# Experimental and Numerical Studies on the Structural Performance of a Double Composite Wall
## 2 Experimental Program
### Test Results
For the DCW-SB(1) specimen in which bolts were placed in the shear span, as shown in Figure 7b, flexural cracking occurred at a shear force of about 160 kN, and shear cracking was observed at a shear force of 389 kN. In the upper surface of the bottom flange, horizontal cracking toward the support occurred at a shear force of 607 kN, as shown in the picture in Figure 7b, and the stiffness of the specimen began to decrease rapidly, starting from a shear force of approximately 900 kN. Finally, after reaching the maximum shear force of 950 kN, the DCW-SB(1) specimen underwent failure as the load gradually decreased. In the DCW-SB(2) specimen with the same details as the DCW-SB(1) specimen, the first flexural cracking was observed at a shear force of 158 kN, and inclined cracking occurred at a shear force of 467 kN, as shown in Figure 7c. After that, the DCW-SB(2) specimen showed behavior that was almost similar to that of the DCW-SB(1) specimen and failed in shear at a shear force of 947 kN. It should be noted that in the DCW-SB(1) and (2) specimens, shear cracks that occurred in the lower PC panel propagated to the upper PC panel, unlike in the DCW-SN specimen, because the integrity of the upper and lower PC panels was improved due to the bolts placed in the shear span. Consequently, the shear strengths of the DCW-SB(1) and (2) specimens increased by about 32% compared with those of the DCW-SN specimen because of the shear contribution of the bolts used for assembling the PC panels. Figure 7e shows the axial strains measured from the gauges attached to the bolts placed in the DCW-SB(1) specimen. Although the bolts placed in the shear span contributed considerably to the shear resistance mechanism of the member, the yield strain was not reached until the maximum load. Therefore, based on the measured bolt strains, this study sought to make a quantitative approach to determine the contribution of concrete and bolts in the DCW member, as shown in Figure 8. The shear contribution of the bolts (\(V_{bolt}\)) was estimated as shown below. \[V_{bolt}=A_{bv}\epsilon_{bolt}E_{bolt}\frac{d_{s}}{s_{bv}}\left(\text{when } \epsilon_{bolt}\leq\epsilon_{y,bolt}\right), \tag{2}\]  
\[V_{bolt}=A_{bv}f_{yb}\frac{d_{s}}{s_{bv}}\left(\text{when }\epsilon_{ bolt}>\epsilon_{y,bolt}\right), \tag{3}\]  
where \(\epsilon_{bolt}\) is the measured bolt strain from the shear test; \(E_{bolt}\) is the elastic modulus of the bolt, which is 149 GPa; \(A_{bv}\) is the sectional area of the bolt, \(\epsilon_{y,bolt}\) and \(f_{yb}\) are the yield strain and stress of the bolt, respectively; and \(s_{bv}\) is the bolt spacing. In the DCW-SB(1) specimen, the shear contribution of concrete (\(V_{c}\)) was calculated by excluding the shear contribution of bolts (\(V_{bolt}\)) from the total shear force acting on the member. As a result, it was found that concrete resisted most of the external shear force at the early stages of the DCW-SB(1) specimen behavior, and bolts began to contribute to the shear resistance after the inclined shear cracking. The bolt contribution (\(V_{bolt}\)) at the ultimate strength of the member was approximately 1/3 of the total shear force. In addition, when the shear strength was reached the shear contribution of the concrete (\(V_{c}\)) of the DCW-SB(1) specimen was smaller than that of the DCW-SN specimen without bolts. This is because the DCW-SB(1) specimen exhibited a greater deformation capacity because of the shear contribution of the bolt; thus, the width of the critical shear crack generated in the DCW-SB(1) specimen at the ultimate state was larger than that of the DCW-SN specimen. Note that the maximum shear crack width observed in the DCW-SB(1) specimen before shear failure was 0.9 mm, while the maximum shear crack width in the DCW-SN specimen was 0.4 mm.