Low-Cycle Fatigue Properties and Model for Flexure-Shear Critical Reinforced Concrete Columns Considering Cyclic Damage Effects

AbstractTo investigate the low-cycle fatigue properties of flexure-shear critical columns, nine reinforced concrete (RC) columns were subjected to monotonic and constant-amplitude cyclic loading. The effects of loading displacement amplitudes and shear span ratios on failure modes, load-displacement response, strength degradation, and energy dissipation capacities of RC flexure-shear columns were explored. Test results indicated that the low-cycle fatigue and damage properties of column specimens were dependent on the displacement amplitudes. The cumulative damage effects and shear effects induced by cyclic loading were intensified with increasing displacement amplitudes and decreasing shear span ratios, respectively, resulting in flexure-shear failure. The maximum loading cycles (i.e., fatigue life) of low-cycle fatigue specimens decreased apparently as displacement amplitudes increased, with a maximum variation range of 98.8%. Meanwhile, the low-cycle fatigue characteristics of flexure-shear columns were also relevant to energy dissipation capacities. The normalized energy dissipation capacity of specimens diminished exponentially with increases in loading cycles due to the cyclic effects, and the cumulative energy dissipation decreased significantly as displacement amplitude increased. Test columns had a maximum degradation rate of energy dissipation up to 0.43 times that of the first hysteresis cycle. Furthermore, a new fatigue-life model was proposed based on the cumulative damage properties of cyclic loading columns. This model considered the effects of deformation and energy dissipation on low-cycle fatigue properties, providing a basis for evaluating the damage properties of flexure-shear critical columns subjected to low-cycle fatigue loading.