Date of Submission

4-2026

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering

Department

Civil and Environmental Engineering

Advisor

Byungik Chang, Ph.D., P.E., M.B.A.

Committee Member

Goli Nossoni, Ph.D.

Committee Member

Hyungjoo Choi, Ph.D., P.E.

Committee Member

JosephLevert, Ph.D., P.E.

Keywords

Lateral Load Distribution, Steel Girder, Concrete Deck, Vessel Collision, Wind Loading, Distribution Factor, STAAD-Pro, Bridge Engineering, AASHTO LRFD

LCSH

Structural analysis, Lateral loads, Girders, Concrete bridges, Wind-pressure, Concrete bridges--Design and construction

Abstract

Bridges are critical components of modern transportation infrastructure, and their structural response under extreme loading conditions is essential for ensuring safety and serviceability. A key challenge in current bridge engineering practice is accurately understanding and predicting the lateral load distribution in steel girder–concrete deck bridge systems subjected to wind and vessel collision loads. While the AASHTO LRFD Bridge Design Specifications provide well-established provisions for vertical load distribution, magnitudes and load combinations (Article 3.4), they do not explicitly define lateral load distribution factors (LLDFs) for such extreme lateral loading conditions or address the role of the deck in redistributing these loads among girders. This study investigates the lateral load distribution behavior of steel girder–concrete deck bridge systems under wind and vessel collision loading. Numerical models were developed using STAAD-Pro for both with-deck and without-deck configurations to evaluate load transfer mechanisms. Based on these models, a parametric study was conducted following AASHTO LRFD provisions to examine the influence of key structural parameters, including bracing type, girder spacing, diaphragm spacing, girder depth, span length, and deck thickness. Lateral load distribution factors were calculated as the ratio of the force or reaction carried by each girder to the total applied lateral load. The results indicate that lateral loads are predominantly resisted by the fascia girder, with distribution factors reaching up to 93.8% under vessel collision and 85.22% under wind loading near the loaded exterior side (Bay-1). The load gradually decreases across the bridge width toward the interior bays, reaching values as low as 12.1% for vessel collision and 10.79% for wind at the farthest bay (Bay-5). The presence of the concrete deck provides significant horizontal diaphragm action, enhancing load redistribution and increasing overall structural stiffness. In contrast, the absence of the deck shifts the load transfer mechanism primarily to the bracing system, resulting in less efficient and more variable distribution patterns. The parametric analysis shows that bracing type, diaphragm spacing, girder spacing and deck thickness are the most influential parameters governing lateral load distribution, while girder depth, and span length have comparatively minor effects. These findings highlight the importance of system-level behavior in lateral load transfer and demonstrate that current design assumptions, such as uniform load distribution, may not accurately represent actual structural response. The results of this study provide a basis for improving the understanding of lateral load distribution mechanisms and offer recommendations for future refinement of bridge design provisions.

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