## 4 3D FDEM Modeling of Demolition of a Small-scale RC Structure
### Simulation Results of the Demolition of a Small-Scale RC Structure  
Figure 15 compares the demolition process of an RC structure between 3D FDEM simulation and experiment observation [7] at equivalent elapsed times after removing the two-main columns in 1 st floor due to blast load. Note that, although the two columns were removed by a detonator in the experiment, 3D FDEM simulation just removed the corresponding parts at once, which should be acceptable since the time-scale of interest is several hundred to thousand milliseconds (ms), while the detonation-induced removal completes roughly within several hundred microseconds. At 400 ms, the RC structures both in FDEM and the experiment have clearly started to tilt, and it continuously inclines until 600 ms due to gravity. With the further inclination, the newly created surface due  
Figure 13: Crack patterns as a result of (**a**) the numerical simulation and (**b**) experiment (This figure has been reproduced from [34] with permission from American Concrete Institute). to the removal of the columns on the 1 st floor dynamically contacts with the ground. At 1000 ms, the RC structure overturns using the initial contact part as a rotation axis. After that, one of the original RC structure surfaces finally makes contact with the ground at 1200 ms. Then occurs the sliding of the contact face against the ground at 1400 ms in both the FDEM and experiment. Up to this stage, the FDEM and experiment show very similar behavior. However, after this stage, the RC structure is broken into multiple segments in the experiment but is nearly preserved in the numerical simulation at 1600 ms. A possible source of difference between experiment and simulation at this stage is the reinforcement bar's formulation. The beam and column were connected in the experiment using epoxy resin. However, in FDEM, the beam and column are reinforced, which makes the nominal strength of the RC structure in the FDEM higher than that in the experiment. Figure 14: A numerical model for simulating the demolition of a small-scale RC structure: (**a**) numerical model of the RC structure and (**b**) embedded rebars in the RC structure. Figure 15: Comparison of 3D-FDEM (**left-side**) and experiment (**right-side**) results from the demolition of a small-scale RC structure (This figure has been reproduced from [7] under the terms and conditions of the CC BY-NC license). The time profile of x- and y-displacement at the specific point \"A\" (see Figure 14a) on the RC structure model is also compared as shown in Figures 16 and 17. It can be found that the FDEM and experiment are observed after 800 ms, which could be explained by the aforementioned reason (i.e., experiment used the epoxy resin to connect the beams and columns). As illustrated in Figure 16, the differences in the direction of the y-axis between numerical simulation and experiment begin at 800 ms. From 800 ms on, the y-axis displacement in numerical simulations moves more easily toward the ground as the equal time elapses. At 1000 ms, Figure 15 illustrates this behavior. Both the experimental and numerical models are collapsing after contact with the ground at 1000 ms. However, the experimental model exhibits more brittle deformation than the numerical model. The significant deformation in the bottom part of the numerical model, in particular, results in differences in the y-axis displacement between them. On the other hand, the differences in the direction of the x-axis in Figure 17 demonstrate a similar behavior between experiment and numerical simulation. However, after 1600 ms, the experimental model continues to move due to structure collapse, as illustrated in Figure 15.  
Our future study includes conducting the blasting demolition experiment that realizes the almost same condition as in the FDEM simulation in Figure 14. Thus, this paper does not discuss this demolition any further in detail.