Stability Performance Of Multi-celled Concrete-filled Steel Tubular Walls Under Complex Boundary Conditions

As an innovative steel-concrete composite structure,the multi-celled concrete-filled steel tubular wall(MCFSTW)has been widely used in engineering practice due to its excellent mechanical performance,standardized members,industrialized production,and convenient construction.To ensure the sufficient lateral load-carrying capacity and lateral stiffness of the structure in different directions,MCFSTWs are vertically arranged to form a combined wall limb with varying forms of section.Because two vertical wall limbs can provide out-of-plane constraints to each other,a single wall limb can be regarded as an I-shaped composite wall with three or four simply-supported edges.At present,research on MCFSTWs mainly focuses on seismic performance,and studies on global buckling behavior are rarely reported previously.However,the global stability of MCFSTWs cannot be ignored in engineering practice,so related research is necessary.Based on this background,the stability performance of MCFSTWs under complex boundary conditions is investigated by theoretical analysis,numerical simulation,and experimental study.In this dissertation,seven chapters are included,and the abstracts of chapters1 to 7 are summarized as follows.Chapter 1 is entitled "Introduction".Firstly,the research background of MCFSTW is expounded from three aspects: engineering application,standard design,and academic research.The design requirements and research difficulties are shown in detail,leading to this dissertation’s research content.Secondly,the research status on four types of steel-concrete composite walls,including MCFSTW,is summarized,indicating the research content in this dissertation is urgently needed.Finally,the research scheme and technical route are described in detail by clarifying the research object,content,and method.Chapter 2 is entitled "Numerical simulation approach for global buckling of MCFSTWs".In this chapter,an innovative numerical simulation approach adopting general stiffness shell is proposed;thus,the actual boundary warpage deformation of MCFSTWs when subjected to global buckling could be well simulated.By using innovative and conventional approaches,steel plate wall,double skin composite wall,and MCFSTW are selected for elastic and elastoplastic analysis.Based on the numerical results,the validity of the innovative approach is fully demonstrated.Chapter 3 is entitled "Study on the stability performance of MCFSTWs with two simplysupported edges".Based on the theoretical analysis and numerical simulation,the stability performance of MCFSTWs with two simply-supported edges under axial compression,in-plane bending moment,combined axial compression and in-plane bending moment are studied.Firstly,elastic buckling load formulas are validated.Secondly,the existing stability design methods are verified.Finally,more safe and accurate stability design methods for MCFSTWs under axial compression,in-plane bending moment,combined axial compression and in-plane bending moment are proposed.Chapter 4 is entitled "Study on the stability performance of MCFSTWs with three simplysupported edges".Based on the theoretical analysis and numerical simulation,the stability performance of MCFSTWs with three simply-supported edges under axial compression,in-plane bending moment,combined axial compression and in-plane bending moment are studied.Based on the orthotropic shell theory,the stability theory for MCFSTW with three simply-supported edges is derived.The elastic buckling load formulas can be further obtained according to the stability theory.Finally,the existing stability design methods are verified,and a more accurate and reliable stability design method for three loading conditions is proposed.Chapter 5 is entitled "Study on the stability performance of MCFSTWs with four simplysupported edges".Based on the theoretical analysis and numerical simulation,the stability performance of MCFSTWs with four simply-supported edges under axial compression,in-plane bending moment,combined axial compression and in-plane bending moment are studied.Based on the orthotropic shell theory,the stability theory for MCFSTW with four simply-supported edges is derived.According to the stability theory,the elastic buckling load formulas are obtained,and the exact formulas are modified to make them more suitable for engineering design.Finally,the existing stability design methods are verified,and a more reliable stability design method is proposed.Chapter 6 is entitled "Experimental study on the stability performance of MCFSTWs under axial compression".In this chapter,MCFSTWs with two and three simply-supported edges are tested under axial compression.According to the test results,the failure modes of the test specimens under two boundary conditions are analyzed and concluded.To explain the test phenomena more clearly,a refined finite element model is established.By comparing the test results,numerical results,and the stability curves proposed in this dissertation,the validity of test results and stability curves are proved.Chapter 7 is entitled "Conclusion and prospect".This chapter summarizes the work completed in this dissertation and the contents that need to be improved and deepened.