Integral Abutment Bridges
| February 27, 2011 |
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.
Table 1 shows responses regarding status of use of integral abutment bridges and problems associated with integral abutment bridges.
The 2009 survey on integral abutment bridges also addresses the issue of costs associated with the use of integral abutment bridges. Tables 2 and 3 show the state responses on the issue of construction and maintenance costs of integral abutment bridges compared to conventional bridges.
Summary of Responses
The responses to the survey indicate that nine states do not use integral abutment bridges. Out of the nine states that do not use integral abutment bridges, three states (Alabama, Delaware and Louisiana) never used integral abutments, three states (Alaska, Arizona and Mississippi) discontinued their use due to serious problems, and three states (Florida, Texas and Washington) discontinued their use either because they realized no performance advantage over their conventional practice (Florida and Texas) or they concluded that semi-integral abutments offer more advantages compared to integral abutments (Washington). The status of use of integral abutment bridges is illustrated in Figure 2.
The responses also indicate that 25 states have no problems with the use of integral abutment bridges. In addition, 12 states (California, Colorado, Maine, Michigan, Missouri, Nebraska, New Mexico, New York, North Carolina, Oklahoma, Utah and West Virginia) report either minor or moderate problems with the use of integral abutment bridges. Four states (Indiana, Kansas, South Dakota and Virginia) had moderate problems with integral abutment bridges in the past; they found a solution to their problems and do not report any more problems. However, three states (Alaska, Arizona and Mississippi) had serious problems with integral abutment bridges; as a result, each state discontinued their use. The status of problems with integral abutment bridges is illustrated in Figure 3.
The responses to the issue of construction costs of integral abutment bridges compared to conventional bridges indicate a lower construction cost in twenty-seven states, higher construction cost in five states (Arkansas, Georgia, Maryland, Nebraska and Utah), and same construction cost in three states (Indiana, Kansas and New Hampshire). The status of construction costs of integral abutment bridges and conventional bridges is illustrated in Figure 4.
The responses with regard to the issue of maintenance costs of integral abutment bridges compared to conventional bridge indicate a lower maintenance cost in thirty-two states, and same maintenance cost in three states (Georgia, Hawaii and Nebraska). Not surprisingly, no state reports a higher maintenance cost with the use of integral abutment bridges. The status of maintenance costs of integral abutment bridges and conventional bridges is illustrated in Figure 5.
Forty-one states use integral abutment bridges. The number of integral abutment bridges, both statewide and nationwide, has increased considerably in the last few decades. Eight states have more than 1,000 integral abutment bridges; among them, Missouri with more than 4,000 and Tennessee with more than 2,000 integral abutment bridges. The responses received from the state departments of transportation confirm the fact that use of integral abutment bridges almost always results in lower bridge maintenance costs compared to conventional bridges. The responses also confirm that in the vast majority of states, the construction cost of building integral abutment bridges is lower compared to conventional bridges.
In addition, most states report no problems with integral
abutment bridges; a limited number of states report minor to moderate problems with the use of integral abutment bridges. A number of states that previously had problems with integral abutment bridges were able to come up with solutions to these problems. As a result, they do not report any more problems with the use of integral abutment bridges.
However, it is very important to recognize that many problems are avoided because integral abutment bridges are built within the limitations imposed by the design parameters outlined in each state’s Bridge Design Manual. These design limitations prohibit the use of integral abutments for very long bridges and in situations that involve complex structural and soil conditions. In addition, there are limitations on skew, curvature and type of piles to name a few.
Apparently, more research on integral abutments is needed in order to advance the use of integral abutment bridges. More research that predicts the behavior of integral bridges based on theory, in addition to empirical evidence will lead to the introduction of national guidelines for integral abutment bridges, which will provide legitimacy to this cost-effective method of bridge construction. The current absence of such a document acts as a deterrent to the use and further advancement of integral abutment bridge construction.
Acknowledgments from the Author
This article is based upon the responses received from the following state departments of transportation: Alabama, Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Hawaii, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin and Wyoming. Their help is gratefully acknowledged.
Amde M. Amde (formerly Amde M. Wolde-Tinsae) is a professor of structural engineering in the Department of Civil and Environmental Engineering at University of Maryland. He is also a registered professional engineer and president of AMA & Associates. Other faculty positions held include Iowa State University and McMaster University. He holds two U.S. patents and has published more that 200 technical papers.
Andreas Paraschos is a professional engineer in the state of New York and a structural bridge engineer with the New York City Department of Transportation/ Division of Bridges.
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