Research On Residual Stress Model And Hysteretic Performance Of Welded Box-section Hybrid Strength Steel Columns

With the development of modern civil engineering in the direction of"higher,longer,and more flexible",high-performance materials（such as high-strength steel）have been widely applied.Compared with ordinary steel,high-strength steel structure has significant advantages in terms of mechanical performance,building function,construction technology,social economic and environmental benefits.As the yield strength of steel increases,the yield-strength ratio increases and the elongation after breaking decreases.The length of the yield platform shortens or even disappears.And the strain strengthening effect of high-strength steel is not obvious.The high yield-strength ratio and poor ductility limit the application of high-strength steel in seismic fortification areas.Therefore,the development of a steel component with high strength and good ductility is the key issue for the current wide application of steel structures（especially high-strength steel structure systems）in earthquake-resistant areas.Based on this,this paper proposes a new type of welded box-section hybrid strength steel columns.First,the distribution of residual stress were measured by the cutting method,and a residual stress model which is suitable for welded box-section hybrid strength steel columns was proposed.Second,the reciprocating load tests of 8 welded box-section hybrid strength steel columns were carried out,revealing the influence of sensitive factors such as axial compression ratio,strength matching method,plate width-to-thickness ratio on the hysteretic performance of steel columns;finally,a three-dimensional finite element model was established using ABAQUS finite element software,and parameter analysis was conducted for each key factor.The scientific method and calculation formula suitable for the hysteretic performance of welded box-section hybrid strength steel columns are proposed,and the seismic design recommendations are also proposed for the welded box-section hybrid strength steel columns.And a series of experimental studies,finite element simulations and numerical analyses have been carried out on the residual stress model and hysteretic performance of the columns:（1）The residual stress measurement tests of 4 different cross-section forms were carried out.The box-section specimens were cut and measured using the Whittemore handheld strain gauge YB-25,and the effects of flange width-thickness ratio,steel plate thickness and steel strength on the value and distribution of residual stress were studied.Among them,the steel strength includes Q345 and Q690,the flange width-to-thickness ratio changes from 12.07 to23.46,and the web height-to-thickness ratio range is 20.56～23.43.Besides,the length of measuring members is 250mm,and measurement accuracy is 0.01mm.Based on the above and combined with the existing residual stress models at home and abroad,a set of not only suitable for single-strength steel welded box section,but also can be used to calculate the maximum residual tensile stress and average residual compressive stress of welded box-section hybrid strength steel.（2）The seismic performance test of welded box-section steel columns was carried out,a total of 8 test pieces.The hysteresis test of the welded box-section steel column with different strength grade matching methods,width-to-thickness ratio and axial compression ratio was carried out by using the hydraulic loading device of MTS loading system（MTS）.Among them,The different steel strength grade matching include Q345 and Q690,the range of flange width-to-thickness ratio is 12.07～23.46,the web height-to-thickness ratio ranges from 20.56 to 23.43,and the height of columns is 1200mm.According to the test phenomena and data conclusions,the influence of sensitive factors such as axial compression ratio,strength matching method,plate width-to-thickness ratio on the hysteretic performance（seismic performance）of the steel column is revealed,and a high strength and good ductility columns is designed.Steel members provide data references for the establishment of finite element models and numerical simulations.（3）The finite element analysis software ABAQUS was used to establish a three-dimensional finite element model,which took residual stress and material nonlinearity into the finite element model,and carried out parameter analysis for each key factor.The formulas for calculating the relationship of the relative maximum load-bearing capacity(H_max/H_y)and ductility coefficient（μ）of the welded box-section steel columns under different axial compression ratios,the width-to-thickness ratio and the slenderness ratio are proposed.Besides,the formulas can provide data support for the application of seismic engineering practice of the welded box-section steel columns.In summary,this paper proposes a welded box-section hybrid strength steel column,which has the characteristics of delaying the occurrence of local buckling without reducing the axial and lateral bearing capacity of the steel column itself,that is,it can effectively improve the hysteretic performance of steel structure columns.The established finite element model is used to provide reference for engineering application and academic research.