Simple beam connection and bolt forces

[haynewp]

I was recently thinking about what bolt stresses are induced during the rotation of the end of a steel beam under an assumed pinned condition.

For example, you have an steel angle that is attached to the face of a thick concrete wall. The angle is being used to connect a W12 to the wall to support a floor. I usually think about vertical shear to design the bolts connecting the beam to the angle in this case, but what about the force that is induced in the bolts as the beam end rotates and slightly deforms the bolt holes to achieve a theoretical pinned end? Has anyone else looked at this before? Textbook references?

 

[apsix]

It is recognised that the connection strength may be less than the sum of the bolt strengths due to the rotation of the beam end. The connection strength will depend on support stiffness as well as beam stifness.
The only American reference I could find is ;
Richard, R.M. et al, "The analysis and design of single plate framing connections with A307 bolts", Engineering Journal, AISC, Vol 17 No. 2 1980 pp 38-52.

 

[JAE]

In the AISC Manal - the single plate connection tables have two optional support conditions - rigid and flexible. In their commentary they discuss the two....in your example of the concrete wall, you'd of course have a rigid connection and this affects the connection capacity.....

away from my office right now so I'm not sure if this also applies to the double angle connections as well.

 

[JStephen]

You mention about deforming the holes to achieve this condition. I think in most cases, the movement would be so small that the hole sizes would be adequate to allow the movement. That doesn't mean that you wouldn't generate some stresses in the parts from shifting the bolts slightly, but it need not be a deformation of the holes to do it.

 

[Ron]

While the overall movement might be small, the strain in the bolts, particularly the top bolts is certainly realized. Whether we choose to model the connection as fixed or pinned doesn't really matter to the connection....it feels something in between those two. For ease of analysis, I would consider the connection to be fixed or partially fixed, and consider the stress on the bolts to be interactive tension-shear .

 

[jike]

With a single or double angle, most of the rotation is achieved thru the deformation of the top of the angle pulling away slightly from the face of what it is attached to. This is why that you don't want to use too thick of angle since you want the deformation to take place. You also don't want to weld across the top of the angle as this will restraint the deformation from occuring.

There is some end rotation that can occur as the bolts move in holes but most occurs in the deformation of the angle leg.

With a single plate shear tab connection, there is no pulling away and therefore, it must be designed to include the additional forces developed from moments. Note that there are 2 sets of tables for shear tabs, one for standard holes and one for short, horizontal slotted holes.