The Tennessee Department of Transportation (TDOT) is a national leader in the design and construction of jointless bridges with abutments which are integral with the bridge deck. Their criteria for pile-supported integral abutments limit the horizontal movement of an abutment due to temperature variations to 25.4mm (1.0 in.) in each direction. Temperature ranges of –18° to 49°C (0 to 120°F) and – 4° to 35°C (25° to 95°F) are used for steel and concrete bridges, respectively. These values, applied with the TDOT criterion for lateral movement, lead to upper limits of bridge lengths of 152m (500 ft.) and 244m (800 ft.) for steel and concrete bridges, respectively. They have, however, exceeded these limits significantly and commissioned research testing to examine and possibly extend these limits.
The University of Tennessee has constructed concrete abutments on top of piles to simulate the behavior of actual integral abutments. Lateral load was applied to the abutments to induce horizontal displacements in the piles consistent with those which occur due to temperature change. The pile supported integral abutments were first tested to the displacement limits corresponding to TDOT criteria, and then to displacements well beyond the current design limits.
Sam Howard, a PhD candidate at the University of Tennessee is using ANSYS Academic products (Finite Element Analysis) to simulate the pile-abutment interface. Parameter functions will be used to explore for steel piles the design width of 30 and 36 inches. Also, steel piles will be modeled for weak axis bending. For concrete piles a 36 inch abutment width will be modeled. From the modeling results, an analytical recommendation of maximum allowable displacement that was justified by field research will be made.
Calibration of the numerical models will involve altering the modeled concrete pile length and modulus. Based on the first pull test cases for the concrete pile supported abutments to ½ inch and ¾ inch horizontal displacements, parameters will be varied to obtain resultant pull loads which match the experimental results. If reasonable agreement can be obtained, then those parameter will be used to examine larger horizontal displacements with the experimental runs at 1, 2, and 4 inch horizontal displacements. Concrete stress in the pile and abutment at the interface will be examined for cracking and crushing. Additionally, upon calibration of the concrete pile/abutment model, additional analysis will explore abutment width and substituting an H-pile section for the prestressed concrete pile. The H-pile will be modeled as simple rectangular sections.
Bridge Abutment
Simulation of bridge abutment showing lateral deflection (outline shows initial position) plus pricinple stress contours.