Bearing displacement is a necessary monitoring index for a long-span bridge because abnormal bearing displacements could result from structural deterioration or damage. Therefore, an early warning method is established for bearing displacement of long-span bridges. In this study, a novel time-varying temperature–displacement nonlinear model, which can eliminate the model error induced by temperature field simplification, is first proposed to accurately estimate bearing displacement. Then, early warning methods for abnormal displacement and out-of-bounds displacement of bearings are established using estimation errors, and different warning levels are delineated depending on combinations of the two types of early warning, followed by an implementation procedure for the early warning method. Finally, the long-term monitoring data of a large-span bridge are utilized to validate the advantage of the proposed time-varying model and the effectiveness of the early warning method. The results show that the modeling and prediction errors of the time-varying model are smaller than that of the linear model. Additionally, attention needs to be paid to the changes in the warning information for bearings with large modeling errors, which will correspond to a relatively high warning level.

Tie-down cables are critical components of uplift-restraint bearings in bridges. Damage of a tie-down cable substantially affects the safety of a bridge and driving conditions. In this study, a damage identification method for the tie-down cable in cable-stayed bridges is developed by using vehicle-induced displacement. First, a vehicle-induced displacement is derived through theoretical mechanical analysis. By introducing an area reduction factor for the tie-down cable, a displacement-based damage index is proposed, and the changing regularity of the proposed damage index is comprehensively illustrated in different damage cases. Then, the numerical simulation with the corresponding area reduction of the tie-down cable is implemented for a cable-stayed bridge to validate the rationality of the damage index. The results demonstrate that the proposed damage index is not affected by the weight of the vehicles and is effective in detecting the area reduction of tie-down cables without the information of vehicle weights. The changing regularity of the damage index can reflect the damage cases of tie-down cables. For the actual application of the proposed method, the damage index possessing a minimum initial value, which is obtained when vehicles pass in the outermost lane of a bridge, is optimum.