# Deflection - difference between pin and fixed joints

1. Aug 1, 2012

Deflection -- difference between pin and fixed joints

Hello all

I have a question regarding deflection. What is the difference between pin and fixed joint in frame l(first picture fixed the second pin),
I can summarize my question in points:
1.fixed connection introduces equal theta as picture indicates, because structure rotate in the same amount and the angle between to members will still 90,while pin joint, theta will differ , does this implies the 90 degree doesn’t satisfy??

2. Does pin joint means hinge or

3. Please give me example in reality illustrate both joints
4. Any additional information that could help is appreciable.

Many Thanks

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2. Aug 1, 2012

Re: Deflection

Also another question regarding the same problem ,assume i have a beam and the internal support is pin, if we draw the deflected shape it will deflect and gives theta, right….., but imagine you have steel column connected to left beam and right beam by connection at web of beams (which means pin connection), here the right column will deflect and gives theta different than the left, while as i said previously in analysis, it deflect as one unit with one theta, so please explain this in details
Hope my question is clear

3. Aug 2, 2012

Re: Deflection

If my question is not clear i can explain it more!!!!!

4. Aug 2, 2012

### PhanthomJay

Re: Deflection

That's right, the members at the joint are no longer pependicular in the deflected shape.
ideally, yes, with a single bolt or pin connection. In actuality many multiple bolt connections are consisdered pinned, although they are semi rigid.
If you anchor 2 columns at the base a distance L apart, and attach a beam to the column tops using a single bolt at each end, that's a pinned joint; if you instead weld that beam to the columns with a full penetration weld, that's a fixed joint.

I'm not sure what you mean, but your pictures tell the story.

5. Aug 4, 2012

Re: Deflection -- difference between pin and fixed joints

Thank you very much.
So when we sau rigid joint ,that implies fixed one, which always considerd in structural engineering book....Right

6. Aug 4, 2012

### PhanthomJay

Re: Deflection -- difference between pin and fixed joints

A rigid joint is one where the members that frame into the joint do not rotate relative to each other at that joint. If a member frames into another member say at a 60 degreee angle, they remain at 60 degreees to each other at that joint under loading or rotation or translation of that joint. I'm not sure about the handbook question...not all joints are rigid, like when a beam frames into a column and is attched to the web of the column with clip angles, it is assumed pinned, in which case if the angle between them was 90 degrees before loading, it is no longer 90 degrees when the beam is loaded, it would be slightly less.

7. Aug 6, 2012

### pongo38

Re: Deflection -- difference between pin and fixed joints

I don't know if this helps but I have attached a hand sketch of the exaggerated deflection of a 3-hinged arch in which the left hand knee is rigid and the right hand knee is pinned. The exaggerated nature of the sketch shows the beam bending, but also a small sway to the right to accommodate the difference in behaviour between right and left sides. In interpreting this figure it is important to distinguish between first order displacements (central deflection of beam bending, and beam end rotations) from second order displacements (lateral sway, column bending). Practically the columns remain straight.

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8. Aug 6, 2012