Recent developments in plastic design analysis of steel moment frames

Plastic Design Analysis (PDA) is a recently developed, case specific procedure that aims at direct displacement based lateral design of steel moment frames. PDA is a byproduct of the classical Plastic Analysis and Design (PAD) method of approach. While PAD can only estimate the ultimate loading at failure, PDA has been developed to address such important design issues as the P-delta effects, sequential hinging and lateral displacements at incipient collapse. This is achieved by, first relating the global stiffness of the sub frames of the structure to the most critical target drift and then providing as much capacity as demand imposed on the elements of the frame. Such schemes embrace envelopes of several initial designs within which member sizes could be rearranged for any purpose while observing the prescribed performance conditions. In the interim, a practical method of forecasting the sequence of formation of the plastic hinges is introduced. PDA, as introduced in this article, is based on several complimentary design concepts and novel formulae that have not appeared in the literature before.

► Modification of sequences of formations of plastic hinges in order to reduce maximum drift at ultimate loading.
► Introduction of the equivalent portal frame for the preliminary assessment of system response prior to failure.
► Presentation of several generic and numerical examples dealing with maximum plastic displacements at incipient collapse.
► Introduction of new formulae for the plastic design of regular portal frames.