Since the mid-1990s, a type of steel column that commonly features slender cross-sectional elements has become more prevalent in buildings along the West Coast of the United States and in other seismically active regions. Although these columns have complied with modern design standards, our understanding of how they would perform during an earthquake has been limited by a lack of full-scale testing.
Using an earthquake-simulating device known as a shake table, researchers at the National Institute of Standards and Technology (NIST) and the University of California San Diego (UC San Diego) identified deficiencies in the performance of these columns, with many buckling prematurely. Based on the results, documented in a NIST report, and a detailed analysis of the test data, the researchers devised new limits for column slenderness, described in a paper published in the Journal of Structural Engineering last April. The American Institute of Steel Construction (AISC), a standards organization, has adopted the proposed limits in a draft for public feedback of the 2022 edition of AISC 341, a standard that provides guidance on designing earthquake-resistant steel buildings.
“A lot of current design provisions are based on scaled-down column tests or a very small number of full-scale tests. But the full-scale testing we conducted here has allowed us to begin filling in the knowledge gap regarding the performance of these kinds of columns under extreme loading conditions,” said NIST structural engineer John Harris. “The results have supported the development of enhanced guidance for new buildings and could inform decision making on modifying columns in existing structures.”
Throughout the 1990s, engineers gained substantial insight into the way structures respond to real earthquakes, such as the 1994 Northridge earthquake, which devastated the greater Los Angeles area. As a result, building codes began to impose strict requirements on the degree that buildings could sway during earthquakes — a measure known as story drift.