WHICH WAY IS MORE ACCURATE TO MODEL BOLTS

[EngineerII]

Hello,

I work in a structural engineering company. I have created various models in FEMAP using plate elements and solid elements. In some of my models, I used degree of freedom springs to model bolts, in other models I used beam elements. Which way would be more accurate? To me it would seem like degree of freedom springs would be more accurate since you can enter seperate stiffness values: axial stiffness, torsional stiffness, and shear stiffness, where as when you use beam elements, you only have one stiffness of the bolt based on the diameter for the beam element you use.

 

[bxtsafe]

EngineerII,

I hope the attached file can help you.

Regards,

 

[BlasMolero]

Hello!,
My preferred method is to use CBAR elements to model the bolt and RBE2 rigid elements to model the bolt head & nut with TX,TY,TZ DOF activated only. If you prefer in FEMAP you have a macro to do the job automatically under "Custom Tools > Meshing > Hole to Hole Fastener". In general I make imprints in the geometry to account for washer, then you can edit the previous macho to ask for surfaces, not edges.

Compared DOF SPRINGs with BEAM elements, well, in my opinion is more time consuming, you have to define a property for each stiffness, in such case I would use better CBUSH elements, this is the TOP of NX NASTRAN, with better integration in FEMAP V10.3.

Best regards,
Blas.

PD
Using CBAR elements to define a bolt do not means you have only ONE stiffnest, this is a beam element, then you account for bending, torsion & axial stiffness based in the bolt diameter, simply, OK?.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48011 BILBAO (SPAIN)
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[rb1957]

either method will work adequately. i'd try side-by-side runs to compare the two approaches. at the end of the day, whihc gives you reasonable answers for the least amount of work ...