Troubleshooting suggestions, organized in order of complexity, and listed as follows:
General approach
- It may be best to begin with a simple model, then gradually build upon its sophistication.
- It may be best to begin with a simple model, then gradually build upon its sophistication.
Release only one end
- Ensure that releases are not assigned to both ends of frame objects. Releasing both ends may prevent load transfer, leading to numerical problems. Information on numerical problems is available using the Standard Solver, available through Analyze > Set Analysis Options > Solver Options. Check for instability warnings in the log file by selecting File > Show Input Log Files.
- Ensure that releases are not assigned to both ends of frame objects. Releasing both ends may prevent load transfer, leading to numerical problems. Information on numerical problems is available using the Standard Solver, available through Analyze > Set Analysis Options > Solver Options. Check for instability warnings in the log file by selecting File > Show Input Log Files.
Avoid full fixity and full rigidity
- Rather than applying full fixity to DOF, and full rigidity to structural objects, restrained and rigid conditions should be modeled using sufficiently large stiffness values, perhaps on the order of 1e11. Stiffness values may be assigned using spring constants, property modifiers, or section properties. Full fixity or full rigidity may cause numerical sensitivity in linear solutions, and singularities in nonlinear numerical formulation, leading to convergence problems or instabilities.
- Rather than applying full fixity to DOF, and full rigidity to structural objects, restrained and rigid conditions should be modeled using sufficiently large stiffness values, perhaps on the order of 1e11. Stiffness values may be assigned using spring constants, property modifiers, or section properties. Full fixity or full rigidity may cause numerical sensitivity in linear solutions, and singularities in nonlinear numerical formulation, leading to convergence problems or instabilities.
Assign mass and inertia
- During dynamic analysis, ensure that mass, inertia, and perhaps rotational inertia are distributed throughout the structure. Mass and inertia couple with dynamic behavior as an integral part of mathematical formulation. When links are located at support points, inertia either may be assigned using the link property, or it may be added directly at the joint. Rotational inertia is added by assigning a mass value between 1/10 md 2 and 1/100 md 2, where m is a characteristic mass located a characteristic distance d from the support.