Industrial and commercial concrete contractors have built hundreds of cast-in-place tilt-up and concrete masonry structures in coastal areas that have stood up to numerous killer hurricanes, avoiding the structural damage of adjacent stick-built structures.

Hurricane Isabel smashed into the Carolinas last month and moved into Virginia, Maryland and Delaware, killing more than 30 people and doing millions of dollars in damage. North Carolina, Virginia, Maryland and Delaware have been declared federal disaster areas.

	These townhomes are like small commercial buildings.

As Isabel bore down on North Carolina it was a Category 5 hurricane, but mercifully it steadily dropped in ferocity to a Category 2 hurricane, with winds near 100 mph as it hit land near Cape Lookout. Original estimates of damage was in excess of $4 billion, but have been steadily revised downward.

Once again, concrete structures withstood the fury of this storm. But the real test of the strength of the concrete building process are those solitary coastal homes built right on the water that absorb the first blow from a hurricane.

Hurricanes: a fact of coastal life

In an average year, 10 tropical storms develop over the Atlantic Ocean, Caribbean Sea and the Gulf of Mexico. Many remain over the ocean, but six will probably develop into hurricanes. In an average three-year period, roughly five hurricanes will strike the U.S. coast between Texas and Maine - two are typically intense or major hurricanes.

The Carolinas have been dubbed Hurricane Alley, and for good reason. North Carolina has survived a number of major hurricanes in recent years, including Hurricane Hazel in 1954; the Ash Wednesday storm of 1962; Hugo in 1989; Fran in 1996; hurricanes Dennis and Floyd in 1999; and now Isabel. There were so many hurricanes in the 1950s that the coastline was called Hurricane Alley.

So building on the beach is serious business. Construction considerations include winds, flooding, vertical erosion and scour, the erosion of soil and sediment that provide support for the supporting piers.

Will it stand?
When a buyer invests in a coastal home, he wants to be sure that the house will still be there after each storm passes. Coastal building technology has developed into a wind and water science, but regardless of code requirements, concrete construction has an inherent superiority over other building methods and materials.

"The number one concern of homebuyers considering a coastal purchase is 'Can this house survive most hurricanes and weather events?'" David Pfanmiller, partner of Security Building Building Group LLC (SBG) of Raleigh, N.C. said. "The best answer available anywhere is: 'Yes it will.' Not only will your house be standing tall season after season, but you will save money along the way. You can't find a more comfortable, secure, money-saving residential investment than one of our cast-in-place concrete homes."

Pfanmiller is a cast-in-place concrete evangelist who has taken his message to TopSail Island on North Carolina's Treasure Coast where he has built six, two-story all concrete steel-reinforced duplex townhomes right on the beach.

"We were fortunate," Pfanmiller said. "Hurricane Isabel didn't come in here. We had wind and rain, but nothing serious."

Pfanmiller uses cast-in-place removable aluminum form concrete construction technology that enables crews to form the walls and the floor at the same time, pouring the concrete monolithically. The result is a tightly integrated concrete envelope weighing a million pounds that's not going anywhere in a storm.

There's an architectural roof to create the gables for the look Pfanmiller said he wanted. To achieve the "Fortified" certifiction (See page 14), he had to build the roof structure to the Institute for Business & Home Safety specifications, which are basically Dade County Florida-type code requirements standing up to at least 130 mph winds, and using 5/8th-inch roofing plywood instead of .5-inch.

"Worst case scenario in a catastrophic storm is that you could possibly lose the roof, I guess," Pfanmiller said. "But even if you did, you would still have your sealed structure intact.

"From a design standpoint, as far as wind loading is concerned, you got a rigid connection between the top of the column and the 8-inch slab. That connection, working with the rectangular shape of the column, creates the lateral stiffness that's required for the structure. Then as far as shear uplift, honestly there is none. The big difference between wind loading on the cast-in-place concrete structure and a frame structure is that the concrete townhouse weighs a million pounds. So in the structural analysis, horizontal wind loading and uplift is not even an issue because of the dead weight of the structure.

Flooding is an issue

"From ground up, we drilled 28 12-inch auger-cast piles 45 feet into the ground," Pfanmiller said. "On top of the auger cast piles, we formed up a structural grade beam that was around 20 inches square and it had a case of steel much like a bridge beam that spans from piling to piling. Then on top of the grade beam, we constructed a 12-inch by 30-inch structural column that has two gauges of steel in each column. We went with a rectangular shape because we wanted the shape of the column to also create the rigidity we needed so we wouldn't have to cross brace it with a bunch of ugly cumbersome cross bracing typically seen out of wood frames.

"On top of the 12-by-30 structural column, we've got what I've always called the elevated slab. The elevated slab - the first slab on the first living floor — is elevated 10 feet above existing grade because of the flood elevation of that particular section of the beach. So we elevate the first floor slab and it is an 8-inch structural slab that's got 4 inches of rigid foam attached to the bottom of it to create our thermal envelope on the bottom of that first-floor level. Then on top of the 8-inch structural slab are the two housing lifts.

Storm surge is water that is pushed toward the shore by the by the force of winds swirling around the storm. The advancing surge combines with the normal tides to create the hurricane storm tide, which can increase the mean water level 15 feet or more. In addition, wind-driven waves are superimposed on the storm tide.

"In the particular flood zone that we're in down there, the house was designed for the wave and wind action to work simultaneously. And there are safety factors built into the depth of our pilings for wave scour around the bottom."

You're only as strong as your legs
Each of the 28 pilings is rated for 50,000 pounds. Pfanmiller said the 8-by-8 timber that's put in conventionally the way the local builders do for frame beach homes, is rated at only 12,000 pounds.

The auger cast pile, also known as a continuous flight auger, is a giant drill bit that is fluted all 45 feet so that the entire thing looks like a giant drill bit. It sits in a big crane rig and has a hydraulic drill head on top, a drill bit in the bottom of it and a hollow shaft.

"You can't pull the auger out and leave the hole there because the loose sand will fall back in. So what they do is drill down to the depth the soil engineer requires, then hook up a concrete pump to it and pump in a high strength grout mixture. Actually, as they withdraw the auger they're pumping grout into the void they create right below the auger. They continue to pump as they pull the auger out and the soil engineer knows how much void is created per foot as they pull the auger out and he knows how many cubic feet per surge is in the concrete pump so he literally counts it. That makes sure that you put in more concrete than void that you create and that's how you are assured of a continuous concrete pour."

These are friction piles, not end-loaded piles where all the weight is on the tip of the pile. Basically the friction is created between the sides of the piling and the adjacent sand.

"Sand erosion is only going to happen during the storm surge of a heavy storm, and that's the purpose of the dune between the house and the ocean. It's got to eat the whole dune away before it ever gets to the face of the structure. Even if it does, there's a safety factor in there of 5 to 7 feet of scour (where the wave and water action would actually scour the sand away from the piling) that we can survive without worrying about any structural integrity."

Cost factor
The cost difference between Pfanmiller's beach homes and a comparable wooden structure would be about 12-15 percent higher. Most of that difference is for the pilings and grade beams that will keep the heavier concrete home in place.

"If we could take that building off the ocean front and put it on the mainland, but close to the coast in the same wind load and put it on straight footings, our costs are probably only 8 percent more than conventional construction.

"But the pilings are expensive," he said. "They charged me $9,500 just to move their equipment onto the site to drill these piles.

Energy efficiency
The townhouses are extremely energy efficiency. With the monolithic pour, there are no cracks or joints, so there is little air filitration. This is a tremendously strong box-shell with the potential for a tremendously energy-efficient shell.

"We built a similar size duplex in Raleigh two years ago and had tests done on it, and the building science people who came out and performed the tests said it was the tightest structure they had ever tested from an air infiltration standpoint.

"In each of the units we've built so far, we've put an energy recovery ventilator in them to maintain indoor air quality because we don't have the air exchange that we need to keep the air fresh. What we did at the beach is we put a pickup for the ventilator in the kitchen and laundry room downstairs and one in the upstairs bathrooms to pick up the humidity."

The pickups lead into the energy recover ventilator, which is set up to take the latent energy out of the air as it dehumidifies and exchanges the humid, stale for fresh outdoor air.

"The building we did in Raleigh was an Energy Star-rated building. We went through the process to get it tested and rated. And every structure that I know of in the country that has been built with this technology has achieved the Energy Star rating with no problem. The Energy Star is based on a 30 percent improvement over the model in code, and he said it's been his experience that the people who have lived in our buildings are actually seeing upwards of 50 percent improvement over what their neighbors are paying.

Pfanmiller said that from the standpoint of the builder, energy efficiency is also a marketing issue, and it is difficult to sell energy alone. At the beach, he doesn't press the energy issue as much as he would if he was building inland.

"To me, that's the beauty of our concept. I can list you 10 or 12 benefits of our construction method, and depending on my market, I can just re-prioritize the list and come up with a list that would trip your trigger whether you are an investor looking at durability, lifecycle costs, low operating costs; or whether you want to build on the oceanfront and your paramount interest is the storm resistance.

"The end-run for us in this technology is that we've got a product that can slide the scale and fit into a variety of different markets including commercial.