Study On Seismic Collapse Resistance Of Mega-Braced Frame-Core Tube Structure

Due to the huge size and complicated structural system of the super-tall building,which is quite different from a traditional tall building,the current researches of super-tall building are not sufficient to meet the demand of engineering application.This paper mainly researches on mega-braced frame-core tube structure by using refined modal of a practical engineering,which is one of frequently used structures of super-tall building.The main contents are as follows:(1)Based on the project materials of mega-braced frame-core tube structures above 400m,it's found that such type of structure has some common characteristics,such as the rate of height and width exceeding the limit,the long period and the stronger effect of the frame on bearing shear and overturning moment.In order to acquire the stress characteristics of such structure in detail,the paper carried on elastic analysis on the finite element model of High-silver building.The analysis results show that such structure has long period,which exceeds the range of standard;The force and deformation of the structure causing by earthquake are greater than those causing by wind,so the seismic load is dominant among all types of load.Due to the setting of mega brace,the characteristic of deformation curve is flexural mode.Frame bears higher ratio of shear and overturning moment than core tube under earthquakes.It is worth noting that the mega brace plays a major role in bearing shear and the mega column plays a major role in bearing overturning moment.(2)In order to study the seismic performance of the structure under small,middle,severe and extremely rare earthquakes,the dynamic elastoplastic time history analysis is carried out by using PKPM-SAUSAGE.It's found that the deformation characteristic,internal force distribution,damage degree and yield mechanism of the structure varies at different levels of the earthquake.The yeild order of main lateral force-resisting members is coupling beam,shear wall,brace and mega column.(3)By analyzing the lateral stiffness ratio of brace to braced frame in bottom zone of super-tall projects,the lateral stiffness ratio value range was obtained.The influence of such ratio on the performance of the structure was studied within the value range.Based on the comprehensive consideration of deformation,internal force,damage and yield mechanism of the structure,it is recommended that the lateral stiffness ratio of brace to braced frame in bottom zone can be 0.35 or 0.40.When the ratio is 0.35,the deformation of the structure is small and the effect of truss is strong;When the ratio is 0.40,the damage of the core tube is severe and the damage of the frame is light.(4)Based on the study of the distribution of stiffness along the structure's height,this paper proposed two relations between the lateral stiffness ratio of brace to braced frame and section number.One obeys linear increasing rule,another obeys quadratic parabola increasing rule.By comparing elastic and elastoplastic performances,it is recommended that the relation between the lateral stiffness ratio of brace to braced frame and section number should obey linear increasing rule,such the struture can get reasonable yield mechanism and strong energy dissipation capacity.