Subassemblage Concept for Tall Frame Analysis

A subassemblage for use in the calculation of collapse loads for tall unbraced frames is described, and its features investigated. The subassemblage consists of one or more stories of the building. At the uppermost and lowermost floors of the subassemblage, only one-half of each beam is assumed to contribute to the subassemblage strength and stiffness. The loading and support conditions for the subassemblage closely simulate the boundary conditions present in the actual structure. The PΔ effect, the effects of hinge formation within the span of any beam, panel zone deformations, and column shortening effects may be taken into account. A computer program to calculate subassemblage behavior up to and beyond the ultimate load has been developed. The paper includes a detailed analysis of the PΔ effect.