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<br />CHAPTER 3 <br /> <br />CULVERT STRUCTURES <br /> <br />The inspector should be familiar with the various types of culverts which may <br />be encountered during inspections and should have some understanding of how <br />culverts function hydraulically and structurally. An understanding of the <br />factors which affect durability is also important when evaluating the <br />condition of a culvert. <br /> <br />This chapter discusses culvert types and culvert performance. The section on <br />culvert types reviews the most common culvert shapes, sizes, and materials. <br />The culvert materials addressed are precast concrete, cast-in-place concrete, <br />corrugated steel, corrugated aluminum, and masonry. The sections on culvert <br />performance consist of a review of basic concepts for culvert hydraulics, <br />structural behavior, and durability of culverts. <br /> <br />Section 1. CULVERT TYPES <br /> <br />3-1.0 General. <br /> <br />A wide variety of culvert structures are currently in use as stream crossings, <br />underpasses, and other highway and railroad applications. The inspector <br />should understand that the selection of a specific type of culvert structure <br />may be based on many factors. These factors can include: <br /> <br />a. Engineering Considerations--An analysis of each site is generally <br />performed to determine hydraulic, structural, and durability requirements. <br />Traffic safety requirements are also important considerations which may vary <br />from site to site. <br /> <br />b. Economic Considerations--An economic analysis may include factors such <br />as construction cost, estimated service life, maintenance cost, replacement <br />cost, risk of failure, and risk of property damage. The most economical <br />culvert is the one with the lowest total cost over the design period. It is <br />not necessarily the culvert with the lowest initial cost or the culvert with <br />the longest service life. An economic analysis should be viewed as a tool to <br />aid in the decision-making process. Economic analysis can be sensitive to <br />service life, discount rate, and other assumptions. Additionally, it is often <br />difficult to assign values to subjective factors. <br /> <br />c. Local Considerations--Local construction capabilities, availability of <br />materials, time available for construction, and local policies or preference <br />may have a strong influence on the selection of culvert type. <br /> <br />16 <br />