## 2 Experimental Program
### Impact Test Setup  
The impact tests were conducted by a free-falling striker as presented in Figure 5a. A steel cylinder initially of 60 kg was dropped and guided by a plastic pipe. The height between the bottom of the cylinder and the wood fibreboard placed to act as a mechanical filter was 1600 mm as shown in (b). Two shock accelerometers were placed 110 mm from the midpoint of the beam in the length direction. They were of fabricate HBK Type 4375, see [14], with appropriate sensitivity, maximum acceleration (shock), and resonance frequency. Figure 4: (a) System with springs in series and (b) DIC setup. Figure 3: (a) Test setup used for the quasi-static tests; and (b) schematic of the setup. The striker's drop height and mass were determined using a rigid-plastic model, see, e.g., ref. [15]. This model can only capture flexure-dominated failure modes and assumes constant retardation without any elastic strain energy stored in the beam during impact. The mass and drop height of the striker was updated until a final displacement after retardation of about 9 mm using the rigid-plastic model. This final displacement corresponds to reaching the displacement capacity concerning a flexural failure mode \(u_{u,m}=3.00\) mm, thus enforcing significant damage to the beams. The displacement capacity was calculated using the plastic rotation capacity following the static design provisions in Eurocode 2, see [11], and crushing of the concrete was predicted to determine rotation capacity rather than rupture of the reinforcement. The initial velocity of the beam was determined by assuming a plastic collision of rigid bodies, see, e.g., ref. [16], where the beam was assumed to respond with the generalized mass from deformation in the first mode of vibration calculated following [17]. The plastic collision model predicted an initial velocity of 4.89 m/s at the beam mid-point. The signal measured from the accelerometers was sampled with a frequency of 19.2 kHz using the built-in anti-aliasing filter (2 kHz digital low-pass filter, type Bessel 4 th order); see [18]. From the measured acceleration signal, the velocity and displacement were determined by time integration using the Newmark method; see [19]. A time span of 20 ms was used for the integration, corresponding to the time needed for a significant amount of the energy imparted by the first impact in each test to dissipate. The measured acceleration signals showed oscillation around constant acceleration levels (non-zero mean) and significant drift, which produces error during time integration, an often-observed phenomenon when using accelerometers; see, e.g., [20]. The piezoelectric accelerometers used only measures alternating current (AC), and not direct current (DC), meaning that any constant acceleration level measured is not due to the response of the beam but a measurement error; see [21]. Figure 6 exemplifies the effect of this measurement error on the integrated velocity and displacement. In (a), a non-zero mean occurs for Beams A1-D1 before and after the initial peak, which results in no oscillation around zero velocity in (c). This velocity error produces a higher-order error in (e) for the displacements as the signals are integrated again. The error from the drift and non-zero mean was reduced by applying a second-order high-pass Butterworth filter on the acceleration signals with a cut-off frequency of 0.7-45 Hz (see [22]) depending on the signal. A 10% Tukey window was applied to zero the acceleration signal at its start and end (see [23]), and the velocity was rotated to fulfil the end condition of zero velocity. The effect of applying these signal processing tools on the acceleration, velocity, and displacement is shown by comparing the  
Figure 5: (**a**) Setup used for the impact tests and (**b**) schematic of the setup. results in Figure 6a,b, c,d and e,f, respectively. Therefore, the signals due to integration are seen as approximate; their values are not definite as the time integration procedure with filtering is not exact.