Masonry Magazine April 2006 Page. 51
THE CATASTROPHIC DAMAGE CAUSED BY HURRICANE KATRINA
The catastrophic damage caused by Hurricane Katrina has driven home the vulnerability of residential construction under the onslaught of a natural disaster. But in Florida, where hurricanes are commonplace, building codes dramatically changed since 1992, after the massive destruction of Hurricane Andrew. Since then, the use of concrete masonry as the primary structural component in residential homes is on the rise.
Concrete masonry's high mass gives it a better ability to withstand rain and the impact of flying debris. When reinforced, it withstands high force winds through increased flexural (bending) and tensile (uplift) capacity of the exterior walls that flex, and thus reduce structural shifting.
The proof of indomitable strength of concrete masonry can be seen firsthand at two homes that have been under construction over the past year on Florida's coast. While the buildings were going up, one tropical storm (Arlene) and three hurricanes (Ivan, Dennis and Katrina) came through.
The Adams Residence
BUILDER PAUL HARTZOG, owner of Silver Sands Development and Decks N Such Marine Inc., is building the Adams residence, a 22,000 square foot (2044 m2), reinforced concrete masonry home on a peninsula that juts out into Choctawhatchee Bay in Destin, Fla. Each time the weather prediction called for a hurricane, he prepared for the worst scaffolding was disassembled and removed, materials were tied down or removed, and equipment was put under cover. But as for the house itself, Hartzog said, it was never a worry.
Concrete masonry's high mass gives it a better ability to withstand rain and the impact of flying debris.
"There were no problems with the house during the hurricanes. The first time, Hurricane Ivan, the block was just coming up on the foundation. The second time, Hurricane Dennis, we were dried in and just about to put the tile roof on. This last time, Hurricane Katrina, we were about 90% complete," Hartzog said, adding that the house has come through all three without damage.
"We talked a lot about sustainable materials with the biggest threat being hurricanes," said architect Dennis Chavez, principal of Dougherty + Chavez Architects, who designed the Adams residence. "When you design for structures to be built along water, you have to take into account the phenomenon of high winds and storm surge.
The foundation of the Adams home began by hammering pilings into the ground. "In this particular design we have a footing that is constructed with 14-foot-long (4.27 m) wood timber piles about every 10 feet (3.05 m) on center around the perimeter of the house. That was an extra precaution to resist scour the wave action taking away dirt trying to undermine the foundation," said Chavez.
The foundation was completed using standard 8"x8"x16" (203x203x406 mm) CMUs laid in horizontal courses to bring the foundation up to 11.33 feet (3.45 m) above sea level. Every block course was reinforced with No. 5 (No. 16 M) bars that run vertically through it, and every cell was filled with concrete grout forming the entire exterior envelope of the house. The only wood in the exterior of the house is on the second floor where a few parts of the walls are 2x6 framing.
In terms of design, Chavez said that they have never been limited by the choice to use concrete masonry in construction. "In some ways it is actually better because you have certain design parameters you want to achieve with block and you can do a lot of interesting things," he said.