The combined action of freeze–thaw cycles and chloride-induced corrosion are generally recognized as one of the main causes of the degradation of the mechanical properties and seismic performance of reinforced concrete (RC) structures in the northern frozen coastal regions. To investigate the degradation mechanisms of the seismic performance of RC columns subjected to the combined action of freeze–thaw cycles and chloride-induced corrosion, the impact of freeze–thaw cycles on the chloride diffusion coefficient of concrete was studied through concrete deterioration tests and theoretical analysis. This paper proposed a time-dependent deterioration model for RC columns, which is suitable to consider the combined action of freeze–thaw cycles and chloride-induced deterioration. The proposed deterioration model could be applied to the investigations of time-dependent seismic performance and the seismic fragility of RC columns. Based on the established deterioration model, this paper proposed a time-dependent seismic fragility analysis framework for the aging RC columns, considering the combined action of freeze–thaw cycles and chloride-induced corrosion. In addition, a representative three-span RC continuous T-shaped girder bridge that is located in the high-latitude northern frozen coastal regions of China was taken as the case study, and the time-dependent seismic fragility analysis of RC columns was conducted considering the involved uncertainties in geometric parameters, the deterioration mechanisms of the materials, and ground motions. The time-dependent seismic fragility curves of RC columns were obtained at different service time points. The results indicated that the combined action of freeze–thaw cycles and chloride-induced deterioration had a significant influence on the time-dependent seismic responses of the deteriorating RC columns. Under the combined action of freeze–thaw cycles and chloride-induced corrosion, when the RC bridge was in service for 75 years, the stirrup strength decreased by 3.88% and the cross-sectional area decreased by 30.03%. The peak stress of the confined concrete decreased by 52.1% and its peak strain increased by 12.2 times, respectively. Moreover, the time-dependent seismic fragilities of the aging RC columns under different damage states exhibited a nonlinear increase as the service life increased.

Crosswinds have an obvious influence on traffic safety in pastoral areas because of the special geography position. A Finite element model is established to analyze wind velocity field of embankment. With no sideslip and overturning as targets, the threshold of natural crosswind velocity is analyzed under the influence of the multiple factors including crosswind, traffic velocity, friction coefficient, and alignment by using a static vehicle model. The results will supply guidance for driving safety management and road design in pastoral areas.

Rutting and fatigue cracks have been common hazards for pavement with the development of traffic. The correlation of wheel tracking transverse distribution and pavement fatigue failure is studied in this paper to propose a new pavement maintenance method which changes wheel tracks transverse distribution after drivers' vision is intervened. This new method not only prolongs pavement fatigue life but also improves driving safety. Finite element models are established to analyze fatigue life of asphalt pavement in theory. Results show that this new method can prolong pavement service life by 10%–30% when wheel tracks are shifted 25–50cm.

Because the acceleration pavement testing systems are different in the world, distance between the dual tires is also different, testing data from different systems have bad comparability. Aiming that, finite element models are established according to actual pavement structure, asphalt pavement fatigue life is analyzed when acceleration pavement test was applied. Tire load with different distance between two tires is applied to them for one time and 200 million times, and then fatigue analysis is carried out, which will be used to analyze the differences while the distance between tires is changed. The results show that the difference is slight when one time load is applied, but it is great when 200 million times repeated load are applied. The testing data from different Acceleration Pavement Testing (APT) facilities shall eliminate the disparity before they are compared.