Eccentricity and slenderness ratio effects of arched steel haunches subjected to cyclic loading; experimental study

This paper investigated the cyclic performance of arched steel haunches as a new strategy in the seismic retrofitting of reinforced concrete frames and focused on the slenderness ratio effect. A series of cyclic loading were conducted on six test specimens in two groups with the same nominal length and different axial eccentricities of 0.1 and 0.2 nominal length and with out-of-plane slenderness ratios of 138, 69, and 16. Experimental results indicated that the slenderness ratio played a very important role on cyclic performance in compression and even tension, so that a more desirable hysteretic behavior was achieved when the overall buckling potential was restricted. Therefore, by reducing this ratio, the maximum compressive and tensile strengths increased up to 1.78 and 1.28 times, respectively, and also the dissipated energy and maximum viscous damping upgraded up to 3.32 and 1.43 times, respectively. More difference in tensile and compressive behavior for ultimate strength and plastic stiffness was observed, when the initial eccentricity decreased. Also, with twice increase in the initial eccentricity, the cross-sectional area effect on the maximum strength and plastic stiffness decreased, especially in tension, so that despite the same slenderness ratio and 70% increase in cross-sectional area, these values in tension descended up to 1.31 and 3.5 times, respectively. In addition, the compressive plastic stiffness degraded about 77% due to more degradation in plastic strength.