Decreasing R.C. Beam Weight while Increasing its Ultimate Carrying Capacity

The main research motivation is to find a solution to decrease the beam weight without losing its carrying capacity. The main obstacles in this point is how to prevent shear failure occurrence due to decrease concrete weight and consequently its compressive strength as beams designed to fails due to flexural; moreover not to allow slippage in the bottom reinforcement due to lower compressive strength which lead to lower bonding strength and earlier flexural failure. Seven beams with dimension 100* 200* 1200mm have been tested under three point loading, the control beam casted by normal weight concrete (N.W.C.) while the other six beams casted by normal weight concrete (N.W.C.) in the compression zone only and the light weight concrete (L.W.C.) is placed in the tension zone below the beam neutral axis at the theoretically cracked section which will decrease beam weight by about 35% of the NWC. Three stirrups spacing have been tested (5, 7.5, and 10 cm) to study the effect of stirrups spacing in preventing shear failure and govern the failure to move toward flexural failure. According to the results for the tested beam and to prevent both shear failure and loss of bond between reinforcement and (L.W.C.), three other beams having the previous stirrups spacing have been tested but the stirrups were welded with both upper and lower reinforcement to have truss action between stirrups and reinforcement and enforce the stirrups to carry the shear force. Test results show that the beams casted with L.W.C. could carry to some extend larger load than beams casted with N.W.C. especially when bond the stirrups with the reinforcement in the shear zone of the beam.