Longitudinal Reinforcement Ratios for Lightweight Concrete Beams

This study investigated the reliability and limitation of the minimum and maximum longitudinal reinforcement ratios specified in code provisions regarding the flexural ductility of lightweight aggregate concrete (LWAC) beams. From the load-displacement curves of beams computed using a two-dimensional (2-D) nonlinear analysis approach, displacement ductility ratio was simply formulated and validated through comparisons with test data compiled from 29 normalweight concrete (NWC) and 47 LWAC beam specimens. The 2-D analysis revealed that the displacement ductility ratio of beams decreases with the decrease in the unit weight of concrete. In addition, the ductility of concrete beams rather decreases with the decrease in the longitudinal tensile reinforcement ratio ([[rho].sub.s]) when the latter varies within the ranges not exceeding the minimum requirements. Therefore, based on the proposed displacement ductility ratio model, compensation factors are generalized for LWAC beams to adjust the minimum and maximum longitudinal reinforcement ratios specified in code provisions with respect to retaining a flexural ductility equivalent to that of their counterpart NWC beams. To achieve flexural ductility comparable to that of NWC beams, LWAC beams require more minimum amount and less maximum amount of longitudinal tensile reinforcement when compared with those specified in code provisions. Consequently, the proposed compensation factors can be implemented by examining the reliable ranges for longitudinal reinforcement ratios in LWAC beams. Keywords: beam; compensation factor; displacement ductility ratio; lightweight aggregate concrete; longitudinal reinforcement.