Experimental investigation of full scale two-layer reinforced concrete beams

Two-layer beams (TLB), consisting of steel fibered high strength concrete (SFHSC) in the compression zone and normal strength concrete (NSC) in the tensile one, are studied experimentally. The current study is based on results of previous theoretical investigations and tests that showed high efficiency of such beams, carrying rather big bending moments. According to the previously developed concept, the fiber content for TLB should be calculated, corresponding to the required ductility level of an RC element. Following the results of a previous experimental study that were carried out to select the optimal fiber ratio, the current research is focused on testing full scale TLB. The study is aimed at experimental verification of the data related to interaction of concrete layers in TLB and proving the efficiency of two-layer bending element from beginning of loading and up to the ultimate load stages, including collapse. Development of Poisson deformations was studied to compare them with those obtained in the previous study for cylindrical specimens. The SFHSC layer was cast after the NSC hardening to study the influence of separate casting technology that is more convenient for TLB production in real construction. Three identical specimens with constant fiber content, corresponding to the proper ductility level, were prepared and tested by four-point loading. The results demonstrate the role of fibers in a high strength concrete layer and form a basis for development of TLB design provisions.