## 3 Result Analysis
### Steel Rebar, Steel Plate, and Concrete Strain  
This section analyzes strain trends of the steel rebar, steel plate, and concrete in the mid\(-\)span and quarter\(-\)point sections of PC beams during the drop weight impact test, based on the strain data. However, due to severe strain gauge damage, only the data for a short period of time could be recorded, and no complete development trend could be collected. Figure 16 shows the typical strain-time history curve of a PC beam composed of steel rebar, and Figure 17 shows the strain changes in the steel plate in the mid\(-\)span and quarter\(-\)point portions. In addition, Figure 18 depicts the typical strain-time history curve of a concrete PC beam, all using the B1 test beam as an example. It should be noted that positive values indicate tension, while negative values indicate compression. The strain of the lower steel bar strain gauge 1 rapidly increases after the response and reaches the peak tensile strain. With the spring back of the test beam, the tensile strain gradually decreases and tends to be stable. This is attributed to the overall failure of the test beam, resulting in the bending cracks at the bottom of the beam, removal of concrete from the tension zone, and pulling of the bottom steel rebar. The strain of the upper steel bar strain gauge 3 rapidly appears as tensile strain after the response begins, decreases to a compressive strain after a short period, then transforms into tensile strain and decreases after reaching the strain peak, and finally tends to near\(-\)zero. This illustrates the stress process in which the upper steel bars of the beam are initially pushed, then compressed, and then pulled again. Due to the strain rate effect of the material, the concrete in the compression zone expands and squeezes laterally when the hammerhead contacts the body of the beam, placing tensile strain on the upper steel bar at the first peak stage of the impact force. Subsequently, due to the continuous reflection of the stress wave between the top and bottom of the beam, a compressive strain was produced as the deflection and deformation of the beam increased and the upper steel bars joined the compression. At the same time, downward flexural deformation occurred, the concrete in this area was compressed, and the steel rebar was tensioned. The variations in steel rebars' stress values at the quarter \(-\)point portion are depicted in Figure 16b. The strain response of the lower rebar strain gage 2 and the upper rebar strain gage 4 start almost simultaneously. Among them, the strain of the lower steel bar strain gauge 2 first appears as a short period of compressive strain after starting to respond, then transforms into tensile strain and rapidly reaches the strain peak, and then the strain gradually decreases and approaches a lower strain value. The strain of the upper steel bar strain gauge 4 first appears during a short period of tensile strain after it starts to respond, and then transforms into compressive strain and finally approaches the zero value. The main reason for the abovementioned strain changes is that the beam's bending moment distribution changes significantly with the impact process. The strain change process corresponds to the three change processes of the beam moment distribution: (1) when the hammerhead just touches the beam body, the test beam produces a positive bending moment in the mid \(-\)span, and negative bending moments appear on both sides  
Figure 16: PC beam’s typical steel rebar strain–time history curve. (**a**) Mid \(-\)span section; (**b**) quarter–point section; and (**c**) two positions. Figure 17: PC beam’s typical steel plate strain–time history curve. (**a**) mid–span section; (**b**) quarter–point section. Figure 18: A typical PC beam concrete strain–time history curve. (**a**) Mid–span section; (**b**) quarter–point section; and (**c**) two positions. of the mid\(-\)span.