## 4 Experimental Results and Analysis
### Load-Displacement Relationships and Strains  
The results of the flexure tests on each test specimen are summarized in Table 3, and the load-displacement curves are shown in Figure 13. The maximum load of the CRC was 175.65 kN. The maximum loads on the PCM-A and PCM-B, which were PC modular members, were 141.86 kN and 137.75 kN, respectively, which were 88% and 78% that of the CRC specimen. These results show good agreement with previous studies on PC modular members, that PC modular members usually perform at 70% to 85% of general RC members' capacity [12; 27]. Accordingly, we confirmed that the proposed PC modular beam systems performed as well as monolithic members. Figure 11: Crack patterns of specimens: (**a**) CRC; (**b**) PCM-A; (**c**) PCM-B. Figure 12: Failure of specimens in the midspan: (**a**) CRC; (**b**) PCM-A; (**c**) PCM-B. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Specimen** & \(P_{max}\) **(kN)**1  & \(\delta\) **(mm)**2  & \(M_{n,ACI}\) **(kN-m)** & \(M_{n}/M_{n,ACI}\) \\ \hline CRC & 175.65 & 37.55 & & 1.27 \\ \hline PCM-A & 141.86 & 24.25 & 120.8 & 1.03 \\ \hline PCM-B & 137.75 & 27.50 & & 1.01 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Test results. Figure 13: Load–displacement curves. This study also verified that the proposed system meets the requirements of current design codes, such as the ACI 318-19 standard [28]. The nominal moment strength equations of RC beams presented in the ACI standard are as follows:  
\[M_{n,ACI}=A_{s}f_{y}\left(d-\frac{a}{2}\right) \tag{1}\]  
\[\text{a}=\frac{A_{s}f_{y}}{0.85f_{c}^{\prime}b} \tag{2}\]  
where \(A_{s}\) is the non-prestressed longitudinal tension reinforcement, \(f_{y}\) is the yield strength of the non-prestressed reinforcement, \(d\) is the distance from the extreme compression fiber to the centroid of the longitudinal tension reinforcement, and \(a\) is the depth of the equivalent rectangular stress block, as shown in Figure 14.  
The nominal moment strengths of all the test specimens were calculated to be 120.8 kNm. Experiments showed that the moment strengths of the CRC, PCM-A, and PCM-B were 127%, 103%, and 101%, respectively, compared to the normal moment strength calculated through ACI code. This demonstrated that the proposed beam system could be designed using the design method of typical RC beams. The strain on each specimen was analyzed with gauges attached to the concrete, rebars, and steel plates, as shown in Figure 15. The load-strain curves of PCM-A and PCM-B showed discontinuities because mortar injecting connection zone was crushed as load increased. According to a concrete gauge in the compression zone, the CRC reached the ultimate compressive strain of the concrete, 0.003. In the PCM and PCM-B, the strain gauge was damaged, and its subsequent behavior was not measured. However, the concrete in the compression zone was crushed, and it can be considered that concrete reached the ultimate compressive strain. Furthermore, in the PCM-A and PCM-B, the stiffness decreased at the beginning of the experiment because the load was applied on the mortar of the connection, but the subsequent behavior patterns and stiffness were similar to that of the monolithic reinforced concrete beam specimen. Figure 14: Definition of rectangular stress distribution. For the rebar gauges shown in Figure 15b, the PCM-A and PCM-B did not reach the yield strain of the rebar, 0.002, unlike the CRC. This was due to the strain of the steel plate inserted into the PC module in the tension zone. At the maximum load of the PCM-A and PCM-B, the rebar strains were 0.0018 and 0.0015, respectively, indicating integrity between the PC modules. The strain of the steel plate inserted into the PC module beam system was observed, and is shown in Figure 15c. The yield strain of the steel plate was 0.00138, and steel plates inserted into precast concrete specimens exceeded 0.00138 near the maximum load. This behavior was observed equally in the PCM-A and PCM-B specimens.