Seven-year field monitoring of four integral abutment bridges

Integral abutment bridges (IABs) are now a routine construction and design of choice for many DOTs as bridges are replaced or for new roadways. However, current design and analysis methodologies have not matured substantially because of a lack of available long-term field data. Often current analysis methods predict bridge behavior that is much different from observed. Because of thermal loading, time-dependent effects, and soil-structure interaction, significant irreversible abutment displacements and rotations occur. The primary objective of this paper is to report the actual in situ measurements obtained at four short to medium-long IABs and one weather station, all located in central Pennsylvania. A total of 240 instruments was installed on four IABs during bridge construction and monitored continuously. Monitoring duration at each bridge ranges from 2.5years to nearly 7years, having initiated the program in 2002 and continuing to the present. Because of a unique environmental issue, the bridges were not subjected to traffic until December 2007, allowing isolation of traffic loading to thermal loadings and time-dependent effects. Measured IAB responses that are reported herein include: (1)abutment displacement; (2)backfill pressure; (3)abutment rotation; (4)girder rotation; (5)girder bending moment; (6)girder axial force; (7)pile moment; (8)pile axial force; and (9)strain in the approach slab. All measurements demonstrate that IAB response is cyclical, highly nonlinear, and irreversible over time. This study of field measurements over 7years provides a basis to evaluate and develop future sound IAB analysis and design methodologies.