Externally Prestressed Steel–Concrete Composite Girders under Service Conditions: Flexural Stiffness and Tendon Stress

Abstract Accurately capturing the mechanical behavior of externally prestressed steel–concrete composite (EPSCC) girders is challenging due to the unbonded nature of external tendons and the occurrence of slip at the steel–concrete interface. This paper presents a reliable, design-oriented method for estimating tendon stress and flexural stiffness of EPSCC girders under serviceability conditions. First, analytical expressions are derived to determine the slip-induced deflection in EPSCC girders. Subsequently, a beam–tendon deformation model is developed based on global deformation compatibility, from which an analytical model for the stress increment in external tendons is further derived. Using these foundations, an analytical procedure is developed to calculate girder deflection that accounts for the interface slip effect. Then, a segmented line is introduced to depict the distribution of slip-induced strain, which enables the derivation of a straightforward equation for the effective flexural stiffness of the EPSCC girder. Finally, practical design recommendations are proposed for calculating the deflection of continuous EPSCC girders. Comparisons with experimental results from 18 simply supported and 13 continuous EPSCC girders demonstrate that the proposed method offers greater consistency and accuracy than the design methods considered in this study.