Cantilever Beam on both side of Column

[hemal1214]

Hi,

I am designing a cantilever canopy structure. I have approximately 20'-0" beam on each side of column. The framing is "T" shaped as the cantilevered beams are supported only on one column.

My questions is if anyone has connection design reference for that type of connection? I am planning to support my beam bolted to column cap plate and providing stiffeners between beam flanges along the line of column flange. However, I don't have any reference material about how to size them?

A good reference material would be appreciated.
Thank you

 

[ishvaaag]

You can think of your connection as some end plate connection where the beam takes the place of the column. So your bottom flange of beam gets bolted to the cap (end) plate of column. This way you can determine the requirements for end-plate, the shop welds to cap-end-plate, and bolting.

 

[ishvaaag]

If your question is about the issue of sizing the stiffeners, Chapter J of LRFD 1999 (or comments/appendix to it) used to give guide for stiffeners on webs under point loads, and surely AISC 360-10 has some equivalent provision.

 

[BAretired]

Provide a sketch.

BA

 

[hemal1214]

@ BA retired:

Here is a picture attached for a connection I am looking for. The question is if I put unbalanced snow load on sloped side of beam. It generates significant moment. So, I need to design beam to column connection for that much of moment and I am not sure how to design the connection to support two sided cantilever beam on top of column.

Thank you,
Hemal Golwala

 

[msquared48]

No picture...

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[hemal1214]

I thought I did attache one.

Let me try again.

 

[JAE]

That photo looks like a steel beam on top of a steel column with a cap plate, including vertical stiffeners in the beam.

In this case there are a number of checks that would be required:

1. Tension in the bolts
2. Bending in the bottom flange of the beam due to bolt tension.
3. Vertical stiffener design.
4. Bending in the cap plate due to bolt tension
5. Weld size of cap plate to column.

I'm sure there are others that would come to mind.

I assume the series of columns/beams are tied together to aid in bracing the beam/column assembly, but there may be lengths of beam or column with unbraced flanges (or is that column a tube?)

I would also be concerned with wind, especially concerned with the system being flexible to a degree that you would get some type of wind oscillation. So this may not be a "rigid" structure for wind design (G not equal to 0.85).

 

[azcats]

Don't forget to consider prying action.

Could AISC design guide 4 be adapted for use here?

 

[hemal1214]

Well,

My problem with connection design is: When I consider uniform snow load on each side of the beam. Considering it as a moment connection for dead load + snow load combination: the moment I am getting is 450 kips-ft and the shear I am getting is 35-40 kips. The check of beam prying and column cap plate prying action drives me crazy. I am getting too much of tension in my bolt even though I provide total (6) 1" dia. bolt on each side of column. I am not sure what is wrong.

The dead load is 15psf and the sloped snow load is 35 psf. The Girder span is 23' on each side of column. This girder supports 23'-0" beams on each side at 5'-0" o.c.

Am I doing something wrong?

 

[slickdeals]

Can you handle 450 ft-kips (if that is the correct number) at the base with the 4 bolts that you have?

 

[msquared48]

Have you considered an unbalanced snow load too? It can happen if the melting snow slides down the slope...

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[hemal1214]

@slickdeals: I don't have 450 kips-ft moment at column base. At column base my moment is approximately 120 kips-ft for unbalanced load.

@masquared48

If I consider the whole roof supporting dead load and snow load, my moment(450 kips-ft) on both sides of column are balanced and I am not adding any additional moment in column. So, do I have to design the beam column connection for this moment?

The other scenario is unbalanced load which I consider half the load on one side of roof and full load on the other side of roof. This generates moment (120kips-ft) in the column with fixed support at the column base. So, I need to design fixed connection between column and pier.

However, the question is do I need to design the beam to column connection for 120 kips-ft moment or 450 kips-ft moment?

To design column to pier connection my moment is quiet high and my axial load is not that high giving me a very thick plate size? I am still looking into AISC design guide 1 to figure it out.

 

[JAE]

hemal, you design the connection for the moment at the connection under the unbalanced load. If you can't get a couple of bolts to work with bolt failure or prying action, perhaps a fully welded connection would be required.

 

[BAretired]

However, the question is do I need to design the beam to column connection for 120 kips-ft moment or 450 kips-ft moment?

When the snow load is balanced, i.e. equal on both sides, there is no moment going into the column. You design the beam/column connection to resist axial load only.

When the snow load is unbalanced, the moment at the column is (according to you) 120'k which means that the beam moment is 450'k on one side and 330'k on the other. You design the beam/column connection to resist axial load plus a moment of 120'k.

Notice that the axial load helps to reduce the bolt tension due to moment.

BA

 

[hemal1214]

Thank you all for your replies.

So, for moment connection I am planning to provide (6)-1" dia. bolts on each side of column. I am using chapter 4 of AISC Steel Guide 24 for design guide. However, I am wondering isn't it better to provide welded connection all around between beam bottom flange and column cap plate. wouldn't it make a moment connection and we don't have to worry about prying action.

Thank you

 

[BAretired]

Yes, a welded connection would eliminate concerns about prying action. If the columns are not too long for transportation, the best method is to shop weld them to the beams, but if you must connect in the field, a bolted connection is preferred.

BA

 

[hokie66]

You could do a welded connection in the field, but I would only do that on the ground before the frame is erected. Avoid overhead welding. But the bolted connection is the preferred method in most cases.

 

[connectegr]

Could you use a wide flange column, instead of HSS? This would provide a better end plate (cap plate) moment connection, with bolts around the column flanges.

http://www.FerrellEngineering.com

 

[hokie66]

Whether the connection is welded or bolted, there is still a welded connection at the column cap plate and base plate. Achieving a full penetration weld with a HSS section will require backing bars, and a stiffened connection may be better than an end plate.