Functional Strut-and-Tie Model of Filament Pipes in Extradosed Cable-Stayed Bridges Under Mechanical Loading

Designing reinforcements for concrete towers in extra-dosed cable-stayed bridges is challenging due to the passage of filament pipes, particularly in the D-region, where strain distribution is nonlinear under mechanical loading. The strut-and-tie model (STM) is a widely used approach for designing these regions; however, its development in the presence of filament pipe passages requires further refinement. This study introduces a functional STM based on topology optimization to represent stress flow beneath filament pipe passages. The method retains structural elements essential for force transmission while eliminating less significant ones, thereby establishing optimal load paths. Using ANSYS software, the effects of varying the radius of curvature of the cable saddle on stress distribution induced by filament pipes were analyzed. Results indicate that the curvature radius strongly influences internal forces in STM members: as the radius increases, both stress and internal forces decrease within the tower, clarifying the evolution of force distribution with changing curvature. These findings provide a functional framework for STM applications and are expected to serve as a reference for the comprehensive structural design of concrete towers in extra-dosed cable-stayed bridges.