## 5 Conclusions  
In this study, a PC modular beam system was proposed in order to improve structural integrity and simplify the construction process. To evaluate the structural performance of the proposed system, a monolithic reinforcement concrete beam and two proposed PC modular beams with different connection lengths between the modules were fabricated and a flexural experiment was conducted. The conclusions of this study are as follows:  
1. An initial crack occurred in the midspan of all the test specimens. In the proposed PC modular beam system, PCM-A and PCM-B, cracks progressed along the shape of connection to the compression zone as the load increased after the initial flexural crack occurred. The PCM-B with a 700 mm connection length (twice that of the PCM-A specimen) was more brittle. However, the splicing between the PC modules was ensured because the connections between the PC modules did not detach until the test was terminated;
2. The maximum loads of the PCM-A and PCM-B were 81% and 78%, respectively, of the maximum load of the monolithic specimen. The load resistance capacity of PC modular members is typically about 70-85% compared to standard RC beams; thus, the proposed system performed the same as general PC modular members. Furthermore, the normal moment strengths of the PCM-A and PCM-B specimens obtained experimentally were 103% and 101%, respectively, of that calculated by the  
Figure 17: Diagram for the description of displacement ductility.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Specimen** & **A1** & **A2** & **Displacement Ductility Index, \(\mu\)** & **Normalized Ductility Index** \\ \hline CRC & 4308.6 & 10,565.09 & 3.45 & 1 \\ \hline PCM-A & 2502.5 & 8291.13 & 4.31 & 1.25 \\ \hline PCM-B & 2911.25 & 8748.7 & 4.01 & 1.16 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Comparison of displacement ductility index.  
Figure 18: Comparison of normalized ductility index.  
ACI 318-19 design standard, meaning it was possible to verify the flexural strength of the proposed method using the current design code;
* It was observed for all the specimens that the concrete strains in the compressive zone at the middle of the beam reached the ultimate compressive strain. The rebars in PCM-A and PCM-B did not reach the yield strain of the steel, 0.002, unlike the CRC, the monolithic beam. This is because steel plates inserted into the precast concrete specimens resisted flexural load instead of the discontinuous rebars. This means that the proposed connection showed sufficient structural performance as well as splicing performance;
* The ductility indexes of the PCM-A and PCM-B were 1.3- and 1.2-fold higher, respectively, than that of the CRC. This was due to the improved ductility from the steel plates of the PC modules, and it confirmed that the high integrity was ensured between the PC modules. The connection length had only a small effect on the ductile performance. To provide design guidelines for the proposed PC modular beam, more analytical and experimental studies are needed.  
Conceptualization, K.-M.R. and Y.-H.L.; methodology, K.-M.R.; validation, M.-S.K. and C.-G.C.; formal analysis, K.-M.R.; investigation, M.-S.K. and C.-G.C.; writing--original draft preparation, K.-M.R.; writing--review and editing, Y.-H.L. All authors have read and agreed to the published version of the manuscript.  
This research was supported by a National Research Foundation of Korea grant (NRF-2019R1A4A1028116), funded by the Ministry of Education, Korea.  
Data Availability StatementData sharing not applicable.  
The authors declare no conflict of interest.