Evaluation of Moment Redistribution Demand in Continuous Constructions under Gravity and Seismic Loads

In the current practices of structural design, the concept of moment redistribution in conjunction with linear analysis is well known and widely accepted. There are numerous studies and various references that deal with the issue and different codes propose various provisions for the amount of permissible redistribution. Despite numerous advantages, there are some limitations in the available work about this subject. Nearly all of these studies are restricted to symmetric multi span continuous beams subjected to static gravity load. In reality, continuous beams lie in the structural frames, symmetric configuration may not happen, and more importantly, lateral load also exist. Most of available works assume that a single plastic hinge to form at the center of joints while this study suggests that two distinct plastic hinges to take shape on both sides of an internal support of a frame. Consequently, relevant conclusions of available works suffer serious limitations and shortcomings. In this study, a continuous frame structure is considered, the effect of lateral load has been taken into account, and two distinct plastic hinges have been assumed. An attempt has been made to evaluate the redistribution demand of a continuous construction without the mentioned restrictions. For this aim, a simple solution based on virtual work theory has been used to determine the demand of plastic rotation. Problems associated with the current methods of determination of required moment redistribution are assessed and the necessary amendments are proposed.