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Take a turn: Crimp-curved metal roofing offers quality when facing budget restraints

As the economic crisis continues to take its toll on the construction industry,

projects are subject to tighter cost scrutiny than ever before. To maintain

quality in the face of shrinking project budgets, designers are looking for

creative cost reduction strategies. In metal construction, one solution that

may not come readily to mind is the use of crimp-curved profiled panels.

What It Is

Crimp-curving is a process in which metal panels are fed through a computerized press that is preprogrammed to shape the panel into the specified angles and curves. The curvature can be precisely controlled, allowing fast and accurate installation at the job site while eliminating the problems associated with on-site curving. In addition, the high-tech crimp created by the process is favored by many designers.

People often wonder if the curving process adds cost to the project. In theory, that is true. But crimp-curving greatly increases the strength and rigidity of panels, often allowing designers to reduce the required panel gauge and/or the amount, type or gauge of structural support. The material and labor savings can easily exceed the relatively modest fees for panel-curving, bringing net bottom line savings.

 

Tips

How can you best use crimp-curving to save money for your clients? Consider the following guidelines:

Use the lightest possible panel gauge.

 

Project designers sometimes incorrectly assume that curved panel applications require the same thickness gauge as "straight" panel applications. Though this is true when curving is performed with roll- or stretch-forming machinery, the crimp curving process, which increases the load factor of the panels, allows the use of a lighter-weight profile. For structural roof decks, our company recommends 20- or 22-gauge panels as a more economical alternative to 18 gauge. This was the approach used by JSA Architecture Planning Engineering Interior Design of Pittsburgh when it specified 20-gauge roof deck panels for a maintenance facility for the Pennsylvania Turnpike Commission in Harrisburg, Pa. The crimp-curving process allowed 15 to 20 percent longer spans to be achieved for reduced framing costs while also providing a high-tech look. The ability to use 20-gauge steel instead of 18 gauge was also significant because the project used nearly 30,000 square feet (2,787 m2) of decking.

In addition, by leaving the underside of the deck exposed, the architect was able to express the true structure of the building without covering anything up. The crimp-curved deck and supporting bowstring trusses allowed the firm to convey a theme of motion and transportation that was appropriate to the facility and would not have been accomplished with a conventional dropped ceiling.

Another benefit of crimp-curved roof decks involved the direction of panel application. With conventionally curved decks, curvature is achieved the "easy way"-by laying straight panels parallel to the length of the building. Crimp-curved panels, by contrast, are installed the "hard way"-the precurved panels are applied across the top of the structure. A crimp-curved deck is stronger and more leak-tight and can bring the same economic benefits mentioned previously.

For roofing applications, 24 gauge is the most frequently recommended choice because it is strong and durable yet light enough to be curved down to tight radii. Some 26- gauge panels are suitable for curving, but the yield should be <50 ksi or panels may be brittle and prone to cracking. The 26-gauge panels are best used for gently curved, large radius applications.

Don't over-design. We are often asked to curve panels for designs that involve extra and/or unnecessary layers of material. Again, this usually occurs when designers forget to adjust for the increased load factor achieved with crimp-curving.

 

For example, a canopy or open cover does not require a separate roof and supporting deck-one layer will suffice. Either a roofing or decking panel may be selected and attached directly to framing. The span capabilities of the single-layer cover will be more than sufficient and will require minimal substructure support. On a related note, the structural framing itself can be constructed of cold-rolled framing and purlins, which are more economical and easier to ship and handle than hot-rolled components, bringing additional savings.

Similarly, with roofing applications, you can eliminate costly solid decking and apply the curved roof panels directly to purlins. Most types of exposed fastener profiles can be used in this manner, as well as many concealed fastener profiles with trapezoidal or angular side-walls.

Real-World Applications

A recent airport hangar project in Chino, Calif., used office bungalows with curved design elements as an architectural enhancement. The 24-gauge concealed fastener roofing panels in five lengths were crimp curved to the required specs. Because of their strength and rigidity, the panels could be applied directly over a simple zee-purlin framing system.

Crimp-curving can bring savings in acoustical ceiling and decking applications. At Memorial University of Newfoundland in St. John's, Newfoundland, Canada, Sheppard Case Architects Inc. wanted to design a raised ceiling above a window area in a student gathering center. The St-John's-based architects considered gypsum board and floating panels, but the cost would have exceeded $20,000-more than twice the allotted budget. After further research, they specified 24- gauge S-curved corrugated metal building panels, perforated and lined with acoustical batte. Total cost-even with transcontinental shipping from the curving service center-fell comfortably below the $10,000 budget.

Curved acoustical B-decking also has been used in many school and community gyms and athletic facilities. This economical approach allows a structural roof deck to perform double duty as an acoustical ceiling. As noted previously, whenever you can eliminate an extra layer of material-in this case, a separate acoustical ceiling-material and installation savings can be substantial.

The creative use of crimp-curving can achieve economies in a number of areas. When in doubt about the required panel gauge or substructure support, consult with the technical department of your panel-curving supplier for guidance. It is always best to seek advice in the early planning stages to make sure you optimize your client's savings.

Terry Holman is president of Curveline Inc., Ontario, Calif. Visit www.curveline.com.