Dynamic Response Of R.c Square Members Under The Unequal Transverse Loading

During its service life,a structure may be subjected to various environmental and loading conditions.However,in general,the properties determined under one set of conditions may not be used to determine the behavior of the material under a different set of conditions.For example,it is well known that concrete is a strain rate sensitive material;therefore,its properties determined under conventional static loading cannot be used to predict the performance of concrete subjected to high strain rates.The problem is serious because these high strain rate loadings are associated with large amounts of energy imparted to the structure in a very short period of time,and concrete is a brittle material.Since the strain rate sensitivity of concrete prohibits the use of its statically determined properties in assessing its behavior under dynamic conditions,high strain rate tests are required.This study aims to investigate the conventional RC square members’ response under the effect of an unequal lateral impact force.Impact performances of RC members were first examined by using the drop-hammer impact test system.The importance of unequal lateral impact load was highlighted and addressed by obtaining the RC members’ failure mode and dynamic response characteristics.Five different types were experimentally investigated in detail.A finite element（FE）modeling method was also proposed and demonstrated to reasonably predict RC members’ impact responses.The effect of impact position,hammer height,hammer mass,boundary condition,and axial load ratio on the dynamic response characteristics under impact events was performed.Superior predictions of the numerical model were confirmed with experimental results regarding impact force history,deflection time history,and failure modes,indicating the model’s and parametric studies’ validity.The results revealed that the impact position has a great influence on the response of the members.The maximum defection reduced by 98.5% when the impactor moved from the support to mid-span as well as shifts the failure mode from brittle shear to a more ductile one.On the other hand,the synergistic impact of the height and mass of the striker appeared to affect the maximum deflection and the total duration of the impact process.Regarding the boundary conditions,the change of supports from fixed ends to a simply supported condition is shown to have no effect on the peak impact value.Moreover,the application of a low axial load ratio plays an important role in making the members failed in a flexural manner.On the contrary,the increment of axial load ratio by more than 30% leads the members to exhibit a catastrophic brittle shear failure.Finally,the dynamic equilibrium on two specimens（FH1 and FH3）was evaluated by comparing the impact capacity resistance forces of the RC members with the practical impact one.The findings drawn from the experimental and numerical studies can facilitate improving the impact-resistant performance of structural members.