# Experimental and Numerical Studies on the Structural Performance of a Double Composite Wall
## 2 Experimental Program
### Test Results  
Figure 5(a) shows the flexural behavior of the DCW-F specimen. The vertical axis of the graph represents the total loads acting on the specimen. The first flexural cracking occurred near the loading point at a load of 66 kN, and cracking between the shear keys of the upper and lower panels was observed at a load of 333 kN. The strain of tensile reinforcement reached the yield strain (\(\epsilon_{y}\)) at a load of 739 kN. Afterward, the specimen exhibited ductile behavior and then underwent flexural failure due to the crushing of concrete at the extreme compression fiber near the loading point at a load of 894 kN. As shown in Figure 5(b), the position of the neutral axis increased as the load increased in the section located at the mid-span, and the strain of the tensile reinforcement increased sufficiently by \(1.0\times 10^{4}\)\(\mu\)e or more at the ultimate load. Figure 5(c) shows the measured end slip between the PC panel and the CIP concrete at the end of the DCW-F specimen, and the maximum slip observed during the test was only 0.02 mm. If it is assumed that the strain difference (\(\Delta\epsilon_{c}\)) at the interface between the PC panel and the CIP concrete is uniformly distributed over the longitudinal direction from the support to the loading point, the average strain difference \(\Delta\epsilon_{c,avg}\) can be calculated as follows:  
\[\Delta\epsilon_{c,avg}=\epsilon_{ci,PC}-\epsilon_{ci,CIP}=\frac{s_{e}}{a}, \tag{1}\]  
Figure 5: Loading details (unit: mm): (a) DCW-F specimen; (b) DCW-S specimen series. where \(\varepsilon_{ci,PC}\) and \(\varepsilon_{ci,CIP}\) are the strains of the PC panel and CIP concrete at the interface, respectively; \(s_{e}\) is the end slip; and \(a\) is the length of the shear span. The difference in strain (\(\Delta\varepsilon_{c,exp}\)) between the PC panel and CIP concrete was calculated to be 6.5 \(\mu\)e, which is so small that it can be considered negligible. Therefore, in the following section it was assumed that in the nonlinear flexural analysis of the DCW-F specimen, the PC panel and the CIP concrete are in a fully composite state [16]. Figure 6: Flexural behavior of DCW-N specimen: (**a**) load–displacement behavior; (**b**) longitudinal strain distribution in the section at the mid-span (see Figure 5a for gauge locations); (**c**) measured end slip between the PC panel and the CIP concrete. Figure 7 shows the shear test results of the DCW-S specimen series. The vertical axis of the graphs represents the shear force acting on the specimen in the intended shear failure region--i.e., the end region. In the DCW-SN specimen, where bolts for assembling PC panels were not placed in the shear span, the first flexural cracking occurred near the loading point at a shear force of approximately 160 kN, as shown in Figure 7a. The stiffness of the specimen began to decrease when inclined cracking was observed at a shear force of 367 kN. In addition, cracking between the shear keys in the upper and lower PC panels occurred at a shear force of 527 kN, and web-shear cracking was observed near the support at a shear force of 607 kN. Even after this, the load continued to increase, and the specimen failed in shear at a shear force of 719 kN. Regarding the DCW-SN specimen, it was found that shear cracks that occurred in the lower PC panel could not propagate to the upper PC panel; rather, the crack developed along the shear key interface. Nevertheless, since the rough surface finishing of the PC panel was applied and the shear keys of the upper and lower panels were interlocked with each other, the maximum end slip was only 0.03 mm, as shown in Figure 7d. Figure 7: Shear behavior of the DCW-S specimen series: (**a**) DCW-SN specimen; (**b**) DCW-SB(1) specimen; (**c**) DCW-SB(2) specimen; (**d**) measured end slip (DCW-SN specimen); (**e**) measured bolt strains (DCW-SB(1) specimen).