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  • 1.  Near Fault Factors

    Posted 06-22-2017 08:56 PM
    I would appreciate comments and thoughts about how ASCE7 - (05/10/15) considers the old UBC near-fault(field) factors.  I'm under the impression they are already built-in with the mapped MCE spectral response accelerations and/or the Site Coefficients Fa & Fv, since you can pinpoint exactly your project location.   I have not been able to find any reference on the subject in ASCE7.  
    Do we need to disregard the 2/3Sms as Design Spectral acceleration parameters and use just Sms and Sm1 when in a near-fault area?

    Again, I would appreciate any thought.

    Ramses Sanchez Aff.M.ASCE
    Descon, Srl
    Santo Domingo, Dominican Republic

  • 2.  RE: Near Fault Factors

    Posted 06-23-2017 11:02 AM
    You are correct that near fault effects are included in the site-specific hazard data that you get from the maps or from the USGS web application. I can't point to a specific reference that confirms that, but I work in the San Francisco Bay Area where we have two major nearby faults and we do not apply any additional factors on the Ss or S1 values. You do not need to disregard the 2/3 factor.

    Brian Kehoe P.E., S.E., F.ASCE
    Associate Principal


  • 3.  RE: Near Fault Factors

    Posted 06-23-2017 11:02 AM
    My understanding is the same as your impression that since the Ss and S1 values are now mapped for specific locations, the "near-fault" factors in the old UBC are no longer applicable.  Of course the net result in areas where there previously was a near-fault factor is usually a higher loading since the site-specific Ss can be pretty large in those locations.

    Robert Kuhn P.E., M.ASCE
    Vulcan Materials Co
    Glendale CA