Minimum tension reinforcement ratio for beams made of pumice aggregate lightweight concrete
摘要
Pumice aggregate is frequently used for producing lightweight concrete (LWC) structural members. In this study, mix design was made to produce LWC with density equal to 1850 kg/m3 and 28 days compressive strength equal to 37.34 MPa. This work consists of two series of tests. Firstly, size effect of beam’s section on modulus of rupture of concrete was investigated and found that this property reduces with increasing beam’s depth. Using regression analysis, an equation was obtained for modulus of rupture depending on the section’s depth and later following Mcr = Md criteria an equation was proposed for minimum tension steel ratio for pumice aggregate LWC was obtained. Second series of tests was arranged to assess the validity of the proposed equation and for this purposes seven beams were cast and tested. Steel bar ductility was found to have a significant effect to avoid bar fracture. The proposed equation was found accurate, but there is a need for a safety factor, while the equation based on fracture mechanics approach was found to underestimates minimum tension steel of pumice aggregate LWC and, in contrast, the equation of ACI 318 Code is highly overestimated minimum tension steel and the safety increased with increasing beam’s depth.