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The span range of a shallow bridge may be extended beyond the limits of a slab bridge by using precast prestressed-concrete box beams as illustrated in Fig. 4.6. The beams are prefabricated off-site. They are rectangular and, except for very shallow beams [12 in (305 mm)], which may be solid, have from one to three […]

For short simple spans (up to 30 ft or 9.1 m) and for somewhat longer continuous spans (interior spans up to 55 ft or 16.8 m), reinforced-concrete flat slabs provide a minimum — depth bridge. Figure 4.5 shows a schematic of this bridge type. At a slab depth of about 2 ft (610 mm), the […]

The type of bridge and the span layouts are interdependent. Bridge type cannot be selected without regard to the length of spans, the ratio of adjacent span lengths, and whether spans are to be made continuous. Table 4.2 lists common types of bridges and the maximum span lengths below which they may be an economical […]

Where possible, bridges should be made continuous. Continuous spans are less prone to catastrophic collapse from loss of substructure support due to stream erosion, earth­quake, or vehicle or vessel collision. Bridges with multiple simple spans must have two lines of bearings and an expansion joint at each intermediate support. Two lines of bearings, each having […]

Several types of expansion joint-sealing devices are available. Properly sized and installed, they can greatly reduce, if not eliminate, drainage through the joint. Some of the available types are • Polymer-modified asphalt • Compression seal • Slab-type seal • Strip seal • Modular seal Polymer-Modified Asphalt. For resurfacing projects where an asphalt concrete overlay or […]

Bridge roadway expansion joints are provided to accommodate the thermal changes in the superstructure, and, in the case of prestressed-concrete bridges, to accommodate creep shortening of the superstructure as well. They are required at abutments that are restrained against longitudinal movement and at the end of supported superstructures free to translate due to provision of […]

Joints in bridges fall into two categories: deflection joints and expansion joints. 4.14.1 Deflection Joints Contrary to what the name implies, deflection joints, when placed in concrete barriers and parapets, are used primarily to minimize the vertical shrinkage cracking that would otherwise occur in long, unjointed panels. Some states permit a longitudinal spacing of joints […]

The cost of initial painting and periodic repainting of structural steel bridges can often be eliminated by the use of bare weathering steel. From an economic standpoint, the use of multicoat high-technology paint systems should be reserved to those bridges that are not suitable candidates for weathering steel. To ensure successful long-term performance, the Federal […]

The application of protective coatings to steel bridges, and the maintenance reapplication of coatings, is costly and so alternatives to the use of coated steel should be sought. Where appropriate, unpainted weathering steel should be used instead (see Art. 4.13). If a coated bridge is still the best candidate for the particular location, a long-lasting […]

For the primary superstructure members of a bridge (not including the deck), concrete (reinforced and prestressed) and structural steel are the principal candidates. Concrete and steel both have desirable attributes and shortcomings as bridge materials. In general, bridges of both materials can be designed, constructed, and maintained to ensure long life. Claims of both steel […]