LIFE-CYCLE PERFORMANCE OF NEW YORK CITY BRIDGES

The 1991 annual report of the New York City Department of Transportation (NYC DOT) Bridge Bureau lists 872 bridge structures under its purview. Included are the 4 East River crossings, 25 movable bridges, 5 tunnels, and a large variety of structures over land, with a total number of spans approaching 6,000. The average age of the bridges in this network is approximately 68 years. This is in sharp contrast with the average age of 28 years of the nearly 600 bridges in the metropolitan area, which are managed by New York State Department of Transportation (NYS DOT). As a result of the federally mandated bridge inspection program, which was originated in the late 1970s, it is currently possible to consider the bridge structural condition as a variable with respect to time. The length of the period since inspections began and the large variety of bridge conditions reveal for the first time certain patterns in the life-cycle performance of the bridges in New York City. This deterioration model analysis is regarded as a fundamental tool of the bridge management program stipulated by the Intermodal Surface Transportation Efficiency Act of 1991. Of particular interest are certain bridge components, such as deck, primary member, joints, and the like. The inspection records established by NYS DOT allow review of the performance of such components over time. The results may yield not only an insight into the behavior of various structural members, but also certain indications of their relationship. From the deterioration patterns obtained from inspection records and the knowledge of maintenance, repair, and reconstruction costs, it is possible to select optimal strategies of bridge management and superior design. The conclusions are specific to the geographic area under consideration and the period of the data on which they are based. The term "optimal" implies a certain set of constraints. It is recognized that the optimal state of a bridge network may not be the highest priority in optimizing a local budget. The overall optimization process is beyond the scope of this paper. It is pertinent, however, to investigate the degree to which bridge life-cycle behavior may be assessed in an unconstrained environment and the potential effects of budget constraints during design, construction, and maintenance. Results of deterioration modeling for bridges and bridge components performed at the Bridge Bureau of NYC DOT during the past 2 years are summarized.