Virginia Center for Transportation Innovation and Research

Tech Report

Virginia

Final; Oct. 2006-Aug. 2011.

Virginia Center for Transportation Innovation and Research

NTL-HIGHWAY/ROAD TRANSPORTATION-Bridges and Structures

The purpose of this study was to conduct a field evaluation of a highly skewed semi-integral bridge in order to provide feedback regarding some of the assumptions behind the design guidelines developed by the Virginia Department of Transportation. The project was focused on the long-term monitoring of a bridge on Route 18 over the Blue Spring Run in Alleghany County, Virginia. The 110-ft-long, one-span bridge was constructed at a 45° skew and with no approach slabs. It incorporated an elasticized expanded polystyrene material at the back of the integral backwall. Bridge data reflecting thermally induced displacements, loads, earth pressures, and pile strains were acquired at hourly intervals over a period of approximately 5 years. Approach elevations were also monitored. Analysis of data was used to formulate design recommendations for integral bridges in Virginia. Field results indicated that semi-integral bridges can perform satisfactorily at a 45° skew provided some design details are modified. The relatively high skew angle resulted in a pronounced tendency of the semi-integral superstructure to rotate in the horizontal plane. This rotation can generate higher than anticipated horizontal earth pressure acting on the abutment wingwall. Study recommendations include modifying the structural detail of the backwall-wingwall interface to mitigate crack formation and placing the load buttress close to the acute corner of a highly skewed abutment to reduce the abutment horizontal rotation. The use of elastic inclusion at the back of the semi-integral backwall resulted in the reduction of earth pressures and negligible approach settlements. The study recommendations include proposed horizontal earth pressure coefficients for design and a revised approach to calculating the required thickness of the elastic inclusion. While recommending that the existing VDOT guidelines allow an increase in the allowable skew angle from 30° to 45° for semi-integral bridges, the study also proposes a field investigation of the maximum skew angle for fully integral bridges because of the inherently low stiffness associated with a single row of foundation piles. The study indicates that current VDOT guidelines can be relaxed to allow design of a wider range of jointless bridges. The implementation of integral design has been shown to reduce bridge lifetime costs because of the elimination of deck joints, which often create numerous maintenance problems.

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