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New Construction. Some agencies use asphalt concrete overlays on new decks and protect the deck with a waterproofing membrane below the asphalt overlay. Currently, however, concrete-wearing surfaces are more popular on new bridges than asphalt concrete. Concrete surfaces may be placed as an integral part of the structural bridge deck (monolithic), or placed as bonded […]

Concrete bridge decks designed by the current AASHTO method described above have large amounts of reinforcing steel. (Some say it is enough to drive on, and that the concrete is provided just to make the ride smoother!) In the past, in areas where deicing salts are used, corrosion of the top steel caused extensive spalling […]

During construction, bridge deck concrete can be supported by reusable wood forms, permanent stay-in-place steel forms, or precast prestressed-concrete planks. Where per­mitted, contractors will generally use stay-in-place steel forms rather than removable wood forms. Allowance must be made in the design of the bridge for the extra weight of the steel forms, and for extra […]

AASHTO Standard Specification requirements for design of concrete bridge deck slabs on longitudinal beams are based on distribution of loads in the slab according to Westergaard theory and assume flexural action of the slab. On the basis of these specifica­tions, many states have developed design tables and charts for quick determination of slab thickness and […]

Bridge decks can be constructed of timber, concrete, or steel. Timber Decks. For bridges on unpaved roads or low-volume roads in rural environ­ments, timber decks of modern construction, such as Glulam (glued laminated) decks, can be serviceable and durable. For high-traffic-volume highways, timber is at a great disadvantage because of high cost, difficulty of fitting […]

Aluminum. A few bridges, including highway plate girder bridges and arch-type pedestrian bridges, have been constructed of aluminum. These bridges have generally performed well and have not required much maintenance. The plate girder bridges do not seem to have experienced problems that one might anticipate due to the difference in thermal coefficient between the alu­minum […]

Steel for bridges is available in several different strength levels, each of which may be specified under ASTM A709, Standard Specification for Structural Steel for Bridges. TABLE 4.1 Steels for Bridges ASTM designations Bridge Structural steel AASHTO Type of steel specification* specification designations Structural carbon A709 grade 36 A36 M270 grade 36 High-strength, low-alloy A709 […]

The basic materials most often used to construct bridges are concrete and steel. Timber is occasionally used for deck construction and sometimes for short-span bridges. 4.5.1 Concrete High strength is desirable for bridge concrete to reduce member size and weight, but durability is equally or more important. Component materials must be compatible with each other, […]

Bridge Width. Roadway width on bridges is the inside measurement to the bottom of the sidewalk curb or the bottom of the safety barrier. For bridges on roads where sidewalks are not provided, the bridge width is made equal to the approach roadway width including shoulders, so that the bottom of the barrier curb or […]

AASHTO Specifications. For many years, the basic manual for design of highway bridges has been the Standard Specifications for Highway Bridges adopted by the American Association of State Highway and Transportation Officials (AASHTO). These specifications permit use of either allowable stress design or load factor design. In 1994, however, AASHTO published a completely new alternative […]