## 2 Materials and Methods  
This section outlines the methodology utilized in the viability study of electric resistance welding to manufacture rebar. The focus is on rebar production for the construction of residential buildings. The various formats of rebar products, primarily bars and links, were examined (Figure 1). The material used in all cases was the structural steel B-500-SD [35]. A representative sample was selected to conduct this study of all the possible combinations of diameters used in welding. The first step was to identify the most frequently used diameters in links (8, 10, and, more infrequently, 12 and 16 mm), and the longitudinal bars (10, 12, 16, 20, and occasionally 25 mm). A discrete list of eight joints' thicknesses was compiled by combining the different diameters listed in Table 1. In this way, values joints were available between the minimum of 16 mm up to a maximum value of 32 mm for the test pieces. Figure 1: Rebar production. This selection facilitates the analysis of the different joint thicknesses that are most common in rebar plants that manufacture reinforcements for residential buildings. To study these joints, test pieces of the material S-500 were obtained. The chemical composition of the material used complies with the provisions of article 32 of the Code on Structural Concrete [35]. The samples had a length of 600 mm for Diameter A bars, and of 150 mm for Diameter B bars. Thus, the goal was to make welded rebar specimens in the laboratory: three pieces of Diameter B for each Diameter A piece as shown in Figure 2.  
Based on the characteristics of the material, the above configuration of three joints was designed to obtain a representative average of the welding. The welding equipment of PRAXAIR brand named \"MPH Digital Neumatica\" was utilized. This equipment is regulated by an electronic thyristor control system and allows for modifications in the following aspects: cycle time, power used, and electrode pressure. The digital controller allows the parameters to be adjusted in a simplified manner, along with the possibility of welding cycles with one or two current pulses. The welding current of the first pulse is established following a fixed slope (up-slope), thereby avoiding current peaks in the power supply network. The absence of a power switch increases the machine reliability and presents excellent precision in terms of the parameter repeatability (current/time). Thanks to the weld/no weld switch, it is possible to simulate operating cycles without a current traveling to the spots, thereby allowing for any necessary adjustments of the positions of frame and spots, before beginning the welding operation. The first pulse serves as the initial contact between the bars, and the second pulse consolidates the welding point. The parameters of each of the pulses (current and time), as well as the interval between pulses (cold), can be regulated separately. The different welds were made by modifying the parameters on the MPH Digital Neumatica welding equipment, whose maximum power is 50 kVA, and the thicknesses of the welds ranged from 10 mm to 40 mm. The spot welder device parameters limits were intensity (0%-100 %), pressure (4-8 bar), and time (0-2 s). The following figure shows the welding process. To be able to complete the welding of the test pieces, a fixture was configured to improve the handling and equalization of the welding; see Figure 3a,b. Additional current and voltage meters were installed at the inputs and outputs of the equipment. \begin{table}
\begin{tabular}{c c c} \hline
**Diameter A** & **Diameter B** & **Joint Thickness** \\
**(mm)** & **(mm)** & **(mm)** \\ \hline
8 & 8 & 16 \\
8 & 10 & 18 \\
8 & 12 & 20 \\
10 & 12 & 22 \\
12 & 12 & 24 \\
10 & 16 & 26 \\
12 & 16 & 28 \\
16 & 16 & 32 \\ \hline \end{tabular}
\end{table} 
Table 1: Combinations of different diameters. Figure 2: Configuration of the test pieces. A series of tests were performed to adapt the power of the equipment according to the needs of the joints to be made.