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By: Birendra Kumar Singh
Abstract
Bridges serve as essential components of transportation networks, facilitating the movement of vehicles
and pedestrians across obstacles, such as rivers, valleys, and roads. The stability of a bridge largely
depends on the strength and structural capacity of its deck slab. The deck slab must endure both its own
weight and the additional loads imposed by vehicles. A key aspect of bridge design is assessing the
flexural stress acting on the deck slab to determine if additional support is necessary. When the flexural
stress generated by the combined effect of the slab’s self-weight and vehicular load remains within the
permissible limit of the given concrete grade’s flexural strength, the slab alone can support the loads,
eliminating the need for girders. However, if the flexural stress surpasses the allowable strength of the
concrete, girders must be introduced to provide reinforcement and prevent structural failure. The
required number of girders is determined by the extent to which the flexural stress exceeds the
permissible limit. This can be expressed as the ratio of the actual flexural stress of the concrete to its
maximum allowable flexural strength. A greater deviation from the permissible strength indicates a
higher requirement for girders to distribute the load effectively and maintain structural integrity. A
thorough structural evaluation is crucial in determining the optimal number of girders to ensure the
bridge can safely bear traffic loads without excessive stress on the deck slab. The strategic use of girders
enhances load distribution, prolongs the service life of the bridge, and ensures long-term durability. By
carefully analyzing the flexural stress and integrating girders where necessary, engineers can design
more resilient bridge structures that meet safety and performance standards.
Keywords: Flexural stress of given grade of concrete, safety of foundation, load distribution, deck slab
design, reinforced concrete, girder placement, traffic load assessment, bridge stability
Citation:
Refrences:
1. Ma ZJ, Tadros MK, Baishya MC, Yamane T, Krause GF, McCathy TJ. Flexural Strength of
Continuous Bridge Girders. PCI Journal [Internet]. 2002 Jul–Aug;47(4):80–89. Available from:
https://www.pci.org/PCI_Docs/Design_Resources/Guides_and_manuals/references/bridge_design
_manual/JL-02-July-August_Flexural_Strength_of_Continuous_Bridge_Girders.pdf
2. Zhao X, Xiang W, Yang Y, Wang Y, Tao J, Huang J, et al. Flexural Behavior of Prefabricated RC
Bridge Deck with Different Joint Materials. Buildings [Internet]. 2023 Jun;13(6):1420. Available
from: https://www.mdpi.com/2075-5309/13/6/1420
3. Zhang Y, Li B, Wang H, Liu Y, Zhang J. Bending Performance and Design of Reinforced Concrete
Ribbed Bridge Deck Slabs with Steel-Plate Reinforcement. J Struct Eng [Internet]. 2025
Jan;134(1):04024503. Available from:
https://www.tandfonline.com/doi/full/10.1080/13467581.2025.2455036
4. Alkhrdaji T, Nanni A, Chen G, Barker M. Flexural Load Rating of Concrete Bridge Girder with
Deteriorated Deck. J Bridge Eng [Internet]. 2018 Apr;23(4):04018009. Available from:
https://www.researchgate.net/publication/325800377_Flexural_load_rating_of_concrete_bridge_g
irder_with_deteriorated_deck
5. American Institute of Steel Construction. Bridge Deck Design. Steel Bridge Design Handbook
[Internet]; 2020. Chapter 17. Available from: https://www.aisc.org/globalassets/nsba/design
resources/steel-bridge-design-handbook/b917_sbdh_chapter17.pdf
6. Federal Highway Administration. Optimized Sections for High-Strength Concrete Bridge Girders.
U.S.
Department
of
Transportation
[Internet].
2006.
Available
from:
https://highways.dot.gov/media/6071
7. Federal Highway Administration. Comprehensive Design Example for Prestressed Concrete Girder
Bridge.
U.S.
Department of Transportation [Internet]. 2004. Available from:
https://www.fhwa.dot.gov/bridge/lrfd/fhwanhi04043.pdf
8. Illinois Department of Transportation. LRFD Slab Bridge Design Guide. Illinois DOT [Internet].
2011. Available from: https://idot.illinois.gov/content/dam/soi/en/web/idot/documents/doing
business/memorandums-and-letters/highways/bridges/bm-design-guides/bm-3.2.11-lrfd-slab
bridge-design.pdf
9. Washington State Department of Transportation. Precast, Prestress Bridge Girder Design Example.
WSDOT[Internet].2018.Available from: https://www.wsdot.wa.gov/eesc/bridge/software/Files/Examples/Design_Example.pdf
10. Barker RM, Puckett JA. Design of Highway Bridges: An LRFD Approach. 3rd ed. Hoboken: John
Wiley & Sons; 2013.
