Curvature integration-based flexural stiffness of steel-prestressed concrete composite girders under negative moments

Due to the slip effect in the steel-concrete interface and tension stiffness effect in the concrete slab, accurately predicting the flexural stiffness of steel-prestressed concrete composite girders in the hogging moment region is highly challenging. This paper provides a mechanics-based yet practical method for estimating the flexural stiffness of such girders under service load conditions. Firstly, a validated moment-curvature procedure is developed to analyze the tension-stiffening behavior of the girders. The analysis results indicate that the tension stiffening effect in steel-prestressed concrete composite sections is negligible, allowing their moment-curvature response to be idealized as a bilinear graph in which the interface slip effect is considered. Subsequently, a curvature integration-based method is used to derive expressions for the effective flexural stiffness of the steel-prestressed concrete composite girder. Based on this, an expression for the effective flexural stiffness at the critical section is recommended for design purposes. Finally, the proposed method is validated by comparing its predictions against experimental results from 27 composite girders.