Performance evaluation of reinforced lightweight concrete filled steel tubular beams

This study presents an experimental research to evaluate the flexural performance of Reinforced Lightweight Concrete Filled Steel Tubular beams. 16 beam specimens were tested, 12 specimens as Reinforced Lightweight Concrete Filled Steel Tubular (RLWCFST) beams, two specimens as Lightweight Concrete Filled Steel Tubular (LWCFST) beams and two specimens as Square Hollow Steel Tubular (SHS) beams. The major experimental parameters in the study are: (1) ratio of longitudinal steel reinforcement (ρ) from 3% to 7%; (2) arrangement of longitudinal steel reinforcement (in two or three layers), and (3) the spacing of stirrups (6cm or 12 cm). Based on the test results, the flexural strength, failure modes, ductility, moment-deflection relationships andmoment-strain relationships were studied and their impact on the flexural performance of LWCFST and RLWCFST beams was discussed. The results indicated that the longitudinal reinforcement has important effect on bending performance of RLWCFST beams and provided obvious increasing in bending strength, ductility and stiffness of LWCFST beam and helped the steel tube and concrete to improve their performance. The experimental ultimate moments are compared to theoretical moments calculated by two international design codes namely the AISC-2010 code and the EC4-2004. The two design codes predicted good estimate and safe design moment capacitiesfor RLWCFST beams especially EC4 that limited the maximum ρ with 6%. However, test results showed that exceeding this ratio (6%) up to 7% is possible and EC4 design method is applicable, even if the limitation of ρ was increased up to 7%. Keywords: Lightweight Concrete (LWC), Reinforced LightweightConcrete Filled Steel Tubes (RLWCFST) beams, flexural strength, performance indices, ductility.