## 3 Experimental Results and Discussion
### Dynamic Response and Residual Impact Capacity
Beam A2 showed no second prominent peak in (b), indicating that the imposed  
Figure 9: **(a)** Damage to B2 during sequential impact tests; **(b)** damage to C2; and **(c)** damage to D2. energy was absorbed by the opening of the wide flexural shear crack after the first impact, causing a small or no spring-back. Beam C2 also showed its prominent second peak earlier than the other beams in (b) and (c), indicating significant damage. Beam C2 was deemed to have failed after the second impact test presented in (c), however, there is still a second peak, indicating no propagation of an unstable crack that dissipated all energy. This implies a possible global residual capacity of Beam C2, as the beam was able to spring back, although significant local damage occurred. Beams B2 and D2 showed, during the fifth impact in (d), to respond similarly, with slightly less energy imparted to the striker for Beam B2 after the first impact with the beam, indicating a higher degree of damage. The acceleration after signal processing, time-integrated velocity, and time-integrated displacement are shown in Figure 11 for Beams A1-D1. The response 20 ms after the development of the initial peak shown in Figure 10 was studied. The variation of velocity in time presented in Figure 11c,d shows a similar response for Beams B1 and C1. Their dominating frequency 10 ms after retardation, where free vibration of the beams in the linear range of internal force occurs, is larger than that observed for Beams D1 and A1. The reduced dominating frequency of Beams D1 and A1 post-retardation indicates a larger degree of damage, as a decrease in the dominating frequency points to a decrease in stiffness. The peak and residual displacement after spring-back in (e) and (f) are similar for Beams B1-D1, indicating similar global responses. Beam A1 shows less spring-back than the other beams in (f), as the propagation of significant diagonal cracks absorbs the energy imparted by the striker. The permanent displacement after the spring-back of Beam A1 is higher on the east side compared with the west side, indicating permanent shear deformation. Figure 10: (**a**) Entire signal measured at the west accelerometer for Beams A1–D1 during the first impact test; (**b**) signal during the first impact test for Beams A2–D2; (**c**) signal during the second impact test for Beams B2–D2; and (**d**) signal during the fifth impact test for Beams B2 and D2. The signals for Beams A2-D2 during the first impact test are shown in Figure 12. Here, it is instead B2 and D2 that show a similar response in (c) and (d), with larger dominating frequencies during free vibration after retardation, implying that A2 and C2 sustained a higher degree of damage. The difference in the level of permanent displacement for A2 in (e) and (f) indicates significant permanent shear deformation. Figure 11: (**a**) Signal-processed acceleration at the west accelerometer for Beams A1–D1 during the first impact test; (**b**) acceleration at the east accelerometer for A1–D1 during the first impact test; (**c**) integrated velocity at the west accelerometer for A1–D1; (**d**) integrated velocity at the east accelerometer for A1–D1; (**e**) integrated displacement at the west accelerometer for A1–D1; and (**f**) integrated displacement at the east accelerometer for A1–D1. The signals for Beams B2-D2 during the second and fifth impact tests are presented in Figure 13. The response in terms of velocity and displacement of Beam D1 were similar during the second and fifth impact test. This shows that the response for dynamically flexure-dominated beams does not change with sequential impacts. The response of Beam B2, which showed a hybrid response, changed drastically between the second and fifth test. Low-frequency oscillations occurred for Beam B2 in (d), indicating a high degree of damage to the beam. Beam C2 showed large permanent deformation after the second impact in (e) due to the global flexural shear crack opening.