Simplified Elastic Model for Restraining Effects of Backfill Soil on Integral bridges

This paper presents the formulation of a simple method for the prediction of the additional stresses induced in frame type integral bridges due to thermal expansion of the deck. These stresses are controlled to a large extent by the restraint provided to the deck by the backfill soil adjacent to the abutments. The first part of the paper develops a realistic means of assessing appropriate equivalent elastic stiffness values for the backfill using results from recent high quality laboratory soil testing. A boundary element type approach is then used to derive approximate general expressions, written in terms of the soil stiffness and the flexural rigidity of the abutment, for the lateral and rotational restraint provided by both the abutment and soil. These expressions are subsequently manipulated into a form that enables designers to make use of standard frame analysis computer programs for the prediction of thermal expansion effects. The proposed method is shown to compare well with predictions obtained using a finite element model of the soil and structure.