Structural feasibility of segmental prestressed concrete box girders with multi-directional dry joints and unbonded tendons

초록

This study aims to investigate the structural feasibility of segmental prestressed concrete box girders with multidirectional joints, which are positioned in both longitudinal and horizontal directions, along with unbonded tendons. Aimed at enhancing transportability and modular assembly in bridge construction, four box girder specimens, including a conventional segmented girder (CSG) and three multi-directionally segmented girders (MDSG), were fabricated and tested under monotonic loading. Unbonded steel bars and tendons were utilized to facilitate both longitudinal and horizontal assembly of the specimens. Experimental results showed that all specimens failed due to flexural compression, with initial cracks in the bottom flange joints, ultimately leading to concrete crushing in the compression zone. MDSG specimens demonstrated load-deflection responses similar to CSG, with joint openings stabilizing at higher loads. Flexural ductility indices reached up to 24.6 in MDSG specimens, surpassing those of CSG, while post-cracking capacity ratios indicated adequate post-cracking resilience. Tendon stress increments showed deviations of 3 %-32 % from analytical predictions, suggesting the influence of tendon slip and joint opening effects, highlighting the need for improved predictive models. The tensile stress in the tendon followed a quadratic relationship with mid-span deflection, which was incorporated into the moment versus curvature analysis simulation. Despite minor discrepancies in curvature predictions, the multi-layer sectional analysis model accurately estimated ultimate moments, with minimal differences from experimental values across all segmental girders. These findings demonstrate that segmental box girders with multi-directional dry joints and unbonded tendons exhibit high flexural ductility, stable joint behavior, and adequate post-cracking load-carrying capacity, confirming their feasibility for modular bridge construction.

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