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Florida and Removal of Seismic Design
2

Florida and Removal of Seismic Design

Florida and Removal of Seismic Design

(OP)
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.

 

RE: Florida and Removal of Seismic Design

With the whole state suject to hurricane force winds and in a low seismic activity area, I'm guessing it is assumed that wind controls all lateral designs. I don't know this for sure, but it seems logical.
An interested fact is our company is concentrated in California, but is doing more and more work in Florida. Our CA structural folks find it impossible to believe that there is no seismic requirements in Florida.
 

RE: Florida and Removal of Seismic Design

I can't address the original post, but it is conceivable that a tall heavy structure (say a masonry lined chimney) could be controlled by seismic over wind even in FL.

You say no seismic at all?

RE: Florida and Removal of Seismic Design

I was just looking at Des Moines and they say to use SDC "A". Not really "no seismic" but definitely minimizes the work.
 

RE: Florida and Removal of Seismic Design

They take the sections regarding seismic out of Chapter 16 in the Florida Building Code.
So they're gone.

RE: Florida and Removal of Seismic Design

I'm sure there are exceptions and maybe I'll run into one at some point, but I've checked it in the past and it wasn't even worth the effort to go through...wind prevails.

RE: Florida and Removal of Seismic Design


JLNJ (Structural)     
16 Aug 11 8:30
"I was just looking at Des Moines and they say to use SDC "A". Not really "no seismic" but definitely minimizes the work."

That's probably because the New Madrid fault - slightly south of  Des Moines but east towards the Mississippi river - shook the entire central US region significantly only 200 years ago:  Those series of 7+ and 8+ quakes broke chimneys as far east as Charleston SC (who have also had quakes of its own) and as far north as Ohio and north Illinois.   

But Florida?  Nothing seismic.   Well, really, nothing has fallen over due to known seismic activity.  Everything sticking up that could have fallen down had already been blown over by hurricanes, or sucked down into sinkholes.    8<)
  

RE: Florida and Removal of Seismic Design

Des Moines is several hundred miles from the New Madrid fault. Per the ICC seismic ground motion tables- the impact of the New Madrid fault is negligible that far away. A significant quake would be felt- but minimal damage would occur as a result.

Seismic values in Florida, Des Moines, most of Texas... are all similar. Seismic rarely governs in these locations.

RE: Florida and Removal of Seismic Design

So, the Hatian earthquake a few months ago was not felt in Key West or Miami?

Mike McCann
MMC Engineering

 

RE: Florida and Removal of Seismic Design

Speaking from a Queensland (Australia) perspective - on coastal sites, the cyclone design wind loads will ALMOST always govern design over seismic requirements, so a common design approach is to first design for cyclone loads and then check for seismic. However, there are certain classes of structures and sub-structures where seismic loading will be significant, if not the governing design load case - e.g. inverted pendulum structures such as elevated water tanks, and components of buildings which are inside the building and therefore not subject to direct wind load.

I don't know the Florida codes, but it would be surprising to me to remove ALL requirements for seismic design - is this in fact the case?

RE: Florida and Removal of Seismic Design

There are no seismic design requirements in Florida. I have never heard of anyone talking about even a minor shake. However we did have snow flurries once several years back.

RE: Florida and Removal of Seismic Design

2
The obvious has been stated regarding wind pressure from commonly occurring events such as hurricanes, tornadoes, and even regular thunderstorms that would control over any seismic lateral force that may be anticipated to occur here. True that this does not address interior issues such as heavy equipment anchoring, MEP and ceilings hung from roofs/floors, or the example of a slender but heavy URM smokestack.

I would assume the "no seismic design requirements in the FBC" is based on statistics which is based on history, and some pretty good geophysics knowledge of Florida. Though we only have about 150 years or so of very reliable history of our state in terms of seismic events, owing mostly to the lack of people living here and recording history, ie the factoid below. One could also state that our recorded history in terms of geology,weather, climate, etc. is a blink of an eye in terms of the history of the earth.

In the early 19th Century there were less than 35000 people living in Florida and they were concentrated in the ST. Augustine (north east coast) and Apalachicola River (Panhandle) areas. So if an earthquake happens in the Florida woods and nobody is around to write it down....

See the attached scans of a geology of Florida textbook that have probably the most amount of info I have ever found on the subject.



 

RE: Florida and Removal of Seismic Design

(OP)

Quote:

I'm sure there are exceptions and maybe I'll run into one at some point, but I've checked it in the past and it wasn't even worth the effort to go through...wind prevails.

Depending on building importance and soil classification, a structure in a high-wind region can still fall under Seismic Design Category C, which introduces a lot of detailing requirements, regardless of the seismic risk.  So, I guess Florida doesn't think these requirements are important, since I would assume some structures in soft soils must fall in the SDC C.

Also, I practice in a hurricane prone region (V = 110 mph) along the gulf coast with no history  of significant seismic events. We had a structure recently where IBC seismic loading actually governed various aspects of the lateral design, sometimes by a significant margin on elements that require the seismic over strength factor.
 

RE: Florida and Removal of Seismic Design

(OP)
Also, it seems like the IBC seismic loading would govern the lateral load on any heavy, open platform structure with little wind exposure.

RE: Florida and Removal of Seismic Design

a2mfk:  You buzzard!    Next time scan the paper the same way on both pages!!!!    8<)

So, this report (in early 1980's) lists only 5 events in the past 100 years in FL, and all below a cat 3 earthquake.   

Nothing to worry, mates (realistically).      

RE: Florida and Removal of Seismic Design

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.

RE: Florida and Removal of Seismic Design

There was an earthquake in the Australian city of Newcastle, a definately low seismicity area.

They found that virtually all structural failures were in buildings that would not meet the current wind code.

Yes, there are a few exceptions to the rule but usually buildings that are designed to resist high wind loads have a reasonable resistance to low level seismic activity.

You will also find that most countries in the world that have low sesmicity, do not check any of their buildings for earthquake loads (including the UK)





 

RE: Florida and Removal of Seismic Design

I will say this, if we were to ever have a earthquake of consequence, it would probably cause a lot of damage. We have a LOT of URM structures, most houses built in the 80s or earlier were lightly reinforced if at all. And brick on wood frame probably wouldn't do much better.

Since I obviously don't have to deal with seismic inside Florida, my exposure has been limited to a few out of state projects and that has been quite some time. I found the attached article on this subject but not much info on Florida except Orlando was mentioned in the one table.

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.

Look, Florida is hot as hell and disgustingly humid, there are gators, snakes and all kinds of bugs, we have all these annoying tourists and snowbirds, we can have major hurricanes and our thunderstorms are crazy, and the whole state is an old reef and sandbar that is barely above sea level. Oh, and we have sinkholes. The ground can just decide it has had enough and give up. God cut us a break on earthquakes.

Or the "code guys" may have just said, "Guys, in the snow and seismic part of the FBC do we really need to write down anything?"

And after some blank stares from the rest of the code writers they moved along...

RE: Florida and Removal of Seismic Design

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.

RE: Florida and Removal of Seismic Design

(OP)

Quote:

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.

 

RE: Florida and Removal of Seismic Design

(OP)

Quote:

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.

RE: Florida and Removal of Seismic Design

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.

RE: Florida and Removal of Seismic Design

(OP)

Quote:

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.

RE: Florida and Removal of Seismic Design

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

RE: Florida and Removal of Seismic Design

(OP)

Quote:

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.

RE: Florida and Removal of Seismic Design

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

 

RE: Florida and Removal of Seismic Design

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!

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