Storywise Plastic Design for Multistory Steel Frames

A rational method is developed for the plastic analysis and design of both braced and unbraced multistory steel frames. The method is applicable to the design of rectangular multistory planar steel frames with coplanar loading. A minimum section property configuration is determined to resist the factored gravity load condition alone. A story-by-story optimization procedure is then utilized to determine a favorable force distribution in the frame in order to minimize the additional steel that may be required to resist the factored combination wind plus gravity load condition. For both braced and unbraced frames the method proportions beams, columns, and braces in accordance with the 1970 AISC Manual of Steel Construction Specifications. For braced frames, the method also examines the question of where bracing members should be located, given that there is some flexibility in this regard. An iterative design procedure is used to account for the P-Δ effects. The method described is part of a larger system which also includes a consideration of elastic stress and elastic lateral deflection constraints.