Two LA yer high performance concrete beams for bridges

Two layer high performance RC bear can be used in the traffic direction of long-span bridges. The beam's section consists of two parts. The bottom part is made of normal strength concrete (NSC). The upper one is made of steel fibered high strength concrete (HSC). Using two layer beams is logical, because as the beam span becomes langer and as the service load increases, higher concrete strength is required in the beam's compressed zone to withstand rather big bending moments. As concrete in the tensile zone of the section contributes little to the beams' bearing capacity, this zone is made of NSC. It is an important economical advantage of two layer bears. Steel fibers are used just in the compressed zone made of HSC. Steel fibers yields higher ductility of the HSC layer, allowing proper design of two layer bridge beams to dynamic loads. For such beams the design parameters include the HSC class, whereas the HSC layer depth is known and equals to the height of the upper part. The bottom NSC part of long span beams is usually pre-stressed.