146 Current Usage

The first bridge that uses HPS70W steel in design and construction was the Snyder South Bridge on State Rt. 79 in Dodge County, Nebraska (Figure 14.2). It is a 150-ft (45.7-m) long simple span bridge that provides a 35.5 ft (10.8 m) clear roadway on a concrete deck supported by five 4'6" (137 cm) deep welded plate girders. The bridge was opened to traffic in October 1997. Since then, the number of bridges designed and constructed using some HPS components is on the rise. As of 2003, some 35 States in the United States have over 160 HPS bridges in service, or under design, fabrication, and construction. The bridges vary in length from under 100 ft (Rte 3 over Rte 110, MA) to over 5000 ft (I-55/I-64/I-70/US-40 Poplar Street Complex, IL), differ in the number of spans, and represent various bridge types although Plate or I-girder bridges are the most common. HPS have been used on these bridges as truss gusset plates, to floor systems and main girders. When used as main girders, a design that employs HPS70W steel in the negative moment regions, or a hybrid design that uses HPS70W steel for all bottom flanges and negative moment top flanges but uses conventional Grade 50W or HPS50W in other areas is often employed (see Figure 14.3 for a specific design of a uniformly loaded girder) because it represents a good compromise for strength, weight savings, and economy. Although the unit cost of HPS is higher than conventional steels, savings can often be achieved (Barker and Schrage 2000; Horton et al. 2000, 2003; Price and Cassity 2000; Van Ooyen 2002; Clingenpeel and Barth 2003) because the use of HPS generally results in smaller/shallower members and fewer girders (since greater girder spacing can be used due to the higher strength offered by the high-strength steels), and thus fewer diaphragms, stiffeners, and welds are needed. The resulting structure is also lighter, so savings in the construction of the piers and abutments may be realized. However, in using HPS or other high-strength steels for bridge construction, the designers need to pay more attention to the overall deformations of the structure, global instability of the

FIGURE 14.2 Snyder South Bridge (courtesy of Nebraska DOT and FHWA).

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