Evaluation of Approximate Methods for the Design of Biaxiall Y Loaded Reinforced Concrete Columns

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Addis Ababa University


The ultimate capacity of reinforced concrete sections under normal force and biaxial bending moments can be represented by a three dimensional interaction surface in terms of the normal force and biaxial moments. The surface can be conveniently represented by a family of curves either on a plane of constant normal force relating the two moment components or as interaction diagram on a plane of constant angle relating the normal force and the resultant of the two moment components. However, the curves can not be described by exact and closed form mathematical expressions due to a wide variety of parameters involved in the determination of ultimate biaxial moment capacity of crosssections with normal force. Thus the systematic generation of such curves to be used for design involves obtaining sufficient number of suitable points by iteration which normally requires use of computer programs. In the absence of such facilities, the use of approximate methods becomes mandatory. There are different approximate methods adopted in different codes for the design of biaxially loaded reinforced concrete columns and the purpose of this thesis work is to assess and evaluate the proximity of some of these approximate methods with the exact solution. The approximate methods evaluated include those recommended by EBCS-2 [1), CPllO [2,3) and ACI [4,5).