Study On Scale Effect Of Circular Concrete Filled Steel Tube Members Under Lateral Impact Load

Concrete-filled steel tube（CFST）members are widely used in modern buildings,Bridges and other structures.With the increase of the span capacity and building height,the large section concrete filled steel tube members have been widely used.In the life cycle of the structure,the CFST members are likely to be subjected to lateral impact loads,such as the derailed train impacting on the structural columns of the station,the ship impacting on the pier,the car impacting on the building or the bridge structure,etc.Up to now,the experimental studies on the transverse impact of CFST members at home and abroad are all carried out based on scale tests.Due to the limitation of test conditions,large scale proportions are often used for the extra-large section concrete-filled steel tubular members.At the same time,it is very difficult to strictly follow the geometrical similarity criterion for most of the tests that are subjected to dynamic load and cause plastic behavior（such as the impact test of falling hammer）.Under this condition,it is of great significance to study the applicability of impact similarity criterion.On the basis of the test,the size effect of the circular steel tube concrete members subjected to lateral impact is studied in this paper.The main contents are as follows:（1）The existing concrete-filled steel tube impact test and related impact test system at home and abroad are summarized.It is found that the existing impact test system is limited in scale,which leads to the current impact test of concrete-filled steel tube members mostly using reduced scale test.Through dimensional analysis,the similarity model of CFST subjected to transverse impact is established,the scaling and shrinking ratio relations of each parameter are determined,and the impact similarity criterion of CFST members subjected to transverse impact is analyzed and studied.（2）The numerical model of concrete-filled steel tube subjected to lateral impact was established by LS-DYNA,and the accuracy and effectiveness of the model were verified by comparing with the experimental results.The size effect of concrete-filled steel tube members under transverse impact is studied,and the deflection time history curve,impact time history curve,plastic ultimate bending moment and stress of reduced scale and full scale members are compared.The results show that the size effect is small and the error is less than 10% when the components are not cracked.When cracking or fracture occurs,the size effect is more significant,and the maximum error can reach more than 30%.Combined with the numerical simulation results,the reasons for the size effect of CFST members under transverse impact are analyzed.Gravity,material dynamic strength and material fracture are the factors that do not conform to the similarity criterion,which are also the important reasons for the size effect in the impact test of CFST.（3）A similar model of circular steel pipe concrete members subjected to lateral impact was established.Based on numerical simulation to expand the sample,the platform value calculation model of maximum deflection and impact force of circular steel pipe concrete members was obtained through regression analysis.