AGING INFRASTRUCTURE ISSUES
The infrastructure in the United States is aging and, whether publicly or privately owned, significant resources are required to repair, replace, or modernize it. Due to the high costs associated with these efforts, owners need to identify structures with high risk-of-failure consequences and find the most cost-effective solutions for rehabilitation. High consequence
infrastructure includes:
- Highway and railway bridges,
- Roadways for intra and interstate transportation,
- Dams, locks, and levees for flood control and cargo transportation,
- High rise business, apartment, and condominium towers, and
- Power generation and distribution facilities for Nuclear, Fossil and Hydro utilities.
All infrastructure is susceptible to degradation that comes with aging. The accumulation of degradation and a structure's subsequent failure is difficult to predict due to the numerous
real-world factors that influence rates of degradation. These real-world factors can lead to some structures failing prematurely and others lasting well beyond their original design life. Asset owners need to be on the lookout for:
- A structure that is nearing or has exceeded its expected design life,
- A structure that shows signs of steel corrosion, freeze-thaw damage, or concrete degradation such as alkali aggregate reaction (AAR),
- A structure that is overloaded due to an increase in auto, truck or rail traffic,
- A structure with a known design deficiency when evaluated with modern design code requirements,
- Increases in regional hazards, such as increased seismicity or increased probable maximum flood levels, and other climate change-related issues.
Often, structures are kept in service beyond their original design life. Many older structures are held to a design basis, i.e., code requirements, consistent with the time the structure was designed. Evaluating older structures using current code requirements can potentially affect original safety margins both positively and negatively. Increased capacity limits can be established for steel welded and bolted connections and utilizing actual concrete compressive strengths above original design strength that may provide added safety margin. On the other hand, identifying substandard details relative to current practice, particularly concrete reinforcement detailing will reduce originally considered safety margins. Additional factors that can affect the service life of a large infrastructure projects include environmental conditions, reliability of materials, quality of construction, and loading conditions.
Throughout the country, many structures such as bridges, dams, and power generating facilities remain in active service as they approach or exceed their design (or licensed) service life. Replacement is often prohibitive for many of these structures due to cost. However, failure of these structures could have more significant consequences beyond lost revenue, including loss of life.
