Based on the Yongjiang Bridge, this paper used the numerical calculation and the field dynamic load test to study the coupled vibration and dynamic response of the steel box hybrid girder cable-stayed railway bridge. Each vehicle in the train was simulated with 31 degrees of freedom, and the oscillatory differential equation of vehiclebridge coupling was established by MATLAB software. Afterwards, the field tests were also conducted to determine the free vibration characteristics as well as the strain, displacement, and acceleration of the bridge superstructure under trains moving at different speeds and braking at a specified position from a set speed. According to the dynamic load test and Vehicle-Bridge Coupling Vibration analysis, the following conclusions are obtained: (1) The calculated results of vehicle-bridge coupling vibration agreed well with the measured ones, and the program could be used to analyze the dynamic performance of Railway cable-stayed bridges with steel box composite girders. (2) The measured first-order natural frequencies of transverse, vertical and longitudinal vibration were 0,39 Hz; 0,49 Hz and 0,88 Hz, respectively. The dynamic coefficients are 1,04-1,13, the maximum lateral and vertical accelerations are 1,10 m/s 2 and 1,11 m/s 2 , and the maximum derailment coefficient and load reduction rate are 0,55 and 0,39, respectively. These data showed that the dynamic parameters of bridges and vehicles met the requirements and had good stiffness and dynamic performance. (3) This paper, using the frequency limit of simply supported beam to restrain the natural frequencies of cable-stayed bridges is not appropriate, and it is necessary to propose the natural frequency limit value of cable-stayed bridge.

To study the strengthening effect on recycled concrete columns by carbon fiber composite materials (CFRP) under different levels of seismic damage, four column specimens were designed for pseudo-static tests. The four specimens were respectively non-destructive without strengthening (prototype), non-destructive strengthening, medium seismic damage strengthening and severe seismic damage strengthening, according to the replacement rate of recycled aggregates and the level of seismic damage. The characteristics of the deformation damage and seismic performance indicators of each specimen were compared and analyzed. A decrease was observed in the initial stiffness of the seismically damaged recycled concrete column specimens strengthened with CFRP, while the ductility, peak bearing capacity and energy dissipation capacity of the specimens were improved. On the other hand, with the reduction of seismic damage and the increase of recycled aggregate replacement rate, the ductility and energy dissipation capacity of the reinforced seismic damaged recycled concrete column specimens were enhanced to different levels. In particular, the cumulative energy consumption of the strengthened specimens under medium seismic damage increased most significantly by 32.5%. In general, the hysteretic curves of the strengthened specimens were full, and the average ductility coefficients were 4.1–6.8. CFRP strengthening was more effective in restoring and enhancing the performance of the recycled concrete column specimens with medium and lower seismic damage levels (displacement ratio ≤ 3%).

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