Research On Bearing Capacity Computing Theory Of Lipped C-section Stainless Steel Columns With Various Buckling Modes

Stainless steel is a high-performance green building material with excellent corrosion resistance and durability,low maintenance,and low life cycle cost.It is an ideal material for many applications in construction engineering.The lipped channel section is the most typical section form of stainless steel in construction.The majority of the previous research on the lipped channel columns has focused on pure buckling mode.However,far less work has been carried out on interaction buckling mode.The imperfect existing theory brings difficulties and challenges to the application of stainless steel in practical engineering.Thus,this dissertation mainly focuses on critical buckling stress,section classification,unified model of finite element analysis,multiple buckling mode failure characteristics,multiple buckling modes identification and discrimination,and Direct Strength Method(DSM)in lipped channel columns and aim to develop the design method of the resistances of the lipped channel stainless steel column under various buckling modes.The main research contents and results of this dissertation are:Based on the generalized beam theory(GBT),the distortional buckling critical stress of the lipped channel stainless steel column under axial compression is derived.The instantaneous modulus of elasticity is defined according to the flow law,and the two straight-line stainless steel constitutive model is used to derive the GBT equilibrium equation and eigenvalue calculation formula.Combined with the deformation mode of distortional buckling of the lipped channel section,the calculation formula of the distortional buckling critical buckling stress has been proposed.Since the tangent modulus of the two straight-line stainless steel constitutive model is constant,the calculation process is greatly simplified.Compared the relevant experimental data,prediction results of the proposed method showed good match.The existing local buckling critical stress calculation formula has been validated by experimental results.For the lipped channel stainless steel columns with various buckling modes,experimental investigation of local buckling,distortional buckling and local-global interaction buckling were carried out by the research group.Tensile coupon tests and interactive buckling tests on a total of 21 lipped channel stainless steel columns were carried out,exploring the distortional-global interaction buckling behaviour,resistances,buckling failure mode,load-axial displacement curve,load-lateral displacement curve,load-rotation curve and load-stress curve.Based on the obtained experimental results,three types of failure modes of distortional-global interaction buckling have been found.As long as the test is carefully designed,the specimens can undergo distortional-global interaction buckling failure.Through the study of the finite element(FE)model of the lipped channel stainless steel column under various buckling modes,a unified FE model set up using the ABAQUS software package was obtained.The test results were used to validate the unified FE model.Combining the FE model and the constrained finite strip method(c FSM),the buckling mode participation coefficient is calculated,and finally the criteria for identifying the buckling mode are proposed based on the buckling mode participation coefficient.At the same time,it compares the existing methods of buckling mode discrimination are compared,and the advantages and disadvantages of each method are summarized.According to the buckling load factor-length curve of the stainless steel column obtained by the finite strip method(FSM),the lipped channel section is divided into two types: typical section and atypical section.According to the cross-sectional dimension characteristics(aspect ratio(h/b),flange width to lipped width ratio(b/ a)and web height to lipped width(h/ a)),The judgement rule for typical and atypical cross-sections are proposed.The calculation method for the critical local buckling and distortional buckling stresses is proposed for atypical crosssections.Based on the unified lipped channel stainless steel column buckling bearing capacity calculation model,the formulas for local buckling,distortional buckling,global buckling,localglobal interaction buckling and distortional-global interaction buckling bearing capacity are respectively proposed.For different buckling modes,the calculation formulas are unified in form and only different coefficients need to be selected.Finally,a unified formula of the Direct Strength Method for the bearing capacity of different grades stainless steel columns under multiple buckling modes is established.It avoids the discrimination problem of multiple buckling modes,and at the same time solves the unification problem of different grades stainless steel materials.The relevant test data at home and abroad are collected and compared with the calculation method proposed in this dissertation,which shows that the design method provide good accuracy.