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
President
Ark Engineering, Inc.
Phone: (352) 754-2424
Fax: (352) 754-2412
