Study On The Applicability Of Minimum Floor Seismic Shear Coefficient To Step-terrace Structures

Step-terrace structure is a typical structure of mountainous architecture. Due to the different height of base embedding location, step-terrace structure and ordinary structure have significant differences in force performance. According to the current code in China, the main control measure in the long period structure’s high-rise structure seismic design is checking the minimum floor seismic shear coefficient. Due to layer concept vague of the constrained position in step-terrace structure, how to decline and determine the minimum floor seismic shear coefficient which is apply for step-terrace structure is becoming the problem to be solved.The example is a frame-shear wall structure in this paper, which are two group step-terrace models with main lateral anti-force components in different embedding locations and corresponding conventional structure. Based on analysis of elastic and elastic-plastic analysis, the applicability of the current code stipulated the minimum floor seismic shear coefficient on the mountainous step-terrace structure is studied.The two concepts of local shear coefficient and local shear coefficient are proposed based on declining the names of each part in step-terrace structure. Based on the results of elastic analysis and elastic-plastic analysis, the conclusions are as follows:1, Component internal forces of three step-terrace floors and above floors are less affected by the grounding modes, and it is recommended to carry out the design following the minimum floor seismic shear coefficient as specified in the current code.2, The seismic response is much less than that of the conventional structure, and the internal force distribution is affected by structure arrangement, numbers of step-terrace and so on. Problems of achieving the minimum seismic shear coefficient which is stipulated in current code are difficult to solve.3, The main weak parts of structure are laying on the upper grounding floors and floors nearby in this paper. When step-terrace number is same, the upper grounding picks up more members, local shear coefficient λ_s of structures with stronger bearing capacity and stiffness is bigger, step-terrace layer and grounding layer deformation is smaller, plastic distribution is more uniform. The upper grounding picks up less members, the bearing capacity is weaker, the upper grounding stiffness is smaller, local shear coefficient λ_s is smaller, plastic deformation is concentrated on the upper grounding floor, resulting in the upper grounding easier failure before structural failure. Local minimum seismic shear coefficient of the upper grounding is recommended to be under controlling in order to ensure the upper grounding have enough stiffness and bearing capacity. In the design, a structure plan that the main anti lateral force component is better embedded in the upper grounding is one of the doable plan.4, When structure arrangement of the upper grounding floor are determined, floors of step-terrace structure increase, local seismic shear coefficient ratio Φ increases, deformation of the upper grounding and first floor of step-terrace part increases. The result of elastic-plastic analysis shows that much larger local seismic shear coefficient is easier causing that the upper grounding part first has serious damage and then the overall structure performance has great reduction. Based on the result above, the maximum of the local seismic shear coefficient should be better under controlling.