Modelling of the Bending Behaviour of a Double-Reinforced Beam from Recycled Materials for Application in NZEBs

A number of design approaches of nearly zero energy buildings (NZEBs) are known in literature. The aim of the present paper is to study the bending behavior of a structural bi-material element of a recycled concrete beam reinforced along its lower and upper side by highly-tough thin layers. On one hand, the design of such a structural element would produce a light weight element, since no conventional reinforcement would be involved, and on the other hand, the recycled aggregate of the concrete matrix would make the element applicable to NZEBs. Thus, natural energy resources may be saved. Moreover, thin reinforcing layers guarantee good bearing capacity due to their high toughness, excellent crack resistance under dynamic impacts, as well as fire resistance when fabricated from special polymer materials. The approach of employing such lightweight structural bi-material elements in constructions is energy saving and innovative. The study provides a method of specifying the thickness of the reinforcing layer assuming the existence of a transition area between the two materials and smooth transition between the reinforcing layer and the concrete bulk. It is also assumed that the element operates within the materials linear-elastic zone, without generation of macrocracks within concrete and debonding along the interface. The analytical results found are verified by subsequent experimental evidence available in literature.