The Preload Simulation with the “Thermal” Method

In general the application of a preload inside a member in a Finite Element Model is done by the code by applying MPC equations to the nodes laying on the surface where the preload is to be applied; for example in a bolt modelled with solid elements, the shank will be split at the surface indicated by the user and the two parts will be moved one against the other until the imposed value of the axial force is reached. This operation is transparent to the user and requires a non linear analysis.

Nevertheless not all the calculation codes, especially the ones that come with CAD software, have the possibility to simulate preloads in parts where it may be required.

In such cases a trick (the thermal approach) can be used to simulate preload, even in a linear analysis.

In Chapter 7 of the book “Computational Structural Engineering” this trick is extensively explained, limit of application are given and a comparison with the more advanced methods (i.e. non linear analyses) is shown at Chapter 13.

Nonetheless in many cases this method provides good results, especially in the phase of presizing studies.

In the mentioned Chapter 7, hand calculations are also illustrated and compared with the results generated by the Finite Element Model.