JEC COMPOSITES MAGAZINE - Issue #77 - December 2012 - 32

civil engineering

compression reinforcement consists of self-consolidating concrete (SCC) which is pumped into a profiled conduit within the beam shell. The tension reinforcement consists of prestressing steel which runs along the bottom flange. Whereas FRP materials are generally too expensive and too flexible when arranged in a homogeneous form, the strength and stiffness of the hybrid-composite beam is provided by a more efficient use of materials that are well suited to purely axial tension or compression. The beams are manufactured using a closed-mould, vacuum-assisted resin transfer method (VARTM). In this process, the preforms – that include glass fabrics, steel reinforcement and a lowdensity foam core – are all placed inside of a simple, inexpensive, reusable steel mould. Once the preforms are in place, the mould is sealed and vacuum pressure applied to evacuate all of the air. While maintaining vacuum pressure at 1 atmosphere, a vinyl ester resin is pulled into the mould to wet-out the preforms and consolidate the glass, foam and resin into a monolithic unit. The entire process for the fabrication of a beam takes less than five hours. The beam can be removed from the mould within hours of infusion. In its most simplistic embodiment, the beams are simply supported and the profile of the compression reinforcement follows a perfect parabolic shape, emulating the funicular shape of the applied dead load and live load envelope and drastically reducing the shear carried in the FRP webs. In this simplest embodiment, the beam essentially functions like a tied-arch, in a glass box. The same technology can be employed to manufacture beams with variable depths or widths. The beams can also be easily made continuous over several supports with simplistic splicing technology using the same materials and manufacturing processes. n
More information: www.harbortech.us www.hcbridge.com

North face of Knickerbocker Bridge at low tide

Nate Benoit, P.E., project manager, MaineDOT Bridge Program, concurred, noting that they are already quoting some other projects using HCB. “We believe HCB is a viable technology and is another tool in the toolbox for bridge designers,” said Benoit. “HCB has proven to be a successful technology as demonstrated by the Knickerbocker Bridge project. HCB offers corrosion resistance, is lightweight and it can be used with an accelerated construction schedule. We expect to see more of the technology used for bridge infrastructure projects.” The project has garnered much attention including that of the Technology Implementation Group (TIG) of the American Association of State Highway and Transportation Officials (AASHTO). The purpose of the TIG is to identify and champion the implementation or deployment of a select few proven technologies, products or processes that are likely to yield significant economic or qualitative benefits to the users. In June, the AASHTO TIG met in Bangor, Maine, to develop a promotional campaign highlighting various Departments of Transportation that have already deployed the technology in order to educate their peers as to the benefits of the technology. According to Ken Sweeney, Maine-

DOT’s Chief Engineer, this promotional campaign was started to bring engineers and people from around the country together to see the technology.

Hybrid-composite beams: U.S. Patent No. 6,145,270
In the advent of structural engineering, it became evident that by placing blocks of stone sequentially along a circular curve, it was possible to create a structure that would span a great distance. Centuries later, iron and steel made it possible to span greater distances with much lighter structures. Throughout history, engineers have sought to find creative solutions to facilitate a means to an end. This has often led to experimentation with hybrid structures that utilize more than one type of building material to comprise a structural member. It is this same curiosity that has led to the development of a structural member comprised of several building materials, each with unique performance characteristics. The hybrid-composite beam, developed by HC Bridge Company, LLC, is comprised of three main sub-components that are a shell, compression reinforcement and tension reinforcement. The

32 jec composites magazine / No77 December 2012

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JEC COMPOSITES MAGAZINE - Issue #77 - December 2012

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #77 - December 2012