Experimental Evaluation of Staggered Widening Bridges

Staggered widening is a practice in which the piers of new bridges are not aligned with those of existing bridges owing to the limitations of existing river embankments or road boundaries. When subjected to vehicular loads and foundation settlements, the staggered arrangement of piers leads to an unfavorable differential deflection between the adjacent decks, which results in an additional transverse hogging moment in the existing bridge’s deck. To date, staggered widening bridges have been rarely studied. In this study, a simplified analysis model was developed to account for the mechanical characteristics of staggered widening bridges. The effectiveness of the analysis model was validated through a comparison with the finite-element analysis results. Motivated by this analysis model, a novel full-scale segment model was developed to simulate the transverse flexural behavior of the deck between adjacent bridges. The aim of the segment model was to reproduce the bending moment distribution and flexible boundary conditions of the deck in the elastic stage and then incorporate the effects of crack propagation and stress redistribution through a statically indeterminate configuration. As the loading process continued, the measured structural response deviated from the elastic value and approached the actual response of the bridge. The governing equations of the segment model were derived, and the model parameters were determined. For ease of practice, the segment model was fabricated as a steel–concrete composite structure. The similarity between the fabricated model and the finite-element model was validated using the calculated bending moment distribution and deflection curves. The allowable differential deflections of the deck under both serviceability and ultimate limit states were obtained through a model test. The feasibility of the staggered widening bridges was then determined by comparing the measured and calculated deflection levels.