Built up Section - Compressive Member 1

[RFreund]

For a built up column acting in compression only. How would the intermediate welds or bolts be designed. I understand (I believe) that at the ends the members the weld or bolts should be designed to transfer the full allowable axial load of the member. The intermediate spacing of connectors is restricted to a certain distance and that this prevents buckling of the individual member but how should that weld/connection be sized?

EIT

 

[Lion06]

I haven't done this in a while, but I believe the green book required the kl/r of the individual pieces between welds to be less than 0.75*kl/r of the built-up member. Check out AISC 360-05, I'm sure it's addressed there.

 

[RFreund]

AISC 360-05 requires spacing so that the KL/r of the individual member (Ka/r where a is spacing of connection) is not greater than 3/4 of the KL/r (max) for the entire section acting as one. However I was wondering how to obtain the required forces acting on the intermediate connectors.

Thanks

EIT

 

[Lion06]

If the member is end loaded in axial compression only and you design the welds at each end to develop each element then I don't see any loads acting on the intermediate welds/fasteners other than nominal forces to stabilize the individual elements.

In reality, you'll have some load eccentricity, which means bending and shear. You could check a shear flow, but it will likely be so small that any weld size/length will work.

 

[WillisV]

The force demand for intermediate connectors in double angles can be found here:

http://www.modernsteel.com/steelinterchange_details.php?id=929

 

[RFreund]

Thats what I thought however what would the value of this normal force to stabilize the member be? Could you use something similar to bracing requirement F=0.004Pr? Or is there a rule of thumb to use?

Thanks

EIT

 

[RFreund]

Thanks Guys!

EIT