Experimental and analytical investigation of arched steel haunches under cyclic loading

In this study, the cyclic performance of innovative less-invasive haunches, as fuse elements, called Arched Steel Haunches (ASHs) for seismic retrofitting of reinforced concrete frames was investigated. The axes of these haunches are like circle arcs, which are more geometrically compatible with architecture than straight haunches. Two physical models were proposed to identify the ASHs' behavioral curves. To evaluate the models' accuracy, a series of cyclic tests were conducted on eight ASH specimens in two groups with various axial eccentricities equal to 0.1 and 0.2 of the nominal haunch length. Seven specimens with double cross-sections and various connectors, and later as a single cross-section, were fabricated and then subjected to cyclic loading. The experimental results showed that ASHs as ever subjected to the buckling phase at a larger deformation, more desirable cyclic performance would be achieved in compression and even tension. Furthermore, the specimens without overall buckling potential as a fuse, by reaching their fully plastic strength, exhibited a more symmetrical hysteretic behavior and could upgrade the energy dissipation and maximum equivalent damping ratio about 3 and 2 times, respectively. Different behaviors in tensile and compressive ultimate strength and plastic stiffness were more considerable when the initial axial eccentricity was decreased. It should be noted that the results of this pilot study will be used for further research on the experimental behavior of RC beam-column joints.