Static membrane action in restrained RC beams: Experimental investigation, and numerical and analytical prediction

Artikel i vetenskaplig tidskrift, 2026

Membrane action can substantially enhance the resistance and deformation capacity of restrained reinforced concrete (RC) elements, offering critical additional capacity for elements subjected to impulsive loading. However, its practical utilization remains limited, largely due to the absence of a consistent, simplified approach capable of describing the full structural response. This study conducted experimental investigation of membrane action in six longitudinally and rotationally restrained RC beams subjected to static three-point bending. The specimens varied in slenderness, reinforcement ratio, and fracture strain of the reinforcement. All beams exhibited combined flexural and membrane action, with an enhanced peak resistance attributable to compressive membrane action (CMA). Clear differences in reinforcement fracture and cracking development were observed in the post-peak response across the specimens, reflecting the influence of geometry, reinforcement properties and boundary conditions. The results showed that CMA contributed significantly to the energy absorption capacity of specimens with lower slenderness or lower reinforcement ratios, while more slender beams with reinforcement with higher fracture strain benefited primarily from tensile membrane action (TMA). Reinforcement fracture during the CMA phase was observed in some specimens, underscoring the need for predictive methods that explicitly account for this phenomenon. Two simplified approaches for predicting the full load-deflection response were also presented: a finite element (FE) model and an analytical approach extending an existing framework. The FE model showed good agreement with the experimental results, accurately capturing peak resistance and reinforcement fracture. The analytical model provided satisfactory predictions, particularly during the CMA phase.