PROVES MASONRY MEETS EXPECTATIONS
Irma was a long-track hurricane that began as a tropical wave off the coast of Africa. Irma became a tropical storm on August 30 and then underwent a period of rapid intensification that allowed it to reach major hurricane status, Category 3 or higher, on August 31.
Irma then plowed through portions of the Caribbean, bringing tremendous damage as a Category 5 hurricane. The first landfall of this record-breaking storm was Barbuda. Packing winds of 185 mph, the island was destroyed.
In addition to the incredible devastation that Irma wrought, it also reached several notable extremes. Irma is one of only five hurricanes that has reached maximum sustained wind speeds of 185 mph or greater. It maintained those winds for 37 hours, the longest on record. Irma also tied the Cuba Hurricane of 1932 for the longest lifetime as a Category 5 in the Atlantic Basin.
Irma’s devastation in the islands preceding Florida’s landfall caused panic. Supplies were running out, gasoline ran short and roads clogged as evacuees tried to escape. Community shelters began to overflow. Conditions became unbearable. Pets were not welcome except in a designated shelter though some are considered family.
There are two highways heading north from the east coast and one highway going north from the west coast. It is virtually impossible to evacuate most south Floridians when a major hurricane is bearing down. This was particularly evident in the case of Irma. Reports have estimated that with such catastrophic damage reported on the Islands before this monstrous and dangerous storm, six million people from south Florida were trying to evacuate. Panic set in because the forecast of the storm was to go up the middle of the state, from south to north. To where do people evacuate?
There were 16 homes built with concrete masonry. We found no wind damage to any masonry or concrete exterior wall – none. Failure rate for light frame wall systems was 25%.
On top of the confusion of where to go, forecasters were unsure of where the storm would actually hit. Miami? Naples? Tampa? Time was running short. People were evacuating north, west and east. A family from Boca Raton evacuated to Tampa the Friday before the storm, only to turn around and drive back to Boca Raton late Friday night because the forecast had changed from landfall on the east coast to the west coast. Evacuating to the north took hours with no real hope of escaping the storm as it was traveling north. Some families drove to New Jersey and Ohio to escape. Florida is just not an easy state to evacuate when a monster storm is coming.
If we can’t get out, what do we do? One suggestion is for some residents (not in a mandatory evacuation zone, living in a flood plain or along the immediate coast) to shelter in place. This presumes that we have built and maintained strong homes (or places within our homes) or adequate shelters to move into. This shelter-in-place concept is vitally important and needs to be fully explored as an alternative to evacuation. Shelter in place need not be a windowless place in your home. It could be your masonry home.
Will the threat of future storms deter people from moving to Florida? What do the people already here do during storms? We need to change the paradigm on building durable structures. Resilience – building with strong materials and safe designs – must be incorporated into building codes and promoted by local building authorities to avert catastrophic damage from naturally recurring events.
Actual Wind Speeds
Although Hurricane Irma was a record-breaking storm inflicting catastrophic damage on the islands, Florida was spared its potential fury. After many days as a Category 4-5 storm, it hit Florida as a Category 3 event. This is not to downplay the damage caused by the storm and millions of people being displaced. If, however, the storm had remained a Category 4-5, property damage and loss of life could have been much worse. Except for some localized areas in the Keys, some investigators have characterized Irma’s wind speeds as a non-code event with respect to testing the current building codes. Some Florida media reports and industry building associations are claiming victory with existing codes after the storm. They claim minimal damage for their respective products and thus, tout how well current codes and designs are working. Although the newer codes are better, they are not sufficient.
A strong category 3, 4 or 5 storm with sustained winds between 130 – 157 mph are needed to fully test the state wind code and building requirements. A storm of this magnitude would (and will) expose the weaknesses in current construction practices. That said, we did observe some testing of the existing codes on Big Pine Key, Ramrod Key and Summerland Key, where Irma made initial landfall with the greatest force.
Performance of Masonry
From the observed damage, we believe this limited area of the Keys, where Irma made first landfall, experienced wind intensities like hurricane Andrew (130 to 140 mph – low Category 4). This magnitude of wind is approaching, but still less than, the code design values for South Florida and we would assume that no damage should occur when structures are subjected to them. In the case of masonry, that was true.
During our review of damage from Hurricane Irma in Southwest Florida and the Keys, we found only two instances of failed masonry: an old unreinforced wall that fell over in Naples and an old unreinforced masonry home washed away by storm surge (1811 Long Beach Drive, Big Pine Key). Other than these two instances, we found not one block out of place - perfect performance for every concrete masonry wall. The performance of masonry was regardless of real or imagined tornado or micro-burst wind action. In many cases, nothing was left of the former structure except the concrete masonry walls.
The area where we observed the most structural damage was the eastern side of Ramrod Key along W Indies Drive. Within a group of 51 residential homes, there were 16 homes built with concrete masonry. We found no wind damage to any masonry or concrete exterior wall – none. Failure rate for light frame wall systems was 25%.
The second hardest hit area from Irma was Naples and Marco Island in the SW corner of the Florida peninsula. Maximum wind speeds were documented as Category 2 or 96-110 mph. Damage was, for the most part, as one would expect from a Category 2 storm. The National Hurricane Center describes a Category 2 storm from the Saffir-Simpson hurricane wind scale as:
Extremely dangerous winds will cause extensive damage: Well-constructed frame homes could sustain major roof and siding damage. Many shallowly rooted trees will be snapped or uprooted and block numerous roads. Near-total power loss is expected with outages that could last from several days to weeks.
Metal building and metal siding failure was apparent even though wind speeds were substantially less than what the structures should have been designed to withstand. A notable light frame failure was the Civil Air Patrol building just East of Marco Island.
Ironically, the interior of one end of the building was built out of masonry within the metal exterior. The masonry was completely intact. The metal building was peeled back 100' – 150' until the masonry portion stopped the building’s total unraveling. The multimillion dollar plane housed in this building was, thankfully, moved out the day preceding the storm. The plane survived; the building didn’t.
Development of Masonry Codes
A major re-thinking of residential construction in Florida occurred in 1993 with publication and approval for adoption of the Southern Standard Technical Document (SSTD) 10-93, Standard for Hurricane Resistant Residential Construction(currently ICC 600-2014 from the International Code Council). This prescriptive standard details exactly how both wood and masonry homes should be built to withstand code-force winds. Every committee meeting in the development of this code was a pitched battle between the concrete/ masonry industries and the wood frame industry. The outcome of almost five years of debating over every residential construction detail resulted in the SSTD 10 document, essentially completed in 1991.
Provisions were not adopted into the code because several opposing interests believed it would increase cost of construction unnecessarily. In 1992, Hurricane Andrew ended the haggling. Catastrophic damage, specifically to wood frame structures and roofs, confirmed the inadequacy of the building standards
Unfortunately, provisions were not adopted into the code because several opposing interests believed it would increase cost of construction unnecessarily. In 1992, Hurricane Andrew ended the haggling over the necessity. Catastrophic damage, specifically to wood frame structures and roofs, confirmed the inadequacy of the building standards in force at that time.
Since inclusion of stronger prescriptive provisions in Florida masonry construction, walls built of concrete masonry have suffered very near to zero damage in either hurricanes or tornadoes.
The masonry industry readily adopted and incorporated almost all the strengthening provisions in the SSTD 10-93 as standard masonry construction in Florida and added them to the Florida Building Code – Residential. Since inclusion of the stronger prescriptive provisions in Florida masonry construction, walls built of concrete masonry have suffered very near to zero damage in either hurricanes or tornadoes. We know of only one single wall of one home built to SSTD specs, in the Villages of Lady Lake, that fell over in a 1998 Tornado – and we know the reason – improper embedment of (3) #5 hooks into an 8" bond beam.
Performance of masonry walls built to the SSTD 10 requirements has been a success story in high wind standard development. The first real test of the ’93 Standard came in 1998 when deadly tornadoes ripped through Orlando in the middle of the night killing 42 people. All those killed were in light frame manufactured homes or trailers.
The Florida Concrete and Products Association initiated a study by Joe Belcher, president of JDB Codes Services, and the late Jim Gulde, president of Masonry Information Technologists, of two housing subdivisions severely impacted by the tornadoes, Flamingo Lakes and Parsons Pond. Flamingo Lakes is an older development built under the Southern Standard Building Code Appendix D. This code allowed for walls to be built with 8" deep masonry bond beams, which were run for up to 32' with no vertical steel tie downs. These masonry homes were devastated by the winds.
Directly adjacent to Flamingo Lakes is the Parson’s Pond development where all homes have been built to the increased SSTD 10-93 standards. Bond beam depth in the new standard increased, in most cases, to 16" providing greater strength in resisting uplift and allowing a longer embedment of vertical wall steel into the bond beams. Wall steel spacing was also reduced significantly, from 32' oc down to a spacing determined from a design chart that factors in roof span, wall height and wind speed (in most cases 4' to 12' oc). Also, roof sheathing nail spacing was substantially decreased and gable end bracing was installed.
Strength of Masonry
Many factors explain why Irma and previous Florida wind events had near zero impact on concrete masonry walls built to modern standards.
Product Weight and Stability
This is simple but true. Things that weigh more are harder to blow over. The wind, particularly in gusting, must overcome the inertia of a much higher mass. A home made of 8" concrete masonry weighs 7 to 10 times as much as a home built of light frame materials. In seismic loading with ground accelerations that care nothing about the weight of your wall, this can work against you. But in wind loading, the wind must get the structure moving before it can blow it apart. In this case, mass works in your favor.
Inherent Safety Factors in Design
The word inherent is used to denote an innate characteristic of a product. Consider it the minimum starting point of the design. An example of this is 8" masonry. In many cases actual design calculations might allow you to use a 6" thick wall instead of an 8" wall. But 6" masonry is not typically available so we use 8" masonry as a minimum starting point in the design.
Simplicity of Connections
Connections within the concrete portion of the wall are standard lapped reinforcement poured into grout. As long as bars overlap the correct distance and grout properly fills void areas where bars are located, strength of connections equals the strength of the rebar. With allowable tensile strength of a single #4 bar at 6400 lb, that is a lot of strength.
Simplicity of Proper Installation
Due to many factors, the entire construction industry is focused on workforce development to maintain a certain level of well-trained labor. This is not a masonry issue, but applies to every trade involved in constructing the building envelope. Masonry construction has the advantage of standardized and easy-to-construct connections.
Masonry construction has the advantage of standardized and easy-to-construct connections.
Tested (and Improved) with Time
As mentioned in the section on codes above, masonry construction in Florida has learned from and incorporated into its codes and standard practices the lessons learned from wind storms hitting the state. Over the past 35 years, maximum spacing of vertical reinforcement in masonry walls has reduced from 32' to 10' to better strengthen the homes and buildings of Florida’s communities.
Reinforced Thermal Mass Stands Up to High Winds
Codes in South Florida are designed for structural walls to withstand pressures resulting from nominal design wind speeds of 132-155 mph with gusts of over 180 mph. With winds in the 80-110 mph range hitting Southeast Florida, no structural damage should have occurred with buildings built since the 1970s. When winds exceed 130 mph, as they did in the Keys, things start happening.
The damage that occurred at ground zero – Cudjoe Key to Big Pine Key – is very telling of what could have happened had Irma not diminished before striking Florida. This would have been the story throughout Florida if the dire forecasts of a Category 4 storm or higher would have occurred.
With the difficulty of escaping Florida or sheltering in overcrowded/understaffed designated community shelters when a Category 4 – 5 rips up the spine of Florida, we need to begin building more storm resistant and sustainable dwellings that citizens can shelter in place outside mandatory evacuation zones and in non-coastal / non-flood plain parts of Florida. Shelter in place need not be a windowless place in your home; it could be your masonry home.
Miami-Dade and Monroe Counties have the strictest building requirements in the state, if not the nation. However, there is still more to do to maintain the existing standards and strengthen the sustainable building processes and codes and expand the knowledge and foresight to other jurisdictions throughout Florida. Human nature is to forget as codes and building requirements loosen over time, or as some would say, between storms. Let Irma be a wake-up call to never let our guard down, because people’s lives are at risk.
The masonry industry has a proven track record of endurance over centuries and the nature of the product and current methods of assembly ensure durability in a way that light-frame (or non-mass) simply cannot.
Don Beers, PE, GC, is currently the staff engineer for the Masonry Association of Florida and President of Adrian Engineering Services. Beers was Engineering Services Manager with Rinker Materials for 29 years. He has served as Chairman of the National Concrete Masonry Association’s Codes Committee, the Florida Concrete & Products Association’s Block Committee and on the Board of The Masonry Society (TMS). He is also a member of ASTM, Florida Engineering Society, National Society of Professional Engineers, ASCE, ACI and TMS. Beers is a graduate of the University of South Florida in Civil and Structural Engineering and is a licensed engineer and general contractor in Florida. Don@FloridaMasonry.com | 561-310-9902
Patrick J. McLaughlin owns McLaughlin Management Associates, Inc in Boca Raton FL, a management consulting firm specializing in strategic and tactical planning, marketing and project management work in the cement, concrete and construction industries. He currently does private consulting in market statistics of the concrete, masonry block and cement industries.
McLaughlin began and ran the Masonry Apprentice and Educational Foundation for 13 years and managed the Masonry Association of Florida for eight years. He was involved with the passing of the Florida Concrete Masonry Education Act legislation which created the Florida Masonry Education Council, Inc. He began his career with the WR Grace Company and worked 21 years in various sales, marketing, financial and product and regional management roles. His Bachelor of Science in Chemistry is from Merrimack College and Master’s in Industrial Administration from Purdue University. email@example.com | 561.239.2462
Upon reading the article you will be able to:
1 Identify challenges with evacuations and benefits of shelter in place during natural disasters in Florida.
2 Explain Florida standard construction practices that have made masonry a desirable choice for designing to high winds.