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CANDE News > CANDE Newsletter #7
CANDE Newsletter #7

Feb 6, 2017

Release of CANDE-2017 program – CANDE-2017 is the latest version in the CANDE series of programs and may be downloaded free of charge from the website CandeForCulverts.com. This new version is compatible with all previous input files dating back to the CANDE-2007 program. New capabilities and improvements are discussed briefly below. Detailed developments may be found in the CANDE-2017 Formulations and Solution Manual and the User Manual that accompany the downloads.

NEW CAPABIITIES:
1.   Continuous Load Scaling for Live Loads. Continuous Load Scaling (CLS) is a revolutionary new procedure to simulate longitudinal load spreading from live loads that allows 2D plane-strain solutions like CANDE’s to mimic longitudinal load spreading similar to 3D finite element solutions. CLS offers a superior alternative to the traditional Reduced Surface Load (RSL) procedure wherein the effects of longitudinal load spreading is approximated by reducing the vehicle’s surface load so that the soil stress is corrected at one soil depth, typically the soil depth at the culvert crown. In contrast, the CLS procedure corrects the soil stress at all soil depths by continuously increasing each element’s out-of-plane thickness with the soil depth in accordance with the selected load spreading theory, i.e., the AASHTO Ad hoc Method (AAM) or preferably the Elasticity Based Method (EBM). Detailed developments and comparative solutions of the CLS procedure are to be published Transportation Research Record later this year. For the present, the detailed developments and comparative performance are presented in Chapter 8 of CANDE’s 2017 Formulations and Solution Manual. To implement the CLS procedure, refer to CANDE-2017 User manual and note the last input parameter on line C-2.L3 and set Iscale = 1. Next, manually insert a new line C-2a.L3 and input the requested live-load characteristics.

2.   Extensions to Mohr-Coulomb Soil Model. As first introduced in CANDE-2015, the Mohr-Coulomb plasticity model was restricted to associative flow rules and fixed tension cut-off algorithm. Now, CANDE-2017 offers an option for non-associative flow rules wherein the direction of plastic-straining may be selected normal to any surface, not just the yield surface. In particular, the flow surface may be defined by the soil’s dilatancy angle, which is generally more realistic. In addition, a completely new tension cut-off model has been installed that is more robust, more realistic and offers the user the option to choose the tension cut-off stress level. Detailed developments of the revised Mohr-Coulomb model are presented in Chapter 3 of CANDE’s 2017 Formulations and Solution Manual, and input instructions are provided in Section D of CANDE-2017 User Manual. The motivation for enhancing the Mohr-Coulomb soil model is to allow a direct comparison between CANDE solutions and other finite element programs that are often restricted to Mohr-Coulomb soil models. However for general soil-structure analysis with CANDE, it is recommended to use the Duncan/Selig soil model because it simulates actual soil behavior more accurately than the Mohr-Coulomb soil model.


IMPROVEMENTS AND CORRECTIONS (transparent to user)

•   Improved algorithm for global buckling predictions to properly circumvent constraint-type elements during the determinant search of the combined global stiffness and large-deformation geometric stiffness matrices.

•   Revised concrete pipe-type suboutines to correctly count the number of iterations during oscillating convergence that had been resulting in the lack of updating the concrete responses at the end of a non-converged load step.

•   Corrected an elastic-plastic unloading error for corruagated metal pipe types wherein thrust reversal did not unload elastically from the plastic domain; whereas, moment reversal performed correctly.

•   Fixed a file storing proplem wherein some files created during execution were inadvertantly being stored in Programs(x86) for which Microsoft requests administrator-level permission. Files created by CANDE are no longer stored in Programs(x86).

HOW TO GET CANDE-2017

1.   Go to web site CandeForCulverts.com.and down load the CANDE-2017 package which includes the executable program, installation directions, and 2017 user manual and theoretical manual.

2.   Save the package on your computer.

3.   Open and read the simple installation direction to patch-in the new Cande-DLL.

CLOSING REMARKS and REQUESTS

All CANDE input files that worked with previous versions of CANDE dating back to 2007 will work the same way with CANDE-2017 but perhaps with slightly different answers due to improvements.

To utilize any new option, the input data must be entered directly on the input file (batch mode) because the input GUI menu is not yet updated. Refer to CANDE-2017 User Manual for input format.

Although the new options have been tested by the developer, they are still viewed as undergoing experimental beta testing – so your feedback is welcomed by email, mgkatona@comcast.net .

It is anticipated that CANDE-2017 will become part of another TRB/NCHRP upgrade project wherein CANDE’s GUI will be updated and extended to catch up with all the new capabilities installed since 2011. Your active support in this endeavor is greatly appreciated.

Beta testers are being sought to evaluate a new companion program to CANDE called the CANDE Tool Box (CTB) that greatly simplifies the onerous task of load rating culverts according to LRFR requirements. Interested engineers need only email mgkatona@comcast.net with "CANDE Tool Box" in the subject title. By return email the requester will receive an executable copy of the CTB program along with a comprehensive user manual with illustrations on load rating using CANDE.