Arch Barrel Research Articles

Load Rating of Masonry Arch Bridges: Refinements

In a paper previously published by the first writer, a procedure for load-rating masonry arch bridges was introduced. The procedure uses the Load Factor Method of the 1994 American Association of State Highway and Transportation Officials Manual for the Condition Evaluation of Bridges, applied to a frame analysis model of a masonry arch spanning from abutment to abutment. The procedure is based on the assumption of the arch barrel having no tensile strength. The objective of this technical note is to complement the initial procedure by enabling the assessing engineer to exercise discretion in deciding whether or not a small value of tensile strength should be allowable in determining a suitable rating for masonry arch bridges. In addition the initially proposed strength values, which are considered overly conservative, are increased. The introduction of these refinements will allow a more accurate assessment of the nation’s stock of stone masonry bridges.

Strength of Spandrel Walls in Masonry Arch Bridges

Previous research on the strength of masonry arch bridges has focused on the carrying capacity of the arch barrel in the span direction. Although the results of a spandrel wall collapse may be very serious, the transverse strength of masonry arch bridges has not been widely addressed. Recent experience, however, has shown that the transverse behavior and the strength of the spandrel walls are at least as important as the behavior in the span direction. Although complex computer analysis methods have been proposed for examining the masonry arch bridge as a three-dimensional structure, these methods are not suitable for everyday practical application. An approximate analytical method for the prediction of the strength of masonry spandrel walls is developed based on the conventional analysis of fills supported by retaining walls. The method is based on the determination of loads by Coulomb-Rankine analysis and the determination of resistance by the fracture line method, similar to the yield line method for reinforced concrete slabs. A table that further increases the simplicity and speed of the method is also provided. The proposed method allows the practicing engineer to calculate a factor of safety for the transverse strength of a spandrel wall for different situations, such as moist soil, cracked wall, effect of live load for shallow fill bridges, or existence of parapet walls. Results of these conventional, simplified analyses compare favorably with observed bridge distress and results of a previously validated finite element analysis method.

New techniques in the elastic analysis of arch bridges using image processing

AbstractThe importance of the masonry arch in Britain's infrastructure has never been more significant than at the present time with ever increasing axle loads under new EEC regulations The searches have been shown to be significantly affected by the overlying fill. The effect of this fill is being investigated by a number of methods employing a variety of experimental techniques. This paper presents one such new technique of examining the effects of the fill through monitoring zones of strain on an arch model subjected to load. The model arches were constructed in timber with a dry granular fill and approximately 90 tests were carried out to investigate the effect of load position, fill depth and pier stiffness. Image analysis of the tests permitted identification of the areas of strain within the fill and arch barrel and the location of the hinges at higher loads. Finite element (FE) analysis was used to model the arch in its elastic range and comparisons of the FE strain contour plots with the equivalent images illustrated the validity of using image processing for the determination of the strain characteristics. The practical applications of using such a technique are subsequently highlighted and commented on.