Practical Techniques for Elastic Secondary Stiffness Design to Provide Seismic Stability and Enhance Seismic Resilience

Published

December 2, 2024

Author(s)

Larry Fahnestock, Shitao Shi, Rafael Sabelli, Matthew Speicher

Abstract

Although ductility is a foundational attribute of seismic design, it is not sufficient to provide seismic stability. Instead, persistent positive stiffness that obviates the destabilizing effects of gravity is the essential attribute that prevents earthquake-induced collapse of a structure even at large inelastic drifts. Many ductile seismic force-resisting systems (SFRS) develop distributed yielding of fuse elements that leads to gradual softening, maintaining positive stiffness over a significant drift range. This region of positive secondary (post-yield) stiffness provides favorable performance, although this benefit is not recognized in current standards and is thus not typically considered in design. Secondary stiffness varies between different SFRS and even within different realizations of a particular SFRS. Thus, instead of allowing the post-yield stiffness of a system to be a variable intrinsic property, a more rational and reliable approach is to directly design an elastic secondary stiffness system as a companion to the primary SFRS. The secondary stiffness system is designed to have sufficient stiffness to offset the negative geometric stiffness effects while having sufficient flexibility (considering its strength) to remain elastic to large drifts. In addition to providing reliable seismic stability, the persistent elastic restoring force of the secondary stiffness system has the benefit of bringing the structure back toward its initial plumb position during dynamic earthquake response, which reduces transient and residual drifts. This paper describes a framework of practical techniques for designing elastic secondary stiffness systems to improve seismic performance and seismic resilience. Archetype building designs are presented and their performance is assessed with nonlinear analysis.

Conference Dates

December 2-4, 2024

Conference Location

San Diego, CA, US

Conference Title

18th U.S.-Japan-New Zealand Workshop on the Improvement of Structural Engineering and Resilience

Pub Type

Conferences

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Keywords

stability, seismic, steel, design, structures, building

Citation

Fahnestock, L. , Shi, S. , Sabelli, R. and Speicher, M. (2024), Practical Techniques for Elastic Secondary Stiffness Design to Provide Seismic Stability and Enhance Seismic Resilience, 18th U.S.-Japan-New Zealand Workshop on the Improvement of Structural Engineering and Resilience, San Diego, CA, US, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=959044 (Accessed April 20, 2025)