Are Miami high-rises in danger of collapsing in Cat 5 winds?

[zlaxier]

We saw the problems they had in Cat 1 winds with entire sides of 20 and 30 story buildings with windows smashed.

What happens if a Peak-Katrina type storm with 175mph sustained winds or a Labor Day 1935 storm with 200mph sustained winds hits. I presume on upper floors of high-rises these cat 5 winds could approach 225 mph or 250 mph or greater in gusts.

Would high-rises collapse under these wind loads?

[artist]

I wonder that myself. I knew someone years ago (like almost 30) that worked the high rises. He said he often saw the inspectors come in, green tag it and when they left certain things would be removed to be used for the next job's inspection. That always worried me. This was in the WPB area though.

[Recurve]

Some could. Most likely older, non-highrise multistory buildings would fail for sure. But I'm not a structural engineer, I just slept at a Holiday Inn Express last night.

You get buildings shaking like there's an earthquake going on and masronry structures are going to fail. Steel-beam high-rises would have less resistance once all the windows blow out, I can see having giant steel skeletons left along Brickell Ave.

But I wouldn't want to be around downtown Miami -- or on a high floor-- if a Labor Day or Andrew comes through.

[Beam]

They're built to sway to a certain extent, in order to relive stress caused by hurricane force winds. That being said, none of these structures have been tested in a legendary, high-powered Category 5 such as Labor Day, Camille, Mitch, Katrina, or Wilma. There's no way to know for sure what would happen. Hopefully, we'll never find out.

[windstorm99]

We'll you saw what catagory 1 with some gusts to 2 with wilma did to south florida imagine cat5 winds threw downtown miami i think it would be a disaster.The highest windgusts i recorded with my anemometer at around 7:45am that morning was 85mph.We got very lucky with wilma cause if she would have not gotten stuck down there would have easily seen major hurricane force winds across miami dade and broward counties.Adrian

[Category 5]

Sadly, I think theres only one way we can truely find out.

[Praxus]

Came across something interesting on google answers (can't confirm) - that wind tolerance is measured partly by pounds per square foot of pressure on the structure; and apparently this is the amount generated by different degrees of storms:

TS-----6.1 pounds per square foot
Cat1---21.9 psf
Cat2---36.9 psf
Cat3---49.3 psf
Cat4---68.6 psf
Cat5---96.1 psf

[zlaxier]

When it looked like Katrina would hit New Orleans as a Cat 5, the NWS released this bulletin. It specifically mentions high-rise buildings collapsing.

URGENT - WEATHER MESSAGE
NATIONAL WEATHER SERVICE NEW ORLEANS LA
1011 AM CDT SUN AUG 28 2005

...DEVASTATING DAMAGE EXPECTED...

HURRICANE KATRINA...A MOST POWERFUL HURRICANE WITH UNPRECEDENTED
STRENGTH...RIVALING THE INTENSITY OF HURRICANE CAMILLE OF 1969.

MOST OF THE AREA WILL BE UNINHABITABLE FOR WEEKS...PERHAPS LONGER. AT
LEAST ONE HALF OF WELL CONSTRUCTED HOMES WILL HAVE ROOF AND WALL
FAILURE. ALL GABLED ROOFS WILL FAIL...LEAVING THOSE HOMES SEVERELY
DAMAGED OR DESTROYED.

THE MAJORITY OF INDUSTRIAL BUILDINGS WILL BECOME NON FUNCTIONAL.
PARTIAL TO COMPLETE WALL AND ROOF FAILURE IS EXPECTED. ALL WOOD
FRAMED LOW RISING APARTMENT BUILDINGS WILL BE DESTROYED. CONCRETE
BLOCK LOW RISE APARTMENTS WILL SUSTAIN MAJOR DAMAGE...INCLUDING SOME
WALL AND ROOF FAILURE.

HIGH RISE OFFICE AND APARTMENT BUILDINGS WILL SWAY DANGEROUSLY...A
FEW TO THE POINT OF TOTAL COLLAPSE. ALL WINDOWS WILL BLOW OUT.

AIRBORNE DEBRIS WILL BE WIDESPREAD...AND MAY INCLUDE HEAVY ITEMS SUCH
AS HOUSEHOLD APPLIANCES AND EVEN LIGHT VEHICLES. SPORT UTILITY
VEHICLES AND LIGHT TRUCKS WILL BE MOVED. THE BLOWN DEBRIS WILL CREATE
ADDITIONAL DESTRUCTION. PERSONS...PETS...AND LIVESTOCK EXPOSED TO THE
WINDS WILL FACE CERTAIN DEATH IF STRUCK.

POWER OUTAGES WILL LAST FOR WEEKS...AS MOST POWER POLES WILL BE DOWN
AND TRANSFORMERS DESTROYED. WATER SHORTAGES WILL MAKE HUMAN SUFFERING
INCREDIBLE BY MODERN STANDARDS.

THE VAST MAJORITY OF NATIVE TREES WILL BE SNAPPED OR UPROOTED. ONLY
THE HEARTIEST WILL REMAIN STANDING...BUT BE TOTALLY DEFOLIATED. FEW
CROPS WILL REMAIN. LIVESTOCK LEFT EXPOSED TO THE WINDS WILL BE
KILLED.

AN INLAND HURRICANE WIND WARNING IS ISSUED WHEN SUSTAINED WINDS NEAR
HURRICANE FORCE...OR FREQUENT GUSTS AT OR ABOVE HURRICANE FORCE...ARE
CERTAIN WITHIN THE NEXT 12 TO 24 HOURS.

ONCE TROPICAL STORM AND HURRICANE FORCE WINDS ONSET...DO NOT VENTURE
OUTSIDE!

[stormcrow]

"HIGH RISE OFFICE AND APARTMENT BUILDINGS WILL SWAY DANGEROUSLY...A FEW TO THE POINT OF TOTAL COLLAPSE"

This didn't really sink in in 05 til I read it in this contex. Wonder if anyone has done a similar study to the one that showed a major tower in New York wouldn't survive a cat 3. (it was strenghtened). That stud showed the building would survive winds from 90 degree angles but not directly on the corners hiting 2 sides.

[Scorpion]

I wouldn't doubt it. So far in the history of this country there have been no Cat 5 strikes on major metro areas. I am scared to think what Cat 4/5 winds will do to tall buildings as they have never been tested.

[baitism]

Simple physics would point to structural collapse of older, more rigid buildings. The sheer power of those winds would create such an intense force on the top part of the building that partial or total collapse would be very likely.

[Frank2]

During Wilma and Andrew some buildings had many windows broken and that caused a great deal of internal damage - just a guess, but, the risk is far greater from this type of damage than from the entire building falling down...

[Dionne]

The ultimate failure criteria for structural steel has to do with yield strength. Even the near perfect design for a high rise structural steel building can be compromised simply by the quality of the steel. I have personally seen steel I-beams sag under their own load. There seems to be a misconception about the tops of these buildings being more prone to catastrophic failure. All the load is transfered to the base of the structure.
There is a good chance that the bases of VSM's (vertical support members) are already at or above the 96.1 psf as mentioned earlier refering to a Cat 5's wind loading. Here's where it gets fun. Elasticity and rupture. When structural steel ruptures all hell breaks loose.

I'm going with NOAA and their warning. Yes, high rises could fall in a Cat 5.

[bubbamills]

All of those high rise buildings will become low rise buildings in Cat 5 winds.

[Regit]

During Wilma and Andrew some buildings had many windows broken and that caused a great deal of internal damage - just a guess, but, the risk is far greater from this type of damage than from the entire building falling down...

I tend to agree with this. I think plenty of buildings would be gutted, but I don't think many would totally collapse. One thing that happens when the windows fail is that wind is able to pass through the building, thus taking some of the stress off of the structure. When Hugo hit here, I remember that people who had solid wood fences lost those, while chain link fences remained (except those that were hit by something like a tree). The reason is that the wind had nothing to push against to cause those chain link fences to bend or fall.

[wxman57]

From wind, probably a lot of structural damage but maybe not collaps. But also consider the surge/wave action. A hurricane striking the coast with relatively deep water offshore could cause tremendous beach erosion. If enough of the foundation of a high-rise condo is undermined, it could collapse. Here are a couple shots of a 5-story condo near Pensacola that collapsed when Ivan moved ashore. About 8-10 feet of sand was removed from the foundation and one side of the condo collapsed from 5 stores to 2.5 stories. The same thing could happen to a taller building if enough erosion occurs.



A closer shot taken by Neil Frank (formerly with NHC now in Houston)

[dizzyfish]

wxman57 - those pictures speak volumes. Never thought about the erosion aspect. I wonder how far inland you could get erosion like that in Miami.......

[bubbamills]

Amazing picture showing the erosional force of storm surge. What could a land owner possibly construct to alleviate that situation from happening?

[BigO]

Amazing picture showing the erosional force of storm surge. What could a land owner possibly construct to alleviate that situation from happening?

I'm not a structural engineer, but the obvious answer is deeper pilings.

[hial2]

The ultimate failure criteria for structural steel has to do with yield strength. Even the near perfect design for a high rise structural steel building can be compromised simply by the quality of the steel. I have personally seen steel I-beams sag under their own load. There seems to be a misconception about the tops of these buildings being more prone to catastrophic failure. All the load is transfered to the base of the structure.
There is a good chance that the bases of VSM's (vertical support members) are already at or above the 96.1 psf as mentioned earlier refering to a Cat 5's wind loading. Here's where it gets fun. Elasticity and rupture. When structural steel ruptures all hell breaks loose.

I'm going with NOAA and their warning. Yes, high rises could fall in a Cat 5.

I hate to bring this up,but....remember 9/11 and the Twin Towers????