Site Class F evaluation
Site Class F evaluation
(OP)
I am a structural engineer working on a small commercial building on Long Island, NY. We had assumed Site Class D for the seismic coefficients since we did not have a geotech report. The owner provided some soil borings (no geotech report, just borings) that were done about 8 years prior for a building that is directly adjacent to our site. The borings indicate there is a 15 ft thick layer of organic peat about 10 ft below grade. Looking at the IBC, this would fall under Site Class F. We have told the owner they need to get a geotech engineer to evaluate this and give recommendations. They are refusing because they said they just built the adjacent building without it (they apparently assumed Site Class D). My question is, how much of an amplification effect can we expect this to have on the seismic loads? Are we being sticklers for the Code given that we are in a low seismic area (Ss~0.3 and S1~0.1) and wind loads are probably going to govern anyway? Thoughts...





RE: Site Class F evaluation
RE: Site Class F evaluation
RE: Site Class F evaluation
Mike Lambert
RE: Site Class F evaluation
You need to have the geotechnical engineer provide an opinion on the 100' based seismic site class - it could well be that it is still D.
However, as GeoPaveTraffic suggests, the peat may be a serious issue for your foundation design with regards to settlements...a separate issue from the seismic site class.
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RE: Site Class F evaluation
RE: Site Class F evaluation
RE: Site Class F evaluation
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: Site Class F evaluation
RE: Site Class F evaluation
Usually, the local geotechnical engineers have historical boring data for deep (100 ft.) borings or they have knowledge of the local geology of your region to establish a site class.
So if you hired a geotech in our area it would be really only for asking their opinion/knowledge of the local conditions for the top 100 ft. of material.
The site class is there to adjust the base seismic demand to local overall geological conditions from site class B values which represents how the seismic energy might be magnified by those overall (i.e. deep) soil conditions. Again, the top 15 feet may not matter much to the energy delivered from 1 mile deep.
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RE: Site Class F evaluation
RE: Site Class F evaluation
RE: Site Class F evaluation
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