This paper considers the problem of premature instability of optimised space frames. As loads are increased, plastic hinges start forming in succession, resulting in the possible instability of the deteriorating frame before a plastic mechanism is reached. The problem is formulated, and a method of analysis, which provides a lower limit on the actual failure load, is presented. The analysis establishes the order in which the plastic hinges form, but avoids the repeated inversion of the frame stiffness matrix. The method developed is applied on two simple space frames.
M. M. K. Khalifa