Cross-river bridges located in seismically active areas are exposed to two major natural hazards, namely earthquakes and flooding. As the scour depth increases, more parts of the bridge substructure will inevitably be exposed to unfavorable conditions such as chloride ion (${\mathrm{Cl}}^{-}$) corrosion. To investigate the seismic performance of highway bridges under the action of scour and ${\mathrm{Cl}}^{-}$ corrosion, a spatial finite element dynamic model of a continuous rigid bridge was established and a ${\mathrm{Cl}}^{-}$-accelerated electrochemical corrosion test and quasi-static test were carried out. The results showed that a reasonable scour depth and the combination sub-factors under the joint probability density of scour action and seismic action can be obtained to establish the combined expression of the action effect. ${\mathrm{Cl}}^{-}$ corrosion can cause a reduction in displacement ductility, load-bearing, and energy dissipation capacity, and increase inequivalent viscous damping coefficient of the columns. Seismic damage of the columns grows linearly to twice the ultimate displacement under ${\mathrm{Cl}}^{-}$ corrosion, which becomes more significant with the increase of the reinforcement ratio.

This study investigates the shear properties of ultrahigh performance concrete (UHPC) wet joints through direct shear tests on UHPC flat joint specimens. Four sets of specimens were designed with varying levels of constrained normal stress. The results showed that all specimens exhibited brittle shear damage near the UHPC-NC interface. The application of 1 MPa, 2 MPa and 3 MPa constrained normal stress increased the shear strength by 103.4%, 184.4%, and 272.3%, respectively, compared to the unconstrained specimen. An analytical model is proposed to quantitatively describe the shear stress-slip behavior of the UHPC-NC interface under various levels of constrained normal stress, accompanied by a calculation formula for its characteristic points. The model links normal stress, stiffness, roughness, and defines shear curve descent., allowing for reliable prediction of the shear stress-slip relationship of the UHPC-NC interface. Furthermore, a validated finite element model using ABAQUS software was developed, which aligned with analytical results and further strengthened the reliability of the proposed model. The results suggest that the shear strength of the UHPC-NC interface can be enhanced by adjusting the constrained normal stress, given its high sensitivity as an impact factor. The shear bearing capacity can be described using the proposed model, which consists of a linear ascending segment, a peak point, and a declining damage segment with an exponential evolution pattern, with a recommended damage index parameter of 4.68.