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6 CHAPTER 3 Findings and Applications CANDE-2007 Overview performance under the LRFD option is provided in terms of ratios of factored demand to factored capacities for each de- The results of this research effort enhanced every aspect of sign criterion associated with the selected culvert type. The the CANDE program and its overall architecture. The details of the evaluation methodology are provided in the CANDE-2007 architecture is best viewed from the perspec- CANDE-2007 Solution Methods and Formulations manual tive of a user stepping through the process of solving a par- available from the tool bar in CANDE-2007. ticular soil-culvert problem. To initiate a solution, the user Solution Level (1, 2, or 3) provides a choice that corre- makes several top-level choices that define the character of sponds to successively increased levels of analytical sophisti- problem to be solved as illustrated in the flow chart depicted cation, which permits the user to choose a degree of rigor and in Figure 1 and discussed in the following paragraphs. modeling fidelity commensurate with the details and knowl- Execution Mode is the choice between design and analy- edge of the culvert-soil system under investigation. Level 1 is sis. The analysis mode defines a particular culvert and soil based on a closed-form elasticity solution (7) useful for system in terms of geometry, material properties, and load- screening and comparing various circular-shaped culverts in ing conditions and is solved by the chosen solution level. The deep burial. Level 2, considered the "work-horse" of CANDE, solution output provides an evaluation of the culvert in terms is applicable to many common culvert shapes including cir- of its safety for all potential modes of failure associated with cular, elliptical, box, and arch installations but is limited to the structural material and shape of the culvert. Alternatively, center-line symmetry for both loading and geometry. Level 3 the design execution mode also requires that the culvert is virtually unlimited in modeling the structure shape, soil shape, materials, and loading conditions be defined exactly as system, and loading conditions. Level 2 and Level 3 share a the analysis case. However, the culvert's cross-sectional prop- common finite element solution methodology and only differ erties are not defined but, rather, are determined in accor- in the manner of input data: automatic versus user defined. dance with the desired level of safety specified by the user. For Pipe Groups and Type provides choices for the culvert example, corrugated metal design solutions are given in the material(s) to be analyzed or designed. A single "pipe group" required corrugation size and metal thickness while rein- is a connected series of beam-column elements composed of forced concrete is given in the required area of reinforcement one pipe-type material: aluminum, basic, concrete, plastic, or steel for one or two cages. steel. Level 1 and Level 2 culverts are predefined shapes such Evaluation Methodology is the choice between a working- as round-, box-, and arch-shaped culverts requiring only one stress solution and an LRFD solution. A working-stress solu- pipe group. Level 3 permits up to 30 different pipe groups to tion means the applied loads are the actual (or perceived) set define special types of problems. For example, two or more of loads acting on the soil-structure system. Evaluation of the groups may be defined to represent independent structures culvert's performance under the working stress option is in the same embankment. Alternatively, several element reported in terms of safety factors for each design criterion as- groups may be joined together to model cell-like structures sociated with the selected culvert type. An LRFD solution or composite structures such as a corrugated metal arch roof means the actual-loading schedule is increased by individu- placed on a reinforced concrete U-shaped base or a plastic alized load factors so that the dead loads, earth loads, and live pipe placed inside a corrugated steel pipe for rehabilitation. loads may be assigned individual factors as required by the System Choices refers to a variety of modeling options AASHTO LRFD specifications. Evaluation of the culvert's developed especially for the culvert soil-structure problem.