# Bending Performance of Concrete Sandwich Walls with Actual Boundary Conditions
## 3 Test Results  
### Failure Modes  
In total, 29 regions, each with a width of 100 mm, were divided along its span, identified as #1-29. Specimens WP and WN exhibited similar failure patterns. Specim WP was set as the example used to describe the failure modes. No obvious failure modes and bending deformations were noticed in the specimen before cracking. When the loading force reached 35 kN, cracking was initiated in section #16 and its depth was about 2/3 times that of the wall thickness. When the load increased to 50 kN, another crack appeared in region #12. As the load increased to 78 kN, slight bending deformation was noticed. With the further increase in load, more and more cracks were noticed and penetrated the thickness of the wall. When the load equaled 140 kN, slippage between the concrete layer and XPS was detected, and the crack along the span was noticed. When the load increased to 150 kN, the width of crack along the span grew to 5 mm and the XPS fractured. Afterwards, the deflection of the wall specimen increased sharply when the load reached to 160 kN and the loading procedure was terminated. Typical failure modes of specimen WP are shown in Figure 5.  
Figure 5: Typical failure modes of specimen WP. (**a**) First crack at the load of 35 kN. (**b**) Bending deformation at the end of the test. (**c**) Bending deformation in the test. (**d**) Cracks at the bottom of the wall.  
Moreover, specimens WPO and WNO exhibited similar failure modes. Before the load increased to 33 kN, no test phenomena were detected among the specimens. Subsequently, a series of cracks emerged and spread to the middle of the wall thickness. When the load increased to 52 kN, obvious bending deformation was noticed in the test specimens. A penetration crack along the wall thickness was observed when the load reached 100 kN. At the same time, some cracks also appeared around the openings. As the load increased to 135 kN, slippage between the XPS and concrete was also noticed. With the load further increasing to 145 kN, the deflection increased significantly, whereas the load was kept almost constant. The test also ended at this time. After the loading, it demonstrated that the sandwich wall remained almost flat, and the connection angle exhibited obvious deformation. Typical failure modes are displayed in Figure 6.  
In conclusion, the bottom concrete first cracked under bending. Subsequently, the XPS layer also exhibited fracture and slippage between the XPS and concrete, which was detected both under positive and negative bending conditions. However, the crack was mainly located on the 1/3 and middle span, and did not penetrate the wall along its thickness, which indicated that the two layers of concrete could work together through the steel truss connection. In addition, no local crushing was found during the test. Meanwhile, the additional constraints provided by the actual boundary conditions increased the stiffness and strength of the sandwiched wall to some extent.  
Figure 6: Typical failure modes of specimen WPO. (**a**) Cracks at a load of 50 kN. (**b**) Cracks around the opening. (**c**) Deformation of the connection angle. (**d**) Residual deformation after the loading.