Numerical investigation of the behaviour of RC wide beams under impact loads

The present work sets out to investigate numerically the dynamic responses of simply-supported reinforced concrete (RC) beams under impact loading. The beams comprise wide sections and thus can be also considered as one-way slab panels often used in pre-cast concrete floor construction. The study was carried out using dynamic Non-linear Finite-Element Analysis (NLFEA) and was validated using published experiential data on RC wide beams tested using a drop-weight at high rate. The numerical predictions obtained show that that the response of the RC wide beams under impact loading differs significantly from that established under equivalent static loading. This change predominantly takes the form of an increase in the maximum sustained load which is primarily attributed to (i) the response of a part of, rather than the whole, structural element and (ii) the development of inertia forces rather than material strain-rate sensitivity. The numerical study is based on the assumption that the effect of high loading rates on the behaviour of structural concrete is mainly linked to the development of inertia forces and not the strain-rate sensitivity of its material properties. Thus, the emphasis is on investigating the effect of loading rate on important aspects of structural response (e.g load-deflection curves, deformation profiles, load-carrying capacity, reaction forces, crack patterns and modes of failure) in an attempt to provide insight into the effect of loading-rate on the mechanics underlying RC structural dynamic response. It is also important to consider that during drop-weight testing it is not easy to correlate the measured response to the actual physical state of the specimens as the maximum value of the contact force generated during impact frequently corresponds to a specimen physical state characterized by high concrete disintegration and low residual strength and stiffness. Therefore, the true load-carrying capacity is likely to be significantly lower than the maximum value of the measured applied load. As a result the validated numerical models developed are employed for conducting a parametric investigation in order to determine the true load-bearing capacity of the examined structural forms under different intensities and loading rates characterising the applied load.