Full-scale Experiment on Stiffness Degradation and Identification of Prestressed Concrete Box Girders

To study stiffness degradation under damaged conditions for prestressed concrete (PC) girders, a full-scale model test was conducted on three 30 m PC box girders. First, static and dynamic stiffness identification models of damaged beams were developed. The equivalent static stiffness was calculated based on beam deflections in the mid-section, and the equivalent dynamic stiffness was calculated based on its natural frequencies. Second, full-scale girders were loaded incrementally, and static and dynamic tests were conducted alternatively. The development of cracks, deflections, and frequencies of the experimental girders under different loads were then studied, and the effects of damage conditions on these parameters were analyzed. Third, the reduction coefficients of dynamic stiffness were derived using the finite element model updating method, and the relationship between static and dynamic stiffness with the damage conditions was analyzed. The difference between the static and dynamic stiffness was then explored. Finally, the regression formula of the reduction coefficients of the static and dynamic stiffness with crack feature parameters was established and compared with previous studies. The results show that the initial damage condition of the girder has an effect on the statistical distribution of the crack features. It also illustrates that the degradation of equivalent static and dynamic stiffness of the girder is not consistent, where the final reduction coefficients of static and dynamic stiffness are 0.30 and 0.80, respectively. The reduction coefficient of static stiffness between the full-scale and scale-down model tests is different. The study presents a simple method for the reduction coefficients of static and dynamic stiffness to assess damaged PC box girders in practical engineering. © 2020, Editorial Department of China Journal of Highway and Transport. All right reserved.