Assessment of Second-Order Effect in Externally Prestressed Steel–Concrete Composite Beams

Abstract

Externally prestressed steel–concrete composite (EPSCC) beams in their deformed configuration are characterized by changes in the effective depth of external tendons. However, little information is available on this second-order effect and parameters that are closely related to it, such as the deviator spacing and load type, have never been analyzed. This study will describe an in-depth investigation of the second-order effect in EPSCC beams. By applying an experimentally validated model, numerical simulations will be performed to assess the effect of the ratio of deviator spacing to span length (Sd/L) and load type on the behavior of EPSCC beams. The results show that the second-order effect was negligible for Sd/L <0.25. The ultimate load decreases linearly with an increasing Sd/L from 0.25 to 1. An increase in Sd/L resulted in a decrease in ultimate tendon stress increment. Compared with two-point or uniform loading, one-point loading at midspan led to substantially lower ultimate tendon stress and deflection, and therefore, a lower second-order effect. An equation that considers the second-order effect will be proposed to estimate the ultimate tendon stress in EPSCC beams. The proposed equation showed a good correlation with the numerical simulations.