Abstract: The seismic damage and failure mechanisms of reinforced concrete (RC) bridge piers in irregular bridges, such as curved bridges and skew bridges, are severe under seismic actions. This is primarily because RC piers subjected to combined compression, bending, shear, and torsion effects experience a significant degradation in their seismic performance. However, existing analysis models (e.g., fiber models and shear-lag models) for medium-to-high RC bridge piers (shear span ratios greater than 3) do not take into account the coupled effects of axial compression, bending, and torsion, leading to inaccuracies in simulating the damage mechanisms and predicting seismic responses of irregular bridge systems. In this study, based on the concentrated plastic hinge model and ideal truss model, a comprehensive analysis was conducted on the flexural and torsional behaviors of RC bridge piers. A new formula relating the torsion-to-bending ratio to the torsional strength of the pier was derived. Subsequently, a combined beam-truss model incorporating coupled bending-torsion effects was developed and implemented in the OpenSees platform. The proposed combined beam-truss model demonstrates good capability in simulating the degradation of flexural and torsional strengths under combined loading effects, showing satisfactory agreement with experimental results. Seismic response analyses under bidirectional excitations reveal that the combined beam-truss model predicts lower horizontal shear forces and torsion compared to conventional fiber models. Moreover, the combined beam-truss model exhibits a higher tendency towards torsional plastic deformation and generates larger residual torsional angles. The use of conventional fiber models overestimates the seismic performance of RC bridge piers in curved bridges to some extent.