## 3 Experimental Results and Discussion
### Pushover Tests on Structural Frames
#### 3.2.2 Diagrams of Drift versus Strain in Concrete  
Figure 17 shows the relationship between the drift of the walls and the average vertical strain of the walls' concrete, near but below the connection with the slab, at both the internal and the external faces. In this case, a positive value of strain denotes tension, and a negative value denotes compression.  
Figure 17 reveals the behavior of the connection between the slab and the wall. First, a linear-elastic behavior of the connection, up to a drift of 2%, is observed. In Wall 1, the one in contact with the actuator, compression strain is observed in the exterior face, as well as tension strain in the interior face. On the contrary, in Wall 2, tension strain is observed in the exterior face, as well as compression strain in the interior face. In each loading cycle, the loading and the unloading branches are almost identical and the area under the hysteresis loop is small, which denotes an absence of energy dissipation. During this first phase of the testing, the visual inspections revealed very small horizontal cracks in the walls (especially in the external face of Wall 2 where the tension strain was larger) with a crack width below 0.2 mm, i.e., clearly smaller than 1.6 mm which is the maximum allowable crack width defined by the ACI374.2R-13 [34]. No concrete crushing occurred.  
The maximum measured strain values belong a drift of 2%. Beyond this value, there was a progressive decrease in the maximum measured strain, which denotes that the stiffness of the connection between the slab and the wall decreased and a plastic hinge appeared in this connection. Moreover,  
Figure 17: Diagrams of drift vs. vertical strain. Pushover test on structural frame. (**a**) Drift versus strain in the external face of wall 1; (**b**) drift versus strain in the internal face of wall 2; (**c**) drift versus strain in the internal face of wall 1; (**d**) drift versus strain in the external face of wall 2.  
this plastic hinge showed an asymmetric behavior, i.e., its structural behavior was different when it was subjected to a positive bending (tension in the inner face of the wall and the lower face of the slab) or a negative bending (tension in the outer face of the wall and the upper face of the slab).  
Because of the type of loading cycles of the test, the connection between Wall 1 and the slab was always under positive bending while the connection between Wall 2 and the slab was always under negative bending. Wall 1 showed values of strain (both tension and compression) lower than the values observed in Wall 2. This means that the connection shows a stiffness under positive bending smaller than the one under negative bending.  
Once the drift was beyond 2%, a clear plastic behavior started to be observed. In each loading cycle, the loading and the unloading branches were different and the area under the hysteresis loop increased with the cycles, which denoted an increased ability of the connection to dissipate energy. In this case, the visual inspections carried out during the testings revealed small horizontal cracks in the walls (especially in the external face of Wall 2 where the tension strain was larger). However, the crack widths were always below 1.6 mm which is the maximum allowable crack width defined by the ACI374.2R-13 [34]. No concrete crushing occurred.