Anwar Ahmad, Federal Highway Administration
Typically the term “bridge preservation” is associated with existing bridges. However, bridge preservation actions and strategies should be considered during all phases of a bridge’s life, from the initial planning through design, construction, and its service life until the bridge is decommissioned. Considering preservation throughout these stages is essential to maximize the service life and minimize the overall lifetime cost of the bridge.
The advancement of bridge design, evolution of materials, and innovative construction techniques has facilitated the increase of bridge design life from 50 years to 100 years. Achieving 100 years life for bridges cannot be accomplished with improved design practices, high quality materials, and construction techniques alone. Proper inspection, maintenance, and preservation actions and strategies must be employed throughout the life of a bridge. So, what does all that mean? First let’s start with defining bridge preservation.
Bridge Preservation
Bridge preservation is defined as “actions or strategies that prevent, delay or reduce deterioration of bridges or bridge elements, restore the function of existing bridges, keep bridges in good condition and extend their life. Preservation actions may be preventive or condition-driven.”(1)
Although this definition may appear to be intended for bridges that are in service, a successful bridge preservation strategy will encompasses much more.
Following is a brief discussion of the core stages of bridge life as they relate to bridge preservation:
Planning
Effective bridge preservation strategy begins in the planning stage for a new bridge. It is crucial to select appropriate materials that suit the anticipated bridge environment. Thanks to advanced research, innovations and technology in materials science, we continue to see high quality and high performance bridge materials being produced. Each material type has its purpose and limitations. So, it’s critical that the appropriate material for each bridge element is carefully evaluated and selected based on the intended service for that element in a given environment. Environmental factors include: type of service that will be provided by the bridge; type of crossing; drainage area; traffic volumes; and anticipated use of anti-icing chemicals. Other environmental factors also include the potential for a bridge to be subjected to hazardous materials, vandalism, terrorist attack, or other extreme events. So, in essence, proper planning takes long term preservation and maintainability of the bridge into account.
Design
The bridge community continues to strive towards improving design practices to enhance bridge safety, facilitate materials fabrication, and take advantage of better construction and preservation techniques. In addition to the American Association of State Highway and Transportation Officials (AASHTO) design specifications, most State Highway Agencies (SHAs) have their own bridge standards, specifications, policies and procedures. Some SHAs have developed design check lists as part of their quality control and quality assurance efforts. Some SHAs are incorporating “maintenance and preservation friendly design details” in their design practices and policies. These details include facilitating access to bridge superstructure and substructure components for inspection and maintenance activities; eliminating expansion joints(2) when possible by using continuous span designs or by using integral and semi integral abutment designs; and considering construction sequences of future preservation and replacement activities. Another preservation related strategy that can be incorporated in the design stage is the development of a bridge maintenance and preservation check list or instruction manual for newly designed bridges. Such bridge manuals are currently being developed for signature bridges, but the same principle can be applied to common bridges. Manuals of this type assist bridge managers and engineers in planning and performing the necessary bridge inspection and preservation activities.
Construction
There are a number of contracting methods available to construct bridges such as the conventional low-bid, design bid build, or performance based. Regardless of the contracting method used, ensuring full compliance with the design plans, specifications and materials’ tolerances during fabrication, transportation, erection, and construction is the most critical component of a successful bridge construction project. High quality construction and materials will enable the bridge to function as intended and thus reduce or eliminate the need for premature repairs.
Similarly, good design plans and quality construction materials and practices don’t guarantee a good bridge if not complemented with accurate construction plans and experienced construction personnel.
Inspection and Preservation
From the time the construction phase is completed to the time the bridge is replaced, there are numerous preservation activities that are essential for keeping the bridge serviceable. In addition to conducting routine inspections and maintenance, it’s critical that the appropriate actions and or treatments are applied to the bridge at the appropriate time. For example washing and cleaning the bridge on predetermined frequency is often a cost effective strategy for protecting the steel components from corrosion. However, washing becomes an ineffective strategy if it’s not done regularly. Another example of an effective preservation strategy is selecting the appropriate candidate bridges for waterproofing decks with seals and or different types of overlays. Sealing a significantly deteriorated bridge deck may not be a cost effective strategy, where as sealing a bridge deck that is in good or fair condition on regular basis is a good strategy for protecting and preserving the structural integrity of bridge decks. The FHWA Bridge Preservation Guide – Maintaining State of Good Repair Using Cost Effective Investment Strategies provides additional examples of effective preservation treatments and strategies.
Recognizing the relationship of preservation to the core bridge life stages is important to achieving the desired service life of a bridge; therefore, achieving the desired service life depends largely on the level of collaboration and coordination with the stakeholders and disciplines that are involved in the various stages of the bridge life.
Further Information For more information about bridge preservation, contact Anwar Ahmad at [email protected] or 202-366-8501.
1. FHWA Bridge Preservation Guide – Maintaining State of Good Repair Using Cost Effective Investment Strategies
2. Many expansion joint materials if not properly designed, installed and maintained are susceptible to leaking which if left unchecked leads to accelerating deterioration of superstructure and substructure that are located below the joint.