I would like to request some assistance from the community in modeling a structure that is assembled primarily with many hundreds, if not thousands, of individual fasteners. I'm talking about things like certain bridges, railroad cars, and building skeletons where the components are fabricated from metal plates and structural sections, and minimal welding is involved.
With so many fasteners, it could be tedious to model and represent each feature and represent the contact between the plates and the fastener. It's advantageous for file size and analysis time considerations to construct a model of primarily plate elements, but I don't yet have a firm grip on the best way to simulate contact between bolted plates because of the air gap between their midplanes. So then, should I model the structure with 3D elements and use contact regions, even though this will make the model large and greatly increase the analysis time? Or, is this a situation that is well suited for global/local modeling? Are their other methods that are preferable in this case?
I'd very much like to make sure I approach this using a reasonable and efficient method and don't waste time and resources by proceeding down the wrong path.
If you have thousands of fasteners then programing via API in FEMAP should be needed in orther to create the full model. But you need first to know the correct meshing approach to use, create a simply model and see how runs.
The most efficient way is to mesh plates with CQUAD4 Shell elements. For fasteners you can use the CWELD or CFAST elements, its use in FEMAP is very prowerful, to learn how to do it take a look to my blog in the following address:
Although there are a number of different ways to model structural connections and fasteners in NX Nastran, such as with CBUSH or CBAR elements or RBE2s, CWELDS are generally easy to generate, less error-prone, and always satisfy the condition of rigid body invariance.
Take a look to this video where I show how to mesh & solve FE models using CWELD elements: