Plastic damage and modal characteristics of RC beams subjected to multiple impacts

Engineering structures are susceptible to repeated impact loads. There has been little attention to the damage and structural characteristics of engineering structures subjected to multiple impacts. Repeated impact loading tests are performed on reinforced concrete (RC) beams to examine the cumulative damage effect on their dynamic characteristics. Changes in dynamic properties (frequency and damping ratio) are analyzed using the random decrement technique and the Hilbert–Huang transform (RDT-HHT) method. With the same cumulative impact energy, different distributions of multiple impact energy cause varying degrees of damage to RC beams. The bearing capacity of an RC beam with initial severe damage decreases further with subsequent impacts. The reduction in the first mode frequency of the RC beam gradually converges as the extent of damage increases. If a high-energy impact occurs first or if a single high-energy impact takes place, it leads to a more significant reduction in the first mode frequency under the same cumulative impact energy. The first mode damping ratio of impact-damaged RC beams increases with rising impact energy. However, if the impact energy is excessively high, causing wide cracks or severe concrete spalling, the energy dissipation capacity of the specimen is weakened, resulting in reduced damping of the RC beam.