Another example is the design of pipelines subject to high bending loads caused by soil deformations due to frost heave and thaw settlement. This type of loading is not adequately addressed in existing design standards, nor is it amenable to the elastic stress-based design approach. To withstand bending loads, line pipe capacity is best represented by its tolerance to longitudinal deformations or strains. Safe strain limits have shown to exceed the material yield point by a significant margin.
The RBDA approach
The common theme in these examples is the large degree of uncertainty resulting from limited precedent. This uncertainty can be addressed using a class of design approaches called reliability based design and assessment (RBDA), in which safety is measured by the reliability, defined as the probability that the pipeline will not fail within a specified period of time. The pipeline is then designed and operated to meet a specified reliability target considering all applicable threats.