Design and Construction

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Innovative Cost-Effective Standard Decks for Movable Bridges

Of the 50 states New Jersey ranks third for the number of movable bridges. With an average age of approximately 40 years, more than 50 percent of these bridges are structurally deficient, mainly due to their bridge decks. Many of these bridges, whether state or locally owned, are subjected to significant average daily truck traffic (ADTT). Because of their condition and their location on significant commercial routes in the state, many of these bridge decks are expected to be replaced in the coming years as part of the NJDOT capital program. Bridge decks are the most vulnerable component due to being subjected to repeated abrasive loading from passing vehicles, weather, and road salts as part of winter maintenance.

 

To reduce the demands on the primary moving elements, most movable bridge decks are designed to be lightweight, mostly by employing open or partially filled grid decks. Concrete decks are particularly susceptible to corrosion damage, requiring frequent re-decking. On the other hand, open grid decks are prone to fatigue cracking, the exposed superstructure and movable elements are susceptible to corrosion damage, and contribute adversely to the environment by draining directly into the river below.

 

Steel orthotropic bridge decks are ideal for movable bridges. However, the closed rib decks tend to be costly owing to intensive fabrication demands. An open rib variation of these decks can provide an efficient solution for movable bridges. Moreover, with proper design, these decks can provide a service life of 75 years or more with minimal maintenance. In addition, the ability for steel orthotropic decks to be designed and constructed in modular sections has the potential for reducing time and cost of construction. An experimental and computational research project is proposed for developing a standardized open rib orthotropic deck that can provide a long-lasting, cost-effective solution for replacing decks of movable bridges in New Jersey. In addition, the research proposes to explore alternative deck designs and materials, including solution for bridges having low ADTT (such as aluminum and composite bridge decks).

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Idea No. 148