*4.3. A Simulation Model for Rebar Fabrication's Optimal Production Plans*

Figure 4 shows the models for SHD10 and SHD13 and the corresponding verification processes. There are seven components to the simulation of rebar plant processing: (1) raw steel import, (2) transportation, (3) priority and rebar type setting, (4) cutting, (5) rebar reuse, (6) bending, and (7) machine schedule setting.

First, in the simulation model, a rebar with a particular diameter is put up as an agent to represent the raw steel imported into the rebar fabrication plant. Second, the rebar is transported and assigned to a cutter. It is believed that the hoist's maximum capacity can be gathered and transported all at once (for a hoist, the transport time typically varies with the transport distance). Third, different sites from which to collect various rebar types are taken into consideration before processing. Each agent is assigned a priority, which determines the order in which they move through the cutting process. By identifying various sitespecific combinations in this step, the simulation can ultimately choose the optimum site-specific combination when prioritizing the agent. Fourth, the rebar is cut. Similar to

the case of hoists, for which the capacity is set considering simultaneous transportation, the number of simultaneous cuts is set for the cutters.

**Figure 4.** Simulation modeling that reflects processes within a rebar processing plant.

The cutting machine is employed, and the required time is input to represent the number of times the imported rebar can be cut (with the maximum amount) and the time needed to perform one cut, which adds time to the process. The length of the raw steel and the needed length are taken into consideration while defining the cut steel bars, which are then repeatedly moved to the cutting process. Fifth, we considered the reuse of the cut rebar. The following factors determine the loss rate: the cutting procedure is repeated to reuse the rebar if the original steel is cut and the residual rebar is longer than the type of rebar to be processed, and vice versa. Sixth, the rebars go through bending procedures. The long-term steel without the need for bending is designed to finish the rebar process, and the rebar bending process takes as much time as the number of bends to the specific rebar type. Seventh, the machine schedule employed in the process of fabricating rebar is taken into account. The machine operation in the plant under consideration begins at 8:00 a.m. and ends at 9:30 p.m., with three intervals in between. The suggested model takes into account the machinery turning on and off to match the actual state of a rebar production plant.

By simulating the combination of several locations and the ratio of raw steel by length, we were able to build an optimal production plan for the rebar fabrication plant by calculating the time required for rebar fabrication and the loss rate.

#### **5. Results**

#### *5.1. Optimization*

The situation of importing raw steel with a length ratio of 2:1 (8 m:10 m) corresponds to the largest reduction in the loss rate when taking into account both SHD10 and SHD13 scenarios. The loss accumulation pattern is comparable for length ratios of 1:1, 1:2, and 1:3, as shown in Table 5. Moreover, the loss accumulation patterns are similar for length ratios of 2:1 and 3:1.

To optimize the site combination, the loss rate was analyzed for different combinations of multiple sites. In the considered case, 16 rebar types were selected, and the maximum loss rate was observed when the length of the imported raw steel was only 8 m. A combination of the two sites in the rebar fabrication process corresponded to the optimal production plan.


**Table 5.** Analysis results of four site combinations.

#### *5.2. Model Verification*

The data of the rebar fabrication plant were collected, and a model was built by reflecting the actual environment of the plant. The model was evaluated, and minor system errors were corrected. The model was additionally validated using information on the status of the rebars made at the actual rebar fabrication plant.

The simulation model was noted to exhibit a reasonable performance. According to Figures 5 and 6, the cutting process and flow of the processed rebars into the bending well were stopped as the machinery was shut off for one hour during lunch, 30 min during break time, and 30 min during dinner.

**Figure 5.** Model verification: hourly fabrication flow of D10 rebar.

**Figure 6.** Model verification: hourly fabrication flow of D13 rebar.
