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Industry News
New design factors for pultruded structures

The “Pre-Standard for Load & Resistance Factor Design (LRFD) of Pultruded Fiber Reinforced Polymer (FRP) Structures” is an engineering design method for which structural safety depends on probabilistically derived load factors and material-resistance factors.

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Posted on: 4/1/2011
Source: Composites Technology

The American Composites Manufacturers Assn. (ACMA, Arlington, Va.) on Jan. 17 announced the publication of a new document from the American Society of Civil Engineers (ASCE), titled “Pre-Standard for Load & Resistance Factor Design (LRFD) of Pultruded Fiber Reinforced Polymer (FRP) Structures.” LRFD is an engineering design method for which structural safety depends on probabilistically derived load factors and material-resistance factors. The process enables engineers to determine a reliability index that quantifies structural reliability in probability-based design. The document, first envisioned nearly 20 years ago, was finally initiated in earnest in 2007 at a cost of $1.4 million. Financial support was provided by ACMA and corporate members within ACMA’s Pultrusion Industry Council.

The document was prepared under contract to ASCE by a project team of structural engineers and composites experts. Dr. Mehdi Zarghamee, a principal at Simpson, Gumpertz & Heger Inc. (Waltham, Mass.), was appointed by ASCE as project coordinator, and he worked directly with team authors, the project advisory committee and ACMA’s Pultrusion Industry Council. The “pre-standard” now must go through an American National Standards Institute (ANSI, Washington, D.C.) balloting process, through ASCE’s Fiber Composites and Polymers Standards committee, before it can be adopted as a national standard. The pre-standard is an important step in a long-range initiative by ACMA to create standards for the use of composite materials, thus increasing their use throughout affiliated industries. According to ASCE, the standard will be an important design tool and will help structural engineers and architects use FRP composites in the design of buildings, transportation vehicles and similar structures in the same way that existing standards for other construction materials — such as concrete, steel, wood and aluminum — paved the way for wide use in a broad range of end applications.

According to ACMA’s John Busel, director of the Composites Growth Initiative, the data collected and used in the pre-standard equations will have to come from ASTM 7290 (“Standard Practice for Evaluating Material Property Characteristic Values for Polymeric Composites for Civil Engineering Structural Applications”) to ensure that all pultruders report properties in the same manner: “Every pultruder will need to qualify products using this ASTM test method, which will allow any user of the standard to be confident in the numbers.” Dan Witcher, corporate chief structural engineer at Strongwell (Bristol, Va.), points out that although products may differ from company to company, the equations in the standard can be applied equally, so long as minimum thresholds are met. “The pre-standard also allows means and methods for pultrusion manufacturers, architects and engineers to pre-qualify new and innovative products that they develop, and meet the intention of the standard, to keep these industry-produced products moving forward.”

The ASCE ballot process for the new standard is open to all interested parties, and ACMA encourages participation as a means to get the standard passed quickly to open up new markets for composites. “A structural design standard is essential for any material,” says Witcher. “This is an important milestone.”

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