This paper presents a new-type of fabricated beam-column connections with end plates. The joint details are as follows: the concrete beams are connected to column by end plates and six high strength long bolts passing through the core area. In addition, in order to increase the stiffness and shear strength, stirrups are replaced by the steel plate hoop in the core zone. To examine the fail behavior of the fabricated beam-column connection specimens, a quasi-static test is conducted for nine full-scale models to obtain the hysteresis curves, skeleton curves, ductility, energy dissipation capacity, and other seismic indicators. The experimental results show that all specimens failed in bending in a malleable way with a beam plastic hinge and the hysteresis curves are excellently plump for the end plate connections. From the seismic indexes, the fabricated connection specimens exhibit better seismic performance, which can provide reference for the application of prefabricated frame structure in the earthquake area.
The advantages of prefabricated frame structure include simple construction, flexible arrangement, and green environmental protection, which fully reflects the industrial character of modern architecture. In the frame structure, the node plays the role of load transmission, which is the key part of the seismic of structure. The postearthquake investigation found that, in most cases, the collapse of the frame structure is caused by the failure of the node, which shows that the node connection performance reliability of the prefabricated structure is poorer, so their application has been limited in earthquake area. In order to improve the overall seismic performance of the assembly structure, we need to carry on deeper theoretical and experimental research on the assembly node. In recent years, a lot of researches were conducted and achieved notable results. Mao et al. [
Concrete structure of beam.
Connection type of end plate and anchor plate
Welding form of normal stirrups and end plate
Prestressed reinforcement arrangement form
A total of nine full-scale fabricated beam-column connection specimens are selected for the test investigation, where RC-01 is cast-in-place concrete joint. All specimens are expected to exhibit strong-column-weak-beam behavior [
Arrangement of reinforcement of specimen.
Specimen | Strength of concrete | Section type | Section size |
Longitudinal reinforcement | Stirrup spacing (mm) | Stirrup encryption area (mm) |
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Column | C60 | Rectangle | 400 × 400 | 16Φ22HRB600 | 50 | 30 |
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RC-01 | C60 | Rectangle | 450 × 380 | 12Φ22HRB600 | 50 | 30 |
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#PAN-01 | C35 | Rectangle | 450 × 200 | 4Φ20HTH1080 |
110 | 90 |
#PAN-02 | C35 | 50 | 40 | |||
#PAN-03 | C35 | 60 | 50 | |||
#PAN-04 | C35 | 70 | 60 | |||
#PAN-05 | C35 | 90 | 70 | |||
#PAN-06 | C35 | 100 | 80 | |||
#PAN-07 | C35 | 90 (double stirrup) | 70 (double stirrup) | |||
#PAN-08 | C35 | 100 (double stirrup) | 80 (double stirrup) |
Size and reinforcement of specimens (unit: mm).
Size and reinforcement of #PAN-01~06 specimens
Size and reinforcement of #PAN-07~08 specimens
Size and reinforcement of RC-01 specimens
Double stirrup arrangement form.
According to the standard for test method of mechanical properties on ordinary concrete [
Indexes of reinforcement mechanical performance.
Material property | Diameter | |||||
---|---|---|---|---|---|---|
5 | 6 | 10 | 18 | 20 | 27 | |
Yield strength/Mpa | 1111.01 | 540.64 | 376.62 | 447.85 | 1160 | 1120 |
Ultimate strength/Mpa | 1336.7 | 681.98 | 560.17 | 630.72 | 1230 | 1180 |
Strength-yield ratio | 1.20 | 1.26 | 1.49 | 1.41 | 1.06 | 1.05 |
Percentage elongation after fracture | 1.2 | 8.24 | 10.36 | 12.47 | 12 | 14 |
Pier head material test.
In this test, pseudo static cyclic loading is used and loading method of column end is adopted. The schematic diagram of loading device is shown in Figure
Schematic view of the loading device.
Under the action of low frequency cyclic loading, the shear failure occurs in the core area of the RC-01 because of the fault of the design, and the bending failure of beam end occurs to the #PAN series test specimen of monolayer stirrup with the similar destruction process. When the cracking load is reached, the vertical bending cracks appear in the beam region close to the core area, the crack width is about 0.05 mm, and it is completely closed after unloading. As the load increases, there are more cracks, whose length and width increase constantly with the oblique trend, and the distribution range gradually spreads away from the core zone. When reaching the yield load, the width of maximum crack is about 0.2 mm. In the stage of displacement control, the concrete protective layer falls off, but the concrete internal damage is not serious, which shows that the specimens have good deformation performance. When the horizontal displacement reaches about 150 mm, the bearing capacity of the joint decreases to 85% of the peak load, and the specimens have a visible plastic hinge destruction zone, and the test is stopped. The failure modes of double-layer stirrup specimens #PAN-07 and #PAN-08 and monolayer stirrup specimens are basically identical. The cracking load and ultimate load of the double ring specimen are relatively high; double ring specimens have small damage region at the same time; the main reason is that outer stirrup can better restrain concrete cover, which indicates that double-layer stirrups have a remarkable impact on concrete core. During the whole process of the test, there is no sign of separation between the end plate and the column and no buckling occurring to the end plate. The node core zone is in the state of three-dimensional stress under the restraint of steel plate hoop and there is no shear failure as well as slippage happening. After the test, it is found that the concrete cover of the joint core area is shed, but there are no obvious cracks inside the concrete, which can be seen in Figure
Internal damage state of node core area.
Specimens ultimate failure modes.
#PAN-01 ultimate failure diagram
#PAN-02 ultimate failure diagram
#PAN-03 ultimate failure diagram
#PAN-04 ultimate failure diagram
#PAN-05 ultimate failure diagram
#PAN-06 ultimate failure diagram
#PAN-07 ultimate failure diagram
#PAN-08 ultimate failure diagram
RC-01 ultimate failure diagram
The recorded force-displacement hysteresis curves for all specimens are shown in Figure
#PAN-01
#PAN-02
#PAN-03
#PAN-04
#PAN-05
#PAN-06
#PAN-07
#PAN-08
RC-01
The skeleton curve derived from the hysteresis curve is a valuable tool for quantifying seismic performance index. Figure
Skeleton curve of specimens.
Stiffness degeneration refers to the phenomenon that the horizontal lateral resistant force decreases as the number of cycle goes up while maintaining the same peak displacement. The beam-column node is the key of the structural force transmission, whose degree of stiffness degeneration has a great influence on the overall structure seismic performance. The stiffness degeneration of the structural member can be obtained by the coefficient of bearing capacity decrease, which can be seen in (
Figure
Strength degradation curve of specimens.
Ductility capacity is an important parameter for evaluating structure seismic capacity.
The ductility coefficient
Load characteristic values and displacement ductility of specimens.
Specimen number | Yield load |
Yield displacement |
Limit load |
Ultimate displacement |
Ductility factor |
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RC-01 | Front |
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3.67 |
Back |
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3.49 | |
#PAN-01 | Front |
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2.73 |
Back |
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2.79 | |
#PAN-02 | Front |
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2.66 |
Back |
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2.92 | |
#PAN-03 | Front |
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3.10 |
Back |
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2.55 | |
#PAN-04 | Front |
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2.69 |
Back |
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3.35 | |
#PAN-05 | Front |
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2.69 |
Back |
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3.00 | |
#PAN-07 | Front |
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2.89 |
Back |
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2.62 | |
#PAN-08 | Front |
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2.53 |
Back |
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2.63 |
From Table
When the structure enters the elastic-plastic stage, the component’s energy dissipating capacity determines the seismic performance of the structure to a great extent and in the test, how much energy the component can be absorbed is reflected by the area surrounded by load-displacement curve. In this paper, the component’s energy dissipation is evaluated by equivalent viscous coefficient
Hysteresis loop energy.
Equivalent viscous damping coefficient.
A new-type of fabricated beam-column connection with end plates is presented. To investigate the seismic behavior of the prefabricated node, a quasi-static test is conducted for nine real-size beam-column connections. From the experimental results, the following conclusions can be drawn. From the seismic performance indices such as strength, ductility factor, and energy dissipation capacity, the strength degradation of the fabricated joint is not obvious, and the joint proposed in this paper exhibits favorable ductility and energy dissipation capacity. Under the constraint of the double-layer stirrup, #PAN-07 and #PAN-08 have larger bearing capacity, ductility, and energy dissipation capacity. When the plastic hinge failure appears in the beam end, the damage area is small and drop-out of concrete protective layer is not serious. So it is suggested that the double-layer stirrup can be arranged in the hinge region to improve the seismic performance of the structure. In this test, there are no fracture and sealing off in the weld pier head used in between ordinary reinforcement and end plate, so this connection form can achieve the purpose of force transmission under the action of load, which can be applied in practical engineering.
The authors declare that they have no conflicts of interest.