Abstract:
Response due to impact load is different from that caused due to static load. Broadly, the impact load can be classified into i) low velocity large mass impact and ii) high velocity small mass impact. The first category involves collision of vehicle into crash barriers, piers of bridges, drop of an object on slab etc. whereas the second one includes bullet or missile hitting structures, birds hitting airplane etc. Reinforced concrete (RC) members are often subjected to extreme dynamic loading condition due to direct impact. In context of Civil Engineering problem, an investigation into the impact behaviour of RC members subjected to low velocity high mass is very important. The current work deals with low velocity large mass impact on RC structures.
Full-scale test of RC member under impact load is very expensive and time-consuming work. The numerical finite element (FE) analysis of RC member has become an effective and reliable solution to overcome this problem. Before carrying out numerical simulation of RC member under impact load, some existing literatures on the relevant field based on experimental, analytical and numerical approaches are thoroughly reviewed. RC members have been modeled by nonlinear FE software ABAQUS (2012). The nonlinearity of RC member has been achieved by incorporating nonlinear effects due to cracking and crushing of concrete and yielding of steel reinforcement. The Concrete Damage Plasticity (CDP) model has been used with appropriate parameters to model the nonlinear behaviour of concrete material and elastic-plastic material has been selected for steel reinforcement. Performance of this numerical simulation has been validated against experimental as well as analytical results for static loads.
The numerical simulation is then extended to impact loading. A number of beams and slabs tested by Chan and May (2009) under impact load has been modeled and observed responses have been found to be comparable. The transient impact force histories and crack patterns obtained from FE analysis of these beams and slabs match reasonably well with the test results but a time lag has been observed between peak impact forces for FE analysis. So, CDP model provides consistent results for static as well as impact analysis of RC members. A series of RC beams subjected to low speed high mass impact, tested by Tachibana et al. (2010), has been numerically modeled and analyzed. From the observation of these analyzed beams it is noted that, if only global damage is under consideration and analyzed RC beam is failed completely due to high mass low velocity impactor‟s load then impulse, total area under time-force curve, only depend upon the momentum of impactor. The duration of impact load varies proportionally with the ratio of momentum of impactor to ultimate bending capacity of beam. The beam fails completely, if the mean impact force exceeds 1.37 times of its ultimate bending capacity. The bending capacity of RC column is also be increased by 1.37 times of its actual capacity, if the failure is governed by tension. But axial capacity will be reduced by 0.91 times when failure is by crushing of concrete before tension yielding.
