Finite-Element Modelling of Laterally-Confined Reinforced-Concrete Slabs Designed with NBR 6118:2023

Abstract

Lateral confinement arising from the continuity between adjacent floor elements triggers compressive-membrane action that can greatly enhance the strength and stiffness of solid reinforced-concrete slabs. To capture this phenomenon numerically, a three-dimensional finite-element model was developed in ANSYS using 20-node SOLID186 elements for the concrete— employing a Drucker–Prager plasticity surface with hardening, softening, and dilatancy—and embedded REINF264 elements for the discrete reinforcing bars. The model was calibrated against twelve unconfined and ten confined slab tests from the literature, reproducing ultimate loads with a mean experimental-to-numerical ratio of 0.99 and a standard deviation of 0.06. A factorial parametric study comprising 27 design cases (spans 4–6 m, fck 25–50 MPa, span-to-depth ratios ≈ 40–50) was then conducted to evaluate the slabs’ behaviour with and without membrane action: first with the edges free to expand in-plane, and subsequently with realistic restraint provided by neighbouring slabs modelled as linear-elastic plates coupled to the target panel. Explicit consideration of lateral confinement nearly doubled the predicted ultimate load (average +97 %) and showed an in-plane stiffness of around 120 % of the slab axial stiffness, with the largest gains occurring in shorter spans and higher-strength concretes.