## 4 Results and Discussion
### Effect of Different Extension Time Differences on the Recoil Distance  
Due to the characteristics of structures with small-aspect ratios, two plastic hinges with different positions, as shown in Figure 10, appear in 0.1-0.9 s, resulting in the plastic hinge at the top of the rear row of columns in the rear row of the superstructure for fixed-axis rotation when the delay-time difference is 0.4-0.8 s. When the time difference of the extension is 0.1-0.3 s and 0.9 s, the superstructure undergoes a fixed-axis rotation at the bottom of the rear column. Selecting the outermost unit of the blasting pile and outputting the recoil displacement distance can obtain the recoil distance of the structure under different blasting delay-time differences, as shown in Figure 12.  
Given the uniqueness and irreversibility of blasting demolition operations, it is difficult to conduct repeated experimental verifications of the demolition process. Numerical simulations can repeatedly simulate the blasting process and continuously optimize the design scheme, making it easy for people to understand and analyze. By comparing the recoil distance and explosion height of structural collapse under different delay-time differences, a reasonable fitting formula can be obtained, and the reasonable delay-time difference of such small-aspect-ratio reinforced concrete structures can be analyzed. As shown in Table 3, when the delay-time difference is 0.1-0.3 s and 0.4-0.7 s, the recoil distance increases with the increase in these two groups of delay-time differences, which is due to the use of delayed detonation. With the increase in the delay-time difference between the columns, the structure leans forward, and the horizontal component of the velocity increases significantly. The greater the acceleration in the horizontal direction is, the greater the reaction force on the rear column. Therefore, the support column slides backwards, and the distance of the backwards rotation will also increase. Moreover, the extension time  
Figure 12: \(z\)-axis direction unit displacement time curve. difference of 0.7-0.9 s is too long, and the recoil distance tends to be close to a constant because, with the increase in the extension time, the plastic hinge rotation produced is sufficient. Thus, the forward angle of the structure and the horizontal component of the kinetic energy increase. Then, the recoil distance of the structure increases, but the horizontal component of the kinetic energy does not infinitely increase, resulting in the recoil distance basically stabilizing at approximately 12 m. To study the growth trend of the structural recoil distance of Table 2, the data were fitted to time differences of 0.1-0.3 s and 0.4-0.9 s, as shown in Figure 13.  
The fit-degree indices are all 0.99, which is a good fit. 0.1-0.3 s fitted straight line:  
\[\mathrm{d}=6.37+14\mathrm{t} \tag{2}\]  
0.4-0.9 s fitted curve:  
\[\mathrm{d}=-19.46\mathrm{t}^{2}+36.76\mathrm{t}-5.29 \tag{3}\]  
where d is the recoil distance; is the deferred time difference; and R\({}^{2}\) is the degree of fit index. The analysis of the collapse process with time differences from 0.1 s to 0.9 s shows that the plastic hinge position of the structure changes with the time differences as follows: the plastic hinge is formed at the end of the latter span between 0.1 s and 0.3 s, then moves to the top of the first floor column in the latter row between 0.4 s and 0.8 s, and finally moves to the end of each span at a time difference of 0.9 s. At time differences of 0.1-0.3 s and 0.9 s, the orientation axis is located at the bottom of the latter row of columns, and at time differences of 0.4-0.8 s, the orientation axis and the plastic hinge are in the same position. The recoil distance showed a linear increasing trend of \(\mathrm{d}=6.37+14\mathrm{t}\) in the time difference of 0.1-0.3 s, plunged between 0.3-0.4 s, and showed a parabolic increasing  
Figure 13: Fit of the recoil distance relationship: (**a**) 0.1–0.3 s recoil distance fitting; and (**b**) 0.4–0.9 s recoil distance fitting.