Hello everyone.
I am trying to model a structure made to support photovoltaic panels. This structure has a beam that is connected to a pillar, as you can see in the images bellow:
In order to model the effect of the bolted connection, I am using the tab Nodal Supports , as you can see bellow:
My question is: would it be more accurate to model this connection as completely fixed or should I use the spring option? If I use the spring option, how should I calculate the spring stiffness (maybe assume it as being the torsional rigidity of the pillar)?
Best regards,
Pedro
Hello @PedroSoares 
,
You're absolutely right—this is a crucial part of engineering work: making assumptions about quantities that are difficult, if not impossible, to measure. From my perspective, spring stiffness would be a better option (depending on the stiffness of the pillar). However, it's challenging to determine an exact value for the stiffness, so I recommend looking for some relevant literature on this topic.
Generally speaking, the support stiffness is the result of both the stiffness of the pillar and the bolted connection itself. For example, the support in the y-direction results from the combination of the bending stiffness of the pillar and the axial stiffness of the bolt.
If you have any further questions or need more guidance, feel free to ask! 
Best regards,
Fabian
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