Finite element analysis of reinforced concrete slabs with high-strength concrete and three-layer reinforcement under accidental episodic loading

Abstract

This paper presents numerical finite element analysis of the stress-strain state of a circular reinforced concrete slab with three-layer horizontal reinforcement made of high-strength concrete under quasi-static loading of q = 100 kN/m², corresponding to the normative level of accidental episodic action per DBN V.2.2-5:2023. A three-dimensional finite element model of the welded reinforcement cage was implemented in Lira-FEM software using nonlinear constitutive models for concrete and steel. Punching shear resistance of inclined cross-sections was evaluated using an enhanced model accounting for the dowel effect of horizontal reinforcement at failure angles γ = 34–40°, characteristic of dynamic accidental loading. Modelling results show that maximum shear stresses of ±23.8 MPa concentrate in the plane of the middle reinforcement layer and in the support contact zone, identifying the critical punching crack surface at angles of 30–34°. Bottom layer reinforcement stress σs = 92 MPa remains well below fyd = 335 MPa; maximum deflection of 0.32–0.34 mm with a discrepancy of no more than 7 % between two loading schemes confirms structural stiffness and the adequacy of the quasi-static approach. The dowel contribution of the three-layer arrangement is 8.5 times greater than that of single-layer reinforcement, yielding an analytical bearing capacity FmaxRd = 2 525 kN against VEd = 38.5 kN. The cracking load in the nonlinear formulation reaches 70 % of the design value, consistent with the elasto-plastic behaviour of HSC C50/60. The results provide a basis for full-scale experimental testing and refinement of normative provisions on the application of high-strength concrete in floor slabs under accidental episodic loading..