Deformation capacity and demand in structural steel systems

Structural steel design requires the selection of member sizes based on material strength limits obtained from uniaxial tension tests. Traditional design procedures as well as the material properties referenced during these design procedures do not necessarily address either the loading conditions or the structural element behavior accurately.; Most structural elements are subjected to a more complex three dimensional stress condition than that of pure uniaxial tension. Material deformation is not only a function of the stress state but also subject to specific anisotropic material properties, as well as the effects of production and fabrication processes.; The use of the uniaxial tension test in traditional design is compared to the demands made on structural elements due to three dimensional stress states. The effects of structural steel production, structural member and assembly fabrication, anisotropic differences in deformation capacity of structural steels, and the effects of triaxiality are presented, and related to the deformation demands made on structural steel elements within a rigid connection.; Two column sections, a W14x426 and a W14x176, are considered in a finite element analysis of a rigid connection. A global analysis is used to determine the member lengths for the solid model, based on the inflection points of the members from the global analysis. The parameters for the analysis include material types ASTM A36 and A572 (Gr.50). The load cases for the solid model are a load case which includes an axial load in the column, and a moment applied to the beam. The connections are modeled elastically, with multilinear material properties, and by considering separate materials for the beam and the column.; The results of the finite element analyses of a rigid connection are presented in terms of strain distributions rather than the more traditional stress level approach. It is concluded that the most severe deformation demand of a rigid connection is located in the beam flange, in the vicinity of the beam-column interface, followed by the beam-column interface, the k-line region in the column, and the column flange midthickness region.; It is shown that realistic assessments of the behavior of connection elements and the structural members that frame into the connection cannot be obtained without taking three-dimensional restraint effects into account.