Study On Performance Of H-shaed Steel Members With Large Width-thickness Ratios Under Transverse Impact

Large width-thickness ratios members normally possess larger flexural stiffness,yield moment and critical load for overall stability than those of normal section members with equivalent weight.Moreover,they are considered to be sustainable structures for saving resource and reducing energy consumption.In recent years,structural collapse accidents caused by terrorist attacks,explosions,fires and other extreme disasters often occur at home and abroad,which have a serious influence on the safety of the structure.However,the existing codes have less consideration on the impact resistance design of the structure.It is necessary to investigate the impact behavior of large width-thickness ratios H section members.In view of this,experimental and theoretical studies for the impact behavior of large width-thickness ratios members conducted in this paper.A theoretical model of thin flexible H-section steel members subjected to lateral impact load is established,which provides a basis for the impact resistance design of slender members.The main contents and conclusions can be stated as follows:(1)Experimental work of 13 H section columns under transverse impact load and axial compression were carried out.The boundary conditions of the specimens were fixed at one end and sliding at one end and the impact position was 1/3 from the bottom of the column.The results show that the deformation mode of H-section steel column under impact load is the coupling of overall bending deformation and local deformation.When the impact occurs,the upper flange of H-shaped steel column has obvious depression at the impact site,and the web has obvious asymmetric out-of-plane deformation,forming obvious local deformation,which makes the H-shaped steel column form plastic hinge at the impact point.With the development of deformation,the lower flange of H-shaped steel column near the fixed support produces buckling deformation.In the test,the main parameters affecting the impact resistance of the members including web thickness,flange thickness,impact energy and axial pressure were studied.With the increase of web and flange thickness,the peak value of impact force increases obviously,the platform value of impact force increases,and the duration of platform decreases gradually.Under certain impact energy,the stable impact forces was mainly affected by the flange thickness and the peak impact forces was mainly affected by the web thickness;the impact time of High-section specimens is longer,and the deformation rate of low-section specimens is faster,while there is little difference in deformation between the two cross-section specimens.(2)Then a finite element analysis FEA model was established to predict the impact behaviour of H section members,in which the strain rate effects was considered.Test data of impact force and total deflection from the author and other researchers were used to verify the accuracy of the FEA model and general good results were achieved.Based on the analysis of a large number of parameters,the main factors affecting the mechanical properties of components under impact load,such as impact speed,impact quality and impact location,are analyzed.The results show that the increase of impact energy leads to the increase of energy dissipation of steel members;the impact time is mainly determined by the impact mass;and the maximum impact force is mainly determined by the impact velocity.The impact speed increases the energy dissipation per unit displacement of steel members,while the impact mass can not change the energy consumption per unit displacement.With the increase of the axial compression ratio,the impact force decreases,the displacement increases,the energy dissipation increases gradually,and the influence of the axial pressure on the energy dissipation of components is significant at the stage of impact platform.(3)The local buckling behavior of H-shaped steel members with large width-thickness ratios subjected to lateral impact was investigated theoretically.In the theoretical analysis,Yield Line Mechanism was introduced to establish the theoretical model.Based on energy balance and quasi-static approximation,a theoretical model of lateral impact on thin flexible H-section steel columns considering local buckling is established,and the critical impact energy for failure of members is obtained.The validity of the theoretical model is verified by an accurate finite element model.On this basis,the theoretical model is used to analyze the parameters,including the axial pressure and impact location.With the increase of the axial pressure on the column,the lateral deformation of the column before failure decreases,and the critical impact velocity of the member decreases gradually.The closer the impact location is to the bottom of the column,the greater the critical impact velocity of the component.As the applied axial force decreases,the work done by the axial pressure caused by the axial movement of the column increases and the plastic dissipation energy increases.(4)The realization of the fixed end is a prerequisite to ensure the test results.In this paper,the fixed end of impact test is connected by bolts,and the bolt loosening is a minor damage.It is difficult to distinguish by conventional methods,but it will have a certain impact on the test results.In order to ensure the accuracy of impact test results,the active sensing technology of piezoelectric ceramics is used to monitor the bolt loosening of column foot,and the maximum suitable prestressing force between specimen and splint is 70N?m.The test results show that the pre-stress of the column-foot bolt will affect the actual contact area between the column and the splint,and then affect the peak value of the focusing signal.From the variation law of the focusing signal under-erent pre-tightening forces,it can be seen that the peak value of the focusing signal increases obviously with the increase of the pre-stress value of the column-foot bolt before the pre-stress value reaches saturation.