Integral Abutment Bridges
Integral Abutment Bridges
A survey on the status of use, problems and costs associated with integral abutment bridges
by Andreas Paraschos, P.E. and Amde M. Amde, P.E.
Integral abutment bridges provide an excellent alternative to conventional bridges built with bearings and expansion joints. Integral abutment bridges incur lower construction and maintenance costs compared to conventional bridges. In addition, they have a longer service life and a superior seismic performance compared to conventional bridges. Forty-one states are now using integral abutment bridges. Despite their wide acceptance by state transportation agencies and the engineering community in general, however, use of integral abutment bridges for long bridges and in situations that involve complex structural and soil conditions is still limited.
This article presents the findings of a survey conducted in 2009 by the University of Maryland at College Park that focuses on state integral abutment bridge practices. It summarizes the responses received from the states with regard to the status of use, problems and costs associated with the use of integral abutment bridges.
The Problem with Deck Joints
Early bridge structures were designed as a series of simply supported structures. With the introduction of the Moment Distribution Method in 1930, structural engineers began to design bridges as continuous structures. As a result, it became possible to construct longer bridges. Deck joints were provided in bridges in order to accommodate deck expansion and contraction without compromising the structural integrity of the bridges.
The introduction of deck joints created many problems to bridge owners. Joints are expensive to buy, install, maintain and repair. Repair costs are high. The joints leak throughout time, allowing deicing chemicals to attack the girder ends, bearings and supporting reinforced concrete substructures. The result is corrosion and deterioration of girders, bearings and substructure. Bearings are also expensive to buy and install, and are more costly to replace. Throughout time, steel bearings malfunction due to loss of lubrication or buildup of corrosion. Elastomeric bearings can split and rupture due to unanticipated movements. Because of these problems, it is necessary to continually inspect, maintain and periodically replace the joints. The use of expansion joints and bearings to accommodate thermal movement does not alleviate maintenance problems.
Integral abutments eliminate the need to provide deck joints. In addition, they can save bridge owners a considerable amount of money, time and inconvenience compared to conventional abutments. Because of these reasons, states began building integral abutments. Colorado was the first state to build integral abutments in 1920. Massachusetts, Kansas, Ohio, Oregon, Pennsylvania and South Dakota followed in the 1930s and 1940s. California, New Mexico and Wyoming built integral abutment bridges in the 1950s.
With the National Interstate Highway System construction boom in the late 1950s and mid-1960s, Minnesota, Tennessee, North Dakota, Iowa, Wisconsin and Washington began moving toward continuous bridges with integral abutments as standard construction practice. A testament of their excellent performance throughout the years is the fact that the current policy of the vast majority of states is to build integral abutment bridges whenever possible. This is confirmed by the results of this survey, which indicates that forty-one states are now using integral abutment bridges.
Problems with integral abutment bridges do exist; the severity and cause of problems differ from state to state. The state responses to the 2009 survey on integral abutment bridges conducted by the University of Maryland are shown in Tables 1, 2 and 3. This paper focuses on responses to the following three issues: status of use of integral abutment bridges, problems associated with integral abutment bridges, and construction and maintenance costs of integral abutment bridges compared to conventional bridges. Forty-seven states responded to the survey; responses were not received from Montana, Rhode Island and South Carolina.
Fig. 1. Evolution of integral abutment bridges in the United States.
Use and Problems Associated with Integral Abutment Bridges
The 2009 survey on integral abutment bridges conducted by the University of Maryland indicates that forty-one states are now using integral abutment bridges. Colorado pioneered the use of integral abutment bridges in 1920 followed by Massachusetts in 1930, and Kansas and Ohio in 1935. Eight states — Missouri, Tennessee, California, Iowa, Illinois, Kansas, Washington and Wyoming — have more than 1,000 integral abutment bridges in their inventories. Missouri has more than 4,000 integral abutment bridges and Tennessee has more than 2,000. The state of Washington, having built more than 1,000 integral abutment bridges by the year 2000, has decided to switch to semi-integral abutments.
In addition to being the first state to build integral abutment bridges, Colorado has the longest steel-girder integral abutment bridge in the United States with a length of 1,044 feet and the longest cast-in-place concrete integral abutment bridge with a length of 952 feet. The longest precast concrete integral abutment bridge in the United States was built in Tennessee; it has a length 175 feet.
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