MPA法和Pushover法在掉层框架结构中的适用性对比分析

结合已有的规则结构分析结果,设置不同的掉层跨数、掉层数量的掉层结构,以逐步增量弹塑性时程分析(IDA)结果为依据,运用多模态Pushover法(MPA)和传统的Pushover法进行对比分析。结果表明:相对于规则框架结构,除MPA外,掉层结构的掉层部分在各类侧向力分布模式相对于IDA下的层间Pushover曲线有较大差异。SRSS分布下在掉一、二层位置,过高估计结构的响应。上接地层以上部位各侧向力下的层间Pushover曲线较IDA曲线误差较小。掉层的楼层的层剪力在上接地位置存在明显的突变。掉层跨数的改变对上部楼层弹塑性分析结果影响较小,但跨数的改变会改变同等烈度下结构的层间Pushover曲线和内力响应。与此同时,掉层跨数的增加会减轻"剪力突变"现象。伴随着掉层层数的增加,掉层部分均匀分布和倒三角分布与IDA下层间推覆曲线的差异会扩大。总之,相对于传统Pushover分析,MPA分析的结果更接近于相对准确值,需要进一步研究以提高精度。

Comparative evaluation for the feasibility analysis between the methods of MPA and pushover for the structures propped by the stepped foundation in mountainous city

Referring to the currently exiting research results on the regular structures,this paper is inclined to establish a frame structure with different quantities of dropped stories and dropped spans to evaluate the results of the modal pushover analysis (MPA) based on the mode-superposition response spectrum method and the traditional pushover method and the results of incremental dynamic analysis (IDA).The results of our analysis show that,as compared with the general regular frame structures,the story pushover curves of all kinds of lateral forces can vary from those of IDA except for the MPA at the dropped stories.On the other hand,the internal force of SRSS distribution can likely exceed that of IDA,suggesting that the results may likely overestimate the structural response at the two dropped stories.Thus,the results of the upper floors may tend to be similar to those of the regular structures,with slight difference between story pushover curves of the traditional pushover and IDA.And,in contrast,for the mountain top structures,the story pushover curves of SRSS and MPA can be closer to IDA than the other regular structures and,therefore,more acceptable.Needless to say,there must be a significant mutation in the shear distribution for the structures at the upper grounds,which ought to be paid more attention to in the architectural layout.However,little effect has to be paid to the number of the spans for the upper stories,which may have some effect on the lateral stiffness of the structure,which can be likely to bring somewhat changes to the story pushover curves and internal force response of the structure under the same seismic intensity.As to the shear mutation,it can be reduced by increasing the number of spans at the same time.In so doing,with the increase of the number of dropped stories,it may lead to the increase of the differences of the pushover curves between the lateral force distributions (uniform and invert triangle distribution) and the IDA,too.Hence,it can be concluded that the results of the modal pushover analysis can be made more accurate than the fixed lateral force distribution in the mountainous structures and regular structures.But modal pushover analysis may still have somewhat errors needed to be overcome through further studies,for example,its mode participation order.