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Seismic Design of Foundations

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Kussro

Structural
Jul 26, 2011
4
For a structure assigned to SDC "D" does the overstrength factor apply to the design of the foundations for the columns in a Special Concentric Braced Frame (SCBF)?
 
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ASCE 7-05,Commentary C9.5.2.6.2.11 Elements supporting discontinuous walls or frames - The purpose of the special load combinations is to protect the gravity load-carrying system against possible overloads caused by over-strength of lateral force resisting system.
IBC - 2003: Per Table 1616.5.1.1, Special load combinations would apply to structures with irregularity type 4 in SDC B, C, D, E, and F.
Source - Seismic Design of Reinforced Concrete .... by Paulay & Priestley, Chapter 9, Foundation Structures: A clear distinction must be made between elastic and inelastic response for both the superstructure and the foundation system. To enable a ductile superstructure to develop its full strength under the actions of lateral forces, and hence the intented ductility, the foundation structure must be capable of transmitting overstrength actions from the superstructure to the supporting soil or piles.
Based on the commentary given in ASCE 7, guidelines given in Paulay's book, and from the point of providing a continuous load path, I feel the foundations supporting discontinuous walls or frames in SDC B thru' F should also be checked using special seismic load combinations.
 
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