Research On Seismic Performance And Performance-Based Seismic Design Of High Rise Buildings With Strengthened Stories

High rise buildings with strengthened stories are widely used in our country. This kind of structure makes full used of advantages of core tube and exterior columns and has become an important type of high rise buildings. Seismic design methods in current codes can not be applied to it directly because of the complexity and height of the structure. As a newly developed seismic design method, performance-based seismic design (PBSD) can be easily applied to structures with strengthened stories. However, there are still many key problems on PBSD of this kind of structure need to be solved. Therefore, this paper does some research works on these problems, which are listed as follows:(1) Mechanical performance of high rise buildings with strengthened storiesA 52-story high rise building with strengthened stories is taken as the example whose finite element model is constructed for analysis. The parameters that affect stiffness and internal force of the structure include: location and number of strengthened stories, stiffness ratio of outrigger and core tube and stiffness ratio of exterior columns and core tube. These parameters as well as the structural response to dynamic loads are analyzed in detail. Based on the analyses, the optimum location of strengthened stories, rational range and limit value of stiffness ratio of outrigger and core tube are proposed.(2) Performance level quantification of high rise buildings with strengthened storiesThe story drift calculating method of strengthened stories is established. The performance levels of high rise buildings with strengthened stories are plot out considering relevant domestic and foreign standards and each performance level is quantified based on large amount of shear wall experimental data. This forms a basis for performance-based seismic design.(3) Direct displacement-based seismic design of high rise buildings with strengthened storiesHigher modes whose participation mass are larger than 90% of the total mass of the structure are considered in the design. Based on the mechanical and deformation characteristic of this kind of structure, the bottom stories and stories above the strengthened ones are selected as the "key stories" to control the performance of the building. The structure is replaced by an equivalent single degree of freedom system corresponding to each mode and each equivalent displacement is determined using the proposed method. The target displacement will be obtained by combining contribution of all modes multiplied by a factor. The structural internal force is obtained by target displacement to design and check the structural components.(4) Capacity spectrum method of high rise buildings with strengthened storiesBased on the mechanical and deformation characteristic of this kind of structure, the bottom stories and stories above the strengthened ones are selected as the "key stories" to control the performance of the building. The structure is simplified to be a planar structure, whose dynamic parameters are determined using elastic modal analysis. Higher modes whose participation mass are larger than 90% of the total mass of the structure are considered in the design. Pushover analysis corresponding to each mode is performed on the structure, and then the capacity spectrum method is applied to each pushover curve to obtain the contribution of each mode. The total seismic response of the structure can be obtained by combining the contribution of each mode and deformation of the "key stories" will be checked using the total response.(5) Simplified procedure for calculating seismic load of high rise buildings with strengthened storiesBased on its mechanical characteristics, the structure with strengthened stories is divided into several sections by the strengthened stories. Each section is replaced by an equivalent single degree of freedom system. The simplified calculating model can be obtained by jointing each section in order, and then the seismic force of the simplified model can be calculated using the mode-superposition response spectrum method. Story shear corresponding to each mode can be obtained by combining response of each section. Total seismic force of the structure can be calculated using SRSS method. Comparison of simplified method to rational method shows that the simplified method is accurate enough for actual design.