Modeling and calculations

Our team is at your disposal for the realization of modeling and calculations on elements of mechanisms or structures.
We have more than 15 years of experience in these fields and have used very early shell and plate modeling, ideal compromise for the structural elements between the 3 types of modeling: bars / nodes, plate and 3D.
The rules for calculating the structures defined in the FEM's are based on the classical beam theory, so that the finite element modeling of the bar type is particularly adapted but the lessons learned are very limited.
As the calculation means have evolved considerably since the definition of the FEM rules, we now use the surface finite element methodology.

 

This methodology has numerous advantages:

 

  • the bar-type finite elements provide the nominal stresses at the neutral fiber of the modeled elements, the surface modeling makes it possible to highlight the stress concentrations in the assembly areas.
  • the authors of the FEM rules, aware of the existence of stress concentrations not taken into account in the calculations, even performed using bar modeling, defined the values ​​of the maximum permissible stresses by dividing the value of the elastic limit of the material by a factor between 1.50 and 1.10 depending on the stress case. The surface modeling makes possible to analyze the stress concentrations in a much less arbitrary way and to compare the maximum values ​​with the elastic limit of the steel used.
  • the results related to elements with variable inertia or box structures more generally, are much more relevant in a surface modeling because the eccentricities of the neutral fibers of the modeled elements are taken into account much more precisely.

These arguments presented, and the design of lifting equipments having evolved greatly over the years (less lattice structure and more box structures in particular), it is presently not very reasonable to be satisfied with simple modeling based on bar elements.

The software used is Autodesk Robot Structural Analysis Professional. We also have access to other softwares such as  Ansys or Caesar.

Example of visual output of loading on a STS crane
Example of modal answer on a STS crane
Example of graphic output of loading a crane's boom

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