Shear Behavior and Strength of SRCS Beam-Column Joints
Budi Suswanto1,* , Cheng-Cheng Chen2, Keng-Ta Lin3
Lecturer, Department of Civil Engineering, ITS Surabaya, Indonesia
Former Ph.D. candidate, Department of Construction Engineering, National Taiwan University of
Science and Technology, Taiwan
2
Professor, Department of Construction Engineering, National Taiwan University of Science and
Technology, Taiwan
3
Former Ph.D. candidate, Department of Construction Engineering, National Taiwan University of
Science and Technology, Taiwan
*
Corresponding author: budisw2000@yahoo.com
1
Abstract
Four large-scale beam-column subassemblies were fabricated and tested under cyclic loading to
investigate the shear behavior of steel reinforced concrete column-steel beam (SRCS) beam-column
joints. In the design of beam-column joints, there are two types of column sections; they are
continuously built-in crossing and single H-sections; with adjacent flanges of column being connected
by diaphragm plate in a joint at the level of the beam flanges. To facilitate the analysis of the shear
behavior and strength of the beam column joints, these systems were designed in such a way that the
joints are likely to fail first. Experimental and analytical studies have been carried out to estimate the
structural performance of the designed joints and to predict shear strength of beam-column joints with
two-side and single-side force inputs by using strength superposition method and modified softened
strut-and-tie method. Experimental results from SRCS beam-column subassemblies showed that: (1)
the strength superposition method and modified softened strut-and-tie method were able to estimate
the SRCS beam–column joint shear strength with reasonable accuracy; (2) increased depth of
sectional steel leads to a higher shear strength for the beam-column joint; (3) a combination of corner
stirrups and shaped steel cross-sections was able to provide sufficient lateral support to longitudinal
steel bars and adequate confinement to the concrete in the joint to replace the need for closed hoops;
and (4) significant yielding and shear deformation are experienced by the web of steel sections and
large web shear deformation is considered to be the main cause of fracture in beam flange-to-column
flange welds.
Keywords: steel reinforced concrete column-steel beam (SRCS), beam-column joints, shear behavior,
strength superposition method, modified softened strut-and-tie method.
1. Introduction
With the fast advances in construction technologies, the concrete-steel composite structural
system produces a building with advantages which include both the stiffness of reinforced concrete
and the strength of structural steel. An additional merit of the concrete-encased composite structural
members is that the concrete also protects the steel section from fire damage and local buckling failure.
In this research, steel reinforced concrete (SRC) column and structural steel beams were chosen
to create a new type of beam-to-column connection. The steel beam was selected because of the
convenience in construction. The reason for using the SRC column is to take advantage of its fire
resistance, structural stiffness, and higher strength. In Taiwan, new buildings constructed with SRC
structures have gradually increased since Ji-Ji earthquake in 1999. Statistics showed that the majority
of the collapse buildings were constructed with reinforced concrete.
Steel reinforced concrete column-steel beam (SRCS) structural members are composed of
concrete, a cross-sectional steel shape, longitudinal steel bars, and transverse steel bars for column and
structural steel for beam sections. The beam-column joints of SRCS moment resisting frames (MRFs)
bear significant shearing forces when subjected to earthquake type loading. Thus, the shear design of
beam-column joints is an important aspect in the seismic design of SRCS MRFs.
Figure 1 Types of beam-column joints
Beam
Beam
Beam
Column
Column
Column
Beam
Beam
(a) Interior joint
(c) Exterior joint II
(b) Exterior joint I
Column
Column
Beam
Beam
(e) Corner joint II
(d) Corner joint I
Reinforced concrete (RC) beam-column joints are classified by ACI-ASCE 352 (1985) as interior
joints, two types of exterior joints, and two types of corner joints as shown in Figure 1. The existing
RC beam column-joint classification method is adopted for SRCS structures, because SRCS beamcolumn joints possess many similarities in behavior with RC joints. In this study, four large-scale
SRCS beam-column subassemblies were fabricated and tested under cyclic loading conditions to
investigate joint shear behavior. The applicability of the joint shear strength evaluation method with
two-side and single-side force inputs to these joints was examined. Based on the test results and
utilizing the concept of strength superposition and modified softened strut-and-tie method, a joint
shear strength evaluation method was proposed and shown to estimate joint shear strength.
2. Experimental Program
2.1 Test Specimens
The systems detailed in Table 1 consisted of four SRCS beam-column subassemblies which
included three Type II corner joints and one Type II exterior joint.
Table 1 Test specimen matrix
Column
Specimen
Beam
Joint type
Member
Steel
Member
Steel
type
shape
type
shape
SRCS-XH1
SRC
XH1
Steel
H5
Corner II
SRCS-H2
SRC
H2
Steel
H6
Corner II
SRCS-H3
SRC
H3
Steel
H7
Corner II
SRCS-H4
SRC
H4
Steel
H8
Exterior II
The subassemblies, along with boundary and loading conditions, are designed to simulate part of
a frame subjected to an earthquake-induced moment. In this research, it will be contrary with actual
design in the field. In order to facilitate the analysis of the behavior and shear strength of the beamcolumn joints, these systems were designed in such a way that the joints are likely to fail first. There
are two kinds of column sections. For Type II corner joints (SRCS-XH1, SRCS-H2, and SRCS-H3),
the dimensions of the SRC column sections were 500 mm  500 mm and for Type II exterior joints
(SRCS-H4), the dimensions of the SRC column sections was 480 mm  480 mm. H1, H2, H3, and H4
were ASTM A36 hot rolled shapes. H5, H6, H7, and H8 were ASTM A572 Grade 50 built-up shapes.
2
(a) SRC-XH1
(b) SRC-XH1-TB
#10
Position A1
#4 @ 120
#10
#4 @ 120
Position A2
#10 longitudinal steel bars and #4 transverse hoops
were used for all SRC columns. The steel bars
Corner stirrup
Corner stirrup
used
were rated ASTM SD420, D32 with a nominal yield stress of 412 MPa. The joint area specimen
details are indicated in Figure 2. For the SRC column, corner stirrups were used in the joint rather than
the Corner
closedstirrup
hoops to provide both lateral #10
support toCorner
the longitudinal
steel bars and confinement
of the
stirrup
#10
concrete.
Ld = 280
Ld = 450
2 Detail of specimens in the joint
area
(d) SRC-XH2-A2
400
400
(c) SRC-XH2
Figure
#10
#10
H300x120x19x32
H500x160x19x32
Corner stirrup
Corner stirrup
XH390x180x6x20
XH390x180x6x20
480
(b) SRC-XH-TB
(a) SRC-XH
Corner stirrup
SRCS-XH1
(a) (e)
SRCS-XH1
Position A1
(f) SRCS-H2
(b)
SRCS-H2
Corner stirrup
#10
#10
XH396x199x7x11
H500x120x19x32
400
180
H300x160x19x32
Corner stirrup
H390x180x6x20
H390x180x6x20
480
480
Continuity plate t = 32
(d)
SRC-H-SB
(d)
(e)SRCS-H4
S-XH2
SRCS-H3
(c)(g)
SRCS-H3
(c) SRC-H
2.2 Test Setup and Procedure
The test setup for Type II corner joints is delineated in Figure 3. The column of the specimen was
clamped to a floor beam that was tied down to a strong floor. The top end of the specimen beam was
connected to a servo-controlled actuator with a capacity of 1000 kN.
Figure 3 Test setup for Type II corner joints
Strong wall
Actuator
Connector
P,
LVDT
+
Beam
Clamp
Clamp
Horizontal Support
Lb
Specimen
Load cell
hc
Jack
Column
Floor beam
Lc
Strong floor
3. Test Results and Analysis
3.1 Test Results
The test results of all specimens are listed in Table 2 and the concrete crack patterns that evolved
in all specimens during testing are shown in Figure 4.
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Table 2 Test results for all specimens
P
Specimen
+

+
peak
peak
P
-

-
peak
peak
Pt
Sudden
(kN)
(%)
(kN)
(%)
(kN)
load drop
SRCS-XH1
+214.0
+2.57
-173.8
-1.91
214.0
1st +4%
SRCS-H2
+383.8
+2.00
-345.0
-1.98
383.8
1st +4%
SRCS-H3
+292.9
+3.22
-280.4
-3.84
292.9
2nd +4%
SRCS-H4
+243.0
+2.96
-242.0
-2.00
243.0
-
Figure 4 Crack patterns of specimens at peak load
(a) SRCS-XH1
(b) SRCS-H2
(c) SRCS-H3
(d) SRCS-H4
The bending moment of the beam at the column face, Mbeam, is defined by
M beam  Pt  Lb
……………………………………
(1)
The column shear force, Vcol, can be obtained using Eq. (2):
Vcol
h 

Pt  Lb  c 
2
 
Lc
…………………………………….
(2)
The joint shear strength, Vt, is defined by
Vt  Vb  Vcol
…………………………………….
4
(3)
Table 3 Joint shear strength of the specimens
fc'
Pt
M beam
V col
Vb
Vt
(MPa)
(kN)
(kN m)
(kN)
(kN)
(kN)
SRCS-XH1
28.0
214.0
511.5
214.0
2353
2139
SRCS-H2
27.2
383.8
917.2
383.8
2264
1917
SRCS-H3
25.3
292.9
700.0
292.9
1727
1462
SRCS-H4
33.8
243.0
313.0
243.0
1198
2179
Specimen
3.2 Shear Strength Evaluation Method
3.2.1 Strength Superposition Method
1) Shear Strength Contributed by Structural Steel Shapes
According to AISC-LRFD (2005) specifications, the shear strength provided by the web is
given as
Vsw  0.6 Fyw d c t w
………………………………… …
(4)
where Fyw is the yield stress of the column web, dc is column depth, and tw is column web
thickness.
From test results result, it was revealed that shearing forces applied to longitudinal flanges in
the joint during load testing may reach the yield stress; therefore Eq. (5) was proposed to
evaluate the shear strength provided by the two parallel longitudinal flanges.
2

……………………………
(5)
Vslf  2  0.6 Fyf b f t f 
3

where Fyf is the yield stress of the column flange, bf is width of column flange, and tf is column
flange thickness.
2) Shear Strength Contributed by Reinforced Concrete
The shear strength contribution of reinforced concrete is calculated pursuant to ACI-318-05
(2005) stipulations. The following expressions can be used to calculate the joint shear strength:
(6)
Vrc   f c ' A j ....................................................................
where  = 1.67 for joints confined on all four faces,  = 1.25 for joints confined on three faces
or on two opposite faces,  = 1.00 for all other types of joints, f c ' is the specified compressive
strength of the concrete (MPa) and Aj is effective area of the joint (mm2).
3.2.2 Modified Softened Strut-and-Tie Method
A softened strut-and-tie (SST) method, satisfying equilibrium, compatibility, and constitutive
laws of cracked reinforced concrete, has been proposed for determining the shear strengths of beamcolumn joints by Hwang and Lee (1999). For SRCS beam-column joints, softened strut-and-tie
method was modified to consider the presence of longitudinal web of steel shape at joint. The total
effective area of the diagonal strut can be calculated as summation of contribution of reinforced
concrete and longitudinal web. Furthermore, the contribution of longitudinal flanges to the shear
strength (Vslf) can be obtained using Eq.(5). The procedure to calculate shear strength predictions using
modified softened strut-and-tie method was cited in author’s dissertation report (Chen & Budi, 2009).
3.2.3 Collated Shear Strength Predictions of Beam-Column Joints
The evaluation methods to predict shear strength of SRCS beam-column joints can be explained as
follows:
1. Strength superposition method (ACI + AISC + Vslf)
RC component is calculated from ACI code. The shear strength for SRCS beam-column joints is
calculated as the sum:
Vsrc  Vrc  Vsw  Vslf ……………………………………
(7)
2. Partial composite method (SST(concrete and longitudinal web) + Vslf)
5
RC and longitudinal web components are calculated from SST method.
Vsrc  Vrc sw( SST )  Vslf
…………………………..


(8)
Table 4 Collated shear strength predictions using strength superposition method
Reinforced concrete portion
Specimen
Joint type

Steel portion
fc'
bi
bo
V rc
V sw
V slf
V src
Vt
(MPa)
(mm)
(mm)
(kN)
(kN)
(kN)
(kN)
(kN)
V t /V src
SRCS-XH1
Corner II
1.00
28.0
120
297
631
414
358
1403
2139
1.52
SRCS-H2
Corner II
1.00
27.2
160
260
688
617
0
1305
1917
1.47
SRCS-H3
Corner II
1.00
25.3
120
300
604
340
0
944
1462
1.55
SRCS-H4
Exterior II
1.00
33.8
180
220
748
695
0
1443
2179
1.51
Average =
1.51
COV =
0.02
Table 5 Collated shear strength predictions using partial composite method
Specimen
Joint type

A str
mm
2
C d,n
V slf
V src
Vt
kN
(kN)
kN
(kN)
K
V t /V src
SRCS-XH1
Corner II
1.00
109883
1.21
1929
358
1909
2139
1.12
SRCS-H2
Corner II
1.00
119354
1.21
2039
0
1336
1917
1.43
SRCS-H3
Corner II
1.00
103955
1.23
1680
0
1046
1462
1.40
SRC-H-SB
Exterior II
1.00
103000
1.25
2265
0
1816
2179
1.20
Average =
1.29
COV =
0.12
4. Conclusions
Based on the experimental and analytical results, the following conclusions can be drawn: (1) the
strength superposition method and modified softened strut-and-tie method were able to estimate the
SRCS beam–column joint shear strength with reasonable accuracy; (2) increased depth of sectional
steel leads to a higher shear strength for the beam-column joint; (3) a combination of corner stirrups
and shaped steel cross-sections was able to provide sufficient lateral support to longitudinal steel bars
and adequate confinement to the concrete in the joint to replace the need for closed hoops; and (4)
significant yielding and shear deformation are experienced by the web of steel sections and large web
shear deformation is considered to be the main cause of fracture in beam flange-to-column flange
welds.
5. References
ACI-ASCE committee 352 (1985). Recommendations for design of beam-column joints in monolithic
reinforced concrete structures, ACI Journal, Proceedings, 82 (3), 266-83.
ACI Committee 318 (2005). Building code requirements for structural concrete (ACI 318-05) and
commentary (ACI 318R-05), Farmington Hills (MI): American Concrete Institute.
American Institute of Steel Construction (AISC) (2005). Specification for structural steel buildings,
Chicago (IL): AISC Inc.
Chen, C. C., and Suswanto, B. (2009). “Shear behavior and strength of SRC beam-column joints with
single-side force inputs,” Dissertation report, Department of Construction Engineering, NTUST,
Taiwan, 11-18.
Hwang, S. J., and Lee, H. J. (1999). “Analytical model for predicting shear strengths of exterior
reinforced concrete beam-column joints for seismic resistance,” ACI Structural Journal, vol. 6(5),
846–857.
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