The epitome and anatomy of TC resistant structures

[MiamiensisWx]

As a south Florida resident, it is very clear that the structures and developments that were approved during the 1970s and 1980s often received the most significant damage during recent tropical cyclones. These structures were subjected to very marginal enforcement of local/state code standards, especially in regards to roofing materials, anchoring of roofs, strength of interior/exterior walls, etc. In addition, although codes were present, several standards for commercial/residential buildings and mobile homes did not exist until Andrew permeated the industries. As an aside, the consequences have been very evident: see Century Village west of Boca Raton (after Wilma in 2005) and Lakes by the Bay between Homestead/Cutler (after Andrew in 1992). Countless commercial buildings constructed during the aforementioned '70s/'80s period also suffered from extensive damages during the 2004 and 2005 TCs (across southern Florida and other portions of the state). Sheet rock and thin wall materials have been classified as significant casualties. Conversely, many newer (post-Andrew) structures and older (pre-'70s/'80s) buildings fared very well during recent TCs. Although many structures lost numerous plate glass windows and other glass fixtures after Wilma, the structural "framework" remained intact. In other words, although high rises/office buildings were struck by flying debris (or encountered stronger gusts above ground level) and lost windows, the actual BUILDINGS survived very nicely. The Tiara condominium received extensive, long lasting damage from Frances and Jeanne on Singer Island, but the actual structural framework was sound; the type of walls and integrity of exterior construction was the main issue. Overall, I strongly believe we won't observe numerous high rise collapses if a 1926-type TC strikes the Miami area in the 21st century; flying glass is the biggest conundrum. If any buildings collapse, it will not be influenced by winds; it will be influenced by the effects of strong waves and beach erosion on coastal beachfront structures. This is contrary to popular hype, but it is true and verifiable. Barrier island structures of various sizes collapsed during the 1926 and 1928 hurricanes (in southeastern FL), as well as Frances/Jeanne along east-central Florida and northern Palm Beach County. However, I do harbor considerable concerns in regards to the older PRE-ANDREW buildings that were erected during the 1970s/1980s; as demonstrated by Wilma and other TCs, TS/Category 1 winds can inflict considerable damages, especially on these types of structures.

Careful scrutiny and personal objective reanalysis of past TC history in the region is essential. It is duly noted that many pre-'70s/'80s structures have fared remarkably well during periods of high winds. Many historical buildings in central and southern Dade County survived the eyewall of Andrew in 1992, with some structures receiving remarkably minimal damage. See the Deering Estate at Cutler, the Kampong, and the Barnacle in Coconut Grove as examples. The latter two structures narrowly avoided the eyewall, but they still experienced Cat 1/2 winds. Examine the composition/materials and craftsmanship of these structures (as well as the Bartlett Estate in Fort Lauderdale) and the answers can be discerned.

Bartlett Estate (also known as Bonnet House), Fort Lauderdale, Florida:

http://www.wegoplaces.com/User%20Interface/Images/Itinerary%20Item%20Images/59035.jpg

Note the plantation style layout with open balconies. This structure was specifically designed with the moderating sea breezes in mind; keep in mind that this structure was completed in the (pre-A/C) year of 1926. The open balconies and ground floors could reduce obstacle flow, and the concrete utilized for the support and walls adds significant strength to the building. A wide variety of additional materials were incorporated, including real south FL Taxodium (bald cypress) wood, oolitic limestone for the front "fish" arch, etc. The 1926 Miami hurricane produced maximum sustained winds as high as Category 2 intensity (85 kt/100 mph) in streaks across the Hollywood/Fort Lauderdale area; the majority of the region received Category 1 winds that were comparable to Wilma's winds (or slightly stronger) in the area, though Wilma did produce localized 85 kt (Cat 2) winds in portions of Broward County as well. The Bartlett Estate was slightly farther north than the localized Category 2 streaks to the south and west, but it likely received solid Category 1 winds. It is significant that the sole damage to the main structure was roofing damage. Later, this was the case in Katrina and Wilma (2005). The structure ITSELF remained untouched in these three examples, as well as the 1947 Fort Lauderdale hurricane, which crossed the site in September.

The Barnacle, Coconut Grove, Miami, Florida:

http://www.floridastateparks.org/TheBarnacle/default.cfm

The Barnacle is a testament to the typical (sturdier) construction in the early days of south Florida. Dade County pine (Pinus elliottii var. densa; slash pine) was extensively utilized in the "heart" of this structure, which was completed in the 1890s. The duration and strength of slash pine wood is excellent, and it has been the standard for many south FL structures. Some photographs illustrate the slash pine beams that were utilized for portions of the interior and exterior. The 1926 hurricane passed directly over over the site, and the structure was exposed to the 14 foot storm surge and the TC's eyewall. The site received winds of at least solid Category 2 intensity (1-min) on the Saffir-Simpson Hurricane Scale; although some boat houses were wrecked, the Barnacle itself remained intact. When Andrew produced winds near Category 2 intensity and passed immediately south of the site (with the eyewall narrowly missing it), the residence survived very well again. Another example of solid slash pine construction is the Stranahan House (see this site and site #2) in Fort Lauderdale, which has survived Category 1 winds in 1926, 2005, and a few additional seasons. Note that the Barnacle and Stranahan residences also exhibit a layout that minimizes obstacle flow to various degrees as well.

Many older residences in Key West also exemplify the strength of old growth Dade County/south FL slash pines:

http://keywestproperties.blogspot.com/2007/12/this-old-house.html

Deering Estate, Cutler, Florida:

http://www.deeringestate.com/

The main structure was partially composed of solid stucco, and it staunchly survived the northern eyewall of Hurricane Andrew (and the adjacent 15-16 foot storm surge) in 1992, although the grounds and interior of the structure received extensive damages. Water intrusion was an issue. More than eight years passed before the main structure was successfully opened to the public. The following photograph vividly demonstrates the solid construction of the main residence (center) after Andrew's passage. Note that the site was very close to Andrew's maximum Category 5 winds (1-min) along the immediate coastline between the Burger King Headquarters and Fender Point. Obviously, all regions around the eyewall (from South Miami to the south of Homestead/Florida City) were hit hard, and many areas received 1-min winds that solidly exceeded Category 2 intensity and crept into major hurricane status (Cat 3/4 inland).

http://criticalmiami.com/photos/2008/deering/02.jpg

I believe the Kampong (see site) survived as well, though structural damage to the main building was more significant in this case, if I recall correctly.

In conclusion, several common features of the aforementioned pre-'70s/'80s structures include "hip" roofs (in several cases), open balconies/ground floors (in several cases) with less obstacle flow, durable/strong materials (such as stucco, south FL slash pine wood, etc.), and other facets. The majority of the structures were designed with the hazards of tropical cyclones in mind. Overall, these structures (in addition to post-Andrew buildings) are much more "equipped" to stand against hurricane force winds (1-min) with less structural damage.

Thoughts and comments are recommended...

Miami

[MiamiensisWx]

Bump for pertinent responses, remarks, and comments from interested audiences...

[DanKellFla]

If you really want to read more:
http://www.wbdg.org/resources/env_wind.php
I have not finished it yet.

I agree with you that the likelyhood of an engineered high-rise is unlikely to collapse. There is too much of an investment in those buildings for that to be an issue. To get any sort of financing, the people lending the money have to have confidence that the primary structure won't fail. Although, I had a professor in college that is a civil engineer and he was describing how most of the 2 or 3 story beachfront properties in Broward that were built in the 70s/80s were going to collapse due to wind and surge.

Everything else you point out should be obvious to the people that write building codes. Of course, then you have developers pushing to make things cheaper, builders awarding the lowest bidder and subcontractors taking short-cuts. (I had a huge flood because somebody used vinyl PVC on a 2nd floor bathroom supply line instead of the stainless wire braid that is called out in the code.) It is a constant fight. Obviously, it isn't that technologically difficult to make a structure that survives a strong hurricane. It has been done for more than 100 years. The big problem is making it affordable and verifiable for mass produced houses. Look at all the roofing code violations that were found post-andrew. Although, with the building codes that were enacted in 2002, I think that the state has finally got things right. Hopefully, verifying that will never take place. But, when the inevitable happens. We will see.

[MiamiensisWx]

Bump for intrigued audiences...