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ASCE 7 flood impact load inflation

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The ASCE 7 flood impact loads seem to be undergoing extreme inflation over the last 3 editions due to an decrease in the recommended duration if impact.


The 7-98 Standard recommended a duration of 1 second which in our area could result in a impact load of about 1kip.

The 7-02 version dropped the recommended duration to about 0.1 second which can result in loads of around 4 kips.

The 7-05 version is recommending durations of around 0.03s which can result in loads of around 12 kips.


Does anyone know of a recent design guide or perhaps a contact person on the Chapter 5 subcommittee that could help explain the reasoning behind this escalation and how the new rational method in the 7-05 commentary should be applied? The FEMA Coastal Construction Manual has not been updated in several years and still references the 1s duration of impact and the older ASCE 7-98 load combinations.


Christopher Banbury, PE



Ark Engineering, Inc.

PO Box 10129, Brooksville, FL 34603

22 North Broad ST, Brooksville, FL 34601

Phone: (352) 754-2424

Fax: (352) 754-2412