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Culvert Analysis and Design (CANDE) 2022 Finite Element Analysis Software Update

Description:

ulvert alysis and sign (CANDE) is a computer finite element software dedicated to the analysis and design of buried culverts and buried bridges. CANDE was developed in the FORTRAN programming language and first introduced in 1976 under the sponsorship of FHWA. The software has gained widespread acceptance in the buried structures community with decades of testing and improvement.

An official update to the software was sponsored by AASHTO under NCHRP Project 15-28 and released in 2007 (called CANDE-2007), with subsequent enhancements released in 2011, hereafter referred to as CANDE-2007/2011. CANDE-2007/2011 established compatibility with 64-bit computers and included new modeling capabilities such as large deformation analysis, incorporation of LRFD design methodology, and capability to model multiple, parallel culvert systems. The upgrade also included development of a new Graphical User Interface (GUI) for pre- and post-processing data. CANDE-2007/2011 allows for two-dimensional plane strain analysis and design of all shapes and sizes of buried culverts and buried bridges including specific material models for corrugated metal, reinforced concrete, and thermoplastics, as well as sophisticated soil models.

After the release of CANDE-2007 several industries sponsored further developments of new modeling capabilities. Some of these improvements were motivated by new materials and technologies that are gaining acceptance in the AASHTO community including new pipe types and methods of culvert rehabilitation. One example is the ability to model circular-shaped concrete cross-sections encased in fiber-reinforced plastic tubes. Another industry-sponsored improvement includes the possibility of element subtraction to simulate, for example, strut removal, culvert erosion, or the creation of soil voids, which can be useful in load ratings and for estimating service life.

Additional features released in 2015 and 2017 included introduction of the Mohr/Coulomb plasticity soil model to CANDE, additional updates to the Duncan/Selig and Mohr/Coulomb soil model capabilities within CANDE, and a revolutionary method to accurately simulate three-dimensional live load spreading along the length of the culvert when modeled in two-dimensional space.

These new modeling capabilities are available via industry-sponsored expanded versions of CANDE, the most recent of which is called CANDE-2017. These enhancements are available to experienced users through manipulation of text input files that are run through batch mode at a command prompt; they have not been incorporated into the NCHRP/TRB-sponsored GUI.

As part of ongoing AASHTO-sponsored NCHRP Project 15-54, “Proposed Modifications to AASHTO Culvert Load Rating Specifications,” slated for completion in 2019, a new CANDE Tool Box (CTB) was developed to adapt the existing software to load rating applications. The CTB is an external add-on to CANDE that allows users to manipulate existing model mesh to accommodate non-symmetric loads and add pavement layers, account for live load distribution through pavement and soil including AASHTO dynamic load allowance and multiple presence factors, move live loads across the model surface to simulate a vehicle traversing a culvert, compute vehicle load rating factors at controlling locations based on prescribed design criteria, and other enhancements to decrease computing time. The CTB currently launches through an external executable file with menu options selected in a command prompt-like window while generating text output reports; these steps are not currently supported by the GUI.

ulvert alysis and sign (CANDE) is a computer finite element software dedicated to the analysis and design of buried culverts and buried bridges. CANDE was developed in the FORTRAN programming language and first introduced in 1976 under the sponsorship of FHWA. The software has gained widespread acceptance in the buried structures community with decades of testing and improvement.

An official update to the software was sponsored by AASHTO under NCHRP Project 15-28 and released in 2007 (called CANDE-2007), with subsequent enhancements released in 2011, hereafter referred to as CANDE-2007/2011. CANDE-2007/2011 established compatibility with 64-bit computers and included new modeling capabilities such as large deformation analysis, incorporation of LRFD design methodology, and capability to model multiple, parallel culvert systems. The upgrade also included development of a new Graphical User Interface (GUI) for pre- and post-processing data. CANDE-2007/2011 allows for two-dimensional plane strain analysis and design of all shapes and sizes of buried culverts and buried bridges including specific material models for corrugated metal, reinforced concrete, and thermoplastics, as well as sophisticated soil models.

After the release of CANDE-2007 several industries sponsored further developments of new modeling capabilities. Some of these improvements were motivated by new materials and technologies that are gaining acceptance in the AASHTO community including new pipe types and methods of culvert rehabilitation. One example is the ability to model circular-shaped concrete cross-sections encased in fiber-reinforced plastic tubes. Another industry-sponsored improvement includes the possibility of element subtraction to simulate, for example, strut removal, culvert erosion, or the creation of soil voids, which can be useful in load ratings and for estimating service life.

Additional features released in 2015 and 2017 included introduction of the Mohr/Coulomb plasticity soil model to CANDE, additional updates to the Duncan/Selig and Mohr/Coulomb soil model capabilities within CANDE, and a revolutionary method to accurately simulate three-dimensional live load spreading along the length of the culvert when modeled in two-dimensional space.

These new modeling capabilities are available via industry-sponsored expanded versions of CANDE, the most recent of which is called CANDE-2017. These enhancements are available to experienced users through manipulation of text input files that are run through batch mode at a command prompt; they have not been incorporated into the NCHRP/TRB-sponsored GUI.

As part of ongoing AASHTO-sponsored NCHRP Project 15-54, “Proposed Modifications to AASHTO Culvert Load Rating Specifications,” slated for completion in 2019, a new CANDE Tool Box (CTB) was developed to adapt the existing software to load rating applications. The CTB is an external add-on to CANDE that allows users to manipulate existing model mesh to accommodate non-symmetric loads and add pavement layers, account for live load distribution through pavement and soil including AASHTO dynamic load allowance and multiple presence factors, move live loads across the model surface to simulate a vehicle traversing a culvert, compute vehicle load rating factors at controlling locations based on prescribed design criteria, and other enhancements to decrease computing time. The CTB currently launches through an external executable file with menu options selected in a command prompt-like window while generating text output reports; these steps are not currently supported by the GUI.

CANDE has proven to be a great example of industry-government cooperation and technology transfer, and is freely available at the CANDE website (www.candeforculverts.com). With the new capabilities since 2007, CANDE usage by owners, industry members, and practitioners across the nation has grown and CANDE continues to be a hallmark software for analyzing, designing, and now load rating culverts and other buried structures.

While CANDE has seen increased utilization, like any software, there are desired improvements that the user community has identified with time and with increasing capabilities and technological advances. Potential improvements that would greatly benefit users include the following:

  • Modernize the CANDE analysis engine and transition the programming from the existing FORTRAN coding language into a more user-friendly, modern, object-oriented language such as C#. The current CANDE-2007-developed GUI was written in C# while the CANDE analysis engine, including that of the CTB, remains in FORTRAN.
  • Modernize and improve the existing first-generation GUI that was developed for CANDE-2007. Concurrently, integrate features that have been developed since 2007 into the GUI, including industry- and AASHTO-sponsored enhancements such as the new material and soil models, and the recently developed CTB. The GUI framework has not been updated since 2007 and thus users will greatly benefit by this upgrade through reduced effort in model development and increased user friendliness, especially when compared to the current method of implementing the enhancements through manual manipulation of text input files or through the external CTB executable file and command prompt menus.
  • Provide an enhanced mesh generation routine to allow users to automatically create non-standard or more sophisticated mesh geometries and configurations such as culvert systems with multiple parallel barrels (e.g. multiple cell box culvert) or sloping grade elevations. Current user-defined mesh generation (used for sophisticated geometries) is performed through external commercial software sources such as CandeCAD Pro or NASTRAN, though neither software is directly compatible with recent features added to CANDE. This will allow users to more easily utilize CANDE for a larger variety of culverts, storm drains, sewers, and buried bridges.
  • Improve finite element model generation capabilities when importing a mesh generated from external sources such as CandeCAD Pro or NASTRAN. Currently, when working with a user defined mesh, much of the model input data including element material properties, section properties, interface elements, and boundary conditions must be input manually via text input files when importing a user defined mesh from NASTRAN.
  • Enable importing culvert geometries directly from AutoCAD drawings.
  • Develop a vehicle library module that allows users to select and/or define any live load vehicle configuration. This will reduce user effort associated with analyzing non-standard vehicles or multiple vehicles, and enhance live load analysis automation.
  • Provide better control over visual post-processing by allowing for definition of contour plot ranges and parameters. Current plotting parameters, such as contour plot ranges, are automatically set and not editable. These ranges often obscure results of interest to the user when overall contour ranges are automatically set to include extreme values at isolated areas. This will allow the user to better visualize load paths and soil stresses for increased confidence and understanding of results, and be able to compare results from different analyses with the same contour plot ranges.
  • Upgrade CANDE to reflect updates to the buried structure provisions of the AASHTO LRFD Bridge Design Specifications that have occurred since CANDE-2007 was released. CANDE-2007 included LRFD design, but the design component has not been updated to reflect changes to the code since its original release.
  • Make GUI and any necessary analysis engine updates to incorporate latest enhancements to the Duncan/Selig soil model to simulate plastic-like unloading and reloading behavior and include the traditional Mohr/Coulomb elastic-plastic soil model into the suite of CANDE’s soil modeling options.
  • Provide a new official release version of CANDE that incorporates the above-mentioned industry-sponsored improvements plus the other improvements listed herein with full functionality from input file generation, post-processing, and GUI compatibility.
  • Create a tracking system to allow collection of bugs or recommended updates and needed revisions to allow future updates to CANDE.
Objective:

The main objective of this research is to provide better value to owners of buried structures through the development, testing, and release of a newly updated version of CANDE called CANDE-2022. The value to owners will be realized through increased ease of use of this software to provide more cost-effective culvert and buried bridge designs with better interpretation and understanding of modeling results and to directly allow load rating for buried structures as required for safety on the national highway inventory. The improvements will allow for (1) easier comparison of possible designs of alternate types of structures or materials including owner verification of designs submitted by others, (2) analysis and design of structures such as buried bridges that have seen increased use and economic viability compared to traditional girder-type bridge structures, (3) direct utilization of the software for culvert or buried bridge live load analysis and load rating factor determinations, (4) analyzing culverts and other buried structures for any vehicle configuration including permit loads, (5) incorporation of inspection results to complete analysis of in-service culverts and buried bridges, and (5) simplified utilization of CANDE for a greater diversity of culvert and buried structure systems through integration of a variety of enhancements into an updated GUI and modern object-oriented language analysis engine.

Benefits:

As infrastructure ages, roads and bridges are being rebuilt and rehabilitated with tighter project budgets while simultaneously requiring lower life-cycle cost and longer design life. With this reality in mind, potential benefits include increased ease of use by owners for a larger variety of culvert systems, alternate designs including growing use of buried bridges in place of traditional at-grade bridge spans, incorporating newer materials and technologies. These improvements require increased and simplified use of the software for culvert and buried bridge live load analysis, design of newer systems, and load ratings for all bridge-class structures. The CANDE software provides this capability, if updated to current standards.

Related Research:

The proposed improvements and functionality of CANDE software are integral to the objectives of the sponsoring community, yet independent of other research topics with no research overlap potential. Among other improvements, the proposed research would directly improve the functionality of the CANDE Tool Box add-on developed as part of the much larger NCHRP Project 15-54, “Proposed Modifications to AASHTO Culvert Load Rating Specifications,” that is completing in 2019 by integrating the tool box into an updated GUI. The proposed updates would also help owners evaluate structural deficiencies or rehabilitation options that may follow culvert inspections performed in accordance with the new AASHTO Culvert Inspection Guide, developed under NCHRP Project 14-26 and set for publication by AASHTO in 2019.

Tasks:

To meet the above research objectives, the task group developing this research statement envisions the following tasks for this project:

  1. Survey the CANDE user community to identify all existing issues with the latest version of CANDE, including the CTB, to determine additional needs not addressed above, and to prioritize all proposed improvements.
  2. Collate and synthesize survey results with planned GUI improvements and develop a detailed work plan to achieve user-defined objectives.
  3. Present the detailed work plan to the NCHRP project panel including summary of survey results, planned GUI screen views, and proposed developments for all new modeling capabilities.
  4. Revise the detailed plan per comments from NCHRP panel and undertake the development of the CANDE-2022 program including potential migration of the CANDE analysis engine from its native FORTRAN language to a modern, user-friendly, object-oriented programming language such as C#.
  5. Edit and update CANDE-2022 Guideline and User Manual, Solutions and Formulations Manual, and Tutorial of Applications Manual, including additional tutorial problems that build on previous tutorial examples but demonstrate enhanced features of the updated software.
  6. Beta-test CANDE-2022 program through a combination of volunteers from NCHRP panel members, user community, and industry personnel.
  7. Disseminate the final CANDE-2022 program and documentation.
  8. Propose methodology to collect comments and feedback for future improvements to the CANDE analysis engine and the associated GUI.
Implementation:

No follow-up research is necessary for the research statement. Post-implementation of the CANDE-2022 program will include open dialog with the user community for feedback and addressing any concerns, which are expected to be minimal. It is anticipated that once users and potential users receive notification of the CANDE enhancements, usership will increase with little continued effort due to the inherent value of the software improvements. Potential barriers and impediments to implementation are limited to notification of uses and potential users, which will be overcome by notifying registered CANDE users, advertising the software upgrades on the TRB/NCHRP and CANDE web site, conducting TRB webinars, and outreach to relevant programs within TRB/SHRP. CANDE is also expected to see increased usership following the 2019 publication of the AASHTO Culvert and Storm Drain System Inspection Guide (following the recent completion of NCHRP Project 14-26), and through the soon-to-be completed NCHRP Project 15-54 to update AASHTO culvert load rating specifications.

Relevance:

There are over 200 registered users of CANDE including owners such as DOT personnel and engineers from industry, consulting firms, and academia. Of these 200+ registered users, 63 are from state DOTs and represent 75% of the US states. Use of CANDE is expected to further increase after incorporating the proposed enhancements. The orginal developer, Dr. Mike Katona, has retired and will no longer provide updates to the CANDE software, leaving further improvements in the hands of the NCHRP research program.

Sponsoring Committee:AFF70, Culverts, Buried Bridges, and Hydraulic Structures
Research Period:Longer than 36 months
Research Priority:High
RNS Developer:Mr. Jesse L. Beaver, PE, P.Eng Simpson Gumpertz & Heger Inc. 41 Seyon St., Bldg. 1, Ste. 500 Waltham, MA 02453 781.907.9272 JLBeaver@sgh.com Mr. Brent J. Bass, PE (MA) Simpson Gumpertz & Heger Inc. 41 Seyon St., Bldg. 1, Ste. 500 Waltham, MA 02453 781.907.9327 bjbass@sgh.com Dr. Michael G. Katona MGK Consulting Gig Harbor, WA 98335 253.851.5242 mgkatona@comcast.net Mr. Mark Mlynarski, PE (PA) Michael Baker International Moon Township, PA 412.269.7933 mmlynarski@mbakerintl.com Dr. Timothy J. McGrath, PE (MA) TJMcGrath, LLC Arlington, MA 781.424.3972 tjmcgrathllc@gmail.com Dr. Mark C. Webb, Pr. Eng. (RSA) Simpson Gumpertz & Heger Inc. Waltham, MA 781.907.9441 mcwebb@sgh.com
Source Info:Mlynarski, M., M.G. Katona, and T.J. McGrath, “Modernize and Upgrade CANDE for Analysis and LRFD Design of Buried Structures,” National Cooperative Highway Research Program Report 619, National Academy of Sciences, 2009.

CANDE-2007/2011 Software Download: http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=408

CANDE-2017 and CANDE Tool Box Download (requires CANDE-2007/2011 from above):

http://www.candeforculverts.com/download.html
Date Posted:02/14/2020
Date Modified:02/14/2020
Index Terms:
 
Subjects    
Highways
Pipelines
Design
Geotechnology
Bridges and other structures

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