Steel Structures 7 (2007) 119-128 www.kssc.or.kr

Cyclic Loading Tests on Composite Joints

with Flush End Plate Connections

SHI Wen-long1*, LI Guo-qiang2, YE Zhi-ming1 and R. Y. Xiao3

1Department of Civil Engineering, Shanghai University, Shanghai, 200072, China2Department of Structure Engineering, Tongji University, Shanghai, 200092, China

3Department of Civil Engineering, University of Wales Swansea, UK

Abstract

The tests on composite joint specimens with flush end plate connections subjected to cyclic loads have been conducted inTongji University. One bare steel joint specimen has also been tested for comparison. Various instrumentations have been usedto measure: beam strains, column strains, rebar strains, connection deformations and deflections of specimens. The testobservations are reported in detail in this paper. The main results are as follows: (1) the moment-rotation relationships of theconnections are obtained from the tests, which demonstrate that the hysteretic loops are stable and show good energy dissipationability; (2) the composite joint specimens show large strength resistance and good ductility, and all the rotations of connectionare greater than 0.03rad as required by the FEMA-97; (3) similar failure modes have been identified from the observation ofthe composite specimens, which are found to be concentrated around the joint zone; and (4) the slippage between the concreteslab and steel beam is very small, which shows that between the concrete slab and steel beam the full composition can beobtained by the proper design for the shear connectors.

Keywords: Flush endplate, Composite joint, Low cyclic loading, Joint behavior, Moment-rotational relationship

1. Introduction

It has been convenient to assume full rigid or pinned

connections to simplify analysis for steel frame design.

However, for the sake of cost and construction, a great

number of connections have been designed as semi-rigid

ones. Composite slab and semi-rigid connection constitute

a new type of semi-rigid composite connection. Composite

action of connection is achieved through longitudinal

reinforcement and headed shear studs. A great deal of

experiments and earthquake calamities have shown that

semi-rigid composite connections have excellent mechanical

and aseismic performance. In practical engineering, the

using of semi-rigid composite connections can reduce

steel consumption and expedite construction. In the last

twenty years, a lot of tests (Silva and Simoes, 2001; Sun

and Li, 2004; Laszlo Dunai, 2004; B. M. Broderick and

A. W. Thomson, 2005) and theoretical studies on the bare

steel and composite joints were carried out (Tsuji Bunzo,

2001; Changbin Joh and Wai-Fah, 2001; Rene Maquoi

and Jean-Pierre Jaspart, 2002). The previous experimental

research on composite connections was carried out under

symmetrical and monotonic loading (Xiao and Nethercot,

1994; Anderson and Najafi, 1994). There has been

limited research work conducted on composite joints

under non-symmetrical loading and cyclic loading to

quantify the hysteretic characteristics and the effects of

unbalanced connection moments on the joint. In China,

some semi-rigid bare steel and composite joints (Guo,

2003; Yang, 2004; Gao, 2002), bare steel (Guan, 2003)

and composite frames (Wang, 2005) with semi-rigid

connections have been tested under static loads, cyclic

loads (Guo, 2002) and fire (Lou, 2005) since 1992.

In this paper, one bare steel joint and two composite

joints were tested under cyclic loading. Special attention

has been paid to: (1) stiffness, moment resistance, rotational

capacity of composite joints; (2) hysteretic behavior of

composite joints; (3) effect of stiffeners on behavior of

joints; (4) moment-rotation relationship of composite

joins and damage mode; (4) difference of performance

between the bare steel and composite joints.

2. Configurations of Specimens

Under the action of lateral loading, typical moment-

resisting frame structures may be simplified for analysis

purposes into a series of two-dimensional sub-frames

with interior joints as shown in Fig. 1, where the moment

inflection points are assumed at the middle of beam spans

and column heights, allowing sub assemblages with interior

joints to be isolated for evaluating their performances.

*Corresponding authorTel: +86-21-65985318; Fax: +86-21-65983431E-mail: swlsxf@163.com

120 SHI Wen-long et al.

2.1. Specimens description

One bare steel joint and two composite joint specimens

denoted as SJ1 and CJ3, CJ4, respectively, were tested.

Two beams H300 × 150 × 6 × 10 of 1.6 m long were

connected to a column H200 × 200 × 8 × 12 to form a

cruciform specimen as shown in Fig. 2. The beams were

connected to the column flanges by means of 10 mm

thick end plate and M20 Grade 10.9 bolts, as shown in

Fig. 2b. All standard steel members and end plates are

made of Q345 steel. A common form of metal decking

floor system, which comprises a concrete slab supported

by profiled metal decking sitting on steel beams, was

adopted for all composite specimens. The beam-to-slab

connections are connected by welded-through shear

connectors. Longitudinal reinforcement bars pass across

the column line continuously. The longitudinal reinforcement

consisted of Φ10@120 bars, while the transverse reinforcement

consisted of Φ6@200 bars. The reinforcement ratio is

0.8%, which is defined as the reinforcement area divided

by the concrete area above the ribs of the metal sheeting.

The common used 0.8 mm thick profiled steel sheeting

DP688 was chosen as bottom shuttering for the specimens.

The profiled steel sheeting was filled with cast-in-place

normal weight concrete with design strength of 30 N/

mm2. The composite slabs were 1,200 mm wide and

140 mm thick. Spaces between column flanges at the slab

level were solidly cast with concrete. CJ3 was similar to

CJ4 except that the panel zone was stiffened with

transverse plate welded to the column web.

2.2. Specimen design and fabrication

All specimens were fabricated in the Structural

Laboratory at the Tongji University. The bare steel

components were firstly assembled in situ. The profiled

metal decking was then placed on the steel beams and

shear studs were installed by welding. After the joint

Figure 1. Location of specimen.

Figure 2. Specimen of composite joint.

Cyclic Loading Tests on Composite Joints with Flush End Plate Connections 121

assembly, formwork was set up with the metal decking as

bottom shuttering, plywood as side shuttering. Concrete

casting work was then carried out. The casting of cubes

and cylinders for material tests was done at the same

time. The cube and cylinder samples and the slab were

cured under the same conditions.

3. Instrument Arrangement

Strains in the reinforcement and on the steel beam and

column were measured using strain gauges. The

arrangement of strain gauges is shown in Fig. 3. After

assembly of the test specimens, all the instruments were

mounted on the specimens. Inclinometers were used to

measure the rotation of the column and the relative

rotation of the beam so as to provide full information

from which the moment-rotation relationship could be

derived. The arrangement of inclinometers is shown in

Fig. 4. Displacement transducers were used to measure

the deflection of the specimens on the bottom flange of

the beam and also to monitor slippage between steel

beam and slab. The relative rotation of the beam to

column can also be obtained from the deflection values

within the calibrated horizontal length of the beam. The

arrangement of LVDT is shown in Fig. 5.

4. Loading Procedure

The experimental set-up included a supporting frame

and a loading system is shown in Fig. 6 and Fig. 7. The

lateral loading was applied to the specimen at the top of

the supporting frame by a computer-controlled hydraulic

actuator with a maximum load capacity of ±1000 kN and

available stroke of ±200 mm. The specimens were loaded

until failure or when the maximum stroke of the actuator

was reached.

Figure 3. Arrangement of strain gauges.

Figure 4. Arrangement of inclinometers.

Figure 5. Arrangement of LVDT.

Figure 6. Test set-up.

Figure 7. Photo of test set-up.

122 SHI Wen-long et al.

5. Material Tests

5.1. Steel coupons

Material for tensile test coupons was cut from the

flanges and webs of the steel beams and columns. Values

of yield strength and ultimate strength for steel members

are listed in Table 1.

5.2. Reinforcement bars

Test specimens were cut from the 6 mm and 10 mm

diameter rebars. The test results are listed in Table 2.

5.3. Concrete

Concrete work was carried out inside the laboratory

with the specimen in the test position. Samples of

concrete to be used for monitoring the concrete strength

were cast at the same time to cast for composite joint

specimens. The compressive and tensile strengths of all

the samples are summarized in Table 3.

Table 1. Measured tensile strengths of steel

No.Yield strength

(N/mm2)Tensile strength

(N/mm2)Yield strain

(%)Elastic modulus(×105 N/mm2)

Extensibility(%)

BW-1 383.9 564.5 0.195 1.97 28.40

BW-2 387.4 559.9 0.190 2.04 32.54

BW-3 401.1 563.5 0.196 2.05 35.46

BF-1 435.8 509.3 0.206 2.12 29.88

BF-2 402.2 495.4 0.199 2.02 29.78

BF-3 431.9 509.2 0.196 2.20 31.19

EP-1 391.9 498.4 0.190 2.06 29.93

EP-2 436.2 507.6 0.209 2.09 29.89

EP-3 428.1 502.9 0.193 2.22 31.34

CW-1 406.3 505.9 0.189 2.15 30.54

CW-2 405.6 489.9 0.167 2.43 31.79

CW-3 397.7 480.5 0.214 1.86 33.40

CF-1 417.0 500.5 0.216 1.93 30.33

CF-2 414.5 497.7 0.192 2.16 30.58

CF-3 397.6 496.9 0.192 2.07 30.26

Average 0409.15 0512.14 0.200 2.09 31.02

Table 2. Measured tensile strengths of rebar

No. Diameter/mmYield strength

(N/mm2)Tensile strength

(N/mm2)Yield strain

(%)Elastic modular(×105 N/mm2)

Extensibility(%)

GJ1-1 6.77 296.97 436.1 0.140 2.12 28.28

GJ1-2 6.59 318.50 443.3 0.157 2.03 30.88

GJ1-3 6.64 310.31 436.1 0.165 1.87 29.98

Average 6.67 308.59 0438.50 0.154 2.01 29.71

GJ2-1 9.92 462.70 607.7 0.248 2.02 33.02

GJ2-2 10.160 433.50 575.2 0.236 1.85 31.94

GJ2-3 10.070 444.10 581.6 0.248 1.90 29.54

Average 10.050 446.77 0588.17 0.244 1.92 31.50

Table 3. Measured strengths of concrete

No. Size of samples (mm) Cube strength (N/mm2) Average

H1-1 150×150×150 40.89

41.48H1-2 150×150×150 40.89

H1-3 150×150×150 42.67

No. Size of samples (mm) Elastic modular (N/mm2) Average

H2-1 100×100×300 40000

41429H2-2 100×100×300 40000

H2-3 100×100×300 42857

Cyclic Loading Tests on Composite Joints with Flush End Plate Connections 123

6. Test Phenomenon

6.1. Specimen SJ1

SJ1 is a bare steel joint specimen used as a benchmark

for comparison with other composite joint specimens. A

gap between end plate and column flange was observed

when the displacement of top of column reached ±25 mm

(Fig. 8a). The obvious shearing deformation was observed

in the panel zone when the displacement reached ±60 mm

(Fig. 8b). The specimen was loaded until the maximum

stroke of the actuator was reached. No local buckling was

observed on the steel components and the lateral load was

keeping on going up.

6.2. Specimen CJ3

The first cracking was observed on the right slab when

the displacement of the top of column reached 25 mm.

The crack started from the tip of column flange and

extended towards the edge. The lateral load was then

unloaded to zero and the cracks on right slab closed

completely. A reversed loading was then applied, and the

first cracking was also observed on the left slab. With the

increasing in loads, the appeared cracks extended and

widened gradually (Fig. 9a). When the displacement

reached 80 mm, a wide gap between slab and column

flange (Fig. 9b) was observed. When the displacement

reached 120mm, the state of composite slab vicinity to

the column is shown in Fig. 9b and Fig. 9c. It is noted

that the slab around the column is badly damaged. A

large shear distortion was observed in the column panel

zone (Fig. 9d). When the displacement reached 160 mm,

the debonding of the concrete from the metal decking and

the inclined cracks starting from the ribs are visible, as

illustrated in Fig. 9e. The former was due to the flexural

deflection of the beam, while the latter was caused by the

shear and bending action in the slab. When the

displacement reached 200 mm, the damage of concrete

slab continued and the crushed concrete was dropped off

from the gap between the slab and column flange. A wide

gap was observed between end plate and column flange

Figure 8. Test photo of SJ1.

Figure 9. Test photos of CJ3.

124 SHI Wen-long et al.

(Fig. 9f). After the test, the concrete slab vicinity to the

column was cut and examined. It was found that the

concrete at the back of column flange was completely

crushed.

6.3. Specimen CJ4

The first cracking was observed on the right slab when

the displacement of the top of column reached 25 mm in

pull way. The lateral load was then unloaded to zero and

the cracks on right slab closed completely. A reversed

loading was then applied, and the first cracking was also

observed on the left slab. With the increasing in loads, the

appeared cracks were extended and widened gradually.

When the displacement reached 80 mm, a wide gap

between slab and column flange (Fig. 10a) was observed.

The debonding of the concrete from the metal decking

was visible (Fig. 10b). After the test, the cracks of

concrete slab are shown in Fig. 10d. The concrete slab

vicinity to the column was cut and examined. It was

found that the concrete at the back of column flange was

completely crushed (Fig. 10f).

7. Test Results and Analysis

In this section, the experimental results of all specimens

under cyclic reversal loading will be described. For

convenience of comparison, the values of the main

parameters, such as cracking moment, yield moment and

corresponding rotation, initial rotational stiffness, damage

modes are listed in Table 4.

7.1. Hysteretic curves of lateral load and corresponding

displacement

The hysteretic curves of lateral load and its displacement

Figure 10. Test photos of CJ4.

Table 4. Experimental results

No. Type of joint Mcr (kN · m) My+ (kN · m) My

− (kN · m) Pu (kN)

SJ1 bare joint / 44.91 -44.91 /

CJ3 composite joint 41.10 78.97 -102.160 64.83

CJ4 composite joint 38.09 82.83 -98.81 60.06

No. Ki+ ( kN · m/mrad) Ki

− ( kN · m/mrad) θy+ (mrad) θy

− ( mrad) Damage modes

SJ1 06.93 0-6.93 42.11 -42.11 Not damaged

CJ3 14.63 -19.51 12.02 -14.69 A, C, E

CJ4 14.88 -17.72 11.25 -13.62 A, C, E

Note: (1) Mcr: cracking moment; (2) My+, θy

+: positive yield moment and corresponding rotation; (3) My−, θy

−: positive yield momentand corresponding rotation; (4) Pu: the maximum lateral force; (5) Ki

+: positive initial rotational stiffness; (6) Ki−: negative initial

rotational stiffness; (7) In the ‘Damage modes’ column: A = reinforcement yielding; B = end plate yielding; C = yielding in shearpanel zone; D = bolt yielding or fracture; E = concrete cracking; F = welding fracture in column web; G = yielding in beam flange.

Cyclic Loading Tests on Composite Joints with Flush End Plate Connections 125

at the top of column (P-∆) are shown in Fig. 11. It can be

seen that the P-∆ hysteretic curves are symmetrical about

centerline of column cross section because of the

symmetry of specimens about centerline of column cross

section. For specimens CJ3 and CJ4, the maximum lateral

force ratio between push and pull is 0.93 and 1.06

respectively.

7.2. Hysteretic curves of moment-rotation of the

connections

The hysteretic curves of moment-rotation for left and

right connections are shown in Fig. 12. It can be seen that

the hysteretic loops are stable and ductile and show good

energy dissipation capacity. The hysteretic curves for left

and right connections are nearly same because of

symmetry of left and right connections. For the specimen

SJ1, the maximum moment is corresponding to the

maximum rotation under positive and negative moment.

It indicated that no strength degradation was achieved for

the specimen SJ1.

The curves for left and right connections are in good

agreement because of the symmetrical construction

details. For the specimens CJ3 and CJ4, pinching, indicated

by the reduction of stiffness, is noted. In composite joints,

pinching is mainly caused by the opening and closure of

the cracks in the concrete slab. The slippage between

steel components and the slippage between the composite

slab and steel beam also contribute to the pinching effect.

For the specimens CJ3 and CJ4, the maximum moment is

not corresponding to the maximum rotation under positive

and negative moment respectively. This phenomenon

indicated that strength degradation was achieved for the

specimens CJ3 and CJ4. In addition, the hysteretic curves

of moment-rotation for specimens CJ3 and CJ4 are the

nearly same as that of specimen SJ1 after these two

composite joint specimens reached their maximum lateral

force. It indicated that the performance of composite

joints is in agreement with that of bare steel joint because

of losing composite action of concrete slab.

Figure 11. Hysteretic curves of P-∆.

Figure 12. Moment-rotation curve of the connections.

Figure 13. Shear force-rotation curve in the column panel zone.

126 SHI Wen-long et al.

7.3. Hysteretic curves of shear force and corresponding

rotation

Under a lateral loading, the connection on one side was

subjected to a hogging moment, while the connection on

the other side was subjected to a sagging moment. In

consequence, the column panel zone bore a large shear

distortion. The hysteretic curves of shear force and

corresponding rotation in the column panel zone for all

three specimens are shown in Fig. 13.

7.4. Energy dissipation

The energy dissipation capacity is the factor of utmost

importance when evaluating the performance of a structure

subjected to seismic attacks. Its value is generally

deformation-dependent and serves as an indication of

dissipation energy for the structure through the inelastic

range. The dissipated energy Ji in the ith loading cycle is

defined as the area encircled by the restoring force-

deformation curve. The energy per cycle may be further

separated into two parts, Ji+ for positive loading and Ji

−

for negative loading. Since the asymmetrical characteristics

of a composite connection under sagging and hogging

actions, the moment-rotation response is thus non-

symmetrical. This may lead different values of dissipated

energy for positive and negative loading semi-cycles.

The energy dissipation of all three specimens is shown

in Fig. 14. It can be seen that in the first eight cycles, the

energy dissipation is very small. This indicates that the

specimens are in elastic state. After the eighth cycle, the

energy dissipation of specimens keeps on going up with

the increasing in cycles.

7.5. Skeleton curves

The skeleton curves of P-∆ are shown in Fig. 15. It can

be seen that the composite joint specimens have larger

strength resistance and stiffness than the bare steel joint

specimen does owing to the presence of reinforcement

bars and concrete slab. The composite joint specimens

show the nearly same performance as the bare steel joint

does after reaching maximum lateral force.

7.6. Strain of beams

The strain of left steel beam of specimens SJ1 and CJ4

is shown in Fig. 16. For the specimen SJ1, No. 2 and No.

6 strain gauge readings are much higher than the other

strain gauges’. The maximum data obtained from No. 2

strain gauge is nearly 1000 µε, while that of No. 6 strain

gauge is nearly 2000 µε. The readings of No. 1 and No.

7 strain gauge located on the beam flanges are very small.

Figure 14. Cumulative energy dissipation of specimen.

Figure 15. Skeleton curves of P-∆.

Figure 16. Strain of left beam of specimen SJ1 and CJ4.

Cyclic Loading Tests on Composite Joints with Flush End Plate Connections 127

From the data obtained from these strain gauges, the

follow conclusions can be drawn: (1) For the flush end

plate connection, the strain of beam flanges is very small

because of lack of restriction, especially for the bare steel

joint; (2) The strain of beam web in level of bolts is large

because of strong restriction of bolts; (3) There is a gap

between end plate and column flange because of

pretension of bolts. Thus, the beam flanges begin to bear

load after these gaps disappear when loading. (4) The

steel beam of specimen SJ1 is yielding while the steel

beam of specimen CJ4 is still elastic.

7.7. Slippage between steel beam and concrete slab

The slip between steel beam and concrete slab versus

displacement of the top of column is shown in Fig. 17. It

can be seen that the readings of LVDT7 and LVDT8 keep

on going up with the increasing in the lateral displacement.

There is no obvious difference in readings between

LVDT7 and LVDT8 during the whole test. For the

specimen CJ3, the maximum readings of LVDT7 and

LVDT8 are 0.22 mm and 0.275 mm respectively. The

reading ratio is 0.8. The slippage strain is 159 µε, which

is defined as the difference in reading of LVDT7 and

LVDT8 divided by the spacing between this two LVDT.

For specimen CJ4, the maximum readings of LVDT7 and

LVDT8 are 0.165 mm and 0.146 mm respectively. The

reading ratio is 1.13, while the slippage strain is 55 µε.

8. Conclusions

Through the experimental studies, the concluding remarks

may be summarized as:

(1) The composite joints with flush end plate connection

have good moment resistance and rotational capacity

under cyclic loading. The ultimate rotations of all three

specimens are beyond 0.03rad, as required by the FEMA-

97 for earthquake-resistance.

(2) The cyclic test results indicated that the hysteretic

loops of the connection moment-rotation curves are stable

and plummy, even though pinching in large inelastic

ranges was observed.

(3) The presence of the column web stiffener can increase

the moment capacity and initial rotational stiffness of the

connection, but not very much.

(4) Failures of composite joints are observed to be

concentrated in the nodal zone.

(5) By a proper full shear design, the slippage between

slab and steel beam is so small that these two components

can be assumed to work well together.

Acknowledgment

The studies presented in this paper are sponsored by the

Natural Science Foundation of China through the

Outstanding Youth Project (No. 50225825). The financial

support from NSFC is especially acknowledged.

References

Anderson, D. and Najafi, A. A. (1994). “Performance of

composite connections: major axis end plate joints”, J.

Constr. Steel Res., 31, 31-57.

B. M. Broderick and A. W. Thomson, Moment-Rotation

Response of Flush End-Plate Joints Under Cyclic

Loading, International Journal of Steel Strucutures, Vol.

5(5), 441-451.

Changbin Joh and Wai-Fah (2001), Seismic Behavior of

Steel Moment Connections with Composite Slab,

International Journal of Steel Strucutures, Vol. 1(3), 175-

183.

Chen yu, Dong shimim, Li liping (1995), “Introduction to

pseudo dynamic test method in the code of aseismic test

on building structures”, Building Science, Vol. 2, pp. 52-

57.

Gao huajie (2002), Experimental study on the semi-rigid

composite joints with seating cleat connection, Master

Thesis.

Guan kejian (2003), Experimental study and non-linear

analysis on the steel frame buildings, PHD Thesis.

Guo Bing (2002), Collapse Mechanism and Design

Criterion of Steel Beam-to-column Extended End-plate

Connections under Cyclic Load, PHD Thesis.

Guo Yiqing (2003), Experimental Study of Semi-rigid End-

plate Composite Joints, Master Thesis.

Laszlo Dunai (2004), Experimental and Numerical Studies

on the Cyclic Behavior of Steel and Composite Joints,

International Journal of Steel Strucutures, Vol. 4(4), 197-

208.

Figure 17. Slippage between slab and beam.

128 SHI Wen-long et al.

L.Simoes da Silva, Rui D. Simoes, Paulo J.S. Cruz (2001),

“Experimental behavior of end-plate beam-to-column

composite joints under monotonical loading”, Engineering

Structures, 1383-1409.

Lou Guobiao (2005), Behavior and Design of Extended

Endplate Moment Connections with High-strength Bolts

in Fire, PHD Thesis.

Rene Maquoi and Jean-Pierre Jaspart (2002), A Simple

Approach for the Design of Steel and Composite Frames

accounting for Effective Overall Stability, International

Journal of Steel Strucutures, Vol. 2(1), 1-11.

Shi Wenlong, Theoretical and Experimental Research on

Composite Joint with Flush Endplate Connections, PHD

Thesis.

Sun Feifei, Li Guoqiang, Hu Linghua (2004), “New

Development in Experimental Research on Beam-to-

column Composite Joints”, Progress in Steel Building

Structures, Vol. 6, No. 2, pp. 37-42.

Tian shizhu, Zhao tong (2001), “Research on pseudo

dynamic test”, World information on earthquake

engineering, Vol. 17(4), 60-66.

Tsuji Bunzo (2001), Ultimate Strength and Collapse

Mechanism of Steel Concrete Composite Moment

Frames under Seismic Loading, International Journal of

Steel Strucutures, Vol. 1(2), 91-94.

Wang Jingfeng (2005), the Practical Design Approach of

Semi-rigidly Connected Composite Frames under

Vertical Loads, PHD Thesis.

Wang rui, Zai houqin, Wang yuda (2001), “an experimental

study on pseudo dynamic testing technique of structures”,

Jiangshu Building, 18-22.

Xiao, Y., Choo, B. S. and Nethercot, D. A. (1994),

“Composite Connections in Steel and Concrete. Part 1-

Experimental behavior of composite beam-column

connections”, Journal of Constructional Steel Research,

Volume 31, Pages 3-30.

Yang Li (2004), Behaviors Study on Semi-rigid Composite

Joints under Low Cyclic Loading, Master Thesis.

Yao zhengang, Liu zhuhua (1996), Test on Building

Structures, Tongji University Press, Shanghai.

Zhu bolong (1989), Aseismic Test on Structures, Bei Jing,

Earthquake Press of China.