Elasto-Plastic Behavior of Single-Story Single-Bay Orthogonal Steel Space Frame Under Angular Earthquake

A study of the elasto-plastic behavior of single-story single-bay orthogonal steel space frame under an angular earthquake ground motion is investigated. The building frame is subjected to a horizontal earthquake ground motion not aligned with the building’s principal axes. Such a frame can develop biaxial bending and torsion in its members. The governing differential equations of equilibrium for the typical biaxially loaded sway beam-column are presented and iteratively solved using a finite-difference scheme. The effects of warping and residual stresses are accounted for in the analysis. The equations are used to predict the quasi-static elasto-plastic response of the frame when subjected to an angular concentrated horizontal load applied at the frame top. A pushover analysis model for the space frame is used to assess the effect of the angular load on the frame response. An experimental shake table study is conducted on a model steel space frame and subjected to sinusoidal and El Centro base excitations with three different frame orientations. The transient dynamic frame response is compared with that predicted using SAP-2000. The model frame is then tested at a 30-degree angle with a quasi-static point load up to collapse to compare with pushover analysis. Upon validating the theoretical analysis, a study of full-scale frames with HSS or wide flange members is carried out to determine the influence of the angular load on the frame response. The study conducted shows that the performance of the single-story single-bay steel space frames is adversely affected by the application of horizontal angular earthquake loading.