Research on ultimate collapse load of fabricated reinforced concrete column and composite frame structure of steel beams

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Experimental methods include model selection, “New RCS beam-column joint” model, experimental prototype and model, experimentation, loading, failure column elimination, and data test pattern. They are briefly described below.

Model selection

The “new RCS beam-column joint”15 which was developed by our research group was applied to the beam-column connection of the prototype structure, and the prototype structure was designed according to the requirements of Chinese building codes17,18,19. The experimental model was taken from the A to B span and 1 to 2 floors of the prototype structure, and it was reduced to 1/2.

Model “New RCS beam-column joint”

The “new RCS beam-column joint”15 includes steel hoop, cross web, level stiffener and cantilever beam section. The specification of the steel hoop for joints was 350mm × 350mm × 500mm × 12mm. The transverse and horizontal stiffeners were welded on the inside and the 2000 mm long cantilever beam was welded on the outside. The “new RCS beam-column joint”15 specifications are shown in Table 1, and construction and connection are shown in Figs. 1 and 2, respectively.

Table 1 Specifications of the “new RCS beam-to-column connection”.
Figure 1

Construction details of the “new RCS beam-to-column connection”.

Figure 2
Figure 2

Connection diagram of the “new RCS beam-column connection”.

Experimental prototype

In this article, the prefabricated RCS structure prototype (3×4 bays, 5 floors) was designed according to the requirements of Chinese building codes.17,18,19. C40 (HRB335, Q345) was used for concrete (rebar, steel member). The cross section size of the steel beam (concrete column, open trough steel plate composite floor) was 600mm × 300mm × 13mm × 18mm (700mm × 700mm, 80mm) . The seismic design intensity of the prototype structure was 7 degrees18, whose peak ground acceleration (PGA) corresponding to the probability of exceeding 10% in 50 years was 0.1 g, where g refers to the acceleration due to gravity. The perspective view and the plan view are shown in Figs. 3 and 4.

picture 3
picture 3
Figure 4
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Experimental model

The experimental model was taken from the A to B span and 1 to 2 floors of the prototype structure, and it was reduced by half. The membrane effect of the slab was not taken into account in the experimental model, and the size of the cross section of the steel beam (concrete column) was taken as 300 mm × 150 mm × 6.5 mm × 9mm (350mm × 350mm). In addition, the experimental model had a span of 3 m in the X and Y directions, and the first (second) floor of the experimental model had a height of 2 m (1.8 m). In addition, the foundation was replaced using a floor beam. The same batch of concrete material characteristic was tested and the average compressive strength (Fcu) was found to be 39 MPa. The experimental model is shown in Fig. 5, and photographs of the stage reinforcement, column reinforcement and foundation are shown in Figs. 6, 7 and 8.

Figure 5
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Figure 6
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Photograph of the stage reinforcement.

Picture 7
number 7
Picture 8
figure 8

Strengthening of the foundation.

Experimental scheme

In order to explore the ultimate collapse load of the precast RCS structure, the test model was subjected to the instantaneous failure experiments twice under different load levels. The failure column was constrained vertically after the remaining RCS structure was stationary, then the load was increased during the second experiment.

Loading scheme

The first experimental load was the design load of 2.5 layers of the most influential area of ​​the prototype structure. After the first experiment, it was found that the remaining RCS structure had less deformation and was in the early elastic stage. Additionally, the design load of 2.5 layers was well below the ultimate collapse load value. In order to explore the ultimate collapse load, the load was increased based on the first experiment, and the second experimental load was taken as the 5-layer design load in the most affected area of ​​the prototype structure. Due to the limited loading space of the experimental model, the load could not be added to continue the experiment after the second experiment. However, in order to explore the value of the ultimate collapse load, the finite element program SAP2000 was used for the simulation analysis in this work.

During the first experiment, the load applied was 68.4 kN. When the remaining RCS structure was stationary, the steel columns and several pieces of thin steel plates were used to vertically constrain the break columns. The first experimental load is shown in Fig. 9. In the second experiment, the applied load was 140.4 kN, and the second experiment load is shown in Fig. 10.

Figure 9
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Picture 10
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Second experimental load.

Failure column deletion scheme

During the first experiment, the weakest part of the breaking column consisted of the steel column, the steel roll bar and the steel plate embedded from bottom to top. The photograph of the failure column is shown in Fig. 11a. The two steel columns and several pieces of thin steel plates were used to vertically constrain the failure column after the remaining RCS structure was stationary.

Picture 11
figure 11

Photographs of the breakdown column.

During the second experiment, the weakest part of the breaking column consisted of the steel sheet, the steel column and the steel plate embedded from top to bottom. The photograph of the failure column is shown in Fig. 11b. It has been observed that the accidental impact event is one of the conditions that cause progressive collapses. In order to get a clear idea of ​​accidental crashes, the weakest part of the failure column was quickly removed using a vehicle pulling force. In addition, one end of the wire rope was attached to the reserved rings, and the opposite end of the rope was attached to the tow hook of the car. The method of demolishing the failed column in the second experiment was found to be the same as in the first experiment.

Date test pattern

In order to meet the requirements of data acquisition, the dynamic data acquisition instrument was used to record displacements and deformations. The displacement sensors were set in the Z direction of the top of column 2A and in the X (Y) direction of column 1A (2B). Four beam-to-column joints were selected and named Joint 1, Joint 2, Joint 3, and Joint 4. The top flange steel plate A, the web steel plate C, the top flange steel plate bottom flange A and B were defined as strain measurement points. in each joint, and they were named I, II, III, IV, respectively. The displacement and deformation test points are shown in Fig. 12, and the strain distribution is shown in FIG. 13.

Picture 12
figure 12

Displacement and deformation test points.

Picture 13
figure 13
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