Based upon the Morris and Fenves yield criterion for space frameworks, two initial force schemes are presented to analyze the elastoplastic behavior of space frameworks. One is the initial force iterative scheme, which follows the initial stress scheme proposed by Zienkiewicz, et al. The other is a self-equilibrating force scheme, which predicts the next yielding sections and determines the corresponding load increments, deflection and internal forces of the system by solving a set of quadratic equations. Several sample problems are presented. The results show that the load deflection curves obtained by using either scheme are identical. Note that for plane frameworks, element forces and load parameters corresponding to the subsequent yielding sections are identical to those obtained by using the classical limit analysis.

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