Some of the earliest work in the area of application of composites to civil structures was performed by Meier at EMPA in Switzerland in the 1980s (2, pp. 243–251). Since then, numerous research studies and field applications have been performed. A series of conferences in the United States, Canada, and Europe has focused on the subject of composite applications to civil structures and served as a show- case for the various studies being done in this area (3–10). Com- posites have been considered for repair and strengthening as well as for new structures. In addition, several researchers have written sur- vey papers discussing promising applications of composite materials for a variety of civil structures (11, pp. 288–301; 12; 13, pp. 15–30; 14; 15, pp. 295–298). In recent years, several composite bridges have been built in the United States and abroad (16 ). Details of one such bridge and its performance as determined by a diagnostic load test are presented here. BRIDGE DESCRIPTION During the summer of 1999, Bridge 1-192 on Old Milltown Road in New Castle County, Delaware, was rehabilitated. The simply sup- ported, one-lane bridge carries light local traffic over Mill Creek. The original structure was a single-span, concrete slab-on-steel girder bridge. The superstructure consisted of a 203-mm concrete slab supported on six longitudinal steel girders spaced 859 mm on cen- ter. The clear span of the bridge was 10.7 m, and the out-to-out width of the deck was 5.0 m. The bridge has a skew angle of 58 degrees relative to the centerline of the roadway. The Delaware Department of Transportation (DelDOT) deter- mined that the bridge needed repairs because of deterioration of the concrete slab. The solution was to remove the existing concrete slab and replace it with a lightweight polymer composite slab. Both the existing steel stringers and the existing abutments were retained, although in the repair, an integral abutment detail was utilized. The completed bridge is shown in Figure 1 (this photograph was taken during the diagnostic test). The polymer composite slab was made using sandwich construc- tion with two thin face sheets separated by a core. The one-piece slab was fabricated by Hardcore Composites of New Castle, Delaware, using E-glass fibers and vinyl-ester resin. The fabrication processes included placing QM6408 precut fiber preforms in the desired geo- metric configuration and infusing the vinyl-ester resin using a vacuum-assisted resin transfer molding (VARTM) process. The 25.4-cm deep glass fiber–reinforced polymer (GFRP) slab weighed less than 1.4 kN/m 2 , roughly 30 percent of the original concrete slab. Thin neoprene pads were placed on top of the steel stringers before the deck slab was set to help alleviate hard spots that would be caused by having a flat slab sit directly on top of girders with slight elevation differences. The slab was connected to the steel stringers using metal Because of the continued deterioration of U.S. bridges combined with the increasing cost of bridge maintenance, the U.S. bridge inventory contin- ues to experience a backlog of structurally deficient bridges. One poten- tial solution is the implementation of new high-performance materials. Because of their many beneficial characteristics, including being light- weight, having high strength- and stiffness-to-weight ratios, and being corrosion resistant, advanced polymer composites represent one such alternative. In 1999 the Delaware Department of Transportation reha- bilitated a deteriorated concrete slab-on-steel girder bridge by removing the concrete slab and replacing it with a lightweight glass fiber–reinforced polymer (GFRP) deck. In the rehabilitation, the existing abutments were slightly modified and the original steel girders were retained. On July 28, 1999, a diagnostic load test of the bridge was performed using a fully loaded 10-wheel dump truck. The test included stationary load cases, semi- static load passes, and dynamic load passes. The details of the GFRP slab- on-steel girder bridge as well as the bridge performance as determined from the field load test are presented. The United States faces the dilemma of a deteriorating transporta- tion infrastructure. It has been widely reported that approximately 40 percent of America’s 600,000 public bridges are either struc- turally deficient or functionally obsolete (1), with the rehabilitation and replacement cost estimated at close to $150 billion. This prob- lem has created an urgent need for an effective means of structural repair, rehabilitation, or replacement. Increased load-carrying require- ments, material degradation (corrosion, cracking, spalling), design deficiencies, and in-service structural damage are among the many factors causing structural deficiency. Because of their many benefi- cial characteristics, advanced polymer composites represent a new and promising solution for a variety of problems. Composite ma- terials have a high strength-to-weight ratio and are generally not affected by the harsh highway environment (they do not corrode and they have excellent fatigue resistance). With increased use, advanced composite materials can have competitive acquisition costs com- pared with those of traditional construction materials and offer sig- nificant potential for reducing overall life-cycle costs. In addition, composites are very lightweight, and the construction techniques used for advanced composites can greatly speed the construction or repair process, saving significant monies in both owner-agency and transportation-system-user costs. Finally, by careful selection of the fibers and resins used to manufacture fiber-reinforced polymer (FRP) composites and by the tailoring of fiber architecture and selection of the appropriate manufacturing technique, FRP composites can be fabricated with the desired structural properties and geometry. Transportation Research Record 1770 ■ 105 Paper No. 01-3290 Performance of Glass Fiber–Reinforced Polymer Deck on Steel Girder Bridge Michael J. Chajes, Harry W. Shenton III, and William W. Finch, Jr. M. J. Chajes and H. W. Shenton III, Department of Civil and Environmental Engi- neering, University of Delaware, Newark, DE 19716. W. W. Finch, Jr., Struc- tural Testing Incorporated, P.O. Box 9817, Newark, DE 19714-9817.