Permanent Buildings and Foundations

The Business Newsmagazine for the Concrete Builder

Concrete Walls Protect Best Against Wind-Blown Debris

THE ENGINEERS: Concrete's strength and mass "successfully meet the criteria to protect in a severe storm."
The answer, my friend, is blowing in the wind.

    The proof is in the pudding. Concrete walls do make a big difference in protecting life and property when winds blow with hurricane and tornado force, according to new scientific research conducted by the Wind Engineering Research Center at Texas Tech University.
      You already know the most dangerous part of a tornado is not high winds but the debris which they carry. With that knowledge Texas Tech engineers compared the impact resistance of concrete residential wall construction with conventionally framed walls.
      “The results of the tests were not surprising, but they were dramatic,” says Donn Thompson program manager of residential technology at the Portland Cement Association which co-sponsored the research. “Concrete’s strength and mass successfully meets both the criteria needed to protect occupants in a severe storm -- structural integrity and missile-shielding ability.”
      Consider that testing designed to assess property damage from hurricanes employ a criterion of a nine-pound missile traveling at about 34 miles per hour. Using a compressed air cannon that simulated wind speeds up to 250 mph, the researchers loaded a 15 lb. 2x4 and hurled it at up to 119.9 mph toward different wall sections 16.6' away to test their effectiveness in deflecting missiles.

      The researchers used ten wall sections representing the most common home building techniques: a wood frame wall, a steel frame wall, a 6" reinforced concrete wall, a 6" thick reinforced concrete wall built with block insulating concrete forms (ICFs), a 4" thick reinforced concrete wall built with panel ICFs, and a concrete wall built with a waffle grid ICF system, the thinnest point being 2" thick. All of the wall panels were finished as they would be in a completed home.
      The engineers first demonstrated the performance of a wood frame wall composed of 2x4 wood studs at 16" o.c., 3½" batt insulation, 5/8" gypsum board interior finish, and vinyl siding with a ¾" plywood sheathing. The 15 lb. 2x4 was launched at 109 mph toward the wall panel and passed through the panel without visible or apparent decrease in speed.
      A second test used a wall with the same materials as the first, except a 3" brick veneer with a 1" airspace replaced the vinyl siding, and this time the 2x4 was thrown at 69.4 mph. Notwithstanding the brick veneer and the slower speed, and the missile penetrated the wall and lodged there. As the 2x4 impaled the wall, the brick veneer shattered, cracking horizontally and vertically from point of impact, and the missile penetrated exterior and interior sheathing, insulation and gypsum board.

THE GUN: Texas Tech cannon blasts away to simulate wind blown damage.

Next in the lineup were the steel frame panels. The test used 16" o.c. steel studs, 3½" batt insulation, 5/8" gypsum board interior finish, and vinyl siding over ¾" plywood sheathing. This time the engineers shot the 2x4 out of the cannon at 103.5 mph. and the 2x4 made a neat hole in the wall, passing completely through to the other side. Next the testers set up a steel frame wall with synthetic stucco instead of siding. The speed was reduced to 50.9 mph, but the missile shot through the wall just as it had through the steel stud/vinyl clad wall.
      The subsequent wall types tested consisted of several different kinds and thicknesses of concrete walls. The first was an unfinished wall 6" thick, with #4 vertical rebar at 12" o.c. When the dust cleared after the 2x4 struck the wall at 102.4 mph, the concrete wall was not damaged; there was no cracking, spalling or scabbing. The only sign of the missile was a few splinters of wood smashed into the face of the wall. The next wall, essentially the same only with rebar spaced 24 o.c., was hit by a 2x4 at the same speed and once again the wall remained unscathed.
      Next, the engineers built a 6" flat concrete wall with block ICFs. It had #4 vertical rebar, 12" o.c., and was finished with vinyl siding. The missile, launched at 103.8 mph, penetrated the siding and the foam form but the concrete wall itself was undamaged.
      A similar test followed on 6" ICF walls with #4 vertical rebar spaced at 24" o.c. and an exterior finish of brick veneer with ties spaced 1' each way. The missile, launched at 99 mph, once again pierced the brick veneer and dented the foam forms, but the concrete wall was unharmed.
      The test was repeated using a 4" flat concrete wall formed in panel ICFs, with #4 rebar at 24" o.c., and faced with vinyl siding. As in previous tests, the vinyl offered no resistance while the concrete stood firm; there was no sign of cracking, scabbing, or spalling.
      In the final experiment the researchers built an ICF waffle grid wall and aimed the 2x4 directly at the thinnest point of the wall, a 2" thick section. The wall contained #4 vertical rebar in each 6" thick vertical core at 24" o.c., and a synthetic stucco finish. The missile, flying at 100.2 mph, penetrated the stucco finish and the foam form, but left the concrete wall intact and untouched.
      “The results of this test essentially prove that concrete homes offer the greatest protection from natural disasters,” says Thompson. “Because hurricane wind velocities are generally less than the maximum speeds in these tests, concrete homes are the most stable choice in coastal hurricane-prone areas, as well as inland tornado-prone areas, to provide superior resistance to airborne debris.”

To purchase a copy of the video, “Concrete Homes, Built-In Safety,” at $4.95, plus shipping and handling, call PCA Publications at 800-868-6733.

Article from the January 1, 2002 issue, pages 10-11. © R. W. Nielsen Co.