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The validity of the simplified limit design method for the design of structures. Parkhill, Douglas Leonard

Abstract

Practice in the field of limit design has tended to place certain restrictions on structural loading patterns in order to simplify the calculations involved in the limit design procedure. The loads considered in this simplified approach are assumed to either remain constant and fixed, or if they vary then this is to be in such a manner that their magnitudes stand in a constant relationship one to the other. Actual structural loadings seldom satisfy these restrictive conditions and the question naturally arises as to whether or not this simplified limit design procedure is valid for general use in practical design problems in which external loads may be wholly independent in their individual actions. This question is investigated in the present paper through the examination of several practical forms of structure which portray the more adverse conditions of independent and variable loading to be met in practice. These structures are, respectively, single and double bay gable bents of lightweight construction, and two forms of multispan bridge girders. The study indicates that all of these structures are able to support the ultimate loads predicted by the simplified limit design method; the actual ultimate loads exceeding the predicted values by up to twenty percent. It is concluded that structural failure in practice can always be expected to occur within acceptable limits of the ultimate load capacity as predicted by the simplified method.

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