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Structural Performance Study And Application Of High-rise Buildings Considering Foundation Stiffness

Posted on:2018-04-17Degree:DoctorType:Dissertation
Country:ChinaCandidate:B DiFull Text:PDF
GTID:1312330536481251Subject:Structural engineering
Abstract/Summary:PDF Full Text Request
As stiffness is an objective measure,foundations cannot be infinitely stiff.The foundation stiffness restraints on superstructure are inevitably limited,precluding the theoretical rigid-base condition.The finite foundation stiffness affects the lateral stiffness and free vibration characteristics of superstructures and changes their long-term working performances.Under an external load,foundations may undergo sliding,settling and rocking movements that influence the seismic performance and overall stability of the superstructure.The Foundation stiffness effect is directly related to building use and structural safety.Foundation stiffness effect analysis belongs to the research category of soil-foundation-structure interaction(SFSI).Global and domestic SFSI research began in the early 20 th century and has been studied from variable levels and viewpoints.The significance of SFSI has gradually been recognized.SFSI analysis has assisted our understanding of the mechanisms and working states of superstructures and has improved the reasonability and accuracy of structural design.However,SFSI is large-range and extremely complicated.It will take much more time and effort to apply its theoretical achievements in practice.In various countries,the design codes of buildings and engineering practices usually adopt the fixed-base or immovable hinge assumption,neglecting the influences of the surrounding soil and foundation stiffness on the anti-seismic,anti-wind and overall stability performance of superstructures.It is a pressing issue of practical significance to have systematic study and analysis of high-rise building foundation stiffness effect and come up with a foundation stiffness control method for structural design so as to solve practical engineering difficulties.Beginning with the calculation and simulation of foundation stiffness,this thesis researches the influence of foundation stiffness on the structural performance of high-rise buildings.It then proposes a quantitative method of foundation stiffness control in structural design.This method offers both important theoretical insights and engineering application value in the structural design of high-rise buildings.The main contents and achievements of this research are the calculation and simulation of foundation stiffness,the theoretical and numerical analysis of foundation stiffness effects,experiment comparison analysis and engineering applications.These researches were undertaken sequentially as described below.The foundation stiffness calculation methods were based mainly on the American codes,technical reports and relevant research achievements of academic papers.These data were collected and summarised.In the dynamic foundation stiffness calculation for high-rise buildings,an important parameter is the average effective shear wave velocity of the soil layer.Taking this parameter as the foundation,basic procedures of dynamic foundation stiffness calculation for high-rise buildings were proposed.To guarantee perfect coupling of the rotational and vertical stiffness of a 3D rectangular foundation,the study presented an improved simulation method for shallow foundations.A GUI programme was developed to calculate the stiffness values of different foundation types,such as shallow foundation,pile foundation,pile-raft foundation and basement exterior wall,etc.Moreover,an interface programme for ABAQUS was compiled.The interface programme improved the modelling efficiency of complicated structural models and could be used for seismic performance analysis of high-rise building structures with compliant bases.In the theoretical analysis,structural calculation diagrams were constructed for shear-type,bending-type and shear-bending structures.Based on the theoretical Equivalent Continuum method,equations describing the structural deflection and internal force redistribution caused by foundation deformations of high-rise buildings were established.These equations and their solutions provided theoretical references for quantitatively and qualitatively analysing the foundation stiffness effect in high-rise buildings.The effects of horizontal,vertical and rotational foundation stiffness on the primary structural performances of high-rise buildings,i.e.lateral stiffness,internal force distribution and overall stability,were clarified.For controlling the degeneration of overall lateral stiffness,degree of internal force redistribution and the amplification of second-order gravity effects,limits were imposed on the rotational foundation stiffness ratio in the structural design of high-rise buildings.This innovative concept can be easily implemented by engineers.In the finite element numerical analyses,the research objects were typical reinforced concrete frames and shear wall-frame structures.The effects of foundation stiffness on the seismic behavior of building structures on various sites were investigated in response spectrum and elastic–plastic dynamic analyses.The calculation results were compared with those of fixed-base structures.By changing the structural design parameters and shear wave velocities of the underlying soil layers,structural models with various foundation stiffnesses were developed for further parametric analysis.In incremental dynamic analyses,the effects of foundation stiffness on the energy dissipation mechanism and internal force distribution in the superstructure,from the elastic stage to collapse,were also determined.Static pushover tests of reinforced-concrete shear wall-frame model structures with fixed-base and compliant-base were conducted.The structural cracking processes,yielding sequences,failure mechanisms and bearing capacities were compared.Solid element models of the specimens were then subjected to nonlinear pushover analyses.The simulation results well agreed with the test results,confirming the correctness and accuracy of the finite element analysis.Based on the test and simulation results,preliminary suggestions for the seismic design of shear wall-frame structures accounting for foundation stiffness were proposed.Finally,the research achievements were applied to the structural design of a domestic super-high-rise building.Based on the foundation stiffness calculation and model interface programme developed in this thesis,the foundation stiffness effects of the superstructure were studied.The proposed limitations on the rotational foundation stiffness ratio exerted a significant effect in super-high-rise buildings and improved the structural emergency capacity of the project.
Keywords/Search Tags:high-rise building, foundation stiffness, seismic behavior, overall stability, lateral stiffness, internal force distribution
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