Florida and Removal of Seismic Design 2

[abusementpark]

Does anyone know the history of how Florida decided to not require use of the IBC seismic design provisions? Did they do an rigorous study to prove that IBC was overstating their seismic risk? Or was it more of a quick "common sense" judgment?

Also, I know other jurisdictions have either removed or softened the IBC seismic requirements. Any information on this as well would be appreciated.

 

[Ron]

a2mfk....nice summary. Nicely stated.

One point to also note is that any "hard rock" plates that might shift under Florida are extremely deep. The overlying limestone (ok...the geologists think it is so ratty they don't even like to call it "limestone") is soft, fissured, discontinuous and generally works like a nice cushion for deep movement.

As for Ocala...it is hot as hell in August, with little wind for relief. A personal observation from growing up there.....but like the rest of Florida...there is no equal. Any kid who grew up and went swimming in any of the local springs or limerock mines (locally called "lime pits") will agree.

 

[abusementpark]

abusementpark...most of the populous areas of Florida are in a wind zone exceeding 110 mph. A 10 mph increase in wind speed (to 120 mph) results in a 19% increase in wind load, so that usually kicks it over.

Right, but there still exists some significant areas of the state that are V<110 mph with similar seismic risk (according to IBC) to place where I practice. And the other big questions to me why did the IBC feel that all these seismic detailing requirements were necessary for structures in Category C, regardless of the seismic risk indicated by the maps? Obviously, Florida doesn't think they are important.

 

[abusementpark]

Abusement- I can only assume that PERHAPS they took the worst case scenario for Florida, which would be the center of the State, where the wind speed is only V=100mph. Say Ocala, Florida, where by the way John Travolta can fly his 747 to his house, literally. Then look at the map (see my attachment above) of probable epicenters for Florida and note that "Continued subtle tectonic adjustments withing the Osceola complex are plausible, and are the probably sources of the few Florida earthquakes." The Osceola complex is fairly close to Ocala, judging from that map which is not meant to be highly accurate. Then which will govern design, V=110mph or a mild tremor that has a 5:150 year occurrence probability.

From a geophysics standpoint, there is just not anything under or near Florida that the experts believe is unstable to the point where it needs to be considered.

Then, why did the IBC make Florida and other low seismic, hurricane prone regions design for seismic loading? Aren't these provisions supposed to be carefully considered through years of research including involvement of top seismologists, earthquake engineers, etc.?

We designed structures for only wind in many hurricane prone regions for the entire latter half of 20th century. Then, IBC comes in and now requires seismic design and we have recently found that it can actually govern some structures. Something seems peculiar about that. I wonder if more states along the gulf coast shouldn't follow the actions of the FBC, particularly in high wind regions.

 

[Ron]

abusementpark...careful...remember that codes are political documents that sometimes cause the technical provisions to take second place. The IBC is a model code....capable of adoption as it is or modified for local application. It really should be modified for local application as is done in many states, one of which is Florida. The Florida Department of Building Codes and Standards uses the IBC as a model code and makes it own revisions to produce the Florida Building Code.

 

[abusementpark]

abusementpark...careful...remember that codes are political documents that sometimes cause the technical provisions to take second place. The IBC is a model code....capable of adoption as it is or modified for local application. It really should be modified for local application as is done in many states, one of which is Florida.

Oh, I agree. It certainly seems like an insurmountable task to produce an "international" document that doesn't overlook certain design aspects of various regions.

However, some of the leaders of NSCEA don't feel this way and have strongly urged local engineering groups to not support any efforts to remove the IBC seismic provisions from the local adoption.

 

[Ron]

ab...and there are those who are equally lobbying to remove it!

 

[abusementpark]

ab...and there are those who are equally lobbying to remove it!

Yes. I guess thats why I was wondering how was Florida was able to get it out so quickly.

 

[msquared48]

Apparently there are a lot of movers and shakers in Florida. If so, why were the provisions removed? It's an oxymoron.

In part, I can see the logic, but I am still distrustful that we "Know" the seismicity of any region, let alone Florida. There are hidden faults everywhere, active and "inactive", and our documented geologic history is hardly sufficient to rule out a seismic event anywhere, really.

Mike McCann
MMC Engineering

 

[a2mfk]

Ron, not really related, but you are an Ocala native and in the business... Do you know if this project is converting an abandoned mine to a golf course? I know they have done this in Beverly Hills, FL and probably in other places. Makes for some interesting topography in an otherwise fairly flat state.

Google earth coordinates:
29°15'52.68"N
82° 8'33.02"W

It borders portions of 441 and 326, north of Ocala. It has been abandoned or unused since I have been driving by it on my way to FSU from home since 1993, and in the last year there has been a TON of earth moving and grading, and some utility work that suggests a neighborhood also. Shocked that in Ocala, in this market, they would build a new golf course and neighborhood when both markets are underwater...

Travolta's place is just east of there, can't miss that runway!