Theses and Dissertations

Date of Award

5-2025

Document Type

Thesis

Degree Name

Master of Science in Engineering (MSE)

Department

Civil Engineering

First Advisor

Siang Zhou

Second Advisor

Mohsen Amjadian

Third Advisor

Philip Park

Abstract

Cross-frames are critical for load distribution and stability in steel I-girder bridges with complex geometry, especially during construction. However, they are often designed with standardized cross-sections that are uniform throughout the bridge. This thesis presents an optimization approach for cross-frame cross-sections for skewed steel I-girder bridges with integral and stub abutments with skews ranging from 15⁰-60⁰. This optimization, using Method of Moving Asymptotes (MMA), minimizes girder flange lateral bending stress while maintaining or reducing the total volume of the cross-frames from the original design. Validated 3D finite element models in CSI Bridge showed that the optimization achieved around 20% decrease for flange lateral bending stress, while the total cross-frame volume decreased by 30% for integral abutment bridges. The stub abutment bridge showed small benefits with 0.56% stress reduction and 6.6% volume savings. Optimized designs met AASHTO slenderness and AISC stability requirements, and live load analyses confirmed structural integrity for optimized bridges. Additional studies on cross-frame orientation suggest that aligning cross-frames close to the bridge skew reduces flange stresses while slightly increasing cross-frame stresses and girder layover. These findings provide insight into cross-frame behavior for skewed steel I-girder bridges and suggest approach for bridge optimization.

Comments

Copyright 2025 Nisha Sthapit. https://proquest.com/docview/3240631207

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