Research On The Seismic Design Spectrum And Minimum Base Shear-gravity Ratio Of Long-period Structure

Seismic design response spectrum is the foundation to determine the forces applied to the building under earthquake. It is one of the core provisions of engineering structures seismic design. With the rapid development of high-rise buildings, from the perspective theoretical research or from the engineering structural design point, there are several obvious shortcomings of the seismic design response spectrum of seismic codes. It no longer meets the seismic design of long-period structure, which is urgent to be mended.Based on the domestic and international research about seismic design response spectrum, the attenuation law of the long period seismic design response spectrum is going to be explored, mainly related about the shape parameters and segment position of the long period seismic design response spectrum. It is discovered that the seismic design of long-period structure with high damping ratio which is based on absolute acceleration spectrum is too conservative. It also shows that the dynamic magnification factor of the long period seismic design response spectrum is strongly influenced by the construction site. The factor varies a lot from construction site I to IV.Meanwhile, a large number of dynamic and time-historical analysis are undergone to two long period structure model A(T1=5.38s) and model B(T1=7.51s) with the elastic analysis software YJK, to explore the relationship among the base shear-gravity ratio, construction site and the dynamic characteristics of the structure itself. It is showed that the minimum base sheargravity ratio of the seismic codes is conservative and should be loosend up. The base sheargravity ratio and the maximum story drift of long period structure are greatly influenced by the construction site.The response of the same structure in soft soil construction site is much more fierce than that in hard soil construction site. According to the analizing result of model A and model B, the amplification factor of the base shear-gravity ratio of long period structure under I, II, III and IV four categories of construction site conditions is 0.87, 1.00, 1.19 and 1.32, respectively.The result of the research will offer a reference method to the controversial issue about the seismic design of long-period structure. It will provides basic support for the next generation structural seismic design.