Direct Shear Tests and Capacity Model for Sliding-Type Splicing Connections in Widened Bridges

In the widening of multi-span continuous concrete box-girder bridges, conventional splicing structures often fail to accommodate differential shrinkage and creep between new and existing decks, leading to transverse deformation and cracking. To address this, a novel sliding-type splicing structure is proposed, which allows longitudinal deformation through pre-set sliding interfaces. To investigate its vertical shear performance, 15 full-scale Z-shaped specimens of five configurations were tested under three lateral compressive stresses (2, 5, and 10 MPa). Key parameters examined include steel tube shape, wall thickness, flange slab thickness, and welding type. Results show that semi-circular tubes induce a compressive failure mode via a “compressive arch” effect, increasing ultimate capacity by 11.9% compared to square tubes (at 2 MPa lateral stress). Conversely, insufficient tube wall thickness (5 mm) reduces capacity by 35.2% (at 2 MPa), indicating a minimum thickness requirement. Based on the observed shear transfer path, a capacity model accounting for concrete compression/shear and dowel action was developed. The model agrees well with test results, with an average error of approximately 8%. Comparisons with AASHTO LRFD and ACI 318 formulas show that the proposed model outperforms traditional shear–friction theory, which yields conservative predictions by about 15% (AASHTO) and 47% (ACI), highlighting the need for a dedicated model for this structural type. These findings provide a theoretical basis for the design and application of sliding-type splicing connections.