ELASTOPLASTIC BEHAVIOR OF PANEL ZONE IN STEEL BEAM-TO-CONCRETE FILLED CIRCULAR STEEL TUBE COLUMN MOMENT CONNECTIONS: Model of restoring force characteristics

This paper proposes a new practical model of a restoring force characteristic on the panel zone within steel beam-to-concrete filled circular steel tube column moment connections for predicting the elastoplastic behavior of the panel zones including strength reduction after ultimate strength. The proposed model for a skeleton curve is provided as a multi-linear model having a cracking strength point, a yield strength point, an ultimate strength point and strength reduction points for 95%, 90% or 80% of ultimate strength. The skeleton curve model up to the ultimate strength point is based on the previous shear force-deformation model proposed by the writer, while the deformations of these strength reduction points is provided as new regression formulations obtained from previous test results. The writer proposes a new hysteresis loop model including stiffness reduction. The proposed models agree approximately with experimental results up to large deformations.