Evaluation Of Seismic Performance Of Step-Terrace Structure By Pushover Method

Step-terrace structure has been widely used as a typical kind of mountain building. As most mountainous regions of our country are in earthquake-prone zone, it is important to study the seismic performance of the step-terrace structure. At home and abroad, current seismic design code has no specific provision about step-terrace structure. In view of rigid foundation assumption and the consideration of soil-structure interaction of step-terrace structures in different conditions, Pushover method used to assess their seismic performance is of great theoretical significance and practical value.Based on Pushover method, this paper uses the SAP2000 finite element software to assess their seismic performance of step-terrace mountain structure with rigid foundation assumption and the consideration of soil-structure interaction, and problems needed to pay attention and recommendation for structural design are also provided. In view of displacement/performance seismic philosophy, there are some discrepancies in the response of the upper structures between the consideration of pile-soil-structure interaction and rigid foundation assumption. The consideration of pile-soil-structure interaction is closer to the reality. The main conclusions of this paper are as follows:①In the assumption of rigid foundation, the damage of off-layer part is lighter than upper structure, and the most serious damages appear in the beam-end of 1-3 layer of the upper structure and upper grounding column; as the increasing of the number of the off-layer and the off-across, the grounding column of the first layer will damage prematurely, and the napping limit state is reached.②The followings are acquired from the comparison with the step-terrace structure with fixed-support of the upper grounding column: all the indexes of the seismic performance will decline when upper grounding column is hinged-support; for the condition of sliding support, the plastic damage of the upper grounding layer will be alleviated if the number of off-cross layer is more than 4/5 of the total number of structure across, and the plastic damage of off-layer part will be lighter; when isolation bearings are used, the indicators of seismic performance will get better controlled, which means that the structure seismic performance is good.③In the consideration of the pile-soil-structure interaction, the plastic damage of the off-layer parts in the step-terrace structure will aggravate, and plastic failure will take place in the pile foundation of upper structure; the beam and column connected to the upper grounding column may be weak parts and the pile foundation of upper structure may also get damaged seriously if there are many off-layers and off-crosses.④It is feasible to evaluate the seismic performance of step-terrace structure by the Pushover method; without considering the effects of higher modes in the Pushover analysis, the seismic response may be underestimated if the off-layers are no less than 3 layers. And the uniform distribution pattern and the MPA method can make a well evaluation of seismic performance of off-layer parts.