ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/306906
by M. Myint Lwin 54 | ASPIRE , Fall 2007 F H WA F H WA T here are about 600,000 highway bridges in the United States with state and local governments owning most of them. More specifically, 47 percent are owned by the states and 51 percent owned by local governments, such as counties and municipalities. The remaining 2 percent are federally and privately owned. Concrete, steel, prestressed concrete, and timber are the predominant materials used in bridge construction. Other materials, such as, masonry, cast or wrought iron, aluminum, and composites are used in less than 1 percent of the bridges. The average age of the highway bridges in the United States is about 45 years. Many are approaching 100! As the aging bridges are used by an increasing number of vehicles and subjected to higher vehicular loads, forces of nature, and corrosive environment, their physical conditions are deteriorating, their load-carrying capacities are reduced, and their roadway widths are becoming inadequate. Over 28 percent of the nation's highway bridges are considered structurally deficient or functionally obsolete. The U.S. Congress finds and declares that it is in the vital interest of the United States that a highway bridge program be carried out to enable states to improve the condition of their highway bridges over waterways, other topographical barriers, other highways, and railroads. This is to be accomplished by replacement and rehabilitation of bridges that are determined to be structurally deficient or functionally obsolete, and through systematic preventive maintenance of bridges. Highway Bridge Replacement and Rehabilitation Program The Surface Transportation Assistance Act of 1978 replaced the Special Bridge Replacement Program (SBRP) with the Highway Bridge Replacement and Rehabilitation Program ( H B R R P ) e x t e n d i n g f u n d i n g t o i n c l u d e rehabilitation to restore the structural integrity of a bridge on any public road, and rehabilitation work necessary to correct major safety defects. The Surface Transportation Assistance Act of 1982, the Surface Transportation and Uniform Relocation Assistance Act of 1987, and the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA) continued the HBRRP. Additionally, ISTEA allowed federal participation in bridge painting, seismic retrofitting, and calcium magnesium acetate applications. The Transportation Equity Act for the 21st Century (TEA-21) continued HBRRP. It authorized the set-aside of $100 million for each FY1999-2003 for discretionary allocation by the secretary for major bridges with the provision that a maximum of $25 million would be made available for seismic retrofit of bridges, including projects in the New Madrid fault region. It also authorized a set-aside of $25 million for FY1998 for seismic retrofit of the Golden Gate Bridge. TEA-21 changed the HBRRP eligible work activities to include sodium acetate/formate or other environmentally acceptable, minimally corrosive anti-icing and deicing compositions, and installing scour countermeasures. T h e S a f e , A c c o u n t a b l e , F l e x i b l e , a n d Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU) of 2005 continued the HBRRP for replacement or rehabilitation of structurally deficient and functionally obsolete highway bridges in the states. Under this legislation, painting, seismic retrofit, systematic preventive maintenance, installation of scour countermeasures, and the application of calcium magnesium acetate, sodium acetate/formate, or other environmentally acceptable, minimally corrosive anti-icing and deicing compositions are eligible for HBRRP funding. Eligibility for Federal Funds for Rehabilitation In general, rehabilitation project requirements necessary to perform the major work required to restore the structural integrity of a bridge as well as work necessary to correct major safety defects are eligible for federal-aid funds. Bridges to be rehabilitated shall, as a minimum, conform to the provisions of 23 CFR Part 625, Design Standards for Federal-Aid Highways, for the class of highway on which the bridge is a part. An AASHTO-approved sufficiency rating formula is used as a basis for establishing eligibility and priority for rehabilitation of bridges. The sufficiency rating formula is a numerical rating system, 0 to 100, based on the bridge's structural adequacy and safety, essentiality for public use, and its serviceability and functional obsolescence. In general, the lower the rating, the higher the priority. A rating of 100 represents an entirely sufficient bridge, which does not require any work. A rating of 80 or less will be eligible for rehabilitation. A rating of less than 50 will be eligible for replacement. A rating of 0 represents an entirely insufficient or deficient bridge. A more detailed description of the sufficiency rating formula may be found in the FHWA Report No. FHWA-PD-96-001 Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation's Bridges. Systematic Preventive Maintenance SAFETEA-LU has a special rule for preventive maintenance, allowing a state to perform seismic retrofit, systematic preventive maintenance, or installation of scour countermeasures for a highway bridge without regard to whether the bridge is eligible for replacement or rehabilitation. This legislation makes systematic preventive maintenance activities, such as crack sealing, expansion joint repair, controlling deterioration, seismic retrofit, scour countermeasures, and painting, eligible for federal-aid funds. A state may carry out preventive maintenance for a highway bridge without regard to sufficiency rating or deficiency status. Systematic preventive maintenance implies the use of an effective Rehabilitation to Improve Safety, Reduce Congestion, and Extend Service Life of Highway Bridges 10802_Aspire_Fall07.indb 54 8/30/07 3:05:51 PM