Experimental and theoretical study of rotational stiffness of pier-girder joint in integral rigid-frame bridge system

Integral rigid-frame bridge systems, characterized by high structural integrity and efficient load transfer, are widely used in modern bridge engineering. Classical rotational stiffness theories typically idealize joints as either fully rigid or pinned, which neglects the semi-rigid behavior of pier-girder interfaces. This study investigates the rotational stiffness of pier-girder joints and proposes an analytical formulation based on curvature integration. A large-scale three-span integral rigid-frame bridge model, which consisted of a double-limbed thin-walled pier and a concrete-filled steel tubular pier, was designed and constructed based on a prototype bridge. The deflection response at the cantilever end was measured during vertical loading tests, and the corresponding rotational deflection of the test model was determined. Experimental results were compared with finite element simulations, showing excellent agreement. Bland-Altman analysis and regression metrics further confirm the high predictive accuracy of the proposed model. The formula was implemented in a full-scale bridge finite element model. Results indicate that accounting for joint rotational stiffness reduces transverse bending moments and longitudinal displacements at pier tops under temperature, vehicle, and settlement loads, implying a reduction in sectional demand and thus less conservative designs. The proposed method enables more accurate design and provides a robust basis for structural safety assessment.