n Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese - Proposed guidelines for the design and construction of rubble masonry concrete arch bridges : technical paper

Volume 40, Issue 3
  • ISSN : 1021-2019



Practical design and construction considerations, other than detailed material specifications, are discussed with reference to precedent, experimental testing and the theoretical modelling. The choice of site and positioning of the rubble masonry concrete (RMC) structure in relation to the flow of the river is critical. Ideally, these structures should be founded on, and anchored to, bedrock. Aperture size should be maximized and the structure should be designed to present the minimum obstruction to the flow of water and debris. Three methods of structural analysis are discussed, including a finite element model that is used to explore a typical arch structure's sensitivity to four different aperture shapes of equal area as well as a circular arch's response to submersion in water. A parabolic aperture was found to be optimal in limiting tensile stresses in the masonry and submersion was demonstrated to increase these tensile stresses by as much as 20 per cent. Cracks were modelled at points of maximum tension and shown to play a useful role in relieving tensile stress without compromising stability. An inference is drawn that these structures are sufficiently tolerant of the magnitude of geometrical errors expected from the use of low-level skills and limited supervision. Consideration of several failure mechanisms indicates that the RMC arch problem is primarily one of equilibrium rather than of material strength and that structural stability without reinforcing can be ensured.

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