High-Performance Steel (HPS): Structural steels have high strengths, enabling engineers to design and build long-span bridges. However, extra care must be taken in welding, corrosion protection and crack prevention. To overcome these concerns in structural steels, a cooperative research program between the FHWA, the U.S. Navy and the American Iron and Steel Institute (AISI) developed HPS for bridges and structures. HPS has improved weldability, and resulted in excellent corrosion resistance, high crack tolerance and very high strengths. The combination of these improved properties of HPS leads to cost-effective applications in bridge design and construction. Many states are taking advantage of these properties in new bridge designs to improve long-term performance, lower first cost and reduced life-cycle cost through lower maintenance and repair costs.
Fiber-Reinforced Polymers/Composites (FRP): FRP has unique properties, such as high strength, light weight, corrosion-resistance, high toughness, etc., which make it very good for strengthening, repair and seismic retrofit of bridges and structures. FRP has great potential for providing engineering solutions for rebuilding our aging infrastructure. It has attracted the interest and attention of the research community, government and private industry to find ways to successfully integrate FRP in structural applications. In recent years, FRP has been used as rebars and prestressing tendons in concrete structures, sheets and laminates for strengthening concrete and steel members, wraps and shells for seismic retrofit of concrete columns, and structural shapes for bridges and decks.
Ultra-High-Performance Concrete (UHPC): A fiber-reinforced cementitious composite, UHPC is the next level of high-performance concrete. UHPC has very high compressive strengths in the range of 20 ksi to 30 ksi, and tensile strengths as high as 1.5 ksi. It has high durability – very low permeability and is highly resistant to abrasion, freeze-thaw and scaling. The cost of UHPC is steep at the present time. It is now used cost-effectively in a few applications, including closure pours between precast panels, precast deck panels and some girders.
5. Self-Consolidating Concrete (SCC): SCC is a concrete that does not require vibration during placement. SCC flows into and completely fills intricate and complex forms under its own weight, passes through and bonds to congested reinforcement under its own weight, and is highly resistant to segregation. SCC offers many advantages for the precast concrete industry and cast-in-place construction. For example, low noise levels in the plants and construction sites, eliminated problems associated with vibration, less labor involved, faster construction, and improved quality and durability. States are using SCC in precast, prestressed bridge elements, and cast-in-place projects.
6. Lightweight Concrete (LWC): Benefits over normal-weight concrete include reduced dead load of structure, enhanced durability (better curing), and reduced handling, transportation and erection costs (although actual material costs are higher).
7. Seismic Retrofit of Bridges: Older bridges are susceptible to damage or collapse due to earthquakes. FHWA has developed Seismic Retrofit Manuals to help states with state-of-the-practice in seismic retrofit of bridges. Seismic retrofit is a cost-effective way to protect our investments in bridges and structures. States with high seismicity are assessing the vulnerabilities of their bridge inventory and develop a program for seismic retrofit.
8. Accelerated Bridge Construction (ABC): ABC is taking advantage of prefabricated bridge elements and systems (PBES) to help highway agencies dramatically reduce construction time and traffic disruptions, resulting in improved safety in the work zone. PBES approaches offer high quality because they are manufactured offsite under controlled conditions. With the use of self-propelled modular transporters (SPMT), an entire bridge can be fabricated off the bridge site and then transported to the bridge site for overnight installation. SPMTs can be used to remove and replace bridges efficiently and effectively.
9. Improved bridge safety programs and practices:
We updated the National Bridge Inspection Standards regulations in 2005;
We are currently enhancing our oversight of compliance with the regulations (data-driven, risk-based process);
We have additional staff dedicated to bridge safety;
Following the I-35W collapse, we issued gusset plate inspection and load rating guidance to bridge owners.