Research On Bearing Capacity Of A New Type Of L-shaped Steel Reinforced Concrete Special-shaped Joint

The research on the adaptability of reinforced concrete special-shaped column structure system in the 8 degree seismic fortification area shows that the bearing capacity of the joint becomes the controlling factor of the maximum applicable height of the special-shaped column structure in the 8 degree seismic fortification zone.According to the regulations of special-shaped column in China,the maximum applicable height of reinforced concrete special-shaped column frame structure in 8degrees(0.2g)area is 12 m.The height limit of 12 m in zone 8 seriously restricts the promotion and application of special-shaped column frame structure in high-intensity area.In order to improve the adaptability of special-shaped column frame structure in high-intensity area,the relevant theoretical analysis and experimental verification show that the addition of steel bone in the joint zone is an effective method.In order to promote the application of profiled steel in special-shaped column joints,at the same time the new type of profiled steel is also promoted to reduce the inconvenience caused by the tie-up of longitudinal reinforcement of beam and stirrups in the core area of joints during the construction process of the traditional solid-section steel.In this paper,in order to investigate in depth the working mechanism and measure efficiency of this type of section steel joint,the experimental study and finite element simulation analysis of this new type of section steel joint were carried out.In this paper,the overall analysis and calculation of a six-storey concrete frame structure test model with special-shaped columns completed in Tongji University in2003 under the condition of 8-degree zone(0.2g)are carried out.Combined with the test results completed in the previous period,an L-shaped joint is selected from the second floor of the model for the design of the specimens.Three full-size L-shaped joints were produced and three full-size L-shaped steel concrete special-shaped column joints were tested under low-cycle repeated loading.In this test,the seismic performance tests of unreinforced steel in joint zone,reinforced steel in joint zone and the addition of short steel bars on the section steel were completed.The test results were processed and calculated to obtain the hysteresis curve,skeleton curve,strength degradation and energy dissipation capacity of specimens and other seismicperformance indicators.The test results show that compared with PL specimens without profiled steel,the core zone of joints with new profiled steel has larger hysteretic loop area and better energy dissipation capacity in the post-yielding stage.At the same time,compared with PL,the ultimate bearing capacity of specimens with profiled steel increases by about 20%.The nonlinear finite element analysis software was used to simulate the two specimens with profiled steel in the test.The simulation results coincide well with the test.On the basis of this modeling method,six finite element models with profiled steel are established.The other factors that affect the bearing capacity of the joint including the thickness of section steel,the form of the opening of the steel,the density of short steel bar and so on has carried on the finite element calculation and analysis.The finite element analysis software results show that:1.When the thickness of section steel exceeds a certain value,the effect of section steel on improving the bearing capacity of members is no longer obvious.2.Compared with rectangular cutting,triangular cutting can reduce the stress concentration without increasing the amount of steel used.At the same time,different forms of cutting have less influence on the bearing capacity of members.3.The reinforcement of short steel bars is an advantageous structural measure for areas with high seismic fortification requirements.4.In the production of joint steel,attention should be paid to strengthening the welding of the strip part and the web part.Finally,this paper analyzes the calculation of the crack-resistance capacity and discusses the calculation of the shear capacity of the concrete-shaped column joints with the new type of steel.