topic Re: Instability in rigid link nodes in Robot Structural Analysis Forum

Instability in rigid link nodes

Wendy_smith — Tue, 08 Aug 2023 15:08:00 GMT

Hello,

I have placed rigid links in my model. I have W10x33 beams resting on top of W24 girder beams. The W10's are bolted to the top flange of the W24's. I placed a rigid link between the nodes for the bolt. When I run the calculation for just dead load, I have instabilities in the nodes on the W10's for the rigid link. Iam not sure what I am doing wrong. I have attached my model and a screenshot. Any help would be greatly appreciated.

Re: Instability in rigid link nodes

Simau — Tue, 08 Aug 2023 16:28:49 GMT

@Wendy_smith

Set Bolt rigid link like this

Re: Instability in rigid link nodes

Wendy_smith — Mon, 14 Aug 2023 14:51:10 GMT

@Simau,

Thank you for your response. Why am I setting my Bolt rigid link like that? What does that do? What does a Welded rigid link look like? Thank you for the help.

Re: Instability in rigid link nodes

Simau — Tue, 15 Aug 2023 10:28:10 GMT

@Wendy_smith

In your model, you set bolt as below

Which means that your bolts don't block anything (Ux Uy an Uz are free)

In my bolt setup, to ux uy uz, i added rx to avoid instability. Bolt rx corresponds to the strong W 24x104 inertia (UY)

What does a Welded rigid link look like?

As below

Re: Instability in rigid link nodes

HoshangMustafa — Fri, 25 Aug 2023 09:27:52 GMT

@Simau,

Bolt rx corresponds to the strong W 24x104 inertia (UY)

Did you mean:

Bolt rx corresponds to the strong W 24x104 inertia (Iy)

Re: Instability in rigid link nodes

Simau — Fri, 25 Aug 2023 09:43:15 GMT

@HoshangMustafa

Sorry about the typo.
Correct, its Iy

Re: Instability in rigid link nodes

HoshangMustafa — Sun, 27 Aug 2023 20:04:35 GMT

Hi @Simau

Using ux uy uz, and rx blocked directions for a rigid link, how one can design the connection manually? I think these blocked directions are delivered to the connection. So how one can use these blocked directions to design the connection manually?

Re: Instability in rigid link nodes

Simau — Mon, 28 Aug 2023 13:40:09 GMT

@HoshangMustafa

Below a workaround, but maybe there is a quicker solution.
Select all W10 33 members, then look at fz diagram to calculate reaction at these nodes.You may then design your bolts under these reactions.
To be conservative you can select all W 10 33 members and take design reaction as max Fz + Min Fz

Re: Instability in rigid link nodes

Simau — Mon, 28 Aug 2023 13:41:21 GMT

@HoshangMustafa

Message 8 updated (you don't need to split W10 33 members)

Re: Instability in rigid link nodes

HoshangMustafa — Mon, 28 Aug 2023 14:18:38 GMT

Hi @Simau

your attached picture:

there seems to exist 4 bolts, two on each side, correct?

In the model, there exists only one rigid link at this place, isn't it?

How one can use (one) rigid link results to design these (4) bolts?

Re: Instability in rigid link nodes

Simau — Mon, 28 Aug 2023 15:37:15 GMT

@HoshangMustafa

Yes there are 4 bolts (but its only an example). A bolt is designed with Reaction/4
You may use the classic scheme:

Re: Instability in rigid link nodes

HoshangMustafa — Mon, 28 Aug 2023 18:23:11 GMT

Hi @Simau

you wrote:

A bolt is designed with Reaction/4

This is for gravity loads. For lateral loading (i.e., wind load) how rigid link can be applied if there is eccentricity?

Re: Instability in rigid link nodes

Simau — Mon, 28 Aug 2023 19:10:25 GMT

@HoshangMustafa

Please complete your model with loads you need and create combiations. If you apply wind loads to claddings, efforts will be mostly parallel to local axis Z of the purlins.

Look at "reactions" in local axis x y z , you will find that the efforts in the x and y directions are negligible.

Re: Instability in rigid link nodes

HoshangMustafa — Mon, 28 Aug 2023 20:04:54 GMT

Hi @Simau

ignore lateral load, assume gravity load as follow:

Can rigid link simulate this condition?

Re: Instability in rigid link nodes

Simau — Mon, 28 Aug 2023 20:31:21 GMT

@HoshangMustafa

Yes, just add Rz as blocked direction in bolt parameters

Re: Instability in rigid link nodes

HoshangMustafa — Mon, 28 Aug 2023 21:11:54 GMT

Hi @Simau

My concern was about the share of each bolt from the load, i.e., rigid link simulating for this case (a group of bolts, each bolt receiving a share of load based on its distance from the load).

Re: Instability in rigid link nodes

Simau — Tue, 29 Aug 2023 08:50:59 GMT

@HoshangMustafa

It's not possible.
The rigid link will give you the the whole torsional moment , but not the sharing of this moment between the bolts. You have to calculate the distribution manually.

You may try a small model simulating this connection (see model attached)

Re: Instability in rigid link nodes

HoshangMustafa — Mon, 28 Aug 2023 21:55:24 GMT

Hi @Simau

Can you upload the model with earlier version (2018)?

Re: Instability in rigid link nodes

Simau — Mon, 28 Aug 2023 21:58:00 GMT

@HoshangMustafa

Very sorry, but old versions are no longer installed here.

Re: Instability in rigid link nodes

Simau — Tue, 29 Aug 2023 08:53:11 GMT

@HoshangMustafa

here is what I modeled.
A steel plate on 6 supports subjected to a torsion moment of 100 kNm