Beam stub attachment to column 1

[BAGW]

Hi,

I am looking at a cantilever stub as shown below. I have always used the distance to center line of the column for the design forces (100 x 4 = 400k-ft). Seems like its very conservative approach. Can someone clarify below queries

1) Stub deign forces = 100 x 2 = 200k-ft
2) Stud weld connection to column = 100 x 2 = 200k-ft
3) Column design forces = 100 x 4 = 400k-ft
4) Column web/flange local check forces = 100 x 2 = 200k-ft or should this be 400k-ft as well?

Thanks

 

[dik]

1: OK
2: OK
3: OK
4: The shear force used for the connection of the flange to the web varies depending on the depth of the stub length of the column. I would use a bolted stiffened end plate connection at the column and add a couple of 3'8" deep stiffener plates at the column to beam. I cannot imagine a 4' deep steel beam unless the axial or flexural (more likely) loads are extremely high... for 200 K-ft (assuming factored), I would be anticipating members in the order of 12" to maybe 16" deep.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[palk7 EIT]

Hi Dik, why should we consider 400kip-feet as column forces, because the cant. connection will experience 200kip-feet and it is this 200kip-feet from the connection (bolted or welded) will be transferred to the column isn't it? Thank you for the explanation

 

[dik]

The distance from the load to the centroid of the column is 4'. It has nothing to do with the connection being bolted or welded... I suspect strongly that a bolted connection would be less costly.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

Like mud... and sketch improved a bit... I wish I could get things right the first time... I should have added that the shear to connect the flange to the web would be based on the calculated V, and not related to the moment as I explainted in my initial response (initial response edited to correct misunderstanding). I knew what I meant in my first response... it just didn't come out right...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

Because the moment at the column centreline is the Moment from the stub (200 K-ft) plus the moment from the 100K shear * the 2' distance to the column centreline.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[BAGW]

dik,

For the column local checks, cant we just use the shear resulting form the 200k-ft moment? Why should we use 400k-ft? 400k-ft is more for the column global check correct?

 

[dik]

If you do a FBD for the column only, you will have a 200 K-ft moment plus a 100K vertical force at the stub connection... The shear results from the vertical load as well as the the horizontal load at the top resisting the 'overturning'. I'm not sure what moment induced shear you are referring to.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[KootK]

For the column local checks, cant we just use the shear resulting form the 200k-ft moment? Why should we use 400k-ft? 400k-ft is more for the column global check correct?

I believe that assessment to be substantially accurate. Consider the following.

1) The transverse column shears generated by [V x e / h_column] do need to make their way into the joint panel zone but;

2) They should be relatively small and;

3) Critically, they do not need to travel through the stiffeners to get there.

As examples:

4) Column web crippling can be based on 200k-ft.

5) Column web panel zone shear buckling probably should be based on the shear generated by the 200k-ft acting over the panel zone plus V x e / h_column. That second term is likely to be much less than 400k-ft however.

 

[dik]

and, do you really need members that deep?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[KootK]

5) Column web panel zone shear buckling probably should be based on the shear generated by the 200k-ft acting over the panel zone plus V x e / h_column. That second term is likely to be much less than 400k-ft however.

I rescind that. Some quick, and probably unreliable FBD work leads me to believe that the shear demands are subtractive rather than additive. We expect a column shear diagram to look something like below, right?