Finger-Plate and Flat-Plate Expansion Device Design Evaluation

The objective of this project is to investigate the causes of premature deterioration of a number of existing finger-plate and flat-plate expansion devices under high traffic volumes and to suggest new designs and retrofits for improved performance. The main contributions to the failure of the finger-plate expansion devices were found to be fatigue failure of the weld between the finger plate and the support beam as well as vertical misalignment due to poor construction. The dynamic impact of truck traffic was also found to be a contributing factor. The failures of flat-plate expansion devices were generally initiated by misalignment of the sliding plate and support angle due to rotation in the bridge span or poor alignment during construction. Experimental testing showed that the dynamic impact in the finger-plate device is generally between 40 and 70% and could be as much as 160%, and the effect of misalignment of the fingers can result in an increase in stress of up to 30%. The experimental results were used to validate finite-element models (FEMs), which also show high stresses in the weld between the finger plate and support beam concentrated over the stiffener location. New and retrofit designs of the finger-plate connection device concentrated on the use of bolted connections to reduce stress concentrations, to improve support structure, and to increase adjustability for alignment.