Evaluation of finger plate and flat plate expansion devices

Abstract

The objective of this project was to learn the causes of premature deterioration of MoDOT finger plate and flat plate expansion devices under high traffic volumes and use that information to design new Load and Resistance Factor Design (LRFD) finger plate and flat plate expansion devices that are intended to last 40 years or more with minimal maintenance. In addition, repair and retrofit best practices and details were developed as part of this project. To fully evaluate the expansion devices, a literature review and survey of current expansion devices used by transportation departments across the United States was conducted. The finger plate expansion devices were found to fail primarily due to fatigue failure of the weld between the finger plate and the support beam beneath it as well as vertical misalignment due to poor construction. The flat plate expansion device was found to perform inadequately if the bridge span experiences rotation causing a gap between the sliding flat plate and the support angle or if construction of the device is deficient. Experimental testing was conducted on the finger plate device on Eastbound Blanchette Bridge on Highway I-70 in St. Louis and the flat plate expansion device on Route 350 passing over Highway I-435 in Kansas City. The test results showed 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 additional stresses up to 30%. The results were used to validate Finite Element Models (FEMs) of the current expansion device designs. The FEM models showed high stresses in the weld between the finger plate and support beam concentrated over the stiffener location.