Experimental studies on load-carrying capacity of HFR-LWC beams accompanying membrane action

Abstract

Membrane action has not been quantitatively described in current analyses but is regarded as a “hidden” safety factor in the existing design manuals. The ultimate resistances and failure patterns of beam-like members will be greatly altered by the membrane effects introduced by special constraints. This paper describes the results of an experimental campaign on 10 hybrid fiber reinforced-lightweight aggregate concrete (HFR-LWC) beams, aiming at investigating the effect of membrane action on their bearing capacities. Membrane forces (N and M) are introduced at the element supports through specifically designed clamps formed by two steel plates tensioned with a variable number of tie rods. The influences of the constraint stiffness, reinforcement ratio and fiber content are investigated and discussed. The membrane action effects on the load-carrying capacity are sensitive to both the structural deflections and the constraint stiffness. The ultimate load of the beam would be substantially underestimated if membrane action is neglected. Greater membrane actions are beneficial for the development of the bridging effect of the hybrid fibers and the interlocking effect of the coarse aggregates, thus giving rise to more ductile failure and a higher bearing capacity of HFR-LWC beams.