Design of Seismically Resistant Tree-Branching Steel Frames Using Theory and Design Guides for Eccentrically Braced Frames

The International Building Code (IBC) and the 
California Building Code (CBC) both recognize four basic types of 
steel seismic resistant frames; moment frames, concentrically braced 
frames, shear walls and eccentrically braced frames. Based on 
specified geometries and detailing, the seismic performance of these 
steel frames is well understood. In 2011, the authors designed an 
innovative steel braced frame system with tapering members in the 
general shape of a branching tree as a seismic retrofit solution to an 
existing four story “lift-slab” building. Located in the seismically 
active San Francisco Bay Area of California, a frame of this 
configuration, not covered by the governing codes, would typically 
require model or full scale testing to obtain jurisdiction approval. 
This paper describes how the theories, protocols, and code 
requirements of eccentrically braced frames (EBFs) were employed 
to satisfy the 2009 International Building Code (IBC) and the 2010 
California Building Code (CBC) for seismically resistant steel frames 
and permit construction of these nonconforming geometries.

 





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