×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# Beam Rotation (Precast)2

## Beam Rotation (Precast)

(OP)
I am designing a beam that will pick up (2) other beams.  The supporting beam is pocketed for the (2) beams, so there is torsion induced in the beam.  I have designed the section for the shear and torsion, and it is adequate.  My question is how to I make sure that the beam will not rotate such that the (2) beams will have a tendency to slip off the supporting beam.  I have placed a welded top connection for connecting the (2) beams to the supporting beams, but I just want to make sure there will not be a tendency for rotation that is not negligible.

I have discovered an equation for deflection due to torque
= tl^2/8GJt  for "fixed both ends"(PCI Handbook 6th ed)
t=torque
l=span of beam
G=shear modulus
J=torsion constant

Is this the correct way of doing this?

### RE: Beam Rotation (Precast)

Can you create a moment connection at the end of the two supported beams such that the twisting angle of the supporting beam is limited by the end rotation of the other two beams?

### RE: Beam Rotation (Precast)

(OP)
The opposite end of the 2 beams is supported by columns with a doweled connection, which allows for some beam end rotation.

The end at the supporting beam could likely be designed that way.  I do not like welding the bottom of the beams and it is recommended practice not to do so.  However, I believe a welded connection at the top and bottom of the supported beams to the supporting beam would be OK if I still allow the column end of the supported beams to be free to rotate.

So you are saying the I can use the supporting beams which are applying the torque as a means to also brace the supporting beam from rotation.  Is that a correct description?

(This is similar to using "kick back" support (a steel brace) to tee stems for long spandrels to prevent out of plane rotation, right?)

### RE: Beam Rotation (Precast)

jike's point is a good idea.  Just remember to consider long term shrinkage and creep (longitudinally down the supported beams).

### RE: Beam Rotation (Precast)

I am not a precaster but I believe they use this technique to resist twist. You are using the moment capacity of the supported beams to resist the twist of the supporting beam. It is a self limiting rotation if the proper connection can be made.

I assume the rotation is only in one direction. If so, can you use a combination of grout on top and a weld plate on the bottom to resist the rotation? The erector may have to shore the beam or use wedges until the grout is cured.

I am not familiar with a "kick back" support.

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!