Equivalent Frame Analysis of Unbraced Concrete Frames


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Title: Equivalent Frame Analysis of Unbraced Concrete Frames

Author(s): M. Daniel Vanderbilt

Publication: Special Publication

Volume: 72


Appears on pages(s): 219-246

Keywords: beams (supports); columns (supports); connections; deflection; frames; lateral pressure; mathematical models; multi-story buildings; reinforced concrete; structural analysis.

Date: 12/1/1981

A reinforced concrete building may be approximately analyzed as a series of crossing plane frames. The beam-column connections can be modeled using either the lateral-torsional member or equivalent beam width techniques. The lateral-torsion-almember definition and associated frame and member modeling rules which comprise the equivalent frame method of ACI 318-77 were calibrated against tests of real structures while methods of computing effective beam widths are based largely on theoretical analyses of elastic plates. Comparisons of the two methods in analyzing a test building for lateral loads are given. Both methods can be forced to produce computed deflections which agree favorably with test data. However, compatibility of lateral de-flections of separately analyzed parallel frames at the same floor level is not assured. Two methods for forcing compatibility of lateral deflections at each floor level of a building are described and shown to produce computed deflections which compare favorably with test data. Limitations of both equivalent frame and equivalent beam width methods are discussed.