Experimental case study for practical implementation of real pre-stressed two layer reinforced concrete beams

The present study summarizes a long-term 14 -year research program, focused on investigation of reinforced concrete (RC) two -layer beams (TLB). In the frame of this program the TLB idea was proposed in 2007. The idea was based on using high strength steel fibered concrete (SFHSC) in the compressed zone of RC bending elements and normal strength concrete (NSC) in the tensile one. Further development of the above-mentioned idea included testing SFHSC at material level, experimental investigation of non - pre -stressed simple supported 3 m and continuous 4 m (2 x 2 m) two-span TLBs and testing pre-stressed simple supported 3 m TLBs (PTLBs) that represented a model of long -span prestressed concrete beams. The present paper presents a case study, aimed at investigating real 8 m long PTLB behavior at four-point bending and its comparison with pre-stressed single - layer beam with the same span. Like in the previous research stages, interaction of concrete layers in a PTLB was examined. No de-bonding between the layers was observed that demonstrates proper interaction between the layers, like in the 3 m long PTLBs. Results, obtained in the present study, enable to recommend PTLBs for practical implementation as effective real pre-stressed concrete elements for new structures and also for repairing existing ones.