Modeling of Reinforced Concrete Slabs under High-Mass Low-Velocity Impact

There is a growing need for analytical tools that can accurately model the behavior of reinforced concrete (RC) structures under extreme loads, particularly with respect to blast and impact. Current capabilities are almost entirely confined to hydrocodes (e.g., LS-DYNA) and such procedures have often met with limited success as they typically require complex micro-modeling representations of the structure, which is expensive in preparation and computation, and many of the commercial programs have shown deficiencies in their abilities to adequately capture cracked concrete response, particularly with regard to brittle shear-critical behavior. This paper presents the application of an alternative modeling procedure for RC slabs and shells subjected to blast and impact loads. The nonlinear finite element program employed uses a layered thick-shell element with RC constitutive modeling done in accordance with the formulations of the Disturbed Stress Field Model, a smeared rotating crack procedure shown to be capable of accurately capturing the behavior of shear-critical elements under conventional static loads. The smeared modeling approach differs from that typically employed by hydrocodes and results in simple model construction and reduced computation cost. The program is used to model the response of intermediate-scale RC and steel fiber-reinforced concrete slabs tested under repeated high-mass low-velocity impacts. Using simple finite element meshing techniques and material behavioral models requiring only basic user input, good correlation between the observed and modeled slab response was attained. The analyses provided high accuracy estimates of peak and residual displacements and successfully captured the punching shear failure modes observed experimentally.