Bracing Requirements of Plane Frames

Abstract

Secant formulation for the elastic‐plastic limit analysis of planar frames with rigid and semirigid connections is presented. A series of one‐, two‐, three‐, and 14‐story braced frames are considered. The results of limit analysis of these frames for different bracing areas are included. In evaluating these results, both strength and serviceability criteria are considered. Based on these studies, semiempirical formulas are developed to calculate the required bracing areas for frames with type‐FR and type‐PR connections. The effect of connection flexibility in semirigid frames is accounted for by introducing a correction factor to the formula developed for rigid frames. The performance of the proposed formulas are evaluated by comparing with the results of limit analysis, and good correlation is observed. A step‐by‐step scheme is presented for easy calculation of the required bracing area. The limitations of the scheme are also identified. In the case of semirigid frames, if the connections do not have enough moment capacity to allow plastic hinges to be formed in the members, the connections must be treated as hinged.