Development of Criteria for the Seismic Design and Analysis of Tall Buildings in California (Abstract)
by Jack Moehle and Yousef Bozorgnia
Moehle, Jack, Yousef Bozorgnia (2007). Development of Criteria for the Seismic Design and Analysis of Tall Buildings in California (Abstract). SMIP07 Seminar on Utilization of Strong-Motion Data, p. 113 - 114.
Several west coast cities are seeing an upsurge in the construction of high-rise buildings. Many of these buildings feature framing systems, materials, heights, and dynamic properties not envisioned by our current building code prescriptive provisions. Rather than force these buildings to conform, many jurisdictions are allowing these new designs to proceed under the alternative procedures provision of the building code, which allows alternative lateral-force procedures using rational analyses based on well-established principles of mechanics in lieu of the prescriptive provisions. Most designs are opting for a performance-based approach in which a rational analysis demonstrates serviceability and safety equivalent to that intended by the code prescriptive provisions. Several questions arise in a performance-based design. What is equivalent performance? How should it be demonstrated? If dynamic analysis is conducted for a range of anticipated earthquake ground motions, how should the ground motions be selected and how should the design value determined? How should performance designs be reviewed?
The Tall Buildings Initiative is funding a range of short to intermediate-term projects in 2006-2009. The final product will be a set of written guidelines containing principles and specific criteria for tall building seismic design. The document is intended to support ongoing guidelines and code-writing activities of collaborating organizations, as well as being a stand-alone reference for designers of high-rise buildings. The main points relevant to the CSMIP program include: Selection of earthquake ground motions; Modification of earthquake ground motions to represent the design shaking level, including scaling and spectrum matching methods including considerations of epsilon and conditional mean spectra; Interactions between incoming ground motions and building foundations; and Interpretation of the results of multiple response history analyses for determination of design values.
This project is under way at the time of this presentation, including new funding from the CSMIP program. The presentation reviews the salient issues and current progress in addressing them.