THE VIRGINIAN-PILOT
Copyright (c) 1994, Landmark Communications, Inc.
DATE: Sunday, December 11, 1994 TAG: 9412110058
SECTION: LOCAL PAGE: B1 EDITION: NORTH CAROLINA
SOURCE: BY LANE DEGREGORY, STAFF WRITER
DATELINE: KITTY HAWK LENGTH: Long : 122 lines
Darrin Holt probes pilings.
With a hammer, a dime-sized disc and a lap-top computer, the structural engineer can tell you how far your home's support system is stuck into the sand, whether a wooden piling is broken or rotten, and how much your house has sunk.
Holt began his work on bridges, as a contractor for the state Department of Transportation.
This month, the Raleigh resident expanded his business to include private homes, commercial properties and even underwater pier pilings.
``We really hadn't considered doing homes until someone suggested it as another need,'' said Holt, senior analyst for FDH Inc., which he runs with two North Carolina State professors. ``But we know beachfront property owners need to see how many feet of pilings they have left in the ground. They want to find out how many storms their structure can stand. We can answer the first question - and help predict the second.''
Holt, who earned a doctorate at N.C. State, began working with professors John S. Fisher and Robert A. Douglas when he was a graduate student. The three were researching technology to test bridge-piling depths for the state transportation department. They received an $80,000 grant from the DOT and Federal Highway Administration.
In return, the engineers gave highway administrators their computer programs.
The software took nine years to develop.
But the procedure is simple - and experts say the results are beneficial.
Holt or one of his contractors nails two roofing nails into the side of a piling. He attaches tiny magnetic discs called accelerometers to each nail. The discs are hooked onto waterproof cables, leading into a computer. Holt hits the piling with a hammer, and the computer records motion waves that travel through the wood, between the two nails. Crystals in the accelerometers measure the movement. An oscilloscope records and displays the data in waves. Computer programs interpret the graphs.
Within a day, Holt can determine how far the piling penetrates the ground.
``This procedure is very intriguing,'' said Chet Forrester, Kitty Hawk building inspector. On Friday, Holt tested two Outer Banks oceanfront homes that had been damaged during Hurricane Gordon last month. Forrester seemed impressed with the product.
``Down here, we require oceanfront structures to have 16 feet of pilings imbedded, and other homes to have at least eight feet,'' Forrester said. ``We inspect pilings on the ground before they go in. But we have no way of telling whether the builder cut it off after he drove it.
``This type of work would give homeowners an idea of how much pilings they really have in the ground. Or how much is left, on old homes,'' the building inspector said. ``I can see where the banks might even make this part of their mortgage package requirements.''
In Virginia Beach, building codes require that engineers evaluate pilings of new structures before city officials can issue occupancy certificates. No minimum piling depth is required. But experts must determine whether the support system is imbedded deep enough.
``I can see how engineering firms could use something like this in their evaluations,'' said Cheri Hainer, Virginia Beach building codes administrator. ``How far deep your pilings have to go in here depends on where you can get good soil.''
Since Holt and his professors developed the piling-testing technology themselves, no other company in the world can perform exactly the same services. Holt said he knows of about three other businesses in the United States which are measuring piling depths. Forrester had never heard of such an advancement.
Before Kitty Hawk cottages, Holt measured pilings on a dozen state bridges. He evaluated homes in other oceanfront areas, and hopes to expand.
Already, transportation department officials from South Carolina and Massachusetts have requested bridge-probing demonstrations.
``We need to know the length of our pilings so we can tell whether the bridges will be safe through storms,'' said Jimmy Lee, a bridge maintenance engineer with the state highway department in Raleigh. ``Their work allowed us to evaluate the conditions of bridges in a way that we could not have done otherwise. It's a good system.
``Their accuracy is very good.''
When they were testing methods in 1991, Holt and his partners measured pilings on bridges the transportation department had figures for.
Until recently, highway crews didn't keep track of how far they drove pilings into the ground. But there are some recent records.
Compared to the actual depth numbers, the researchers' figures were accurate within 10 percent every time.
``We're just doing wooden pilings now. But we're working on concrete and steel supports, and hope to be able to evaluate those soon,'' Holt said.
``We don't need to check every piling to tell about a structure, either. Six or seven spot checks will give you a pretty good idea of what you've got. You can check up on your builder - or determine whether to buy a new elevated home.''
Because their work in the private sector is so new, Holt said he and his partners have not yet set a fee for their services. Prices will be determined on a case-by-case basis, he said.
Average costs should range from $100 to $150 per piling.
``We can test nine pilings in two hours, without at all impacting the house or structure,'' Holt said. ``We have to go back to the office in Raleigh to run the data. But that only takes a day.
``Results would definitely be available within one week.'' ILLUSTRATION: Color photo
DREW C. WILSON/Staff
As Darrin Holt, right, observes waves of movement through an
oscilloscope, Ted Stark, left, strikes a piling to start the test.
Holt is a senior analyst for FDH Inc., which he runs with two North
Carolina State professors.
Graphic
TESTING ON HOMES
This month, FDH Inc. of Raleigh began testing pilings on private
residences to determine how far the support system has sunk into
the sand. The work averages $100-$150 per piling. Six or seven
pilings per building need to be tested.
Company owners, two North Carolina State professors and a
doctoral recipient from N.C. State's structural engineering program,
are looking for Outer Banks and other coastal engineering affiliates
to train in field work for their piling-measurement program.
For more information, call FDH Inc. at (919) 859-3106. Or write
P.O. Box 33037, Raleigh, N.C., 27636-3037.
by CNB