Effect of concrete type on equivalent lateral confinement pressure in columns under axial loads

Abstract

The objective of this study is to evaluate the effect of the concrete type, compressive strength of concrete (fc′), amount of transverse reinforcement (Ash), and tie-configuration on the stress–strain curve of confined concrete obtained from the axial performance of lightweight aggregate concrete (LWAC) columns. Sixteen LWAC columns were tested under a concentric axial load. The test results show that the slope of the descending branch in the axial strain against applied axial load decreases with an increase in Ash and decrease in fc′. This trend was more prominent in all-lightweight aggregate concrete (ALWAC) columns compared with sand-lightweight aggregate concrete (SLWAC) columns. For a similar Ash, the strength gain factor (Ks) and equivalent uniform lateral pressure (fle) of ALWAC columns were slightly lower than those of the SLWAC columns, which were considerably lower than those of normal-weight concrete (NWC) columns. In particular, the descending slope of the stress–strain curves of confined concrete was more brittle in ALWAC columns with conventional crossties, lower Ash, and higher fc′ compared to SLWAC with diamond-shaped ties. Consequently, there was a significance discrepancy between measured and predicted values of the stress–strain curves of confined concrete proposed by Saatcioglu and Razvi in the ALWAC column with an Ash value of 1.0, a fcd value of 40 MPa, and conventional crossties, resulting in the highest mean (γm) and standard deviation (γs) of the normalized root-mean-square error (NRMSE).