Behavior of reinforced high and ultra-high strength concrete slabs under high mass low-velocity impact loading

The reinforced concrete (RC) structural elements during its design life may be subjected to accidental dynamic loads produced as a result of vehicular impacts, heavy drop weights, and explosive impacts. The structural elements may have to withstand forces with higher magnitudes and intensities than the typical static loading. Given its remarkable mechanical properties and durability, Ultra-High Strength Concrete (UHSC) slabs offer exceptional compressive strength and load carrying capacity; however, their response under low velocity impact loading remains underexplored. The primary motive of this study is to establish a framework that quantifies the influence of slab geometry, boundary condition, reinforcement ratio, concrete compressive strength and impactor properties on maximum dynamic contact force and mid-span deflections. This paper presents an experimental and numerical investigation into the response of two-way simply supported RC slabs under high-mass, low-velocity impact loading. The experimental investigation evaluated ten specimens made of normal strength concrete (NSC), high strength concrete (HSC) to assess the influence of compressive strength and reinforcement ratio on peak impact force, failure patterns and displacement. Furthermore, a non-linear Finite Element (FE) model was developed in ABAQUS and validated against the experimental contact force–time history. The validated framework was subsequently extended to numerically predict the dynamic response of UHSC slabs under impact conditions. The numerical FE results indicate that UHSC slabs exhibit greater impact resistance, reduced the mid-span deflections and enhanced scabbing controls. Based on the FE parametric findings an Equivalent Static Factor was derived to predict the maximum load carrying capacity of two-way simply supported UHSC-RC slabs when subjected to low-velocity impact loading of upto 6 m/s. Furthermore, multi-regression analysis-based equations were also developed to estimate the maximum impact force and maximum mid-span deflection of two-way simply supported UHSC-RC slabs when subjected to low-velocity impact loading. The ESF factor and MRA equations were developed using limited dataset and are not intended for design use. The predictive equations and ESF offer simplified approximation to assess the impact resistance of two-way simply supported RC slab under low velocity (upto 6 m/s) impact load evaluated in this study and require further experimental validation before the broader application.