## 3 Experimental Results and Discussion  
### Damage Processes and Failure Mode  
The results of the strain measurement indicated that the beam segments remained elastic during the test, and the damage occurred in the links only. Table 3 summarizes the process of visually identified damage and the cause of ultimate failure. In this study, the failure of the specimen was defined as the point where the shear strength dropped to below the link beam plastic strength \(V_{\mathrm{P}}\). Paint coating bulging, web buckling, flange buckling, flange-to-end plate weld fracture, and failure mode were observed in the links. Figure 7 shows the specimens and provides a close look at the primary failure mode. During the first to third cycles of test loading, all specimens were in elastic stage, and no obvious damage phenomenon was observed. There were three stages of cumulative damages of all specimens under the low-cycle cyclic loading. The first stage was the initial stage of damage process, which was characterized by the initiation of the specimens' web yield. The yield of web spread from both ends of the link to the middle of the link increased with the loading displacement, where the web paint coating cracked or became slightly bulged. The duration of this stage was long, and cracks on the web paint coating developed continuously, which is considered to be the major stage of energy dissipation and damage accumulation. With the increase of loading displacement, the damage accumulated continually and then the process turned gradually into the second stable stage. In this stable stage, some micro-cracks appeared on the welds of Specimens L1, L2, and L6 (see Figure 7a). For other specimens, the paint coating bulged more obviously and partial paint coating tended to fall off (see Figure 7g). The surface darkening of the steel could be observed. Strain measurement indicated that the yield range slowly spread to the edge of the web. The link's shape changed from rectangular to rhombic, and slight shear deformation of the web could be observed. The last stage is the failure stage. As shown in Figure 7b, the weld cracks of Specimens L1, L2, and L6 increased gradually and tended to be the same. The final stage was the failure stage. to transfixion. However, the welds at the end plate could not continue to bear the loading due to fracture or excessive cracks. The web and end plate of Specimens L3 and L4 dislocated relatively, and the flange of these specimens came up as slight local buckling (see Figure 7c). For Specimens L5, L7, and L8, the end of flange came up as large local buckling. As shown in Figure 7e, the webs of these specimens came up as some larger buckling, which failed by shear yield. From the above-mentioned damage processes, eight specimens showed primarily three types of failure modes. The failure mode of Specimens L1, L2, and L6 was brittle failure of the link flange-to-end plate weld that cracked (see Figure 7f), which was mainly caused by the distribution of complex residual stress at the welds of the end plate due to the lack of a welding access hole. Specimens L3 and L4 failed by local buckling of the flange after shear yield of the web (see Figure 7d), which was likely caused by the energy dissipation of the link web yield coupled with the flexure yield of the flange. Specimens L5, L7, and L8 failed by shear yield of the web, which was mainly caused by the incessant interactive actions of the plastic development and deformation of the link web (see Figure 7h). In general, the failure modes of Specimens L3, L4, L5, L7, and L8 were considered to be ductile failure. As a result of the welding access hole adopted in the links, stress concentration at the weld was relieved. From the above failure mode and damage process analyses, it was observed that cracks are the major causes of damage to the EBF specimens. However, the strain gauges used cannot monitor the damage to the EBF in real time and there is a lack of research on real-time monitoring of the onset and development of these cracks in EBF structures.