                             THE VIRGINIAN-PILOT 
              Copyright (c) 1995, Landmark Communications, Inc.

DATE: Sunday, November 26, 1995              TAG: 9511220224
SECTION: CAROLINA COAST           PAGE: 18   EDITION: FINAL 
TYPE: Real Estate 
SOURCE: Chris Kidder 
                                             LENGTH: Long  :  124 lines

RESEARCHERS TRACK WINDS TO IMPROVE CONSTRUCTION

Hurricane season is just about over, but there are a few folks who hope we get a big blow before winter fades into spring next year. Their wish for high wind is fueled by the best intentions: They want real-life data on wind so they can develop improved construction materials and methods for coastal building.

These wind storm aficionados are engineering faculty and students at Clemson University in South Carolina. They're part of Project Blue Sky, a hazard mitigation program started by the town of Southern Shores. The program is funded by the town, the Federal Emergency Management Agency, the state of North Carolina, other state agencies and 15 corporations that have a stake in the housing market.

Project Blue Sky is unique because the dynamics of wind on single family structures have never been seriously studied before. It cost too much, says Dr. Scott Schiff, assistant professor of civil engineering at Clemson University. Engineering studies for large structures were done because the dollars at stake justify the expense. But no one builder built enough single-family houses to investment in testing and there were no incentives to encourage joint studies.

Then there was Hurricane Hugo. And Andrew. The property losses from single-family dwellings made up the bulk of the $20 billion in cumulative losses. It was enough to change how government and private industry looked at the information used to build homes.

By the time Opal hit this year, Project Blue Sky was already under way. Clemson faculty Schiff, Ben Sill and Dave Rosowsky joined other Project Blue Sky advisers as part of the post-hurricane evaluation teams surveying the damage.

One of the biggest problem areas for wind damage in all subdivisions affected by Opal was porches and other appendages to the main structure of a house.

``There still seems to be a problem with attachment,'' says Schiff, although the same problems were noted after previous storms.

Schiff studied damage at Seaside, Fla., a planned community that features tightly packed residential areas.

``It was difficult for wind to get into the community,'' explains Schiff. ``That resulted in lower wind loads even though the community wasn't designed with wind resistance in mind.''

Dr. Ben Sill looked at how Opal's damage was affected by the settings of structures. He discovered that tree canopies actually protected houses from wind damage in this storm.

There are a number of public misconceptions about what makes a house wind-resistant, the Clemson crew points out. Wind isn't merely a force against a building; one of its more damaging aspects is uplift, the wind dynamic that allows heavier-than-air flight. Houses are built to be held to the ground. Little attention is paid to the fact that in many high wind situations, a roof wants to fly.

Wind shutters demonstrate the need to consider what wind actually does, says Schiff. Most shutters are nailed into the frame, anticipating wind blowing against the shutter. ``But when the wind switches around as it does in a circular storm system, the suction can pull shutters right off the house,'' he says.

The Clemson crew isn't waiting for a hurricane to start assessing where our buildings fall short. Earlier this year, a group of students dismantled a Southern Shores house, retrofitting its walls and roof with hurricane straps and various nailing techniques, to see just how much uplift the building could sustain. Results of these tests will be published in the next few months.

In the meantime, experiments with wall sections are under way at the Clemson Wind Load Test Facility where various types of hurricane straps and the methods builders commonly use to attach the straps are being tested. The Project Blue Sky team is looking for alternative methods that provide better results at comparable cost.

New methods of mixing and applying epoxy glue are promising for retrofit, say team members. Adding hurricane straps is often impossible without dismantling sections of a house. Epoxy, which has performed very well in uplift testing, can be applied much more easily.

One of the team's most significant findings for Project Blue Sky, so far, concerns the common practice of nailing hurricane straps to the inside of the top plate (the wood member that runs along the top of wall studs and joins to the rafters above it).

Clemson tests have shown that attaching the strap in this manner contributes to ``top plate roll'' and early failure of a wall when uplift pressures are applied to a roof. When the top plate rolls, nails holding the strap in place pull out of the wood and the strap is useless. The top plate doesn't roll when straps are attached on the outside, something that can easily be done at no extra expense.

``No one expected this,'' says Tom Reed, a graduate student working on the hurricane strap experiments. The failure probably would not have been discovered in the field because once a wall fails it usually breaks apart.

Other Project Blue Sky testing involves more sophisticated equipment than hammer and nails.

Clemson is one of only a few schools involved in wind engineering, says Schiff. The school's ``boundary layer'' wind tunnel is one of the nation's largest. (A boundary layer wind tunnel simulates winds close to the ground.) Computer controlled, the wind tunnel looks deceptively simple: Imagine a truck trailer inside a big garage, with turbine engines at one end, and you get the picture.

The engines generate a constant peak wind of just 30 mph, not too much more than a normal breeze by Outer Banks standards. Scaling results up from there works fine, says Schiff. There's no need to blast experimenters and their models across the state.

Last weekend, Clemson students were in Southern Shores, gathering information for an upcoming wind tunnel test. Students will build a miniature neighborhood with typical houses found in the town. They hope to include sand dunes and trees and duplicate neighborhood densities. They hope to build models of houses with dormers, covered porches and other architectural details that have been earmarked as potential trouble spots.

Then they'll fire up the wind tunnel, spread a sheet of laser light over the model and watch how wind behaves as it sweeps over the barrier island. Each model is loaded with hundreds of wind pressure sensors, which feed information into a bank of computers in the control room.

Clemson hopes to complement these wind tunnel tests with data from Southern Shores houses outfitted with similar sensors this winter. Hurricane-force winds are necessary for the data to be useful, says Schiff, but the engineering team would like just one shot at the real thing. MEMO: Chris Kidder covers Outer Banks real estate for The Carolina Coast. Send