Direct strength design of cold-formed steel members with perforations.

摘要

Cold-formed steel (CFS) structural members are commonly manufactured with holes to accommodate plumbing, electrical, and heating conduits in the walls and ceilings of buildings. Current design methods available to engineers for predicting the strength of CFS members with holes are prescriptive and limited to specific perforation locations, spacings, and sizes. The Direct Strength Method (DSM), a relatively new design method for CFS members validated for members without holes, predicts the ultimate strength of a general CFS column or beam with the elastic buckling properties of the member cross-section (e.g., plate buckling) and the Euler buckling load (e.g., flexural buckling). This research project, sponsored by the American Iron and Steel Institute, extends the appealing generality of DSM to cold-formed steel beams and columns with perforations.;The elastic buckling properties of rectangular plates and cold-formed steel beams and columns, including the presence of holes, are studied with thin shell finite element eigenbuckling analysis. Buckled mode shapes unique to members with holes are categorized. Parameter studies demonstrate that critical elastic buckling loads either decrease or increase with the presence of holes, depending on the member geometry and hole size, spacing, and location. Simplified alternatives to FE elastic buckling analysis for members with holes are developed with classical plate stability equations and freely available finite strip analysis software.;Experiments on cold-formed steel columns with holes are conducted to observe the interaction between elastic buckling, load-deformation response, and ultimate strength. The experimental results are used to validate an ABAQUS nonlinear finite element protocol, which is implemented to simulate loading to collapse of several hundred cold-formed steel beams and columns with holes. The results from these simulations, supplemented with existing beam and column data, guide the development of design equations relating elastic buckling and ultimate strength for cold-formed steel members with holes. These equations and the simplified elastic buckling prediction methods are presented as a proposed design procedure for an upcoming revision to the American Iron and Steel Institute's North American Specification for the Design of Cold-Formed Steel Structural Members.