## 3 Experimental Results and Discussion
### Failure Mode and Damage Processes  
At the beginning of the experiment, the specimen RSL-1 is basically in the elastic range with no obvious change. With the increase of displacement, the specimen enters the plastic stage from the elastic stage. When the displacement reaches 24 mm, varnished leather bulging appears outside the right flange of channel B steel (as shown in Figure 6a). When the displacement reaches \(-30\) mm, the varnished leather of the inner panel of the stiffened ribs in the area of link and the bolt position next to the stiffened ribs on the upper side will be bulging (as shown in Figure 6b). As the displacement reaches 30 mm, the lateral flange on the front side of channel A steel shows the bending phenomenon of stiffening ribs to the inside (as shown in Figure 6c). When it was in the second cycle of 30 mm, the lacquer skin of the flange of channel A is bulging, and that of the channel steel of B side is bulging, and the peeling area of lacquer skin is further expanded (in Figure 6d). The overall deformation of link continues to increase as the displacement continues to increase (as shown in Figure 6e). When the displacement reaches \(-60\) mm, the varnished leather of the web plate of the upper bolt position of the stiffening rib of channel B steel falls off completely (as shown in Figure 6f). When the displacement reaches 72 mm, the web is torn and the specimen is damaged (as shown in Figure 6g). Figure 5: Loading Protocol. Figure 6: \(Cont.\)There are similar experimental phenomena between specimen RSL-2 and specimen RSL-3.When the displacement reaches \(-\)15 mm, the bolt is under stress and noise accompanied the course of bulging. The central flange of channel B steel is slightly bent outwards (as shown in Figure 7a). When the displacement reaches \(-\)25 mm, both channel A and channel B show flange bending deformation, and the lower side flange of the link is curved inward (as shown in Figure 7b). When the displacement reaches 40 mm, the lacquer skin on the inner side of the right flange on the lower side of the channel B steel cracked and bulged (as shown in Figure 7c). When the displacement reaches \(-\)55 mm, the lacquer skin of web plate of channel A and B steel bulged. As the displacement reaches \(-\)74 mm, the load will no longer continue to increase and the experiment stopped (as shown in Figure 7d). Figure 6: Failure modes of RSL-1. (**a**) vanished leather bulging; (**b**) vanished leather bulging; (**c**) flange bending; (**d**) lacquer skin bulging; (**e**) overall deformation increase; (**f**) vanished leather falls off; (**g**) web damaged. Figure 7: _Cont._  
As previously mentioned, both channel A and channel B steel of specimen RLS-4 show flange bending deformation, and the upper lateral flange of the connection part is all curved inward as the displacement reaches \(-28\) mm (as shown in Figure 8a). When the displacement reaches \(28\) mm, varnished leather bulging appears outside the right flange of the channel A steel (as shown in Figure 8b). When the displacement reaches \(34\) mm, the bending deformation of upper and lower flanks at the joint of channel steel of A and B surface continues to increase (as shown in Figure 8c,d). When the displacement reaches \(-55\) mm, the painted skin of web plate of channel A and B steel bulged. When the displacement reaches \(-72\) mm, the load will not continue to increase until the test stops. Figure 8: Failure modes of RSL-4. (**a**) flange bending; (**b**) vanished leather bulging; (**c**) flange bending; (**d**) flange bending. Figure 7: Failure modes of RSL-2. (**a**) flange bending; (**b**) flange cured inward; (**c**) lacquer skin cracked; (**d**) specimen damaged. Samples RLS-5 to RLS-8 have similar experimental phenomena as what mentioned before, which are not described here one by one.