Three-dimensional macro-modeling of beam-to-rectangular hollow section column joints under cyclic loading. Part 1: Modeling of cyclic out-of-plane behavior of single isolated plate element

A rectangular hollow section (RHS) is compact and has remarkable structural performance, and therefore, RHS tubes are regarded as efficient column members for building steel structures. While the omission of continuity plates (diaphragms) at beam-to-column joints substantially simplifies the fabrication of the beam-to-tubular column joints, it causes the joints to decrease in rigidity, and thus, to be semi-rigid owing to a local out-of-plane deformation of the column tube. Presently, there is a lack of suitable modeling for this type of beam-to-column joint that can describe the three-dimensional semi-rigid behavior of the joint. The purpose of the present study is to establish a three-dimensional macro-model of the beam-to-RHS column joints, especially under cyclic loading conditions. In Part 1 of this two-part paper, the out-of-plane behavior of a single plate element of the RHS tubular column is discussed. A spring component model for the nonlinear out-of-plane behavior of the single column plate, including the membrane action, has already been established under monotonic loading. In this study, the existing model is extended to describe the cyclic behavior of the single column plate by assuming that the out-of-plane deformation is virtually divided into elastic–plastic and membrane contributions.