Study On Dynamic Response Of Square Concrete-filled Steel Tubular Members Under Impact Loading At Different Impact Angles

Compared with circular concrete-filled steel tubular members,Square concrete-filled steel tubular members has many advantages in joint construction,so it is increasingly being applied in practical engineering.The structures may be subjected to accidental impacts by vehicles and ships.Statistics show that the angle of impacting on the structure is often random.However,the cross-section of concrete-filled square steel tubular structure is not extremely symmetrical,so the dynamic response of the structures varies with different angles of impacting.Therefore,it is necessary to study the relationship between the dynamic response of square concrete-filled steel tubular members and the angle of impact load.In this paper,the dynamic response of square concrete-filled steel tubular(CFST)members subjected to impact loads at different impact angles is studied from three aspects: experiment,finite element simulation and theoretical analysis.The main research contents are as follows:1.Drop-weight impact tests were carried out to study the effects of impact height,wall thickness of steel tube,axial pressure and boundary conditions on the dynamic response of square concrete-filled steel tubular structures with impact angle of 0 degrees.The test results show that the buckling deformation of square concrete-filled steel tubular specimens around the impact location weakens the overall stiffness of the specimens,which is not conducive to the impact resistance of the structure;the overall stiffness of the specimens(including the effects of constraints and the cross-section properties of the specimens)has a great influence on the displacement amplitude,and the greater the stiffness of the specimen is,the smaller the displacement is.2.According to the common impact forms in practice,the simplified integral deformation model and corner damage model of square concrete filled steel tubular(CFST)under impact loads with different impact angles are established by using the parameters verified by experiments.The results of finite element model calculation show that the dynamic response law along the longitudinal direction of square concrete-filled steel tubular structure under impact load at different impact angles is the same;when the impact body directly impacts the corner of square concrete-filled steel tubular structure,it is likely to cause local damage and large local deformation in the impact area,weakening the overall stiffness of the structure;when the specimens are under the same impact energy,the smaller the momentum is,the shorter the impact duration is,and the more obvious the strain rate effect is,so that the peak value of impact force increases and the maximum displacement decreases.3.Based on the theory of transition hinge,the inverse relationship between the maximum displacement of the clamped-clamped beam and the plastic ultimate moment of the cross-section of the beam under lateral impact load at any position is obtained,and the formulas for calculating the plastic ultimate moment of the cross-section of square concrete-filled steel tubular structures at different impact angles are derived.The calculation results show that the plastic ultimate moment of concrete filled square steel tubular structure decreases with the increase of impact angle,so its maximum displacement increases with the increase of impact angle.4.By comparing the results of finite element calculation and theoretical derivation,it is found that the local restraint of local buckling deformation of square steel tube can effectively improve the impact resistance of concrete filled square steel tube structures.