Unique Connection Help 1

[VAStrEngr]

I need some help choosing the best way to make a connection.

The situation: 3x3x1/4 square tube being connected to the underside of a W27x84. It must be a rigid moment connection (used to support a sign being canilevered out)

Considerations: I know the conroversy about leaving it to the detailer or having the EOR design the connection...but my preference is to design what I can. Plus, I think that only applies to simple connections...not moment connections.

Obviously, I am thinking weld here and probably on four sides with the vertical welds taking the vertical/horizontal load and the top and bottom welds resisting the moment. Am I on the right track? When welding tubes, are there provisions I need to account for which need to be included on the contract drawings?

Thanks!


Picture attached illustration the situation...initial weld locations shown in magenta.

 

[connectegr]

I think your detail works. As shown you have concentrated loads at the top wall and beam flange welds. The loads are very small. The checks are found in Chapter K of the AISC Spec.

I have attached an alternate, with a little less field welding and bolts for erection and the shear load.

http://www.FerrellEngineering.com

 

[VAStrEngr]

Limiting field welds are an important step was hoping to avoid. Thanks for the sketch...I will definately keep it in mind.

 

[ajh1]

Be very conscious of your torsional forces on the W27 beam. Without proper kickback bracing you are going to see rotation which tends to do ugly things to things out at the end of the cantilever. It doesn't take much rotation to create unacceptable deflections (sagging) of the supported sign in this case. The stresses will likely not be a big deal but the movements may kill you.

 

[VAStrEngr]

Excellent point. Both the front face and the rear of the W27 is accessible. Would adding a angled kick plate to the rear of the W27 help this or do you think I need a full depth stiffner there?

 

[VAStrEngr]

How about adding a stiffner beneath the tube? Still keeping the weld at the bottom side of the flange but now the bending is transferred more to the web of the W27.

 

[connectegr]

The forces you show are very small. If the HSS is adequate for the moment, then the concern is local bending of the beam flange and web. Determining a tributary area for checking the flange and web in weak axis bending can be difficult. But, simply adding a small stiffener, should provide adequate stiffness.

Adding the stiffener below the HSS, shortens the cantilever length, thus reinforcing the HSS. But, similar bending still occurs in the beam flange and web. If necessary a combination of both can be used, stiffener below HSS and backup stiffener in beam.

Depending on the number of HSS connections along the length of the W27, the W27 should be adequate for the torsion. Note, that the end connections for the W27 should probably be full depth.

http://www.FerrellEngineering.com

 

[MrStohler]

Ditto to ajh1. The W27 is very likely to have more than adequate strength BUT the torsional deflection needed to develop that strength could produce unacceptable results.

All of the details suggested appear to address the connection of the HSS to the beam flange, but I would suggest that there are two possible sources of torsion that merit consideration.

1st, the entire W27 might be able to rotate between its ends, you should review the span and determine if any connecting members restrain rotation.

2nd, local warping of the flange, the web below the fillet could behave similar to a fulcrum and the top flange could "tip". This affect would be greatest at the HSS and warping of the flange would diminish in relation to distance from the HSS.

Personal experience has been a stern teacher with regard to torsion on open sections (wide flange, channels, etc.). An owner does not care if the section has adequate strength if it does not provide adequate serviceability.