Bahavior and Analysis of an Integral Abutment Bridge

In order to quantify the influence of temperature changes on integral abutment bridge movements, thirty-two Sokkia RS30N reflective targets were strategically attached to a bridge along its length. These targets were surveyed every month for twelve consecutive months. These changes in length coincided with restraint conditions between purely fixed and simply supported. Movement of expansion joints was also recorded. The movements of the expansion gaps at opposite corners appear to exhibit similar movements. This behavior indicates a type of twisting motion occurring within the bridge as a result of unequal movements at the east and west sides of each abutment. This motion suggests that the bridge abutments experience forces that incite weak axis bending in the abutments, especially in the north abutment. These quantitative bridge movements were compared to predicted behavior from a finite-element model. A detailed finite-element model of the bridge was created using SAP2000 (Computers and Structures, Inc.) software. The detailed model was developed using solid elements for all components of the bridge except piles and bents. Longitudinal surface springs were placed at the abutment elements in order to simulate the soil-abutment interaction. A typical temperature load was assigned to the bridge deck and girder elements to compare the calculated stress concentrations in the model with the observed cracking on the abutment. The model produced high stress concentrations in the abutment adjacent to the bottom girder flange. This corresponded to the same location of observed cracking. The finite-element model also showed lateral movement of the north abutment. This lateral abutment contributed to the unequal movements of the bridge spans. Once the comparison between the measured bridge behavior of the survey and the findings of the detailed finite element model was completed, a simplified model was used to evaluate the bending moment and stresses in the abutment of the 400 South Street Bridge. The simplified model was also used to perform a parametric study on the influence of skew, span length, and temperature gradient on weak-axis abutment moments