Experimental and Analytical Studies of Continuous Steel-Stringer Lateral-Torsional Buckling Resistance
Publication: Journal of Bridge Engineering
Volume 28, Issue 6
Abstract
In the 1950s and 1960s, some Louisiana’s bridges were constructed using steel twin-girder or truss systems, in which floorbeams are carried by the main members and continuous (spliced) stringers are supported by the floorbeams. The main members are either two-edge (fascia) girders or trusses. One of the byproducts of this type of design is that stringer bottom flanges are in compression in the negative moment region over the floorbeams, which could result in lateral torsional buckling (LTB) should inadequate lateral bracing be provided. When the continuous stringers are load-rated using AASHTOWare Bridge Rating analysis software (BrR 7.1), their LTB resistance is calculated in accordance with American Association of State Highway Officials (AASHTO) LRFD Bridge Design Specifications, which do not account for potential bracing provided by a noncomposite deck and could underestimate flexural strength. As a result, the rating may be low enough to require restrictive load posting or even bridge closure. This paper summarizes extensive experimental and numerical studies investigating the behavior of this type of floor system by testing two-span, continuous, steel stringers in a grillage that included three stringer lines, an interior transverse support (floorbeam), and transverse diaphragms at the end supports. The tests and finite-element analysis studies encompassed a variety of unbraced lengths and support conditions with steel diaphragms or timber ties acting as bracing members. The findings demonstrated that, for the systems examined, minimal bracing could substantially enhance LTB resistance and supported the use of higher flexural strengths than those currently predicted using AASHTO Specifications. This paper illustrates the use, challenges, and successes in LTB modeling beams with various support and bracing conditions. The most flexible cases were the most difficult to achieve close agreement with experimental results.
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Acknowledgments
The authors would like to thank the Louisiana Transportation Research Center (LTRC) for funding this project. The investigators are grateful to the Project Review Committee Members for their guidance and support. Special thanks go to Dr. Walid R. Alaywan, Senior Structures Research Engineer, for his leadership and efforts. The authors are also grateful to Peter Hilsabeck and Emmanuel Akintunde at the University of Nebraska–Lincoln for assisting with the laboratory testing. Any statements expressed in the paper are those of the individual authors and do not necessarily represent the views of ASCE, which takes no responsibility for any statement made herein.
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Information & Authors
Information
Published In
Journal of Bridge Engineering
Volume 28 • Issue 6 • June 2023
Copyright
© 2023 American Society of Civil Engineers.
History
Received: Jul 26, 2022
Accepted: Jan 16, 2023
Published online: Apr 5, 2023
Published in print: Jun 1, 2023
Discussion open until: Sep 5, 2023
ASCE Technical Topics:
- Analysis (by type)
- Bracing
- Bridge engineering
- Bridges
- Bridges (by material)
- Construction engineering
- Construction methods
- Continuum mechanics
- Design (by type)
- Dynamics (solid mechanics)
- Engineering fundamentals
- Engineering mechanics
- Finite element method
- Flexural strength
- Floors
- Forces (type)
- Load and resistance factor design
- Load factors
- Material mechanics
- Material properties
- Materials engineering
- Methodology (by type)
- Numerical analysis
- Numerical methods
- Solid mechanics
- Steel bridges
- Strength of materials
- Structural design
- Structural engineering
- Structural systems
- Torsion
- Wood bridges
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