Reinforced Concrete Slab Stairs Seismic Performance Research

It's very important to research the security of the stairs as a vertical transportation facilities connecting the floors in the buildings. In recent years, the reinforced concrete stairs are severely damaged, especially in the frame structures. After the Wenchuan earthquake, it has been paid attention to the research on the seismic performance of the stairs, and the seismic requirements of the stairs has been added to the relevant norms,but there is still a lack of systematic research. Therefore, the seismic performance of plate stairs in frame structures are studied by this paper.According to the investigation of the earthquake damage at home and abroad, the earthquake damage of the stairs in the frame structure is summarized and analyzed. This paper analyzes the defects of traditional stair design, and introduces the principle and practice of the stairs with sliding support.The six solid models of the staircase are established by finite element software ANSYS. The laws of crack development, stress distribution, deformation and ultimate bearing capacity and so on are studied by static analysis under vertical load and horizontal load. There are three types of staircase models: the one is the pure frame structure that doesn't consider the stair components; the second is the model with the ordinary plate stairs; the third is the model with the sliding support stairs. In this paper, the influence of the stairs on the seismic performance of the staircases are considered. The ordinary plate stairs can increase the lateral stiffness of the staircases, since stair components can bear larger horizontal force, it is easy to be damaged before the main structure in the earthquake. Sliding support stairs have little effect on the staircases and its lateral stiffness, bearing capacity and deformation are relatively close to the pure frame. The effect of longitudinal ladder beams on the seismic performance of the staircases is studied, and the stairs structure with longitudinal ladder beams has greater stiffness and bearing capacity than that without longitudinal ladder beams. The influence of the size of the ladder beams connected with the ladder plates on the seismic performance of the staircase is studied, the stair structure with the big ladder beams has larger stiffness and bearing capacity than the small ladder beams.There are three models of the whole frame structure are established by the finite element software ANSYS for modal analysis, the existence of the stairs changes the order of the first two modes of vibration in the frame structure, indicating that the stiffness contribution of stairs on the running direction is more obvious, it is found that increasing the number of longitudinal ladder beams can improve the stiffness of the structure by comparing the natural frequencies of vibration.Finally, some specific suggestions are put forward for the seismic design of the ordinary and sliding support reinforced concrete frame stair structure.