## 4 Discussion
### Maximum Strength Evaluation
#### 4.2.4 IRBM--FNM (Internally Reinforced Brick Member Fixed by Nut with No Filling Mortar)  
In this specimen, not only could superior workability be achieved but also a remarkable enhancement in structural performance, by eliminating the mortar filling work and the fixing of the SI rods. Due to the unbonded characteristics, the strain increment was delayed compared to that of IRBM--F. Hence, from the strain data, the stress of the bottom side rod was considered to be in the range between the yield (\(\sigma_{y}\)) and tensile (\(\sigma_{t}\)) strength. The strain of the top side was found to be less than the yield strain (\(\epsilon_{y}\)). In addition, due to no mortar filling work, the specimen tended to rotate as a rigid body, with respect to the damaged section, after the crack development at the joint mortar. The neutral axis was very close to the extreme compression fiber at the maximum strength, as was found in IRBM--F. Based on these results, as well as considering a conservative estimation of the maximum strength \(Q_{max,IRBM--FNM}\), the strain of the bottom rod was assumed to be \(\epsilon_{y}\). Then, the deformation compatibility condition was established, as shown in Figure 13. Since the SI rod was unbonded, the total elongation of the bottom rod (\(\delta_{br}\)) could be expressed as Equation (8). When the rotation center was located at the extreme compression fiber, the relationship between \(\delta_{br}\) and the total elongation of the top rod (\(\delta_{tr}\)) could be derived from Equation (9). The strain of the top rod (\(\epsilon_{tr}\)) and thus its stress (\(\sigma_{tr}\)) could be obtained based on the material test of the SI rod. Then, \(Q_{max,IRBM--FNM}\) could be calculated from Equations (6) and (7), where \(\sigma_{y}\) and \(\sigma_{tr}\) are substituted for the bottom rod stress (\(\sigma_{br}\)) and the top rod stress (\(\sigma_{tr}\)), respectively, and the estimated \(Q_{max,IRBM--FNM}\) was 102.92 kN. The evaluated value is shown along with the test result in Figure 10d and Table 4, where the ratio of the calculation to the experiment was 0.85. Even though the estimation was slightly lower than the experiment, it showed reasonable agreement with the test result.  
\[\delta_{br}=\epsilon_{y}\times L \tag{8}\]  
\[\delta_{br}:\delta_{tr}=d_{br}:d_{tr}=\epsilon_{y}\times L:\ \epsilon_{tr}\times L \tag{9}\]  
where \(L\) is the total length of the rod inside the specimen (970 mm in this study).  
Figure 12: Force equilibrium condition.  
From the test results of IRBM--F and IRBM--FNM, it was proved that the proposed material and methods enabled effective utilization of the internal reinforcement, and they could contribute to the improvement of structural performance in masonry construction. On the other hand, in the test specimen, the stress of the SI rods was determined based on the experimental results. In actual cases, it is difficult to specify those stresses. Therefore, for practical use, it might be an alternative to temporarily set \(\sigma_{br}\) to be either \(\sigma_{y}\) or \(\sigma_{t}\) and \(\sigma_{tr}\) to be 0. The calculation results using these values were approximately 70-80% of the maximum strength by the experiments. Although the calculations underestimated the test results, conservative performance evaluations considering seismic safety could be achieved by these assumptions and manner.