# Structural Performance of a Precast Concrete Modular Beam Using Bolted Connecting Plates
## 4 Experimental Results and Analysis
### Load-Displacement Relationships  
The test results are summarized in Table 3, and the load-displacement curves are illustrated in Figure 11. The maximum loads of the MCF and PCF specimens determined by the flexural tests were 175.65 and 155.13 kN, respectively. According to load-displacement  
Figure 10: Crack propagation of shear test specimens: (**a**) MCS; (**b**) PCS.  
Figure 9: Crack propagation of flexural test specimens: (**a**) MCF; (**b**) PCF.  
curves, it was confirmed that the stiffness of the PCF was greater than that of the MCF in the elastic region. Therefore, as shown by the crack propagation, it can be confirmed that the occurrence of the flexural cracks was delayed in the PCF than in the MCF. The MCF specimen was a monolithic RC beam manufactured from concrete with a compressive strength of 24 MPa, but in the PCF, high-strength non-shrink mortar with a compressive strength of 60 MPa was injected into the gap between modules. Therefore, the PCF can resist deformation more easily than the MCF. In addition, the splicing performance of the PCF was confirmed, because there was no region where the stiffness decreased before the maximum load was reached.  
In the shear tests, the maximum loads of the MCS and PCS were 226.25 kN and 200.96 kN, respectively. The stiffness of the two specimens was similar in the elastic region. In the flexural test, the PCF specimen showed greater initial stiffness than the MCF specimen, because the connection region resisted most of the flexural load in the pure bending area. However, in the shear test, the stiffness contribution of the joint was not observed, because the connection and concrete module resisted the shear load together. Unlike the PCS, the stiffness of the MCS decreased until reaching the maximum load after the elastic region. This is because the shear cracks in the support progressed to the compression zone as the shear load increased, and numerous cracks developed in the concrete as shown in Figure 10. In addition, the bolted connecting plate in PCS effectively resisted the shear force, so the stiffness did not decrease until the maximum load. After reaching the maximum load, the load decreased more gently than in MCS, so it is considered that the bolted connecting plate had better ductility. Accordingly, the proposed PC modular beams demonstrated similar capacity as the monolithic RC beams. These  
Figure 11: Load–displacement curves.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Specimen** & \(\mathbf{P_{max}}\) **(kN)** & \(\mathbf{\delta_{n}}^{1}\)**(mm)** & \(\mathbf{M_{exp}}^{2}\)**(kNm)** & \(\mathbf{V_{exp}}^{3}\)**(kN)** \\ \hline MCF & 175.65 & 37.55 & 153.42 & N/A \\ PCF & 155.13 & 32.54 & 135.3 & N/A \\ MCS & 226.25 & 12.70 & N/A & 113.13 \\ PCS & 200.96 & 8.21 & N/A & 100.48 \\ \hline \hline \end{tabular} \(\mathbf{\delta_{n}}^{1}\): The displacement when the maximum load is applied. \(\mathbf{M_{exp}}^{2}\): The bending moment of each specimen. \(\mathbf{V_{exp}}^{3}\): The shear strength of each specimen.  
\end{table}
Table 3: Summary of the test results.  
results show good agreement with previous studies, which demonstrated that PC modular members performed at 70-85% of the capacity of general RC monolithic members [38,39]. In addition, the flexural test results were compared to the previous study [20] that proposed the L-shaped PC module and connecting plate. The proposed method of this study had 1.1 times the flexural capacity compared to that of the previous study [20]. This can be attributed to the aspect that the proposed PC modular beam in this study was a linear-shaped module, so the gap between the PC modules could be completely filled with non-shrink mortar, unlike in the previous study [20]. It was demonstrated that the splicing performance of a PC modular beam was affected more by the bolted connecting plate than by the geometrical characteristics of the PC modules.