The R factor isn't meant to be applied at this level of element design. Response modification coefficients, R values, are applied to the force analysis of the lateral system based on the lateral force resisting system chosen. If your foundations support a building then R wil be chosen from ASCE 7 table 12.2-1 based on the system of the building above (e.g. braced frame, moment frame, shear wall, etc.).
The foundation loads from that analysis, column reactions, are applied to the foundation elements. You may need to apply the overstrength factor, omega, also from Table 12.2-1 to some parts of the design (connections of column bases, etc.) but generally speaking footings and piles etc. are proportioned based on the analysis results using the R you chose for the building.
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Brett King P.E., M.ASCE
Senior Structural Engineer
GHD Inc.
Lake Oswego OR
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Original Message:
Sent: 08-16-2017 05:28
From: Mohamed Fouda
Subject: Reduction factor (R) in seismic analysis by IBC 2006/ ASCE 2005
Hi Everyone,
I would like to ask about the magnitude of the reduction factor (R) in seismic analysis by IBC 2006/ ASCE 2005 when design the pile cap/shallow foundation and calculate the actual loads on each pile.