Investigation of Sand Lightweight Concrete Beam-Column Joints Subjected to Quasi-Static Loading

The use of sand-lightweight concrete made with expanded shale aggregate is prevalent throughout the United States and other developed countries. Sand-lightweight concrete is approximately twenty percent lighter than its normalweight counterpart. Lateral earthquake forces applied to a building structure are directly proportional to its mass, so the potential for better seismic performance is clear. Unfortunately, concrete made with lightweight aggregate behaves differently in key aspects when compared to normalweight concrete that can negate its design force reducing advantage. Specifically, lightweight concrete is more brittle in nature than normalweight concrete and as such is less ductile. Ductility is key in seismic design because the structure must be able to absorb the energy produced by the earthquake. This study focused on determining the particular behavior of reinforced sand-lightweight concrete beam-column joints of moment frame buildings under a quasi-static cyclical loading that simulated a seismic event. Six half-scale experimental test specimens and sixty-five non-linear finite element models were used to evaluate the performance of the joints. The experimental portion of this study found that if designed and detailed in accordance with ACI 318-11 standards and if joint shear stress is kept within a reasonable limit, sand-lightweight beam column joints can perform as well as similarly built normalweight concrete specimens. This finding was true even for concrete compressive strengths up to 8000 pounds per square inch. The parametric finite element modeling portion of this study showed the effect on joint performance by varying the following four key parameters: the compressive strength of concrete, the amount of joint shear reinforcement, the longitudinal beam steel reinforcement ratio, and the axial load applied to the column.