A decade ago, Jack P. Moehle got a bee in his bonnet about the sorry state of the approvals process for performance-based seismic design of tall buildings. As a peer reviewer of several projects, he witnessed a contentious permitting process that pitted structural engineers against each other and worried many building officials. In at least one city, they were so wary of PBSD that they refused to consider any tall building designed using the high-end method, which its supporters see as the future of seismic engineering.
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The guide, hailed by practitioners as a big step toward the production of better-performing, more economical and more constructible tall buildings in seismic zones, presents a recommended alternative to the prescriptive design procedures contained in codes. It also serves as the basis for designs intended to achieve higher performance than mandated by code. The project brought forward many recent advances in seismic engineering, including ground-motion representation and structural modeling technology.
Based on best practices and agreed-upon definitions and methods, the guide presents a consensus-based framework for PBSD. In the past, "each project had its own set of project-specific criteria, and building officials in different cities were responding differently," says Moehle. The UC Berkeley professor of engineering calls the project his most important in more than 30 years of research.
The guide already has eased the approvals process. "There is a much greater comfort level on the part of building officials to accept PBSD," says PBSD pioneer Ron Klemencic, president of Magnusson Klemencic Associates, Seattle.
Moehle's work is not yet done. During the project, he found examples of incongruent research, code language and practices. He is now part of an effort to rectify that through model-code changes.
