100
STRUCTURAL RESEARCH SERIES NO. 830 I. NSF/CEE-84035 PB85-'1496J1 SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by Paul R. Philleo and Daniel P. Abrams A Report to the National Science Foundation Research Grants CEE-8119385 and PFR-8007094 Department of Civil, Environmental, and Architectural Engineering College of Engineering and Applied Science University of Colorado, Boulder REPRODUCED BY NA T!.ONAL TECHNICAL INFORMATION SERVICE u.s. DEPARTMENT OF COMMERCE SPRINGFiElD, VA. 22:5:

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Page 1: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

STRUCTURAL RESEARCH SERIES NO. 830 I. NSF/CEE-84035

PB85-'1496J1

SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS

by Paul R. Philleo and Daniel P. Abrams

A Report to the National Science Foundation Research Grants CEE-8119385 and PFR-8007094

Department of Civil, Environmental, and Architectural Engineering

College of Engineering and Applied Science

University of Colorado, Boulder REPRODUCED BY

NA T!.ONAL TECHNICAL INFORMATION SERVICE

u.s. DEPARTMENT OF COMMERCE SPRINGFiElD, VA. 22:5:

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Structural Research Series No. 8301:

SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS

by

Paul R. Philleo

and

Daniel P. Abrams

A report to the

NATIONAL SCIENCE FOUNDATION

Research Grant CEE-8119385 and PFR-8007094

Department of Civil, Environmental, and Architectural Engineering

College of Engineering and Applied Science

University of Colorado Boulder

February 1984

Any opinions, findings, conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

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Page 5: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

ABSTRACT

The objective of this study was to investigate the

ability of reduced-scale models of reinforced concrete

beam-column joints to predict the response of large-scale

prototypes. Six large-scale (approximately three quarter

scale) specimens and six medium-scale (approximately one

quarter scale) specimens were tested. Data from these

tests were combined with data from tests of small-scale

(approximately one-twelfth scale) specimens which were

tested as part of a previous investigation. Each specimen

was subjected to a reversed lateral load which was applied

at the top of each column. Specimens of different scales

were compared with regard to their load-rotation responses.

Explicit scale factors based on the load-rotation

relationship were derived.

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ACKNOWLEDGEMENTS

The investigation described in this report was part

of a continuing study of reinforced concrete structures

subjected to earthquake motions. The work was funded by

the National Science Foundation under grants PFR-8007094

iv

and CEE-8119385. Experimental work was done at the Structural

Research Laboratory at the University of Coloradoo

The writers wish to express their appreciation to

Professors Gerstle and Frangopol for their critical review of

the manuscript, and to numerous graduate students, especially

Bill Epp, Scott McNary, and Peter Waugh, for their support.

Acknowledgement is also due to Dave Jones and his staff for

assisting with the fabrication of the test apparatus.

This report was prepared as a thesis for the degree of

Master of Science in Civil Engineering by Paul Philleo under

the direction of Daniel Abrams. Any opinions, findings, and

conclusions or recommendations expressed in this publication

are those of the authors and do not necessarily reflect the

views of the National Science Foundation.

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CONTENTS

ACKNOWLEDGEMENTS • . . . . . . LIST OF TABLES . .

LIST OF FIGURES

CHAPTER

1. INTRODUCTION

1.1 Objective and Scope

1.2 Related Research Elsewhere

2. OUTLINE OF EXPERIMENTAL WORK

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

Introductory Remarks

General Configuration of the Test Specimens • • . • • . . . • .

Description of the Large-Scale Specimens • . . . . . . . . .

Description of the Medium-Scale Specimens •

Materials .

Fabrication •

Test Apparatus

Instrumentation

Testing Procedure

3. SCALE RELATIONSHIPS OF EXTERIOR JOINTS

3.1 Introduction

3.2 Description of Large-Scale Specimen Response

iv

vii

.viii

1

1

2

6

6

6

9

16

17

19

19

24

26

32

32

32

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CHAPTER

4.

5.

3.3 Comparison of Large and Small-Scale Specimens . • •..

SCALE RELATIONSHIPS OF INTERIOR JOINTS

4.1 Introduction

4.2 Description of Large-Scale Specimen Response . . ...

4.3 Comparison of Large-Scale Interior and Exterior Joints. .• •. .

4.4 Differences due to Different Reinforcement

4.5

4.6

Comparison of Large and Small-Scale Specimens . . . . . • .

Comparison of Large and Medium-Scale Specimens

SUMMARY AND CONCLUSIONS

5.1 Summary •.

5.2 Conclusions

5.3 Recommended Future Research •

REFERENCES

APPENDIX

vi

45

50

50

50

65

65

70

73

76

76

77

79

80

85

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vii

TABLES

Table

2.1 Summary of Specimens Tested 7

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FIGURES

Figu~e

2.1 Configuration of Test Specimens 8

2.2 Specimen Dimensions • 10

2.3 Beam and Column Cross Sections 11

2.4 Shear Reinforcing Detail 13

2.5 End Connections for Large-Scale Specimens 14

2.6 Details of End Connections 15

2.7 Measured Properties for Concrete and Steel 18

2.8 Forrnwork for Large and Medium-Scale Specimens . . . • . • . . 20

2.9 Large-Scale Test Apparatus 21

2.10 Medium-Scale Test Apparatus 22

2.11 Small-Scale Test Apparatus 23

2.12 Description of Physical Quantities Measured 25

2.13 Instrumentation . • . . 27

2.14 Beam Rotation LVDT Arrangement 28

2.15 Location of Strain Gages in Large-Scale Specimens 29

2.16 Displacement Histories 30

3.1 Load-Rotation Response for Exterior Joint 33

3.2 Response of Exterior Joint 34

3.3 Load-Strain Response for Exterior Joint 35

3.4 Photographs of Damage of Exterior Joint 40

3.5 Crack Widths for Exterior Joint . 42

. ,';'

\1.1 I

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ix

FIGURE

3.6 Comparison of Small-Scale and Large-Scale Specimens . 46

4.1 Load-Rotation Response for Interior Joint 51

4.2 Load-Displacement Response for Interior Joint . . . . . . . . . 52

4.3 Measured Beam Rotations in Interior Joint 53

4.4 Load-Strain Response for Interior Joint 54

4.5 Photographs of Damage of Interior Joint 60

4.6 Crack Widths for Interior Joint . 62

4.7 Load-Rotation Response for Specimen LIJ4 66

4.8 Photographs of Damage of Specimen LIJ4 67

4.9 Crack Widths for Specimen LIJ4 69

4.10 Comparison of Small-Scale and Large-Scale Specimens . . . . . . . . . . . . 71

4.11 Comparison of Medium-Scale and Large-Scale Specimens . . . . . . . . 74

A.l Load-Rotation Response for Specimen LEJI 86

A.2 Load-:-Rotation Response for Specimen LIJI 87

A.3 Load-Ro~ation Response for Specimen LIJ2 88

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CHAPTER 1

INTRODUCTION

1.1 Objective and Scope

The overall objective of this experimental study was to

examine the behavior of large-scale reinforced concrete beam-column

joints and to compare the behavior with reduced-scale models. The

test variables were the configuration and the size of the test

specimens. Interior and exterior joints were tested and behavior of

specimens at three different scales was studied.

Two large-scale exterior and four large-scale interior

joints were constructed and subjected to lateral load reversals. An

additional six interior joint specimens were constructed at medium­

(1/4) scale and subjected to deflection histories similar to the

large-scale specimens. One exterior and one interior joint were

tested as a pilot test program by others (10). All other specimens

were tested by this investigator. Small- (1/12) scale interior and

exterior joints were tested at the University of Illinois (12).

Steel and concrete properties and reinforcing ratios for all three

scales were kept similar so direct comparisons between scales could

be made.

This report pertains to all the testing of beam-column joint

specimens at the University of Colorado. A description of test

procedures are presented in Chapter 2. The responses of exterior

J

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2

joint specimens and scale relationships of that component

configuration are described in Chapter 3. A similar description for

interior joints constitutes Chapter 4. Sonclusions reached during

the investigation, including recommendations for future scaling

studies, are summarized in Chapter 5.

1.2 Related Research Elsewhere

Use of models to represent behavior of structures is not a

new subject. The early Greeks and Romans used models to design

structures in the absence of mathematical algorithms. In more

recent times, models have been used to predict forces and

deformations in beams, flat plates, box girders, and arch dams, to

name only a few. In Europe, laboratories have been established for

the specific purpose of model studies. Examples of these are the

Laboratorio Nacional De Engenharia Civil in Portugal, the Instituto

Sperimentale Modelli E Strutture in Italy, the Cement and Concrete

Research Association in England, and the Institut fur Modellstatik

at the University of Stuttgart.

In the United States and Japan, tests of small-scale

building models have stimulated new research related to improved

methods of analysis and design. A few examples of innovative

improvements which have used test data from small-scale building

models as a reference are noted in the following. Takeda (19)

formulated complex behavior of reinforced concrete members subjected

to load reversals with a set of rules so that nonlinear dynamic

response could be calculated. Nonlinear analysis of reinforced

concrete frames has been suggested as a design tool (22,23) using

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3

similar hysteresis rules. Newmark (18) suggested a simplified

analysis procedure using an elastic analysis with response spectra

modified to include effects of inelastic response. Shibata and

Sozen (20) proposed a design method that used a linear analysis to

represent nonlinear behavior. A substitute structure with member

stiffnesses chosen on the basis of nonlinear behavior was used with

conventional modal analysis procedures. Biggs (21) has evaluated

this approach with the inelastic response spectrum approach and the

equivalent base shear approach. Further simplified analysis

approaches include representing a MDOF structure with a SDOF model

(24), and using modal analysis for bilinear systems (25). New

trends to obtain a simple design criterion for reinforced concrete

frame structures concentrate on simply limiting the drift (26)

without an explicit description of the lateral forces.

Numerous building models have been subjected to simulated

earthquake motions (2,3,4,5,7,8,9) at the University of Illinois.

Other models have been tested in New Zealand (27) and California

(28,29,15), and many tests will probably be done in the future.

Small-scale components of some of these models have been tested by

subjecting them to slowly applied loading reversals (12,13,14,30).

Compa~ison of large-scale components (31,32,33,34,35,36,37, 38,39)

with these small-scale components has been made but only

qualitatively because specimen geometries, amounts of reinforcement,

and loading patterns have not been kept consistent. The question of

modeling was not an issue.

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4

Past research on modeling of reinforced concrete behavior at

a small scale is not new. A publication of the American Concrete

Institute (40) summarizes work done in the sixties. Most of this

work was not concerned with dynamic response, but rather direct

scaling of materials to monotonically increasing loads. Work by

Staffier (41) in the seventies addressed the problem of strain-rate

effects on model reinforcement. Krawinkler (42) and Moncarz (43)

investigated correlations between large and small-scale specimen

response. Similar small-scale component models as those described

at the University of Illinois (12,13,14,30) were tested. Their work

did not study the sensitivities of response of a multistory

structure to differences inherent in scaling at the component

level. Verification of conclusions deduced from small-scale

building tests was not within the scope of the research. Various

model studies of multistory concrete buildings have been done in the

People's Republic of China at the Academy of Building Research in

Beijing (44).

Previously at the University of Colorado, Bedell and Abrams

(11) studied scale relationships of concrete columns. A sustained

axial force representing gravity loads was varied for different

specimens to investigate differences in behavior attributable to

inconsistent model~ng of gravitational accelerations. Scale

relationships were defined which showed the ratio of strengths of

different scale specimens to be proportional to the square of the

length scale factor for that particular component.

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5

In a U.S.-Japan cooperative effort in Tsukba New Town, a

full-scale seven-story building was tested to failure (1). As part

of the effort, many subprojects have sprouted in the United States.

These projects form a comprehensive study of testing reinforced

concrete buildings for earthquake resistance. Large-scale

components have been tested at the University of Texas. A one-fifth

scale model was tested on an earthquake similator in California

(47), while a one-tenth scale model was tested in Illinois (45).

Another multi-investigator research program was a study of

the Imperial County Services Building in El Centro, California which

was damaged severely by an earthquake in 1979. Large-scale

components of this building have been tested in California. A

one-tenth scale model was tested on an earthquake similator in

Illinois to test the usefulness of small-scale models in estimating

response of full-scale structures (46).

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CHAPTER 2

OUTLINE OF EXPERIMENTAL WORK

2.1 Introductory Remarks

Two exterior and four interior large-scale beam-column joint

specimens, and six interior medium-scale specimens were tested as

outlined in the first chapter. This second chapter presents details

of specimen design, fabrication, instrumentation, and test

procedures used for the tests. In addition, figures showing the

dimensions and details of the small-scale specimens tested at the

University of Illinois are included so the reader may compare

specimens at different scales. A summary of all specimens tested is

given in Table 2.1.

2.2 General Configuration of the Test Specimens

The configuration of each beam-column joint was chosen so

that forces would be transferred across the specimen similarly to

those transferred in a similar element in a multi-story frame

structure. Boundary conditions at the ends of the beams and columns

were chosen to replicate idealized points of contraflexure in a

laterally loaded frame. A horizontal load P was applied at the top

of the column (Fig. 2.1) which represented the story shear. A pin

connection at the base of the column, and a roller support at the

end of each beam simulated appropriate restraint conditions.

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TABL

E 2

.1

SUM

MAR

Y O

F SP

ECIM

ENS

TEST

ED

SPEC

IMEN

TY

PE

SCA

LE

INV

ESTI

GA

TOR

NU

MBE

R TE

STED

Ex

teri

or

Join

t L

arg

e S

tew

art

(1)

1

Inte

rio

r Jo

int

Lar

ge

Ste

war

t 1

Ex

teri

or

Join

t S

mal

l K

reg

er

(2)

5

Inte

rio

r Jo

int

Sm

all

Kre

ger

4

Ex

teri

or

Join

t L

arg

e P

hil

leo

1

Inte

rio

r Jo

int

Lar

ge

Ph

ille

o

3

Inte

rio

r Jo

int

Med

ium

P

hil

leo

6

(1)

Ste

wart

, J.

and

Abr

ams,

D

.P.,

"C

om

par

iso

n o

f L

arg

e an

d S

mal

l-S

cale

R

ein

forc

ed

Co

ncr

ete

Beh

avio

r",

Mas

ters

T

hesi

s,

Un

ivers

ity

o

f C

olo

rad

o,

July

, 1

98

2.

(2)

Kre

ger

, M

.E.

and

Abr

ams,

D

.P.,

"M

easu

red

Hy

stere

sis

Rela

tio

nsh

ips

for

Sm

all-

Sca

le

Bea

m-C

olum

n Jo

ints

",

Civ

il

En

gin

eeri

ng

Stu

die

s,

Str

uctu

ral

Res

earc

h S

eri

es

No.

4

53

, U

niv

ers

ity

of

Illi

no

is,

Urb

ana,

A

ug

ust

, 1

97

8.

'-.I

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8

!z ... ~ ! ... ~

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Page 21: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

9

Column and beam lengths were chosen to replicate ratios of

moment-to-shear in an actual frame, and equaled one-half of story

heights or bay widths. Proportioning of flexural strengths was done

so that the beams would be weaker than the columns. Nonlinear

behavior was expected to occur at the ends of the beams while the

column was expected to crack but not yield.

2.3 Description of the Large-Scale Specimens

Specimens dimensions are shown in Fig. 2.2. The large-scale

specimens were nine times larger than the small-scale specimens,

which was equivalent to 3/4 scale; however. large-scale specimens

were considered to be full size because reinforcing bars were #5 or

#6, cross sections were at least 343 x 343 mm (13.5 x 13.5 inches),

and the maximum aggregate size was 20 rom (3/4 inch). To define the

exact scale any closer would require a firm definition of a standard

beam or column size which would be meaningless.

Amounts of longitudinal reinforcement in the beams and

columns of five large-scale specimens (Fig. 2.3) were chosen to

match reinforcing ratios in the small-scale specimens (Fig. 2.3).

Beams were reinforced with three #6 bars on the top and bottom faces

(area of steel on one face was equal to .84% of the effective depth

times the width). Columns were reinforced with eight #5 bars (area

of steel was equal to 1.02% of the gross cross sectional area). The

beams in the sixth specimen were reinforced with five #4 bars on

each face (Fig. 2.3). This area of steel was slightly less (.62%)

than the others, but corresponded to the maximum number of bars

allowed by ACI provisions (16). The reinforcement was changed

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10

I b

- --I-f-

b

I I

1 a a

a b

Large Scale 1370 I11III 1030 I11III

Medium Scale 457 !DIll 343 mm

Small Scale 152 mill 114 mID

Fig. 2.2 Specimen Dimensions

Page 23: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

a

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ars

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Page 24: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

12

in this specimen to investigate the effect of bar development length

on the steel-concrete bond within the joint region. The column

reinforcement in the sixth specimen was identical to the other five.

Symmetrical layers of beam reinforcement were not

representative of an actual structure which would be governed by

gravity loadings, but was done so that behavior could be compared

with the small-scale specimens. Column shears for the interior

joint specimen were expected to be twice those for the exterior

joint specimen, however the same reinforcement was used for each

because axial forces in an actual structure subjected to lateral

loads would be much larger in the exterior than interior columns.

Although the effect of column axial load was not part of this

investigation, proper replication was felt necessary for

correlations with possible future studies.

Stirrups and ties were provided with a high factor of safety

similar to that used in the design of the small-scale specimens. In

all six large-scale specimens, #3 closed hoops were used in the

columns and beams '(Fig. 2.4), and were spaced according to ACI

requirements (16).

Forces were transferred to the specimens by means of steel

"T" sections which were bolted to embedded plates (Fig. 2.5 and

2.6). The plates were tied to the longitudinal reinforcing bars in

the beam or column, and were held in place during casting by bolts.

These bolts were removed when the forms were stripped. This detail

enabled the "T" sections to be used on all six specimens. Roller

bearings were press-fitted to a hole in the "T" sections to produce

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13

-a - b

1-1--- I--- t---~ I- f-- r-~ ~ I--~

I 1::::= ~ ~ I::::=:

I I--- f....- bi

U '\ "\ I ~s INTERIOR JOINT T

II 1I

-~

- ~

a bT r I--

-.;;;..... I'-':-- -{

t>r v I--

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EXTERIOR JOINT I I

Io-.~

a b s Large-Scale 102 mm 76 mm #3 closed hoops

Medium-Scole 34 mm 2S mm #9g wire closed hoops

Small-Scale 11 mm 8 mm #16g ,ire spirals

Fig. 2.4 Shear Reinforcing Detail

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r A

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Page 27: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

Fig . 2 . h DL'ldi Is nf End COnnL'l'lLons

)5

Page 28: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

16

the pin connection at the column base and beam ends (Fig. 2.6).

2.4 Description of the Medium-Scale Specimens

The medium-scale specimens were three times largeL' than the

small-scale specimens, which was equivalent to 1/4 scale (Fig.

2.2). These specimens were designed to be the smallest possible

into which conventional reinforcing bars would fit for longitudinal

reinforcement. The beams (Fig. 2.3) were reinforced with two #3

bars on the top and bottom faces (area of steel equaled 1% of

concrete area). The columns were reinforced with six #3 bars (area

of steel equaled 2.4% of concrete area). The columns were heavily

reinforced to make sure they remained much stiffer than the beams.

Shear reinforcement was provided by #9 gage wire which was cut from

a spool and bent to form closed hoops (Fig. 2.4). Stirrup and tie

spacing was scaled down from the large-scale design and therefore

coincided with the ACI seismic design provisions (16).

Forces were transferred to the medium-scale specimens by

means of holes through the specimen which were lined with steel

conduit. A bolt extended through these holes and through ball

bearings that had been press-fitted into supporting channels. When

properly connected, the specimen could rotate about the ball

bearing, thus producing the necessary pin connections at the beam

and column ends. The medium-scale test apparatus will be discussed

in more detail in Section 2.7.

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17

2.5 Materials

The concrete used in the large-scale specimens was

manufactured and delivered by a local pre-mix concrete firm. Type 1

Portland Cement was used and the maximum aggregate size was 20 mm

(3/4 inch). The mix proportions by weight were .6:1:2.8:3.6 (water:

cement: fine aggregate: coarse aggregate). The concrete used in the

medium-scale specimens was designed and manufactured in the

laboratory. Again Type 1 Portland Cement was used, but the maximum

aggregate size was scaled down to 7 mm (1/4 inch). The mix

proportions by weight were .5:1:2:2.2. Physical properties of the

concrete were determined from samples taken during casting and

tested one day after each specimen was tested. The measured

stress-strain characteristics of the concrete are presented in Fig.

2.7a. Compressive tests were done on 152 by 205 mm (6 by 12 inch)

cylinders in a 1300 kN (300 kip) testing machine. Compressive

strains in the concrete were measured with a mechanical dial gage

sensitive to .03 mm (.001 inch) over a gage length of 127 rom (5

inches). Modulus of rupture tests were done in a 45 kN (10 kip)

testing machine, and split cylinder tests were done in the 1300 kN

testing machine.

The reinforcing bars, hoops, and wire were purchased from a

local manufacturer. The longitudinal reinforcing steel consisted of

deformed bars conforming to ASTM A-615 Specification for Grade 60

steel. The stress-strain characteristics are presented in Fig.

2.7b. These tests were done in a 500 kN (100 kip) capacity load

frame operated in strain control at a rate of .0005 per second.

Page 30: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

CONCRETE

30

2D

- LARGE-scALE

..... MEDIUM-SCALE

- - - - SMALL-scALE

.002

STRAIN a

.003 • 0Q.4

~~------~--------~------~------~

300

.OOS

LARGE-scALE

MEDIUM-SCALE

- - - - SMALL-scALE

.010

STRAIN b

.01S .020

Fig. 2.7 Measured Properties for (a) Concrete and (b) Steel

18

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19

Strain was related to elongation of the bar measured over a 25 mm (1

inch) length.

2.6 Fabrication

The reinforcing cages were secured together with #16 gage

wire ties. Conventional reinforcing chairs were used to hold the

cage in position during casting. The large-scale specimens were

cast upright in plywood forms stiffened with battens (Fig. 2.8).

The medium-scale specimens were cast flat in wood forms with one

side exposed (Fig. 2.8). The concrete was compacted with a high

frequency vibrator. Cylinder and prism samples were taken

intermittently during casting. All specimens and samples were cured

under moistened burlap for seven days, at which time the forms were

removed. Thereafter the specimens were air cured until the testing

date, 28 days after casting.

2.7 Test Apparatus

Each specimen was loaded with an apparatus which was

designed to simulate the transfer of forces through actual building

elements. Diagrams of the apparatus used to test large, medium and

small-scale specimens are presented in Figs. 2.9-2.11. For the

large and medium-scale tests, load was applied with a 156 kN (35

kip) ram which was mounted on a concrete reaction-block structure.

The reaction block was constructed of four modules which were

prestressed to the test floor. The ram was controlled

electronically so that lateral displacement of the top of the column

would be at a constant rate. This provided a safeguard against

Page 32: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

b

Fill· 2 . 8 Formwork fo r (a) Large and (b) Medium-Scale Specimens

to

Page 33: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

SW Iv

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Page 34: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

f(

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Page 35: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

©f 19 mm .p Bolt (Typical)

o

19 mm Steel Mount inc; P 10 t e

23

,-__ specimen~ L ____ -4 __ --,

~+ ___ -++ 4-4----._+--- 4--1--- --+-L_ --I ! r-----I~ __ ---1

13 mm 41 0/2") Threaded Bolt W/Coupler

451mm ( 1.5')

Fig. 2.11

I

Collar With Fitted I ' I

8011 Beoring L I I

at 4 Locations +.-J

Note: Support Removed f Of Ex.1erio( Join1 Specimens ----...-j

P in Support ----.

Small-Scale Test Apparatus, from Kreeger (12)

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24

excessive instantaneous damage if a specimen were to suddenly loose

strength.

The ram was connected to the specimen with a swivel head

which permitted rotation in the vertical and horizontal planes with

negligible resistance. Swivel heads were located on each end of the

ram so that transverse forces would not exist across the ram and

possibly load the specimen out of plane. Roller supports were

simulated at the ends of the beams using a set of steel channels

which were connected at the top and bottom to fixtures with roller

bearings. For the range of lateral displacement used in this test

series, the channels permitted horizontal movement with negligible

resistance and essentially no vertical movement. Out of plane

movements of the specimens were prevented with a set of cables and

turnbuckles which were attached to the beam ends and secured to the

test floor at an angle of 33 degrees with the horizontal.

2.8 Instrumentation

For all specimens, applied load, joint rotation, load-level

displacement, and rotation at beam ends were measured (Fig. 2.12).

In addition, the strains in the reinforcement in the large-scale

specimens were measured. The applied load was measured with the 156

kN (35 kip) capacity load cell with a sensitivity of 0.1%. The

joint rotation was measured using a pair of 127 mm (5 inch) LVDT's.

A rigid aluminum bar, 1830 mm (72 inches) for the large-scale, and

686 mm (27 inches) for the medium-scale was secured to the joint

region on each side of the specimen. A rigid rod connected these

aluminum bars to the core of the LVDT. The load-level displacement

Page 37: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

APP

LIED

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LE

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ENT

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T

ROTA

TIO

N 1#

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ST

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RO

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ON

Fig

. 2

.12

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\.Jl

Page 38: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

26

was measured with a 102 mm (4 inch) LVDT in a similar arrangement

(Fig. 2.13).

Inelastic rotations within a specified gage length of 152 rom

(6 inches) for the large scale, and 76 mm (3 inches) for the medium

scale, at the ends of the beams were measured. One 25 mm (1 inch)

LVDT was mounted on the top and bottom faces of each beam and

attached to the column face. Swivel connections were provided so

that free rotation of the LVDT and the core was possible (Fig.

2.14). All displacement transducers had sensitivities of less than

.5 of the range of the particular instrument. Prior to testing,

each transducer was calibrated on a vertical milling machine

sensitive to .003 mm (.0001 inch).

Strains in the longitudinal reinforcement in the large-scale

specimens were measured at locations indicated in Fig. 2.15. Strain

gages were attached to the middle reinforcing bar in each beam.

Voltage outputs from the load cell, LVDT's, and strain gages

were fed into an analog-digital converter. The resulting binary

coded number was read by a Hewlett-Packard 9825T computer which then

stored the number permau~ntly on magnetic tape. Following testing,

the numbers on tape were converted to measurements by the 9825T, and

plotted using a Hewlett-Packard 7225B plotter.

2.9 Testing Procedure

Each large and medium-scale specimen was loaded through

repeated cycles of ever increasing rotation (Fig. 2.16). The first

six cycles led up to the yield load, and the remaining cycles

represented loading in the post-yield region. Joint rotation was

Page 39: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

2080 mm

[IJ'~ .' : ' :~'

, " " '/I' !? " .' "

" ,'i:, ". , ~, I,

5action A-A

RIGID ROO ± 102 14M LVOT

A A

~~~--~-----.~~~~ :!:. 127 14M LVDT

'o:t -0)

o '! 127 14M LVOT

Fig. 2.13 Instrumentation

27

Page 40: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

28

I r -

FREE ROTATION CONNECTION

t! J Ii E

I 0 r h It)

r 152 mm l

--

CYD1' IIlI.DER\TTACHED TO SPEC'''''''

\ L W

I • I ~ 25 M~ LVDT

......

Fig. 2.14 Beam Rotation LVDT Arrangement

Page 41: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

J ,...,

Ie

#1 r'\

'I-'

I

-. -. ,..., -. '{g ~ 111 #i2 m #10

#2 #3 '#4 tIS #6 -. -. 1'1'\ ,..... ,..... '-v 'V 'v 'V ';7

216 mm 216 ! D 152 I 152 216

-

216 mm 216 lJIII 152 I 102

Fig. 2.15 Location of Strain Gages in Large-Scale Specimens

29

-. #(4

#7 ~

'I-' )

216

Page 42: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

o cri

o N

o . ... o d

c . ... I

(I) :z III :::t -U III n. (I)

III ...I < U (I) I

...I

...I < :::t (I)

o o N cri I I

SNVIOV~ '001* NOI~V~O~ ~NIOr

o cri

o o N ..:

o d

o . ... I

(I) :z III :::t -U III n. (I)

III ...I < U (I) I

:::t ::J -0 III :Ii:

C :z < III

" a: < ...I

o cri I

SNVIOVH '001* NOI~V~~ ~NIOr

30

CIJ <lJ

'M H 0 +-J CIJ

'M ::c +-J j::l <lJ S <lJ 0 CO

'"" p.. CIJ

'M ~

\0 .-<

N

CO 'M r,..;

Page 43: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

31

the controlling variable due to its non-dimensional nature.

The tests were monitored by a continuous plotting of load

versus rotation and load versus load-level displacement. All

measured parameters were read at intervals such that a smooth curve

could be obtained later when the data were reduced. Crack patterns

were photographed at the end of each cycle, and at maximum rotations

for large-amplitude cycles. Widths of significant cracks were

recorded at maximum positive, negative, and zero rotations. Each

test took approximately eight hours to complete.

Page 44: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

CHAPTER 3

SCALE RELATIONSHIPS OF EXTERIOR JOINTS

3.1 Introduction.

This chapter is a description of how accurately the response

of a large-scale exterior joint was predicted by its small-scale

counterpart. Because the large-scale specimen so nearly resembled

an actual building element, it was considered the control in this

investigation. Its response is described in detail here, then the

response of the small-scale specimen is compared to it. The reader

should recall no medium-scale exterior joints were tested. This was

because the mechanisms exhibited by the exterior joints were simple

compared to those in the interior joints, so it was felt further in­

vestigation of the exterior joint at medium scale was not necessary.

3.2 Description of Large-Scale Specimen Response

The load-rotation curve for a large-scale specimen is

shown in Fig. 3.1. It is divided into two graphs for a clearer

presentation. Curves showing load-displacement, load-rotation at

the beam end, and load-strain relationships are shown in Figs.

3.2-3.3. Photographs of damage in the joint region are shown in

Fig. 3.4. Measured widths of significant cracks are listed in Fig.

3.5. The data from just one specimen is presented because the

31-

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33

e,~ ____ ~ ______________ ~ ____ ~ ____________ _

EXTERIOR JOINT Sl'ECIMEN

,r-----~------~--------~~~~----------~----------~

-211

-ell .. .. .. .. .. OJ .. .. .. oJ ~ '" .,; '" oJ I I I I

JOINT ROTATION -11111. RADIANS

a

911

EXTERIOR JOINT SPECIMEN lit

<411

211 i

~ • 61

i -21

-<411

-ell

-ell .. ., .. OJ .. OJ .. OJ .. OJ .. OJ .. of oJ oJ 'i '" "' .; oS N 01 I I I I I

JOINT ROTATION -1111, RADIANS

b

Fig. 3.1 Load-Rotation Response for Exterior Joint

Page 46: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

~ JDINT SPECllEM I

~+-----~------~------~-----+------~----~~----~----~ .. gj I

-211

~ .. .. rt 't

.. •

.. ;

.. ..

extERIIJI JOINT SPEClIEN I t

.. It .. .. '" .. • 1 .: i' 1 iii iii -I

BEAll IIITAnlll.1&I, RADIANS

Fig. 3.2 Response of Exterior

• .. • - • i

OJ .. n .. - ell ell 01

Joint

34

Page 47: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

ElCTERIDR JOINT SPECIMEN

S'TRAIN CAGE.- 1

a~ ______ ~ ____ ~ ______ ~ ____ ~

-211

~~--__ -. ______ ~ ____ ~ ______ ~ ____ ~ ____ ~ __ ----~-----4

60 ~-

-2Q

-60

Fig.

.. N

1 or

EXTERIOR JOINT SPECIMEN

STRA IN CAGE no. 2

'" ,

• ..

o d

STEEl.. STRAIN .,00

b

... II '" .. .. ..

3.3 Load-Strain Response for Exterior Joint

35

Page 48: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

z:

'" si a ...J

a

'" ...J

~

z "

80

60

40

20

o

-20

-EO

-80

" ,

N

Fig.

---,-------,------,----,----,---,- ---.,----1 EXTERIOR JOINT SPECIMEN

STRA IN GAGE no. :3

EXTERIOR JOINT SPECIMEN

STRA IN GAGE no. 4

'" ,. '" ,.

a ci

STEEt.. STRAIN -lOa

a ci

c

STEEL STRA IN .100

d

/

1 1

1

j I '"

N

3.3 Load-Strain Response for Exterior Joint

36

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37

EXTERIDR JOINT SPECIMEN

STlIAIN CAGE.... S

J~----+-----+-----~----~~~~----~------------t

~~~------~~-------N~-----~'-----~.:-----~"------:N;-----~~:-----~~ 111 1 '" Ii '" '" '"

EXTERIDR JOINT SPECIMEN

STlIAIN CACE.- a

21

-ea ... (It N " • ~ N (It ... '" Ii III 1 III III 1 Ii III

I I

stm.. STlIAIN -1111

f

Fig. 3.3 Load-Strain Response for Exterior Joint

Page 50: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

~ o ..J

::l

~ ..J 0. a. <:

HO ,.----...--------,r------,-----,------,---,------r--~

EXTERIOR JOINT SPECIMEN J 511

STRIIIN G"CiE no. 7

4U

_._----+ ...... _. -...... +-.-----+---~---+--+----+- ......

-4D

8D.O

60. U

40. 0 ~ 20. a ~

i

--'"

EXTERIOR JOINT SPECIMEN

STRA IN OAGE no. 8

\ "

\'\~' '., " .. ~\

o ci

".

STEEL. STRAIN .100

g

j

ll.ll ~-----I----i---+--~~~---t------j I

-20. 0 ~

-40. U \

I I

-60. a ~

-80. 0 L-.. -.--L..-----l.---.......J----J......---~---_:O:----\Il:::-----:.O ~ ~ ~ ~ 9 ~ m ¢ ~

ci

STEEL. STRAIN -\00

h

Fig. 3.3 Load-Strain Response for Exterior Joint

38

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39

u----~--------~--~----~--~----~---+----~--_t

IDI'TiRIDR JOINT SPEl:IMEN

211

~

~ II

fil

i -21 r -411

I

.....a 111 N .. .. .. • .. .. .. N ... .. .. 01 01 f "' 01 '" '" .I .. I I I I

IITEEI.. II'TIIAIH -1.

i

Fig. 3.3 Load-Strain Response for Exterior Joint

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L

-

/~

Fig. 3 . 4 Photographs oE Damage of Exterior Joint

Page 53: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

Fig . 3 . 4 Pho t ographs or Damage of Exterior Joinl

1ft

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42

Cycle

5 .8 .8

6 1.0 .9

7 1.6 1.6

8 1.8 .2 2.0 .2

9 2.5 1.0 2.5 .8

10 3.0 1.6 3.0 1.6

11 3.5 1.6 3.0 1.4

12 5.0 2.0 3.0 1.4

13 5.0 2.5 3.5 1.6

14 5.0 3.0 5.0 2.5

IS 5.0 3.0 5.0 2.5

Fig. 3.5 Crack Widths for Exterior Joint

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replication of the response between specimens was quite good. The

following description of the characteristics response of the

large-scale specimen was made in reference to the load-joint

rotation relationship shown in Fig. 3.1.

43

As seen in Fig. 3.1a, the response to initial loading showed

a high elastic stiffness up to point A, which was at 20 kN (4.5

kips). At this point the first flexural cracks opened, which caused

the stiffness reduction seen in the response curve. This stiffness

reduction was also seen in the load-strain curves in Figs. 3.3.

During unloading the stiffness matched the original elastic

stiffness. Loading in the opposite direction produced an identical

response; a high elastic stiffness up to cracking at point B, a

slight reduction in stiffness until unloading began, and a high

unloading stiffness back through zero load.

The remaining five cycles shown in Fig. 3.1a represent all

those in the pre-yield range of loading. During each successive

cycle the loading stiffness decreased from the previous cycle. This

was due to progressive cracking of the specimen, as shown by Figs.

3.4 and 3.5. Unloading stiffness remained high, but by the sixth

cycle a noticeable stiffness reduction occurred near the loading

axis at point C. At this stage, the original flexural cracks had

opened wide enough so a crack on the top of the beam could not close

before a crack on the bottom of the beam began to open. This left

very little of the beam actually in contact with the column and

created, momentarily, a soft section. The stiffness increased

starting at point D in Fig. 3.1a because the cracks in the top of

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the beam were then able to close. This was supported by the

load-strain relationships in Figs. 3.3a and b which showed no

increase in compressive strain upon further loading.

44

The eight curves shown in Fig. 3.1b represent the response

in the post yield range of loading. When the load reached 58 kN (13

kips) at point E, yield occurred. This was evidenced by the

load-strain curves in Fig. 3.3. Yielding caused the stiffness

reduction seen after point E. In this range the unloading stiffness

again started out very high, but the stiffness reduction near the

load axis became more pronounced. In the last two cycles, cracking

was so extensive that by the time the top cracks were able to close,

the bottom cracks had opened far enough to prevent a noticeable

increase in stiffness. The load-strain relationships in Fig. 3.3c

and d showed a considerable change in compressive strain in later

cycles which was caused by open flexural cracks. The particularly

low stiffness along segment FG in the final cycle could have been

due to a slight deterioration in bond. However, since the bars were

anchored securely with a 90 degree bend, this effect of bar slip was

minimal in the exterior joint.

Other general observations resulting from testing the

exterior joints were as follows:

1) The shapes of the load-rotation and load-displacement

curves were essentially the same. This indicated the deformations

of the column were nearly elastic during the test.

2) The shapes of the load versus joint rotation and load

versus beam rotation curves were similar, which indicated that most

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of the nonlinear action of the beam occurred at the column face.

Furthermore the beam rotations were a significant amount of the

total rotations, which suggested nonlinear behavior in the joint

region.

3) The strength of each specimen did not deteriorate with

cycles of large deformation.

45

4) If a new maximum rotation was not reached during the

current cycle, there was little reduction in stiffness upon loading.

5) If during the current cycle, the specimen was loaded to no

more than the maximum load of the preceeding cycle, there was a

reduction in the area bounded by the hysteresis loop. This

represented a decrease in the amount of energy dissipated which was

a result of increased deformations within the joint region.

6) Each specimen's ability to deform exceed the stroke length

of the loading actuator (+-5 inches). In no case did a crushing

failure or reinforcement fracture occur.

3.3 Comparison of Large and Small-Scale Specimens

For ~omparison purposes the load-rotation curve for the

large-scale specimens was reproduced in Fig. 3.6 along with a

similar curve for the small-scale specimens. In this figure the

vertical axis for the small-scale specimens was normalized to

increase the flexural strength for direct comparison with the

response of the large-scale specimen. The adjustment factor was the

square of the length scale factor (9) multiplied by the ratio of the

products of the reinforcing ratio and the measured yield load:

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46

aO.----r--~~--._--~----·~--_r----r_--_r--_.----~--_,--_,

eo EXTERIOR JOINT S~ECIMEN

- - P ult.

zo

o ~--~---4----+----+--~~~-H~~~--1----+----+----+---4

-20

-lID -i' uit. __ _ __ __

JOINT ROTATION 0100. RADIANS

a

- - - - - - - P ult.

21

-4

-811 -P ult. _ _ _ _ _ _ _ _

... • n • n • n • II • II • n • aI ; ; ~ ~ 1 '" "' ~ ~ III III oj I I ,

JOINT' RllTATlIlN .1" IWIlNIS b

Fig. 3.6 Comparison of (a) Small-Scale and (b) Large-Scale Specimens

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47

Conventional principles of mechanics assumed for ultimate strength

design were used to determine this scaling factor. The horizontal

axis, rotation, was nondimensional and therefore not adjusted.

Within the range of rotation of +-.010 radians, the

stiffness characteristics exhibited by the large-scale specimens

were modeled well by the small-scale specimens. The response of the

small-scale specimens showed similar trends to the response of the

large-scale specimens with regard to stiffness reduction at first

cracking, a gradual degradation of stiffness upon loading, and a

high unloading stiffness which reduced near zero load. The

small-scale specimens also modeled the slight stiffness increase

upon loading representing crack closure. One further similarity was

that no substantial loading stiffness reduction occurred in cycles

which did not contain new extreme rotations.

When looked at qualitatively, the two figures in Fig. 3.6

gave further information regarding the effects of scaling on

strength and stiffness. A normalized cracking load of about 30 kN

(6.75 kips) was observed for the small-scale specimens. This was

somewhat higher than that of the large-scale specimens. This may

have been attributable to a higher strength in the mortar from which

the small-scale specimens were cast. The normalized maximum load of

the small-scale specimens was approximately 60 kN (13.5 kips) which

matched that of the large-scale specimens.

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48

In the load reversal region, the reduced stiffness segment

extended through a rotation equal to approximately .010 radians for

the small-scale specimens, as compared to approximately .005 radians

for the large-scale specimens. This may have been attributable to

bond deterioration which was more prevalent in all of the

small-scale specimens tested. The relatively weaker bond resulted

in the lower average stiffness of a complete cycle for small-scale

specimens.

The weaker bond resistance of the small-scale specimen may

be inferred by the change of slope of the load-rotation curve (Fig.

3.6a). During the first large amplitude cycle, in the first

quadrant of loading, a significant change of stiffness was observed

after cracking but before yield of reinforcement should have

occurred. It should also be noted that no appreciable cracking had

occurred due to diagonal tension within the joint of the specimen.

This change of slope may have been attributable to a localized

deterioration in bonding of beam reinforcement within the column.

During subsequent cycles of loading, the stiffness in this range was

greatly reduced. This tendency was also observed during the third

cycle following the first large amplitude cycle.

Because of the limited range of the response of the

small-scale specimens, direct comparisons with the large-scale

specimens could not be made for rotations greater than .010

radians. However, as previously mentioned, specimens at both scales

resisted nearly equal loads at maximum rotations. These loads were

slightly less than loads calculated by conventional mechanics used

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49

in ultimate strength design (16) which have been shown in the

figure. In addition, the unloading slopes during large amplitude

cycles were very similar for specimens at both scales. These

similarities suggest that the large-scale specimens' behavior could

be represented well by the small-scale specimens for loading cycles

in the non-linear, or post-yield, range of response.

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CHAPTER 4

SCALE RELATIONSHIPS OF INTERIOR JOINTS

4.1 Introduction

This chapter is a description of how accurately small-(1/12)

and medium-(1/4) scale interior joints models could predict the

response of large-scale prototypes. As with the exterior joints,

the large-scale specimen was considered the control, and its

response is explained in detail. A brief description of the fourth

large-scale specimen follows, P?inting out the differences in

response due to a different distribution of longitudinal

reinforcement. Then the small, and finally the medium-scale

specimen responses are compared to that of the large-scale specimen.

4.2 Description of the Large-Scale Specimen Response

The load-rotation curve representing the first three large­

scale specimens is shown in Fig. 4.1. The load-displacement,

load-beam rotation, and load-strain relationships are plotted in

Figs. 4.2-4.4. Photographs of damage and crack information are

presented in Figs. 4.5 and 4.6. Data is presented for just one

specimen because replication with other specimens was very good.

The characteristic response is described with reference to the

load-rotation response of Fig. 4.1.

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51

1~r-------~--------~--------T-----------------~------~

INmlIDR JOINT 5P£ClNEN

98

.t--------.--------~----~~~~----~------~------~

-

-laft----------.~------~~---------.~--------n.---------.~------~ft ~ f 1 ~ ~ ~ ~

!lIT!RtDR JOINT i!KC1ME11

Fig. 4.1 Load-Rotation Response for Interior Joint

Page 64: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

1811

INTE

RIO

R JO

INT

Sf'E

CltE

N

1211

811

i 041

1

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fit ... ~ .....

-811

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li III

III

III

III

III

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III

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II ... D

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Fig

. 4

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esp

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for

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rio

r Jo

int

l.n

N

Page 65: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

-128

-1S~ __ .-+I ____ ., _____ ", __ ~----~ __ ~----~--__ ~ __ ~ ____ ~ __ ~----, .. . .. ot ot i

• -I .. ; • Pi

.. '"

• - • /II • 01

lST----+----~--~----~--~----~----~--~----~--~----~--_T

INTERIIlR JOINT SPECIMEN

-1.+-__ ~----~--~----~--~----~--__ ~--~----~--~----~--~ • 1

Fig. 4.3

n n • .. • r 1 '" 01 -

VEST IEAII RUTATlIII -1l1li. RltDl/lllS

.. - • N n N • 01

Heasured Beam Rotations in Interior Joint

53

Page 66: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

~

~ III

~ '"

1~~----------~----~----~------------------~-----r

INTERlDR JOINT SPECIMEN 121

STRAIN CAGE.... I

a~ ____ +-____ +-____ ~ __ ___

-121

-IML---__ ~-------. .-.----~~~----~-------~~-----: ... ------~~:-----~~ ; ; 1 1 = · · · ·

181

1211

£11

411

/I

-411

-121

-1M V1 N ~ ~ I I

INTERIDR JOINT SPECIMEN

51Wo\IN (lAta _ 2

.. a ~

1 1 1 • .. a 01 01 oS,

.. .. H .I

Fig. 4.4 Load-Strain Response for Interior Joint

54

Page 67: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

55

150 i--INTERIOR JOINT SPECIMEN

120 ~ STR~ IN CACE no. 4

"r ~

.0

~ 5 0 Gl

~ <

--0

~r ~ -'t

-WII -- I .. ~ N 0 "! ~ ~ I " d

STEel.. STRAIN -100 C

160 r-----

1 I i I

It<TERIOR JOINT SPIiCIHEN i 120 f- ~

i ~.# I I I STRA I N CACE no. 5

},f'

~ 80 f-

I

I f' I ~. ~

40 I .-0".9~ " ~,/ "

-- .. -::

1 I a f-- -----t--

I I

-40 ~ i j

-30 1-

-120

I J I I

--160 L __ ~ '" "! 0 "! ~ ~

I I I d

STEEL STRA IN -100

d

Fig. 4.4 Load-Strain Response for Interior Joint

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100 ,--- - ~-"----r------,-----,-- ---r-----,---~--,__-----, I

i 120 f--

! I

80 ~

~~ or

-40 ~

I -~ I

-120 r I

INTERIOR JOINT SPECIM~N

STRA. I N GACE no. 6

-160 L_...l-. ___ "--__ --' ___ -'-___ -'-___ ~--_::__--__:: ~ m N 0 ~ m ~

I' 1" d

STEEl. STRAIN 0100

e

1a~----~~--~----~----,_----------~----~----_r

121

81

-121

INTERIlIR JOINT !ll'£C11EM

sntt.lll ct.GIt _ T

.. N .. ; ; ; • ..

III III N

III '" III

Fig. 4.4 Load-Strain Response for Interior Joint

56

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~

~ fa

i

l~~----~--~~--~----~----~----~----~----~----~----t

1211

41

I

-41

---I.

-11. .. N .: .: I I

INTERIDR JOINT SPECIMEH

STRIIIM GAC!! _ II

.. a .. 't ~ 1

• .. ~ II

t1IIL mAIM -1_ g

.. II

.. ~

II ..

1~~ ________________________ ~~ __ -, ________________ -----+-----, INTERIDR J01NT SPECIMEH

1201

STRIIIH GAOl _ 1.

I~--------------------~~~~--~~--~----t

-12111

h

Fig. 4.4 Load-Strain Response for Interior Joint

57

Page 70: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

:<

~ " , a UJ

--' Q.

!l;

1':0

ao

40

a

-40

-80

-120

-160

INTERIOR JOINT SPECIMEN

STRA IN CACE no. 11

OJ

"

Q

d

STEEL. STRAIN *\00

i IS~ ____________________ ~ __________ ~ ____ ~ ____ -,

INTERIOR JOINT SPECIMEN 1211

STRAIN GAG! _ 12

I~-------------------J~~----~--------~

-1211

-lSl-------+-------+-------+-----~:_----~~----~N=_----~~=_----~.~ 11: • • • •

Fig. 4.4 Load-Strain Response for Interior Joint

58

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~

~ f3

i

1111

lIITIIUa. JaINI' SPECIMEN 1211

!IT1IAIN CAGE _ 13

III

414

I

-41

-1211

1111~----~----~-----+-----;------~----+-----~-----r

ItmIIJIlR JDJNI' SPIClMEII 1211

STRAIN CAGE _ 14

-1211

-IIII·~·~-----"+-------N~-----~~------.~----~~~----~N~-----:"~----~. ... .. .. .. .. 1 111 ..

Fig. 4.4

S'!1!EL STRAlH el.

1 Load-Strain Response for Interior Joint

59

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Fig . 4 . 5 Photographs of Damage of Inlerior Joinl

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Fig. 4 . 5 Photographs of Damage of fnteri()r Joint

6/

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62

C 1 C

Cycle Al E F

4 .5 .3 .4 .3

5 1.4 .5 1.4 .6 .6

6 1.4 .2 .5 .2 .7 .3 .7

7 2.0 .2 .5 .2 .7 .3 1.0

8 2.0 .2 .7 .2 1.8 .6 1.0

9 2.0 .2 1.4 .2 1.8 .4 1.0 .4

10 3.0 .5 1.4 .2 1.8 .4 1.0 .6 .3

11 3.0 .5 1.4 .2 2.0 1.4 1.0 .6 .3

12 3.0 .5 1.4 .2 2.0 1.5 1.5 .6 .7

13 3.0 .5 2.5 .7 2.5 .6 1.5 .6 1.2 1.0

14 4.0 .6 3.5 .4 3.0 .4 2.5 1.6 1.2 1.0

15 5.0 1.4 4.5 1.0 5.0 .6 2.5 2.0 1.2 1.2

Fig. 4.6 Crack Widths for Interior Joint

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63

Referring to Fig. 4.la, the specimens responded to initial

loading with a high elastic stiffness up to the cracking point A,

whi~h occurred at 40 kN (9 kips). Cracking caused a stiffness

reduction which continued until the unloading point. This phenomena

was also observed in the load-strain responses in Fig. 4.4. The

unloading stiffness matched the loading stiffness. As was always

the case, loading in the opposite direction produced an identical

response: a high elastic stiffness reduced when cracks opened at

point B. The reduced stiffness continued until unloading, upon

which the stiffness assumed its high elastic value back through zero

load.

The remaining five cycles shown in Fig. 4.1a represent all

those in the pre-yield range of loading. The gradual decrease in

loading stiffness was caused by progressive cracking in the

specimens. Unloading stiffnesses continued to be high, but near the

load reversal point (point C in Fig. 4.la) a stiffness reduction

became apparent. This was due partially to open flexural cracks on

both faces of the beams, but more importantly, it was due to some

deterioration of the steel-concrete bond within the joint region.

Since the curve between points C and D had some slope, it indicated

the specimens were resisting load. This suggested that the bond had

not been completely destroyed. At point D, flexural cracks on beam

faces A and D (Fig. 4.6) closed, thereby causing a stiffness

increase.

The family of curves in Fig. 4.lb represents the response in

the post-yield range of loading. Yield occurred at a load of 118 kN

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64

(26.5 kips) as shown in by load-strain graphs in Fig. 4.4. Yield

caused the stiffness reduction seen at point E on Fig. 4.1b. The

response curves in this range showed the unloading stiffness to

start out very high, but to gradually decrease as the curve

approached zero load. In the load reversal region between points F

and G, the stiffness was observed to decrease more and more. This

was caused by progresive bond deterioration of the beam bars within

the joint. By the final cycle the bond had been completely

destroyed and the curve in that region was essentially horizontal.

With no bond resistance, the tensile force in the beam bars was

constant across the width of the joint. This phenomenon, coupled

with the fact that no concrete was in compression because of open

flexural cracks, caused the specimens to have no resistance to

loading. The specimens could resist load only after the column had

rotated far enough to close some of the flexural cracks and subject

the concrete to flexural compressive stresses.

The progression of bond deterioration could also be inferred

from the load-strain relationships. As more of the bond was

destroyed, a longer segment of a bar was put into tension.

Eventually, when the bond was completely destroyed, the segment of a

bar within the joint region was constantly in tension. This was

seen in Figs. 4.4c,d,h,i,j which were the responses indicated by all

the strain gages within the joint.

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65

4.3. Comparison of Large-Scale Interior and Exterior Joints

The six general characteristics listed at the end of Section

3.2 for exterior joints were also observed during the tests of

interior joints. However, the two configurations showed two

distinct differences in their responses. First, the interior joints

resisted twice the load, at both cracking and yield, as did the

exterior joints. This would be expected since the interior joints

had two beams extending from them. The second difference was the

exterior joints showed much less stiffness loss in the load reversal

range of the response. This was because bond deterioration in the

exterior joints was not nearly as great as in the interior joints.

4.4 Differences due to Different Reinforcement

The reader should recall the fourth large-scale interior

joint specimen was reinforced differently from the first three.

While the area of steel in the beams was kept essentially the same,

smaller diameter bars were used. This section discusses the effect

of that change. Fig. 4.7 shows the load-rotation relationship for

this specimen. Photographs of damage and crack information are

given in Figs. 4.8 and 4.9.

The effect of using smaller bars could be seen by comparing

Figs. 4.7 and 4.1. For smaller bars (Fig. 4.7), the pinching of

each hysteresis loop in the vicinity of the origin was not nearly as

pronounced as for larger bars (Fig.-4.1). As discussed in Section

4.3, pinching of a hysteresis loop was an indication of slip of the

beam reinforcement as a result of bond deterioration in the joint

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188

I 12

11

sa

i 4&

~ II

fit ... ~ -4

&

-sa

-121

1

-161

11 IS

11

1 15

1

'i N

7

I

Fig

. 4

.7

SPEC

IMEN

LIJ

4

111

151

111

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as .

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... I

I

JDIN

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Page 79: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

'i 1.1

" , --.­II" ,.

-

i LI 6

(I (. , --.. -,

Fig . 4 . 8 Photogr aphs of Damage of Specimen LIJ4

b/

Page 80: SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN … · SCALE RELATIONSHIPS OF CONCRETE BEAM-COLUMN JOINTS by ... subjected to earthquake motions. ... model studies of multistory concrete

tl ~,

) } /

" ., - .-

I tl 15 /

r f

I

) '"' I '\, r

Fig . 4 . 8 Pho t ograph s of OamD~c uf Specimen 1.[.14

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Cycle

3

4

5

6

7

8

9

10

11

12

13

82

A 1

.2

.4

.7

.9

1.6

1.4

1.6

2.0

2.5

3.0

3.5

.2

.2

.6

.4

.9

.5

1.0

.9

1.8

1.8

2.5

.5 .2

.6 .2

1.2 .4

1.6 .5

2.5 .5

3.0 .5

3.5 1.8

3.5 1.0

4.0 3.5

4.0 3.5

4.5 5.0

.5 .2 .2 .2

.6 .2 .4 .2

1.2 .4 .7 .6

1.6 .5 .9 .4

2.5 .5 1.6 .9

3.0 .5 1.4 .5

3.5 1.8 1.6 1.0

3.5 . 1.0 2.0 .9

4.0 3.5 2.5 1.8

4.0 3.5 3.0 1.8

4.5 5.0 3.5 2.5

Fig. 4.9 Crack Widths for Specimen 11J4

69

E F

.2 .5

.2 .5

.4 .5

.4 .5

.3 .6

.3 .6

.5 1.0

.4 .8

.5 .8

.6 1.0

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70

region. The load-rotation curve (Fig. 4.7) suggested bond

deterioration was not as prevalent in the fourth specimen as in the

first three. The reason for this was the shorter development length

of the smaller diameter bars in the fourth specimen. This enabled

the steel to accept higher tensile forces before the bond was

damaged. For this reason, in the future attention should be given

to modeling the ratio of reinforcement development length to the

width of the column.

Another effect of the shorter development length was that

the steel yielded at a lower load of 100 kN (22.5 kips). Ultimately

though, the fourth specimen exhibited essentially the same strength

as the first three. During the final cycle, the loading stiffness

had reduced to where no noticeable yield point could be defined.

This could have been attributable to the Bauschinger effect in the

steel, since by this point the steel had been loaded past its yield

point several times.

Like the first three specimens, the fourth specimen showed

an ability to deform which exceeded the range of the loading

actuator. No crushing failure occurred, nor did the reinforcing

steel ever fracture.

4.5 Comparison of Large and Small-Scale Specimens

For comparison purposes, the load-rotation curve of Fig. 4.1

was reproduced in Fig. 4.10 along with a similar curve from tests of

small-scale specimens. In this figure the vertical axis

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71

160

INTERIOR JOINT SPECI~EN 120

SO

z " ~ .w 9 ffi ::; .. .. <

lil N ::; -40 <

~ z

-90

-120

-leo 0 "' 0 "' 0 ~ 0 ~ 0 Ul 0 Ul 0

~ 'l' 'l' i i , c:i

'" '" .. JOINT ROTATION .100. RAOIANS

a

1.

IImRIIIt JOINT 9P!CIMEN 121

• 48

~

! • iii

i -411

... -121

-1 •

• .. • n • n • n :! ., • WI •

'1 '" '" - - 0; '" '" .: '" oJ 01 I I I I

JOINT ROTATION *1_ RADING b

Fig. 4.10 Comparison of (a) Small-Scale and (b) Large-Scale Specimens

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for the response of the small-scale specimens was normalized as

previously described in Section 3.3.

72

Within the range of rotation of +-.010 radians, the

small-scale specimens showed similar characteristics to the

large-scale specimens with regard to a stiffness reduction at first

cracking and a gradual stiffness degradation upon loading.

Furthermore, unloading stiffnesses between the two scales matched

very closely. The normalized maximum load of the small-scale

specimens was 120 kN (27 kips), essentially the same as for

large-scale specimens.

The good correlation between scales was not as evident in

the load reversal range of the response (+-lOkN). After just one

load cycle into the nonlinear range, the small-scale specimens lost

bond across the width of the column. The gradual stiffness

degradation caused by progressive bond loss, which was

characteristic of the large-scale specimens, was not modeled at

small-scale. For the small-scale specimens, one complete large

amplitude cycle was sufficient to pull the bar from each side of the

joint in each direction, thereby destroying the bond. Bond

resistance was hampered in the small-scale specimens for two

reasons: first, mechanical anchorage was reduced because the wire

which made up the reinforcement was smooth. Second, the tensile

development length of the wire was approximately 130 rom (5 inches)

based on pullout tests (45). This was considerably greater than the

column width of 50 mm (2 inches). In the large-scale specimens the

development length of the reinforcement was 460 mm (18 inches) based

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73

on the ACI document 318-77 (16). This was equal to the width of the

column. Future small-scale specimens may model prototype structures

better if a wider column, bmall diameter wire, or some form of

mechanical anchorage is used.

Subsequent load-cycles of the small-scale specimens revealed

forms of behavior conistent with those described above. After the

large-scale specimen had been put through enough large-amplitude

cycles to completely destroy its bond, its response was very similar

to that of the small-scale specimen. The small-scale specimens did

exhibit some general trends which were characteristic of the

large-scale specimens. Their strength and ability to deform were

never exceeded, subsequent cycles to greater extremes caused reduced

loading stiffnesses, unloading sti.ffnesses began high but decreased

substantially near zero load.

In summary, the small-scale interior joint specimens did not

model the hysteretic response of a large-scale spe~imen in the load

reversal region of the response, until the large-scale specimen had

gone through several large-amplitude loading cycles. Apart from

this deviation, the small-scale specimens were able to mimic both

the strength and the elastic stiffness characteristics of the

large-scale specimens.

4.6 Comparison of Large and Medium-Scale Specimens

The load-rotation curves for the large and medium-scale

specimens are shown in Fig. 4.11. The vertical axis of the response

of the medium-scale specimen was normalized according to the

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74

lSI

INTERIOR JOINT SPECIIIElI 1211

911

~

~ 4

iii ~ II .. <

~

i -4

-811

-1211

-1811 os '" .. It1 os It1 .. It1 .. '" .. It1 .. Pi N N i i .; .; .; N N Pi , , , ,

JOINT ROTIITlDII -!IIIII. AADIAIIS

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IIlT'ERIDR JOINT SPEI:IIEN lZ11

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-lilt .. .. os II> .. II os .. os It .. ., II

'l' 01 01 ; , , , , .. .. " ~ 01 01 ,,;

JlltNT ROTATlDH -lilli, AADIANS

b

Fig. 4.11 Comparison of (a) Hedium-Scale and (b) Large-Scale Specimens

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procedure outlined in Section 3.3. In this case the length scale

factor was 3.

75

The responses in Fig. 4.11 showed that all the sClffness

characteristics exhibited by large-scale specimens were modeled well

at 1/4-scale. Since conventional concrete was used in fabricating

medium-scale specimens, cracking strengths between scales were

essentially the same. Since standard deformed bars were used in the

medium-scale specimens, the degradation in stiffness due to bar slip

was modeled well. The only noticeable differences in the responses

was in the normalized maximum load for the medium-scale specimens,

which was slightly higher than the maximum load for the large-scale

specimens. Unlike the small-scale, medium-scale models of

beam-column joints showed they can be used to replicate behavior of

full-scale prototypes well enough to be used as design aids.

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CHAPTER 5

SUMMARY AND CONCLUSIONS

5.1 Summary

The purpose of this investigation was to determine if

reduced scale models could depict the behavior of reinforced

concrete beam-column joints under lateral load reversals. This was

done by examining the differences in response of several test

specimens. Specimens were constructed at large-scale (3/4-scale),

medium-scale (1/4-scale), and small-scale (1/12-scale). Large-scale

specimens were the control specimens. This investigator tested one

large-scale exterior joint, two large-scale interior joints, and six

medium-scale interior joints. One large-scale exterior joint and

two large-scale interior joints were tested by others at the

University of Colorado. All of these tests, combined with the

results of tests of small-scale interior and exterior joints done at

the University of Illinois, provided the data necessary to make

comparisons. In this report data was presented for only one

specimen of each scale and configuration because replication between

like specimens was very good. Comparisons were based on the

strength, stiffness, and energy dissipation characteristics

exhibited by the hysteretic load-rotation relationship of each test

specimen.

76

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77

5.2. Conclusions

The results of the research have shown that a reduced-scale

model of a beam-column joint can depict the response of a prototype

within both the linear and nonlinear ranges. Specific conclusions

and recommendations derived from the study are given below:

1) Reduced-scale specimens can be proportioned directly with

the length scale factor. All depth, width, and cover dimensions can

be scaled exactly. Allowance should be given to the percentage and

strength of reinforcement.

2) Story shears resisted by a reduced-scale beam-column jOint

can be related to forces resisted by a large-scale specimen

according to the following relations:

~S

3) Scale relationships for small-scale specimens were highly

dependent on the configuration of the component. For tests of

exterior joints, where the longitudinal reinforcement was securely

anchored in the joint region, overall stiffnesses and strengths were

represented well by small-scale specimens. Tests of the interior

joints did not show such good correlations between scales. Demand

for more bond resistance was inherent for the interior joints

because of the simultaneous push and pull on the beam reinforcement

across the width of the joint. Bond degredation occurred at both

small and large-scales, but to varying extents. Small-scale

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78

specimens suffered complete bond loss after only one large amplitude

loading cycle. The loss of bond in the large-scale specimens was

more gradual. This demonstrated the need to develop a more

effective means of anchorage for small-scale reinforcement. The

ratio of the development length of reinforcement to the width of the

column should be considered when designing specimens at

small-scale. Use of small-scale specimens may be used to represent

the hysteretic characteristics of a reinforced concrete beam-column

joint for verification studies of numerical models. However,

precise quantitative representations of these characteristics using

a small-scale model may be inappropriate.

4) Bond degradation was found to be highly dependent on the

development length of longitudinal reinforcing bars. In tests of

large-scale specimens, one reinforced with #4 bars had significantly

less bond loss with no loss in strength than those reinforced with

#6 bars.

5) Specimens fabricated at 1/4-scale, using conventional

concrete and standard deformed reinforcing bars, had very similar

strength and stiffness characteristics to 3/4-sca1e specimens.

Variance between load-rotation curves for large and medium-scale

specimens was smaller than that for large-scale specimens reinforced

differently. Furthermore, the variance was smaller for physical

models constructed at 1/4-sca1e than that for numerical models and

prototypes. Results of the research show that medium-scale

specimens may be used directly for design and analysis of full-scale

reinforced concrete frame structures.

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79

5.3 Recommended Future Research

This study determined that simple components of

two-dimensional reinforced concrete frame structures can be

represented well by medium-scale models. Future research should

focus on more complex structures to determine if similar scale

relationships to those put forth in this report can be applied to a

variety of components. Components which could be investigated

should include unsymmetrically reinforced rectangular beams,

T-beams, three-dimensional frames, walls, shell structures, and

cable-stayed or segmentally prestressed bridges. Data from such

tests could be used to verify existing nonlinear analysis

techniques.

Future research should ~lso concrete on the development of

small-scale technology. It would be very advantageous to produce a

1/12-scale model which could predict the response of large-scale

specimens as accurately as a 1/4-scale model.

The results of this study have shown it would be conceivable

to test a 1/4-scale model of a concrete frame structure to examine

the lateral load resistance in many full-scale structures. In a

moderate-sized structural engineering laboratory, it would be

feasible to test a model as tall as twenty stories.

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BIBLIOGRAPHY

1. "Recommendations for a U. S.-Japan Cooperative Research Program Utilizing Large-Scale Testing Facilities", U.S.-Japan Planning Group Cooperative Research Program Utilizing Large-Scale Testing Facilities, Earthquake Engineering Research Center, University of California, Berkeley, Report No. 79-26, September, 1979.

2. Gulkan, P., and M.A. Sozen, "Inelastic Response of Reinforced Concrete Structures to Earthquake Motions", Journal of the American Concrete Institute, Vol. 71, No. 12, December, 1974, pp. 601-609.

3. Otani, S., and M.A. Sozen, "Simulated Earthquake Tests of Ric Frames", Journal of the Structural Division, ASCE, Vol. 100, No. ST3, March, 1974, pp. 687-701.

4. Aristizabal-Ochoa, J.D., and M.A. Sozen, "Behavior of Ten-Story Reinforced Concrete Walls Subjected to Earthquake Motions", Civil Engineering Studies, Structural Research Series No. 431, University of Illinois, Urbana, October, 1976.

5. Lybas, J.M., "Concrete Coupled Walls: Earthquake Tests", Journal of the Structural Division, Vol. 107, No. ST5, May, 1981, pp. 835-856.

6. Healey, T.J., and M.A. Sozen, "Experimental Study of the Dynamic Response of a Ten-Story Reinforced Concrete Frame with a Tall First Story", Civil Engineering Studies, Structural Research Series No. 450, University of Illinois, Urbana, August, 1978.

7. Moehle, J.P., and M.A. Sozen, "Earthquake-Simulation Tests of a Ten-Story Reinforced Concrete Frame with a Discontinued First-Level Beam", Civil Engineering Studies, Structural Research Series No. 451, University of Illinois, Urbana, August, 1978.

8. Abrams, D.P., "Experimental Study of Frame-Wall Interaction in Reinforced Concrete Structures Subjected to Strong Earthquake Motions", Seventh World Conference on Earthquake Engineering, Istanbul, Turkey, September, 1980.

9. Moehle, J.P., and M.A. Sozen, "Experiments to. Study Earthquake Response of RIC Structures with Stiffness Interruptions", Civil Engineering Studies, Structural Research Series No. 482, University of Illinois, Urbana, August, 1980.

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10. Stewart, J. and Abrams, D.P., "Comparison of Large and Small-Scale Reinforced Concrete Behavior", Masters Thesis, University of Colorado, July, 1982.

81

11. Bedell, R., and Abrams, D.P., "Scale Relationships of Concrete Columns", Structural Research Series No. 8302, Department of Civil Engineering, University of Colorado, Boulder, January, 1983.

12. Kreger, M.E., and D.P. Abrams, "Measured Hysteresis Relationships for Small-Scale Beam Column Joints", Civil Engineering Studies, Structural Research Series No. 453, University of Illinois, Urbana, August, 1978.

13. Gilbertsen, N.D., and J.P. Moehle, "Experimental Study of Small-Scale Ric Columns Subjected to Axial and Shear Force Reversals", Civil Engineering Studies, Structural Research Series No. 481, University of Illinois, Urbana, July, 1980.

14. Abrams, D.P., and M.A. Sozen, "Experimental Study of Frame-Wall Interaction in Reinforced Concrete Sructures Subjected to Strong Earthquake Motions", Civil Engineering Studies, Structural Research Studies No. 460, University of Illinois, Urbana, May, 1979.

15. Aktan, A.E., Bertero, V.V., Chowdhurry, A.A., and Nagashima, T., "Experimental and Analytical Predictions of the Mechanical Characteristics of a liS-Scale Model of a 7-Story Reinforced Concrete Frame-Wall Building Structure", Earthquake Engineering Research Center, University of California, Berkeley, Report No. 83-13, 1983.

16. "Building Code Requirements for Reinforced Concrete (ACI-77)" , American Concrete Institute, Detroit, 1977.

17. Gavlin, N.Lo, "Bond Characteristics of Model Reinforcement", Civil Engineering Studies, Structural Research Series No. 427, University of Illinois, Urbana, April, 1976.

18. Newmark, N.M., "Current Trends in the Seismic Analysis and Design of High Rise Structures", Chapter 16 in Earthquake Engineering, Prentice-Hall, Inc. Englewood Cliffs, N.J., 1970, pp. 403-424.

19. Takeda, T., M.A. Sozen and N.N. Nielsen, "Reinforced Concrete Response to Simulated Earthquakes", Journal of the Structural Division, ASCE, Vol. 96, No. 8T12, December, 1970, pp. 2257-2573.

20. Shibata, A., and M.A. Sozen, "The Substitute-Structure Method for Seismic Design in RIC", Journal of the Structural Division, ASCE, Vol. 102, No. ST1, January, 1976, pp. 1-18.

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82

21. Biggs, J.M., W.K. Lau, and D. Persinki, "Aseismic Design Procedures for Reinforced Concrete Frames", Department of Civil Engineering, Massachusetts Institute of Technology, Publication No. R79-21, Order No. 653, July, 1979.

22. Derecho, A.T., S.K. Ghosh, M. Iqbal, and M. Fintel, "Strength, Stiffness, and Ductility Required in Reinforced Concrete Structural Walls for Earthquake Resistance", Journal of the American Concrete Institute, No.8, Vol. 76, August, 1979, pp. 875-896.

23. Fintel, M., and S.K. Ghosh, "Aseismic Design of a 31-Story Frame-Wall Building", Proceedings of ASCE/Engineering Mechanics Division Specialty Conference: "Dynamic Response of Structures: Experimentation. Observation, Prediction, and Control", Atlanta, Georgia, January, 1981, pp. 874-886.

24. Saiidi, M. and M.A. Sozen, "Simple Nonlinear Seismic Analysis of R/C Structures", Journal of the S~ructural Division, ASCE, Vol. 107, No. ST5, May, 1981, pp. 937-952.

25. Tansirikongkol, V. and D.A. Pecknold, "Approximate Modal Analysis of Bilinear MDF Systems", Journal of the Engineering Mechanics Division, ASCE, Vol. 106, No. EM2, April, 1980.

26. Sozen, M.A., "Review of Earthquake Response of R/C Buildings with a View to Drift Control", Seventh World Conference on Earthquake Engineering, Istanbul, Turkey, September, 1980.

27. Wilby, G.K., "Response of Concrete Structures to Seismic Motions", Ph.D. Thesis, Department of Civil Engineering, University of Canterbury, Christchurch, New Zealand, July, 1975.

28. Hidalgo, P., and R.W. Clough, "Earthquake Simulator Study of a Reinforced Concrete Frame", Earthquake Engineering Research Center, University of California, Berkeley, Report No. 74-13, December, 1974.

29. Oliva, M.G., "Shaking Table Testing of a Reinforced Concrete Frame with Biaxial Response", Earthquake Engineering Research Center, University of California, Berkeley, Report No. 80-28, 1980.

30. Abrams, D.P., "Measured HystereSis Relationships for Small-Scale Beams", Civil Engineering Studies, Structural Research Series No. 432, University of Illinois, Urbana, November, 1976.

31. Popov, E.P., V.V. Bertero and H. Krawinkler, "Cyclic Behavior of Three R.C. Flexural Members with High Shear", Earthquake Engineering Research Center, University of California, Berkeley, Report No. 72-5, October, 1972.

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32. Soleimani, D., E.P. Popov and V.V. Bertero, "Hysteretic Behavior of Reinforced Concrete Beam-Column Subassemblages", Journal of the American Concrete Institute, No. 11, Vol. 76, November, 1979, pp. 1179-1196.

33. Viwathanatepa, S., E.P. Popov, and V.V. Bertero, "Selsmic Behavior of Reinforced Concrete Interior Beam-Column Subassemblages", Earthquake Engineering Research Center, University of California, Berkeley, Report No. 79-14, June, 1979.

34. Vallenas, J.M., V.V. Bertero and E.P. Popov, "Hysteretic Behavior of Reinforced Concrete Structural Walls", Earthquake Engineering Research Center, University of California, Berkeley, Report No. 79-20, August, 1979.

83

35. Zagajeski, S.W., V.V. Bertero, and J.G. Bouwkamp, "Hysteretic Behavior of Reinforced Columns Subjected to High Axial and Cyclic Shear Forces", Earthquake Engineering Research Center, University of California, Berkeley, Report No. 78-05, 1978.

36. Hanson, N.W., and H.W. Conner, "Seismic Resistance of Reinforced Concrete Beam-Column Joints", Journal of the Structural Division, ASCE, Vol. 93, ST5, October, 1967, pp. 533-560.

37. Uzumeri, S.M., and M. Seckin, "Behavior of Reinforced Concrete Beam-Column Joints Subjected to Slow Land Reversals", Department of Civil Engineering, University of Toronto, Report No. 75-05, March, 1974.

38. Otani, S., and W.T. Cheung, "Behavior of Reinforced Concrete Columns Under Biaxial Lateral Load Reversals", Department of Civil Engineering, University of Toronto, Publication 81-02, Fe bruary, 1981.

39. Jirsa, J. 0., "Development of Loading System and Initial Tests: Short Columns under Bidirectional Loading", Department of Civil Engineering, University of Texas at Austin, CESRL Report 78-2, 1978.

40. Zia, P., R.N. White and D.A. VanHorn, "Principles of Model Analysis", Models for Concrete Structures, Special Publication of American Concrete Institute No. 24, 1970.

41. Staffier, S.R., and M.A. Sozen, "Effect of Strain Rate on Yield Stress of Model Reinforcement", Civil Engineering Studies, Structural Research Series No. 415, University of Illinois, Urbana, February, 1975.

42. Krawinkler, H., "Possibilities and Limitations of Scale-Model Testing in Earthquake Engineering", Proceedings of the Second U.S. National Conference on Earthquake Engineering, Earthquake Engineering Research Institute, August, 1979.

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43. Moncarz, P.D., and H. Krawinkler, "Material Simulation in Dynamic Model Studies of Steel and Reinforced Concrete Structures", Seventh World Conference on Earthquake Engineering, Istanbul, Turkey, September, 1980.

84

44. Scholl, Roger E., ed., "EERI Delegation to the People's Republic of China", Earthquake Engineering Research Institute, Berkely, CA, January, 1982.

45. Kreger, M.F. and Sozen, M.A., "A Study of the Causes of Column Failures in the Imperial County Services Building During the 15 October 1979 Imperial Valley Earthquake". Civil Engineering Studies, Structural Research Series No. 509. University of Illinois, Urbana, August, 1983.

46. Wolfgram, Kathy, Report on I/IO-scale Model of Japanese Full-Scale 7-Story Test Structures, University of Illinois, 1984.

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APPENDIX

Load-Rotation Curves

for Other Large-Scale Specimens

05

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86

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