Effect of Concrete Strength and Reinforcement on Time-Dependent Deflection of Posttensioned Slabs

Abstract

Posttensioning is an effective construction method for structures with large spans, intensive loadings, and cost-efficiency considerations. The investigation developed a comprehensive understanding of how various reinforcement ratios and compressive strengths of concrete contribute to deflection of posttensioned two-way slabs. Furthermore, the numerical analysis compared the efficiency of various codes of practice to design the required reinforcement ratio in the presence of constant posttensioning tendons ratio and layout to provide the strength and deflection requirement. The interaction between the compressive strength–deflection and reinforcement ratio–deflection to find the optimum values of compressive strength and reinforcement ratio in a posttensioned two-way slab was also investigated. The finite-element model of a posttensioned 10 × 10 × 0.2-m (32.8 × 32.8 × 0.65-ft) two-way slab was analyzed and evaluated. The study confirmed the considerable effect of posttensioning to decrease the reinforcement ratio and deflection in a two-way slab. Also, a wide range of differences in design of a similar section of posttensioned concrete slab was observed by applying different codes of practice. The intensive effect of the concrete strength on the posttensioning design of slabs, especially in the lower ranges of compressive strength, was evident during the numerical analysis. Additionally, the reinforcement ratio shows a minor effect on the deflection of a posttensioned slab.