Optimum Stiffness-Weight Design of Peripheral and Ladder Frames

Abstract

The equation for the torsional stiffness of a rigid jointed rectangular plane frame is given and non-dimensionalized to provide simple comparative criteria. The effect of extreme variation in member properties is discussed. Design charts for certain cases are given. It is shown that the equation may be modified for ladder frames of uniform spacing, under certain simplifying assumptions. The equations have been applied to model frames giving good agreement with experimentally determined values. The members are analysed in terms of their stiffness-weight ratios and the weight parameter is calculated for families of peripheral and ladder frames. For frames of the same torsional stiffness the optimum designs are then discussed. The effect of a constraint on minimum flexural stiffness on the optimum design of a ladder frame is discussed.