Topology optimization of steel deck building diaphragms

Abstract

This paper improves the roof diaphragm designs in steel buildings for lateral loads, such as those from wind and earthquakes, by maximizing the in-plane stiffness. The design of floors and roofs are typically dominated by gravity loads, however, the diaphragm's ability to transfer and resist in-plane shear forces is a key element in the structure's lateral force resisting system. The steel deck diaphragms are profiled steel sheet panels attached with fasteners and are typically placed with the same orientation throughout the entire diaphragm. Through variation of the layout of the steel profile and number of fasteners, the diaphragm's in-plane shear strength and stiffness cover a large range of values. In addition, the profiled nature of a steel panels results in different in-plane stiffnesses parallel and perpendicular to the deck profile. Through topology optimization, different roof diaphragm layouts are optimized for improved lateral stiffness by selecting a bare steel diaphragm type and orientation of the panel for each element. The optimized designs are complex and are interpreted into realizable steel diaphragm designs. Comparison of the designs finds that the optimized design is the stiffest followed by the realizable design. The traditionally designed diaphragms are much more flexible than both the realized and optimized designs. This work is part of a larger initiative (steeli.org) that aims to better understand and improve the role of diaphragms in the seismic response of steel buildings. Future work includes studying the non-linear behavior of optimized diaphragms and optimization that includes stress constraints to control initial yield.