Modeling of Direct Load Transmission in Lightweight-Concrete-Core Sandwich Beams

The direct load transmission behavior of hybrid sandwich beams consisting of a bottom fiber-reinforced polymer skin and a top concrete skin was investigated experimentally. The sandwich core consisted of lightweight concretes of different brittleness (sand lightweight aggregate concrete [SLWAC] and all lightweight aggregate concrete [ALWAC] mixtures). Cracking and ultimate load prediction using classical strut-and-tie models was inaccurate because these models do not take differences in material brittleness into account. A continuous direct load transmission model is proposed that consists of a diagonal bottle-shaped strut with an infinite number of transverse ties. The statically indeterminate system allows stress redistribution resulting front post-peak material softening after concrete cracking to be taken into account. This led to accurate modeling of the varying experimental responses due to different material brittleness. The arch rise of the bowed compression strut decreased after cracking due to the available width of the diagonal strut being reduced to the distance between initiating and propagating cracks parallel to the strut. The arch rise, furthermore, decreased with increasing material brittleness.