P8 6-29

Figure 6.33. Strain history of SML 13 for wall P8 6-30

Figure 6.34. Strain history of SML 15 for wall P8 6-30

Figure 6.35. Strain history of SML 19 for wall P8 6-31

viii
LIST OF FIGURES

Page

Figure 6.36. Strain history of SML 20 for wall P8 6-31

Figure 6.37. Strain history of SML 21 for wall P8 6-32

Figure 6.38. Strain history of SML 23 for wall P8 6-32

Figure 6.39. Pre-test crack observations for wall P8 6-33

Figure 6.40. Post-test crack observations for wall P8 6-33

Figure 6.41. Pre-test crack observations for wall P4 6-34

Figure 6.42. Post-test crack observations for wall P4 6-34

Figure 6.43. Lateral load versus piston displacement for wall P2 ... 6-35

Figure 6.44. Lateral load versus wall displacement for wall P2 6-35

Figure 6.45. Strain measuring locations for wall P2 6-36

Figure 6.46. Strain history of SML 3 for wall P2 6-37

Figure 6.47. Strain history of SML 5 for wall P2 6-37

Figure 6.48. Strain history of SML 6 for wall P2 6-38

Figure 6.49. Strain history of SML 8 for wall P2 6-38

Figure 6.50. Strain history of SML 10 for wall P2 6-39

Figure 6.51. Strain history of SML 11 for wall P2 6-39

Figure 6.52. Strain history of SML 12 for wall P2 6-40

Figure 6.53. Strain history of SML 13 for wall P2 6-40

Figure 6.54. Pre-test crack observations for wall P2 6-41

Figure 6.55. Post-test crack observations for wall P2 6-41

Figure 6.56. Lateral load versus piston displacement for wall P5 .... 6-42

Figure 6.57. Lateral load versus wall displacement for wall P5 6-42

Figure 6.58. Strain measuring locations for wall P5 6-43

Figure 6.59. Strain history of SML 3 for wall P5 6-44

ix
LIST OF FIGURES

Page

Figure 6.60. Strain history of SML 4 for wall P5 6-44

Figure 6.61. Strain history of SML 5 for wall P5 6-44

Figure 6.62. Strain history of SML 6 for wall P5 6-45

Figure 6.63. Strain history of SML 8 for wall P5 6-45

Figure 6.64. Strain history of SML 10 for wall P5 6-46

Figure 6.65. Strain history of SML 13 for wall P5 6-46

Figure 6.66. Piston displacement history for wall P5 6-47

Figure 6.67. Lateral load history for wall P5 6-47

Figure 6.68. Pre-test crack observations for wall P5 6-48

Figure 6.69. Post-test crack observations for wall P5 6-48

Figure 6.70. Lateral load versus piston displacement for wall P3 .. 6-49

Figure 6.71. Lateral load versus wall displacement for wall P3 .... 6-49

Figure 6.72. Strain measuring locations for wall P3 6-50

Figure 6.73. Strain history of SML 5 for wall P3 6-51

Figure 6.74. Strain history of SML 6 for wall P3 6-51

Figure 6.75. Strain history of SML 8 for wall P3 6-51

Figure 6.76. Strain history of SML 10 for wall P3 6-52

Figure 6.77. Strain history of SML 11 for wall P3 6-52

Figure 6.78. Strain history of SML 12 for wall P3 6-53

Figure 6.79. Strain history of SML 13 for wall P3 6-53

Figure 6.80. Piston displacement history for wall P3 6-54

Figure 6.81. Lateral load history for wall P3 6-54

Figure 6.82. Pre-test crack observations for wall P3 6-55

Figure 6.83. Post-test crack observations for wall P3 6-55

x
LIST OF FIGURES

Page

Figure 6.84. Lateral load versus piston displacement for

wall PI 6-56

Figure 6.85. Lateral load versus wall displacement for wall PI ... 6-56

Figure 6.86. Strain measuring locations for wall PI 6-57

Figure 6.87. Strain history of SML 3 for wall PI 6-58

Figure 6.88. Strain history of SML 5 for wall PI 6-58

Figure 6.89. Strain history of SML 7 for wall PI 6-59

Figure 6.90. Strain history of SML 10 for wall PI 6-59

Figure 6.91. Strain history of SML 11 for wall PI 6-60

Figure 6.92. Strain history of SML 12 for wall PI 6-60

Figure 6.93. Strain history of SML 13 for wall PI 6-61

Figure 6.94. Piston displacement history for wall Pi ............. 6-62

Figure 6.95. Lateral load history for wall PI 6-62

Figure 6.96. Pre-test crack observations for wall PI 6-63

Figure 6.97. Post-test crack observations for wall PI 6-63

Figure 6.98. Lateral load versus piston displacement for

wall C5 6-64

Figure 6.99. Lateral load versus wall displacement for

wall C5 6-64

y* Figure 6.100. Strain measuring locations for wall C5 6-65

Figure 6.101. Strain history of SML 1 for wall C5 6-66

Figure 6.102. Strain history of SML 3 for wall C5 6-66

Figure 6.103. Strain history of SML 4 for wall C5 6-67

Figure 6.104. Strain history of SML 5 for wall C5 6-67

Figure 6.105. Strain history of SML 6 for wall C5 6-68

xi
LIST OF FIGURES

Page

Figure 6.106. Strain history of SML 7 for wall C5 6-68

Figure 6.107. Strain history of SML 8 for wall C5 6-69

Figure 6.108. Strain history of SML 9 for wall C5 6-69

Figure 6.109. Strain history of SML 10 for wall C5 6-70

Figure 6.110. Strain history of SML 11 for wall C5 6-70

Figure 6.111. Strain history of SML 12 for wall C5 6-71

Figure 6.112. Strain history of SML 13 for wall C5 6-71

Figure 6.113. Strain history of SML 15 for wall C5 6-72

Figure 6.114. Pre-test crack observations for wall C5 6-73

Figure 6.115. Post-test crack observations for wall C5 6-73

Figure 6.116. Lateral load versus piston displacement for wall C4 . 6-74

Figure 6.117. Lateral load versus wall displacement for wall C4 ... 6-74

Figure 6.118. Strain measuring locations for wall C4 6-75

Figure 6.119. Strain history of SML 3 for wall C4 6-76

Figure 6.120. Strain history of SML 4 for wall C4 6-76

Figure 6.121. Strain history of SML 5 for wall C4 6-77

Figure 6.122. Strain history of SML 6 for wall C4 6-77

Figure 6.123. Strain history of SML 7 for wall C4 6-77

Figure 6.124. Strain history of SML 8 for wall C4 6-78

Figure 6.125. Strain history of SML 9 for wall C4 6-78

Figure 6.126. Strain history of SML 10 for wall C4 6-79

Figure 6.127. Strain history of SML 11 for wall C4 6-79

Figure 6.128. Strain history of SML 12 for wall C4 6-80

Figure 6.129. Strain history of SML 13 for wall C4 6-80

xii
LIST OF FIGURES

Page

Figure 6.130. Pre-test crack observations for wall C4 6-81

Figure 6.131. Post-test crack observations for wall C4 6-81

Figure 6.132. Lateral load versus piston displacement for wall C3 .. 6-82

Figure 6.133. Lateral load versus wall displacement for wall C3 .... 6-82

Figure 6.134. Strain measuring locations for wall C3 6-83

Figure 6.135. Strain history of SML 3 for wall C3 6-84

Figure 6.136. Strain history of SML 4 for wall C3 6-84

Figure 6.137. Strain history of SML 5 for wall C3 6-84

Figure 6.138. Strain history of SML 6 for wall C3 6-85

Figure 6.139. Strain history of SML 7 for wall G3 6-85

Figure 6.140. Strain history of SML 8 for wall C3 6-86

Figure 6.141. Strain history of SML 9 for wall C3 6-86

Figure 6.142. Strain history of SML 10 for wall C3 6-87

Figure 6.143. Strain history of SML 11 for wall C3 6-87

Figure 6.144. Strain history of SML 12 for wall G3 6-88

Figure 6.145. Strain history of SML 13 for wall C3 6-88

Figure 6.146. Pre-test crack observations for wall C3 6-89

Figure 6.147. Post-test crack observations for wall C3 6-89

Figure 6.148. Lateral load versus piston displacement for wall C2 .. 6-90

Figure 6.149. Lateral load versus wall displacement for wall C2 .... 6-90

Figure 6.150. Strain measuring locations for wall C2 6-91

Figure 6.151. Strain history of SML 3 for wall C2 6-92

Figure 6.152. Strain history of SML 4 for wall C2 6-92

Figure 6.153. Strain history of SML 5 for wall C2 6-93

xiii
LIST OF FIGURES

Page

Figure 6.154, Strain history of SML 7 for wall C2 6-93

Figure 6.155. Strain history of SML 8 for wall C2 6-94

Figure 6.156. Strain history of SML 9 for wall C2 6-94

Figure 6.157. Strain history of SML 11 for wall C2 6-95

Figure 6.158. Strain history of SML 12 for wall C2 6-95

Figure 6.159. Strain history of SML 13 for wall C2 6-96

Figure 6.160. Piston displacement history for wall C2 6-97

Figure 6.161. Lateral load history for wall C2 6-97

Figure 6.162. Pre-test crack observations for wall C2 6-98

Figure 6.163. Post-test crack observations for wall C2 6-98

Figure 6.164. Lateral load versus piston displacement for wall Cl . 6-99

Figure 6.165. Lateral load versus wall displacement for wall Cl ... 6-99

Figure 6.166. Strain measuring locations for wall Cl 6-100

Figure 6.167. Strain history of SML 3 for wall Cl 6-101

Figure 6.168. Strain history of SML 4 for wall Cl 6-101

Figure 6.169. Strain history of SML 5 for wall Cl 6-102

Figure 6.170. Strain history of SML 7 for wall Cl 6-102

Figure 6.171. Strain history of SML 9 for wall Cl 6-103

Figure 6.172. Strain history of SML 11 for wall Cl 6-103

Figure 6.173. Strain history of SML 12 for wall Cl 6-104

Figure 6.174. Piston displacement history for wall Cl 6-105

Figure 6.175. Lateral load history for wall Cl 6-105

Figure 6.176. Pre-test crack observations for wall Cl 6-106

Figure 6.177. Initial diagonal crack observation for wall Cl 6-106

xiv
LIST OF FIGURES

Page

Figure 6.178. Post-test crack observations for wall Cl 6-106

Figure 7.1. Diagonal tension failure 7-10

Figure 7.2. Load displacement curve for test P10 7-11

Figure 7.3. Load displacement curve for test P9 7-12

Figure 7.4. Load displacement curve for test P6 7-13

Figure 7.5. Load displacement curve for test P8 7-14

Figure 7.6. Load displacement curve for test P2 7-15

Figure 7.7. Load displacement curve for test P5 7-16

Figure 7.8. Load displacement curve for test P3 7-17

Figure 7.9. Load displacement curve for test PI 7-18

Figure 7.10. Load displacement curve for test C4 7-19

Figure 7.11. Load displacement curve for test C3 7-20

Figure 7.12. Load displacement curve for test C2 7-21

Figure 7.13. Load displacement curve for test Cl 7-22

Figure 7.14. Envelope curves for planar wall tests 7-23

Figure 7.15. Envelope curves for corner wall tests 7-24

Figure 7.16. Resultant load-displacement curve for test C5 7-25

Figure 7.17. Resultant load-wall displacement curve for test C5 .. 7-26

Figure 7.18. Overturning 7-27

Figure 7.19. Axial load versus restraining moment 7-28

xv
ACKNOWLEDGMENTS

The investigation reported herein was conducted for and sponsored by the Bureau

of Mines, Department of the Interior. The assistance of the following Bureau

of Mines personnel during the actual testing is gratefully acknowledged:

Mark Stagg, Dave Siskind, Dan Vick, Michael Stevens, and G. Robert Vanderbos.

The National Concrete Masonry Association provided both the concrete block

and an experienced mason to fabricate the walls. Their contributions are gratefully acknowledged.

Special thanks go to Mark Stagg, William Kovacs, and Spencer Wu for their

diligent review of this report.

xvi
1. INTRODUCTION

Blasting in mines and quarries present potential problems when they are adjacent to residential developments. Blasting generates ground motions which

radiate from the blast source some distance determined by a number of parameters

such as blast size, soil and rock type and layering. The ground motion can induce vibrations in a residential dwelling. The characteristics of the vibration (frequency, acceleration, velocity, and amplitude) may range between

levels such that no vibration is perceived by people and no damage occurs to

the residence structure to levels which cause distress to people and damage

to structures. It is clearly necessary that only blasting which minimizes or eliminates undesirable effects on adjacent people and their dwellings be permitted. However, such an outcome is only possible if rational, effective

criteria are available by which blasts may be designed.

The Bureau of Mines has been extensively investigating the problem of blastinduced ground motion damage to residential structures with the final goal

being blast designs which minimize damage to residences. As part of their

investigation the Bureau of Mines required detailed information on the fatigue

characteristics of concrete block masonry walls. Such walls, usually unreinforced and ungrouted, are commonly used to form the basement walls and provide

support to the dwelling superstructure.

The experimental research program described herein was carried out under

contract to the Bureau of Mines by the Structures Division, Center for Building

Technology, National Bureau of Standards. The research program involved the

testing of 10 planar walls and 5 corner walls. The focus of the research was

on the fatigue characteristics of the walls when subjected to in-plane lateral

forces. In addition, however, the walls were also tested to obtain their

maximum lateral load capacities.

1.1 SCOPE

The purpose of this report is to document the experimental investigation as prescribed by the sponsor. The emphasis has been placed on details of the test

program and its results rather than interpretations. The reader will find

sufficient information by which independent interpretations may be developed.

Chapter 2 is a description of the test apparatus and to a limited extent

procedure. The Tri-directional Test Facility is described and its salient

features are discussed as they apply to this investigation.

The material properties for both mortar and concrete block are presented in

chapter 3 and the test specimens are described in chapter 4 including geometry,

materials, and construction.

A more detailed description of test procedures is presented in chapter 5. The

method of wall placement and testing are explained. The instrumentation used

to measure wall behavior are also described.

1-1
A description of each wall test is presented in chapter 6. The loading histories

are described and the pertinent acquired load, displacement, and strain data are presented

.

Chapter 7 includes the interpretation of the acquired data emphasizing the

points of interest to the sponsor.

The summary and conclusions are presented in chapter 8.

1-2
2 TEST SETUP

The test setup (figure 2.1) is the Tri-directional Test Facility ( TTF ) , a permanent loading apparatus designed to test building components using threedimensional loading histories. In this chapter, the general characteristics

of the TTF and the specific manner in which it was used for this investigation

are described.

2.1 TRI-DIRECTIONAL TEST FACILITY (TTF)

The TTF is a computer controlled loading apparatus which can apply forces/

displacements in all six degrees of freedom at one end of a 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 (x, y, z). The application of such actions are accomplished by seven closed-loop, servo-controlled

hydraulic actuators which receive their instructions by means of computer

generated commands. Referring to figure 2.1 it is possible to observe the major

components of the TTF. The reaction system is composed of the structural tie

down floor and two vertical buttresses. The load distribution system is the

two x-shaped 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 of which four are visible in the figure. The control system is not visible

in the figure, but includes the servo-control electronics, the data acquisition

equipment, and a mini-computer. The general concept of the facility is simple

though its operation is complex. The test specimen is fitted between two very

stiff members (crossheads), one of which is fixed in place, while the other is

free to move in any direction. The movement of the free crosshead is dictated

by the actions of the hydraulic actuators.

A schematic of the crosshead and actuator arrangement is shown in figure 2.2.

The load capacity of each actuator is also shown in figure 2.2.

2.1.1 Reaction System

The loads transmitted by the lower crosshead are resisted directly by the

structural tie down floor. The reaction of the horizontal hydraulic actuators

is provided by the two buttresses which also transmit the forces to the tie

down floor (figure 2.2).

The lower crosshead is attached to the tie down floor by means of post-tensioned

high strength bolts. The lateral (or shear) forces are resisted by means of

positive stops rather than friction. The overturning forces are resisted by

tension in the tie down bolts. The upper crosshead has no reactive capacity

other than that provided by action of the hydraulic actuators. The vertical

actuators are attached to both crossheads, but only use the lower crosshead

for reaction. The horizontal actuators transmit forces both to the lower

crosshead by means of the test specimen and to the vertical buttresses.

The structural tie down floor is a 6 ft thick heavily reinforced concrete slab.

The tie down floor has vertical embedded receptacles for attaching objects to

the floor by means of high-strength bolts. In addition, the embedded

2-1
receptacles include provisions for including shear sleeves concentric with the

bolts. The shear sleeves bear directly against embedded steel plates so that

shear is not resisted by the bolts. The vertical buttresses are monolithically

cast reinforced concrete. The buttresses are post-tensioned both vertically

and horizontally. The vertical post-tensioning provides the shear and overturning capacity by being attached to the tie down floor by means of rock

anchors placed in the floor. The buttresses include mounting locations on the

face near the crossheads by which the hydraulic actuators may be attached.

The attachment method permits continuously variable height adjustment to

accomodate leveling of the horizontal actuators at any practical height above

the floor.

2.1.2 Load Distribution System

The load distribution system includes the two steel crossheads and the attached

reinforced concrete footings. The primary function of the steel crossheads is

to transmit the concentrated actions of the hydraulic actuators as more uniformly distributed forces. The crossheads are purposely designed to be

extremely stiff to limit the compliance of the loading members. The crossheads

are heavily stiffened pairs of 21 in. deep wide flange shapes welded along their

adjoining flanges to produce a box shape. The resulting width of the loading

surface is about 26 in. The reinforced concrete footings are additions solely

for the testing of concrete masonry components. The top footing is 18 in. deep

and the bottom footing is 21 in. deep. Each footing is attached to the crosshead by 40 post-tensioned 1-1/2 in. diameter high-strength bolts. The footings

provide a transitory medium between the steel crosshead and the masonry walls

and reduce the severe discontinuity in material properties. In addition, as discussed later, the footings permitted a simple method of attaching the walls

to the crossheads, namely, epoxy mortar.

2.1.3 Load Application System

As illustrated in figure 2.2 there are seven hydraulic actuators to control the

action of the upper crosshead. The hydraulic actuators are servo-controlled

which simply means that the action of each actuator is electrically controlled

so that the actual response of the actuator is at all times equal to the

response commanded of the actuator. The commands are in the form of an applied

analog signal generated either locally or by the computer. The action required

of each actuator is quite complicated for simultaneous multi-directional movements or when the overall geometry changes due to actuator movements are large.

The hydraulic actuators are displacement controlled which means that the

variable which is used in the command-response loop is the displacement of the

actuator's retractable piston. Such control ensures that specimen instability

cannot occur during a test since at any moment the location of the upper cross- head is fixed by the relative lengths of actuators. The force seen by each

actuator can vary, but the displacement is controlled. The end fittings of

each actuator are swivels which permit sufficient rotation in all directions

to accommodate crosshead movements without introducing bending into the actuators. Such fittings are required since otherwise the _+ 6 in. travel of the

actuator pistons (exception: the single horizontal 220 kip actuator has +3 in.

2-2
travel) could produce geometry changes sufficient to introduce substantial

extraneous bending forces in the hydraulic actuators. Each hydraulic actuator

has an internal, integrally mounted linear variable differential transformer

(LVDT) to measure piston movement and a load sensing transducer mounted in

line with the piston. The resulting information permit the global forces and

displacements imposed by the upper crosshead to be measured.

2.1.4 Control System

The control system coordinates the actions of the TTF. Through the control

system the operator interacts with the hydraulic actuators to control loading,

acquires test data, and manipulates the test data to display the acquired

information in the most meaningful form. The major parts of the control system

are the servocontrollers , the data acquisition equipment, the computer, and a variety of computer peripherals such as printers, plotters, and video terminals.

The computer connects all the parts of the system to each other. The computer

acquires the data on the test environment through a high-speed analog-to-digital

converter. The computer instructs the hydraulic actuators through the servocontrollers by issuing analog commands to the controllers which then actually

perform the analog loop function. The computer receives instructions from the

operator and transmits responses to the operator by means of the peripherals.

Specially developed software enable the computer to understand instructions

submitted by the operator, sense the test environment, manipulate the upper

crosshead, and display the condition of the test specimens on a real-time

basis. In addition, to the real-time capabilities there are post-test data

analysis and presentation software to further refine the manner in which data

is displayed.

2.2 USE OF THE TRI-DIRECTI ONAL TEST FACILITY

In the previous section, the general capabilities and features of the TTF were

described. The actual use of the TTF for the investigation reported herein

varied considerably from the intended use of the TTF. In this section, the

differences and actual techniques are described. The TTF is directed to slow

loading rate tests due to the available computing power and hydraulic flow rate.

The requirement of high rate cyclic loadings imposed by this investigation

precluded the use of computer controlled loading. The computer directed data

acquisition and display functions were retained, but in a modified form.

2.2.1 Load Application Technique

The single direction and very small magnitude of displacement application

permitted the walls to be tested without computer control and only a minor loss

of response capability. The small displacement magnitudes meant that geometry

corrections of the applied actions were not required as long as the position of

the crosshead was centered and leveled on the masonry wall.

2-3
Great care was taken to assure these conditions and the set up procedure did

involve computer controlled crosshead movement. The procedure for a test began

with the application of an axial (vertical or z axis) compressive load to the

wall. This presented some difficulty since the vertical actuators had to be

displacement controlled in order to achieve the desired condition of rotational

fixity. The compressive load was introduced by gradually applying a uniform

vertical displacement to the wall until the desired load level was attained.

The vertical actuators were computer controlled for this action. Upon reaching

the proper load the displacement was then maintained by the servo-controllers

without further direction by the computer. The application of the in-plane (x

axis, figure 2.2) lateral displacement was done by the single 220 kip actuator

and its movements were also controlled by a servo-controller. However, the

varying commands were produced by a frequncy generator having many different

wave forms (e.g., sine wave and ramp) and not by the computer. The out-of-plane

horizontal hydraulic actuators were locked against displacement during a test.

2.2.2 Data Acquisition and Display

Because of the high sampling rate required to properly assess wall performance

only selected portions of the data could be displayed on a real-time basis.

The remainder of the acquired data could be displayed only after a test. The

sheer volume of data taken required large amounts of time for preparation to

display and then display. As an example, one of the tests produced close to

8 million data points. Needless to say, the most efficient form of data display

was plotting which is used extensively for that reason in this report.
2-5

Figure

2.1.

Overall

view

of

test

setup

(looking

to

the

north)
90 kip ACTUATOR

W(X)

Figure 2.2

220 kip

ACTUATOR

N(Y)

DOWN

(Z)

UPPER

CROSSHEAD

150 kip

ACTUATOR

(typ)

LOWER

CROSSHEAD

TTF ISOMETRIC REPRESENTATION BUTTRESS

*

90 kip 90 kip

220 kip

V\A— UPPER CROSSHEAD

PLAN VIEW

Schematic of crosshead, buttress, and actuator arrangement

2-6
3. MATERIALS

All materials used in tha wall panel construction and associated prisms were

commercially available and were representative of those commonly used in

building construction.

3.1 CONCRETE MASONRY UNITS

Two types of concrete masonry units 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 in one end.

These units are illustrated in figure 3.1

The half block at the end of alternate courses of the wall panels were made by

sawing the kerfed corner block in half through the kerf, using the square end

and discarding the end containing the steel sash groove.

All the concrete masonry units for this testing program were manufacturered

the same day using mixture proportions that would produce units with ultimate

strength over the gross area of 1,000 psi. The mixture proportions were:

1950 lbs lightweight expanded shale aggregate

1250 lbs sand

200 lbs portland cement

190 lbs NewCem

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

furnace slag manuf acturered by Atlantic Cement Co., Inc. It meets the requirements of ASTM C989-82, grade 120 and when blended within the range of 25 to 65

percent with portland cement, meets the requirements of ASTM C595 Standard

Specifications for Blended Hydraulic Cements. This mixture produced 118.2

units with 3.3 pounds of cementitious materials per unit. The block machine

was set for 1.75 second feed, 1.25 second finish with a 0.25 second delay.

The dimensions and physical characteristics of these units are given in

table 3.1.

3.2 MORTAR

One type of mortar was used throughout this testing program in fabricating the

wall panels, prisms, and mortar cubes. The mortar was a portland cement-lime

mortar that was proportioned within the limits of a type N mortar according to

the specifications of ASTM C270-80a. The materials used in the mortar were:

3-1
1. Sand - a natural bank sand that was dug locally with its primary end use being masonry mortar. Sieve analyses were performed according to

ASTM C144-81 and the results appear in table 3.2. The fineness modulus

was 1.57.

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

Type I portland cement meeting the specifications of ASTM C150.

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

lime, Type S, meeting the specifications of ASTM C270.

These materials were proportioned 1:1:5 with 1 part by volume of cement, 1 part by volume of lime, 5 parts by volume of sand. The parts were mixed in a typical 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

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, a sample was taken for determining the initial flow rate, and the air content of the mortar

was taken (air content was not always measured because it did not vary significantly during the course of construction). A set of three, 2 in. x 2 in. mortar

cubes was made at this time, also. After the mason built the wall specimen

and three prisms, a second set of three, 2 in. x 2 in. mortar cubes was made.

The finish time was then recorded. Thus, each batch of mortar produced a wall

specimen, three prisms and two sets of three 2 in. x 2 in. mortar cubes.

Retempering of the mortar was permitted once per batch.

3-2
Table 3.1 Dimensions and Properties of Concrete Masonry Units

Hollow

Stretcher

Hollow

Corner/ Sash

Groove

Width (in.) 7.66 7.64

Height (in.) 7.55 7.58

Length ( in .

)

15.66 15.67

Minimum Face Shell

Thickness (in.) 1.34 1.32

o Gross Area (in. ) 120.0 119.7

Net Solid Area (%) 49.6 55.2

Gross Compressive

Strength (psi) 1310 1440

Density (lb/ft^) 98.2 98.2

Absorption (lb/ft^) 14.4 14.3

3-3
Table 3.2 Masonry Sand Sieve Analysis

*

Screen

Size

Number

Cumulative

Percent

Retained

4 0.1

8 0.6

16 2.0

30 11.0

50 56.9

100 86.6

100+ • • • •

Total 157.2 r 100 = 1.57 Fineness Modulus

* Average results of three samples of masonry sand taken during construction of

walls PI - P10 and Cl - C5.
Figure

3.1

Concrete

masonry

units

4. TEST SPECIMENS

A detailed description of the wall and prism specimens and the methods of

fabrication are presented in this section.

4.1 DESCRIPTION OF WALLS AND PRISMS

Two styles of walls were built for testing in this program. The first style

was a planar wall 64 inches long and 64 inches tall. The second was a corner

wall with each leg of the 90° corner being 48 inches long and the height being

64 inches. These were nominal dimensions. The prisms (figure 4.1) were nominally 16 inches long by 24 inches high (this was accomplished by laying three

blocks in a vertical stack.)

4.2 FABRICATION OF WALLS AND PRISMS

The specimens previously described were fabricated by an experienced mason

using techniques representative of good workmanship. They were built of materials that had been stored in the laboratory environment for at least 30 days.

After fabrication the specimens were air-cured until they were tested. All

fabrication and curing took place in a controlled-environment laboratory that was maintained at 73°F +_ 3°F with 50 percent _+ 5 percent relative humidity.

The block in these walls were laid in a running bond^ with the mortar joints on both sides of the walls cut flush and not tooled. The bottom course of block

in the planar walls was laid dry on the laboratory floor using small wooden

wedges for shimming any block that did not sit steadily on the floor. The

bottom course of block in the comer walls was laid dry on a channel-iron base

that was welded to form a flat base with a 90° included angle. (Because of

level imperfections in the floor surface, it was easier to level the channeliron base with wood wedges than to level the block individually, although

individual block unsteadiness was still corrected on an as-needed basis with

wooden wedges.)

In the planar walls, the first unit laid was a kerfed corner block at the end

of the course without head joint mortar. Head joints were subsequently formed

by buttering one end of the next block to be laid in that course just before

placing it in the wall. In this way, all head joints were "shoved" and there

were no closure units or "slushed" head joints. The end block on each course

was alternatly a kerfed corner and a half corner. All blocks were laid in

mortar using face shell bedding only with the exception of the outside edges

at the end of each course where mortar was applied to the end cross web.

Stretcher blocks were used in the wall interior. Each course was leveled by

the mason, using a 4 foot level. The end blocks were plumbed and then all

intermediate blocks were brought into horizontal alignment using the level as

a straightedge.

Units in successive courses are laid half-over (overlapping 50 percent) with

head joints in alternate courses in vertical alignment.

4-1
In the construction of the corner walls, the first block laid on each course

was the kerfed corner block that formed the corner of the two intersecting

legs of the wall. Successive units were buttered and shoved into place to

complete the course on both legs. The mason then leveled the top of the block

on both legs, plumbed the corner block and the two end blocks and then brought

the intermediate block into horizontal alignment using the level as a straightedge. This was done on each course.

In the construction of the prisms, three stretcher blocks were laid by stacking

them vertically using face shell bedding only. The mason used his level to

maintain the levelness of each block and the plumbness of the prism. Three

prisms were constructed as companions to each wall specimen using mortar from

the same batch that the wall was built from.
I

3

bo

•H

4-3

re

4.1

Typical

walls

and

prisms

5. TEST PROCEDURES

Testing as well as the methods of handling, positioning, bonding the specimens

to the testing facility, and instrumentation are discussed in this section.

5.1 PRISM TESTING PROCEDURES

High strength plaster was used for capping the prisms. In order to get a plane surface, the prism was placed on a thin layer of wet plaster that had

been spread on a plate glass surface, carefully checking that the prism was perpendicular to the glass. After that surface hardened, the process was repeated on the opposite end of the prism. These plane surfaces allowed the

prisms to be placed directly into the testing machine with uniform bearing.

The prisms were tested in accordance with ASTM C140-75 in a testing machine

capable of 400,000 pounds force in compression or tension. A spherically

seated upper bearing block covering the entire bearing surface of the prism

was used.

The load was applied at any convenient rate for the first 30,000 to 40,000

pounds force while the balance of the load was applied at a rate of 40,000

pounds per minute until failure occurred. This event took place between 1 and

2 minutes later. Maximum load was then recorded. Average prism strengths

based on gross area are given in table 5.1.

5.2 WALL TESTING PROCEDURES

The techniques for handling and positioning the planar walls were quite

different than those used for the corner walls but the bonding of the specimens, the typical instrumentation, and the testing was similar.

The planar walls were gripped with a fixture that clamped the walls

longitudinally. This device is shown diagramatically in figure 5.1 and in use

in figure 5.2. Four pick-up points were provided with two on each side of the

wall. These points were located symmetrically on either side of the longitudinal

center line of two channel-irons that bolted to the structural steel tube

( ST 6 x 12) that provided the clamping force on the wall. Slotted holes were

provided for minor differences in wall lengths.

A 'C* hook (figure 5.3) similar to a crane pallet lifter was used to lift the

walls. A pair of turnbuckles was attached to each of the two forks of the

lifter and each pair straddled the wall. These four turnbuckles permitted the

walls to be easily aligned such that the walls were level and plumb. The ’ C’

hook lifting a planar wall is pictured in figure 5.2. The twin vertical legs of

the ' C' hook allowed it to straddle the south leg of the upper crosshead as the wall moved northward to the east-west centerline of the testing facility.

Positioning of the planar walls was accomplished with the aid of two mechanical

stops that held the walls in proper horizontal position. Vertical positioning

(for level and plumb) was accomplished by using small wooden wedges under the

edges of the walls.

5-1
After making certain the wall could be installed on the centerline, plumb

and level, the crane was used to move the wall several feet off the centerline

to make placement of the bonding material easier. A mixture of epoxy having

additives that gave it non-sag characteristics with clean, dry sand was used as an epoxy mortar. While no cubes were made or tested, manufacturer's literature

suggested that the compressive strength would be in excess of 10,000 psi and

the modulus of elasticity would be 1.24 x 10^ psi. Face shell bedding of the

wall specimen was used as the wall was placed within the stops, lowered into

the epoxy mortar and then wedged into a plumb and level position. To complete

the installation, the upper footing and crosshead was lowered onto a layer of

face shell ‘bedded epoxy mortar on the top of the wall. A compressive vertical

load of 500 to 1500 pounds force was applied to seat the upper footing securely

in the epoxy mortar. The hydraulic rams that applied this load have a no-flow

characteristic that prevents movement (i.e., loading) when the servocontrollers are turned off. Thus, when the proper preload was sensed, the

hydraulics and the servo-controllers were shutoff and the epoxy mortar was allowed to cure under a controlled load. The initial set took place within

1 hour and no tests were done until it had hardened at least 16 hours.

The corner walls presented unique handling and testing problems. The clamping

forces on the lower courses of the wall necessary to provide enough grip for

handling without applying any torque to the corner was accomplished by using

two interwoven boxes - one box clamped on each leg of the wall. The vertical

lifting force was applied through a sling around the intersections of the

interior struts, top and bottom, of the two clamped boxes, see figure 5.4.

Since the center of gravity of the corner wall held in the pick-up device was

on a line bisecting the angle of the corner wall approximately 11 inches from

the inside corner, the overhead crane could pick up the assembly and install

it directly into the test facility with the sling just clear of the upper

crosshead. Again, two plywood positioning fixtures were used to locate and

position the corner wall as it was lowered into the epoxy mortar. The processes

of mortaring, plumbing, and leveling were essentially the same as described for

the planar walls.

The initial plan was to apply the racking load to the corner wall

horizontally along a line that bisected the corner angle. After the first

test, it was decided that this loading did not produce the type of failure

that was of interest at this time, the decision was made to load transversely

along the axis of one leg of the corner wall.

5 . 3 INSTRUMENTAT ION

The typical instrumentation for the planar walls is shown in figure 5.5. LVDTs

(linear variable differential transformers) measured displacement in the plane

of the wall and were mounted in a vertical array at each end of the wall. The

strain measuring devices, mounted on one face of the wall only, were strain

amplifying devices utilizing strain gages mounted on a flexible leaf spring,

see figure 5.6. Load and position information was also taken from the load cells

and LVDTs in the hydraulic actuators that controlled loading and positioning of

the upper crosshead during the testing. Typical instrumentation for the corner walls is shown in figure 5.7.

5-2
Table 5.1 Average Mortar and Prism Data

*

**

Wall

ID

Average Maximum

Cube Stress*

PS I

Average Maximum

Prism Stress**

PSI

PI 2400 747

P2 2300 658

P3 2240 653

P4 2230 625

P5 2430 664

P6 2360 715

P7 3480 632

P8 2290 664

P9 2460 736

P10 2320 710

Cl 1370 688

C2 1410 649

C3 1310 736

C4 1370 710

C5 1120 736

Calculated by averaging the strengths of at least three cubes.

Stress computed on the basis of gross area of the block. Each average is

based on strengths from three prism tests.

5-3
r

Figure 5.1 Planar wall lifting rig

5-4
Figure 5.2 View of typical wall placement (looking to the west)

5-5

Figure 5.4 Corner wall pickup

5-7
LYOT

Figure 5.5 Typical planar wall instrumentation

5-8

s

i
Figure 5.6 Strain measuring device

5-9
LVDT

Figure 5.7 Corner wall instrumentation

5-10
6. TESTING PROGRAM

A total of 15 wall specimens, 10 planar, and 5 corner were fabricated and

tested. A description of typical planar and corner walls is presented in

chapter 4. The central purpose of the investigation was to determine the

damage susceptibility of concrete block masonry walls when subjected to repeated

cyclic loadings. Damage in this investigation included visual cracking as well

as load carrying capacity reduction. The primary parameter in the investigation

was loading history. This chapter describes the testing program as it was actually performed and includes a general discussion of loading histories, a general overview of the type of information presented for each wall test, and

lastly a section for each wall describing the test loading history and resulting

data. Data analysis, interpretation, and conclusions are presented in

chapters 7 and 8.

6.1 LOADING HISTORIES

A loading history describes the magnitude, rate, direction, and duration of

applied loads during a test. The term load is used as a general notation for

any imposed action. In fact, the wall specimens were actually subjected to

controlled displacements rather than controlled forces.

Except for one test, the directions of loading were the same for each test.

There was a vertical displacement imposed on the wall to produce vertical com- pression in the wall. This is termed precompression in the following discussion. The vertical displacement was not intentionally varied after the desired

precompression level was achieved. The main part of each test was the action

of an imposed lateral displacement. The lateral displacement (figure 6.1) was directed along the length of the planar wall and along the length of one leg

of the corner wall. One corner wall was subjected to approximately equal

displacements along each leg resulting in a diagonal displacement path.

There was a limited examination of the effect of loading rate on behavior using

one wall, but essentially rate was not a parameter studied in this

investigation.

The principal variable in the loading history was magnitude and duration of

displacement. The actual variations used in the test program reflected the

exploratory nature of the investigation. The results of each test influenced

the loading history selected for the next test. Thus, except for two wall

tests there were no replicates, instead, each test was used to define limiting

conditions. Such a program precludes detailed investigation of parameters,

but it enables a much broader examination of the problem to be made with a limited number of tests.

The initial loading history choices were selected based on the assumption that

the walls would be susceptible to damage and that the measured strains across mortar joints at cracking would be comparable to the strains observed in field

tests conducted by the Bureau of Mines on actual residential dwellings. Two

basic loading histories were selected. The first was simple monotonic loading

and the second was cyclic using fully reversed displacement levels about the

6-1
initial undisplaced position. However, testing indicated that the fully

reversed cyclic displacements reaching the strain observed in the field did

not cause visible damage. As a result, a third loading history was adopted

which was termed cyclic with prestrain. This loading history involved the

initial application of a lateral displacement which caused a preselected level

of measured strain. Cycling of the displacement then began about this offset

displacement. The cyclic displacement amplitude (disregarding the offset

component) was kept the same in the tests and was + 0.003 in. The value of + 0.003 in. of displacement was established by the sponsor. The value was obtained from a simple analysis of a basement wall assumed stationary at its

base and subjected to a ground particle velocity of 0.1 in/sec. The motion

was assumed to be sinusoidal with a frequency of 6.5 Hz. The first set of

cycles in each test was continued for at least 100,000 cycles. Further cycles

at larger displacements were also done, but the number of cycles varied

depending on the observed effect of such cycling.

6.2 TEST DATA DESCRIPTION

Four types of measurements were taken during the tests: 1) loads imposed by

each hydraulic actuator, 2) displacements of the wall profile relative to a fixed reference, 3) the hydraulic actuator piston displacements, and 4) strains

on a wall side surface. The instrumentation itself was described in chapter 3

and will not be discussed here. In the interest of simplicity, only the most

relevant data is presented in this chapter, the redundant, uninformative, and

extraneous data has been omitted for clarity. A consistent form of data

presentation has been adopted to ease discussion and aid future comparisons.

In the sections which follow, the different data presentation forms are described.

6.2.1 Load Versus Displacement Curves

Two different load-displacement curves are presented. The first is the lateral

load (the in-plane lateral load, or expressed another way, the lateral load

measured in the east-west direction [figure 6.1]) versus the displacement of the

east-west hydraulic actuator piston. The second load-displacement curve is

the lateral load versus the in-plane displacement of the upper course of the

wall. The two curves are different because the displacements are different.

The first curve (load versus piston displacement) is very reliable because both

measurements are relatively immune to extraneous events. However, the piston

displacement is not a good measure of the actual wall displacement since the

piston displacement is affected by the total test system compliance. The

second curve (load versus wall displacement) more accurately reflects the wall

behavior, but its displacement measurement is affected by such things as local

wall distortions (such as splitting), accidental bumping, and a non-rigid

connection to the wall. Each curve serves a useful purpose, the load versus wall displacement gives a good indication of wall stiffness and behavior up

to the onset of major cracking while the load versus piston displacement gives

a reliable, complete history for cross-test comparisons.

6-2
6.2.2 Strain Histories

Each of the wall test descriptions includes a sketch of the wall with the

approximate location of each strain measuring device. A typical sketch showing

mounting locations is figure 6.8. The mounting devices are represented by a dumbbell shaped symbol and an associated reference number. The number is a position number and has no purpose other than for identification. In this

report, the strain measuring locations are referred to by the acronym SML

followed by a position number. The orientation of the dumbbell symbol denotes

the direction of measurement with the cross bar of the dumbbell lying parallel

to the direction of measurement. Only vertical and horizontal orientations

were used on the walls. With few exceptions the strains were measured across head (vertical) and bed (horizontal) mortar joints. A strain measuring device

placed across a bed joint is shown in figure 5.6. The strain values were

computed by dividing the measured displacement of each device by the initial

measured gage length. For strains measured across mortar joints the gage

length was taken to be the nominal thickness of the mortar joint (0.51 in.).

The presentation of the strain histories takes one of two forms depending

on the loading history of the test. For the non-cyclic test the strains are plotted versus the piston-displacement. The cyclic tests were not done to

provide strain versus displacement histories, but rather to observe strain

versus repetition histories. Therefore, for cyclic tests strains are plotted

as a function of a relative index of test duration. The index of test duration

has no direct relation to any physical unit of measure such as time. The index

is a non-dimensional guide which identifies common points in the test for

purposes of comparison of data within a test. For the cyclic tests the pistondisplacement and lateral load are also plotted against the same index so that

the strains can be related to displacements and loads if necessary. As a general rule only data from horizontal SMLs which measured tensile strains are presented. All of the strains are plotted using the same scale and limits for ease in comparison. The limits of + 2000 microstrain were chosen as a reasonable compromise between the range in which changes become pronounced and the

peak values that the strains could achieve.

6.2.3 Crack Patterns

Sketches of the crack patterns are presented. One sketch indicates the cracks

observed on the wall prior to testing. The other sketch shows only the cracks

which formed at what is termed load capacity failure.

The pre-test crack inspection was done only on the instrumented side of the

wall. In general, the cracks marked in this observation were anything which

might be assumed to be a crack during the test.

The method in presenting the cracks was to sketch the crack path. In general,

any crack which parallels a mortar joint was a crack at the block-mortar

interface. The crack line is drawn on the side of che joint which exhibited

the interface crack. The failure crack patterns are shown only on one side of

the wall (instrumented side) because with the exception of local spalling the

crack patterns were identical on either side.

6-3
6.3 TEST DESCRIPTIONS

The wall test descriptions are presented in the sequence in which they were

tested. The first three wall tests were used as shakedown tests to verify the

suitability of the general testing procedure.

6.3.1 Wall P10

Equipment malfunctions occurred during the test of wall P10. The first

malfunction caused an out-of-plane bending to be applied to the wall. The wall

exhibited a crack along the tension side face shell at the first mortar bed

joint down from the top of the wall. In order to continue the test the bending

moment was removed and a compressive axial load of about 13 kips (55 psi net area stress) was applied to close the crack and prevent slip along the crack.

The loading history consisted of a single-cycle in which the east direction

peak displacement was large, but not sufficient to cause diagonal cracking.

The displacement to the west, however, caused diagonal cracking. The test was then terminated because of a malfunction in the data acquisition equipment.

There was no pre-test inspection for cracking and no strain measuring equipment

was mounted on the wall. The load versus deflection curves are shown in

figures 6.2 and 6.3. The post-test wall condition is shown in figure 6.4.

6.3.2 Wall P7

An unusually large number of problems occurred during this test which limited

the usefulness of the data. For this reason data from this test is omitted

except for a picture of the post-test cracking pattern (figure 6.5).

6.3.3 Wall P9

The purpose of this test was to observe the effect of displacement rate on wall

behavior. The limitations of the equipment imposed a maximum displacement rate

of 0.75 in/sec. The test for rate effect was composed of two half-cycle loadings to a displacement approximately one-half of that which caused diagonal

cracking in the previous tests. The first loading was done such that the

displacement was reached at an equivalent cyclic frequency of 0.003 Hz while

the second loading had an equivalent frequency of 3 Hz.

This test suffered an equipment malfunction which affected the test procedure.

The malfunction caused an in-plane moment to be applied to the wall which

caused bed joint cracking of both face shells at the first joint down from the

top of the wall. The moment was removed and a vertical compressive load of

18 kips (75 psi stress on the net area) was applied to the wall to close the

crack and prevent slip along the existing crack.

Subsequent to the first two loadings, the displacement was increased at the

maximum rate until load capacity failure occurred — load capacity reduction

with increasing displacement. Diagonal cracking occurred near the failure

point. The test was continued using cycles with increasing displacement limits.

6-4
The load-displacement relationships are shown in figures 6.6 and 6.7. The

general loading history can be observed in these figures. The strain measuring

locations are shown in figure 6.8 while the strain histories are presented in

figures 6.9 and 6.10. The load-displacement curve using the wall displacement

is truncated to show only the test up to diagonal cracking because damage to

the wall occurred in the region of the instrument making post-crack measurements unreliable. The strain histories only show the loading part of each of

the first three loading increments (prior to diagonal cracking). The unloading

portion of the histories are omitted for clarity. The crack observations are shown in figure 6.11 and 6.12.

6.3.4 Wall P6

The test of wall P6 was the first cyclic test performed in the series. The

general loading history was cyclic fully reversed about the original undisplaced

position. An axial compressive load of 4 kips (15 psi on the net area) was applied to the wall as precompression. The displacement varied sinusoidally

with a frequency ranging between 2 and 4 Hz depending on the cyclic displacement amplitude. The maximum rate of loading was a constant, so that the frequency of loading varied with the required cyclic displacement. The cyclic

displacement limits at each stage were selected somewhat arbitrarily to produce

a desired cyclic tensile strain at a minimum of one SML. The first stage was based on achieving a tensile strain of 50 microstrain.

There were three stages during the test which had 100,000 cycles of the

displacement sine wave. The first stage had displacement limits of -0.002 and

0.001 in measured at the top course of the wall. In further discussions, all

displacements will be wall displacements at the top course. The second stage

cycling had displacement limits of -0.003 and 0.005 in while the third stage

had displacement limits of -0.010 and 0.011 in. After the third stage cycling

was completed, the cyclic displacement amplitude was gradually increased while

cycling until diagonal cracking and load capacity failure occurred. This last

stage involved about 10,000 cycles. The load-displacement curves are shown in

figures 6.13 and 6.14. The large number of cycles tend to overlap and cause the

solid appearance of the curves. The strain measuring locations are shown in

figure 6.15. The pertinent strain histories are shown in figures 6.16 through

6.21. For convenience in relating the strains to loading the piston displacement and lateral load are similarly plotted in figures 6.22 and 6.23. The crack

observations are shown in figures 6.24 and 6.25.

6.3.5 Wall P8

The loading history for this test was a series of ramp functions. Each ramp

started from the zero displacement condition and the displacement increased

linearly to a maximum value at which point the displacement was returned to zero. The increase was done at a slow rate, but the return to zero was done at

the maximum velocity. Each ramp had an incrementally larger displacement limit.

The precompression axial load was about 5 kips for a net area stress of 20 psi.

The load-displacement curves are presented in figures 6.26 and 6.27. The curves do not show the release portion of each ramp (except for the last) for

clarity. The strain measuring locations are shown in figure 6.28 and the strain

6-5
histories as functions of piston displacement are shown in figures 6.29 through

6.38. Again, the release portion of each ramp are not shown for clarity. Each

ramp can be identified by its limiting displacement and is differentiated by

different line types. The reader will note that the line types each occur twice

due to a limited number of line types available. The crack observations are presented in figures 6.39 and 6.40.

6.3.6 Wall P4

The displacement was applied at a higher velocity than intended and the data

acquisition equipment sampled at too slow a rate to adequately describe the

test. The data for this test are omitted from discussion and only the crack

observations (figures 6.41 and 6.42) are presented.

6.3.7 Wall P2

The loading history for this test was a series of ramp functions similar to

those described for wall P8 (section 6.4.5). The precompression axial load

was approximately 14 kips for a net area compressive stress of 60 psi. The

second ramp reached the failure condition of the wall which was not expected

based on the test of wall P8. A third ramp clearly demonstrated that the wall

had indeed reached a failure condition. After the third ramp, the axial com- pressive load was increased to 23 kips (100 psi net area compressive stress)

and several more ramps were applied.

The load-displacement curves are shown in figures 6.43 and 6.44. The curve for

the wall displacement is terminated at the third ramp peak because the measurements after that point were severely affected by wall cracking and spalling in

the measurement region. The strain measuring locations are shown in figure 6.45

and the pertinent strain histories are shown in figures 6.46 through 6.53.

Only the data for the first three ramps are shown and the release portion of

each ramp is not shown for clarity. Each ramp can be identified on the basis

of its peak displacement and the line type. The crack observations are presented in figures 6.54 and 6.55.

6.3.8 Wall P5

The loading history was cyclic with prestrain. The prestrain was introduced

by monotonically increasing the lateral displacement until a pre-selected value

of strain at one of the SMLs was reached. For this test the prestrain level

was selected to be 1400 microstrain in tension at any one of the horizontal

SMLs. Vertical SMLs were predominantly influenced by flexural effects and so were considered not to be suitable indicators for shear prestrain. Prior to

applying the prestrain, a 14 kip vertical precompression was applied to the

wall. The resulting net area compressive stress was approximately 60 psi.

The 1400 microstrain value was first reached at SML 10 at a lateral displacement

of 0.043 in as measured at the top course of the wall. The load deflection

curves are presented in figures 6.56 and 6.57. The cyclic displacement amplitude

was + 0.003 in. initially, but was increased to + 0.006 in. in an effort to

increase the cyclic strain amplitude. During cycling, the lateral load capacity

6-6
decreased until a stable level was reached at about 70 percent of the level

before cycling. Also during cycling a diagonal crack formed and after 25,000

cycles the cycling was stopped and the displacement returned to zero. The

displacement was then gradually increased until the load displacement-curve

showed a sharp descending branch and the crack widths became excessive. This

action of returning to zero displacement and then applying the displacement

was then repeated twice.

The strain measuring locations are shown in figure 6.58 and the pertinent strain

histories are presented in figures 6.59 through 6.65. The piston displacements

and lateral load are shown in figures 6.66 and 6.67 as an aid in studying the

strain histories. The crack observations are presented in figures 6.68 and

6.69.

6.3.9 Wall P3

The loading history for this test was cyclic with prestrain. The prestrain

was selected to be 300 microstrain in tension at any one of the horizontal

SMLs. The axial precompression was 14 kips for a net area compressive axial

stress of about 60 psi. The prestrain was first reached at SML 10 at a displacement of 0.007 in. measured at the top course of the wall. The first stage

of cycling was done at a frequency of 5 Hz and a cyclic displacement amplitude

of + 0.003 in. The value of + 0.003 in. was selected on the basis of achieving

a cyclic strain amplitude of + 50 microstrain at SML 10. After 100,000 cycles

were done at the first stage the displacement was increased without cycling

until 600 microstrain in tension was achieved at SML 10. Cycling was again

initiated with the same frequency and the same cyclic displacement amplitude.

The cyclic displacement amplitude was kept constant for comparative purposes.

Cycling was continued at the second stage for 100,000 cycles. Subsequently,

displacements were increased, but not the cyclic displacement amplitudes to

reach 1650, 2350, and 3800 microstrains (tension) at SML 10. Only 10,000 cycles

were done at each of these three strain levels. The final part of the test was a continuous increase in displacement (with cycling) until a diagonal

crack formed. With the formation of the crack the displacement was increased

without cycling.

The load-displacement curves are presented in figures 6.70 and 6.71. The strain

measurement locations are shown in figure 6.72 and the useful strain histories

are shown in figures 6.73 through 6.79. The piston displacement and lateral

load are plotted like the strain histories for comparison in figures 6.80 and

6.81. The crack observations are presented in figures 6.82 and 6.83.

6.3.10 Wall PI

The loading history was cyclic with prestrain. The axial precompression load

was 14 kips resulting in a net area compressive stress of about 60 psi. The

first 100,000 cycles were done about a displacement of 0.036 in. measured at

the top course of the wall. The maximum horizontal tensile strain was 35

microstrain at SML 3. The cyclic displacement amplitude was + 0.003 in. and

the frequency was 6.5 Hz.

6-7
After the first 100,000 cycles the displacement was increased without cycling

until the tensile strain at SML 13 reached 690 microstrain. The corresponding

displacement was 0.044 in. Cycling was begun again at the same frequency and

cyclic displacement amplitude. The lateral load slowly decreased with cycling

until about cycle 840. At this point a diagonal crack formed and the lateral

load dropped much more rapidly as cycling continued. The lateral load capacity

stabilized after about 11,000 cycles. After completing 15,000 cycles the

cycling was stopped and the displacement was increased without cycling to fully

develop the wall crack pattern.

The load-displacement curves are shown in figures 6.84 and 6.85. The strain

measurement locations are presented in figure 6.86 and the pertinent strain

histories are shown in figures 6.87 through 6.93. The piston displacement and

lateral load are similarly presented in figures 6.94 and 6.95. The crack

observations are shown in figures 6.96 and 6.97.

6.3.11 Wall C5

The loading history was a simple half-cycle to a displacement which failed the

corner wall. The displacement, however, was directed along the diagonal or z-axis of the corner wall as described in figure 6.1. The axial precompression

was 16 kips which produced a net area stress of about 50 psi.

The load-displacement curves are shown in figures 6.98 and 6.99. Each figure

shows two curves. One curve is the east-west component of load versus the

east-west component of displacement and is the solid line. The other curve is

dashed and is the north-south load component versus the north-south displacement

component. The strain measurement locations are shown in figure 6.100. The

strain histories are shown in figures 6.101 through 6.113. The displacements

shown depend on which face the SML is mounted. Those SMLs mounted on the eastwest leg of the wall have their strains plotted against the east-west component

of the piston displacement. The SMLs mounted on the north-south leg of the

wall have their strains plotted against the north-south component of the piston

displacement. The crack observations are shown in figures 6.114 and 6.115.

6.3.12 Wall C4

The load history was a half-cycle to a maximum displacement which failed the

corner wall. The displacement was directed only along the east-west leg of

the wall (figure 6.1). The axial precompression load was 16 kips which produced

a net area stress of about 50 psi.

The load-displacement curves are shown in figures 6.116 and 6.117. The strain

measurement locations are presented in figure 6.118 and the pertinent strain

histories in figures 6.119 through 6.129. The crack observations are shown in

figures 6.130 and 6.131.

6.3.13 Wall C3

The loading history was a half-cycle to a maximum displacement which failed

the corner wall. The displacement was directed only along the east-west leg

6-8
of the wall (figure 6.1). The axial precompression load was 16 kips which

produced a net area stress of about 50 psi. The load-displacement curves are shown in figures 6.132 and 6.133. The strain measurement locations are presented in figure 6.134 and the pertinent strain histories in figure 6.135

through 6.145. The crack observations are shown in figures 6.146 and 6.147.

6.3.14 Wall C2

The loading history for this test was cyclic with prestrain. The displacement

was directed only along the east-west leg of the wall (figure 6.1). The axial

precompression load was 16 kips which produced a net area stress of about 50 psi.

The first prestrain level was selected to be 300 microstrain in tension at any

one of the horizontal SMLs. The resulting displacement was 0.002 in measured

at the top course of the wall. The strain level was reached at SML 12 first.

The cyclic frequency was 6.5 Hz and the cyclic displacement amplitude was + 0.003 in. After 100,000 cycles the strain at SML 12 was quite high, but no other SMLs reported significant tensile strains. Upon examination of the wall

it was concluded that SML 12 was unduly affected by a local flaw. Therefore,

it was decided to ignore the data from SML 12 for determining prestrain levels.

The second prestrain level was selected to again be 300 microstrain in tension,

but at some other SML. The level was reached at SML 5 at a displacement of

0.016 in. Another 100,000 cycles were performed at 6.5 Hz and a cyclic displacement amplitude of + 0.003 in. Again, very little change was observed

except for SML 5. The final stage of the test was an attempt to have all of

the SMLs along a diagonal show tension before initiating cycling. However,

failure of the wall occurred very quickly just before the last SML along the

diagonal went into tension.

The load-displacement curves are shown in figures 6.148 and 6.149. The strain

measurement locations are shown in figure 6.150. The pertinent strain histories

are shown in figures 6.151 through 6.159. The piston displacement and lateral

load are similarly plotted in figures 6.160 and 6.161. The crack observations

are presented in figures 6.162 and 6.163.

6.3.15 Wall Cl

The loading history for this test was cyclic with prestrain. The displacement

was directed only along the east-west leg of the corner wall (figure 6.1). The

axial precompression load was 16 kips which produced a net area stress of

about 50 psi.

The first 100,000 cycles were done about a displacement of 0.034 in. measured at

the top course of the wall. This displacement level corresponded to the point

at which the first SML (SML 9) in the expected diagonal cracking region reached

300 microstrain (tension). The cyclic frequency was 6.5 Hz and the cyclic

displacement amplitude was + 0.003 in. After the first 100,000 cycles were

completed the displacement was increased to 0.060 in. which resulted in a strain

of 1200 microstrain (tension) at SML 9. Another 100,000 cycles were performed

at the same cyclic frequency and displacement amplitude. Upon completion of

the second group of 100,000 cycles the displacement was incrementally increased

6-9
and at each step at least 10,000 cycles were performed. This continued until a diagonal crack formed. The displacement was then increased without cycling

until the lateral load capacity dropped. The initial diagonal cracking did not

penetrate the block at each corner of the diagonal, but when the maximum lateral

load capacity was reached the diagonal crack split these end blocks. The loaddisplacement curves are shown in figures 6.164 and 6.165. The strain measurement locations are shown in figure 6.166. The strain histories and similarly

plotted piston movement and lateral load are shown in figures 6.167 through

6.175.

The crack observations are shown in figures 6.176, 6.177, and 6.178. It was observed that while no diagonal cracking was observed during the first 100,000

cycles some cracking along the mortar joints did occur. The cracking, however,

was not along the same path that the final failure crack followed. The first

cracking which seemed to be part of the failure crack occurred during the

incrementally increased displacements after the second 100,000 cycles and

formed in the blocks (figure 6.177).

6-10
ri s

6-11
0.03 0.06

©-

i

Figure 6.2. Lateral load versus piston displacement for wall P10

Figure 6.3. Lateral load versus wall displacement for wall P10
Looking to the north.

Figure 6.4. Post-test crack observations for wall P10

6-13
Looking to the north.

Figure 6.5. Post-test crack observations for wall P7

6-14
Figure 6.6. Lateral load versus piston displacement for wall P9

Figure 6.7. Lateral load versus wall displacement for wall P9

6-15
Looking to the north.

5 4

I 3

-

1

.2

4

t8

3 l 7 1«

I -10 9

^

1 1

13

I 12

l

16 I 14 15

J

7

,18

l

20 19

I

Figure 6.8. Strain measuring locations for wall P9
Figure 6.9. Strain history of SML 9 for wall P9

Figure 6.10 Strain history of SML 17 for wall P9

6-17
\

i

(

1 _ J

1

1

1

1

1L t

1

1

Figure 6.11. Pre-test crack observations for wall P9

Looking to the north.

Figure 6.12. Post-test crack observations for wall P9

6-18
-0.09

Figure

-0.09

1

| 0.03 0.0S 0.09

LATERAL DISPLACEMENT IN INCHES

. Lateral load versus wall displacement for wall Pb

6-19

Figure 6.14
5 4 3

“

1• 2

! „6

2 5 7

1

Iria

10 * Iti?

15

l 14

J 1 6*

I 17

19

"

t22 21l

18

" ,2 0

2 -23

I l 25 24

26

2 2

Looking to the north.

Figure 6.15. Strain measuring locations for wall P6

6-20
STRAIN

FROM

SUL

6

IN

MICROSTRAIN

STRAIN

FROM

SML

1

IN

-1600

-8

00

600

1600

3

!

-800

test duration index

gure 6.16. Strain history of SML 1 for wall P6

Figure 6.17. Strain history of SML 6 for wall P6

6-21
STRAIN

FROM

SML

11

IN

MICROSTRAIN

STRAIN

FROM

SMI.

10

IN

MICROSTRAIN

-60°

600

1600

-n

-800

800

1600

TEST DURATION INDEX

igure 6.18. Strain history of SML 10 for wall P6

TEST DURATION INDEX

Figure 6.19. Strain history of SML 11 for wall P6

6-22
Figure 6.20. Strain history of SML 18 for wall P6

Figure 6.21. Strain history of SML 19 for wall P6

6-23
Figure 6.22. Piston displacement history for wall P6

Figure 6.23. Lateral load history for wall P6

6-24
Figure 6.24. Pre-test crack observations for wall P6

Looking to the north.

Figure 6.25. Post-test crack observations for wall P6

6-25
Figure 6.26. Lateral load versus piston displacement for wall P8

Figure 6.27. Lateral load versus wall displacement for wall P8

I

6-26
3

1- 2

5,

*"

l -4

10

? 8t

*"

I “•6

,7

i I 12,

*"

I * -1 1

18, -<» l’

4 --13

21 -

* 17* l_i?2 :

*16

-20 -19

! -23

24 25

Looking to the north.

Figure 6.28. Strain measuring locations for wall P8

6-27
STRAIN

FROM

SML

I

IN

MICROSTRAIN

Figure 6.29. Strain history of SML 1 for wall P8

Figure 6.30. Strain history of SML 4 for wall P8

6-28
Figure 6.31. Strain history of SML 6 for wall P8

Figure 6.32. Strain history of SML 11 for wall P8

6-29
Figure 6.33. Strain history of SML 13 for wall P8

Figure 6.34. Strain history of SML 15 for wall P8

6-30
o

o.

CD

z

22Z

o

o-

<D

OOCO

0.08 0.16 0.24 0.32 0.40

ACTUATOR PISTON DISPLACEMENT IN INCHES o748

Figure 6.35. Strain history of SML 19 for wall P8

Figure 6.36. Strain history of SML 20 for wall P8

6-31
o.-te

Figure 6.37. Strain history of SML 21 for wall P8

Figure 6.38. Strain history of SML 23 for wall P8

6-32
Figure 6.39. Pre-test crack observations for wall P8

Looking to the north.

Figure 6.40. Post-test crack observations for wall P8

6-33
_ J - \ l

1

1 _ > k=

1 J= c

J J 1

1

1

]

. e=

1

Figure 6.41. Pre-test crack observations for wall P4

Looking to the south.

Figure 6.42. Post-test crack observations for wall P4

6-34
LATERAL DISPLACEMENT IN INCHES

8

-

i

Figure 6.43. Lateral load versus piston displacement for wall P2

Figure 6.44. Lateral load versus wall displacement for wall P2

6-35
1 2

1 l -

-3

-4

-5 -6

-7

][• - -8

-10 -1 1

14 -12 J3

l 15

Looking to the south.

Figure 6.45. Strain measuring locations for wall P2

6-36
STRAIN

FROM

SML

5

IN

MICROSTRAIN

STRAIN

FROM

SML

3

IN

MICROSTRAIN

-800

800

1600

-600

800

1600

—rr—

0.03 ,0.06 0.09 0. 12 0.15

ACTUATOR PISTON DISPLACEMENT IN INCHES

0. 18

Figure 6.46. Strain history of SML 3 for wall P2

/

{

i

t

ACTUATOR PISTON DISPLACEMENT IN INCHES

Figure 6.47. Strain history of SML 5 for wall P2

6-37
STRAIN

FROM

SUL

6

IN

MICROSTRAIN

Figure 6.48. Strain history of SML 6 for wall P2

Figure 6.49. Strain history of SML 8 for wall P2

6-38
o

OtD

0.03 0 . 06 J?.„09 0.15

ACTUATOR PISTON DISPLACEMENT IN INCHES

H

w o

Orie

Figure 6.50. Strain history of SML 10 for wall P2

Figure 6.51 Strain history of SML 11 for wall P2
STRAIN

FROM

SML

12

IN

MICROSTRAIN

Figure 6.52. Strain history of SML 12 for wall P2

Figure 6.53. Strain history of SML 13 for wall P2

6-40
I

) 1 1 i

i

1 j

1 A 1

1 i

1

1

-I r

Figure 6.54. Pre-test crack observations for wall P2

Figure 6.55. Post-test crack observations for wall P2

6-41
8-

1 Figure 6.56. Lateral load versus piston displacement for wall P5

8-

C/l & o„ £ oi- z

9oJ

i °- H

** 5

/ S' 0.04 yrf. 06 /^f.08 o.'io / / /s' LATERAL DISPLACEMENT li/lp/sES.

8-

1 Figure 6.57 . Lateral load versus wall displacement for wall P5

6-42
1 2

1_

-3 -4

-5

-• J 7 - -3

-•9 -10 -1 1

14 -12 -13 15

I I

Looking to the south.

Figure 6.58. Strain measuring locations for wall P5

6-43
STRAIN

FROM

SML

5

IN

MICROSTRAIN

2000

Figure 6.59. Strain history of SML 3 for wall P5

Figure 6.60. Strain history of SML 4 for wall P5

Figure 6.61. Strain history of SML 5 for wall P5

6-44
STRAIN

FROM

SMI,

8

IN

MICROSTRAIN

Figure 6.62. Strain history of SML 6 for wall P5

Figure 6.63. Strain history of SML 8 for wall P5

6-45
Figure 6.64. Strain history of SML 10 for wall P5

Figure 6.65. Strain history of SML 13 for wall P5

6-46
Figure 6.66. Piston displacement history for wall P5

Figure 6.67. Lateral load history for wall P5

6-47
Fi gure

Figure 6

6.68. Pre-test crack observations for wall P5

Looking to the south.

.69. Post-test crack observations for wall P5

6-43
Figure 6.70. Lateral load versus piston displacement for wall P3

Figure 6.71. Lateral load versus wall displacement for wall P3

6-49
1

t 2

I

-3

-4 -5

-6

— 7 -8 ]9 - -10

-1 1

14 -12 -13 15

l

Looking to the south.

Figure 6.72. Strain measuring locations for wall P3

6-50
Figure 6.73. Strain history of SML 5 for wall P3

Figure 6.75. Strain history of SML 8 for wall P3

6-51
3000 -1000 5000

TEST DURATION INDEX

w O

OOD

I

Figure 6.76. Strain history of SML 10 for wall P3

6-52

Figure 6.77.
6-53
LATERAL

LOAD

IN

KIPS

1000 2000 3000 4000 5000

TEST DURATION INDEX Figure 6.80. Piston displacement history for wall P3

Figure 6.81. Lateral load history for wall P3

6-54
( i J

1 \

i i i

1

!

1 i

1

1

i > _J i “

{ ]

' 1 1 1

'

Figure 6.82. Pre-test crack observations for wall P3

Looking to the south.

Figure 6.83. Post-test crack observations for wall P3

6-55
0.03 0 . 0.09 0.12 0.15 o?ie

LATERAL DISPLACEMENT IN INCHES

Figure 6.84. Lateral load versus piston displacement for wall PI

Figure 6.85. Lateral load versus wall displacement for wall PI

6-56
1

T 2

r

-4 -5

-6 -7

-ii 1[• I

-3

-10

-8 —-12

14

1 -13 15II

Looking to the south.

Figure 6.86. Strain measuring locations for wall PI

6-57
STRAIN

FROM

SML

5

IN

MICROSTRAIN

Figure 6.87. Strain history of SML 3 for wall PI

Figure 6.88. Strain history of SML 5 for wall PI

6-58
STRAIN

FROM

SML

10

IN

MICROSTRAIN

Figure 6.89. Strain history of SML 7 for wall PI

6-5?
Figure 6.91. Strain history of SML 11 for wall PI

Figure 6.92. Strain history of SML 12 for wall PI

6-60
STRAIN

FROM

SML

13

IN

MICUOS'J'RAIN

-1600

-800

800

1

G

00

Figure 6.93. Strain history of SML 13 for wall PI

6-61
LATERAL

LOAD

IN

KlI'S

500 1000 1500 2000

TEST duration index 2500 3000

Figure 6.94. Piston displacement history for wall PI

Figure 6.95. Lateral load history for wall PI

6-62
I L_

_ _1

1 {

] r — 1

s 1 , 1

1

l !

V

1 1 u J

1

Figure 6.96. Pre-test crack observations for wall PI

Looking to the south.

Figure 6.97. Post-test crack observations for wall PI

6-63
6-64
Figure 6.100. Strain measuring locations for wall C5

6-65
STRAIN

FROM

SML

3

IN

MICROSTRAIN

Figure 6.101. Strain history of SML 1 for wall C5

Figure 6.102. Strain history of SML 3 for wall C5

6-66
Figure 6.103. Strain history of SML 4 for wall C5

Figure 6.104. Strain history of SML 5 for wall C5

6-67
Figure 6.105. Strain history of SML 6 for wall C5

Figure 6.106. Strain history of SML 7 for wall C5

6-60
STRAIN

FROM

SUL

8

IN

MICROSTRAIN

Figure 6.107. Strain history of SML 8 for wall C5

Figure 6.108. Strain history of SML 9 for wall C5

6-69
Figure 6.109. Strain history of SML 10 for wall C5

Figure 6.110. Strain history of SML 11 for wall C5

6-70
Figure 6.111. Strain history of SML 12 for wall C5

!

I

Figure 6.112. Strain history of SML 13 for wall C5

6-71
STRAIN

FROM

SML

15

IN

MICROSTRAIN

Figure 6.113. Strain history of SML 15 for wall

6-72
Figure 6.114. Pre-test crack observations for wail C5

Figure 6.115. Post-test crack observations for wall C5

6-73
Figure 6.116. Lateral load versus piston displacement for wall C4

Figure 6.117. Lateral load versus wall displacement for wall C4

6-74
Figure 6.118. Strain measuring locations for wall C4
r

o

o.

8-

0.08 0.16 0.24 0.32 0.40

ACTUATOR PISTON DISPLACEMENT IN INCHES 0.48

Figure 6.119. Strain history of SML 3 for wall C4

Figure 6.120. Strain history of SML 4 for wall C4

6-76

I
Figure 6.123. Strain history of SML 7 for wall C4

6-77
STRAIN

FROM

SML

9

IN

MICROSTRAIN

2 Ol

§81

i 0.08 °16 0.24 0.32 0.40

ACTUATOR PISTON DISPLACEMENT IN INCHES 0.48

Figure 6.124. Strain history of SML 8 for wall C4

Figure 6.125. Strain history of SML 9 for wall C4

6-73
STRAIN

FROM

SML

10

IN

MICROSTRAIN

Figure 6.126. Strain history of SML 10 for wall C4

Figure 6.127. Strain history of SML 11 for wall C4

6-7?
STRAIN

FROM

SML

13

IN

MICROSTRAIN

Figure 6.128. Strain history of SML 12 for wall C4

Figure 6.129. Strain history of SML 13 for wall C4

6-30

I
NOTE: Only tho Eaat-Waat Itg was HiaptetH

prior to tha taat

Figure 6.130. Pre-test crack observations for wall C4

Figure 6.131. Post-test crack observations for wall C4

6-81
Figure 6.133. Lateral load versus wall displacement for wall C3
Figure 6.134. Strain measuring locations for wall C3

1

|i

6-33
Figure 6.135. Strain history of SML 3 for wall C3

Figure 6.137. Strain history of SML 5 for wall C3

6-84
Figure 6.138. Strain history of SML 6 for wall C3

Figure 6.139. Strain history of SML 7 for wall C3

6-35
Figure 6.140. Strain history of SML 8 for wall C3

Figure 6.141. Strain history of SML 9 for wall C3

6—86
STRAIN

FROM

SML

10

IN

MICROSTRAIN

Figure 6.142. Strain history of SML 10 for wall C3

Figure 6.143. Strain history of SML 11 for wall C3

6-37
STRAIN

FROM

SMI,

13

IN

MICROSTRAIN

Figure 6.144. Strain history of SML 12 for wall C3

Figure 6.145. Strain history of SML 13 for wall C3

6-80
NOTE: Only tha Eaat-Waat lag waa laapactad

prior to tha taat

Figure 6.146. Pre-test crack observations for wall C3

Figure 6.147. Post-test crack observations for wall C3

6-3?
LATERAL

LOAD

IN

KIPS

igure 6.148. Lateral load versus piston displacement for wall C2

igure 6.149. Lateral load versus wall displacement for wall C2
I

I

I _ ... Figure 6.150. Strain measuring locations for wall C2

i

!

6-91
STRAIN

FROM

SML

4

IN

MICROSTRAIN

STRAIN

FROM

SML

3

IN

MICROSTRAIN

F

igure 6.151. Strain history of SML 3 for wall C2

Figure 6.152. Strain history of SML 4 for wall C2

6-92
Figure 6.153. Strain history of SML 5 for wall C2

Figure 6.154. Strain history of SML 7 for wall C2
STRAIN

FROM

SMI,

9

IN

MICROSTRAIN

STRAIN

FROM

SMI.

8

IN

MICROSTRAIN

Figure 6.155. Strain history of SML 8 for wall C2

Figure 6.156. Strain history of SML 9 for wall C2

6-94
STRAIN

FROM

SML

12

IN

MICROSTRAIN

STRAIN

FROM

SML

11

IN

MICROSTRAIN

Figure 6.158. Strain history of SML 12 for wall C2

6-95
STRAIN

FROM

SHI,

1

I

IN

MICHOSTRAIN

Figure 6.159. Strain history of SML 13 for wall C2

6-96
Figure 6.160. Piston displacement history for wall C2

Figure 6.161. Lateral load history for wall C2

6-97
NOTE: Only th« Eaat-Waat lag was iaiy«et«4

prior to tha taat

Figure 6.162. Pre-test crack observations for wall C2

Figure 6.163. Post-test crack observations for wall C2

6-98
Figure 6.164. Lateral load versus piston displacement for wall Cl

Figure 6.165. Lateral load versus wall displacement for wall Cl

6-99
Figure 6.166. Strain measuring locations for wall Cl

6-ino
Figure 6.167. Strain history of SML 3 for wall Cl

Figure 6.168. Strain history of SML 4 for wall Cl

6-ini
o

CD- 'S

1100 2200 3300 MOO

TEST DURATION INDEX

5500 6600

Figure 6.169. Strain history of SML 5 for wall Cl

Figure 6.170. Strain history of SML 7 for wall Cl

6-102
STRAIN

FROM

SML

II

IN

MICROSTRAIN

STRAIN

FROM

SML

9

IN

MICROSTRAIN

Figure 6.171. Strain history of SML 9 for wail Cl

Figure 6.172. Strain history of SML 11 for wall Cl

6-103
Figure 6.173. Strain history of SML 12 for wall Cl
ACTUATOR

PISTON

DISPLACEMENT

IN

INCHES

Figure 6.174. Piston displacement history for wall Cl

Figure 6.175. Lateral load history for wall Cl

6-105
Figure 6.176. Pre-test crack observations for wall Cl

Figure 6.177. Initial diagonal crack observation for wall Cl

Figure 6.178. Post-test crack observations for wall Cl

6-106
7. ANALYSIS AND INTERPRETATION

In this chapter the data and observations presented in chapter 6 as well as supplemental information are evaluated and interpretations presented.

7.1 FAILURE MODE AND CRACKING

The failure mode associated with the load capacity failure point was of the

diagonal tension form. The diagonal cracking which formed near the failure

load/displacement ran from compression corner to compression corner

(figure 7.1) and stairrstepped through the joints in most cases. Extensions

of the mortar joint cracks did extend into the block but did not connect to

form a continuous crack. A good example of such cracking is found in test P8

(figure 6.40). In some tests, a diagonal crack formed just prior to failure,

but at failure another diagonal crack formed separate from the first. The

first crack then became barely visible and all subsequent crack opening occurred

in the second crack.

An interesting observation was that the diagonal cracking first formed near the

center of the wall. The wall was still capable of resisting more load at

this stage of crack development. However, coincident with load capacity failure

the corner blocks split to complete the diagonal crack.

Local cracking around various mortar joints occurred prior to formation of the

diagonal crack. Such cracking in some cases confused the interpretation of the

strain data. In all probability such cracking occurred at joints already

weakened by shrinkage cracking or at joints with little bond capacity simply

due to construction. In any event, the local cracking not on the diagonal did

not cause shifting of the crack pattern or affect the expected failure crack.

In discussing failure and cracking up to now no mention has been made of

flexure. Flexural tension cracks did occur, but the final failure at the

maximum load capacity was not a flexural failure, as is discussed in

section 7.7. The flexural failure of the wall occurred early in the test, but

because an alternate load resisting mechanism was available, namely diagonal

compression, additional load resistance was available. Since the flexure

failure mode was not critical in these tests it has been omitted from

discussion.

7.2 EFFECT OF LOADING HISTORY

The effect of loading history on overall wall behavior is best illustrated

using load displacement curves. The in-plane load versus in-plane ram pistondisplacement curves (hereafter simply referred to as load-displacement curves)

were presented in chapter 6, but for convenience only the significant part of

each curve is shown in figures 7.2 through 7.13. Only the quadrant of the plot

which includes the load capacity failure point is shown to enhance clarity.

The load capacity failure point is defined for purposes of this report to be

that point at which load capacity decreases with increasing displacement. Also

noted on each of the figures (7.2 through 7.13) is the displacement at which

diagonal cracking was observed. As an aid to comparison, the envelope curves

7-1
are plotted on the same axis for the planar walls (figure 7.14) and corner walls

(figure 7.15). An envelope curve is simply a curve which describes the outline

of the extreme perimeter of a multi-cycle curve. The major test parameters

for each wall are presented in table 7.1.

Loading history can have a pronounced effect on the overall wall behavior as demonstrated by the envelope curves of both the planar and corner walls

(figures 7.14 and 7.15). However, it appears that the effect is only significant past a certain load-displacement level. The test PI (figure 7.8) illustrates this behavior very clearly in that 100,000 cycles were performed at a load-displacement level with no apparent effect on the stiffness and load

capacity of the wall. However, the next sequence of cycling at a larger loaddisplacement level caused a significant drop in load capacity and the formation

of a diagonal crack. The same behavior was exhibited by walls C2 and Cl,

figures 7.11 and 7.12, respectively.

The three tests PI, C2, and Cl used only a small cyclic displacement amplitude

and some question as to the effect of larger cyclic displacement test amplitudes is raised, but test P6 (figure 7.4) which was a fully reversed cyclic test

exhibited the same general behavior. The test results suggest, then, that

loading history can significantly affect the overall response of the wall,

but only if some threshold value of load/displacement is exceeded. With the

test results available it is not possible to define the actual threshold value

for susceptibility, but it is clear that in general terms the load threshold

is a sizable proportion of the walls actual load capacity failure level. For

general design considerations such a high threshold would generally imply that

normal service condition loadings would not produce any cyclic effects.

The actual effect that loading history has on the overall wall behavior when

the susceptibility threshold is reached can not be fully described with the

limited data available. It does not appear that stiffness within the small

cyclic displacement range, is noticeably affected but the load capacity corresponding to a particular displacement level can be dramatically reduced. The

magnitude of the effect on stiffness may be dependent on some particular parameter in the general loading history because while tests PI and P5 (figures 7.9

and 7.7) exhibited almost no stiffness reduction in the range of cyclic displacements, tests P8 and P3 (figures 7.5 and 7.8) exhibited noticeable stiffness reduction. The difference in behavior between the two sets of tests may

be due to a significant difference in cyclic displacement range. While the

stiffness of the walls measured between small changes in displacement does not

seem particularly affected by cycling, it is clear the cycling reduces the

in-plane stiffness of the wall as measured from the zero displacement position

to the achieved displacement. Cycling in the susceptible range causes the

displacements associated with a certain load to increase, reduced stiffness.

Higher load resistance may only be achieved at the expense of larger displacements. A good example of this behavior is test Cl (figure 7.13) in which the

load capacity lost due to cycling was recovered but only by a significant

increase in lateral displacement.

The discussion up to now has focused on behavior prior to the load capacity

failure point. It is clearly evident that post-failure behavior is extremely

7-2
poor with large reductions in load capacity, a negative stiffness. The effect

of repeated excursions into the failure zone is much more pronounced than

excursions in the susceptibility range. Test P5 (figure 7.7) shows quite

graphically the kind of severe degradation which comes about by cycling to

displacements greater than the failure displacement.

The effect of loading history on the overall wall behavior has been described

in terms of global parameters, applied load, and displacement. The general

observation was that there was no effect until a definite threshold value of

load-displacement was reached. The effect of loading history on the measured

local strains was masked by the general variability of the local strains.

It would seem, however, that the effect is much the same on the strains as it was for the overall behavior, but not nearly so pronounced. During cycling

between constant displacement levels some local strains showed a tendency to

increase in an absolute sense, but the cyclic strain amplitude did not significantly change. This observation is not true, of course, for the strains

measured across the diagonal cracks after the load capacity failure point. In

this case, the strains in some cases grew both absolutely and in terms of the

cyclic amplitude. In summary, the value of local strains was most dependent

on the displacement level itself and not on the repetitions of achieving the

displacement level.

Included in loading history is rate effect. The cyclic tests were all run at

between 2 and 6 Hz with most at 6 Hz. This frequency was considered high

enough that the dynamics of vibration loading was at least represented. For

information purposes, however test P9 was used to examine the likely effect

of strain rate. Two half cycle loadings to about half of the expected maximum

load capacity at two very different loading rates (section 6.4.3) indicated

that the rate did not affect the wall response. This can be seen by the loaddisplacement curve (figure 7.3) and the strain histories (figures 6.9 and

6.10). However, the third loading to load capacity failure at a high rate

suggests that such a conclusion is not true for the entire loading history.

It is seen in figure 7.14 that a comparison shows that test P9 maintained its

initial stiffness to a higher maximum load capacity compared to the other

tests. There is insufficient information at present to positively determine

the effect of rate because of the changing parameters between the walls tested.

For example, test P9 had a higher initial precompression compared to the others

and it is not possible at this time to separate the effect of precompression.

7.3 CORNER WALL VERSUS PLANAR WALL BEHAVIOR

The following discussion excludes the corner wall displaced along its z-axis

which is discussed separately.

There did not seem to be any reason to differentiate the behavior of planar

walls from corner walls. The effect of the outstanding leg in the corner walls

was negligible on the cracking pattern and general wall behavior. Comparing

the envelope curves in figures 7.14 and 7.15 shows the corner walls have a slightly smaller stiffness and a uniformly lower maximum load capacity. These

reductions can be attributed to the smaller size of the in-plane leg of the

corner wall (48 x 64 in) as compared to the planar wall (64 x 64 in). The

7-3
diagonal cracking of the corner walls did not include any portion of the outstanding leg and as in the planar walls extended essentially from compression

corner to compression corner along the diagonal in a stair-step fashion.

7.4 EFFECT OF Z-AXIS DISPLACEMENT

The final failure mode of the z-axis displaced corner wall was a diagonal crack

in both legs from the compression corners at the upper surface of the wall to

the compression corner at the wall intersection on the bottom surface (figure

6.115). It is evident that each leg contributed to the total lateral load

resistance. It would also seem that the total load resistance was roughly

equally divided between the two legs as indicated in figure 6.98. The actual

loading history imposed on the wall as shown in figure 6.98 shows that the

imposed displacement in the north-south direction lagged behind the displacement in the east-west direction. This may have influenced the total wall

behavior since the east-west leg may have failed before the north-south leg

causing a major redistribution of the additional imposed load onto the northsouth leg. The resultant load-displacement diagram, plotted to the same scale

as the curves in figure 7.15 is presented in figure 7.16. It is clear that

the stiffness of the z-axis loaded wall suffered a major reduction in stiffness

at a fairly low level of displacement. The first load plateau on the curve is

at a level which is comparable to the total load capacity of the other corner

walls. However, the wall continued accepting load at substantially higher

displacements as shown in figure 7.17 which presents the complete resultant

curve. An interesting fact from the complete curve is that the maximum resultant lateral load capacity was approximately equal to the value obtained by

taking the average maximum load value of walls C3 and C4 (also, both montonic

tests) and multiplying by /2 . It would seem that the total (resultant)

capacity of a corner wall can be computed by finding the resultant of the

component resistances.

7.5 LOCALLY MEASURED STRAINS

An important component of the instrumentation was strain measuring devices

mounted across mortar joints on one wall surface. Similar instrumentation

had been used in the field studies and it was expected that the information

gathered in the different studies could be correlated. The devices themselves

worked well, but their usefulness was limited. The strain measuring devices

were to serve several purposes: 1) provide information on the relationship

between measured strain and visible cracking; 2) serve as a benchmark between

field studies and the tests reported herein; and 3) indicate the level of

damage or distress in a wall.

It appears that as used in the research reported herein, the strain measuring

devices did not produce strain values which correlated with the onset of visible

cracking. This is not surprising considering the difficulty of observing small

cracks on a very disjointed and textured surface typical of a concrete block

wall. There are many surface disruptions at joints which appear as cracks. In some cases strains of over 1000 microstrain were measured with no cracking

visible even with magnification. In other cases cracks were visible at

locations where as litle as 500 microstrain was measured.

7-4
The usefulness of locally measured strains as benchmarks between tests is also

extremely limited. The strains measured at single points in a matrix material

were unduly affected by local irregularities and flaws. It was apparent that

in early stages of a test the strain values reflected the general variability

of the materials. A joint crossed by a strain measuring device and having

unusually weak tensile bond due to shrinkage cracking, for example, could show

large strains during the test and not be part of the final diagonal cracking.

The local strains reflected the general breakdown of the matrix bond between

the blocks and are a result of many things, including just a gradual breakdown

as a result of repeated movements. It is clear that no single local strain

value provided reliable information as to the state of damage in the wall.

So far the impression has been negative as to the usefulness of the local

strains. However, as a general measure of wall behavior the strains do serve a very useful function to the researcher. Taken as a whole rather than individually the strains can provide clues as to the proximity to failure. For

example, one strain gage could be measuring a very high local tension strain,

but if other gages along the probable diagonal crack path indicated only small

tensile strains or compression strains then it would be clear that total

failure was not imminent. However, a great deal of judgment is obviously

required since a diagonal crack can form quite suddenly.

7.6 DAMAGE THRESHOLD

As indicated in an earlier section, the tests indicate that there is a load-displacement threshold above which the walls are subject to damage due to

cycling. What constitutes damage is, of course, somewhat arbitrary. If visible

cracking is the criteria then the threshold value becomes vague since some visible cracking of the local nature can occur at almost any time. If damage

is taken to mean that a loss in load capacity occurs with repeated excursions

to a particular displacement level then it is easier to establish a threshold

value. The clearest illustration of the existance of a threshold comes from

the corner wall tests. The envelope curves shown in figure 7.15 clearly show

a consistent break in the curves at a definite displacement value though not

load. This consistency can be taken as evidence that it is displacement

(strain) which is the critical parameter for defining the threshold. The

planar walls show the same general trend (figure 7.14), but the curves are harder to compare because of the changing test parameters not found in the

corner wall tests. From previous discussions it is clear that it would be

extremely difficult to relate the global displacement threshold to a local

strain value as measured by the strain devices. However, a global strain

approach may lead to a more reliable and uniform relationship.

7.7 APPLICABILITY OF TEST RESULTS

The failure of the walls is best described as a diagonal tension failure with

the accompanying diagonal cracking. This mode of failure was expected, and,

in fact, desired since the observed crack pattern in the field studies was along diagonals of the walls. However, the supplementary requirements that

proved to be necessary to produce the diagonal tension failure for in-plane

shear make it doubtful that the diagonal cracking of typical concrete block

7-5
masonry walls in residential dwellings is due solely or even primarily to

in-plane shear forces.

In table 7.1 there is reference to the axial load applied to the wall at the

time the maximum load capacity is reached. The values are considerably higher

than the precompression axial loads which are also listed. This apparent

discrepancy points to the manner in which the load resisting mechanism of the

walls change during the test. Normally, a resistance is determined by the

weakest resistance mechanism. For the simple case of an unreinforced wall

subjected to a lateral (in-plane) load the most likely weak link is flexure.

Using an incremental summing technique and assuming a representative stressstrain curve for concrete block masonry the ultimate flexural capacities of the

walls were computed. The resulting capacities (table 7.2) indicate that at

best (assuming a 100 psi tension capacity) the equivalent ultimate lateral

load is about 9 kips. A value of 9 kips is approximately one-half of even the

minimum lateral load capacities measured in the test. Flexural tension cracks

were observed in the test so the flexure mechanism was active during at least

part of the test. Clearly, flexure was not the only mechanism present.

The second mechanism which permitted the increased lateral resistance was the

formation of a compression strut (figure 7.1). However, the compression strut

could only become active as a result of the boundary conditions imposed on the

wall. A flexural failure, if it were to occur in these walls, would lead to

overturning of the wall-almost as a rigid block rotating about the lower com- pression corner (figure 7.18). Such overturning would be accompanied by an upward movement of part of the wall. However, the test setup intentionally

restrained vertical displacement to prevent rotation of the upper wall surface.

The result is a reaction point which resists overturning which then increases

the apparent lateral load resistance. The restraint reaction increases or adds

to the axial load intentionally applied to the wall.

In the end the reaction force can only increase to the level where the

combination of axial load and lateral load acting principally at opposite

corners cause a diagonal tension failure.

The fact that the compression strut mechanism comes into play only after

exceeding the flexural capacity of the wall can be shown by the plots of total

applied axial load versus measured restraining moment in the tests. For

clarity, only results from the monotonic tests are shown in figure 7.19 the

tests P2 , C3, and C4 have comparable levels of axial precompression stress.

It is clear that the applied axial load only begins to increase past the precompresion at a definite applied moment which agrees well with the computed

flexural capacities of the walls accounting for the actual precompression

stress (table 7.2). In addition to the increase in axial load it was found

that the location of axial thrust varied as the compression strut mechanism

came into play. At the time of failure the axial thrust had moved to the

extreme compression end of the wall leading to an applied force distribution

as shown in figure 7.1.

The implications of the preceding discussions do not invalidate the tests.

Rather, the information illustrates the applicability of the test behavior

7-6
to actual design situations. Because of the requirement for vertical restraint

it is clear that to apply the wall behavior from these tests to single family

residential construction would be unwise. The tests are more applicable to

components in high-rise load bearing construction where it is more likely that

sufficient vertical restraint is present.

1

7-7
Table 7.1. Wall Test Parameters

H

At Point of Maximum In-Plane Load

Wall

Precompression

Axial Load

(kips)

Loading

History

Type

In-plane

Load

(kips)

Axial

Load

(kips)

In-plane Ram

Displacement

(in.)

In-plane Wall

Displacement

(in.)

PI 14 Cyclic/ Pres train 24.4 28.8 0.087 0.050

P2 14 Monotonic/Ramps 22.2 29.6 0.226 0.073

P3 14 Cyclic/ Pres train 21.2 36.6 0.135 0.061

P5 14 Cyclic/ Pres train 27.0 35.9 0.162 0.106

P6 4 Cyclic/ Reversed 17.5 16.9 0.082 0.053

P8 5 Monotonic/Ramps 27.3 33.0 0.167 0.129

P9 18 Cyclic/ Pres train 30.0 37.2 0.131 0.087

P10 13 Cyclic/ Reversed 19.4 21.8 0.093 0.063

Cl 16 Cyclic/ Pres train 23.2 54.1 0.256 0.136

C2 16 Cyclic /Pres train 21.7 35.5 0.138 0.080

C3 16 Monotonic 19.1 31.7 0.129 0.084

C4 16 Monotonic 17.6 30.6 0.129 0.084
Table 7.2. Axial Load - Moment Interaction Values

Planar Walls Corner Walls

Axial Load

(kips)

Moment

(kip-inches)

Axial Load

(kip)

Moment

(kips-inches)

40 1129 40 1156

30 887 30 907

20 615 20 629

14 438 16 509

10 315 10 322

5 158 5 162

3 96 3 98

Notes: The values are based on an ultimate compressive strength of

1400 psi.

Net bedded area section properties were assumed.

The stress-strain history was assumed to follow Hognes tad’s curve.

The corner wall values are for the outstanding leg in tension.

7-9
Imposed

Displacement

Note: Upper wall surface rotations are restrained

during lateral displacement

Figure 7.1. Diagonal tension failure

7-10
LATERAL

LOAD

IN

KIPS

Figure 7.2. Load displacement curve for test P10

7-11
1.ATERAL

LOAD

IN

KIPS

First observed diagonal cracking

Figure 7.3. Load displacement curve for test P

7-12
First observed diagonal cracking

0.00 0.16 0.24 0.32

LATERAL (PISTON) DISPLACEMENT IN INCHES

0.40 0.40

gure 7.4. Load displacement curve for test P6
LATERAL

LOAD

IN

First observed diagonal cracking

Figure 7.5. Load displacement curve for test P8

7-14
LATERAL

LOAD

IN

KIPS

o„

ro

Figure 7.6. Load displacement curve for test P2

7-15
LATKRAL

LOAD

IN

KIPS

Figure 7.7. Load displacement curve for test P5

7-16
LATERAL

LOAD

IN

KIPS

Figure 7.8. Load displacement curve for test P3

7-17
IAl'LRAL

LOAD

IN

KIPS

Figure 7.9. Load displacement curve for test PI

7-18
I.ATEKAL

LOAD

IN

KII'S

o,

r>

Figure 7.10. Load displacement curve for test C4

7-19
LATERAL

LOAD

IN

KIPS

Figure 7.11. Load displacement curve for test C3

7-20
UTERAL

I.0A1)

IN

Kll'S

Figure 7.12. Load displacement curve for test C2

7-21
LATERAL

LOAD

IN

KIPS

Figure 7.13. Load displacement curve for test Cl

7-22
LATERAL

LOAD

(kips)

LATERAL (piston)

DISPLACEMENT (inches)

Figure 7.14. Envelope curves for planar wall tests

7-23
LATERAL

LOAD

(kips)

30 r

0.08 0.16 0.24 0.32 0.40

LATERAL (piston) DISPLACEMENT (inches)

0.48

Figure 7.15. Envelope curves for corner wall tests

7-24
RESULTANT

LATERAL

LOAD

IN

KIPS

Figure 7.16. Resultant load-displacement curve for test C5

7-25
RESULTANT

LATERAL

LOAD

IN

KIPS

Figure 7.17. Resultant load displacement curve for test C5

7-26
Vertical

Offset

Imposed

Displacement

Solid line represents undisplaced wall

Dashed line represents displaced wall

Figure 7.18. Overturning

7-27
TOTAL

APPLIED

AXIAL

LOAD

IN

KIPS

Figure 7.19. Axial load versus restraining moment

7-28
8. SUMMARY AND CONCLUSIONS

8.1 SUMMARY

An experimental research project investigating the susceptibility to cracking

of unreinforced, ungrouted, concrete block masonry walls due to cyclic loading

was undertaken. Ten planar and five corner walls were tested. All of the walls

with the exception of one corner wall were subjected to in-plane lateral displacements. A single corner wall was subjected to bidirectional displacements

such that the wall was displaced along its z-axis. The loading history was

the principal variable with the objective being to determine if visible cracking

could be produced through numerous cycles of changing displacements. The

parameters most varied were number of cycles and the initial displacement

imposed on the walls prior to cycling. The acquired data included displacements,

loads, and locally measured strains at various locations on the surface of the

walls.

8.2 CONCLUSIONS

A number of conclusions were reached as a result of this investigation. All of

the conclusions are qualitative and bear on the method of testing and general

wall behavior.

• The observed mode of failure was diagonal tension failure of the wall.

• The mode of failure was achieved only by restraining the vertical

movement of the wall so that overturning was prevented.

• The results of the investigation may not be directly applicable to

walls lightly loaded axially.

• In-plane shear capacity is not the most probable limiting load resistance

criteria for unreinforced, ungrounted walls with low levels of applied

axial compressive load.

• The appearance of a complete diagonal crack indicates the onset of

load capacity failure.

® There is a threshold in-plane lateral displacement below which loading

history does not affect observed wall behavior. The threshold is sufficiently large that for the normal design range of loads there is no effect of repeated loadings. Repeated imposed displacements greater

than the threshold displacement cause both stiffness and load capacity

reductions

® The effect of repeated excursions to displacements past the displacement

corresponding to the maximum lateral load capacity cause very large

stiffness and load capacity reductions.

• Local strain readings by themselves are unreliable indicators of crack

severity or wall distress. However, the readings from a number of

8-1
different locations taken together do provide an indication of the

degree of distress in the wall.

• The outstanding leg of a corner wall has a negligible effect on wall

capacity, behavior, and failure mode when displacement is imposed along

the axis of the in-plane leg.

o Corner walls displaced along their diagonal (or z) axis have maximum

resistances equal to the resultant of the in-plane resistance of each

leg.

8-2
U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBSIR 83-2780

2. Performing Organ. Report No. 3. Publication Date

October 1983

4. TITLE AND SUBTITLE

Behavior of Concrete Block Masonry Walls Subjected to Repeated Cyclic Displacements

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. Contract/Grant No.

8. Type of Report & Period Covered

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

Bureau of Mines

Department of the Interior

Washington, DC 20241

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)

An experimental investigation into the behavior of unreinforced, ungrouted concrete

block masonry walls subjected to repeated in-plane cyclic displacements was undertaken.

A total of 15 walls were tested of which 10 were 64 in. x 64 in. planar walls and 5 were

64 in. higher corner walls having equal leg lengths of 48 in. The primary parameter

varied in the investigation was loading history. Monotonic tests at both slow and

rapid strain rates were done. The cyclic tests included fully reversed displacement

patterns and reversed displacement patterns superimposed on static displacement offsets.

The cyclic tests included at least 100,000 repetitions. The test results indicated a pronounced effect of loading history on the wall performance, but only at load/displacements nearing the load capacity failure point.

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

Cracking; cyclic; fatigue; masonry; shear; strain rate; walls

13. AVAILABILITY

yyi Unlimited

| | For Official Distribution. Do Not Release to NTIS

| | Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

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

14. NO. OF

PRINTED PAGES

178

15. Price

$17.50

USCOMM-DC S043-P80
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