Seismic protectionCold-formed steel construction withstands seismic challenges better than expected

Engineering researchers have provided the building blocks necessary for enabling performance-based design for cold-formed steel buildings, structures that have shown in shake-test experiments at the State University of New York at Buffalo to withstand seismic loading much better than previously expected.

Light, strong, and easy to construct cold-formed steel (CFS) buildings are repetitively framed with light steel members and conform to well-defined seismic design codes.

A Purdue University release reports that until this study, however, engineers and builders significantly underestimated the seismic strength of cold-formed steel structures. In fact, following the shake-table experiments at maximum-considered earthquake levels, little to no damage to the structural system was observed and the test specimen had no residual drift.

“There is a large difference between the idealized engineering models of the seismic lateral force resisting system and the superior performance of the full CFS building system,” said project leader Benjamin Schafer, professor and chair of the Department of Civil Engineering at Johns Hopkins University. “In other words, we’ve shown that CFS structures hold up extremely well under earthquake conditions and that it is possible to design CFS structures even more efficiently.”

Funded by the George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES) and the steel industry, the project is aptly named CFS-NEES. The CFS-NEES findings were discussed in two papers presented during Quake Summit 2014, which is part of the 10th U.S. National Conference on Earthquake Engineering on July 21-25 in Anchorage.

The study produced basic data on the hysteretic performance of connections, members, assemblages, and full CFS buildings, enabling true “performance-based design” for CFS buildings. Performance-based design (PBD) is an efficient and increasingly important technique that allows engineers to design structures to withstand specific seismic loads.

“Our aim in the CFS-NEES project has been to develop experimental benchmarks, fundamental characterizations, and generally demonstrate efficient means for modeling cold-formed steel structures, which are inherently complex,” Schafer said.

Until this study, current seismic response systems primarily used mechanisms independent from CFS members, such as bearings or straps, to resist seismic demands.

To acquire the key data on CFS member response to earthquake shaking stress (commonly referred to as cyclic loading), the American Iron and Steel Institute in collaboration with the CFS-NEES effort, funded a companion project to provide explicit data on the cyclic response of cold-formed steel members.