Study On Seismic Behavior Of RC Frame Structure With Stairs And Special-Shaped Columns

In the study of the influence of stairs on the structural performance,most of them are aimed at the rectangular column frame structure and frame-shear wall structure,while the special-shaped column frame structure is almost not involved.Because of the irregular shape of special-shaped column section,compared with the rectangular column frame structure,the overall torsional performance of the special-shaped column frame structure is poor.In order to meet the requirements of the code,the overall structure should be coordinated and symmetrical;The arrangement of stairs will lead to the increase of the overall stiffness of the structure,the uneven distribution of stiffness in the floor plane,and the deterioration of the coordination and symmetry of the overall structure,which will make the influence of stairs on the overall structure of special-shaped columns greater.In this paper,the bottom staircase unit of special-shaped column frame structure is selected as the research object,and its seismic performance is studied by establishing models with different parameters.Based on the static pushover analysis of a staircase model of a reinforced concrete frame with rectangular columns established by ABAQUS,and the comparison between the calculation results and the experimental results of existing academic papers,it is verified that the modeling and calculation method of ABAQUS are reliable.Taking the story height,length,flange width and limb thickness of special-shaped column and concrete strength as parameters,11 different forms of special-shaped column frame staircase models were established by ABAQUS,and the static pushover analysis of the structural models was carried out,and the hysteretic curves,skeleton curves,stiffness degradation curves and equivalent viscous damping coefficient curves were drawn.The effects of different parameters on the yield strength,ultimate strength,stiffness degradation,ductility coefficient,energy dissipation capacity and concrete damage of special-shaped column frame staircase structure are studied.The conclusions are as follows:(1)Under the cyclic load,the shape of the hysteretic loop of the stair of special-shaped column frame changes from "S" shape to shuttle shape gradually,and the energy dissipation capacity is better;the stiffness,bearing capacity and energy dissipation capacity under the positive thrust load are better than those under the reverse tension load;the stiffness of special-shaped column is larger,and the joints between other components and it are easy to be damaged.(2)With the increase of storey height,the initial stiffness and ductility coefficient of the structure decrease,the energy dissipation capacity decreases,and the seismic performance becomes worse.(3)There is no obvious law between the change of the depth length and each seismic performance index.When the depth length is 5.6m,the bearing capacity of the structure is higher,but the energy dissipation capacity is worse,and the damage of the upper stair slab is more serious.(4)When the flange width of the special-shaped column decreases,the tensile bearing capacity and initial stiffness increase,the yield load and compressive bearing capacity decrease,the ductility coefficient increases,and the energy dissipation capacity becomes better,which has a protective effect on the ladder slab and platform slab.(5)The increase of special-shaped column limb thickness and the increase of concrete strength have little effect on the seismic performance of the structure.PKPM and YJK are used to establish an engineering example model,and the results of modal decomposition response spectrum are compared.On the basis of verifying the reliability of the model,modal analysis,response spectrum analysis and elastic time-history analysis are further carried out on the special-shaped column frame structure model without stairs and three special-shaped column frame structure models with stairs but in different locations by PKPM.Through the comparative analysis of the performance parameters of each model,such as natural period,horizontal displacement,inter-story shear force and internal force of components,the influence of the seismic performance of the whole structure with or without stairs and different locations of stairs is studied.The conclusions are as follows:(1)If the stairs are considered to participate in the overall calculation,the direction of the first two structural modes will be changed,the overall stiffness of the structure will be improved,the interlayer shear force along the direction of stairs will be increased,and the internal force of the frame components will also be generally increased.When the stairs are far away from the symmetry axis of the structure in X direction,the torsional stiffness of the whole structure will increase,the lateral stiffness in the direction perpendicular to the stairs will decrease,and the interstory displacement and interstory shear in this direction will increase,but the internal force of the frame members in the stairwell will decrease,which is beneficial to the whole structure.(2)The symmetrical arrangement of stairs about the plane centroid of the structure can improve the stiffness of the structure in the direction perpendicular to the stairs,but the inter-story shear force in this direction increases,the internal force of frame members generally increases,and the internal force of stair beams and columns decreases,which has a protective effect on stairs.