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53 Structural Evaluation Phase 2B of the Recommended Practice consists of evalu- ating the structural capacity of each pipe system in the pipe system inventory using the most recent version of the AASHTO LRFD Bridge Design Specifications. The use of previously prepared minimum and maximum fill height tables is the most practical and efficient means of performing the structural evaluations. Structural capacity must be checked for each allowable pipe system combination of material type, material class/ thickness, bedding and backfill material, bedding and backfill compaction, and installation condition. In manual applications of the Recommended Practice (without the benefit of software automation), it is recom- mended that users evaluate pipe system options starting with the lowest available structural class, because structural classes above the minimum approved class are typically acceptable (except in the rare case when the additional wall thickness of the higher class pipe results in a geometric conflict). Structural evaluation methods (e.g., fill height tables) not in accordance with the current AASHTO LRFD Bridge Design Specifications should not be used in this stage of the Recom- mended Practice. Such fill height tables should be applied in Phase 3 if agency policy is divergent from current AASHTO standards. The use of national standards in the technical evaluation stage is one key component of the Recommended Practice, in that it is intended to clearly rely on AASHTO-approved procedures. The intent of completing initial technical evalu- ations using the latest national standards is to maintain the integrity of the Recommended Practice. Where agencies have not adopted national standards, agency-specific evaluations can be implemented as part of Phase 3. As with the other technical evaluation steps, a results matrix is used to present the evaluation results from the structural evaluation stage. The structural matrix is denoted with âSâ identifiers within the box for each pipe system type and high- lighted green in cases calculated to be suitable, or highlighted red and crossed out for pipe system options that do not meet the design criteria. C H A P T E R 9
