Loading Protocols and Backbone Curves: U.S. and Japan Perspectives
Bruce F. Maison, Kazuhiko Kasai, Matthew Speicher
With the gaining popularity of performance-based engineering, it is essential to have reliable estimates of component (e.g., steel beam or column) performance under actual earthquake loading demands. In the United States, a component backbone curve representing the inelastic force-deformation behavior is typically taken as the envelope of laboratory test hysteresis data. A shortcoming is that the backbone curve is dependent on the loading protocol used in the tests, and customary standard tests can lead to overly pessimistic estimates of component behavior. This can cause rejection of buildings that would otherwise be considered acceptable should component behaviors be based on tests using realistic earthquake loading patterns. It is therefore recommended that future tests consider realistic earthquake loading protocols so that the results are best suited for performance-based engineering. Alternatively, a Japanese skeleton curve concept using decomposition of standard test data may be a way to leverage the current wealth of available standard test data thereby providing a better description of component seismic performance than simply taking an envelope of standard test data. The skeleton curve consists of horizontally stacked hysteretic loops that resemble a monotonic curve. To demonstrate this concept, a simple adaptive component model incorporating skeleton curves is presented. The model accounts for both in-cycle and cyclic strength degradation. It is shown to mimic observed monotonic and cyclic behaviors depending on the displacement loading history. The model is simple and can be easily incorporated into structural analysis computer programs used for building evaluation. Ongoing work includes more validation of the adaptive model as well as possible extension to other materials such as reinforced concrete and wood components.
Proceedings of the 17th World Conference on Earthquake Engineering
, Kasai, K.
and Speicher, M.
Loading Protocols and Backbone Curves: U.S. and Japan Perspectives, Proceedings of the 17th World Conference on Earthquake Engineering, Sendai, JP, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=929714
(Accessed December 8, 2023)