Effective Cross-Frame Framing Arrangements and Simplified Design for Straight Skewed and Nonskewed Steel I-Girder Bridges
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Author(s)
Kamath, Ajit Manohar
Advisor(s)
Sherman, Ryan J.
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Abstract
Straight skewed steel I-girder bridges exhibit three-dimensional behavior due to deformation compatibility considerations. Differential vertical displacements occur because intermediate cross frames connect to the girders at different locations along the girder lengths due to the skew. The cross frames twist the girders because of their high in-plane stiffness, imparting approximately equal twist rotations at the cross-frame-to-girder connections. The continuity effects with the girders can result in large cross-frame forces. Traditionally, many of these structures have been designed using 1D line girder analysis (LGA). Recent research has shown that the cross-frame framing arrangement significantly impacts the transverse load path and the overall three-dimensional behavior of these structures. Gaps in understanding the influence of cross-frame framing arrangements on three-dimensional actions lead to uncertainty regarding the extent to which LGA can be applied for design.
This research evaluates the influence of cross-frame framing arrangements on the three-dimensional behavior of straight skewed bridges under dead, live, and fatigue loads based on the 10th Edition of the AASHTO LRFD Specifications. A 3D FEA parametric study was completed considering a range of geometric variables and cross-frame framing arrangements. Six framing arrangements, consisting of contiguous, staggered, and variations of lean-on framing, were studied for moderately skewed (skew index, Is ≤ 0.3) and highly bridge geometries (0.3< Is < 0.97). The influence of the framing arrangement on the bridge’s three-dimensional behavior is assessed and guidelines are provided for developing effective framing arrangements for straight skewed and nonskewed bridges. Recommendations are provided for simplified design using LGA, the selection of framing arrangements and sizing of cross frames.
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Date
2023-09-05
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Text
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Dissertation