United States Department of Transportation
i
Soil-Structure Interaction Studies for Understanding the Behavior of Integral Abutment Bridges
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2012-03-01
[PDF-21.72 MB]
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Abstract:Integral Abutment Bridges (IAB) are bridges without any joints within the bridge deck or between the superstructure and the abutments. An IAB provides many advantages during construction and maintenance of a bridge. Soil-structure interactions at the abutments occurring during thermal loading of a bridge are complex, especially in skewed and long span IABs. The uncertainties in understanding these interactions affect the ability to properly predict the long term behavior of these bridges. This project was developed to understand the complex interactions in an IAB and to propose design guidelines to build new IABs with longer lengths and larger skew angles. Two computer simulation tools, TeraGrande and TeraDysac, were validated in Phase I. Phase II of the project involved instrumenting an Oklahoma IAB to collect data to study the behavior of IABs under Oklahoma weather conditions and construction practices. So far more than 30 months of data from the Oklahoma IAB has been collected. The field measured bridge temperatures for Oklahoma IAB agree with the temperature range specified in AASHTO LRFD Bridge Design Specifications. Earth pressure measurements show that fairly significant amount of abutment back pressures occur during summer. Crack meter and tiltmeter measurements show that the majority of bridge translation is accommodated by the abutment pile movements in IABs. Abutment piles of IABs are experiencing bending moments beyond the yield bending moment at shallow depths. The behavior of the Oklahoma IAB was also studied with the use of computer programs LPILE and GROUP. The computed bending moments for abutment piles confirm that piles have yielded at shallow depths. The three-dimensional model developed in GROUP shows biaxial bending of abutment piles in skewed IABs. Field measured bending moments for the south abutment pile have lower values than the computed bending moments; very likely due to the installation of these piles in pre-drilled holes. In order to accommodate the thermal movement in IABs and to reduce the bending moments in the abutment piles, a smaller pile section should be placed in weak axis bending and in pre-drilled holes with low stiffness material, especially at shallow depths. Using longer spans with larger girders will increase the axial load on the abutment piles and therefore long-span IABs should be designed with caution. Biaxial bending of abutment piles in skewed IABs increases stresses in the concrete superstructure and therefore structural components for IABs with larger skew angles have to be designed carefully to accommodate the thermally induced deformations
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