4.5 No deflection in beam Single beam loaded with UDL – No deflection.
All calculations are done at node points. If a beam element doesn’t have any internal nodes, no calculations can be done within the span of the beam. Therefore, no deflections can be calculated along the length of the beam.
Solution: define more segments for the beam.
4.6 Too many pins Top chords and vertical members are all pinned at the apex.
4.7 Unconnected models The column is 1 mm too short.
One of the unique properties of a stiffness matrix in both matrix structural analysis and the finite element method is that the entries on the main diagonal are positive and non- zero, or positive definite. A ‘Stiffness matrix not positive definite’ error is caused when an analysis encounters a negative or zero number on the diagonal of the stiffness matrix.
This is usually caused by one of the following:
• Instability, e.g. neglecting to restrain the rotational degree of freedom at the fixed end of a cantilever. • Parts of the model are not connected. • Numerical instability, e.g. connecting a 5m deep beam to a 5mm deep beam (resulting in an ill- conditioned matrix).
For more information see the following articles on our website:
• Unconnected Models Article: https://support.prokon.com/kb/articles/sumo-unconnected-models- message. • Unconnected Models YouTube video: https://youtu.be/VYgMk6BYSZg
4.8 Node is not connected to the model Floating Line Load stops short of a column: a node is generated over the punched-out area of the slab.
Sumo automatically handles the node generation and numbering. This means that the model is completely dependent on the user input. This example shows how a node can be generated that is unconnected from the structure.
To resolve this, we can extend the line load to the position of the column.
Sumo Workshop Training Manual
Page 2
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