Date

2016

Document Type

Thesis

Degree

Master of Science

Department

Structural Engineering

First Adviser

Sause, Richard

Abstract

Implementation of steel orthotropic bridge decks is limited due to fatigue performance concerns and high initial cost owing to fabrication demands brought on by elaborate designs and detailing to achieve acceptable fatigue resistance of the welded connections in the deck. Simpler details that provide acceptable fatigue performance can result in improved manufacturability, reduced fabrication cost, and increased implementation of orthotropic steel decks. Modern orthotropic decks are designed with ribs that pass continuously through matching cutouts in the floor beam, often with an extended cutout in the floor below the rib, and with or without internal bulkhead plates or stiffeners. The rib-to-floor beam welded connection is the most labor intensive and fatigue sensitive. Accordingly, existing generalized rib-to-floor beam connection types that are in-service in North America were identified and assessed for manufacturability. The connection types that appeared promising in terms of fatigue performance and potential for automated fabrication were further analyzed.Multi-level 3D linear elastic finite element analyses (FEA) were performed using a model of a steel orthotropic deck integrated with steel box girders developed in a previous study. Additional submodels were developed with variations of the rib-to-floor beam connections and floor beam depths. The response of the critical rib-to-floor beam connection, under critical symmetric and eccentric loading conditions, with respect to the FB, was analyzed under the rear axle loads of an AASHTO fatigue truck to assess the fatigue performance of the critical rib-to-floor beam connection.The study showed that the stresses in the floor beam were primarily in-plane, and the contribution of the out-of-plane stress component was negligible. For the depth of the floor beams considered in this study, no appreciable effect of the floor beam depth could be discerned. The rib-to-floor beam connections within the shear span of the floor beam adjacent to the primary load carrying component. The load bearing floor beams, both with and without an extended cutout, experienced significant stress concentrations at the floor beam cutouts. Without an internal stiffening, the connection with an extended cutout that terminates square on the rib wall and having wrapped-around fillet welds, although promising for automated fabrication, exhibited greater stress concentration compared to a connection that employed a complete joint penetration groove welded detail and tangential termination on the rib wall.No evidence of rib-to-floor beam connection automation could be found in the published literature or in the anecdotal information. The literature review identified that continuous welding of RFB connections would be a challenge due to welding against and with gravity. Welding against gravity would be the preferable method for depositing welds of acceptable profile and shape. For continuous welding, the deck may have to be manipulated either by standing vertically up or by rotating about an axis. For fitted floor beams, match cutting would be necessary if a tight fit-up is specified. Alternatively, a larger fit-up gap along with PJP welded connection would be more cost-effective.

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