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

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 (S-d/L) and load type on the behavior of EPSCC beams. The results show that the second-order effect was negligible for S-d/L S-d/L from 0.25 to 1. An increase in S-d/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.