Heyman’s Limit Analysis method is a plastic theorem of analysis. Limit analysis provides a highly effective means of verifying the safety of structures and has been applied to masonry arch bridges for many years (Gilbert, 2007). The main assumptions for this method of assessment are listed below:
Main Assumptions
- Masonry in the arch has no tensile strength and is compressible
- Sliding between masonry units cannot occur
Conditions and Theorems of Plastic Limit Analysis (Horne, 1979)
- Equilibrium Condition. The computed internal actions must represent a state of equilibrium between internal and external loads.
- Mechanism Condition. Sufficient releases must be made for the structure to be made into a Mechanism
- Yield Condition. The stresses in the material must be everywhere less than or equal to the material strength.
The following considerations have been made incorporated for the assessment of masonry arch bridges in regards to the backfill:
- The lateral restraint of the arch movements are considered by the introduction of horizontal forces in the equations, this represents the passive pressure on the side of the arch remote from the load.
- The spread of the load through the backfill is by a pre-established spread rule by a constant angle (Boussinesq etc)
