The angle steelconcrete column used in the new frame structure means that the rigid angle steel is placed in the column instead of the longitudinal reinforcement. The steel plate hoop welded to the longitudinal angle steel is used instead of the stirrup to form a spatial steel frame and concrete component. To ensure the normal use of existing houses in the building and adding floors, avoid transferring the load during the construction phase to the roof of the original house. The corresponding skeleton curve is extracted from the hysteresis curve of the specimen. Based on experimental research, the force performance of the normal section of the angle steelconcrete column was discussed, and the calculation formula of the normal section bearing capacity of the angle steelconcrete column was discussed.
Keywords
 hysteretic curve equation
 prefabricated concrete
 mechanical performance
MSC 2010
 34C55
At present, the retrofitting of existing houses has become one of the hot issues in urban construction in my country. To ensure the normal use of existing houses in the process of building and adding floors, some scholars have put forward the idea of ‘selfsupporting floors in the construction phase.’ In the construction phase, the prestressed steel truss bears the frame beam's weight and construction load. This solves the problem that the original roof cannot bear the new construction load, ensures the normal use of the original building during the construction process, saves investment, and shortens the construction period due to the integration of structural force and construction measures. However, the angle steel of the builtin truss chord of the frame beam occupies a larger space when passing through the builtin column. This affects the arrangement of the frame column longitudinal reinforcement, the frame beam prestressed reinforcement, and the horn tube, and at the same time, it is not convenient for the prestressed reinforcement to be anchored.
The angle steelconcrete column used in the new frame structure means that the rigid angle steel is placed in the column instead of the longitudinal steel bars. The steel plate hoop welded to the longitudinal angle steel replaces the stirrup to form a space steel skeleton and concrete component. Because there is no additional longitudinal reinforcement on the outside of the angle steel, the thickness of the concrete protective layer of the angle steel skeleton can be relatively reduced, roughly the same as that of ordinary reinforced concrete columns [1]. This increases the moment arm of the angle steel, enables the column to play a greater role, and facilitates embedded parts. At the same time, the angle steel frame can be prefabricated in the factory to simplify the construction procedure and speed up the construction progress. Good economic benefits will be achieved in actual projects.
There are not many reports on the study of the force performance of the normal section of the angle steelconcrete column. The corresponding skeleton curve is extracted from the hysteresis curve of the specimen [2]. The specimens all suffered a large eccentric bending failure. Based on experimental research, the force performance of the normal section of the angle steelconcrete column was discussed. The experiment in this article provides a reference for the elasticity analysis of the structure.
The specimen is shown in Figure 1. The sheer span ratios of the 6 test columns are all 3. The crosssectional dimensions are all 200 mm × 200 mm. The clear height of the pillars is 1200 mm. Each test column has 4 Q345 angle sheets of steel ⌞30 × 3, and the steel content is 1.75%. The arrangement is shown in the AA section of Figure 1. The stirrup is made of steel plate hoops, and the steel plate hoop is 3 mm thick Q235 steel [3].
The average compressive strength
The main parameters of the test piece
0.33  1.18  
0.33  1.36  
0.33  1.55  
0.37  1.36  
0.37  1.55  
0.37  1.82 
As shown in Figure 3, the loading device is mainly composed of an Lshaped beam, a fourbar linkage, a reaction frame, and a hydraulic servo actuator [5]. The fourbar linkage mechanism allows the Lshaped beam to move freely in the vertical and horizontal directions without rotating, thereby realizing the boundary condition that the top of the column is the embedded end. Hydraulic servo actuators apply horizontal repeated loads fixed on the reaction wall. A 1000 kN pressure sensor is arranged on the jack to measure the axial force. Rollers are arranged between the distribution beam and the Lshaped beam so that they can slide freely. Since the fourbar linkage mechanism cannot bear the horizontal and vertical loads, the horizontal and vertical loads are the specimen's horizontal shears and axial force.
First, apply the axial load with a hydraulic jack, keep it at a constant value, and then apply the horizontal load. The application of horizontal load adopts the method of loaddisplacement dual control. Before the specimen yields, the load is controlled in stages until the specimen yields, which corresponds to one cycle of each load step [6]. Displacement control is adopted after the specimen yields. The multiple of the yield displacement is taken as the level difference for controlled loading. The horizontal load is cycled three times for each controlled displacement until failure. Keep the loading and unloading speed consistent during the test to ensure the stability of the test data.
The six specimens all failed under bending and had good flexibility, and the failure process was similar. Taking the test piece PPECC5 as an example, the two faces perpendicular to the horizontal load direction are the front faces, namely, face 1 and face 2. The other two sides are sides. The force in the pushing direction of the actuator is positive, and the force in the opposite direction is negative [7]. When the horizontal force direction is positive, the upper face 1 of the column and the lower face 2 are under tension. The specimen is elastic before the horizontal repeated load reaches 45 kN. When the positive horizontal load reaches 45 kN, and the negative horizontal load reaches 50 kN, horizontal cracks appear in the front tension area of the upper and lower ends of the column. With the increase of the displacement of the column top, new cracks continue to appear in the front pull area of the upper and lower ends of the column, and the cracks have further expanded. At the same time, horizontal cracks also appeared on both sides of the upper and lower ends of the column [8]. When the displacement of the top of the column reaches 30 mm, the concrete at the upper and lower ends of the column will spall in a large area, and the angle steel and steel plate hoops will be exposed, and the angle steel will appear to be buckled under compression. The loadbearing capacity of the component drops rapidly, and the specimen is destroyed.
The loaddisplacement hysteresis curve of the specimen is shown in Figure 4. The following characteristics can be seen from the hysteresis curve:
When the horizontal load is less than the cracking load, the specimen is elastic. As the load increases, the loaddisplacement curve gradually deviates from the straight line, and there is a certain residual deformation when unloading [9]. After the load reaches the yield load, the stiffness of the test piece gradually decreases, and the decreased amplitude increases with the increase of the number of cycles.
Figure 5 shows the skeleton curves of six test pieces. It can be seen that the deformation capacity of the specimens with the same hooping ratio decreases, but the horizontal bearing capacity gradually increases [10].
The analysis of the previous test process shows that the damage of the test piece occurs at the end of the test piece, and the ultimate flexural bearing capacity of the damaged section can be obtained by Eq. (1):
Comparison of test results and calculated results





104.54  15.95  458  55.92  51.53  0.92  
97.89  19.53  458  53.42  51.53  0.96  
114.25  15.06  565  61.38  55.52  0.90  
121.85  16.38  565  65.55  55.52  0.85  
106.66  14.89  565  57.54  55.52  0.96 
We did not consider the effect of section strain gradient on improving the concrete compressive strength of eccentrically compressed members. The equivalent rectangular concrete compressive strength is still taken as
The flexural bearing capacity of the section of the 6 test columns obtained according to the above calculation formula is shown in Table 2. Compared with the test result
When
We have completed the test of sixangle steel concrete columns with steel plate hoops under the horizontal lowcycle reciprocating load and obtained the test column's failure form and hysteresis curve. The hysteretic curve extracts the skeleton curve of sixangle steelconcrete columns. The specimens all suffered a large eccentric bending failure. The force performance of the normal section of the angle steelconcrete column is discussed based on experimental research. At the same time, the formula for calculating the bearing capacity of the normal section of a large eccentrically loaded angle steelconcrete column is given. The paper introduces the calculation formula for the bearing capacity of the normal section of a small eccentric load angle steelconcrete column.
Comparison of test results and calculated results





104.54  15.95  458  55.92  51.53  0.92  
97.89  19.53  458  53.42  51.53  0.96  
114.25  15.06  565  61.38  55.52  0.90  
121.85  16.38  565  65.55  55.52  0.85  
106.66  14.89  565  57.54  55.52  0.96 
The main parameters of the test piece
0.33  1.18  
0.33  1.36  
0.33  1.55  
0.37  1.36  
0.37  1.55  
0.37  1.82 
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