Guidelines for Bridge Management Systems
|Publication Date:||1 January 1993|
Scope of the Problem
There are approximately 577,000 bridges throughout the United States. Most of these bridges were constructed during two great building booms, the Depression years and the Interstate construction era.' A large percentage of the roughly 90,000 bridges built in the 1930s are reaching the end of their useful life and must be replaced or rehabilitated. The 223,000 bridges built between 1956 and 1975 are beginning to pass through their midlife and most will require deck replacement or major repairs.
The vagaries of political support and funding for bridges have left many states and localities with insufficient funds to address these important needs. Even agencies that have kept up with most of their needs occasionally encounter funding shortfalls. Limited funds must be managed as wisely as possible.
Over the next two decades bridge managers will be attempting to balance limited, inadequate resources against increasing bridge needs. Structural failure cannot be tolerated, yet funds often must be thinly spread because they are limited. The best action for each bridge, considered alone, is not necessarily the best action when faced with funding constraints. InsufFrcient funds often mean delaying or downscoping the ideal type of project. Also, some agencies try to keep all bridges for which they are responsible open and without load restrictions, but others find that limited funds necessitate posting and closing of deteriorated bridges.
Besides ensuring the best use of limited funds, other concerns in the management of the nation's bridges are safety, preservation of investment, and serving commerce and the motoring public. Highway and transportation agencies must carefully monitor potentially severe safety problems such as bridges subject to collapse due to scouring or lack of structural support. They must identify premature deterioration and damage of bridges and use these funds to avoid further deterioration and correct damage through proper maintenance and repair. These agencies also must strive to reduce inconvenience and disruptions to commerce and passenger travel due to load and clearance restrictions or closing of bridges.
The complexity of the bridge management problem is magnified by the wide variety of bridge designs and materials ranging from simple concrete slabs to steel trusses to cable-stayed bridges. Bridges of different designs and materials deteriorate at different rates. and so do their components. Bridges are made up of major components: deck, superstructure and substructure, and numerous subcomponents such as the roadway wearing surface, railings, joints, bearings, girders, bracing, abutments, and piers. Decisions as to the timing and the nature of maintenance and repairs to components depend not just on their deterioration rate but also interconnections among them. For example, a deteriorated steel girder may result from chloride contaminated water leaking through poor deck expansion joints. Repair of the joints should precede or accompany the repair or replacement of the girder.
Public officials, administrators, and bridge engineers have increasingly acknowledged the need for new analytical methods and procedures to assess the current and future conditions of bridges and determine the best possible allocation of funds among various types of bridge maintenance, repair, rehabilitation, replacement, and improvement work. The advent of BMS is a response to this need.
A BMS facilitates budget and program formulation by providing a structured process based upon sound economic and engineering analysis. This process also helps to mediate among all the players that interact in bridge funding and spending decisions: professional staff, administrators, elected officials, and the general public.
Each state has responsibility for managing from roughly five hundred to more than twenty thousand bridges. The scope and complexity of the bridge management problem is such that guidelines are needed for state agencies regarding the development, implementation, and enhancement of a BMS. These guidelines are intended to inform state agencies of the essential fundamental characteristics of a BMS, implementation options, and reasonable expectations, and to promote areas of uniformity in state practices and data collection. These guidelines will also be useful to regional and local agencies and to bridge and turnpike authorities.