A consideration that frequently receives too little attention in bridge design is durability. Probably the most important decisions made regarding the future durability/longevity of a bridge are made at the very beginning of the design process. These are upper department of transportation (DOT) management decisions regarding bridge design life, geometric parameters (e.g., number of lanes, shoulders, underneath clearances), average daily traffic, average daily truck traffic, design truck loading, material requirements, policing of overweight truck policies, preventative maintenance programs, and others. Thirteen actions are recommended in this article for consideration by DOT managers to enhance the durability/longevity of highway bridges. The actions are quite specific and are discussed in detail. They address design life and load considerations, geometric parameters, design traffic volumes, material requirements, training programs, and preventative maintenance programs. Changes in all or a number of the areas recommended could have a very significant positive impact on future bridge durability/longevity.

A factor that typically receives too little consideration in bridge work is durability, and the time to begin thinking about durability is at the beginning of the bridge planning and design phase. Once a bridge is designed and constructed, much of its eventual durability and longevity has been determined. Assessments of bridge durability performance were made based on data available in the literature along with a subset of the data available in the historical bridge records of the Alabama Department of Transportation. From these reviews it was determined that bridges in Alabama are currently providing service lives of approximately 55–60 years. A recent Federal Highway Administration edict that main artery highway bridges be designed for 75 year service life means that Alabama must improve the durability performance of its bridges. Improvements can best be made at the planning, structural design, and material selection stages, that is, in the design phase. Primary areas of focus in which to make changes and improvements can best be pinpointed by looking at durability performance of individual bridge subcomponents.

To gain a better understanding of how highway bridges in Alabama are performing in the area of durability/longevity, a review of the historical bridge records of the Alabama Department of Transportation was performed. Because of the large number of bridges, it was decided to select the subset of old bridges that were replaced during the 1980–93 period to evaluate their durability performance. Based on an analysis of this data subset, the most structurally deficient major component was the deck, followed by the substructure. The superstructure performed best. The worst performing subcomponents were the wearing surface, deck structure, curbs, expansion joints, abutment wings, and abutment backwall. The best performing subcomponents were the drains, rivet/bolt/weld connections, and piers or bents. The major reason for decks to fail functionally was the deck geometry. However, the structural condition of decks at the time of functional obsolescence was also near failure. The data indicated that simple span construction was superior to continuous span construction for enhancing durability. Simple spans excelled in performance in every component and subcomponent except for the curbs, columns of the bents or piers, and the alignment of members.

A design consideration that probably receives too little attention in bridge design and in concrete mixture design as well, is durability. One of the primary factors affecting concrete bridge durability is cracking. This cracking results primarily from thermal and drying shrinkage and from static and dynamic truck loadings. Structural designers have greater control of the ultimate cracking and durability performance of bridges than any other group. Specific actions are recommended in this article for the consideration of structural designers to mitigate concrete cracking and thus to enhance bridge durability. Most of the actions pertain to the deck, which is the bridge component that typically exhibits the greatest deterioration rate. An example illustrates dramatic improvements in bridge deck performance in the transverse direction for only a 2.54 cm (1 in.) increase in thickness. In the longitudinal direction, a 2.54 cm (1 in.) deck thickness increase also results in significant beneficial effects.

This article reports on the results of two actions that were taken to assess the nature, extent, and primary causes of highway bridge deterioration in Alabama. The first was a mail survey questionnaire that was sent to all state and county bridge maintenance engineers in the state. The questionnaire indicated that almost all engineers felt additional attention was needed at each phase of bridge evolution—planning, structural design/materials selection, construction, and maintenance—to enhance durability. Most of the group surveyed felt that concrete bridges (both prestressed and reinforced) were more durable, that support girders and bent caps were the better performing subcomponents, and that joint and bearing assemblies were the weakest performing elements. The second action was a detailed interview with Alabama Department of Transportation (ALDOT) bridge maintenance engineer in conjunction with site visits to numerous ALDOT bridges. The major types and causes of bridge deterioration identified during these visits were faulty deck joints, poor drainage, concrete cracking/spalling, faulty bearings, corrosion of structural steel, fatigue of structural steel, abutment erosion, foundation scour, and poor quality construction/inspection.