TENSION STIFFENING EFFECTS IN FLEXURAL REINFORCED LIGHTWEIGHT AGGREGATE CONCRETE BEAMS SUBJECTED TO LONG-TERM CYCLIC LOADS

The present study experimentally investigated the tension stiffening in flexural reinforced concrete (RC) beams cast by lightweight aggregate concrete (LWAC) under long-term cyclic loads, i.e., high-cycle fatigue loading conditions. Based on the strain measurement from tension steels in RC beams, the reduction in bond-related tension stiffening induced by fatigue was described. The comparisons of the companion reinforced normal weight concrete (NWC) beams of equivalent concrete strength of 40 MPa were made. The measured total response of mean steel strains during fatigue tests was evaluated from the aspect of the elastic and plastic strain components. The experiment results showed that the mechanism of mean steel strain evolution with cyclic loads in LWAC beams was essentially different from NWC beams. On the whole, LWAC beams had a lesser reduction in tension stiffening due to the better bond between reinforcement and concrete. This was demonstrated by the more linear curves in the applied load mean steel strain diagrams after the initial cracking. In addition, compared to NWC beams, there also were a slight growth of the elastic strain components and a higher degree of local plasticity developed at the location of the primary flexural cracks in LWAC beams.