Research On The Local Buckling Behavior Of Hot-rolled SHS And RHS Based On CSM

With the development of production technology,the use of hot-rolled square and rectangular hollow sections?SHS/RHS?in building constructions has been increased rapidly.In most of modern steel design codes,the resistances of steel cross-sections are determined by their resistances of deformation and local buckling,following the traditional cross-section classification approach.However,some research show that this classification approach which divides cross-sections into different classes to design them separately has some shortco mings.The CSM is a deformation-based approach that offers more consistent and continuous resistance predictions and allows for the beneficial influence of strain hardening.At present,it is mainly used in the structure design of stainless steel and cold-formed steel cross-sections,while its theories and utilization in hot-rolled steel members are poor.This thesis investigates the local buckling behavior under different load conditions and different codes'design method of hot-rolled SHS/RHS using the finite element?FE?method,and trys to extend the CSM to the design of hot-rolled SHS/RHS steel members.The main results are as follows:?1?Using FE software ABAQUS,numerical models considering both initial local imperfections and residual stress were established and validated against existing test results.It suggested the numerical models weren't sensitive to the change of initial local imperfections.?2?Based on validation of the FE models,parametric studies were performed to assess the ultimate capacity of hot-rolled SHS/RHS over a wider range of cross-section slenderness?_p^—and the ratio H/B.With the increased of?_p^—,the capacity of hot-rolled SHS/RHS decreased.With the increased of ratio H/B,the capacity of hot-rolled beam-columns?strong axis?increased,while the capacity in other conditions didn't change.Empirical expressions were proposed to calculate cross-section slenderness?_p^—in compression and bending considering the effect of ratio H/B.?3?By comparing the FE results with the corresponding European,American and Chinese design codes,the accuracy of these design methods for the local buckling capacity of SHS/RHS under different load conditions was evaluated.It suggested some results using European codes were discrete,some results using American codes were conservative,most results using Chinese codes were both discrete and conservative,and the limit ratio of width to thickness of steel plate in European,American and Chinese codes was needed to be revised.A new coefficient of section plastic development?₁ caculated by?_p^—was proposed to take the place of?=1.05 in Chinese design code.?4?The CSM design base curve and material model of hot-rolled SHS/RHS were determined in this thesis.With theoretical derivation,simplified design expressions of hot-rolled SHS/RHS under compression and bending were given.Upon FE results,the cross-sections limit slenderness?_p^—in CSM was suggested to be 0.6.A new CSM expression for stocky hot-rolled cross-sections under compression plus bending was then proposed,and the reliability and accuracy of the simplified expressions and proposal expressions in all cases were assessed by comparing its design results with the results of design code and FE.For all cases considered,the CSM,through a rational exploitation of strain hardening,offers a more accurate prediction of observed physical behavior.