Evaluation of Dynamic Response for Freeze–Thaw Damaged RC Beams Subjected to Impact Loading

The impact resistance of in-service freeze-thaw damaged reinforced concrete (RC) bridges is a hot issue in the engineering field. Drop weight impact tests were conducted on RC beams after freeze-thaw cycles (FTCs), and the failure modes and dynamic impact responses were investigated. As the number of FTCs improved, RC beams transitioned from flexural to flexural-shear failure, tending to transition toward shear failure after 125 cycles. With the increase in the degree of freeze-thaw damage, the peak impact force and impact response duration of the RC beams decreased, and the impact energy dissipation was also significantly reduced. Conversely, the peak midspan deflection initially decreased and subsequently increased. Considering the uneven distribution of freeze-thaw damage from the surface to the interior of the concrete, a two-degree-of-freedom model for RC beams subjected to FTCs under impact loading was established. The proposed model can reflect the impact dynamic response process of the beams and shows good agreement with the experimental data.