Beam Classifiaction 3

[PVdesigner]

Hi all, though i am not a structural engineer, I came accross a weird problem.

Case I.
When a beam is attached to the inner surface of a cylinder (100" I.D )by means of Clips ( Gusset Plate ) and bolts, on both side , can we consider it as a fixed beam ? Beam doesnot have any seating.

Case II.

For same beam, in addition to Clips, If the beam rest upon the seat ( a continous ring of 2" width ) at both ends , Can we consider it as a fixed Beam. How the Load (Reactin at support ) is shared by clip and ring ? Any idea will be highly appreciated. Thanks.

 

[msquared48]

What shape is your beam that attaches to the cylinder?

If it is an I beam, I would assume that it its not fixed unless the flanges of the beam are attached to the cylinder, not just the web.

Additionally, I would be concerned with buckling of the cylinder wall with the application of the moment from the beam.

Mike McCann
MMC Engineering

 

[hokie66]

The beam would have to be designed with pinned ends. And it is not likely that you would have enough capacity in the cylinder walls to use a fixed connection.

 

[PVdesigner]

Thanks to both of you.
Actually, the Beam is inverted Tee with it's flanged flushed to the ring I.D & is used to support the bed load acting over the entire crossection. This assembly is been used inside the pressure vessel ( Reactor ). The clip is welded to the cylinder wall and attached to the beam web by bolts. Local stresses will be calculated to check if the cylinder undergoes buckling or not. However the cylinder is 1.5" thick and may not undergo bucking. Since, the beam is fixed to both ends by bolts, would it be wise to consider as fixed Beam and go from there. Please reply Thank you all

 

[hokie66]

In a case like that, I would make the most conservative assumption for each element. I would assume the beam pinned for design of the beam, and fixed for checking the wall. With a 1.5" wall thickness, I don't think local deformations of the cylinder wall will be significant.

 

[msquared48]

I would agree with Hokie, subject to the diameter of the cylinder and the depth of the tee.

Could you pleasepost them too. Thanks.

Mike McCann
MMC Engineering

 

[hokie66]

He did say the cylinder was 100" I.D. So not very big, and very thick.

 

[JStephen]

If it's a small tee, it might be more accurately described as fixed. However, the pinned assumption is generally more conservative. Also, if you consider it fixed, you get reversed moments at the connection, which puts the stem of the tee in compression, which complicates the allowable stress determination.

 

[hokie66]

He did say the tee was inverted, which means the stem is in compression full length if the connection is pinned.

 

[frv]

PVdesigner-

The essential characteristic of a fixed connection is rotational restraint. This is generally achieved by welding the flanges to the supporting member.

A shear plate is almost always considered pinned because it really does not provide any restraint for rotation. It may seem that it does, but the rotations in question are relatively small, so even the slop in the bolt holes is sufficient to allow that member end to rotate somewhat.


I agree with hoke in that you should probably check the beam as simply supported and the tank wall as fixed.

 

[PVdesigner]

Great Brains out there, Thanks

Beam is shop fabricated ( Two members welded together) which is 8" High and 5" wide. In such shear plate connection, how the reaction at the beam ends is shared by the 2" wide circular ring and the share plate. For example Shear plate thickness is calculated as

| 6 x M |
t = SQRT | ------------------------------ |
| Allowable bending stress x h^2 |

M : (R x e )End Moment due to the reaction "R" at the bolted connection. "e" being the distance from the bolt hole center to the wall. "h" is the shear plate height.

There is a 2" wide ring welded around the the cylinder I.D
Since this ring plate is also welded to the base of shear plate, does it undergoes bending due to the beam weight & load ? My assumption is that all the weight of beam and loads to be carried by shear plate. Please suggest me with methods to calculate. Here is the attached figure for this connection. Thanks

 

[PVdesigner]

Correction


t = SQRT {6 * M }/{ Allow. Bending Stress * h^2}

 

[civilperson]

Bolted connections to web are usually assumed to be pinned. The addition of the ring for seating the beam would perhaps produced partial fixity, (NOT fixed).