Impact response prediction of square RC slab of normal strength concrete strengthened with (1) laminates of (i) mild-steel and (ii) C-FRP, and (2) strips of C-FRP under falling-weight load

Abstract

Reinforced concrete (RC) slab is an indispensable component of all kinds of structures to carry gravity loads in general. Quite often than not, the slabs are subjected to impact loads from accidental mishaps, falling construction equipment, and falling boulders and rocks which are not considered in the structural design. Design codes of practice for RC structures permit the structural design based on the experimental investigation which is not viable because of constraints such as experimental facilities, materials, and time requirements. However, current advancements in the computational techniques available make it possible to obtain the comprehensive response of the slabs subjected to impact loadings. In the present research work, different strength-enhancing techniques such as steel/C-FRP sheet laminates and C-FRP strips are considered for impact resistance enhancement of two-way normal strength concrete slab, 1000 mm × 1000 mm × 75 mm, with 0.88 % conventional tension steel reinforcement subjected to a free-falling concentrated load of 1035 N. For this purpose, a 3-D finite element model of impacting test setup is formed in ABAQUS-v.6.15 explicit commercial computer code. Computational analyses and simulations of free-fall impact are carried out on the validated ABAQUS model by allowing a 105 kg steel weight (impactor) from a height of 2500 mm with an initial impacting velocity of 7 m/ sec on the top surface of the slab at its centroid. The Concrete Damage Plasticity model is implored for nonlinear elastic and inelastic behaviors, degradation of stiffness, and loading rate effect on concrete. The nonlinear behavior of the reinforcing bars is taken into account. Steel is idealized with the Johnson-Cook model but the C-FRP laminate is defined or modeled with ABAQUS Hashin’s criterion. It is found that the used strengthening techniques improve the response of the slab in terms of displacement and damage severity, and alter the mode of failure.