The use of modified amplification factors in assessing in-plane instability of unbraced frame structures
Date
2010-04-08T12:35:15Z
Authors
Joseph, Stephen Brendon
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Abstract
Kemp’s (1999) amplification factor method is tested in its ability to model the
nonlinear in-plane behaviour of several unbraced rectangular steel portal frames. The
evaluation is by means of comparison to results obtained from physical tests and
advanced finite element analyses of the portals. The failure load calculations are
favourable, but the load-“amplification factor” (load-X) relationships differ
substantially between test methods. These differences are ascribed to Kemp’s bilinear
representation of the load-X relationship, the tendency of his amplification factor to
underestimate loss of elastic flexural rigidity, and the assumption of a single
amplification factor for an entire structure. Modifications are proposed to the limits
of the bilinear load-X graph, and to the failure criterion of Kemp’s method. These
modifications maintain the simplicity and accuracy of the failure load prediction,
improve the modelling of the load-X relationship, and provide a means of recognising
upper and lower bound collapse loads