PUBLICATIONS

NBSIR 88-3796

Literature Review of

Strengthening Methodologies of

Existina Structures

Long T. Phan

H. S. Lew

Mark K. Johnson

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Structures Division

Gaithersburg, MD 20899

June 1988

00

56

88-3796

988

.2

C 75 Years Stimulating Amenca'a Progress

1913-1988

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

BCE

Research Information Center

National Bureau of Stanuaros

Gaithersburg, Maryland 20899

NBSIR 88-3796

LITERATURE REVIEW OF

STRENGTHENING METHODOLOGIES OF

EXISTING STRUCTURES

Long T. Phan

H. S. Lew

Mark K. Johnson

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Structures Division

Gaithersburg, MD 20899

June 1988

U.S. DEPARTMENT OF COMMERCE, C. William Verity, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

ABSTRACT

This report reviews research studies relevant to structural

strengthening of existing reinforced concrete members and frames. The

majority of these studies dealt exclusively with restoring or improving

seismic resistance of concrete columns and frames. A number of case

histories where various strengthening techniques were applied in practice

are reviewed. Most studies identified ultimate failure in the

strengthened structures as being primarily due to failure of the joining

elements. Improved load resistance and ductility in concrete structures

have been reported in most of these studies.

Key words: Anchors, beams, columns, deflection envelopes, ductility,

epoxy adhesive, hysteresis curves, infill walls, lateral load carrying

capacity, lateral stiffness, reinforced concrete frames, strengthening,

steel braces, wingwalls , walls.

ii
.
TABLE OF CONTENTS

Page

ABSTRACT ii

LIST OF TABLES iv

LIST OF FIGURES v

1. INTRODUCTION 1

1.1 GENERAL 1

1.2 SCOPE OF REPORT 2

2. SUMMARY OF RESEARCH STUDIES 3

2.1 INTRODUCTION 3

2 . 2 REINFORCED CONCRETE AND STEEL FRAMES 3

2.2.1 Infill Walls 4

2.2.2 Frame Strengthening by Steel Braes 15

2.2.3 Frame Strengthening by Adding Wingwall. 17

2.3 REINFORCED CONCRETE AND MASONRY WALLS 19

2.4 REINFORCED CONCRETE COLUMNS 27

2.5 REINFORCED CONCRETE BEAMS 34

3. CASE HISTORIES OF REPAIR AND STRENGTHENING TECHNIQUES 37

3.1 INTRODUCTION 37

3.2 COMMON TECHNIQUES 37

3.2.1 Infill Walls" 37

3.2.2 Steel braces 39

3.2.3 Wing Walls 40

3.2.4 Encased Columns 41

3.2.5 Epoxy Bonded Reinforcement 42

4. SUMMARY AND AREAS OF NEEDED RESEARCH 44

4 . 1 SUMMARY 44

4.2 AREAS OF NEEDED RESEARCH 46

5. REFERENCES 48

iii
. I $
LIST OF TABLES

Table No. Page

2.1 Sugano and Fujimura's Test Specimens 50

2.2 Summary of Sugano and Fujimura's Test Results 50

2.3 Descriptions of Higashi, Endo , and Shimizu's Frames 51

2.4 Summary of Higashi, Endo, and Shimizu's Test Results 53

2.5 Summary of Makino's Test Results 55

2.6 Summary of Corley et al.'s Test Results 55

2.7 Kahn's Brick Masonry Test Results 56

2.8a Shear Strength of Cement Grout Specimen 57

2.8b Shear Strength of Sand/Polyester Grout Specimens 57

2.8c Shear Strength of Sand/Epoxy Specimens 57

2 . 8d Shear Strength of Specimens with Cement Grout

and Axial Force 57

2 . 8e Shear Strength of Specimens with Sand/Polyester

Grout and Axial Force 57

2.9a Results of Out-of -Plane Tests 58

2.9b Results of In-Plane Tests 58

2.10 Summary of Test Results 59

2.11 Descriptions of Bett, Klingner, and

Jirsa's Test Specimen 60

2.12 Holman and Cook's Test Results 61

IV
'*
LIST OF FIGURES

Figure No. Page

2.1 Hayashi , Niwa, and Fukuhara's Frame Specimens 62

2.2 Hayashi, Niwa, and Fukuhara's Test Setup 63

2.3 Hayashi et al . ' s Test Results

a) Hysteresis Curves 64

b) Envelopes of Hysteresis Curves 64

2.4 Hysteresis Curves and Crack Patterns of Sugano and

Fujimura's Test Specimens 65

2.5 Envelopes of Sugano and Fujimura's Hysteresis Curves

a) Infilled Frames 66

b) Steel Braced Frames 66

2.6 Strength of Connection vs. Frame's Lateral Strength 67

2.7 Details of Higashi et al.'s Specimens

a) Specimens in 1977, 78 Series. 68

b) Specimens in 1979 Series 69

c) Specimens in 1981 Series 69

2.8 Details of the Connection Between Infill Wall and Frame

a) 1977, 78 Series 70

b) 1979 Series 70

c) 1981 Series 70

2.9 Higashi et al.'s Test Setup

a) One -bay, One -story Frame 71

b) One-bay, Three- story Frame 71

c) Two -bay, Three -story Frame 71

2.10 Envelopes of Higashi et al.'s Hysteresis Curves

a) 1977 Series 72

b) 1978 Series 72

c) 1979 Series 73

d) 1981 Series 73

2.11 Reinforcement Arrangement in Kahn's Specimens

a) Bare Frame Reinforcement Details (Specimen 2) 74

b) Monolithic Shear Wall Reinforcing Details (Specimen 1) . 74

c) Cast- in-Place Infilled Frame (Specimen 3) 75

d) Single Precast Infill Panel (Specimen 4) 75

e) Multiple Precast Infill Panels (Specimen 5) 76

V
2.12 Hysteresis Behavior of Kahn's Specimens

a) Specimen 1 . 77

b) Specimen 2 77

c) Specimen 3 . . 77

d) Specimen 4 78

e) Specimen 5 78

2.13 Envelopes of Hysteresis Curves of Kahn's Specimens........ 79

2.14 Dimensions and Reinforcement Arrangement of

Shiohara et al . ' s Specimens 79

2.15 Hysteresis Curves of Shiohara et al .

'

s

Specimens. 80

2.16 Measured Displacement Components of

Shihara et al . ' s Specimens 80

2 . 17 Description of Aoyama et al . '

s

Test Specimens ............. 81

2.18 Hysteresis Behavior of Aoyama et al . '

s

Specimen P-1-0..... 82

2.19 Crack Patterns in Aoyama et al . '

s

Test Specimen P-1-0 82

2.20 Deflection Envelopes of Aoyama et al . '

s

Test Specimens.... 82

2.21 Makino et al . '

s

Steel Frame Specimens A2 and B2 83

2 . 22 Local Buckling in Steel Column. ........................... 83

2.23 Hysteresis Curves of Original and Strengthened Frames 84

2 . 24 Mallick' s Test Frames 85

2.25 Dowel Layout for Jones and Jirsa's Steel Bracing Scheme... 85

2.26 Connection Details

a) Brace- to-Collector Connection. 86

b) Brace- to -Channel Connection. 86

2.27 Load-Drift Relationship of the Steel Braced Frame 87

2.28 Deflection Envelopes. . 87

2.29 Roach and Jirsa's Strengthening Scheme

a) Strengthening Concept. 88

b) Connection Mechanism Between Old and New Concrete 88

c) Reinforcing Details 88

2 . 30 Hysteresis Curves 89

2.31 Envelopes of Hysteresis Curves of Frames Strengthened

by Adding Wingwall and Steel Bracing 89

VI
2.32

Dimensions and Reinforcement Arrangement of

Corley, Fiorato, Oesterle, and Scanlon's Walls 90

2.33 Specimen B5 with Damaged Web and

with Web Concrete Removed 90

2.34 Specimen B5R After Repair 90

2.35 Reinforcement Arrangment in Specimen BUR 91

2.36 Drilling Holes for Diagonal Reinforcement in BUR 91

2.37 Hysteresis Curves of Corley et al . '

s

Original

and Repaired Specimens

a) Specimens B5 and B5R 92

b) Specimens B9 and B9R 93

c) Specimens Bll and B11R 94

2.38 Jabarov, Kozharinov, and Lunyov's Test Specimen

a) Specimen's Dimensions 95

b) Reinforcement Details 95

c) Strengthening with Diagonal Reinforcements and

Welded Wire Mesh 95

2.39 Load Parallel to Bed Joints vs. Strain Parallel to Bed

Joints Relationships for Kahn's Wall Panels

a) Dry Surface Condition 96

b) Epoxied Surface Condition 96

c) Wet Surface Condition 96

2.40 Plecnik, Cousins, and O'Conner's Static Shear Specimens... 97

2.41 Hayashi , Niwa, and Fukuhara's Column Specimens

a) Column Cross-Section 98

b) Reinforcement Arrangement 98

c) Test Setup 98

2.42 Hayashi, Niwa, and Fukuhara's Test Results

a) Hysteresis Curves 99

b) Envelopes of Hysteresis Curves 99

2.43 Dimensions and Reinforcement Arrangement

of Kahn's Column Specimens 100

2.44 Strengthening Using Steel Bands (Specimen 2) 100

2.45 Strengthening Using Plain Steel Rod (Specimen 3) 100

2.46 Strengthening Using U-Shaped Clamps (Specimen 4) 100

vi i
2.47 Hysteresis Curves of Kahn's Columns

a) Specimen 1, Unstrengthened 101

b) Specimen 2, Steel Bands 101

c) Specimen 3, 6 -mm Plain Rod 101

d) Specimen 4, U-Shaped Clamps 101

2.48 Details of Bett, Klingner, and Jirsa's Columns..... 102

2.49 Hysteresis Curves of Bett, Klingner, and Jirsa's Test

Specimens

a) Specimen 1-1. 103

b) Specimen 1-1R. 103

c) Specimen 1-2. 103

d) Specimen 1-3. 103

2.50 Envelopes of Bett, Klingner, and Jirsa's Hysteresis

Curves 104

2.51 Reinforcement Repair Schemes in Augusti, Focardi,

Giordano, and Manzini's Test Program. 105

2.52 Typical Moment-Displacement Relationship. ................. 105

2.53 Reinforcement Details of Stppenhagen and Jirsa's

Encased Columns 106

2.54 Shear Reinforcements

a) Bent #4 Bars in Beam-Column Joints. 106

b) Bent #3 Bars in Window Regions . 106

2 . 55 Load-Drift Relationships 107

2 . 56 Final Crack Patterns 107

2.57 Specimen Configuration and Dimensions in

Holman and Cook's Test Program.... 108

2.58 Reinforcement Arrangement on Beam's Cross-Section 108

2.59 Load-Center Deflection Curves 108

2.60 Arrangement of External Reinforcement in Vanek's Study.... 109

2.61 Crack Patterns in Beams 109

2.62 Load-Center Deflection of Plated Beams 109

3.1 Concept of Infilling Technique 110

3.2 Connection Between New Shear Wall and Column Ill

Arrangment of Cross Braces on North and South Facades

of the Tohoku Institute of Technology in Sendai, Japan.... 112

V i i i

3.3
3.4 Spandrel Beam Locations 112

3.5 Details of Braces to Frame Connection 112

3.6 Concept of Wingwall Addition 113

3.7 Connection between Wingwall and Column 113

3.8 Details of Nene's Strengthened Column 114

IX

1. INTRODUCTION

1.1 GENERAL:

Strengthening of existing buildings is often called for when there

is a need to upgrade them to satisfy new building code requirements or

to improve the load carrying capacity. This report presents a summary

of experimental studies on strengthening methods (chapter 2) , case

histories of field applications of strengthening methods to existing

structures (chapter 3) , and recommendations for areas needing further

research (chapter 4) . While all building codes clearly specify the

structural requirements for the design of new construction, the design

for strengthening of an existing building is still based mostly on

engineering judgement. This is due largely to the lack of an established

approach based on research on methods of strengthening and for assessing

the structural performance of strengthened structures. The 1982

Rehabilitation Guidelines [1.1] developed by the U.S. Department of

Housing and Urban Development provided general guidance for damage

assessment of common building structural systems such as masonry bearing

walls and simple wood, steel, and concrete frames. However, these

guidelines are intended for use on a voluntary basis in conjunction with

existing building codes and standards, and are only applicable to repair

work. For strengthening of structures, an engineer must rely on his own

judgement in assessing areas of weakness in a structure and then develop

an appropriate strengthening scheme based on that assessment.

Furthermore, techniques which have been used to strengthen existing

structures are not based on experimental data. Thus, accurate assessment

of the expected performance of the strengthened structure is difficult

to make

.

1.2 SCOPE OF REPORT:

To identify relevant studies in strengthening methodologies, a literature search was conducted using the data base of the Engineering

Index System and the National Technical Information Service. These two

data bases identified over 200 abstracts based on key word input. Review

of the abstracts revealed a limited number of papers and reports which

1
dealt with structural members and frames. Additionally, papers published

in proceedings of national and international conferences on earthquake

engineering, proceedings of the U.S. -Japan seminars on repair and

retrofit of structures, and research reports of U.S. and Japanese

universities have been reviewed. Review of the literature clearly

revealed that a disproportionally large number of studies dealt with

seismic strengthening of reinforced concrete and masonry structures.

This indicates that there is a considerable concern for strengthening of

existing reinforced concrete and masonry structures in earthquake

regions. On the other hand, the limited number of reports on

strengthening of steel or timber structures suggests that strengthening

of these types of structures is rather straightforward or has been less

frequent and therefore not of a great concern. This is probably because

attachment of new structural members to steel or timber structures can

be accomplished simply through the use of mechanical fasteners or welding

for steel structures.

Thus, this report reviews studies of structural strengthening of

damaged and undamaged reinforced concrete and masonry structures.

Studies which dealt primarily with repair of damaged structural members

are not included in this review.

2
2. SUMMARY OF RESEARCH STUDIES

2.1 INTRODUCTION:

Much of U.S. research efforts in strengthening of existing

structures have focused on developing means to improve seismic

performance of various structural members such as beams, columns and

walls. Since the 1971 San Fernando earthquake, a number of research

programs were initiated in the U.S. to examine the effectiveness of

various methods for repairing damaged structural members and for seismic

retrofitting of old buildings.

Having experienced extensive damage to concrete and wood structures

during the 1968 Tokachi Oki earthquake and the 1978 Miyagi Ken Oki

earthquake, extensive studies on repairing of damaged structural members

and retrofitting of existing buildings have been undertaken by Japanese

researchers. Most of their results have been published in Japanese.

This chapter reviews experimental studies reported in both U.S. and

Japanese papers and reports. These include strengthening methods for

reinforced concrete and steel frames, concrete and masonry walls,

concrete beams and columns

.

2.2 REINFORCED CONCRETE AND STEEL FRAMES:

Methods used in strengthening reinforced concrete and steel frames

may be grouped into three main categories: infill walls, steel braces,

and wingwalls

.

2.2.1 Infill Walls:

Eight major experimental investigations on the effectiveness of

infill walls to resist lateral forces and to increase lateral stiffness

have been reported. These investigations included one -bay, one -story,

and one -bay, three -story reinforced concrete frames and one -bay, onestory steel frames strengthened by various infilling techniques proposed

by Hayashi et al [2.1], Sugano and Fuj imura [2.2], Higashi et al [2.3],

Kahn [2.4], Shiohara et al [2.22], Aoyama and Yamamoto [2.23], Makino et

al [2.5], and Mallick [2.6]

.

3
(1) In the study conducted by Havashi . Niwa and Fukuhara [2.1], a series of six 1/3-scale, one-bay, one-story reinforced concrete frames,

W-l to W-6, were tested. The specimens consisted of one rigid frame

without infilled wall (specimen W-l)

,

one monolithic wall/frame system

(specimen W-2)

,

and four rigid frames strengthened by cast- in-place

infilled concrete walls (specimens W-3, W-4, W-5 and W-6). The primary

objectives of this study were 1) to examine quantitatively the

effectiveness of the infill wall technique as a method for strengthening

frames, and 2) to study the influence of different methods of joining

the new infilled concrete wall to the existing frame.

The four strengthened frames differed by the type of the joining

elements used in connecting the infilled walls to the existing frames and

in their distributions on the wall/frame interfaces. Two different types

of joining elements were used in this study, precast concrete shear keys

and wedge anchors. The precast concrete shear keys, approximately 3/4

in, (2 mm) thick, 1.5 in. (4 mm) wide, and 3.0 in. (8 mm) long, were

epoxy-bonded onto the innerface of the frame for specimen W-3. Wedge

anchors were used for the remaining three specimens W-4, W-5, and W-6.

In specimen W-4, wedge anchors were installed only under the upper beam,

with the other three inner sides of the frame roughened. In specimens

W-5 and W-6, wedge anchors were installed on all four sides of the

specimens, and the inner sides of the frame were roughened except for

specimen W-6 in which only the bottom surface of the beam was roughened.

Figure 2.1 shows the typical configuration of the test specimens, methods

for strengthening, and the arrangements of the reinforcement in each

specimen. The frames were subjected to reverse cyclic lateral load,

applied on the sides of each frame at the level of the top beam center

line, in combination with a constant axial load of 12 ton, maintained on

top of each column, as shown in Figure 2.2. The test results, presented

in the form of hysteresis curves and their envelopes, are shown in Figure

2.3.

4
The lateral stiffness of all of the infilled frames was

significantly greater than the stiffness of the bare frame. In fact, the

lateral stiffnesses of infilled frames approached or were even slightly

greater than the stiffness of the monolithically-cast wall/frame. The

lateral force capacities of the infilled frames were 3.5 to 5.0 times

that of the unstrengthened frame, and 0.55 to 0.72 times that of the

monolithic wall/frame. Hayashi, Niwa, and Fukuhara also observed shear

failure of both types of shear connectors along the top beam/infill wall

interface at large deflection.

(2) A similar but more comprehensive experimental program was

conducted by Sugano and Fuj imura [2.2]. This test program consisted of

ten 1/3-scale, one-story, one-bay frames. For strengthening, cast-inplace concrete wall panels, steel panels, and specially shaped precast

concrete blocks were used as infilled walls. Of the ten specimens

proposed, five were strengthened using using infill walls while two were

strengthened by steel bracing. The remaining three specimens included

an unstrengthened frame and two monolithic wall/frames with walls of 1.5-

in (40-mm) and 3.0- in (80-mm) thick. The behavior of the two specimens

strengthened by steel braces, B-C and B-T, will be discussed in the next

section under frame strengthening by steel bracing. Details of the five

infilled frames specimens are described here; details of all specimens

are given in Table 2.1.

1. Specimen W-HA was infilled with a cast- in-place concrete wall

3.0- in (80-mm) thick, the infilled wall was connected to the

frame by 0.4 -in (10 -mm) diameter wedge anchors, spaced at 3.75-

in (100 mm) intervals all around the entire frame.

2. Specimen W-CO was also infilled with 3.0-in thick cast- in-place

concrete wall. However, the connectors were a combination of

both mortar shear keys and wedge anchors . The mortar shear keys

were epoxy-bonded and bolted at 5.6-in (150-mm) intervals all

around the frame

.

5
3. Specimen W-40W was a monolithic wall/frame with wall of 1,5 in.

(40 mm) thick. The existing wall was thickened by a cast- inplace concrete wall panel of the same thickness. However, no

connection was provided between the infilled wall and the frame.

4. Specimen W-BL was infilled with specially shaped precast

concrete blocks with holes at the center to accomodate vertical

reinforcement. The gaps between the concrete block wall and the

frame were filled with mortar. Vertical reinforcement was

connected to the top and bottom beams using wedge anchors, which

were placed at 7.5 in. (200 mm) intervals.

5. Specimen W-S was infilled with a steel panel bolted at 3. 75- in

(100-mm) intervals around the entire frame. The space between

the steel panel and the frame was filled with mortar.

Each specimen was subjected to a combined lateral reversed cyclic

deformation of increasing magnitude and axial load. The axial load in

each column was to simulate the vertical load and was provided by

prestressing a non- grouted steel bar, embedded in the column, to about

13% of the specified concrete strength. The effectiveness of the

strengthening techniques proposed in this testing program was evaluated

based on the ultimate lateral load capacity, ductility, and the energy

absortion of each specimen. The test results are summarized in Table

2.2. The hysteresis curves, associated envelopes, and a comparison of

the strength of different connections are shown in Figures 2.4, 2.5, and

2.6. In terms of improving lateral force capacity, this study reached

conclusions similar to those of Hayashi, Niwa and Fukuhara [2.1]. The

lateral force capacities of the infilled wall were found to be 3.5 to 5.5

times that of the unstrengthened frame and 0.62 to 0.98 times that of the

monolithic wall/frame. The lateral stiffnesses of the infilled walls

were also significantly greater than that of the unstrengthened frame.

However, however it was found that in contrast to the results of Hayashi,

et al [2.1], the lateral stiffnesses were slightly less than that of the

monolithic wall/frame, as indicated by the envelopes of the hysteresis

curves (see Figure 2.5).

6
Sugano and Fuj imura also examined the required strength of the shear

connectors as a function of the lateral load capacity by plotting the

ratio of the ultimate lateral force capacities of the infilled frames and

the monolithic wall (Qu/Qwu) against the nominal shear stress on the

wall/top beam interface, as shown on Figure 2.6. From this plot, Sugano

and Fuj imura concluded that in order to provide a bare frame with a lateral force capacity of at least 60% of that of a monolithic

wall/frame, the connection between the top beam and the infilled wall

should be designed to have a shear strength of at least 10 kg/cm^

.

Further, the lateral force capacity of an infilled frame could be

increased to 98% of that of a monolithic wall when a shear strength of

at least 20 kg/cm^ could be provided by the shear connectors, as in the

case of specimen W-HA. Data obtained from Kokusho and Endo also

indicated that a frame infilled without the use of shear connectors could

possess a lateral force capacity of at least 40% of that of a monolithic

wall

.

(3) Another major research study in strengthening of frames was

conducted by Higashi. Endo and Shimizu [2.3, 2.7]. This study, spanning

over several years, consisted of four series of reinforced concrete and

mortar frame specimens. The 1977 and 1978 series included fourteen 1/3-

scale, one-bay, one-story concrete frames, the 1979 series included eight

1/8-scale, one-bay, one-story reinforced mortar frames, and the 1981

series [2.7] consisted of four three-story two-bay reinforced mortar

frames

„

Various strengthening techniques were evaluated in this study,

including

:

1. Infilling with cast- in-place concrete panels which were

connected to the frame by wedge anchors

.

2. Complete or partial infilling with precast concrete panels, also

connected to frame by wedge anchors.

3. Bracing with steel frame, steel truss and steel braces.

4. Enhancing web reinforcement in columns with steel plates.

7
Description of the test specimens and the strengthening techniques

used in this study are given in Table 2.3. The details of all 26

specimens in the four test series are shown in Figure 2.7 and details of

the connection between the infilled wall panels and a frame are shown in

Figure 2.8.

All specimens were subjected to reversed cyclic loading in

combination with a constant axial load applied and maintained on top of

each column throughout the loading history. The axial load, which was

designed to simulate gravity load in the structure, was selected such

O that a compressive stress of 30 kg/cm^ would result in each column of all

specimens. The typical test setups for one -bay one -story, one -bay three -

story, and two -bay three -story specimens are as shown in Figure 2.9.

Both qualitative and quantitative comparisons of the effectiveness

of different strengthening techniques studied in this test program were

provided in the forms of the envelopes of hysteresis curves as shown in

Figure 2.10, and the antiseismic capability indexes Cg as summarized in

Table 2.4. The Cg index, defined as (Qu

/2N)72/z- 1 where Qu , N and /i denotes the ultimate lateral force capacity, the axial load in each

column, and the ductility factor, respectively, was adopted by Higashi,

Endo , and Shimizu as a measure of the antiseismic capability of each

specimen. In general, strengthening by complete infilling of frames with

either cast- in-place or precast concrete wall panels, connected by

sufficient number of wedge anchors, was found to be the most effective

strengthening technique in this study. This technique provided the

infilled frames with almost the same lateral force capacity and ductility

as that of monolithic wall/frame. In the one-bay, three-story specimens

(series 1979) , both the lateral force capacity and the ductility of

frames infilled by cast- in-place concrete wall appeared to be higher than

those of identical monolithic wall.

(4) The effectiveness of four different infilling techniques were

investigated by Kahn [2.4]. In this test program, five one-half scale,

one-bay, one-story reinforced concrete frames were tested statically

8
under reversed cycle deflections of increasing magnitude. The five

specimens include one monolithically cast wall/frame (specimen 1) , one

bare frame (specimen 2), one frame infilled with cast- in-place wall

(specimen 3) , one frame infilled with a single precast concrete panel

(specimen 4) , and one frame infilled with multiple precast concrete

panels (specimen 5) . The reinforcement arrangements of frames and of

infilled walls are shown in Figures 2.11 (a) to (e) . The hysteresis

behavior of all five frames are shown in Figures 2.12 (a) to (e) , and the

envelopes of hysteresis curves are shown in Figure 2.13.

The monolithic wall/frame (specimen 1) showed the greatest lateral

load carrying capacity of all specimens (150 kips) . Failure occurred at

a deflection 1-1/2 times the yield deflection in this specimen. Specimen

3 attained the same ultimate lateral load capacity. This specimen failed

due to deterioration of the joint between the cast- in-place wall and the

top beam. Brittle failure also occurred at a deflection of 1-1/2 times

the yield deflection. Specimen 4 attained 75% of the lateral strength

of the monolithic wall/frame (specimen 1) , while its ductility was twice

as large. This specimen maintained its maximum load over 3-1/2 times its

yield deflection in one direction. In the other direction, weld fracture

and pullout of the panel- to -frame connections caused rapid loss in load

capacity and ductility. The multiple precast panels (specimen 5)

attained 50% of lateral strength of the monolithic wall/frame. Four

interior panels failed in shear. This specimen showed little cyclic

degradation until the interior panels failed in shear at a relative

deflection angle of 0.02 radians.

The results of these tests showed that the multiple precast panel

infilling technique is the most effective technique to provide increased

ductility for frames, and the cast- in-place infilled wall technique is

superior for providing frames with increased lateral strength and

stiffness

.

(5) Effects of anchorage deterioration on flexural strength of

frames infilled with a cast- in-place wall were investigated by Shiohara

,

9
et al [2.22]. Four 1/3-scale, one-bay, one-story reinforced concrete

frames were tested: one was a monolithic wall/frame (specimen P2005)

,

and three were infilled with concrete walls (specimens C2005-I to III).

Prior to infilling, all of the inner sides of the frames were roughened

to depths of about 0.2 in. (5 mm). Splice bars, 0.5 in. (13 mm) in

diameter and 12 in. (300 mm) long, were inserted into predrilled holes

in the frames and anchored using epoxy adhesive to provide connections

between frames and infill walls. In specimens C2005-I and C2005-II, all

splice bars were embedded to a depth of 5.0 in. (130 mm), and in specimen

C2005-III, they were insetred to a depth of 4.5 in. (117 mm). All

infilled walls were heavily reinforced for shear (0.85%) so that a flexural failure would prevail. Round bars were used as flexural

reinforcements in two specimens, C2005-II and C2005-III, and deformed

bars were used in specimen C2005-I. Specimen dimensions and the

reinforcement arrangement are shown in Figure 2.14.

Gravity load was simulated by applying a constant axial load of 44

kips (20 ton) at the top of the columns. Five cycles of statically

reversing lateral load were applied at both ends of the upper girder.

In all specimens, ultimate strength was attained in the second cycle of

loading, and the specimens were further loaded to failure in the fifth

cycle

.

Figures 2.15 and 2.16 show the relationships between the lateral

load and the horizontal displacement of girders relative to the bases,

and the displacement components. The load-deflection curves (Figure

2.15) show that the infilled frames had lateral strengths of up to 0.77

to 0.86 times that of the monolithic wall/frame. The ductility factor

as measured by the ratio of the yield displacement to the displacement

at failure of specimen C2005-I which had deformed bars for flexural

reinforcements was twice as large as those of specimens with plain round

bars (C2005-II and C2005-III) . Degradation of lateral force resistance

was not observed in any of the specimens up to a deflection angle of

1/100 rad. The displacement component plots (Figure 2.16), composed of

measured shear displacement, flexural displacement, and slip at the

10
interface between the girder and the infilled wall, showed that shear

deformation accounted for 60-70% of total deflection up to a deflection

angle of 1/150 rad. The remainder was mainly due to flexure deflection.

As the specimens were further deformed, deflection due to shear gradually

decreased while shear slip on the girder/wall interface increased until

ultimate failure occurred. A lower strength observed in the infilled

frames when compared with that of the monolithic wall/frame was

attributed to pull-out failure of splice bars under combined tension and

shear. The embedment depth of the splice bars had little affect on the

strength and slippage at construction joints between the wall and the

frame

.

(6) The effect of number of connectors used in connecting steel

infilled panels with concrete frames was investigated by Aovama et al

[2.23]. In this study, five one-bay, one-story concrete frames were

infilled with 0.2 in. (4.5 mm) thick steel panels with 0.35 in. (9 mm)

diameter headed studs which were welded to the rims of the steel panels.

The 0.4 in. (10 mm) diameter resin anchors were inserted into predrilled

holes in the concrete frames. The gap between the frame and the infilled

steel panel was filled with non- shrink mortar. The number of connectors

and location of openings in the steel panels were varied in each

specimen. Dimensions of the test specimens are given in Figure 2.17.

Specimen P-1-0 was made of welded steel plates 0.2 in. thick with no

opening, and had 21 headed stud and 21 resin anchors. Specimen P-l-S had

an opening at the center and twice the amount of shear studs and anchors.

Specimen P-l-C had 59 welded shear studs and 63 resin anchors. The

opening in this specimen was located at the top of the panel. Specimen

P-2-G had 39 studs and 41 resin anchors. It had the opening located at

the top of the panel. Specimen P-l-N had an infilled panel identical to

specimen P-l-S (opening at center), except that the ratio of bending

moment to shear force in this specimen was increased by changing the

ratio of axial load to horizontal load. More longitudinal reinforcing

bars were also provided for the columns of this specimens.

11
A constant axial load corresponding to the stress of 30 kg/cm^ was

applied on each column for specimen P-1-0, P-l-S, P-2-C and P-2G. For

specimen P-l-N, the axial load N was changed in accordance with applied

shear force Q (N = 15.0 + 0.286 Q ton). Reversed cyclic loads were

applied at both ends of the girder. Hysteresis behavior and crack

patterns for specimen P-1-0 are shown in Figures 2.18 and 2.19, and the

envelopes of the hysteresis curves of all five specimens are shown in

Figure 2.20. The initial slopes of the hysteresis envelopes show that,

prior to attaining ultimate load, the lateral stiffness of strengthened

frames was not affected by either the location of the opening in the

steel panel or the number of connectors. However, the complete

hysteresis envelopes show that specimens P-1-0 and P-l-S, which had a smaller number of connectors, had less lateral load resistance and

ductility.

(7) The use of cast- in-place reinforced concrete infilled walls in

strengthening portal steel frames has been studied by Makino . et al

[2.5]. This test program, consisted of six portal steel frames of two

types, A and B. Three type A specimens were frames with wide -flange

steel columns oriented such that in-plane bending would be against the

strong axes of the columns, and three type B specimens had columns

oriented such that bending would be about their weak axes. Typical

configurations for both types of specimens are Shown in Figure 2.21.

Each type of specimen investigated in this program consisted of one

original unstrengthened frame (specimen AO or BO)

,

one damaged and then

strengthened with infilled concrete wall (specimen Al or Bl) , and one

undamaged frame infilled with concrete wall (specimen A2 or B2) . For the

repaired and the strengthened specimens, headed studs 0.5 in. (13 mm) in

diameter and 4 in. (100 mm) long were welded onto the inner sides of the

frames to provide connections between the frames and the cast- in-place

infilled walls. The infilled concrete wall had about 5% flexural

reinforcement in both directions and was cast vertically through delivery

mouths provided under the top beams. However, local buckling in the

12
steel columns of the repaired specimens was not repaired in the

subsequent test as shown in Figure 2.22.

All specimens were subjected to a combination of constant axial load

applied to the top of each column and reverse cyclic lateral load applied

at the top of the test frame, except for two specimens B1 and B2 where

only one -directional lateral load was applied instead. The constant

axial load had a magnitude corresponding to 30% of the yield strength of

the columns. The test results, in the form of hysteresis curves, are

given in Figure 2.23 and summarized in Table 2.5. From these results,

it was found that the damaged and then strengthened specimens, Al and B1

,

had higher lateral force capacity but smaller ductilities than those of

the undamaged infilled frames (specimens A2 and B2) . Makino , et al

concluded that the infilling technique can be effectively used in

recovering the lateral force capacity of locally buckled portal steel

frames. Further, they suggested that for estimation of the lateral force

capacity of the frames, the infilled wall can be considered as a compressive bracing of rectangular cross section with an effective width

of about 5.4 times the thickness.

(8) The effect of combined axial and lateral loads on the behaviors

of steel frames with infilled walls was investigated by Mallick [2.6].

Tests were conducted on a series of two-bay steel frames infilled with

cement mortar panels, with and without shear connectors. The combined

loading, applied at the joints as shown in Figure 2.24, consisted of

vertical (V) and lateral (H) loads, and moment produced by the vertical

load with an eccentricity (e)

.

The frames were loaded so that a rigid

base condition could be achieved along the central member as shown in

Figure 2.24. The vertical load and the associated moment were applied

by prestressing a high strength steel rod 0.2 in. (5 mm) in diameter

passing through the extended arm of the steel frame. The lateral load

was applied gradually by a hydraulic jack. Mallick found that, in

general, the infilled frames with shear connectors were laterally stiffer

than those without shear connectors up to the failure load. Further, the

frames behaved linearly until the first tension crack occurred in the

13
infilled panels; this corresponded to approximately 66% of the ultimate

load. In the infilled frames without shear connectors, the failure was

due mainly to the crushing of one of the loaded corners along with the

separation cracks at the boundary junction. The stiffness of both types

of frames were observed to be increased as the magnitude of the vertical

load and the associated moment decreased.

2.2.2 Frame Strengthening By Steel Braces:

(1) Steel bracing was used by Jones and Jirsa [2.8, 2.9] to

strengthen a damaged two -bay, two -story reinforced concrete frame. The

frame was a 2/3 -scale model of a portion of typical exterior moment

resisting frames, representative of strong spandrel beam-weak column

frames

.

The strengthening scheme adopted in this study involved the

attachment of structural steel diagonal bracings to the exterior of the

damaged frame through use of 5/8 in- diameter (16 mm) standard threaded

dowels. The dowels were epoxy grouted into the concrete frame at

locations along the columns and the spandrel beams. The vertical

channels (MC6xl5.1) were bolted to the sides of the concrete columns by

dowels placed at 8 in. (20 cm) intervals and embedded 5-1/2 in. (14 cm)

deep. The horizontal collector sections (WT3x6) were connected to the

spandrel beams by dowels embedded 4-1/2 in. (11.4 cm) deep at 9 in. (23

cm) interval in the first and the third floors and 18 in. intervals in

the second floor. With the column channels and beam collectors in

place, all threaded dowels were tightened to a uniform torque of 75 ft1b (102 N-m) . The layout of dowels is shown in Figure 2.25, and the

connection details of brace members are shown in Figure 2.26.

The strengthened frame was subjected to five sets of load cycles

corresponding to five different levels of drift. The load-drift

relationship of the strengthened frame is shown in Figure 2.27, and the

envelopes of the load-drift relationships are shown in Figure 2.28. The

results of the test indicated that the lateral stiffness of the

strengthened frame was approximately 1.5 times that of the bare frame.

14
However, it should be pointed out that this lateral stiffness was

contributed mainly by the added steel frame, since the contribution of

the existing concrete frame had been reduced by the cracking caused by

previous tests. Further, the lateral force capacity of the steel bracing

strengthened frame appeared to be 6 times higher than the lateral

strength of the bare frame. This capacity was governed by buckling of

brace members and the quality of the joints that connect bracing members.

The epoxy-grouted dowels, observed the authors, performed well as evidenced by limited pullout and no dowel shear failure.

(2) Uses of in-plane steel braces in strengthening reinforced

concrete frame were also studied by Sugano and Fuj imura [2.2] and

Higashi, Endo and Shimizu [2.3, 2.7] as mentioned in section 2.2.1. In

the test series conducted by Sugano and Fuj imura [2.2], compression

braces of H-section steel and tension braces of 1.1 in. (28 mm) in

diameter round plain bars were used to strengthen two frames, B-C and BT (see Table 2.1). The compression braces in specimen B-C were attached

to the frame at the beam/column corners by connecting bolts which were

set on cover plates welded to the ends of the braces. The space between

the frame and the steel cover plates was filled with mortar. The plain

bar tension braces in specimen B-T were welded at each end with a connecting steel plate. This plate was in turn bolted by high-strength

bolts of 0.6 in. (16 mm) in diameter to other plates that were anchored

into the frame at each beam/column corner.

These braced frames were subjected to the same loading condition

described in section 2.2.1, lateral reversed cyclic deformation in

combination with axial stress of 13% the specified concrete strength.

The test results are given in Table 2.2 and in Figures 2.4, 2.5 and 2.6.

From the test results, it appeared that in terms of lateral force

capacity, both steel bracing schemes provided less increased capacity

than infilled wall techniques. In frame B-C having compression braces,

the lateral force capacity was measured about 3.5 times that of the

unstrengthened frame (62% of that of the monolithic wall/frame system)

.

15
In frame B-T having tension braces, the lateral strength was 3.7 times

that of the unstrengthened frame ( 66 % of that of the monolithic

wall/frame system). However, in terms of displacement ability and energy

absorption, the specimen with tension braces (B-T) exhibited the most

ductile behavior when compared with all other techniques

.

(3) Higashi. Endo and Shimizu [2.3, 2.7] , in their 1978 and 1979 test

series, also experimented with steel bracing technique. In the 1978

series, three one-bay, one-story frames were strengthened using steel

braces, a steel frame, and a steel truss (specimen No.7-SB, N0 . 8 -SF, and

No.9-ST respectively). In the 1979 series, two one-bay three-story

mortar frames, No.6-3SB and No.7-3SF, were strengthened by adding steel

braces and a steel frame into all three stories of the frame (see Figure

2.7). All steel members were attached to frames through use of wedge

anchors. The test results obtained from these specimens, shown in Figure

2.10 in the form of the envelopes of the hysteresis curves, indicated

moderate increases in lateral stiffness and load capacity of the steel

braced frames. However, the increase in ductility was substantial when

compared with the infilled frames. The seismic capabilities of the

specimens strengthened by steel bracing and steel frame appeared to be

as large as that of the monolithic wall/frame, as indicated by the

seismic capability index Cg in Table 2.4.

2.2.3 Frame Strengthening By Adding Wing Wall:

Addition of wingwalls is another strengthening technique which can

provide reinforced concrete frames with increased lateral strength and

ductility. This technique was used by Roach and Jirsa [2.9, 2.10] as an

alternative strengthening scheme to the steel bracing scheme studied by

Jones and Jirsa in the same testing program [2.8, 2.9]. The two-bay,

two -story frame was strengthened by casting reinforced concrete wingwalls

around the exterior three sides of the columns along their entire

heights. The added wingwalls were designed in accordance with the ACI

318-83 code provisions [2.11] for structural walls and their widths were

selected such that their nominal shear stress would be limited to about

4/f' c (90 inches wide for the prototype structure or 60 inches for 2/3-

16
scale specimens) . This selection was aimed at providing the strengthened

frame with sufficient lateral stiffness to satisfy the code drift

requirements without excessively reducing the window openings and to

allow the spandrel beams to develop full flexural strength.

The newly cast wingwalls increased the column width from 12 inches

(30 cm) to 60 inches (150 cm) and the thickness from 12 inches (30 cm)

to 13.3 inches (34 cm) and were detailed to ensure monolithic behavior

of the structural system as illustrated in Figure 2.29. Connections

between the added wingwalls and the original frame included a coat of

epoxy adhesive between the original and the new concrete and No. 4 rebar

dowels which were epoxy- grouted into the beam faces and the sides of the

columns. Adhesive bond was increased by sandblasting the surface of the

existing frame prior to application of epoxy.

The strengthened frame was subjected to four sets, three cycles

each, of reversed cyclic deformation which corresponded to 0.05%, 0.125%,

0.25% and 0.5% drift. The results, presented in hysteresis curves and

associated envelopes, are shown in Figures 2.30 and 2.31. The initial

lateral stiffness of the strengthened frame was measured from the

hysteresis curves as being 1250 K/in, which is more than three times that

of the bare frame. The lateral capacity of the strengthened frame was

limited by the flexural capacity of the spandrel beams rather than the

shear capacity of the columns as in the case of the unstrengthened frame.

The observed crack patterns indicated that flexural hinging had developed

at all critical beam cross sections. In addition, the flexural

reinforcements in the beams were yielding at ultimate and flexural cracks

with widths of up to 1/4 in. (6 mm) were noted. In comparison, the

columns with added wingwalls exhibited little distress. Maximum stresses

in the longitudinal reinforcement in columns were only about one -half of

the yield stress at ultimate loads. The measured lateral capacity of the

frame with wingwalls indicated that an increase in strength of 5 times

were obtained by this strengthening scheme.

17
2.3 REINFORCED CONCRETE AND MASONRY WALLS:

A limited amount of research on repair and strengthening of

reinforced concrete and masonry walls is reported in the literature.

Four such studies are presented in this section. The purpose of the

study conducted by Corley, Fiorato, Oesterle and Scanlon [2.12] was to

evaluate the effectiveness of repair techniques proposed for damaged

structural concrete walls. The other studies, conducted by Plecnik,

Cousins and O'Conner [2.13], Jabarov, Kozharinov and Lunyov [2.14], and

Kahn [2.15] , involved repair and strengthening of masonry walls by adding

external reinforcement and concrete or mortar overlays.

(1) In the study conducted by Corley. Fiorato. Oesterle and Scanlon

[2.12], three reinforced concrete walls with barbell-shaped cross

section, named B5 , B9 and Bll, were loaded laterally as vertical

cantilever with forces applied at the top. A constant axial force,

corresponding to an axial stress of 545 psi, was maintained on the top

of specimen B9 . The dimensions of the walls and the reinforcement

arrangements are shown in Figure 2.32. All three walls were loaded until

significant loss in load carrying capacity occurred. The damaged walls

were then repaired using three different techniques and retested to

destruction. Detailed description of the repair techniques used for each

wall is as follows:

In specimen B5 , the damaged web concrete was removed up to the

8 ft-6 in. (2.6 m) level. The criterion used was to remove all

concrete that could be taken out easily with hand tools. Reinforcing

steel was left intact and no new reinforcement was added. New

concrete of the same thickness of 4 in. (10 cm) was then cast in

vertical lifts of 3 ft (0.9 m). The gap between the top portion of

new concrete and old wall was handpacked with concrete. The repaired

specimen was named B5R. Figures 2.33 and 2.34 show the damaged

specimen B5R with web concrete removed and the same specimen after

completion of repairs.

18
The same repair procedures were used to repair specimen B9 and

the repaired wall was designated as B9R. However, rather than

replacing the web at its original thickness of 4 in. (10 cm) , a 6 in.

(15 cm) web was constructed.

In specimen Bll, not only was the damaged web concrete replaced

using the same repair procedures as in specimens B5R and B9R, but

additional diagonal reinforcement was also added. Prior to replacing

the damaged web concrete, #5 diagonal rebars were inserted through

the boundary columns at a 45° angle and into predrilled holes in the

base block. The bars were then epoxy grouted. Figures 2.35 and 2.36

show the drilling techniques for the diagonal holes and the

arrangement of reinforcement in specimen BUR.

The repaired specimens were subjected to the same loading condition

as the original specimen. The test results, presented along with the ACI

code predictions for flexural and shear strengths of the walls, were

summarized in Table 2.6. The hysteresis curves of all 6 specimens were

given in Figure 2.37.

Examination of the results of specimens B5 and B5R indicated that

replacement of the original damaged web concrete was an effective repair.

Both the lateral strength and stiffness were successfully restored. For

specimen B9R, replacing the original damaged web by a thickened web

resulted in a significant increase in deformation capacity. The original

specimen B9 was able to sustained only 1-1/2 inelastic cycles, with a maximum rotation corresponding to five times yield. However, the

repaired specimen B9R was able to sustain 8-1/2 inelastic cycles, with

a maximum rotation corresponding to six times the yield rotation in

specimen B9 . The ultimate strength of B9R was about equal to that of B9 . For specimen BUR, the addition of diagonal reinforcement resulted in an

increase in maximum nominal shear stress of approximately 18%. However,

the initial stiffness of all three repaired walls were only approximately

50% of those of the original walls. This reduction in stiffness should

19
be considered in the evaluation of dynamic response of repaired

structures

.

(2) The possibility for complete restoration of the initial strength

and stiffness of damaged masonry walls by adding reinforced mortar layers

was investigted by Jabarov. Kozharinov and Lunvov [2.14]. The test

specimen was a two-story, one-bay reinforced masonry structure consisting

of two parallel masonry walls. The walls were connected by cast- in-place

reinforced concrete floor slabs of 3.9 in. (10 cm) thick. Each masonry

wall was 23 ft (705 cm) long, 15 in. (38 cm) thick, and 18.4 ft (560 cm)

high with two window openings of 4 ft by 5 ft (120 cm by 150 cm) in each

story. The masonry blocks had ultimate compressive and bending strengths

of 800 psi (5.5 MPa) and 450 psi (3.1 MPa), respectively, and the cementlime mortar used to joint the masonry blocks had compressive strength of

725 psi (5 MPa) . The test specimen was constructed on rigid foundation,

its configuration and dimensions are as shown in Figures 2.38 (a) and

(b).

The test wall was subjected to both axial and horizontal loads in

combination with vibration generated by a vibro -machine placed on top of

the wall. The axial load, corresponding to compressive stress in the

wall of 20 psi (0.14 MPa) and 9 psi (0.065 MPa), was simulated by putting

dead weights onto the floors of the first and second stories. The

lateral load was applied incrementally, 13.5 kips (60 kN) per increment,

through use of a hydraulic ram. The ram was placed at elevation of 16.3

ft (497 cm), which resulted in a lateral force ratio of 1:2.2 between the

floors

.

The original, unstrengthened wall was tested until a drop in lateral

load capacity was observed. The ultimate lateral load was measured as 204 kips (910 kN) . Extensive diagonal cracks appeared in all three piers

of the first story at 158 kips (705 kN) . In the first story, diagonal

crack was observed in the middle pier at ultimate.

20
The damaged wall was then strengthened using two schemes. In the

first scheme, four end piers of the first floor were strengthened by

reinforced mortar layers 1 in. (2.5 cm) thick. Diagonal reinforcements

were provided in groups of three 5 mm bars as shown in Figure 2.38 (c)

.

The added reinforcement was attached to the masonry surface with the aid

of 8 mm N- shaped steel bars which were anchored into the mortar joints.

The second strengthening scheme was used only after the wall strengthened

by the first scheme had been tested to failure. This second

strengthening scheme involved application of mortar layers, reinforced

by welded wire fabric, to the two middle piers of the first story (see

Figure 2.38 (c)

)

.

The wall strengthened by the first scheme was subjected to the same

loading condition for the original wall and ultimate was 1.3 time the

original wall. The wall, restrengthened by adding reinforced mortar

layers in the middle piers, was able to sustain 97% of the ultimate

lateral load of the original wall. Jabarov, Kozharinov, and Lunyov

concluded that successful restoration of the initial strength and

stiffness of damaged masonry walls can be achieved using the proposed

strengthening techniques.

(3) A similar method of wall strengthening which used reinforced

shotcrete as overlay was studied by Kahn [2.15]

.

In this study, fourteen

3 x 3 ft (1 x lm) single wythe brick panels were constructed using bricks

salvaged from the old Atlanta Civic Center, built in 1928, to simulate

old, existing masonry walls. Nine of the fourteen brick panels were

coated with a layer of 3.5 in. (89 mm) thick dry-mix shotcrete, and three

were coated with a 1.5 in. (38 mm) thick shotcrete layer. The panels

with 3.5 in. (89 mm) shotcrete were reinforced with welded wire fabric

consisting of W4 wire six inches on center each way and placed 1 in.

(25.4 mm) from the brick interface. The 1.5 in. (38 mm) shotcrete layer

was reinforced with an expanded metal mesh which is commonly used for

plaster surfaces, placed at 1/4 in. (6 mm) from the brick interface.

Diagonal load tests, standardized by ASTM in the E519-74 specification,

21
were selected to determine the in-plane capacity of the strengthened

brick panels in this test program.

Four surface conditions of the brick at the time of shotcreting were

considered in order to study the surface effect on the brick- shotcrete

bond. The surface of panels D1 , D2 , D3 were left dry; panels W1 , W2 , W3

and XI, X2 , X3 were thoroughly wetted with water, and panels El, E2 , E3

were coated with epoxy adhesive (Sikastix 370 by Sika Chemical

Corporation) about 10 minutes prior to shotcreting. Shotcrete was not

applied to single wythe panel Cl or to double wythe panel CC1 to

facilitate comparisons. The panels description and the test results are

summarized in Table 2.7. The hysteresis curves for the strengthened

panels are shown in Figure 2.39.

The static ultimate strengths listed in Table 2.7 indicated that

shear capacity of brick panels was increased by approximately 17 times

when strengthened by a 3.5 in. (89 mm) shotcrete layer (0.19 percent

reinforcement each way by welded wire fabric) . For panels strengthened

with expanded metal mesh and 1.5 in. (38 mm) thick shotcrete, the shear

capacity was increased by 6.8 times. It was also observed that composite

action was fully developed between the brick and shotcrete regardless of

surface condition. However, the epoxied and wetted surface panels

displayed significantly greater inelastic deformation capacity than the

dry panels. The ultimate load of the strengthened brick panels was

dependent on the tensile resistance of the welded wire fabric and the

expanded metal mesh. The modest amount of reinforcement used in this

testing program was sufficient to permit post-cracking, inelastic

deformation to develop in the panels.

(4) Plecnik. Cousins and O'Conner [2.13] proposed a different

strengthening method for improving the out-of-plane and in-plane lateral

load capacity of multi-wythe, unreinforced brick masonry walls. The

proposed method involved coring a 2 in. to 4 in. (5.08-12.7 cm) diameter

hole vertically through the wall to the foundation. A reinforcing bar

would be placed in the core hole with filler material poured into the

hole. The filler material could be epoxy, polyester, and cement grout.

22
Two experimental programs, one at the Long Beach State University (LBSU)

and one at the North Carolina State University (NCSU) , were conducted to

examine the effectiveness of several strengthening methods and the

influence of different parameters which affect the lateral load

resistance capacity of unreinforced masonry walls.

In the LBSU testing program, over 70 small scale specimens were

built as shown in Figure 2.40 and tested to failure under static shear

load. All specimens were built using new, solid

8 in. common smooth face brick, manufactured per ASTM specification C62

for Grade SW brick. The mortar joint was prepared according to BIA-M1-

72 except that in some cases the amounts of cement, lime and sand were

varied from that specified for Type M mortar. Type M mortar was used in

the majority of specimens, but several other types were used to determine

the effect of mortar strength on the strength of the specimens.

Reinforcement used included #4, #5, and #6 deformed bars of grade 60

steel, and 3/4 in. (19 mm) diameter undeformed fiberglass rods. The core

at the center of each specimen was filled with either cement grout, a sand/polyester grout, or a sand/epoxy grout. Reference [2.13] described

detailed mixing ratios, properties of filler materials and joint mortar.

The specimens were divided into 5 groups according to the type of

core filler and the " loading condition. Group A included 18 specimens

filled with cement grout, Group B 8 specimens with a sand/polyester

grout, and Group C 13 specimens filled with a sand/epoxy grout. Each

specimen in Groups D and E was also subjected to an axial force in

combination with the static shear load. Specimens in Group D were filled

with cement grout and specimens in Group E were filled with

sand/polyester grout. The test results of each group in Tables 2.8 (a)

to (e) .

A comparison of test results obtained from the five groups and of

unstrengthened specimens indicated that inplane shear strength of the

strengthened specimens can be increased by 55-110%. The test results

further showed that the shear strength of brick masonry is significantly

23
affected by the shear strength of the core material as well as the

applied normal stress. In general, the specimens made with cement grout

were approximately 30% weaker than the specimens made with sand/polyester

or sand/epoxy grouts. The greater the resin content in the sand/epoxy

grout, the greater the shear strength. Sand/polyester grouts were

recommended over sand/epoxy grouts due to higher costs of epoxy

adhesives. An optimum sand/polyester volume ratio was determined to be

between 1:1 and 2:1.

In the NCSU testing program, three existing buildings were selected

for strengthening using the technique evaluated in the LBSU test program.

The three buildings numbered 3, 4, and 5, had three -wythes masonry walls

and were classified as Type III (1982 Uniform Buildding Code)

unreinforced masonry buildings with flexible wood diaphragms at roof and

floor levels. For strengthening vertical holes of either 2 in. or 4 in.

(5 to 10 cm) in diameter, were cored dry using a target electric drill

rig. The holes were located at the center of the wall cross-sections and

were filled with either a cement grout or a sand/epoxy grout after a No.

5 deformed bars had been inserted.

After determining the compressive strength of the brick and the

shear strength of the mortar joint by in-place shear test (shove test),

panels and prisms were cut out of the strengthened walls and transported

to the laboratory for testing. All panels were three wythes thick (12

in.), seven courses high (21 in.) and 2-1/2 brick long (20 in.) with

varying core size and filler material. The panels were subjected to both

cyclic in-plane shear loads and cyclic out-of -plane moment. The results

of 5 out-of-plane tests and 7 in-plane tests were summarized in Table 2.9

(a) and (b) . Typical failure mode of out-of-plane tests consisted of

horizontal cracks forming in the bed joints on the tension face of the

specimens. This was followed by crushing of the mortar on the

compression face. As the number of load cycles increased, the tension

cracks increased in size and number while the mortar continued to crush.

Compression failure of the bricks was not observed. For the in-plane

shear tests, the first signs of failure of the specimens were cracking

24
in the head and bed joints on either face of the specimens with some

cracks going through bricks.

Plecnik, Cousins, and O'conner observed that both the out-of -plane

moment capacity and the in-plane shear capacity of a strengthened masonry

wall with larger core holes (4 in.) are generally greater than those of

wall with smaller cored holes. This was because larger diameter cores

allowed greater flow of the filler material into collar joints, therefore

resulted in a larger effective area to resist both in-plane shear forces,

and out -of- plane moments. Further, as in the LBSU's testing program,

sand/epoxy was found to be superior to cement grout as a filler material

because of their superior strength and flow characteristics.

2.4 REINFORCED CONCRETE COLUMNS:

Various methods for repair and strengthening have been used

primarily to improve shear resistance of reinforced concrete columns to

lateral loads. This section reports five major research studies

conducted by Hayashi, Niwa and Fukuhara [2.1], Kahn [2.16], Bett,

Klingner and Jirsa [2.17], Augusti, Focardi , Geiordano and Manzini

[2.18], and Stoppenhagen and Jirsa [2.19]. In most of the above listed

studies, more than one strengthening scheme was proposed and evaluated.

(1) In the study conducted by Hayashi. Niwa and Fukuhara [2.1],

three of the four 1/2-scale reinforced concrete columns, 18 x 18 in.

(45cm x 45cm) and 71 in. in height (180cm) were encased with welded wire

fabric and mortar, and subjected to both constant axial stress of 40

kg/cm^ and alternately reversed lateral loads. Three different

strengthening schemes were proposed. In two specimens, designated as C2 and C-3, the columns were encased with welded wire fabrics and 1.8 in.

(4.5cm) thick mortar. In specimen C4, the column was strengthened by a thicker jacket of mortar of 3.5 in. (9.0 cm) along with welded wire

fabrics. Specimen Cl was the unstrengthened original column. The

objective of this study was to provide quantitative evaluation of the

effectiveness of the proposed strengthening techniques for improving the

25
lateral load carrying capacity and the degree of improvement in ductility

of the original column. The test specimens are as shown in Figure 2.41.

The hysteresis curves of each specimen and their envelopes are shown

in Figure 2.42 and the experimental results were summarized in Table 2.10

along with the predicted results. It was observed that cracking

developed in the original column Cl relatively early stage before the

reinforcing bar yielded. Thereafter, as deflection increased, the

lateral load capacity decreased rapidly to 53% of the ultimate lateral

load at rotation angle of 1/50 rad. All strengthened specimens reached

higher lateral load and did not show sign of deterioration in lateral

load capacity until tensile reinforcement yielded. No reduction in the

lateral load carrying capacity were observed in these specimens until the

rotation angle reached 1/50 rad. The specimen strengthened with 3 in.

(7.6 cm) thick mortar (C.4) reached its ultimate load capacity without

rupture of mortar and welded wire fabric at the rotation angle of 1/25

rad. These results showed that both shear strength and ductility of

concrete columns can be enhanced using the proposed techniques.

(2) Three different column strengthening techniques using steel

bands, plain steel rods, and U-shaped steel clamps as external

reinforcement were proposed by Kahn [2.16]. In this study, four

specimens representing flexible columns connected to stiff girders were

constructed with square cross-sectional areas of 39 in^ (254 cm^) and

lengths of 11.5 ft (3.5 m) . Specimen 1 was designed as the original

specimen. It was tested to failure in shear due to a combination of

constant axial load of 81 kips (360 kN) and reversed cyclic lateral

deformations corresponding to 4 levels of drift, 0.5 $, i9, 2 Ay, and

4 Ay, where Ay was the deflection level at which the main reinforcement

yielded in tension. After testing, specimen 1 was repaired by removing

damaged concrete and replacing buckled reinforcement. The buckled

reinforcement was cut and welded to straight pieces of 0.3 in. (7.9 mm)

thick, 2.0 in. by 2 . 0 in. (51 mm x 51 mm) steel angles. Hoops of 0.4 in.

(9.5mm) reinforcing bars spaced at 1.5 in. (38 mm) on center were bent

26
around the repaired main reinforcement (Figure 2.43). The repaired

specimen was designated as 1R.

Specimen 2 was strengthened prior to testing by strapping 2.0 in.

wide (50.8 mm) packaging bands around the column. The bands were spaced

4.0 in. (102 mm) on center and secured with pressed clips (Figure 2.44).

The 1/4 in. (6 mm) gap beneath the band hoops was packed with non-shrink

mortar

.

Specimen 3 was strengthened by wrapping a 1/4 in (6mm) plain steel

rod around the column to form a rectangular spiral with a 1.1 in. (28mm)

pitch as shown in Figure 2.45. The splices in the spiral were made by

lap welding the bar. The 0.04 in. (1 mm) spaces beneath the spiral were

filled with mortar.

Specimen 4 was strengthened by confining the concrete by U-shaped

clamps which were held together by A325-3/4 inch bolts (19mm) . These

clamps were fabricated by welding 5/16 in x 2 in bar (7.9m x 50.8mm) to

3-1/8 in thick (79.4mm) steel angle (3 in x 5 in x 2 . 5 in wide) and

spaced 4-1/4 in (108mm) on centers (Figure 2.46).

The hysteresis curves of all four specimens are shown in Figure

2.47. For the strengthened specimens, these curves were nearly identical

in the elastic region. Further, the strengthened specimens demonstrated

ductile response without reduction in shear capacity. The unstrengthened

specimen collapsed due to loss of axial load capacity at a deflection of

1.5 in. (38mm), which represented a ductility ratio, A/Ay, of 1.9. All

strengthened specimens were able to achieve a ductility ratio of 4 with

little deterioration in load carrying capacity. Kahn concluded that by

confining the concrete using the proposed strengthening techniques so that shear force was carried primarily by the concrete, significant

increases in ductility can be achieved.

27
(3) Strengthening of short reinforced concrete columns was studied

by Bett. Klingner and Jirsa [2.17]. In their study, different techniques

were used for repair and strengthening of three nearly full-scale

reinforced concrete square columns. The specimens were numbered

sequentially as 1-1, 1-2, 1-3 and the repaired specimen was designated

as 1-1R. A constant axial compression of 64.8 kips (corresponding to a compressive stress of 450 psi) and a repeated reversed cycles of lateral

deformation were applied to each specimen.

Each specimen in this testing program consisted of a column 36 in.

in height (0.92m) and two large concrete end blocks. The original

specimen 1-1 had eight #6 longitudinal rebars and special 1/4- in. (6 mm)

deformed ties, placed at 8 in. (21 cm) intervals along the column height

and covered with 1 in. (2.5 cm) of concrete. The configuration and

dimensions of the specimens are shown in Figure 2.48.

In specimens 1-2 and 1-3, the strengthening methods involved

sandblasting and encasing columns with a shotcrete jacket reinforced with

closely-spaced transverse steel with and without crossties being cemented

into the existing columns. Table 2.11 shows the descriptions of test

specimens, including a brief summary of the strengthening technique used

for each specimen.

For the repaired specimen (specimen 1-1R) , the repair technique

consisted of two operations. First, all loose concrete cover was removed

with a chipping hammer, exposing the longitudinal steel. Holes were

drilled through the column, and cross ties which were used to anchor

additional longitudinal steel, were inserted and cemented with epoxy.

Second, closely-spaced ties were placed around the column core, and it

was encased with shotcrete. The description of the specimen is given in

Table 2.11.

The hysteresis curves for each test specimen and their envelopes are

shown in Figures 2.49 and 2.50. The unstrengthened specimen 1-1 behaved

elastically up to a story drift of 0.5%. Hysteresis loops remained

28
stable up to 1% of the story drift. Failure in specimen 1-1 appeared to

be dominated by shear as indicated by pinching shape of the hysteresis

loops and strains of the longitudinal reinforcement which were

significantly less than the yield strength. Both strengthened specimens

(specimens 1-2 and 1-3) exhibited stable hysteresis behavior for

deformations up to 1.5% of the story drift, after which a loss in

stiffness became apparent. Failure of the strengthened specimens were

primarily due to flexure as evidenced by the development of strains in

the original column longitudinal reinforcement in excess of the yield

strength. The envelopes of the hysteresis curves showed that the

strengthened specimens achieved much greater lateral strength and

stiffness than those of the original, unstrengthened specimen. The

repaired specimen (1-1R) also exhibited stable hysteresis behavior for

deformations up to 1.5% of the story drift. This specimen failed due to a combination of shear and flexure. The repaired specimen also achieved

much greater lateral stiffness and strength than the original specimen.

Further, the column repaired according to the proposed technique

displayed lateral strength and stiffness that were nearly equal to those

of an undamaged column strengthened with the shotcrete jacket.

(4) Comparative evaluations of different repair techniques for

damaged reinforced concrete columns were conducted by August!. Focardi.

Giordano and Manzini [2.18]. In this study, 24 full-size reinforced

concrete columns were tested to failure under a combination of constant

axial load and cyclic lateral deformations simulating strong earthquake

induced motion. The specimens were then repaired by first removing the

damaged concrete, and either straightening or replacing the buckled

reinforcements by using different schemes. Rheoplastic cement mortar was

then used to restore the damaged portion of the columns to the original

dimensions. The reinforcement was repaired according to different

procedures which can generally be described as follows:

1. Straighten bent or buckled longitudinal rebars by flame

heating

.

2. Straighten bent rebars and add stirrup ties.

29
3 . Cut away portion of bent or buckled rebars and weld in

replacements with and without adding stirrups . The added

stirrups were either single or double hoop ties.

The different repair schemes are shown in Figure 2.51.

The experimental results showed the effectiveness of rheoplastic

mortar for repair of concrete columns. Degradation of lateral stiffness

and strength of the repaired columns was greatly reduced by the addition

of extra stirrups, which helped to prevent buckling of longitudinal

rebars. It was established that lateral strength and ductility of damaged

reinforced concrete columns can be successfully restored by using the

proposed repair schemes. A typical moment -displacement relationship of

a specimen before and after repair is shown in Figure 2.52.

(5) Repaired columns in a concrete frame increase not only the

lateral stiffness but also substantially change the failure mode of the

frame. This latter aspect was investigated by Stoppenhagen and Jirsa

[2.19]. The same 2/3-scale one-bay, two-story concrete frame tested by

Jones and Jirsa [2.8] and Roach and Jirsa [2.10] was used in this testing

program. The general description of the test specimen and the method of

loading have been given in section 2.2.2 [2.8] . The column reinforcement

details are as shown in Figure 2.53. Longitudinal reinforcing steel

consisted of #8 Grade 60 bars. Details of shear reinforcements are shown

in Figure 2.54.

The repair was begun by removing loose concrete from columns and

holes were then drilled on each side of the columns and in the spandrel

beams to accommodate the added stirrups. The longitudinal reinforcements

were then added and tied to the stirrups, and concrete jackets were

vertically cast over the existing columns. Bonding between the new and

old concrete was improved by roughening the existing columns with an

electric concrete hammer. The encased columns increased the depth of the

original columns from 12 in. (30.5 cm) to 30 in. (76 cm) and the width

from 12 in. (30.5 cm) to 20 in. (51 cm).

30
The load-drift relationships for the original undamaged frame and

the frame with repaired columns are shown in Figure 2.55. Final crack

patterns in the encased columns are shown in Figure 2.56. The crack

patterns in the frame clearly indicated that the behavior of the frame

was governed by a flexural failure mechanism in the spandrel beams. It

was also evident from these crack patterns that a point of inflection

developed in the columns. The majority of the flexural cracks in the

columns were concentrated to the top and bottom of the beam- column

joints, while the majority of the diagonal cracks occurred on the

interior face of the columns. The strengthening of columns increased the

strength of the frame against lateral load about five times that of the

original frame, while the initial lateral stiffness of the frame was

about the same as that of the original frame.

2.5 REINFORCED CONCRETE BEAMS:

While there are numerous reports on repair methods for damaged

beams, a limited number of reports on strengthening of beams are found

in open literature. Typically, the strengthening methodology involved

the attachment of steel plates or steel bands to existing beams . The

studies of Holman and Cook [2.20] and Vanek [2.21] are reported in this

section.

(1) Holman and Cook [2.20] evaluated the effectiveness of externally

bonded steel plates on flexural and torsional capacities of reinforced

concrete beams. The test beams were designed to simulate a single bay

spandrel beam with intermediate floor beams framing in at the third

points as shown in Figure 2.57. This type of beam was usually subjected

to a combination of flexural, shear and torsional loads. The test beams

were 4 in. (100 mm) wide and 8 in. (200 mm) deep with an overall length

of 10 ft-6 in. (3.2 m)

.

To simulate floor beams framing into the beams,

two beam stubs were also built into the beams at the third points. The

beams were reinforced with two #6 deformed bars at top and bottom, and

smooth wire of 3/16 in. diameter (5 mm) stirrups were used as web

reinforcements. The beam cross-section is shown in Figure 2.58.

31
The test beams were divided into three groups. Group A beams, the

control group, were tested to failure, and then the damaged beams were

repaired by bonding steel plates to one side of each beam. This repaired

set of beams was designated as Group C. Group B beams had plates

attached prior to testing. Loads were applied through the stubs at

locations 8 in. (20 cm) from the centerline of the beam to produce

torsional load.

For attachment of the steel plates, the concrete surface was first

brushed to remove all loose particles using a stiff bristle brush, and

the steel plate surface was sanded to remove all mill scale. The plates,

8 in. (200 mm) by 36 in. (0.9 m) by 0.25 in. (6.4 mm) thick, were

attached to one side of the beams (see Figure 2.57) using a two-part gel

type epoxy that satisfied the requirements of ASTM C882 Type I.

The test results, presented in Figure 2.59 and in Table 2.12,

indicate that both the strength and stiffness of the beams were enhanced

by this strengthening technique. The repaired beams of Group C exhibited

a gain in ultimate load of 25-40%, while an increase in strength of 35-

45% was observed for the Group B beams. Further, this technique appeared

to have altered the failure mode of these torsionally weak beams. The

observed cracking patterns indicate that all repaired and strengthened

beams (Groups B and C) appeared to have failed in flexure rather than

torsion as in the cases of the Group A's beams. Strong structural

bonding between the steel plate and the beam was noted.

(2) Vanek [2.21] investigated a method of improving the shear

strength of reinforced concrete beams by using externally bonded steel

plates. All specimens had cross sectional dimensions of 4 in. by 6 in.

(100 mm by 150 mm) and had an overall length of 5 ft (1.5 m) . The

specimens initially had insufficient shear reinforcement. They were

divided into three groups.

Group One was comprised of control specimens. Group Two consisted

of beams strengthened by four glued-on steel bands on each side of the

32
specimen. The bands were placed at an angle with the beam axis as shown

in Figure 2.60. Structural bonding betwen the steel band and the

concrete was accomplished by a combination of surface coating with epoxy

adhesive and post- installed dowels. Two steel mandrels of 0.3 in. (8 mm)

diameter, embedded in predrilled holes in the beams and grouted with

either cement mortar or epoxy concrete, served as dowels for each steel

band. Structural bonding between the steel band and the concrete in the

Group three's beams were provided solely by epoxy adhesive.

All beams were centrally loaded by a static concentrated load.

Crack patterns and load-deflection curves are shown in Figures 2.61 and

2.62. The test results show that the shear capacity of concrete beams

can be increased by the bonded external band reinforcement. The

strengthened beams with dowels, Group Two, and the strengthened beams

without dowels, Group Three, showed increased shear capacity of 1.52 and

1.46 times of unstrengthened beams, Group One. A small increase in load

carrying capacity of 5.6% was observed in beams where dowels were used

in addition to surface coating with epoxy adhesive.

33
3. CASE HISTORIES OF REPAIR AND STRENGTHENING TECHNIQUES

3 . 1 INTRODUCTION:

As described in chapter 2, numerous techniques have been proposed

for repair and strengthening of damaged and undamaged reinforced concrete

and masonry structures. These techniques, while different in procedure,

have common objectives:

1. to increase or restore strength, and

2. to increase or restore ductility of existing structural members

or frames

.

In general, reinforced concrete and masonry structural members are

strengthened by adding new load carrying members to the existing

structures. In this chapter, case histories where strengthening of

existing structures or members was done using some of the techniques

described in chapter 2 are presented. Reinforced concrete beams or

concrete beam/column joints have been repaired and strengthened by epoxyinjection or by bonding external reinforcing steel bands or plates onto

the concrete surfaces. Reinforced concrete frames have been strengthened

either with infilled concrete or masonry walls, or with external steel

braces or steel frames. Damaged or understrength reinforced concrete

columns have been strengthened by replacing damaged rebars or adding new

reinforcement and then encasing columns with concrete or mortar jacket.

Reinforced concrete beams or concrete beam/column joints have been

repaired and strengthened by epoxy- inj ection or by bonding external

reinforcing steel bands or plates onto the concrete surfaces.

3.2 COMMON TECHNIQUES

3.2.1 Infill Walls:

Various techniques for infilling open reinforced concrete frames

have been investigated [2. 1,2. 2, 2. 3, 2. 4, 2. 5, 2. 6]. In many cases,

infilled walls are selected primarily to increase lateral stiffness and

ductility of a frame for seismic strengthening. The infilled walls can

either be cast- in-place concrete walls, precast concrete walls, steel

34
panels, or concrete block walls. They are usually connected to the

existing concrete frame through the use of metal shear connectors such

as anchor bolts or, in some cases, epoxy-bonded concrete shear keys.

These joining elements are mostly post- installed anchors and dowels

inserted in pre-drilled holes with epoxy adhesives or epoxy mortar for

grouting. When the number of joining elements are adequately provided,

the lateral load carrying capacity of a frame with infilled wall can

approach that of a monolithic frame -wall system. The general concepts

of the infilling wall technique are illustrated in Figure 3.1.

Infilled walls were used to strengthen the Izumi High School after

the 1978 Miyagi-Ken-Oki earthquake [3.1]. This three-story reinforced

concrete frame building with a narrow rectangular- shaped plan did not

have any shear walls in the transverse direction, and sustained severe

damage to exterior columns . After repairing all damaged columns , shear

walls were added to provide stiffness in the transverse direction. The

following step-by step procedure was used to place cast- in-place infill

walls

:

1. Substrate mortar of columns on the side adjacent to walls was

chipped off.

2. Deformed bars, used as dowels, were installed and grouted by

epoxy adhesive into columns and beams above and below the walls

(see Figure 3.2).

3. Wall reinforcement was placed and spliced to dowels and followed

by placement of concrete.

4. Non- shrink mortar was pumped into the gaps between the walls and

beams above

.

A simple numerical analysis of the building estimated that the

lateral load carrying capacity of the Izumi High School building after

strengthening increased to 0.75 times of the weight of the building, 1.5

times higher than the original undamaged strength.

35
3.2.2 Steel Braces:

In addition to increasing lateral stiffness, steel braces are

effective in increasing the ductility of concrete frames. Various

schemes such as external steel frame bracing, in-plane compression cross

bracing, and in-plane tension cross bracing have been investigated

[ 2 . 2 , 2 . 3 , 2 . 7 , 2 . 8 ]

.

The main buildings of the Tohoku Institute of Technology in Sendai,

Japan [3.2] were strengthened using specially designed steel braces after

it sustained severe damage from the 1978 Miyagi-Ken-Oki earthquake.

Steel cross braces were installed on both faces along the longitudinal

direction of the eight- story reinforced concrete frame building. The

braces were installed with an eccentricity from the surface of the

exterior wall as shown in Figure 3.3.

This eight- story concrete frame building sustained shear and shearbending failure of columns on the north side of the building due to

lateral forces in the longitudinal direction. The column failures were

caused by the weakness in the lateral stiffness of the building in the

longitudinal direction and the influence of the infill spandrel walls.

The cast- in-place infill spandrel walls (see Figure 3.4) increased the

stiffness of the frame, thereby attracting large shear forces to the

columns

.

Strengthening of this damaged building consisted of repairing

cracked columns, beams, walls and slabs, and adding new shear walls in

the transverse direction. To reduce the adverse effect on the columns

due to the infill spandrel walls, holes were drilled in these spandrel

walls to weakened the walls. In the longitudinal direction, steel cross

braces were attached to both faces of the building from the outside. The

brace members were H-sections of weathering steel and were painted with

a rust stablizing agent. The steel braces system was selected because:

1. It would not interupt natural lighting through windows,

2. Installation of braces would not disrupt use of the building,

36
3. Uniform distribution of braces could be selected to eliminate

undesired concentration of shear forces.

The joining elements that provide the brace - to - frame connections

were specially designed. Brace members were fastened by friction bolts

to steel bases which were set against the reinforced concrete beam face.

After filling the gap between the base and the concrete beam with cement

mortar, the steel base was post- tensioned by prestressing steel rods

inserted through bored holes in the concrete beams (see Figure 3.5).

3.2.3 WingWalls

:

Adding wingwalls adjacent to existing columns is another technique

of seismic strengthening of existing building. The wingwalls can either

be cast- in-place or precast concrete walls. The cast- in-place wingwalls

are monolithically cast over existing columns or frames. Surface coating

of epoxy adhesives, in combination with dowels installed in the existing

frame, can be used to provide composite action between the existing frame

and the newly cast wingwall. Precast concrete wingwalls can be attached

to the existing frame with dowel connectors. With adequate connections,

cast- in-place wingwalls can provide as much lateral strength as the

monolithic construction. The addition of precast wingwalls usually

results in less strength but more ductility. The concepts of adding

wingwalls are shown in Figure 3.6.

An example of the application of this technique for retrofitting a residential building in Tokyo is described in detail in Ref 3.3. A fourstory building was strengthened to improve both the strength and

stiffness of the longitudinal frames and to improve ductility of all

columns. Cast- in-place wing walls were attached to columns by means of

mechanical anchors (see Figure 3.7).

3.2.4 Encased Columns:

Encasing a column with a layer of reinforcement and concrete has

been the most common method of strengthening reinforced concrete columns.

This technique has been proven by laboratory experiments to be an

37
effective method to increase strength and ductility of columns

[2.1,2.16,2.17,2.19]. Additional reinforcement can be either vertical

rebars with stirrups, welded wire fabric, or steel straps wound around

the column. The column is then encased by a jacket of either shotcrete,

in- situ concrete, or non- shrink mortar. A coat of epoxy adhesive can be

applied on the surface of the existing column to provide better bonding.

Work by Nene [3.4] applied this technique to repair and strengthen

damaged columns. The damaged columns were first stripped of all

finishing materials and thoroughly washed with a powerful water jet.

Vertical rebars were welded to the beam reinforcement connected to the

column, and new #6 spiral reinforcement was then tied around the column.

A coat of suitable epoxy grade was then applied prior to encasing each

column with a 3-in (76-mm) thick jacket of in-situ concrete. The epoxy

coat served two purposes: one was to provide structural bonding between

the new and the old concrete; the second was to prevent the trapped

moisture in the existing concrete from attacking the new concrete from

inside. Figure 3.8 shows the details of the typical column repaired and

strengthened by this technique.

3.2.5 Epoxy Bonded Reinforcement

:

The steel-epoxy-concrete system has been applied for repair and

strengthening of reinforced concrete beams. Experimental studies of using

epoxy bonded steel plates for strengthening in shear and torsion have

been presented in section 2.5. Insertion of conventional rebars in predrilled holes that intersect diagonal crack planes in beams with epoxy

injection has proven to be successful.

The Kansas Department of Transportation has carried out shear

strengthening of cracked concrete bridge girders using this technique

[3.5]. The technique, known as "post-reinforcement", consists of the

following steps:

38
1. Sealing of the surface of cracks using silicone sealant;

2. Vacuum drilling dust- free holes 6 in. apart and 45° to the

deck surface, thereby crossing crack planes at 90° angle;

3. Filling the holes and crack plane with epoxy pumped under

low pressure; and,

4. Inserting the reinforcing bars into the holes to span the

crack by at least 18 in. (46 cm) . Epoxy bonds the bar to

the wall of the hole and fills the crack plane. The 6 in (15

cm) spacing between holes was selected to ensure that cracks

would be intersected by at least one post- installed rebar.

This technique for repair and strengthening of concrete bridge deck

beams and girders has been used to repair and strengthen over 20 bridges

in Kansas since 1981.

An apartment building in Brussels, Belgium was damaged in 1982 due

to gas explosion [3. 5, 3. 6], and subsequently repaired using epoxy bonded

steel plates. During the first phase of the explosion, the ceiling

concrete slab was loaded upward by the overpressure, and during the next

phase, it was loaded downward by underpressure. As a result, the

concrete ceiling slab sustained large deflections, the maximum deflection

was 2 in (51 mm) . In addition, the concrete was severely damaged by

fire

.

For repair and strengthening, the slab was first lifted to the

horizontal position. The damaged concrete was then removed to expose the

clean, sound, concrete surface. Cracks were then filled by pressure

injected epoxy resin prior to replacing the removed unsound concrete by

epoxy mortar. Steel plates of 0.2 in. by 9 . 8 in. (0.5 cm by 25 cm) were

bonded to the underside of the slab at approximately 2.5 ft (0.8 m) on

centers. Epoxy mortar was used to cover the steel plates. The temporary

support was removed after 7 days of epoxy curing, at which time the slab

deflected about 0.2 to 0.3 in. (5 to 7 mm). These deflections

corresponded to the calculated values.

39
Two possible drawbacks should be pointed out regarding the

application of epoxy resin adhesives. Fire exposure tests of about 200

concrete beams [3.7], cracked by static concentrated load and repaired

by epoxy injection, showed that both strength and stiffness of epoxy

repaired beams reduced rapidly at uniform temperatures exceeding about

250°F. This is because epoxy adhesives are organic thermosetting resin

systems and thus are highly susceptible to softening and pyrolysis at

elevated temperatures. Exposure tests of beams externally reinforced by

epoxy-bonded steel reinforcement and left exposed to the environment for

2 years [3.8] showed that long term exposure in natural condition could

lead to eventual reduction in strength of the exposed beams. The small

overall reduction in strength of the two -years beams was attributed to

the significant amount of corrosion of the steel plate at the steel/resin

interface, which resulted in deterioration of bond between concrete and

the external steel reinforcement. Corrosion appears to be due to

migration of moisture from the concrete through the resin. Microcracking

of the resin has also been observed in samples of broken pieces of resin

extracted from the tested beams.

40
4. SUMMARY AND AREAS OF NEEDED RESEARCH

4.1 SUMMARY:

Numerous research studies on the repair and strengthening of

different structural elements and frames, including reinforced concrete

and steel frames, concrete and masonry walls, and concrete columns and

beams, are reviewed in this report. The majority of these studies dealt

exclusively with restoring or improving seismic resistance of concrete

structures. For each type of structural elements, unique repair and

strengthening techniques were proposed.

Strengthening of reinforced concrete or steel portal frames usually

involves one of the following three techniques: infilled shear walls,

steel bracing, or adding wingwalls . Increased lateral stiffness,

ductility, and resistance to lateral loads are attained by these

techniques. In terms of improving lateral load resistance, infilling the

frame with walls was found to be most effective. The lateral load

resistance of frame infilled with either cast- in-place or precast

concrete walls could attain that of the monolithic wall/frame system when

adequate connections between the existing frame and the infilled wall are

provided.

The steel bracing technique can provide the concrete frames with a moderate increase in lateral stiffness and load resistance when compared

with the infilling technique. However, the steel bracing technique is

most suitable if the improvement in ductility is the primary concern.

The effectiveness of the steel bracing technique, when represented in

terms of the antiseismic cabability index Cg as defined in references,

can be as large as that of monolithic wall/frame system.

Adding wingwalls provides the least increase in lateral stiffness

and force capacity as observed in Higashi, Endo and Shimizu's study.

However, this method can be successfully employed in altering the failure

mechanism in a strong beam-weak column frame. The added lateral

41
stiffness provided to the columns by cast- in-place wingwalls effectively

changed the failure mechanism of a frame from shear failure in columns

to flexural failure in spandrel beams.

Reinforced concrete or masonry walls can be strengthened by adding

reinforced concrete or mortar overlays to the walls. The in-plane shear

capacity of brick wall panels with reinforced shotcrete overlay can be

increased substantially even with a moderate amount of reinforcement.

Both the out-of-plane and the in-plane lateral force capacities of

masonry walls can be increased by filling vertical cored holes with

rebars grouted with different types of filling materials. Large cored

holes (4 in. -diameter) with sand/epoxy as filler material proved to be

superior in providing masonry walls with increased lateral force

capacity.

For reinforced concrete columns, many different encasing techniques

were proven to be effective in providing concrete columns with added

strength and ductility. Significant increase in ductility may be

obtained using welded wire fabrics, while shear strength can be increased

by confining the concrete core using steel bands or steel straps.

Strengthening of reinforced concrete beams usually requires bonding

of external steel reinforcements such as steel plates, steel angles or

deformed reinforcing rods to the existing beams. Both the shear and

torsional strengths of reinforced concrete beams can be greatly

increased using this technique. Repairing cracked concrete beams with

reinforcing bars secured in concrete beam by epoxy- inj ection have shown

to be effective in increasing the shear capacity.

4.2 AREAS OF NEEDED RESEARCH:

The success of strengthening concrete structures is critically

dependent on the interaction between the new and existing elements. This

interaction is provided by different types of post- installed shear

connectors and/or epoxy adhesives. For frame or wall strengthening,

42
shear connectors range from precast concrete shear keys to conventional

mechanical or epoxy- grouted anchors.

Experiments have shown that when a sufficient number of connectors

are used, the full capacity of the reinforcing elements can be mobilized

[2.8], On the other hand, when an insufficient number of connectors are

used, a significant drop in the load carrying capacity of strengthened

members was observed while no damage occurred to the reinforcing

elements. This was due primarily to pullout or shear failure of

connectors. These observations clearly demonstrate the importance of the

relationship between the capacity of the joining elements and the overall

capacity of the strengthened structures. For example, Sugano and

Fuj imura showed that the connection between the top beam and the infilled

wall must have the shear strength of at least 10 kg/cm^ in order to

develop the lateral load capacity equal to 60 percent of that of the

equivalent monolithic wall/frame system. To develop 100 percent, the

O connection must have the shear strength of 20 kg/cm . It is apparent

that understanding this relationship is crucial both in estimating the

capacity of a structure after strengthening and in developing an optimum

strengthening scheme. A more thorough and systematic examination of this

relationship is needed to develop guidelines for the design of

strengthening methodologies. To develop such guidelines, knowledge on

the following is essential:

1. Strength and deformation behavior of joining elements, including

mechanical anchors, epoxy-grouted dowels and epoxy adhesives,

in cracked and uncracked concrete. This can only be achieved

through a comprehensive experimental program.

2. The relationship between the strength of anchors and the overall

capacity of strengthened structures. The theoretical model

should be developed with substantiation of data obtained from

testing of anchors.

3. A quantitative assessment of the effectiveness of various

strengthening techniques that are deemed practical for field

application in improving the load carrying capacity and

43
ductility of reinforced concrete members and frames. Such

assessment can be acquired through a comprehensive experimental

program in strengthening methodologies. This assessment,

coupled with knowledge on behavior of anchors, can be used to

establish an empirical approach which will enable the designer

to accurately predict the strength and behavior of a strengthened structure.

44
5. REFERENCES

1.1 "Guideline for Structural Assessment" Rehabilitation

Guidelines 1982, U.S. Department of Housing and Urban

Development, National Institute of Building Sciences,

Washington D.C.

2.1 T. Hayashi , H. Niwa and M. Fukuhara. "The Strengthening Methods

of Existing Reinforced Concrete Building" , Proceedings of the

Seventh World Conference on Earthquake Engineering, September

1980, Istanbul, Turkey, p.p. 89-96.

2.2 S. Sugano and M. Fujimura. "Aseismic Strengthening of Existing

Reinforced Concrete Buildings", Proceedings of the Seventh

World Conference in Earthquake Engineering, September 1980,

Istanbul, Turkey, p.p. 449-456.

2.3 Y. Higashi, T. Endo and Y. Shimizu. " Experimental studies on

Retrofitting of RC Structural Members." Proceedings of the

Second Seminar on Repair and Retrofit of Structures. Ann

Arbor, Michigan. May 1981. p. 126-155.

2.4 L.F. Kahn. "Reinforced Concrete Infilled Shear Walls For

Aseismic Strengthening", UMEE 76R1, Dissertation, Department

of Civil Engineering, the University of Michigan. Jan 1976.

2.5 M. Makino , A. Kawano , Y. Kurobane , M. Saisho, and K. Yoshinaga.

"An Investigation for the Design of Framed Structures with

Infill Walls .Proceedings of the Seventh World Conference on

Earthquake Engineering, September 1980, Istanbul, Turkey, p.

369-372.

45
2.6 D.V. Mallick. " Infilled Frame Construction in Seismic

Regions." Proceedings of the Seventh World Conference on

Earthquake Engineering, September 1980, Istanbul, Turkey, p.

486-492.

2.7 Y. Higashi, T. Endo and Y. Shimizu. "Effects on Behaviors of

Reinforced Concrete Frames by Adding Shear Walls", Third

US/Japan Seminar on Repair and Retrofit of Structures, San

Francisco, May 13-15 1982. p.p. 265-290.

2.8 E.A. Jones and J.O. Jirsa. "Seismic Strengthening of a Reinforced Concrete Frame Using Structural Steel Bracing"

,

PMFSEL Report No. 86-5, The University of Texas at Austin, May

1986.

2.9 T.D. Bush, C.E. Roach, E.A. Jones and J.O. Jirsa. "Behavior of

a Strengthened Reinforced Concrete Frame." Third US National

Conference on Earthquake Engineering, Vol. 2, 1986, pp . 1203-

1214, Charleston, South Carolina.

2.10 C.E. Roach and J.O. Jirsa. "Seismic Strengthening of a Reinforced Concrete Frame Using Reinforced Concrete Piers",

PMFSEL Report No. 86-4, The University of Texas at Austin, May

1986.

2.11 American Concrete Institute. " ACI 318-83", Box 19150, Redford

Station, Detroit, Michigan. November 1983.

2.12 W.G. Corley, A.E. Fiorato, R.G. Oesterle, and A. Scanlon.

"Evaluation, Repair, and Strengthening of Reinforced Concrete

Building." Proceedings of the US/PRC Workshop on Seismic

Analysis and Design of Reinforced Concrete Structures. Ann

Arbor, Michigan. May, 1981. p. 227-251.

46
2.13 J. Plecnik, T. Cousins and E. O'Conner. "Strengthening of

Unreinforced Masonry Buildings", Journal of Structural

Engineering, Vol. 112, No. 5, May, 1986. p.p. 1070-1087.

2.14 M. Jabarov, S.V. Kozharinov, and A. A. Lunyov. " Strengthening

of Damaged Masonry by Reinforced Mortar Layers." Proceedings

of the Seventh World Conference on Earthquake Engineering,

September 1980, Istanbul, Turkey, p. 73-80.

2.15 Kahn, L.F., "Shotcrete Strengthening of Brick Masonry Walls",

ACI Concrete International, Vol. 6, No. 7, July 1984.

2.16 L.F. Kahn. "Strengthening of Existing RC Columns for Earthquake

Resistance" . Proceedings of the Seventh World Conference on

Earthquake Engineering, September 1980, Istanbul, Turkey, p.p.

327-334.

2.17 B.J. Bett, R.E. Klingner and J.O. Jirsa. "Behavior of

strengthened and Repaired Reinforced Concrete Columns under

Cyclic Deformations", PMFSEL Report No. 85-3, The University

of Texas at Austin, December 1985.

2.18 G.Augusti, F. Focardi, S. Giordano and E. Manzini.

"Rehabilitation of Damaged Reinforced Concrete Elements: An

Experimental Investigation" , Proceedings of the Seventh World

Conference on Earthquake Engineering, September 1980, Istanbul,

Turkey, p.p. 335-342.

2.19 D.R. Stoppenhagen and J.O. Jirsa. "Seismic Repair of a Reinforced Concrete Frame Using Encased Columns", PMFSEL Report

No. 87-2, The University of Texas at Austin, May 1987.

2.20 J.W. Holman and J.P. Cook. " Steel Plates for Torsion Repair

of Concrete Beams". Journal of Structural Engineering,

Vol. 110, No . 1

,

Jan. 1984, American Society of Civil Engineer.

47
2.21 T. Vanek, "Shear Strengthening of Old Concrete Beams", CI/SfB

(2q)f(x7) UDC 691.32-421.

2.22 H. Shiohara, Y. Horokawa, T. Nakamura, and H. Aoyama. " Earthquake Strengthening Method of Existing Reinforced Concrete

Buildings". Transactions of the Japan Concrete Institute, Vol.

6, 1984. pp. 725-732.

2.23 H. Aoyama, Y. Yamamoto. "Aseismic Strengthening of Existing

Reinforced Concrete Buildings by Steel Panel Shear Walls With

Rims". Transaction of the Japan Concrete Institute, Vol. 6,

1984. pp. 733-740.

3.1 M. Yokoyama and H. Imai. "Earthquake Damage At Izumi High

School in 1978 Miyagi-Ken-Oki Earthquake and Methods of Repair

and Strengthening" , Proceedings of the Seventh World Conference

on Earthquake Engineering, September 1980, Istanbul, Turkey.

p . p . 81- 88

.

3.2 S. Kawamata and M. Ohnuma. "Strengthening Effect of Eccentric

Steel Braces to Existing Reinforced Concrete Frames",

Proceedings of the Seventh World Conference on Earthquake

Engineering, September 1980, Istanbul, Turkey, p.p. 513-520.

3.3 M. Hirosawa, Y. Kitagawa and Y. Yamazaki. "Retrofitting of

Medium-Rise RC Housing Structures." Proceedings of the Second

US/Japan Seminar on Repair and Retrofit of Structures,

Michigan, May, 1981.

3.4 R.L. Nene . "Repairs and Restoration of Reinforced Concrete

Columns". ACI SP-85, Rehabilitation, Renovation, and

Preservation of Concrete and Masonry Structures, 1985. p.p.

SP85-12 259-263.

48
3.5 R.P. Webster and L.E. Kukacka. " In-situ Repair of Deteriorated

Concrete in Hydraulic Structures: Feasibility Study."

Technical Report REMR-CS-6, U.S. Army Engineer Waterways

Experiment Station.

3.6 V.D. Gemert and R. Maesschalck. "Structural Repair of a Reinforced Concrete Plate by Epoxy-bonded External

Reinforcement." Int. J. Chem. Compos. Lightweight Concrete,

p.p. 247-255, 1983.

3.7 Joseph M. Plecnik et al .

,

"Preliminary Report on Experimental

Testing of Epoxy Repaired Concrete Beams", Third US/Japan

Seminar on Repair and Retrofit of Structures, San Francisco,

May 13-15, 1982, p.p. 32-55.

3.8 A.J.J. Calder, "Exposure Tests on Externally Reinforced

Concrete Beams-First Two Years", Supplementary Report 529,

Transport and Road Research Laboratory, Department of the

Environment, Department of Transport, Crowthorne, Berkshire,

1979.

List Of References By Topics:

o. Beam Strengthening :

o. Column Strengthening:

o. Wall Strengthening:

o. Frame Strengthening:

2.20, 2.21, 3.5, 3.7, 3.8.

2.1,

2.16, 2.18, 2.19, 3.4.

2.12, 2.13, 2.14, 2.15.

2.1, 2.2, 2.3, 2.4, 2.5, 2.6,

2.7, 2.8, 2.9, 2.10, 2.22, 2.23,

3.1, 3.2, 3.3.

49
Table 2.1 Sugano and Fujimura's test specimens [2.2].

Specimen

Initial

Stiffness

*1

Load C<Q»

*1

ipacity

i *3

*2

Displacement

at Qu

(x lO

- -^ rad.)

Ultimate

Displacement

(x 10~^ rad.)

*4-

Energy

Absorption

(ton x cm)

*5

F 1.0 1.0 17.7 28.6

W-80S 22.0 5.6 1.00 4.2 8.7 241

W-40S 13.7 4.1 0.73 4.2 4.7 99

W-HA 24.0 5.5 0.98 6.7 9.5 227

W-CO 25.5 4.9 0.87 4.2 9.6 212

W-40W 26.3 4.9 0.87 3.1 4.5 234

W-BL 7.3 3.5 0.62 7.4 10.0 130

W-S 11.8 4.3 0.77 6.1 8.8 182

B-C 6.5 3.5 0.62 4.0 >10.0 114

B-T

J 5.7 3.7 0.66 7.9 >10.0 255

*1 Ratio to Frame F *2 Ratio to Frame W-80S *3 Mean of peak loads

*4 Displacement at the load 0.8 x Qu *5 Cumulative area of hysteresis

loops until the displacement 0.01 rad.

Table 2.2 Summary of Sugano and Fujimura's test results [2.2].

50
1977

TEST SERIES

No . 1 - FI Bare, unstrengthened one-bay, one-story

concrete frame.

No. 2-PW One-bay, one-story frame strengthened by

cast- in-place infilled walls, connected by

9mm. dia. wedge anchors, spaced at 120mm.

intervals along the top and bottom beams.

No. 3-C3

i

Infilled by three precast concrete panels,

connected to top and bottom beam by wedge

anchors

.

No. 4-C3C Infilled by three precast concrete panels

with shear cotter, connected to top and

bottom beam by wedge anchors.

1978

TEST SERIES

No. 1-F2 Unstrengthened one-bay, one-story reinforced

concrete frame identical to specimen 77-1

(FI).

No. 2-SP Both columns were reinforced by adding

steel plates on the two sides of the

columns that are parallel to the frame

plane. The steel plates were epoxy-bonded

and bolted to columns by pairs of wedge

anchors spaced at 90mm. intervals along

the column height.

No. 3-C2A

1 Partially infilled frame with two precast

concrete walls, attached to frame at locations next to columns by wedge anchors.

No. 4-C2B Partially infilled frame with two precast

concrete walls at the center, leaving two openings next to columns.

1 No. 5-C4 Completely infilled frame with 4 precast

concrete panels, connected to frame by

wedge anchors .

,

No. 6-C40 Completely infilled frame with 4 precast

concrete slit walls, also connected by

wedge anchors.

No. 7 - SB Strengthened by steel bracing with brace

members bolted to steel sections that are anchored into frame by wedge anchors

.

1

1 No. 8-SF Strengthened by steel frame

No. 9 - ST

1 Strengthened by steel truss placed at center of frame and anchored into top and

bottom beam using wedge anchors.

No. 10- FW Monolithic wall/frame system.

i

Table 2.3 Descriptions of Higashi, Endo and Shimizu's frames [2. 3, 2. 7],

51
1979

TEST SERIES No. 1-3F

| Three-story, one -bay reinforced mortar frame

,

unstrengthened

.

No. 2-3PV

|

1 Strengthened by infilling all three

stories with cast- in-place concrete walls,

50mm. thick, and connected to frame using

pairs of 6mm. -dia. wedge anchors placed at 40mm. intervals at top and bottom beams.

No. 3-3C2A Strengthened by partially infilling each

story by two precast concrete panels at locations next to columns.

1

No. 4-3C4 Strengthened by complete infilling each

story by four precast concrete walls,

anchored to top and bottom beams using

pairs of 6mm. diameter.

No. 5-3C40 Strengthened by infilling each story with

four precast concrete slit walls, anchored

to top and bottom beams by wedge anchors

.

No

.

6-3SB Strengthened by adding steel bracing into

all three stories.

No. 7-3SF

i Strengthened by adding steel frame into all

three stories.

No. 8-3FW Monolithic wall/frame system.

1981

.TEST SERIES

No. 1- 3F2 Unstrengthened three-story, two-bay

reinforced mortar frame.

No. 2-3PW2 Strengthened by infilling all stories and

all bays with 50mm. thick cast- in-place

concrete walls. 6mm. dia. wedge anchors,

spaced at 40mm. intervals were used in

connecting the infilled walls to top and

bottom beams of each story.

No. 3-3C2A2 Strengthened by partial infilling each

story and each bay by cast- in-place wing

walls, connected to frame by 6mm. dia.

wedge anchors, spaced at 40mm. intervals.

No. 4-3FU2 Monolithic three-story, three -bay wall/frame

system, with wall reinforcement anchored

into frame

.

-

52
•

SPE

77 series 78 series

No. 1 No. 2 No. 3 No. 4 No. 1 No. 2 No. 3 No. 4 No . 5 No . 6 No . 7 No. 8 No. 9 No. 10

INITIAL STIFFNESS .ton

XlC? N/cm an 2.18

(22.2)

44.6

(445.0) 13.3

a 36.0)

18.8

0.92.0) 2.53

(25.8)

2.99

(30.5)

13.9

Q.41.3)

7.82

(79.7)

48.3

(492.5) 14.10.44.1) 7.27(74.1)

4.29

(43.7)

3.68

(37.5!

58.8

600.0)

YIELDING

POINT

load Xld1 N Qy (ton)

9.4

(9.6)

39.2

(40.0)

19.6

(20.0)

43.1

(44 .0) 9.1(9.3)

9.8

(10.0)

12.6

(12.8)

9.3

(9.5)

39.0

( 39 . 8) 9.6(9.8)

17.3

(17.6)

16.1

(16.4)

14.5

(14.8)

49.0

(50.0)

deflection

<5y ( an) 1.15 0.47 0.45 0.86 0.96 1.00 0.50 0.50 0.50 0.20 0.48 0.76 0.77 0 .5 1

!

]

MAXIMUM

load X10

1* N Qmax (ton)

10.5

(10.7)

39.2

(40.0) 32.4(33.0)

45.1

(46.0)

10.9

(11.1)

11.5

(11.7)

15.4

(15.7)

14.2

(14.5)

39.2

(40.0)

15.7

(16.0)

25.6

(26.1)

25.7

(26.2)

18.2

(18.6)

56.9 1 (58.0)

deflection

6ro (an)

1.65 0.47 1.89 1.03 1.95 2.00 2.00 2.00 0.73 2.00 3.54 4.00 1.97 0.87

ULTIMATE

load Xld* N Qu (ton)

10.5

(10.7)

35.3

(36.0)

32.4

(33.0)

45.1

(46,0)

10.9

(11.1)

11.4

(11.6)

13.8

(14.1)

12.9

(13.2) 39.2

(40.0)

15.1

(15.4)

25.6

(26.1)

24.9

(25.4) 18.2(18.6)

56 .9 (58.0)

deflection

6u ( an) 1.65 0.73 1.89 1.03 1.95 3.52 3.35 2.56 0.73 4.00 3.54 5.50 1.97 0.87

CE 0.61 2.18 3.74 2.26 0.81 1.19 2.07 1.67 2.31 4.01 4.03 3.88 1.57 3.75

(a)

79 Series

Specimen

No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 No . 7 No. 8

Initial Stiffness

x 10

s N/an (ton/an)

0.59

( 6 ) 14.71( 150 ) 1.27

( 13 ) 4.41

( 45 ) 5.39

( 55 ) 4.41( 45 ) 3.43

( 35 ) 15.20

( 155 )

YIELDING

POINT

load x 10" N Qy (ton)

1.03

(1.05)

7.44

(7.59)

1.44

(1.47)

4.18

(4.26)

3.38

(3.45)

6.03

(6.15)

4.71

(4.80)

7.44

(7.59)

deflection

6y mm

2.2 2.3 2.1 5.2 2.0 4.4 4.4 2.9

I

MAXIMUM

load x 10

15 N Qmax (ton)

1.91

(1.95)

8.47

(8.64)

2.97

(3.03)

5.74

(5.85)

5.12

(5.22)

7.80

(7.95)

5.97

(6.09)

8.47

} (8.64) !

| deflection

6m mm

9.4 7.0 16.8 21.2 14.9 12.0 18.8 7.0

ULTIMATE

load x 10 4 N Qu (ton)

1.91

(1.95)

8.15

(8.31) — 5.74

(5.85)

5.00

(5.10)

7.65

(7.80) — 8.12

(8.28)

deflection

6u nun 9.4 9.8 20.0 21.2 17.8 15.1 20.0 9.0

0.89 3.80 2.15 2.61 3.48 ^3.15 2.89 3.15

1 _

(b)

Table 2.4 Summary of Higashi , Endo and Shimizu's test results [2. 3, 2.7].

a) 1977,78 series.

b) 1979 series.

c) 1981 series.

53
Specimen

81-No. 1 79 81- No.

2

79 81- No.

3

79 81- No.

4

79

P N No.l P N No.

2

P N No.

3

P N Ko.S

Initial Stiffness

Kc (ton/cm) 37 • 6 2S0 ISO 63 13 273 1SS

Yield

load

Py (ton) 2.6 1.1 12.8 7.6 S.2 l.S 13.6 7.6

deflection

iy (mm) 3.S 2.2 3.S 2.3 4.0 2.1 3.5 2.9

Maximum

load Pm (ton) 3.4 3.4 2.0 12.8 11.1 8.6 6.7 6.4 3.0 14.0 11.2 8.6

deflection

im (mm) 1S.1 7.0 9.4 S.J 6.8 7.0 11.1 7.0 16.8 S .3 3.S 7.0

Ultimate

load Pu (ton)

- 12.0 8.3 6.4 - 13.7 8.3

- deflection

6u (mm)

- 7.0 9.8 12.6 - 6.9 9.0

N.8. P ; positive loading

N ; negative loading

(C)

54
Specimens Qi

(ton)

R i (•10-J)i Qu

(ton)

Ru (-10-3)

AO

A1 10.6 1.34 44.4 13

A2 12.4 1.03 34.9 13

BO

81 17.8 2.10 33.0 12

B2 15.0 1.60 31.4 30

QiQu“

RiRuinitial crack load

ultimate load

lateral displacement to height

lateral displacement to height

ratio at Initial crack load

ratio at ultimate load

Table 2.5 Summary of Makino's test results [2.5].

Specimen

Confined

Boundary

Element

Axial

Load pel

ACI Design Pull Yield Load Maximum Load

Failure Modi4 * Flexure Sheer Calculated Observed Obs. Calculated 121 Observed Obs. Obs.

kips /F (11 C kips kipa JTC kips JT

C

Calc. kips JT

c kips JTC Calc. AC I 131

B5 Yes — 129 6.6 127 6.5 123.1 6.3 138.0 7.1 1.12 213.7 11.0 171.3 8.8 0.80 1.33 WC

BS1 Yes - 129 6.8 127 6.7 123.1 6.5 - - - 213.7 11.5 167.8 8.9 0.79 1.30 MC

B9 *« 545 173 9.0 148 7.7 165.6 8.6 186.4 9.7 1.13 241.6 12.6 219.6 11.4 0.91 1.48 WC

B9R Yes 450 173 5.6 162 5.2 165.6 5.3 - - - 241.

«

7.7 218.7 7.0 0.91 1.35 wc

BIX Yes - 129 6.1 in 6.0 122.4 5.8 141.7 6.7 1.16 210.1 9.9 163.3 7.7 0.78 1.29 wc

Bilfi Yes - 129 6.8 180 9.5 122.4 6.5 - - - 210.1 11.1 171.0 9.1 0.81 1.33 wc

(1) Lateral load in terae of nominal shear streee v • v-- - (pel) o.8i b/r

V C

(2) Calculated monotonic flexural strength from analysis baaed on strain compatibility using measured material properties including strain hardening

of reinforcement.

(3) ACX taken as the lamer of flexure or sheer design strength with capacity reduction factor 4 1*0.

(4) HC ° Web Crushing _

1 kip 4.448 kM, 10 JT (pal) • 0.08304/T (MPa) c c

Table 2.6 Summary of Corley et al's test results 2 . 12 ]

.
Shotcrete Cracking load Ultimate load Surface thickness on diagonal' on diagonal' Specimen condition (in.)* Reinforcement (kips)* (kips)*

Cl 6.2 6.2 0 0 CC1 - - - 18.00

18.00 D1 dry 3.1 wwf* 87.4

60.2

121.8

84.2 D2 dry 3.8 wwf 83.9

61.7

147.6

82.2 D3 dry 3.4 wwf 92.3

72.8

131.9 111.6 El epoxy 3.1 wwf 76.6

58.8

121.8

103.5 E2 epoxy 3.8 wwf 75.7

87.4

133.9

104.5 E3 epoxy 3.8 wwf 79.1 45.5

138.0

100.4 W1 wet 3.4 wwf 76.5

83.2

142.0 85.3 ]W2 wet 3.9 wwf 82.2

38.1

148.1 106.5 W3 wet 3.5 wwf 87.8

58.1

150.2 87.3

! X1 wet 1.5 exp. met.} 65.0 22.5

67.0

69.0 X2 wet 1.5 exp. met

59.0 1 39.5

61.0

47.5 X3 wet 1.4 exp. met.

50.0

22.0

52.0

41.0

*1 in. - 25 mm. 1 kip » 4.5 kN.

"Top value indicates load across original diagonal. Lower value is the reversed cycle load across second diagonal. WF 6 x 6 - W4 x W4.

~ (Expanded metal.

Table 2.7 Kahn's brick masonry test results [2.15].

56
Sample number

(1)

Typed

grout*

(2)

Type ot mortar*

(3)

Shear stress over gross area (Ibs/sq In.) (4)

Average lor group

(Ibs/sq In.)

(5)

1 1, 1/10, 3 1. 1/4, 3 171.1 2 1. 1/10, 3 1. 1/4. 3 153.1 —

3 1, 1/10, 3 1, 1/4, 3 142.2 155.7 4 1, 1/4, 3 1. 1/4. 3 93.8 —

1 > 1, 1/4, 3 1. 1/4. 3 78.1 —

6 1, 1/4. 3 1. 1/4, 3 185.9 —

7 1, 1/4, 3 1, 1/4, 3 150.8 —

8 1. 1/4. 3 1, 1/4, 3 107.0 123.1 9 1, 1/8, 1.5 1. 1/4, 3 160.9 —

10 1. 1/8, 1.3 1. 1/4. 3 56.3 —

11 1, 1/8, 1.5 1, 1/4, 3 56.3 —

12 1. 1/8, 1J 1, 1/4, 3 127.3

13 1, 1/8, 1.3 1. 1/4. 3 213.3 122.8

14 1, 1/8. 1 1, 1/4, 3 160.9 —

13 1, 1/8, 1 1, 1/4, 3 .; 160.9 —

16 1, 1/8. 1 1, 1/4, 3 112.5 —

17 1, 1/8. 1 1. 1/4, 3 150.8 —

18 1. 1/8. 1 1, 1/4, 3 246.1 166.2 Cement, lime, sand proportions by volume.

Note: I psi • 6.89 IcN/m1.

T Sand/ ShMT tutu Average luf l Sample polyester Type ol over gross group number proportions* mortar* area (Ibs/sq In.) (bs/sq In.) (D (2) (3) (4) (5)

1 2/1 1/6, 1/4. 3 350.0 —

2 2/1 1/6, 1/4, 3 262.5 —

3 2/1 1/6, 1/4. 3 306.3 —

4 2/1 1/6. 1/4, 3 181.3 275 0

3 2/1 1. 1/4, 3 160.9 —

6 2/1 1. 1/4. 3 204.7 —

7 2/1 1. 1/4, 3 160 9 —

8 2/1 1. 1/4. 3 204.7 182.8

Tolyester/sand proportions by volume.

“Cement, lime, sand proportions by volume.

Note: 1 psi ~ 6.89 kN/m1

.

Table 2.8b Shear strength of sand/polyester

grout specimens [2.13],

Table 2.8a Shear strength of cement

grout specimen [2.13].

Sample number 0)Typed

epoxy

(2)

Type d mortar*

(3)

Shear street over gross

area (bs/sq In.) (4)

Average

lor group

flbe/aq in.) (5)

1 I 1. 1/4, 3 191.4 2 I 1, 1/4. 3 246.1 218.8 3 a 1, 1/4, 3 196.3 —

4 n 1. 1/4, 3 171.1 183.7 5 m 1/9, 1/12. 3 256.3 i 6 m 1/6, 1/4, 3 150.8 —

7 m 1/6, 1/4, 3 246.1 .j 8 m 1/6, 1/4, 3 246.1 —

9 m 1/3, 1/4. 3 171.1 214.1 10 IV 1/9, 1/12, 3 246.1 246.1

11 V 1/9, 1/12. 3 204.7 1 12 V 1/9, 1/12, 3 204.7 —

13 V 1/9, 1/12. 3 137.5 182.3 Cement, lime, sand proportions by volume.

Note: 1 psi - 6.89 kN/m1

Table 2.8c Shear strength of sand/epoxy

specimens [2.13].

Sample timber (D

Typed

grout*

(2)

Typed

mortar*

(3)

Shear atreaa over groea area

flba/aq In.) (4)

Averaga

lor group

(Iba/aq In.) (5)

Normal

strata (Ibe/aq In.) (8)

1 1 1/8. 3 1 , 1/4.3 223.4 29.9 2 1 1/8. 3 1, 1/4,3 500.0 — 62.5 3 1 1/8, 3 1, 1/4. 3 350.00 43.8 4 1 1/8. 3 1 , 1/4. 3 350.0 43 8

5 1 1/8. 3 1, 1/4, 3 306.3 — 38.3 6 1 . 1/8, 3 1. 1/4.3 350.0 — 43.8 7 1, 1/8, 3 1. 1/4.3 3500 — 43 8 8 1. 1/8, 3 1. 1/4,3 350.0 — 43.8 9 1. 1/8, 3 1, 1/4. 3 262.5 — 32.8 10 1, 1/8, 3 1, 1/4. 3 350.0 — 43.8

11 1. 1/8, 3 1, 1/4, 3 262.5. — 32.8 12 1, 1/8, 3 1 , 1/4. 3 434.4 54.3 13 1. 1/8, 3 1, 1/4,3 306.3 38.3

14 1, 1/8, 3 1 , 1/4.3 284.4 284.3 35.6 'Cement, lime, send ratio by volume.

Note: 1 pci - 6.89 kN/m2

.

Table 2 . 8d Shear strength of specimens with

cement grout and axial force [2.13],

Sand/ Shear atreaa potyasitr ovw grots Average Normal Sample propor* Typed arts lor group stress number ton* nwt*4 flba/aq In.) flba/aq In.) flba/aq In.) (1) (2) (3) (4) (5) (8)

1 3/1 1, 1/4, 3 331.3 21.9 2 3/1 1, 1/4. 3 331.3 39.1 3 3/1 1, 1/4, 3 296.9 39.1 4 3/1 1, 1/4, 3 331.3 39.1 5 3/1 1, 1/4, 3 243.8 306.9 6 2/1 1, 1/4, 3 362.3 50.0 7 2/1 1, 1/4, 3 362.3 54.7 • 2/1 1. 1/4, 3 453.1 51.6 9 2/1 1, 1/4, 3 465.6 51.6

10 2/1 1, 1/4, 3 351.6 51.6

11 2/1 1, 1/4, 3 304.7 51.6

12 2/1 1, 1/4, 3 267.2 51.6

13 2/1 1, 1/4, 3 414.1 54.7

14 2/1 1, 1/4, 3 414.1 54.7

13 2/1 1, 1/4, 3 455.5 54.7 16 2/1 1, 1/4, 3 414.1 387.7 54.7 Sand/polyester ratio by volume.

“Cement, lime, sand ratio by volume.

Note: t psi - 6.89 kN/m1

Table 2 . 8e Shear strength of specimens

with sand/polyester grout

and axial force [2.13].

57
Bunding nundar

and ipaclman numbar (D

Cora andtypa

(in.) (2)

Qroaa croaatacttonal araa

(•q m.)

(3)

Maximum

load (fca) (4)

Maximum

moment

On./*))

(5)

Cyda of maximum

load

(6) 40 2-Grout 300 2.260 70,100 1 5M 2-Grout 273 2,800 85,400 1 5D 2-Grout 260 2,400 68,400 1 3E Epoxy 273 2,450 66,200 4 4A 2-Epoxy 260 2.500 123.800 6

Note: 1 in. « 2.54 cm; 1 lb « 0.453 kg.

Table 2.9a Results of out-of-plane tests [2.13]

BUUng numbar

and apadman

numbar

(1)

Cora aba

andtypa

(2)

Qroaa croaa- aacbonaf araa

(•d In.)

(3)

Maximum

load (fca) (4)

Maximun

sheer street (fea/aq *.)

(5)

Cyda of maximum

load

(0) 48 2-Grout 308 7,895 25.6 3E 4-Epoxy 252 27,600 109.5 1 5C 2-Grout 246 25,000 101.6 1 5L 2-Epoxy 252 12,500 49.6 1 3C 4-Grout 240 20,400 85.0 1 3M 4-Grout 252 15,100 59.9 1 4H 2-Epoxy 280 13,200 47.1 5

Note: ! pd • 6.89 kN/m1

; 1 tb - 0.453 kg and 1 in. * 2.54 cm.

Table 2.9b Results of in-plane tests [2.13].

58
n M a 1 s 1 i 1 1 n< s

(|) TON c»*

hf nd i n* crarkint load

if) TON

shf ar r racki ok 1 nad

(3) TON

y i r 1 <1

s t i I'ntfl

h

of

h

f anr 1 ion

141 TON

u 1 1 i aa 1

r

si r enKl

h

of

t- lam l ion

<»> TON

ill 1 laalr

s h i- »

r

s 1 i en* l

h

n 1 l i aa

1

r

s 1 i »-n»(l h TON

, . ) (2) (1) (2) (1) (2) (1)

rw (2)

c-l 164.5 69.9 12.25 15.0 25.8 25.8 33.82 36.16 30.9 30.5

C-2 278 0 109.7 11.90 15.0 33.1 30.8 33.35 35.36 46.7 41.6

C-3 278.0 100.0 1 1.90 15.0 33.1 3 1.5 33.35 35.36 46.7 42 6

C“4 497.4 93.8 12.35 ' 15.0 42.0 32.5 34.05 36.1 1 57.5 39.1

C-5 344.8 79.5 12.35 15.0 32.6 — 34.05 36.1 1 43.8 37.1

Calculated values(l) and experimental results(2)

Rote:

(1)

* 2]j^rdA)dx

]

( 2 ) Qbc-(i .8

(3) Q«c.o.G55+0.15N/3D-c<^b

(4)

. (5) e-Function Method

(6) Qau

f 0.053Pc°*^( 180«-Fc ) i M7^rn

2.7

x b*j

Fc: concrete strength

Table 2.10 Summary of test results [2.1]

(1) Predicted results.

(2) Experimentally obtained results.

59
Test Specimen Column Test

Mo. No. Cross Section Description

12' Long, steel: # 6 *s

Ties: 6mm § 8

"

Identical 12" x 12" cores used for all specimens.

Description : original specimen

Test : reversed unidirectional

loading

Deflection limit: 21 drift

17"

2 1-2

17"

17"

Long: #3's t # 6’s

Ties: 6mm § 2-1/2"

Crossties: #3's § 9

"

2- 1 / 2" shotcrete shell

Description : sandblast, add 4-#3

longitudinal bars and 6mm ties at 2-1/2". Shotcrete to 17" x 17".

Test : reversed unidirectional

loading.

Deflection limit: 2.51 drift

Description : sandblast, add 4-#3 corner bars and 4-#6 midface bars. Anchor midface bars w/13 crossties,

secured with epoxy. 6mm ties g 2-1/2". Shotcrete to 17" x 17 ".

Test: reversed unidirectional

loading.

Deflection limit: 2.51 drift.

Long: #3's, #6 's

Ties: 6mm § 2-1/2"

Crossties: #3's § 9

"

2- 1 / 2" shotcrete shell

Description : Remove all loose cover

Add 4-#3 corner bar 3 and 4-#6 midface bars. Anchor midface bars

w/#3 crossties, secured with epoxy.

6mm ties § 2-1/2". Shotcrete to

17" x 17".

Test : reversed unidirectional

loading.

Deflection limit: 2.51 drift.

Table 2.11 Descriptions of Bett, Klingner and Jirsa's test

specimen [2.17]

.

60
Beam

(D

Load, in kips (kilonewtons)

(2)

Average load, in kips (kilonewtons)

(3)

Calculated load, in kips (kilonewtons)

(4) A1 7.0 7.0 6.0

(31.2) (31.2) (26.7)

A

2

7.0

(31.2)

A3 7.0

(31.2) B1 9.5 10.0 8.3

(42.3) (44.5) (36.8)

B2 10.0

(44.5)

B3 10.5

(46.7)

Cl 8.0 9.3 8.3

(35.6) (41.3) (36.8)

C2 11.0

(49.0)

a 8.8

(39.2)

Table 2.12 Holman and Cook's test results.
jUUUUUUUUUL^

I (

J (

} (

_ ^nnnnnnnnnn^

W—

3

W—

4

tillllil

billing:

W—

5

irimra __ ! ::imiJLS

W— 6 !

b

o

oin

(a)

Axial Load . Loit : ma

(d)

Figure 2.1 Hayashi, Niwa and Fukuhara's frame specimens [2.1].

a) Specimen configuration and strengthening concepts.

b) Reinforcement arrangement.

c) Sleeve expansion anchor used as joining element.

d) Reinforcing details of infilled wall.

62
Figure 2.2 Test setup [2.1].

63
Figure 2.3 Hayashi et al's test results [2.1]

a) Hysteresis curves.

b) Envelopes of hysteresis curves.

64
V)LUU

2

z

o

to

C/5 UJ

tt

O.Su

1 • wrV_-

thr

VA

ii

i

CNI

<uu

3

60

•rH U.

65

INFILLED

CONCRETE

WALL

TENSION

BRACES

(Shear

Key

Connection)
L ll I I 0 5 10 15

R(x 0.001 rad.)

(a)

1 « -1— L_

0 5 10 15

R(x 0.001 rad.)

(b)

Figure 2.5 Envelopes of hysteresis curves [2.2

a) Infilled frames.

b) Steel braced frames.

66
Figure 2

Quy

/C

r.oh

Qwu

0.8

0 . 6 *

0.4 H

10 20

Tj = Qj

/

t • 1 (kg /cm )

Strength of Connection

.6 Strength of connection vs. frame's lateral strength [2.2],

67
(a)

Figure 2,7 Details of Higashi

a) Specimens in

b) Specimens in

c) Specimens in

et al's specimens

1977,78 series.

1979 series.

1981 series.

[2. 3,2. 7] .

68
I nr

>•-010

Sil

Uc a:o

iiji

’'ed*e anchor - No.l*-3CU 64?UO

ddub-Lf

rw1t=50

' L<f) I 3100

rio.0-3FW

n

L^r«:r tD,0JI

J-M>0 £23 3

0 13 1 u :a_

.Coltr-a l££i raift bnr U-Dfc

Horn- ?-?4&0

Footi nr 3»*>»r IMr bar

r.t » rrj

r

p-dVico

vodga anchor

vadga anchor

P Sim

|

1

|

V,' p|

**»lOO

t-bO

1 1 i=:

; v f|

1 no. a

| Monolithic »all with fraao

(b) (c)

69
ancho

70

Figure

2.8

Details

of

the

connection

between

infill

wall

and

frame

[2.

3,

2.

7].

a)

1977,78

series.

b)

1979

series.

c)

1981

series.
7 71 7

! rnrn

ii i

EJ =-E — UnnzzM

]—

L ^

i. .ii. .i . s

1 A

(c)

Figure 2.9 Higashi et al's test setups [2. 3, 2. 7],

a) One -bay, one -story frame.

b) One-bay, three-story frame.

„ c) Two -bay, three -story frame.

71
P(

xlO

N)

CM

cn

72

Figure

2.10

Envelopes

of

hysteresis

curves

[2.

a)

1977

series.

b)

1978

series.

c)

1979

series.

d)

1981

series.
P ( x 1 0* N

)

(C)

Figure 2.10 (Continued)

73
ra ti 4-*5

ift 84rr- z-qr 84 g' • 4-e: a<rr- z-cr Ur

Section o-o

A

r^\

6*xt |

Section b-b

°tr gt^J-s.

”=€5 ^4

J^8 w5J«3

=|:a*'a

2 V2'

: r

3 V2*

Section c-c

Section d-d

Frame Reinforcement Detoil*

(a)

a -J

1

13/16 m 3<P8 3/8“ - 7*- 81/8" 1 0/16

1 :

i i

|

» i i i e I i ! i

J

i i

1 0 * J

-1 - E n

-

...

r-

-1

J

—

!

1

1

1

1 1

i

i i

i i i

i i i

i i i

l i

t i

! 1

i

l

I

1

; 1

1

I

• j

1 1

5 i

11 i

i

l

l

8

l

1

1

1

l i

i

i

|

1

1

I

i t

i |

i 1

1 i

• i»

1 i l

t > i

1 • 1

<

1 -

9 1

1 1

1

•

1

*

Elevation - Monolithic Shear Wall

(b)

Note : Alternate

direction at bendevery other bar /

3 won

vertical *3 bar centered

Section a-a

Figure 2.11 Reinforcement arrangement in Kahn's specimens [2.4]

a) Bare frame reinforcement details (specimen 2)

.

b) Monolithic shear wall reinforcing detail (specimen 1)

.

c) Cast- in-place infilled frame (specimen 3).

d) Single precast infill panel (specimen 4)

.

e) Multiple precast infill panels (specimen 5).

74

4

~

y4

‘

clr

-
Elevation Cast - in - Place Shear Wall

Section a-a

(C)

*<\J V

'o

K•

In *o

CNJ u

JC Q

m

o

o£

o> •

• o

o o>

0% 13 a

.0 m

fO % 5

:

c\j

y8

Clr.

3

3

'l6.

Phillips 3/g" x 5” wedge anchors

12 anchors at 3

7

/q o.c.

", 3'- 1 1 1 */2 plot* 3

12 anchors at 3 ac.

(d)

75
-Phillips ^g* x 5“ wedge anchors

12 anchors at Z

7

/q o.c. — ^2 plate 3" x

3* — II ^2 —

4 ^

12 onchors at 3 ?g" o.c.

(e)

76
Figure 2.12 Hysteresis behavior of Kahn's specimens [2.4]

a) Specimen 1. b) Specimen 2.

c) Specimen 3. d) Specimen 4.

e) Specimen 5.

77
s

<x

GCUJ „

S - -3.00

LATERAL DISPLACEMENT * (INI

78
270

-I

I HI

970 I « 70

500

Figure 2.14 Dimensions and reinforcement arrangement

of Shiohara et al.'s specimens [2.22]

79
Contribution

of

Figure 2.15 Hysteresis curves of Shiohara et al.'s specimens [2.22]

TOT a 1 Dpf1<»rr inn

Figure 2.16 Measured displacement components

of Shiohara et al.'s specimens [2.22]

80
Specimens Steel Panel Stud

n icnor

n RC Frame

P-1-0

P-l-S

P-2-C

P-2-G

LUu ..1 . T-r

4 + +-i

FLANGE:

PL-6x80

WEB: PL-4.5

UG-LG

r6|lc

E :K3E

tzfrr

FLANGE:

PL-6x80

WEB:

PL-4.

S

UG LG

20 RC LC

21 [F±ME

• WFLANGE:

PL-6x80

FLANGE:

PL- 9x80

WEB: PL-4. 5

UG 20

LG 26

RC-LC

13

E 5X

T-i •-

1600 I

FLANGE: PL- 12x80

WEB: PL-9

FLANGE:

PL-6x80

MB: FL-4. 5

UG LG

26

RC LC

13

UG LG R^LC

UG LG

21 RC LC 20

UG 22

LG 27

RC LC

14

UG LG

27

RC LC

14

1.7 60 2.000 r25

bXD=200x2S0

A : 6-D16

3

Hoop 2-4 $ 9 120

bXD=300x3S0

A

t

: 2-D16.2-D1

St: 2-6$ 3120

P-l-N

, 600 ,

FLANGE:

PL- 6x80

WEB:

PL-4.

S

UG LG

26

RC LC

13

UG LG

27

RC LG

14

bxD=200x200

A : 6-D19

9

Hoop 2-4 $ 9120

bXD=300x350

A : 2-D19, 2-D13

V St: 2-6 $ 9120

notes: PL-6x80 was used as steel rim, and PL-U.5x35 as stiffners.

Signatures UG and LG mean the upper and lower girders, and

RC and LC mean the right and left columns.

Figure 2.17 Description of Aoyama et al.'s test specimens [2.23]
Figure 2.18 Hysteresis behavior of

Aoyama et al . '

s

specimen P-1-0 [2.23],

Figure 2.19 Crack patterns in Aoyama et al .

'

test

specimen P-1-0 [2.23].

Figure 2.20 Deflection envelopes of

Aoyama et al . '

s

test specimens [2.23).

82
1200 _

/ H- 123- 05*6 5-

9 ¥ •

*

?

! A

<4

/ Fn

--1 ri

• -> r-

-O' = A2

KCAOED ^STVX)

#-13 #•100 1 ? /

1 S

,i

L

' \ FOUNDATION BEAM

1200

P»-0.53f.

I v-tj J m f7 -r-|

I

1 1 EXTRA BARS 3- #9

P.-053X

\ EXTRA BARS 3-#9

Figure 2.21 Makino et al . ' s steel frame

specimens A2 and B2 [2.5],

Figure 2.22 Local buckling in

steel column [2.5],

83
84

Figure

2.23

Hysteresis

curves

of

original

and

strengthened

frames

[2.5],
2 H

Figure 2.25 Dowel layout for Jones and Jirsa's steel bracing

scheme [ 2 . 8 , 2 . 9 ]

.

85
Figure 2.26 Connection details [2. 8, 2. 9],

a) Brace- to-collector connection.

b) Brace- to-channel connection.

86
Figure 2.27 Load-drift relationship of the steel braced frame [2. 8, 2. 9],

Figure 2.28 Deflection envelopes [2. 8, 2. 9].

87
(a)

(b)

(c)

Figure 2.29 Roach and Jirsa's strengthening scheme [2.9,2.10],

a) Strengthening concept.

b) Connection mechanism between old and new concrete.

c) Reinforcing details.

88
Figure 2.30 Hysteresis curves [2.9,2.10].

Figure 2.31 Envelopes of hysteresis curves of frames strengthened

by adding wingwall and steel bracing [2.8,2.9,2.10],

89
Figure 2.32 Dimensions and reinforcement arrangement of

Corley, Fiorato, Oesterle and Scanlon's walls [2.12],

Figure 2.33 Specimen B5 with

damaged web and with

web concrete removed.

Figure 2.34 Specimen B5R after repair.

90
Hol«t 0» 45* Figure 2.35 Reinforcement arrangement

in specimen BUR.

Figure 2.36 Drilling holes for diagonal

reinforcement in BUR.

4 -# 5 043 * toeh way

91
26

CrutMdf

(a)

Figure 2.37 Hysteresis curves of Corley et al's original

and repaired specimens [2.12].

a) Specimens B5 and B5R.

b) Specimens B9 and B9R.

c) Specimens Bll and BUR.

92
(b)

Figure 2.37 (continued).

93
Specimen B II

(c)

Figure 2.37 (continued)
2-2

©-

0-

Kt

V777* W.V777A T7777Z s.

- -p

N 12.9 \ -J ^

Nil 8 N 10 7 o CD N4I / N 5 2 N6.5 — 77///X 1 ~ JZZZZA1 " ' 'ZEZZZA. s. p -Jt

<55

j <20

f <55 705

120 155

4-4 uA , -Al

l

Li

«r

« eL

i l

196

Joint A

conctete m-eqo

l '350 2» 12 A- jj E’ 565

3o ini B

conczeie m-2oo

#6»-I /

200*200

•»6A-j

j ovei 7 tayeis -^r

tLL

V\i\

Z£JZ±jL

l • S6S ,2» 12 A-j

l 700 maionxi

(b)

(a)

I - »

(c)

igure 2.38 Jabarov, Kozharinov and Lunyov's test a) Specimen's dimensions/ specimen [2.14].

b) Reinforcement details

C)

vSle'sh"

1"8 UUh dla8°nal «“*«««»*. and welded

95
-iter.-ra.arB.

.

?!T

VA

m - WET

Figure 2.39 Load parallel to bed joints vs. strain parallel [2.15]

to bed joints relationships for Kahn's wall panels.

a) Dry surface condition.

b) Epoxied surface condition.

c) Wet surface condition.

96
* -I— Il’i i 1 r-r- v- iii n

r

,ii i 'T |

i i

, .. L r-

'| r-r1 I I "l' -JjJLlJ A ~r i i A • :

i • • .y

Cut-out view of NCSU's test specimen. Out-of -plane test setup.

pi

Jack* ®4 1=

01*1

: i

SfttlM*

7T 1

i i

1

,

i

1 1

i i

i

i XJ

in-plane test setup.

Figure 2.40 Plecnik, Cousins and O'Conner's

static shear specimens

(LBSU's testing program) [2.13],

97
(a)

(b)

Figure 2.41 Hayashi, Niwa and Fukuhara's column specimens [2.1]

a) Column cross-section.

b) Reinforcement arrangement.

c) Test setup.

98
r 1

1 c— 1

! ¥ 4 MW * i Jr - - !

j

1

j

*/• / 1/^ .'J! f.icrioai 1 "" 1

i

' " fIf

- • •

: ’

1

L — Z

{m H

s)

-;a bu : /•

if m

• f / /W .

i /wy

lL ‘ETF

(b)

Figure 2.42 Hayashi, Niwa and Fukuhara's test results [2.11.

a) Hysteresis curves.

b) Envelopes of hysteresis curves.

99
f***'

Figure 2.43 Dimensions and reinforcement arrangement

7 of Kahn's column specimens [ 2 . 16 ].

100
20 20 -.

(a) (b)

Defection (in.) DWIncJion (in)

(c) (d)

Figure 2.47 Hysteresis curves of Kahn’s columns [6].

a) Specimen 1, unstrengthened.

b) Specimen 2, steel bands.

c) Specimen 3, 6 mm plain rod.

d) Specimen 4, U-shaped clamps.

101
18" (46cm)

36" (92cm)

18" (46cm)

_L2

" (5cm)

4 Spaces

at 8"

(21cm)

2

" "^“(Scm)

Figure 2 . 48 Details of Bett, Klingner and Jirsa's columns [2.17].

102
o

CC

CO CM H r—< CN m

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1

o CJ U u U

CO a; a> V a> a> 0) cl Cl Cl a Cl u co 00 00 00 on

a> u u / s CO CO 03 a

103
a

Figure 2.50 Envelopes of Bett, Klingner and Jirsa's

hysteresis curves [2.17].

104
be

I

III / II

II

1

1 II C3L

IM < 41 JILL.-XJI

I

JTTTTt

TTTT~nr

u_-AJl

Figure 2.51 Reinforcement repair schemes in Augusti, Focardi,

Giordano and Manzini's test program [2.18].

Figure 2.52 Typical moment -displacement relationship [2.18].

105
WINDOW RBNFORCFMFNT

#4 STIRRUP

1 IN. (TYP.)

#8 LONG. BAR

f

*

§

(TYP.) «

JOINT REINFORrFMFNT

Figure 2.53 Reinforcement details of Stoppenhagen and Jirsa's;

encased columns [2.19].

STANOARO ACI

bat*'o\act<i !3S e 8EN0S X P

STANDARD ACI

90* BENOS

CO)

10 d 6 e*f f J

' J

I (a)

STANOARO ACI

135* BENOS

(b)

Figure 2.54 Shear reinforcements [2.19].

a) Bent #4 bars in beam- column joints.

b) Bent #3 bars in window regions.

106
r »o

ONrH

CM

</) 6

a> 4JU

ajCL

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rA

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:

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SOUTH

LOADING
H — +=-

!

•

l

> r

I

. ipifiifB

INTERIOR ELEVATION

(I in. 25.4mm)

Figure 2.58 Reinforcement arrangement on beam's cross section.

Figure 2.57 Specimen configuration and dimensions in

Holman and Cook's test program [2.20'

108

Figure 2.59 Load-center deflection curves [ 2 . 2 )].
50 50 050 650 50 50

^

! 1 2 05 1 (10216)

C

1

_>

1 —5

3012 (10425) A

80J 1340 L 80 1500

2®E5

30V12

m

^-55

135 u85 05/550

*9 KS =45

f ploct of dtttruct.on

(th* numCen mdiCOf*

? 1? 1 th* loading k N I

? 132 \'%£££:

;rxrw7

• 4 r

T 53.T0

Figure 2.60 Arrangement of external reinforcement in

Vanek's study [2.21].

Figure 2.61 Crack patterns

in beams [2.21]

.

Figure 2.62 Load-center deflection of plated beams.

109
110

Figure

3.1

Concept

of

infilling

technique.
Adhesive Ahchor shear Mal1

Figure 3.2 Connection between new shear wall and column [3.1].

Ill
Figure 3.3 Arrangement of cross braces on North and South

facades of the Tohoku Institute of Technology

in Sendai, Japan [3.2].

South

Figure 3.4 Spandrel beam locations [3.2]

Figure 3.5 Details of braces to frame connection [3.2]

112
Figure 3.6 Concept of wingwall addition.

Wall Relrtorcement

LI 11

looo loo • D . 100 T 000

Figure 3.7 Connection between wingwall and

700

700
3*-<J LAP

AQUA EPOXY (2 60) CO ATI ON THOROUGHLY

CLEANED SURFACE

6$16 (PROPOSED

REINF)

06 HELICALS © S $ —

($10,4 NOS. © 3

n 4:©

TOP AND BOTTOM OF

BEAMS) TO BE TIED

AROUND AFTER

PLACING VERTICAL

REINFORCEMENT

BRICK BAT (EXISTING)

TO BE CHASEO AT x

COLUMN AND SLAB]

JUNCTION, )

$ OF BEAM

EXISTING

reinforcement

CRACKED

CONCRETE cover

CRACKED CEMENT

PLASTER

SECTION THROUGH

COLUMN (BEFORE)

$6 HELICALS © 6i (t TO BE TIED AFTER

PLACING MAIN

STEEL

2$16 EXTRA

TO BE TERMINATED AT BEAM BOTTOM'

3 THK CONCRETE

CASING (101(2:3) AQUAEPOXY (260

)

COAT

3/4"THK. CEMENT

PLASTER

$ OF BEAM

rCOL. REINF WELDED TO BEAM REINF

IT

SECTION THROUGH

COLUMN (AFTER)

lAQUAEPOXY

LAYER SLAB

FLOOR

BEAM

SECTION THROUGH COLUMN

REPAIRS AND STRENGTHENING OF R C COLUMN

TYPICAL DETAIL S

Figure 3.8 Details of Nene's strengthened column [3.4].

114
NBS-114A (REV. 2 -80

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBSIR 88-3796

2. Performing Organ. Report No. 3. Publication Date

JUNE 1988

4. TITLE AND SUBTITLE

Literature Review of Strengthening Methodologies of Existing Structures

5. AUTHOR(S)

Long T. Phan, H. S. Lew, Mark K. Johnson

6. PERFORMING ORGANIZATION (If joint or other than N BS. see instructions)

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No.

8. Type of Report & Period Covered

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

10. SUPPLEMENTARY NOTES

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

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bi bl iography or literature survey, mention it here)

This report reviews research studies relevant to structural strengthening of

existing reinforced concrete members and frames. The majority of these studies

dealt exclusively with restoring or improving seismic resistance of concrete

columns and frames. A number of case histories where various strengthening

techniques were applied in practice are reviewed. Most studies identified ultimate

failure in the strengthened structures as primarily due to failure of the joining

elements. Improved load resistance and ductility in concrete structures have been

reported in most of these studies.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) anchors, beams, columns, deflection envelopes, ductility, epoxy adhesive,

hysteresis curves, infill walls, lateral load carrying capacity, lateral stiffness,

reinforced concrete frames, steel braces, strengthening, walls, wingwalls.

13. AVAILABILITY 14. NO. OF

PRINTED PAGES

X 1 Unlimited

1 | For Official Distribution. Do Not Release to NTIS ~

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

125

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