A Collapse Mechanics-Based Criterion for the Optimal Proportioning of Steel Moment Frames Subjected to Earthquakes

Abstract

Given a certain steel budget, what is the optimal way of distributing it over the height of a steel moment frame building to maximize collapse resistance during earthquakes? An optimality criterion based on the mechanics of collapse of steel moment frame buildings is developed to address this question. The method is used to reproportion the steel moment frames of an existing 18-story steel moment frame building, keeping the total steel tonnage about the same as that of the original building. The response of the reproportioned building to 18 near-source ground motion records from past earthquakes and synthetic ground motion histories at 636 sites in southern California under a simulated 1857-like great San Andreas Fault earthquake is compared with that of the existing building to demonstrate the effectiveness of the methodology. Design tables of optimal beam and column plastic moment distributions are presented for use in the design of 10-, 20-, 30-, and 40-story buildings with 2-bay and 3-bay moment frame configurations.