00459576

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http://onlinepubs.trb.org...trr/1986/1053/1053-003.pdf

https://scholar.google.co...kson&publication_year=1986

Some timber bridges built in the early 1900s do not have the roadway deck attached to the beams. These laterally unsupported beams are not capable of supporting current truck loads. County and state engineers who have inherited the responsibilities of maintaining these bridges must use considerable skill in developing a lateral bracing scheme for the beams. County engineers are usually working within a definite financial constraint such as the county budget. This paper was written to help engineers understand the history, theory, and practical solutions required for bracing timber beams in old bridges. A history of the early requirements for the design and construction of bridges is reported. The 5-ton loading requirement of the early 1900s does not compare with the current truck loads of 15 tons or higher. A brief discussion of the theory of lateral buckling of beams is presented along with methods to calculate the forces in the bracing. The current AASHTO design practice for laterally unsupported beams is presented. The effect on the allowable stresses resulting from lateral bracing of beams is shown. Some deck-to-beam and beam-to-beam connections are presented as possible solutions to the beam instability problem. The deck-to-beam connections discussed are nailing, bolting, reverse bolting, angles and bolts, and friction. The beam-to-beam connections presented are blocking, cross-bridging, and tension side bracing. The advantages and disadvantages of each type of connection is discussed. Tension side bracing of beams, while perhaps being economically feasible, has not been verified either analytically or experimentally. There are no current design guidelines for tension side bracing.

Publication of this paper sponsored by Committee on Low-Volume Roads. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved

01419458

pp 18-25

1986

Transportation Research Record

030903969X

Print

Figures (12) ; Photos (5) ; References (17) ; Tables (3)

Bolting; Bracing; Bridge construction; Bridge decks; Bridge foundations; Bridges; Construction; Fasteners; Friction; Nails; Timber; Wooden bridges

Lateral stability

Bridges and other structures; Construction; Design; Highways; I24: Design of Bridges and Retaining Walls

TRIS, TRB

Nov 30 1986 12:00AM

• A PREFABRICATED MODULAR TIMBER BRIDGE
• AN OVERVIEW OF TIMBER BRIDGES
• DESIGNING TIMBER BRIDGES FOR LONG LIFE
• LOAD DISTRIBUTION CRITERIA FOR GLUED-LAMINATED LONGITUDINAL TIMBER DECK HIGHWAY BRIDGES
• NEW IDEAS FOR TIMBER BRIDGES
• OHIO'S EXPERIENCES WITH TREATED TIMBER FOR BRIDGE CONSTRUCTION
• PERFORMANCE AND REHABILITATION OF TIMBER BRIDGES
• PROBABILISTIC ASSESSMENT OF THE FAILURE OF LAMINATED TIMBER BRIDGES
• REPAIR OF TIMBER BRIDGE PILING BY POSTING AND EPOXY GROUTING
• ULTIMATE STRENGTH OF TIMBER-DECK BRIDGES