Time-dependent behavior of RC slab-column connections under high sustained loads

Abstract

Reinforced concrete (RC) flat-plate slab-column connections may be exposed to high sustained stresses under gravity loads far exceeding the typical service-level stresses due to design errors, construction defects, or material deterioration. If the connections fail, then collapse of the structure could occur. Plain concrete can fail when exposed to sustained compressive stress in excess of 75% of its short-term strength. However, very little research has been conducted on the time-dependent strength and stiffness characteristics of RC slab-column connections under high sustained loads. This paper presents the experimental results of eleven aged slab-column connections under sustained concentric and eccentric gravity loading. The specimens were constructed at a 0.47-scale and had slab tensile reinforcement ratios of 0.64% and 1.0% without using shear reinforcement. Three specimens were loaded to failure in a short time, while eight specimens were tested for periods of approximately 45 days under high sustained loads (83% to 98% of their peak capacity). Test results showed that high sustained loads may lead to an eventual failure; however, the level of sustained load needs to be very close (∼95%) to the short-term capacity. Under the sustained loads, the deflection of specimens increased by 18% to 39% of the initial deflections. The deflection and steel strain creep rate approximately followed a logarithmic function, but there was a greater increase in deflection than steel strain. A sharp increase in deflection due to tertiary creep occurred only 2 to 3 min before failure, leaving little warning of the impending failure.