New York City Base Wind Speed??? 1

[rolkamatic]

Does anyone know why New York City when it published its new building code in 2008 made the base wind speed in the city to be 98 mph. Per the 2005 ASCE 7 the wind speed across Manhattan was somewhere between 103 and 110, depending on where you interpolated on the wind speed map. With the 2010 ASCE 7 it is now 115 for a Category II building. Was this NYC BC code prescribed value based on any analysis of historic weather data? Was it selected so that the city was not a code prescribed Hurricane Prone Region? (We have hurricane prone regions east of us on Long Island and South of us on the Jersey Shore.) There also is an Exposure category A which for building in areas of tall building give wind speed values maybe 30% less than the previous methods.

I'm curious if what was done was based on some scientific analysis or done for political reasons, appeasing landlords and developers not to have to deal with flying debris zones.

 

[hokie66]

Probably the latter, deemed too expensive to apply the stricter provisions.

 

[bookowski]

I would put my money on the avoiding hurricane zone that you stated. Similar to how they reverted back to the 1" per 50ft rule for building separations instead of following IBC. Or why local law 11 only applies to tall buildings. You would think that NYC would have some of the more advanced codes in the US... or at least up to part but it seems like the $ has a large influence.

 

[bookowski]

And what about the fact that they still have Exposure A? This was deleted from ASCE7 in '02 as it was deemed unreliable even in highly built up city centers.

 

[TXStructural]

In the city, code wind is irrelevant unless a wind tunnel and cityscape model are used. As to why a particular base wind speed was selected, I'm quite certain it was political.

 

[rolkamatic]

Thanks for the input everyone.

Bookowski, "You would think that NYC would have some of the more advanced codes in the US."

You have no idea... Before the 2008 Code was adopted, the effective code dated from 1968 it was most likely the most outdated archaic and unorganized code in the country. Unorganized due to so many amendments and revisions none that substantial or comprehensive, before that was 38 and many building needed to comply with that. A real regulatory patchwork.

In terms of wind tunnel studies I've only seen them on building in excess of 400ft, and there is no requirements. They seem to get done when the curtain wall contractor and structural engineer thinks there can be a savings in terms of more accurate wind design values.

 

[bookowski]

I'm aware and agreed - wind tunnels are only typical at about 30+ stories.

The NYC Code committee is currently taking recommendations for changes to the revision of the code. Unfortunately a lot of people on that committee are related to real estate rather than engineers.