Title: LATERAL STABILITY CONSIDERATIONS OF TIMBER BEAMS IN OLD BRIDGES
Abstract: 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 Year: 1986
Publication Date: 1986-01-01
Language: en
Type: article
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