Dynamic Response Of Concrete Filled Steel Tube Columns Under Lateral Impact And Its Analytical Calculation Method

As a typical extreme dynamic load usually caused by trucks,ships or derailed trains,the lateral impact action can lead to significant damage or even collapse of engineering structures.Therefore,the dynamic response of concrete-filled steel tube(CFST)columns under lateral impact has received increasing attention due to the CFST column is one of the typical structural element forms.First,this paper carries out the lateral impact tests and the finite element analysis(FEA)to obtain the dynamic response behaviours of CFST columns under lateral impact.The focus of the tests and the FEAs is the local dynamic response of the columns.Second,an analysis calculation method is proposed based on the dynamic response characteristics of the CFST columns from the tests and FEAs.The method includes the local dynamic response process.Third,the influence of the local dynamic response on the design is discussed to improve the design calculation process and form a new practical design calculation method.The main contents of this study are summarized as follows:(1)A series of tests are applied to investigate the dynamic response of the clampedclamped CFST columns under lateral impact.The impact point of the tests is located at the 2/9span,and the impactor is a rigid drop hammer.The measuring results of the tests include the deformation and damage of the columns after impact,the dynamic response development of the column,the impact force time history curve and the deflection time history curve.Initially,the global dynamic response mode is summarized according to the deformation and damage of the CFST columns after impact.Next,the dynamic response development of the columns proves the existence of the local dynamic response process,also is used to analyse the local dynamic response behaviour and the damage cracking behaviour of the CFST members.Third,the characteristics of the impact force time history curve are obtained to establish the corresponding relationship from the impact force curve to the local and global dynamic response process preliminarily.In addition,the characteristics of the deflection time history curve is acquired to introduce the matching relationship between the impact force curve and the deformation damage characteristics of the CFST members.(2)Finite element analysis(FEA)exhibits the stress distribution of CFST columns under lateral impact,the influence of the support types and the impact point locations on the dynamic response of the CFST columns,the motion characteristics of the CFST columns during the impact process.First,the stress distribution shows the propagation process of the lateral impact action,it is the basis for further distinguishing the different dynamic response stages in the local and global process.The mechanical behaviours of each dynamic response stage are also summarized based on the stress distribution.Second,the stress distributions illustrate the dynamic response difference between the clamped-clamped,the clamped-simply support and the simply support CFST columns under lateral impact,as well as the distinction of the 2/9 span lateral impact process and the mid-span one.The comparison results reveal the existence of a travelling stress concentration area and its inertial boundary,the mechanical properties of the travelling area need to be coordinated with that of the inertial boundary.Finally,the FEA results display the motion characteristics of the impactor and the CFST column at the impact point during the local and global dynamic response process.Then,a model is presented to simplify the acceleration time history curve(acceleration curve)of the CFST columns at impact point.(3)An analysis method is proposed for the dynamic response of the clamped-clamped CFST columns under lateral impact,based on the travelling hinge theory and the predicted simplified model of the acceleration curve.The method includes the local dynamic response process and the elastic-plastic behaviour of the CFST column,its results contain the complete characteristics of the impact force time history curve and the deflection time history curve.(4)Through modifying the calculation model of the clamped-clamped CFST columns,the analysis method is applied for the dynamic response of the simply supported CFST columns under lateral impact,then the dynamic response of the CFST columns under both lateral impact action and axial compression load.In the case of the simply support,an empirical model is adopted to represent the inertial boundary of the simply support travelling hinge,it is one necessary part for the local dynamic response calculation of the simply support columns.Next,for the axial pressure force superimposed on the lateral impact action,the method considers the influence of the axial pressure force on the local compression and local bending deformation processes,it describes the phenomenon that the axial pressure increases the peak value force.(5)A discuss is conducted to analyse the importance of the local dynamic response and the column elastoplastic behaviour in the lateral impact design calculation.First,the characteristics of the general design calculation models are summarized.Then,according to the general characteristics of the design models,a design calculation formula is derived and reflects the effect of the local dynamic response process and the column elastoplastic behaviour on the design accuracy.Subsequently,two coefficients are put forward to evaluate the importance of the local dynamic response process and the column elastoplastic behaviour in the design calculation.Last,a design calculation method is proposed based on the design calculation formula and the importance coefficients,which can avoid the large design error caused by the lack of the local dynamic response process or the column elastoplastic behaviour during the calculation process.