Connection - Is It Pinned? 3

[Ginger]

I am designing a large thrust frame for launching a tunnelling machine. I have a plate girder (600mm wide by 1960mm deep) standing on end as a vertical beam. Framing horizontally into this girder is an 838 x 292 UB with web horizontal.

At this connection I have notched the top flange of the UB so that the flanges of the beam and girder are flush. For the connection I am using 120 x 120 angle section 700mm long on both sides of the web of the UB which is then bolted through the web of the plate girder to make the connection. A total of 22 no. M30 bolts are required through the girder(11 above & 11 below the web of the UB) to carry the shear.

When reviewing text books for simple connections, this has all of the hallmarks of such a connection. However, the scale of the work and the number of bolts involved has placed a doubt in my mind that this can be considered as a simple connection. Am I worrying unduly that this connection will impart torsion or bending into the girder or is it pinned?

Regards Andy Machon

 

[chandr]

Since the angles clamp only the web of the UB and also due to the flexibility of the web of the girder, the moment that the UB can induce on the girder should be quite small. If the UB carries only shear (no thrust), I don't think there's any problem with your connection.

 

[IJR]

Chandr

I agree with you, however I am not really sure whether shear can be transmitted quite safely especially if it turns out to be high.

Do you want to go on and elaborate?

Thanks
IJR

 

[Ginger]

Chandr / IJR

Thanks for the replies. My thinking was on the same line as Chandr. I have checked the bolts for single shear, bearing etc and I have also checked for block shear failure (ie when the shear failure line runs from bolt hole to bolt hole along the weakest section of the UB). IJR, what concern do you have about the shear carrying capacity of the section? Andy Machon

 

[Ron]

Agree that it is a pinned connection. Rotation about the heel of the angles can occur due to flexibility of the angle as well as flexibility in the web.

 

[Riz]

Ginger,
If the bolts are in double shear than u come across a more robust connection. This will transform the connection implication from pin to partially fixed or worse if subjective shear is far less than the actual.
From my fast calcs, in single shear the bolts resist 2700kN ( if are M30 grade 4.6) Therefore it is imperative to check for such a situation.
Riz

 

[IJR]

Ginger

My worry on the capacity of UB web to transfer shear comes from my not being familiar with beam webs carrying shear perpendicular to the plane of the web.

Usually webs of beams in standard configuration resist shear in vertical plane. Rotating the beam 90 degrees means subjecting shear to two parallel flanges.

Transfer of shear from the two flanges to the webs is what I am not familiar with. I once designed similar beam with large shear and decided to use endplate welded to both flanges instead of web cleats.

As I mentioned before, my doubts reflect my infamiliarity

Thank you for the consideration.

 

[Ginger]

Ron / Riz / IJR

Thanks for your thoughts chaps. IJR, I understand where you are coming from now. I didn't explain that the load is applied by the tunnelling machine to the frame as a horizontal thrust. This frame allows the machine to thrust itself out of the launch chamber into the ground (total force 2000 tonnes!) hence the large sections. Therefore, the UB is carrying the shear in the web along its strongest axis. IJR- can you confirm that this solves the problem as you see it?

Once again,thanks all for your invaluable help.

Best regards Andy Machon

 

[IJR]

Ginger

Thanks for being back. I should have guessed that you rotated the UB about its axis purposely to utilize the section efficiently, but there are cases where we are forced to do that for constructive reasons, e.g connection with a bracing system somewhere at the midspan of the beam.

Back to your situation, I AM CONVINCED NOW THAT YOU HAVE A PIN THERE.

By the way, a pin simply means slight rotation is permitted: One British engineer(Probably McGinley) in his book gives a rotation of 3 rads as sufficient to eliminate moment in web connections. So you see you dont really need to insert a pendulum kind of pin there(joke!!)

Once more and again Ginger for consideration.

IJR