How to Optimize Structural Steel Frameworks

This chapter presents the details of an optimization strategy for the computer-automated design of least-weight structural steel frameworks, where members are sized using standard steel sections in conformity with design code requirements. The underlying features and functions of the corresponding computer software essential for application of the design strategy in professional practice are not dealt with herein, but may be briefly summarized as follows: capability to conduct first-order and second-order analysis of planar and space frameworks; account for the strength/ stability of individual members and the stiffness of the structure as a whole; clause by clause verification of the design in conformance with all the relevant provisions of the governing steel design code, for example, American Institute of Steel Construction (1989, 1986) and Canadian Standards Association (1984); automatic sizing of members using commercially available standard steel sections; account for a broad range of section shapes (e.g., W, T, hollow-box, single and double angle, etc.); determination of local buckling classifications of member sections; calculation ⋅ of effective length factors of members; calculation of the unbraced compression flange length of flexible members; account for fixed, pinned, spring, and roller supports, as well as for pinned and bolted connections; account for various gusset-plate thicknesses for back-to-back double-angle sections; account for strong-axis and weakaxis bending of member sections; capability to specify common section properties for groups of members, to impose limitations on section depths, and to fix the section properties of selected members; and account for a variety of nodal and member load types, as well as for effects due to temperature change and support settlement. A computer software system based on the optimization techniques described in this chapter, and which incorporates all of the foregoing features and functions (Grierson and Cameron 1994), is employed to design several structural steel frameworks, some from professional practice, to illustrate the scope and effectiveness of the design optimization strategy.