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Modernize and Upgrade CANDE for Analysis and LRFD Design of Buried Structures (2008)

Chapter: Chapter 3 - Findings and Applications

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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2008. Modernize and Upgrade CANDE for Analysis and LRFD Design of Buried Structures. Washington, DC: The National Academies Press. doi: 10.17226/14174.
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2008. Modernize and Upgrade CANDE for Analysis and LRFD Design of Buried Structures. Washington, DC: The National Academies Press. doi: 10.17226/14174.
×
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2008. Modernize and Upgrade CANDE for Analysis and LRFD Design of Buried Structures. Washington, DC: The National Academies Press. doi: 10.17226/14174.
×
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2008. Modernize and Upgrade CANDE for Analysis and LRFD Design of Buried Structures. Washington, DC: The National Academies Press. doi: 10.17226/14174.
×
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2008. Modernize and Upgrade CANDE for Analysis and LRFD Design of Buried Structures. Washington, DC: The National Academies Press. doi: 10.17226/14174.
×
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2008. Modernize and Upgrade CANDE for Analysis and LRFD Design of Buried Structures. Washington, DC: The National Academies Press. doi: 10.17226/14174.
×
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2008. Modernize and Upgrade CANDE for Analysis and LRFD Design of Buried Structures. Washington, DC: The National Academies Press. doi: 10.17226/14174.
×
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2008. Modernize and Upgrade CANDE for Analysis and LRFD Design of Buried Structures. Washington, DC: The National Academies Press. doi: 10.17226/14174.
×
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2008. Modernize and Upgrade CANDE for Analysis and LRFD Design of Buried Structures. Washington, DC: The National Academies Press. doi: 10.17226/14174.
×
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2008. Modernize and Upgrade CANDE for Analysis and LRFD Design of Buried Structures. Washington, DC: The National Academies Press. doi: 10.17226/14174.
×
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2008. Modernize and Upgrade CANDE for Analysis and LRFD Design of Buried Structures. Washington, DC: The National Academies Press. doi: 10.17226/14174.
×
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2008. Modernize and Upgrade CANDE for Analysis and LRFD Design of Buried Structures. Washington, DC: The National Academies Press. doi: 10.17226/14174.
×
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2008. Modernize and Upgrade CANDE for Analysis and LRFD Design of Buried Structures. Washington, DC: The National Academies Press. doi: 10.17226/14174.
×
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2008. Modernize and Upgrade CANDE for Analysis and LRFD Design of Buried Structures. Washington, DC: The National Academies Press. doi: 10.17226/14174.
×
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Suggested Citation:"Chapter 3 - Findings and Applications." National Academies of Sciences, Engineering, and Medicine. 2008. Modernize and Upgrade CANDE for Analysis and LRFD Design of Buried Structures. Washington, DC: The National Academies Press. doi: 10.17226/14174.
×
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6CANDE-2007 Overview The results of this research effort enhanced every aspect of the CANDE program and its overall architecture. The CANDE-2007 architecture is best viewed from the perspec- tive of a user stepping through the process of solving a par- ticular soil-culvert problem. To initiate a solution, the user makes several top-level choices that define the character of problem to be solved as illustrated in the flow chart depicted in Figure 1 and discussed in the following paragraphs. Execution Mode is the choice between design and analy- sis. The analysis mode defines a particular culvert and soil system in terms of geometry, material properties, and load- ing conditions and is solved by the chosen solution level. The solution output provides an evaluation of the culvert in terms of its safety for all potential modes of failure associated with the structural material and shape of the culvert. Alternatively, the design execution mode also requires that the culvert shape, materials, and loading conditions be defined exactly as the analysis case. However, the culvert’s cross-sectional prop- erties are not defined but, rather, are determined in accor- dance with the desired level of safety specified by the user. For example, corrugated metal design solutions are given in the required corrugation size and metal thickness while rein- forced concrete is given in the required area of reinforcement steel for one or two cages. Evaluation Methodology is the choice between a working- stress solution and an LRFD solution. A working-stress solu- tion means the applied loads are the actual (or perceived) set of loads acting on the soil-structure system. Evaluation of the culvert’s performance under the working stress option is reported in terms of safety factors for each design criterion as- sociated with the selected culvert type. An LRFD solution means the actual-loading schedule is increased by individu- alized load factors so that the dead loads, earth loads, and live loads may be assigned individual factors as required by the AASHTO LRFD specifications. Evaluation of the culvert’s performance under the LRFD option is provided in terms of ratios of factored demand to factored capacities for each de- sign criterion associated with the selected culvert type. The details of the evaluation methodology are provided in the CANDE-2007 Solution Methods and Formulations manual available from the tool bar in CANDE-2007. Solution Level (1, 2, or 3) provides a choice that corre- sponds to successively increased levels of analytical sophisti- cation, which permits the user to choose a degree of rigor and modeling fidelity commensurate with the details and knowl- edge of the culvert-soil system under investigation. Level 1 is based on a closed-form elasticity solution (7) useful for screening and comparing various circular-shaped culverts in deep burial. Level 2, considered the “work-horse” of CANDE, is applicable to many common culvert shapes including cir- cular, elliptical, box, and arch installations but is limited to center-line symmetry for both loading and geometry. Level 3 is virtually unlimited in modeling the structure shape, soil system, and loading conditions. Level 2 and Level 3 share a common finite element solution methodology and only differ in the manner of input data: automatic versus user defined. Pipe Groups and Type provides choices for the culvert material(s) to be analyzed or designed. A single “pipe group” is a connected series of beam-column elements composed of one pipe-type material: aluminum, basic, concrete, plastic, or steel. Level 1 and Level 2 culverts are predefined shapes such as round-, box-, and arch-shaped culverts requiring only one pipe group. Level 3 permits up to 30 different pipe groups to define special types of problems. For example, two or more groups may be defined to represent independent structures in the same embankment. Alternatively, several element groups may be joined together to model cell-like structures or composite structures such as a corrugated metal arch roof placed on a reinforced concrete U-shaped base or a plastic pipe placed inside a corrugated steel pipe for rehabilitation. System Choices refers to a variety of modeling options developed especially for the culvert soil-structure problem. C H A P T E R 3 Findings and Applications

7Figure 1. Major options to define the top-level input data for CANDE-2007. A suite of soil models is available including the popular hy- perbolic forms of Duncan and Duncan/Selig as well as the standard linear forms for isotropic elastic, orthotropic elastic, and overburden dependent. Predefined model parameters are provided in the program for simulating crushed rock, sands, silts, and clays under a range of compaction conditions. Another system choice is the interface condition between the soil and culvert or between fill soil and in situ soil. The user may select bonded or a friction interface that permits fric- tional sliding and separation during the loading schedule. Still, another system choice is the option to include large deformation and buckling analysis. This is particularly useful for investigating large, flexible culverts under heavy loading. Graphical User Interface CANDE-2007 provides a GUI that greatly eases the task of creating CANDE input documents and also allows the viewing of the CANDE output results graphically. A companion docu- ment, CANDE-2007 User Manual and Guideline, describes in detail the input and output capabilities of the GUI that was de- veloped in the course of this research effort. The GUI provides a multiple document interface (MDI) environment where the user can develop and revise input, review graphic information such as mesh geometry and beam-element graph information, quickly navigate the large CANDE output files through the use of an interactive browser, and access context-sensitive help for the whole system. A sample of the interface is shown in Figure 2. Input Options The key concept behind the GUI input option is that it ultimately creates a CANDE-2007 input document file that contains the same formatted data stream as that of traditional batch-mode input. The traditional batch-mode method of input requires the user to hand type the CANDE input doc- ument via an ASCII text editor in accordance with the writ- ten input instructions in the user manual. In contrast, the GUI is much easier to use because each input command is represented by an input menu that is “tailor-made” to con- form to the user’s previous input choices. Thus, the user does not need to navigate through the entire user manual. Instead, the user just follows the screen input instructions and ac- cesses the context-sensitive help provided by the GUI. The GUI has options to create new CANDE input documents, edit and rerun existing input documents, and import data files from external sources.

8Figure 2. CANDE-2007 multiple document interface. As an illustration, Figure 3 shows the start-up screen for creating a new CANDE input document using the CANDE Input Wizard. Note that several of the top-level choices pre- viously discussed are shown on this screen with radio-button selections. As a consequence of the user’s selections made on this screen, the screens that follow only pertain to the information that is needed for this problem, thereby elimi- nating up to 80% of the non-relevant input directions in the detailed user manual. Since the CANDE-2007 User Manual and Guideline contains more than 180 pages of input instructions, the utility of the GUI input method is readily apparent. Once the key input parameters are provided, a CANDE input document is generated and the user is provided an input menu browser to navigate and modify the input as nec- essary. The key features of the input menu browser are detailed in Figure 4. Output Options Viewing the CANDE output is controlled by the user via a drop-down menu on the GUI toolbar. The drop-down menu offers five viewing choices consisting of three text files and two interactive graphic tools, which are also accessible from individual icons on the tool bar. Short descriptions of the five choices are provided below. • CANDE Output Report. This is the most comprehensive output file and contains text and tables for all the input selections as well as the complete set of structural response data for each load step. The Output Report has an interac- tive table of contents that allows the user to quickly locate output data of interest. Most notably the evaluation of the pipe type is given in the last subsection. The output files contain a myriad of information and can be somewhat

9Figure 3. Start-up screen from CANDE Input Wizard. Figure 4. CANDE input menu overview.

10 Figure 5. CANDE output viewer. cumbersome to navigate in a regular ASCII text editor. To enhance the review of the output report, a topical browser is included as part of CANDE-2007. This browser provides an organized, bookmarked table of contents for the output file that provides quick access to any table in the report (see Figure 5). • CANDE Log File. The log file is a short file that is displayed on the monitor screen during execution. It contains the master input selections along with a history list of each load step analyzed and a trace of iterations required to solve each load step. If the solution is unsuccessful, the log file also provides error messages and, when possible, guidance to correct the error. • Mesh Plot. The mesh plot is an interactive plotting tool for creating and viewing the finite element mesh topology (Levels 2 and 3) including element numbering, nodal con- nectivity, material zones, construction increments, and boundary conditions. Likewise, the tool is used to create and plot solution output such as deformed shapes and color contours of soil stresses and strains. For an overview of the Mesh Plot options, see Figure 6. • Graphs. This is an interactive plotting tool for creating and viewing the structural response of beam-element groups, (i.e., pipe types). Structural responses are plotted contigu- ously over the pipe shape for any load step or sets of load steps. Structural responses include moments, thrusts, and shears as well as responses specific to the pipe type such as plastic penetration for corrugated metal and crack depth for reinforced concrete. A local plot of the pipe is also pro- vided (see Figure 7). • Results Generator. This is an interactive text report gen- erator that features user-defined report selection to create dynamic output reports. Options are available for tabular- izing soil responses and pipe group responses as a function of load step. New Analysis Capabilities In addition to code restructuring, improvements were made in every subroutine of the CANDE Engine, some significant new analytical capabilities were added to CANDE- 2007 that did not exist in the previous versions of CANDE. A companion document, CANDE-2007 Solution Methods and Formulations, describes in detail the complete derivation of these new capabilities developed in the course of this research effort. Provided is a brief synopsis of the new analy- sis capabilities. Multiple Pipe-Type Capability A new architecture called “multiple pipe-type capability” is embedded in CANDE-2007 that removes the old restric- tion of limiting the analysis to just one continuous pipe-type

11 structure. The new strategy allows for multiple element groups rather than just a single group. The connection between element groups is completely arbitrary and can be defined by the user. For example, two groups may be assigned independent node numbers (no nodes in common) so that they become independent structures that only interact through the soil stiffness. Alternatively, element groups may be arbitrarily joined together at common nodes to model cell- like structures or composite structures such as a corrugated metal arch roof placed on a reinforced concrete base. The new architecture provides virtually unlimited modeling capabili- ties to define any configuration within a 2-D framework. The Figure 6. CANDE mesh plot options.

12 Bending moment(lb-in/in) Figure 7. CANDE Graphs window. implementation of the multiple pipe-type capability is oper- able in both the analysis and design mode. Large Deformations and Buckling The large deformation development is based on the so- called “Updated-Lagrange” methodology, which includes the standard small strain-displacement term plus a nonlinear term related to rotation. This strain-displacement expression accurately represents the beam element’s internal strain field due to moderate stretching and large rotations. The word “up- dated” means that the nodal coordinates of all elements are updated to their displaced position after each load step instead of the original undeformed position being used. Incorporat- ing the nonlinear component of the strain-displacement rela- tionship into a beam-column element results in a new matrix called the geometric stiffness matrix, proportional to current thrust level, and a new load vector called the rotational-stretch vector. This method of analysis produces a nonlinear load- deformation curve wherein the load causing instability may be observed by noting the peak load at which the system fails due to large or unbounded displacements. In order to predict the buckling capacity at the end of each load increment, a lin- earized buckling prediction methodology is also incorporated into the program based on determining the scalar multiple of the geometric stiffness that renders the determinant of the combined system stiffness matrix to be zero. Pipe-Type Design Criteria and LRFD Methodology The design criteria for all pipe types have been extensively revised in accordance with the AASHTO LRFD Specifications (6). The design criteria are equally applicable to either work- ing stress or LRFD design methodologies wherein working stress employs service loads and actual resistance, and LRFD employs factored loads and factored resistance. Listed below are the design criteria for the three major categories of pipe materials with emphasis on the new design criteria developed under this research effort.

13 Valley (1)Valley (1) Liner (2) Link (4)Link (4) Crest (3) Period Height WebWeb Figure 8. Profile wall with user-defined subelements. • Corrugated metal. Corrugated steel and corrugated alu- minum have the same design criteria, differing only by the numerical value of design criterion limits such as the yield stress. The strength design criteria include thrust stress limits for material yielding, global buckling, and seam strength. In addition, a new strength criterion is incorpo- rated to warn against full plastic penetration from thrust and bending. Other new additions include revised tables for available steel and aluminum corrugation sizes and updated flexibility factors for handling considerations. • Reinforced concrete. The strength-related design criteria for reinforced concrete include yielding of the reinforcing steel, crushing of concrete, diagonal shear failure (three forms), and radial tension failure of concrete due to ten- sion steel. The theoretical development of the last criterion, which is not well addressed in the AASHTO LRFD Speci- fications, was developed in the course of this research effort. Similarly, the Heger-McGrath prediction for crack width, a service-related design criterion, is also a product of this research effort. • Thermoplastic pipe. Thermoplastic pipe materials in- clude high-density polyethylene, polyvinylchloride, and polypropylene. All thermoplastic pipe materials have the same general design criteria, differing only in pipe material data and duration of loading. Strength-related design cri- teria include thrust stress limits for material failure and global buckling, and maximum outer fiber strain limits from thrust and bending. Performance-related criteria include allowable displacements and tensile strain. Plastic Profile Wall The previous version of CANDE was limited to smooth walls for all plastic pipes. As part of this research effort, the wall type is extended to include a variety of profile wall sec- tions defined by the length and thickness of subelements that form a repeating profile shape along the length of the pipe. The user-specified subelements include two web elements and four horizontal subelements as shown in Figure 8. Almost all the typical profiles that are currently manufactured can be represented by a subset of these subelements includ- ing ribbed profiles, T-ribbed profiles, unlined corrugations, lined corrugations, and box-like profiles. The key feature of the Profile wall-type option is that it in- cludes the nonlinear phenomenon of local buckling in accor- dance with the local buckling equations specified in Section 12 of the AASHTO LRFD Specifications. That is, depending on the level of the compressive strain, some or all of the subele- ments may experience local buckling, which is simulated by removing a central portion of the subelement’s area in pro- portion to the degree of local buckling. Solutions are iterated until convergence occurs. Unification of Nonlinear Iteration Schemes Previous versions of CANDE employed individual itera- tion counters and strategies for each nonlinear algorithm (i.e., pipe material type, soil models, interface models, and now large-deformation models). CANDE-2007 unifies the iteration schemes of all nonlinear models to be easily con- trolled by the user by one command. Now, the user may select one iteration limit that governs all nonlinear models (soil, pipes, interfaces, and large deformations). Also, the user now has the option to continue or stop the analysis if the iteration limit is exceeded. In either case, diagnostics of the nonlinear models are printed showing which model(s) did not converge along with a measure of the convergence error. Bandwidth Minimization A bandwidth minimizer has been installed in CANDE- 2007 that reduces the maximum bandwidth of the system equations characterizing the finite element mesh topology. The motivation for reducing the maximum bandwidth is to reduce computer storage space for the system of equations and to increase the speed of solving large sets of equations. Bandwidth minimization is achieved by strategically renum- bering the node numbers that were originally input by the user. Node renumbering is accomplished by swapping node numbers, one pair at a time, starting with the node number with the highest bandwidth and exchanging it with another node number that optimally reduces the maximum band- width at the first location while generating a bandwidth at the second location that is less than the original maximum band- width. The algorithm (contained in subroutine BMIZER) was developed during this research effort and is unique to the CANDE-2007 program. In addition to the above new features, many additional modifications have been made to improve the program and ease the burden of user input. For example, a simplified method of defining interface angles is now operational in the

14 program. These and other improvements are discussed in the CANDE-2007 User Manual and Guideline. The FORTRAN code has also been updated from the 1989 code to provide a clearer more structured architecture. The FORTRAN analysis program is now compiled as a DLL that is called directly from the GUI. Testing and Evaluation Checking and testing the accuracy and validity of the new capabilities and modifications include comparing CANDE- 2007 solutions with older versions of CANDE, closed form solutions, simplified AASHTO solutions, and general purpose finite element programs conducted. This type of testing, called alpha testing, was accomplished by the proj- ect team during and after the development phase of each new capability. The results of the alpha-testing phase indicated that the new capabilities were accurate and func- tioning as planned. The beta-testing phase, involving CANDE-2007 testers outside the project team, began in May 2007 with the NCHRP project panel serving as the initial beta testers. Sub- sequently, the beta testing was expanded with 35 beta-tester volunteers from the culvert community over a testing period of 3 months. Beta testers had access to a project website and software to easily record all problems and comments. Of the 35 beta testers and 10 panel members, 16 testers recorded problem reports on the project website. By the end of beta testing, 141 beta incidents were logged on the website. The entire list of beta incidents was reviewed by the project panel at an October 2007 meeting. The vast majority of issues dealt with questions about interpretation of input variables. Accordingly, the CANDE-2007 User Manual and Guideline was revised to address these questions. Some comments led to the discovery of bugs in the CANDE-2007 program, which were corrected. Another class of beta-testing comments dealt with desires for future additions to CANDE-2007. These comments will continue to be maintained by the project team for the purposes of building a list of possible future enhance- ments for the CANDE software. The beta-testing phase proved to be very effective in un- covering problem areas in the software as well as areas of potential misunderstanding on the part of the user that could be addressed by enhancements to the CANDE documenta- tion. All beta-testing incidents have been addressed and resolved except for those issues that are classified as a future enhancement. To enhance future regression testing of the software (i.e., comparing a revised version of the software numerically with a previous version), the NCHRP Process 12-50 (8) has been incorporated into the CANDE Engine with the new Process 12-50 tags fully documented in the CANDE-2007 User Manual and Guideline. After beta testing was completed and the panel viewed the results, a list of items that were beyond the scope of this research effort was added to a future development list. These items include the following: 1. Element death option to simulate removal of temporary bracing, excavating of soil, or loss of structural elements due to aging and corrosion/abrasion. 2. Reformulating the Duncan and Duncan/Selig soil model into a plasticity-based model to properly simulate un- loading. 3. Incorporating shear deformation into structural beam- column elements. 4. Possible incorporation into the AASHTOWareTM suite of products such as Virtis or Opis. 5. Enhanced mesh generation capabilities. 6. Load rating capabilities. Applications—Tutorials The applications of the new CANDE-2007 program are best demonstrated with the CANDE tutorial problems. For a complete understanding, the reader is invited to peruse the companion document entitled, CANDE-2007 Tutorial of Applications. List of Tutorial Problems Listed in Table 1 are the 16 tutorial examples (Note: examples 15 and 16 are only input files and do not include the problem description/narration) that cover all aspects of CANDE-2007 capabilities including multiple structures and retrofit problems. Illustration of Tutorial Tutorial examples (Tutorials 1–14) describe the physical nature of the problem to be solved followed by step-by-step input instructions as well as illustrations of graphical solutions and an evaluation of the culvert safety in terms of design cri- teria. To illustrate the contents of the CANDE-2007 Tutorial of Applications, Tutorial Example #4 is highlighted below. Tutorial Example #4 seeks a design solution for a 60-in. inside diameter corrugated aluminum pipe with 30 ft of fill over the top of the pipe using the Working Stress (service) Design method. The problem is shown schematically in Figure 9. The problem employs Solution Level 2, using an automated finite element pipe mesh for a trench installation

15 Problem Description 1 Level-1, Corrugated Steel Pipe, Design m ode (LRFD). Design a 60 in. inside diam eter corrugated steel pipe with 30 ft of fill over the top of the pipe using LRFD design. The design will be with Level 1, which is based on the Burns and Richard elasticity solution. The desired result is the corrugation size and thickness. 2 Level-1, Reinforced Concrete Pipe, Design m ode (LRFD). Design a 60 in. inside diam eter reinforced concrete pipe with 30 ft of fill over the top of the pipe using LRFD design. The design will be with Level 1, which is based on the Burns and Richard elasticity solution. The desired result is the required inner and outer reinforcement. 3 Level-1, HDPE Plastic Pipe, Design m ode (LRFD). Design a 36 in. outside diam eter smooth wall HDPE plastic pipe with 40 ft of fill over the top of the pipe using LRFD design. The design will be with Level 1, which is based on the Burns and Richard elasticity solution. The desired result is the wall thickness. 4 Level-2, Corrugated Alum inum Pipe, Design m ode (Working Stress). Design a 60 in. inside diam eter corrugated aluminum pipe with 30 ft of fill over the top of the pipe using Working Stress (service) design. The design will be with Level 2, using an auto ma ted finite elem ent pipe me sh for a trench installation having no interface elem ents. The desired result is the corrugation size and thickness. 5 Level-2, HDPE Plastic Pipe, Analysis m ode (Working Stress). Analyze a 36 in. outside diam eter smooth wall HDPE plastic pipe with 40 ft of fill over the top of the pipe using Working Stress (service) analysis. The analysis will be with Level 2, using an autom ated finite elem ent pipe me sh for an em bankm ent installation having no interface elem ents. 6 Level-2, Reinforced Concrete Arch, Analysis m ode (LRFD). Analyze a 237-in. span (90-inch rise) reinforced concrete arch supported on spread footings with 2 ft of fill over the top of the arch, using LRFD analysis. The analysis will be with Level 2, using an autom ated finite elem ent arch me sh for a trench installation having interface elements. The automated finite element mesh will be modified using Level 2-extended to apply p oint loads depicting a LRFD design truck at the ground surface above the crown of the arch. Additionally, the live load rating procedure will be dem onstrated using CANDE output. 7 Level-2, Reinforced Concrete Box, Analysis m ode (LRFD). Analyze a 120 in. x 84 in. reinforced concrete box culvert with standard ASTM steel placem ent with 2 ft of fill over the top of the culvert using LRFD analysis. The analysis will be with Level 2, using an autom ated finite element box mesh for an embankment installation. 8 Level-2, Corrugated Steel Pipe, Analysis m ode (LRFD). Analyze a 144 in. corrugated steel pipe with 8 slotted joints and 60 ft of fill over the top of the pipe using LRFD analysis. The analysis will be with Level 2, using an auto mated finite elem ent pipe me sh for an em bankm ent installation havi ng no interface elem ents. The autom ated finite element mesh will be m odified using Level 2-extended to reduce the thickness of the construction steps above the crown of the pipe. 9 Level-2, Corrugated Steel Long Span, Analysis mode (Working Stress). Analyze a 217-in. span (82-inch rise) 3-segm ent type corrugated steel long span arch supported on spread footings with 3 ft of fill over the top of the arch, using Working Stress (service) analysis. The analysis will be with Level 2, using an automated finite element arch mesh for a trench installation having interface elem ents. The autom ated finite element mesh will be m odified using Level 2-extended to apply point loads depicting an LRFD design truck at the ground surface above the crown of the arch. 10 Level-2, Reinforced Concrete Pipe, Design m ode (LRFD). Design a 72 in. inside diam eter concrete pipe set on gravel bedding with 60 ft of fill over the top of the pipe using LRFD design. The analysis will be with Level 2, using an automated finite elem ent pipe me sh for an em bankm ent installation having a 6 in. layer of soft backpacking soil around the circum ference of the pipe and no interface elem ents. The desired result is the required inner and outer reinforcem ent. 11 Level-2, Plastic Pipe (Profile), Analysis m ode (Working Stress). Analyze a 48 in. inside diam eter corrugated plastic (profile) pipe with 40 ft of fill over the top of the pipe using Working Stress (service) analysis. The analysis will be with Level 2, using an auto ma ted finite elem ent pipe me sh for a trench installation having interface elem ents. The automated finite element mesh will be m odified using Level 2-extended to change the haunch zones to a user-defined soil material and the thickness of bedding layer to 6 in. Table 1. Tutorial Example Descriptions.

16 Problem Description 12 Level-3, Reinforced Concrete Box, Analysis m ode (LRFD). Analyze a 120 in. x 84 in. reinforced concrete box culvert with standard ASTM steel placem ent with 2 ft of fill over the top of the culvert using LRFD analysis. The analysis will be with Level 3, using a user-generated finite elem ent me sh for an em bankm ent installation. This problem analyzes the reinforced concrete box culvert from Tutorial Problem 7, which was perform ed using a Level 2 analysis. 13 Level-3, Corrugated Steel Long Span, Analysis mode (Working Stress). Analyze a 217-in. span (82-inch rise) 3-segm ent type corrugated steel long span arch setting on concrete footings with 3 ft of fill over the top of the arch using Working Stress (service) analysis. The analysis will be with Level 3, using an imported finite element arch mesh in XML form at from Tutorial Problem 9 for a trench installation having interface elem ents. This problem analyzes the corrugated steel long span arch from Problem 9, which was perform ed using a Level 2 analysis. 14 Level-3, Reinforced Concrete and Corrugated Alum i num Arch, Analysis m ode (Working Stress). Analyze a two-material structure composed of a reinforced concrete U-shaped base with 15-ft span and 5-ft rise supporting a pin connected, corrugated alum inum arch-shaped roof with 13 ft of fill over the top of the arch. The analysis will be with Level 3, using an imported finite elem ent me sh in XML form at. 15 Level-3, Multiple Plastic Arches, Analysis m ode (LRFD). Analyze three corrugated plastic arches with 42 in. span and 27 in. rise placed side by side with 8.5 in. spacing between the legs (stor m water retention cham bers) with 2 ft of soil over the top of the arches. The analysis will be with Level 3, using a user-generated finite element mesh for a trench installation. The desired analysis result is to evaluate LRFD local and global buckling. (INPUT FILE ONLY) 16 Level-3, Corrugated Steel Pipe Retrofitted with Plastic Pipe Liner, Analysis m ode (Working Stress). Analyze a 48 in. corrugated steel pipe with an eroded invert and retrofitted with a profile plastic pipe with 5 ft of fill over the top of the pipe. The analysis will be with Level 3, using a user- generated finite elem ent mesh for a trench installation. (INPUT FILE ONLY) Table 1. (Continued). without interface elements. The desired results are the corru- gation profile and sheet thickness and a final evaluation. The tutorial leads the user through 10 GUI-input screens that convey the above physical information into a complete CANDE input document. After executing the input file, CANDE generates the symmetric mesh shown in Figure 10 wherein the shaded/numbered layers of soil are construction increments. The initial configuration, shown shaded with a numeric “1” in each box , includes the in situ soil bedding, and culvert. Next, three layers of trench fill soil are placed to the top of the trench (designated with load step numbers 2-4), followed by one larger layer of overfill (load step 5) to a fill height of 1.5 diameters above the crown. The remaining over- fill soil loading is placed in five load steps using equivalent overburden pressure loading. The design solution, taken directly from the CANDE output report, is shown in Figure 11, wherein three design- iteration cycles were required to determine the required thrust area, moment of inertia, and section modulus to sus- tain the soil loading with the desired safety factors. Using the required section properties, CANDE searches through the corrugation tables for aluminum culverts and lists the least weight design solution for each corrugation size. From the list of acceptable corrugation sizes, CANDE selects the corrugation with a combined minimum thrust area and moment of inertia for a final analysis and evalua- tion. In this example, the selected corrugation profile is 2-2/3 in. (period) by 1/2 in. (height) with a metal thickness of 0.135 in. After performing another analysis cycle, the CANDE Output report provides a final evaluation of the selected cor- rugation as shown in Figure 12. All safety factors meet or exceed the user-specified requirements. Excess safety occurs because the available manufactured section properties exceed the minimum required section properties. This example, as do all the tutorial examples, demon- strates how CANDE-2007 differs from general purpose fi- nite element programs. That is, CANDE sorts through all the mechanistic responses of deformations, stresses, strains, thrust, moments, and shears and summarizes the pipe performance in terms of safety factors or demand-to- capacity ratios.

17 Soil Zo ne Type of Soil Young’s Modulus (psi) Poisson’s Ratio Soil Density (lb/ft3) In situ Hard clay 6,000 0.35 120 Bedding Compacted sand 2,600 0.19 120 Backfill in trench Compacted sand 2,600 0.19 120 Overfill above trench Lightly compacted silt 800 0.23 120 Figure 9. Illustration of Tutorial Example #4 with soil zone properties.

18 Figure 10. Soil construction increments for Tutorial Example #4 from GUI.

19 Figure 11. Design solutions for Tutorial Example #4.

20 Figure 12. Final evaluation of selected design.

Next: Chapter 4 - Conclusions and Recommendations »
Modernize and Upgrade CANDE for Analysis and LRFD Design of Buried Structures Get This Book
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TRB's National Cooperative Highway Research Program (NCHRP) Report 619: Modernize and Upgrade CANDE for Analysis and LRFD Design of Buried Structures explores the development, modernization, and upgrading of the CANDE (Culvert ANalysis and DEsign) program to a new program called CANDE-2007. The CANDE-2007 installation files are included on a CD-ROM with this report. The installed program includes integrated help files and 14 tutorial examples. The CD-ROM is also available as an ISO image for downloading from TRB's website.

Links to the download site for the combined appendices and data-viewing ISO and to instructions on burning an .ISO CD-ROM are below.

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