Thermal Response of Integral Abutment Bridges with Mechanically Stabilized Earth Walls

About the report:

The advantages of integral abutment bridges (IABs) include reduced maintenance costs and increased useful life spans.  However, improved procedures are necessary to account for the impacts of cyclic thermal displacements on IAB components, including the foundation piling and the components of mechanically stabilized earth (MSE) walls that are often used around IABs.

As requested by the Virginia Center for Transportation Innovation and Research and the Virginia Department of Transportation (VDOT), this research focused on IABs with foundation piling in the backfill of MSE walls that have a “U-back” configuration, which indicates that the MSE wall has three faces, one parallel to the abutment and two parallel to the bridge alignment.  During this research, more than 65 three-dimensional numerical analyses were performed to investigate and quantify how different structural and geotechnical bridge components behave during thermal expansion and contraction of the bridge.  In addition, a separate series of three-dimensional numerical models were developed to evaluate the usefulness of corrugated steel pipes in-filled with loose sand around the abutment piles.

The results of this research quantify the influence of design parameter variations on the effects of thermal displacement on system components, and thus provide information necessary for IAB design.  One of the findings is that corrugated steel pipes around abutment piles are not necessary. An estimate of the cost savings from eliminating these pipes is presented.

One of the most important outputs of this research is an easy-to-use Excel spreadsheet, named IAB v3, that quantifies the impact of thermal displacement in the longitudinal direction, but also in the transverse direction when the abutment wall is at a skew angle to the bridge alignment.  The spreadsheet accommodates seven different pile sizes, which can be oriented for weak or strong axis bending, with variable offset of the abutment from the MSE wall and for variable skew angles. Both steel and concrete girders are considered.  The spreadsheet calculates the increments of displacements, forces, moments, and pressures on systems components due to thermal displacement of IABs.

In addition, this report provides recommendations for implementing the research results in VDOT practice by proposing modifications to Chapter 17 of VDOT’s Manual of the Structure and Bridge Division, Volume V—Part 2, Design Aids and Particular Details, and to Chapter 10 of Volume V—Part 11, Geotechnical Manual for Structures. The background for each recommended modification is discussed, and specific details for changes to wording and calculations in the manuals are presented.

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