MMC’s Latest Composite Bridge Design
Features Glasforms Beams |
San Jose, Calif. - Glasforms Inc. has produced the latest in fiber-reinforced polymer (FRP) bridge decks for Raleigh, N.C.-based Martin Marietta Composites (MMC). Working with MMC’s design team, Glasforms pushed the limits of pultrusion technology to develop MMC’s fourth-generation composite FRP bridge deck, DuraSpanä. Presently, two bridges—one in California and one in Ohio--are scheduled to receive the FRP deck installations in the summer or fall of 1999. Why DuraSpan™? With a strength and stiffness greater than reinforced concrete (RC), the DuraSpanä pultruded assembled decks are 20% stiffer than a standard RC deck. The decks can exceed AASHTO loads by a safety factor greater than 5 at one fifth the weight of RC deck sections. Furthermore, testing has confirmed that the DuraSpanä deck has an expected 75-year life span for highway use. Where will they be installed? The first in the new generation of decks will be installed in Kings Canyon National Park, just west of Fresno, Calif. The bridge, measuring 66 feet long and 44 feet wide – or wide enough for two lanes of traffic and two pedestrian lanes – will be installed with six deck sections on concrete-filled, filament-wound carbon girders. The second deck, measuring 48 feet long and 46 feet wide, will be installed in Darke County, Ohio. That bridge deck will be assembled in six panel sections that are 8 feet wide by 46 feet long. How were they fabricated? The new FRP bridge-deck beams are produced via the pultrusion process - a continuous laminating process for fiber reinforced plastics where the product is pre-formed dry and impregnated with resin in the die. In total, 26 plies of tri-axial and quadri-axial fabric weighing 13 pounds per foot are fully impregnated in the die, yielding deck beams that weigh 17.5 pounds per foot (also per square foot). The unique blend of fabrics provides high-axial strength and stiffness while enhancing orthotropic composite properties. Glasforms and MMC have aggressively sought to optimize both the product and process to yield a high-performance deck at prices competitive with conventional bridge decks. The new FRP deck design uses a custom-pultruded beam 7.66 inches high by 16 inches wide with wall thicknesses of one-quarter to three-quarter inches. The profile consolidates multiple unique trapezoidal and rectangular sections into chemically bonded, interlocking components. A semi-automated assembly line produces assembled decks from raw materials in less than a day with minimal labor. FRP decks are factory-assembled and inspected before they are shipped for quick and easy installation at the job site. |
