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 2.5 years to nearly 7 years, 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 7 years provides a basis to evaluate and develop future sound IAB analysis and design methodologies.