hi, is it possible to get bolt forces like shown in the attached picture from Prepomax.
because i modelled this in prepomax but the bottom bolts also attracting equal forces.
force has to be maximum at top and zero at bottom right..
(orange arrow is not bolt force)
hi, can modeling assumptions provided? indeed, bolt force at bottom should be low as shown in my analysis previously for similar problems.
It depends on how you are modeling the bolts:
This thread can also be helpful: Best way to find force in bolted connection
As well as many other threads here and on the CalculiX forum if you search for “bolt forces”. This is probably the most common topic here.
Here’s a similar case too: Cantilever Beam - Not Converging on Static Step
I don’t understand well comments on this post. Bolts for moment resisting connection should be preloaded ¿isn’t it?. Why such a difference in bolt stresses are shown? Overall stress range in between them should be small. That’s why preload is aplied, to distribute external loads evenly across the joint and improve fatigue life deminishing the stress range locally and globally on the set of bolts.
Maybe they are. We don’t know anything about the OPs setup so we can only provide general answers about bolt modeling and force evaluation approaches (the question asked is if it’s possible to obtain such forces).
The model shared in the last thread I referenced before can be a good starting point if supplemented with missing features.
Hi FEA,
I refer more to the picture shown as first response .
Ah, ok. It’s the model @synt often shows. Would be nice if he could share the file too.
Extended plate connection primarly under moment load… Seems there should be preload in the connection . Stress due to preload should show in the bolt . Maybe you have preload and doesn’t see noticeble diferences. That would be expected ¿right?.
The moment diagram is wrong!
hi thank you for interesting, unfortunately the models may not to share due to experimental personal test of PrePoMax capabilities in automatic meshing. As can be seen below, it uses quadratics tetrahedral element and only one element trough thickness at end plates and flanges. It can be reliable for fast modeling and checking but result is less accurate. This condition of meshing happens when Gmsh is not yet implemented in 2022 of PrePoMax versions.
regarding prestressed bolt, anyone can try to verify by code regulation manuals. This type of connection is specific for slip critical joint; non-prestressed bolts are common in structural steel works. There small prestressing exists due to bolt tightening, but negligible and being ignored in hand calculations.
Source: Bolt force distribution in endplate beam-to-column connection | IDEA StatiCa
Time to dust off my books on the design of steel structures.
So it’s just the default Netgen mesh ? Would be interesting to update it to hex mesh with Gmsh.
right it’s a mesh using Netgen, around holes and intersection some refinement in number of element rough thickness does automatically by the mesher but is not uniform.
indeed, it seem to be possible to generate all hexahedral element using Gmsh mesher in PrePoMax for improvement, adding weld parts also.
For the beam ok, but for the connection all the bolts are on traction
@anys, your point is correct bolts are preloaded so all the bolts experience same force, but the diagram which I have shared is the difference in the force once the service load comes.
Before service load all the bolts has pre tension load of 100N( assume) when the service load comes the top bolt will has net force of 100N - A= X
Ideally for bottom bolt force shall be 100N+A= X1
But bottom bolt doesn’t take compression
Net force will be 100N
So the diagram shows the net difference from top to bottom.
Right?..
From “Połączenia śrubowe” (Bolted joints) by A. Biegus:
c - linear elastic
d - elasto-plastic rigid connections (thick end plate)
e - elasto-plastic flexible connections (thin end plate)
b - due to preload
c - moment load added, linear distribution until the applied moment balances compression between end plates
d - due to higher moment, assuming elastic behavior of the bolts
I’ve also found this interesting article: https://www.sv-jme.eu/wp-content/uploads/ns_articles/files/ojs/4638/public/4638-25298-1-PB.pdf
the reason to not used in tension dominant bolt reactions. Snug tightening bolt (non-prestressed) is effective since shear loads transmitted through bolt at bottom with less stressed.
There are no shear forces here.
@ANYS if the service load is a pure bending then there will not be any shear in the bolts nor in the I beam, but if the I member is having vertical load and bending moment then yes bolts will have axial force and shear force.
The diagram has only moment so the shear will be zero.
Hi,
Preload does not function in that manner.
The primary benefit of preloading is that, once applied, the bolt load remains nearly constant until the plates reach their separation point. External loads are distributed unevenly between components; the majority of the load is consumed by relieving the contact pressure between the plates.
In a moment-resisting connection like yours, preloading ensures the load is distributed across the bolts so the entire connection behaves rigidly and rotates as a single unit. It also prevents potential prying effects and reduces the stress range in the bolt, which helps prevent fatigue.
I should not have introduced the topic of preloading in the post, but I commented because Synt posted an image where the lower bolt showed zero Von Mises stress, which I found unusual. He mentioned this was just for testing.
The attached example shows how preload changes load distribution. Initial preload of 40kN on each bolt, both models are subjected to the same external pure moment of 30kNm."
Without preload “top figure” upper bolt load ranges from 0 to 26.4 KN.
With Preload, It oviously reaches a large initial load but it later only increases 1 KN. (By the way, that was my guess of what you found in your model. “Equal forces all the bolts”).
Note diference in connection global rotation and stress distribution in the members.
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