Experimental evaluation of seismic response for reinforced concrete beam–column knee joints with irregular geometries

Regular reinforced concrete beam–column knee joints are typically framed by beams and columns with similar heights. However, complexities in modern architecture layouts may result in irregular geometries for the knee joint. The irregular geometry refers to significant differences in the height for the beam and the column framing into the joint. For example, the height of the beam is considerably larger than that of the column, and vice versa. Seismic performance and behavior for the regular knee joint have been well examined through previous experimental research. However, the knee joint with irregular geometry (termed here as irregular knee joint) may have different seismic behaviors compared to the regular knee joint because the irregular geometry can produce different demands, stiffness, strength, and reinforcing bond conditions. Therefore, this article evaluates seismic behavior of the irregular knee joint including failure mode, strength and stiffness degradation, deformation capacity, bond-slip of reinforcement, and energy dissipation capacity through four large-scale static cyclic tests. The test results show that in general the irregular knee joint designed to the current code has low seismic capacity due to poor bond conditions of the reinforcement inside the joint.