Special Report: Stealth Buildings
By Brian Kraemer
Published in the January 2006 issue of Today’s Facility Manager
Buildings have a tendency to age like people. When the building is young it can fall off a bike, get back up, and keep trying until it glides up and down the neighborhood with ease. But as rings get added to the trunk of the oak tree, systems begin to get cranky and things that used to be taken for granted have to be examined.
Building foundations can begin to shift over time due to the outside pressure of the earth pushing in on them. If a bowed foundation is enough to make building occupants worry about their safety, a facility manager must be losing sleep over it. But help is never far away in this age of technology. In this case, facility managers can learn something by looking at the aeronautics industry.
For the past 20 years, engineers have been designing airplanes using carbon fiber. Specifically this material is used on the F117 Stealth and the Boeing 787 Dreamliner because of benefits like high tensile strength and rust and corrosion resistance. Facility managers can take advantage of this lightweight material and stop the foundations of their buildings from shifting too far by installing it on the walls.
Typically, carbon fiber is manufactured through a process called pultrusion—the act that converts carbon filaments into carbon fiber reinforced polymer (CFRP).
“Pultrusion is a process whereby the carbon filaments are drawn through a resin batch, and excess resin is removed so that a ratio of 25% to 75% resin fiber is obtained just prior to the materials entering a pultrusion die,” says Doug Gremel, director, non-metallic reinforcing for Seward, NE-based Hughes Brothers, Inc.
“The die itself is heated and cooled to control the chemical curing of the thermoset resin process. Once the mass of resin and fiber exits the die, it is a finished product,” he says.
The reason the process is called pultrusion has to do with the end of the manufacturing. In this instance, the finished product has to be a shape that will lie flat on a wall and cover it from ceiling to floor, which means something flat and a few inches wide. Imagine a skinny piece of house siding or a flattened rope.
In order to get this pre-hardened shape through the die, the end of the fiber has to be pulled through the resin bath, which turns the fiber into CFRP. This is where the name of the process comes from—pultrusion instead of extrusion.
“A wide variety of fiber materials can be used, ranging from small tows or rovings—which are bundles of fibers—to wide tapes,” says Dr. Abdul-Hamid Zureick, professor, Georgia Institute of Technology.
“In more advanced pultrusion processes, pre-impregnated and prelaid tapes, as well as stitched, woven, and braided fabrics are fed into the shaper to produce products with the desired strength and stiffness in the different directions,” Zureick continues.
This ability to customize the CFRP allows facility managers to shape the product, depending on the application that is needed. From stabilizing a foundation wall to designing a new facility staff Stealth Fighter (to keep those IT guys on their toes), the material can be manipulated to fit the need.
There are certain warning signs that facility managers need to look for to determine whether or not the building foundation is beginning to shift. “Cracks in the wall or floors that look to be structural are the first signs,” says Bob Thompson, professional engineer and owner of Columbus, OH-based Nationwide Reinforcing.
Once these problems begin to appear, it may behoove a facility manager to bring in an outside engineer to examine the problem and decide whether or not some kind of reinforcement is needed. If it is, the installation process is relatively simple.
“Putting CFRP up on the wall of a shifting facility is really very simple,” Thompson continues. “Simply remove any paint or debris from the wall, apply the structural epoxy, and press the carbon fiber on.”
The tensile reinforcement will take effect quickly and stop the problem from becoming worse; it may even breathe new life into the structure or structural element. It provides stability into a shifting foundation and may prolong the life of the building like a pair of braces straightening teeth: it keeps everything that needs to be in line on an even keel.
“The process is ultimately much more cost-effective than making the decision to construct a new building,” says Gremel.
Other options to shore up a shaky foundation include steel I-beams or anchor systems made out of steel. But metal will usually be more expensive and won’t have the same tensile strength, stiffness, or corrosion resistance as CFRPs.
By being progressive, facility managers can extend the life of a building. A highly engineered, specialized product—like carbon fiber reinforced polymer—can keep a building in good shape while adding an element of space age technology.