Integral railway bridges with different transition zone designs

Abstract

Integral bridges interact strongly with their backfills, especially due to seasonal thermal loading. So far, most research has focused on this cyclic soil–structure interaction of integral bridges with granular backfills. However, due to higher train speeds or axle loads, railway transition zones internationally must often be designed with wedge-shaped cement-bound granular mixtures. Also, transition slabs are widely used for longer integral bridges. Therefore, a numerical investigation is presented on the cyclic soil–structure interaction of integral bridges with different railway backfill designs. The main focus lies on the cyclic mobilization of lateral stresses and settlements in the backfill. Next to well-graded granular backfill, the comparison includes two forms of cement-bound wedges as well as concrete transition slabs. The numerical studies further cover both, varying bridge lengths and abutment heights. The obtained results highlight significantly different settlement accumulations for the various transition zone designs. A comparison with analytical design approaches is conducted and recommendations for the design of transition zones for integral bridges with different total lengths are derived. In the second part of the paper, results of a three-year-long monitoring of an integral railway bridge are presented. The cyclic development of both earth pressure and settlements are investigated by means of 3D FE back analysis. The study reveals that the interaction behaviour and earth pressure distribution is strongly affected by a concrete sealing layer of (only) 30 cm at mid-height of the backfill. The measured behaviour can be reproduced well, which further confirms the eligibility of the FE model and its calibrated constitutive model.