Selection of a Trial Column Section

A member subjected to both axial and bending loads must comply with the AISC interaction equations (1.6-1a), (1.6-1b), and (1.6-2). The normal procedure for designing a column so loaded is to select a trial section and check it for compliance with one or more of the interaction equations. Since the checking is an arduous task, it is desirable that the number of checks of trial sections be held to a minimum. The process can be extremely discouraging when designing a structural system where preliminary beams and columns must be sequentially selected and tried several times, as in a rigid framed tiered structure. A method is presented which allows a column section to be selected quickly and in a direct manner. The selection will always be a practical one (approaches closely the value of 1.0 in the interaction equations) and usually is the most economical. It may be used for preliminary design without further checking by the column equations. The members of the final structural system, however, should be formally checked by the interaction equations for the record computations.