Volume 35, Number 9, September 2000
Forces of Nature
Construction Research Laboratory Tests to Keep Structures Standing Tall
by Ellen Giard
Before it goes up, it must come down, and thats what Miamis Construction Research Laboratory (CRL) does. For more than 40 years, CRL has simulated rainstorms, tornadoes, heat waves and other forces of nature on mock-ups of most of the worlds monumental structures. It tested Chicagos Sears Tower, the Twin Towers in New York and the Petronas Towers in Kuala Lumpur, Malaysia, long before they were built.
And theres no doubt that anyone in the business of fabricating, manufacturing or installing curtainwall, has at some time come to the point in which the product needed to be tested. CRL clients, which include project architects, owners, subcontractors, general contractors and developers, all build their own mock-ups at the test facility. Those standing behind the project want to know that it will still be a standing, safe and secure structure 100 years later. As one of the worlds largest curtainwall testing facilities, CRL tests more than 100 projects a year by constructing a wall mock-up of the actual building at its Southern Florida lab, which can accommodate more than 30 wall mock-ups simultaneously. CRL president and principal A.A. Sak Sakhnovsky, a former research assistant professor at the University of Miami, started the company in 1955. Today, the lab is accredited by the American Architectural Manufacturers Association (AAMA), Miami-Dade County and the State of New York Division of Housing and Community Renewal.
Mock-ups are tested to the same conditions the actual structure will endure.
Weathering the Storm
In accordance with AAMA, the American Society for Testing Materials (ASTM) and the National Association of Architectural Metal Manufacturers (NAAMM) standards, CRL tests full-scale mock-ups for conditions relevant to the actual location the structure will be constructed. Water and air pressure, seismic and structural conditions and extreme high or low temperatures are several of the tests conducted at the facility. John Ely, vice president and senior test engineer explained that whenever there are plans for any high-rise structure to be erected, those involved in its construction need to know how its exterior façade will perform. We test to find out how the pieces and parts will interface, he said. Standard data does not say how a structure will work with other elements and thats why we test.
According to the labs vice president and principal Richard Sembello, testing requirements for a building in a specific city should be the same for all buildings in that city, but will vary from area to area. A city in Virginia, for example, would test for windloads of 35 pounds per square-foot. In Miami, a building would be tested for 120-pound windloads per square- foot, he explained.
Depending on the size of the project being tested, lab fees range from $2,000 for a small project to more than $30,000 for the larger ones. If corners are added to the mock-up that will increase the lab fee, because they have to be reinforced to support the structure Ely said.
Right as Rain
Regardless of how experienced and talented the engineers who design any given curtainwall structure are, nothing is ever perfect the first go round. Since building configurations, shapes and products change, the assembly methods and installation change. Sembello explained that the main stumbling block CRL faces when testing lies in air and water leakage. Ninety-five percent of new walls fail the first water test. It usually takes three or four tests before the building is finalized, he said.
Our job is to find out what works and what doesnt work, added Ely. We determine the reason it failed, whether in the design or workmanship, and then develop a repair program for the mock-up that would also work on the actual project, he added.
And if a mock-up does not pass the first go-round of testing, it doesnt necessarily mean starting over from scratch for the contract glazier. Most problems are resolved right on site at the lab. Most of the problems we find are in the workmanship, usually an oversight in the installation, said Roger Ulbricht, president of Flour City International, a curtainwall manufacturer and installer of Johnson City, Tenn., which has tested many of its projects through CRL.
Riding the Wind
Hurricane resistance testing is common for buildings constructed in Southern Florida.
Like most areas of the industry, the demands and challenges of construction testing have risen. Twenty years ago we tested to lower wind load values and only for water and structure, Sembello said. Now we are testing for all parameters that affect the walls. The tests have become more challenging as the [wall] systems have gotten larger and more complicated and require higher design and wind loads. Sembello also noted that as building facades become more and more complex, the products used also become more multifaceted. It is not uncommon to see three and four wall systems on one building, he said.
Although testing is essential to ensure a buildings success, it also provides a learning opportunity. Ulbricht said testing allows companies to find glitches it may have missed in the assembly process. Testing provides the means and the methods for the hoisting and installation, he said. It also gives the owner and architect the opportunity to see what the structure will look like full-size.
Ellen Giard is assistant editor of USGlass magazine.
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