seismic design of exterior beam-column joint

INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING

Volume 2, No 1, 2011

© Copyright 2010 All rights reserved Integrated Publishing services

Research article ISSN 0976 – 4399

Received on July, 2011 Published on September 2011 160

Seismic Resistance of Exterior Beam Column Joint with Diagonal Collar

Stirrups

Bindhu K.R1, Sreekumar K.J

2

1-Assistant Professor, Department of Civil Engineering, College of Engineering,

Thiruvananthapuram, Kerala, India

2-P. G. Student, Dept. of Civil Engineering, College of Engineering, Thiruvananthapuram,

Kerala, India

[email protected]

doi:10.6088/ijcser.00202010100

ABSTRACT

The performance of beam-column joints have long been recognized as a significant factor

that affects the overall behaviour of reinforced concrete (RC) framed structures subjected to

large lateral loads. The reversal of forces in beam-column joints during earthquakes may

cause distress and often failure, when not designed and detailed properly. In the present study,

four one third scaled exterior beam-column joint specimens were prepared with only one of

them conforming to the guide lines of IS 13920: 1993 for seismic resistant design. Second

one was detailed with additional diagonal collar stirrups at joints and beam reinforcements

and the third one is cast without collar stirrups but having additional beam reinforcements.

The fourth specimen was having same longitudinal reinforcements of the first specimen but

with increased spacing of ties in the joint region. All the specimens were subjected to similar

reverse cyclic loading to simulate earthquake loading in structures. The loading was applied

by displacement control mode. Based on the experimental findings and subsequent analysis,

it is found that, second specimen having additional beam reinforcements and diagonal collar

stirrups at joints exhibits a better performance than the others.

Keywords: Beam-column joint, ductility, energy dissipation, reinforcement details, ultimate

load

1. Introduction

The performance of beam-column joints have long been recognized as a significant factor

that affects the overall behaviour of reinforced concrete (RC) framed structures subjected to

large lateral loads. The beam-column joints that are not detailed and built in accordance with

seismic codes present a serious hazard that can affect the overall ductility of a structure

subjected to severe earthquake shocks.

The failure of reinforced concrete structures in recent earthquakes in several countries has

caused concern about the performance of beam-column joints (Durrani and Wight 1985).

Since past three decades extensive research has been carried out on studying the behaviour of

joints under seismic conditions through experimental and analytical studies.

Various international codes have been going periodic revisions (Tsonos 2007). Among the

Indian codes IS 13920:1993 deals with ductile detailing of reinforced concrete structures

subjected to seismic forces. However, despite the significance of the joints in sustaining large

deformations and forces during earthquakes, specific guidelines are not explicitly included in

Seismic Resistance of Exterior Beam Column Joint with Diagonal Collar Stirrups

Bindhu K.R, Sreekumar K.J

International Journal of Civil and Structural Engineering

Volume 2 Issue 1 2011

161

Indian codes of practice (IS 456: 2000, IS 1893 : 2002, IS 13920: 1993, SP 34:1987). One of

the basic assumption of the frame analysis is that the joints are strong enough to sustain the

forces (moments, axial and shear forces) generated by the loading, and to transfer the forces

from one structural element to another (beams to column, in most of the cases). Confinement

of joint can be done to satisfy the above condition (Asha and Sundarrajan 2006, Bindhu et al.

2008, Bindhu et al. 2009a).

2. Present Study

The main objectives of the present study was to confine the R.C beam column joint by

providing diagonal collar stirrups at joint region and to investigate the strength, ductility and

energy dissipation capacity of beam-column joint specimens having various reinforcement

arrangements and thereby to compare the behaviour of the specimens made of non-

conventional confining reinforcement pattern with conventional reinforcement pattern as per

IS 13920: 1993.

An eight storey building was modelled and analyzed using STAAD Pro. A typical exterior

beam-column joint of the building was designed and detailed as per IS 13920:1993 and

scaled to the laboratory conditions (Tsonos et al. 1992, Tsonos 2000, Murty et al. 2001,

Murty et al. 2003, Jain and Murty 2005 a, Jain and Murty 2005 b, Ingle and Jain 2005,

Bindhu et al. 2009b).

2.1 Details of Beam-Column Joint

The experimental program included four 1/3 scaled specimens (C1, C2, C3 & C4). The

specimen C1 was conforming to IS 13920, C2 with additional beam reinforcements and

diagonal collar stirrups over C1, C3 with additional beam reinforcements over C1 and C4

similar to C1 but with increased spacing of ties at joint. The size of the beam was 800 mm x

100 mm x 150 mm and column 1000 mm x 100 mm x 150 mm. The dimensions and

reinforcement details of test assemblages are shown in Fig.1 and Fig.2.

3. Casting of Specimens

The cement used was Ordinary Portland Cement 43 grade conforming to IS 8112:1989. River

sand passing through 4.75 mm IS sieve and having a fineness modulus of 3.16 was used as

fine aggregate. Crushed granite stone of maximum size not exceeding 12.5 mm was used as

coarse aggregate.

The mix was designed in proportion of 1:1.33:2.47 by weight respectively and the water-

cement ratio was kept as 0.45. The 28 day average compressive strength from 150 mm cube

test was 34.55 N/mm2. The reinforcement cages used for different specimens are shown in

Fig.3. The specimens were cast in horizontal position inside wooden moulds and were de-

moulded after 24 hours and then cured in water tank.





162

Figure 1: Reinforcement details for Specimens C1 and C2

REINFORCEMENT DETAILS FOR SPECIMEN C2.

6 Nos. 8mm TOR.

3mm TOR TIES.

2 Nos. 8mm TOR.(TOP.)

3mm TOR STIRRUPS

@ 35 mm C/C.3mm TOR STIRRUPS

@ 50 mm C/C.

3mm TOR TIES @ 25 mm C/C.





6 Nos. 8mm TOR.

3mm TOR TIES.

2 Nos. 8mm TOR.(TOP.)3mm TOR STIRRUPS

@ 35 mm C/C.

3mm TOR STIRRUPS

@ 50 mm C/C.





2 Nos. 8mm TOR.(BOTTOM.)



3mm STIRRUPS. ( 100mm c/c/.)

3mm TOR TIES (2 Nos.)

3mm STIRRUPS. ( 50mm c/c.)


3mm TOR STIRRUPS

@ 100 mm C/C.





163

Figure 2: Reinforcement Details for Specimens C3 and C4


6 Nos. 8mm TOR.

3mm TOR TIES.


3mm TOR STIRRUPS

@ 35 mm C/C.

3mm TOR STIRRUPS

@ 50 mm C/C.







3mm STIRRUPS. ( 100 mm c/c.)

3mm STIRRUPS. ( 50mm c/c/.)


6 Nos. 8mm TOR.

3mm TOR TIES.

2 Nos. 8mm TOR.(TOP.)3mm TOR STIRRUPS

@ 50 mm C/C.





3mm TOR STIRRUPS

@ 100 mm C/C.





164

Figure 3: Reinforcement Cages Prepared for Different Specimens





165

3.1 Experimental Setup

The test set up in the laboratory is shown in Fig. 4. The specimens were tested in an up right

position and static reverse cyclic loading was applied. Both ends of the column were hinged

properly within the self straining test frame. A deflection control test was conducted in which

the specimen was subjected to an increasing deflection with increments not exceeding 2.5

mm up to the failure. The specimens were instrumented with hydraulic jacks, LVDTs, dial

gauges and strain gauges to monitor the behavior during testing. Lateral loading, at deflection

increments of 2.5 mm was applied in a cyclic manner by means of hydraulic jacks having a

capacity of 100 kN and 200 kN for downward and upward loading respectively. It was

applied at a distance of 100 mm from the free end of the beam until failure of the specimens.

One dial gauge was placed at the loading point of beam to control deflection at the point of

application of load. Electrical resistance strain gauges were pasted on the reinforcement in

order to measure strains. The specimens were evaluated in terms of ultimate load carrying

capacity, load displacement relationship, and energy dissipation characteristics.

Figure 4: Test Setup in the Laboratory

3.2 Crack Pattern and Failure Mode

The crack patterns in different specimens are shown in Fig. 5. For specimen C1 and C2, the

initial diagonal and column beam interface hairline cracks occurred in the third cycle of

loading in positive direction and fifth cycle of loading in negative direction. For specimen C2,

further cracks were developed at the column beam interface only after sixth cycle in both

positive and negative direction. However, in specimen C3, the cracks in the joint at diagonal

direction started after third cycle of loading in positive direction and fifth cycle of loading in

negative direction. The specimen C2 failed due to the advancement of crack width at the

interface between column and beam. Among the specimens, C2 specimen which was

additionally detailed with collar stirrups and beam reinforcements exhibited the best

performance. For this specimen, no major cracks were noticed at the joint and the joint





166

remained intact through out the test. Hence the failure was dominated by tensile failure than

the joint failure. The improvement of performance by developing further cracks away from

the joint face to the beam region can be noticed for the specimen with collar stirrups. The

crack width is also less for this specimen compared to other specimens. The specimen C3 and

C4 without collar stirrups have diagonal cracks at the beam-column joint region. This may be

due to the higher flexural capacity of beam compared to the column.

Figure 5: Crack Patterns of Different Specimens

3.3 Ultimate Load Carrying Capacity of Specimens

The ultimate load carrying capacities of all the specimens were observed and Fig.6 shows the

comparison of the same. For the specimen C1 detailed as per IS 13920: 1993, the ultimate

load is 38 kN. But for the specimen C2 detailed as per IS 13920: 1993 with collar stirrups and

additional beam reinforcements, the ultimate load is 72 kN. Incase of the specimen C3





167

detailed without collar stirrups at joint but with additional beam reinforcements, the ultimate

load reached is 65 kN.

0

10

20

30

40

50

60

70

80

C1 C2 C3 C4

Specimens

Lo

ad

in

KN

Figure 6: Comparison of Ultimate Load Carrying Capacity of Different Specimens

Similarly for the specimen C4 which is similar to C1 but with increased spacing of ties in

joints, ultimate load reached is 35 kN. These results show the effectiveness of the diagonal

collar stirrups with additional beam reinforcement in the enhancement of ultimate load

carrying capacity.

3.4 Hysteretic Loops

The hysteretic loops of the load displacement relationship for the four specimens tested in

the laboratory are shown in Fig. 7 through Fig.10. It is observed that the specimen C2 with





168

-20.00

0.00

20.00

40.00

60.00

80.00

100.00

-25 -20 -15 -10 -5 0 5 10 15 20 25

Deflection in mm

Lo

ad

in

kN

Figure 7: Load-Displacement Hysterisis Loop for Specimen C1

-20.00

0.00

20.00

40.00

60.00

80.00

100.00

-25 -20 -15 -10 -5 0 5 10 15 20 25

Deflection in mm

Lo

ad

in

kN






169

-20.00

0.00

20.00

40.00

60.00

80.00

100.00

-25 -20 -15 -10 -5 0 5 10 15 20 25

Deflection in mm

Lo

ad

in

kN


-20.00

0.00

20.00

40.00

60.00

80.00

100.00

-25 -20 -15 -10 -5 0 5 10 15 20 25

Deflection in mm

Load

in k

N


additional beam reinforcement and diagonal collar stirrups developed better hysteretic loops

with higher curve area compared with other specimens. The performance of the specimen C2

over the specimen C3 shows the enhanced strength and behaviour of joints with diagonal

collar stirrups.

3.5 Ductility

The displacement ductility factor is the ratio of the maximum deformation that an element

can undergo without significant loss of initial yield resistance to the initial yield deformation

(Park and Paulay 1975). Fig. 11 through Fig.14 shows the lateral load displacement envelope





170

curves of all the specimens. Table 1 gives the experimental results of ductility factor. It can

be seen that the specimen C2 detailed with diagonal collar stirrups at joint and additional

beam reinforcements had more ductility than that detailed without collar stirrups.

-20.00

-10.00

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

-25.00 -20.00 -15.00 -10.00 -5.00 0.00 5.00 10.00 15.00 20.00 25.00

Defflection in mm

Lo

ad in

kN

Figure 11: Load Displacement Envelope for C1

-20.00

-10.00

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

-25.00 -20.00 -15.00 -10.00 -5.00 0.00 5.00 10.00 15.00 20.00 25.00

Deflection in mm

Lo

ad

in

kN

Figure 12: Load-Displacement Envelope for C2





171

-20.00

-10.00

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

-25.00 -20.00 -15.00 -10.00 -5.00 0.00 5.00 10.00 15.00 20.00 25.00

Deflection in mm

Lo

ad

in

kN


-20.00

-10.00

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

-25.000 -20.000 -15.000 -10.000 -5.000 0.000 5.000 10.000 15.000 20.000 25.000

Deflection in mm

loa

d i

n k

N





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Table 1: Displacement Ductility of Test Specimens

Specime

n

Displacement in mm Displacement

ductility

Average

displace

ment

ductility

Yield Ultimate

+

direction

-

direction

+

directio

n

-

directio

n

+

directio

n

-

directio

n

C1 7.50 5.00 17.50 17.50 2.33 3.50 2.92

C2 5.00 5.00 22.5 22.50 4.50 4.50 4.50

C3 7.50 7.50 22.50 17.50 3.00 3.50 3.25

C4 5.00 5.00 15.00 17.50 3.00 3.50 3.25

4. Energy Dissipation Capacity

Structures with high energy dissipation characteristics are able to withstand stronger shaking

and better seismic response. The amount of energy dissipated during a particular loading

cycle is calculated as the area enclosed by the corresponding load versus displacement

hysteretic loop (Paulay et al. 1978). The cumulative energy dissipated is given in Table 2.

Table 2: Cumulative Energy Dissipation for Various Specimens

Sl

No. Specimen designation

Energy dissipation

(kN-mm)

1 C1 922.16

2 C2 1187.73

3 C3 974.43

4 C4 864.25

Fig. 15 shows the energy dissipation capacity versus number of cycles. It can be seen that, in

the first four cycles, the specimens do not have greater energy dissipation. However, in the

final cycles, the specimens have greater dissipated energy. The reason is that higher lateral

load produces greater area (dissipated energy) bounded by the load displacement curve. It is

clearly observed that the specimen detailed with diagonal collar stirrups and additional beam

reinforcements had more energy dissipation capacity than the others.





173

0

50

100

150

200

250

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

No.of cycles

En

erg

y d

issip

ati

on

cap

acit

y i

n k

N-m

m

C1 C2 C3 C4

Figure 15: Comparison of Energy Dissipation in Each Cycle of All Specimens

5. Conclusions

Seismic performance of reinforced concrete moment resisting framed structures mainly

depends upon the inelastic behaviour of joints. Based on the experimental investigation

conducted on exterior beam-column joint under static reverse cyclic loading, the following

conclusions are drawn.

The load carrying capacity of the specimen additionally reinforced with beam and

diagonal collar stirrups (C2) is nearly 98 % higher than the specimen detailed as per IS

13920(C1) and 10 % more than the specimen with additional beam reinforcements (C3).

Also the specimen detailed with increased spacing of ties at joints gave unfavorable

results; i.e., a reduction of 10 % with regard to load carrying capacity (C4).

Ductility of the specimen additionally detailed with diagonal collar stirrups and beam

reinforcements is compared and found that it is 54 % higher than that of the specimen

detailed as per IS 13920: 1993 without collar stirrups, and 5 % higher than specimen

detailed as per IS 13920, but having additional beam reinforcement.

Energy dissipation capacity of the specimen detailed additionally with diagonal collar

stirrups and beam reinforcements is observed to be 22.36 % higher than that of the

specimen detailed as per IS: 13920: 1993.

Acknowledgements

The research presented in this paper has been supported through a project entitled “A study of

strengthening of joints in multistory RC structures subjected to seismic loading” awarded to





174

College of Engineering, Trivandrum by All India Council for Technical Education through

research promotion scheme. The authors gratefully acknowledge the AICTE for the same.

6. References

1. Asha, P and Sundararajan, R., (2006), “Evaluation of seismic resistance of exterior

beam-column joints with detailing as per IS 13920: 1993”, Indian Concrete Journal,

33(1), pp. 29-34.

2. Bindhu, K.R., Jaya, K.P. and Manicka Selvam, V.K., (2008), “Seismic resistance of

Exterior beam-column joints with non-conventional confinement reinforcement

detailing”, Journal of Structural Engineering and Mechanics, An International Journal,

30(6), pp.733-761.

3. Bindhu, K.R., Jaya, K.P. and Manicka Selvam, V.K., (2009a), “Behaviour and

strength of exterior joint sub assemblage subjected to reversal loadings”, Indian

Concrete Journal, 83 (11), pp.9-20.

4. Bindhu, K.R., Sukumar, P.M and Jaya, K.P., (2009b), “Performance of Exterior

Beam-Column Joints under Seismic Type Loading”, ISET Journal of Earthquake

Technology, 46(2), pp.47-64.

5. Durrani, A.J. and Wight, J.K., (1985), “Behavior of Interior Beam-to-Column

Connections Under Earthquake-Type Loading”, ACI Structural Journal, 82(3),

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6. Ingle, R.K. and Jain, S.K., (2005), “Explanatory examples for ductile detailing of R.C

buildings”, Report IITK – GSDMA-EQ22-V3.0, IIT Kanpur, Kanpur.

7. IS 13920:1993, “Indian Standard Ductile Detailing of Reinforced Concrete Structures

subjected to Seismic forces”, Bureau of Indian Standards, New Delhi, India.

8. IS 1893 (Part 1):2002, “Indian Standard Criteria for earthquake Resistant Design of

Structures”, Bureau of Indian Standards, New Delhi, India.

9. IS 456:2000, “Indian Standard Plain and Reinforced Concrete Code of Practice”,

Bureau of Indian Standards, New Delhi, India.

10. Jain, S.K. and Murty, C.V.R. (2005a), “Proposed Draft Provisions and Commentary

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11. Jain, S.K. and Murty, C.V.R. (2005b), “Proposed Draft Provisions and Commentary

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12. Murty, C.V.R., Durgesh, C.R., Bajpai, K.K. and Sudhir, K.J., (2001), “Anchorage

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pp.274-280.

13. Murty, C.V.R., Durgesh, C.R., Bajpai, K.K. and Sudhir, K.J., (2003), “Effectiveness

of Reinforcement Details in Exterior Rreinforced Concrete Beam- Column Joints for

Earthquake Resistance”, ACI structural journal, 100 (2), pp.149-155.

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15. Paulay, T., Park, R. and Priestley, M.J.N., (1978), “Reinforced Concrete Beam-

Column Joints under Seismic Actions”, ACI structural journal, 75(11), pp.585-593.

16. SP 34:1987, “Indian Standard Handbook on Concrete Reinforcement and Detailing”,

Bureau of Indian Standards, New Delhi, India.

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seismic design of exterior beam-column joint

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