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CANDE Newsletter #5

Jan 29, 2015

CANDE-2015 program – The latest Cande version, called CANDE-2015, may be downloaded free of charge from website. New capabilities and improvements in CANDE-2015 include all those in CANDE-2013 as described below in items 1 to 5 plus two new soil model options described in items 6 and 7. The capabilities listed below are not available in the official CANDE-2007/2011 program maintained at the Transportation Research Board NCHRP website; however, they are made available to the Cande user community through the good graces of the industries sponsoring the developments.

1.   Deeply corrugated steel structures. Recently, AASHTO adopted a new combined moment-thrust design criterion that applies to deeply corrugated steel structures with corrugation heights greater than 5 inches. The combined thrust-moment design criterion (AASHTO Equation incorporates the plastic moment of the corrugated section as a resistance measure in addition to the thrust yield stress. Also, AASHTO introduced a new equation to predict the global buckling resistance of deeply corrugated structures (Equation These new design criteria are programmed into CANDE-2015 Steel pipe type and may be activated at the user’s discretion. (Industry sponsors Atlantic Industries and Contech Construction Products)

2.   Variable plastic profile properties. Typically, the section properties of plastic profile pipe are uniform around the pipe’s periphery; hence, previous versions of CANDE were restricted to uniform section properties per pipe group. However, arch-shaped storm water chambers often employ changes in the plastic profile geometry from bottom to top. CANDE-2015 has been revised to allow variable profile geometries around the structure. This applies to all types of plastic including HDPE, PVC, and PP. (Industry sponsors Advanced Pipe Services and Prinsco)

3.   Link elements with death option. Links, which are new constraint-type elements in CANDE-2015, are useful for connecting one beam-element group to another in either a pinned connection or fixed-moment connection. More importantly, the link element offers a user-specified death option that allows the simulation of temporary support removal during construction. Alternatively, by placing links around a group of soil elements, it is possible to simulate soil removal (excavation) or the creation of voids during the loading schedule. (Industry sponsors Contech Construction Products and MGK Consulting)

4.   CONRIB pipe type. CONRIB is a new pipe type in CANDE-2015 that offers modeling capabilities for rib-shaped reinforced/concrete cross-sections in addition to standard wall cross sections. More significantly, the concrete constitutive model offers the option to simulate the nonlinear ductile behavior of fiber reinforced concrete (FRC) in tension as well as the standard nonlinear behavior in compression. Applications include all concrete culverts and foundation walls with or without steel reinforcement. (Industry sponsor Con/Span Bridge Systems)

5.   CONTUBE pipe type. CONTUBE is another new pipe type added to the pipe library that permits modeling circular-shaped concrete cross sections encased in fiber-reinforced plastic (FRP) tubes spaced at uniform distances. Applications for the CONTUBE pipe type include arch-shaped soil bridges as well as pile-support systems based on the new AASHTO publication LRFD Guide Specifications for Design of Concrete-Filled FRP Tubes. (Industry sponsor Advanced Infrastructure Technologies)

6.   Mohr/Coulomb plasticity model. The classical Mohr/Coulomb elastic-perfectly plastic model is now included in the suite of available constitutive models that may be assigned to continuum elements to describe soil behavior. Four material parameters are required to define the model: Young’s modulus and Poisson ratio in the elastic domain and cohesion intercept and friction angle in the plastic domain. Suggested model parameters are listed in the User Manual. (Industry sponsors Contech Engineered Solutions and MGK Consulting)

7.   Modified Duncan/Selig model for plastic-like behavior. Although the Duncan/Selig soil model is considered superb in simulating the nonlinear loading behavior of soils, the original model did not produce permanent deformation upon unloading. The new modified Duncan/Selig model produces permanent deformations upon unloading similar to advanced plasticity models. No new material parameters are introduced into the new formulation; thus, the existing data base of Duncan/Selig parameters remains valid for the modified formulation. The user has the option to use either the Original or Modified version. (Industry sponsors Contech Engineered Solutions and MGK Consulting)

In addition to the new capabilities listed above, several corrections and improvements have been reprogrammed in CANDE-2015 that are transparent to the user and are listed below:
•   An improved method to divide quadrilateral elements into two triangles that are more nearly equal in size in subroutine Genend (2013).
•   Correction of nonlinear algorithm for corrugated metal that incorrectly increased the amount of plastic penetration due phantom moments in subroutine Emod (2013).
•   Modified the static condesation algorithm for internal degrees of freedom to avoid a rare division by zero problem occuring in quadrilateral elements in subroutines Stifns and Stress (2013).
•   Increased the allowable number of beam nodes from 999 to 2999 to accommodate special modeling needs such as simulating reinforced earthn strips (2015).
•   Improved convergence and iteration technique for local buckling of Plastic profile pipes (2015).
•   Improved convergence methodology for CONRIB pipe type (2015).
•   Corrected small errors in the computation of shear capacity for reinforced concrete shear capacity relating to AASHTO Section, i.e. Cande case NSHEAR =1 (2015).

Obtaining CANDE-2015. To get the CANDE-2015 package follow the steps below.

1.   Go to home page on CANDE web site and down load the CANDE-2015 package which includes the executable program, installation directions, an updated user manual and an updated theoretical manual.

2.   Save the package on your computer.

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

Comments on CANDE-2015
•   All CANDE input files that worked with CANDE-2007/2011(or with CANDE-2013) will work the same way with CANDE-2015 – there are just more options in CANDE-2015 as described above.
•   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 updated. Refer to CANDE-2015 User Manual for work around techniques.
•   Although the new options have been tested for a year or more, they are still viewed as undergoing experimental beta testing – so your feedback is welcomed in the CANDE Forum or email.
•   With your support it is hoped that CANDE-2015 will eventually become part of another TRB/NCHRP upgrade project wherein the GUI will be updated and extended. TRB culvert committees AFF70 and AFS40 have drafted a Research Need Statement called “CANDE-2017 Upgrade” that requests ASSHTO support to upgrade and enhance the GUI as well as other improvements to CANDE. Your active support in this endeavor is greatly appreciated.