Critique of column relocation requested

[CTW]

The attached drawing shows an elevation of one area of an existing mezzanine. The column needs to be relocated 30" to towards the 11 ft span. The existing beams (W14x22) are simply supported over each column but have two bolts in each web and a plate between the webs of the beam.

Here's how I'm considering approaching this. Once the column is moved 30", I'll analyze the beams with the 30" cantilever receiving the end reaction from the adjacent 22 ft beam. In reality, the knee brace will tend to pick up most of this reaction but I'll only consider this for the column analysis. I'm trying to be fairly conservative with my approach.

For some reason, this approach is not sitting well with me so I'd like some other opinions. Maybe it's because I'm tired and stretched thin at work, but it has not been my best day.

 

[BadgerPE]

Could you weld the flanges together to create a moment connection thus eliminating the hinge? Then evaluate beam as a continuous member?

 

[larsacious]

I agree with your approach. You should check the connection for the reaction. If you get lucky and the plate is thick enough you might be able to get away with just adding a field weld and ignoring any contributiong the bolts might have. You should check local buckling of the web of the proposed, cantilevered beam (i doubt that it will be an issue). You may want to add a web stiffener plate to both sides of the web anyway just to stabilize against any possible racking. You are also going to increase the load on the column so you should check this as well.

What do you plan on doing with the foundation? What purpose do the angle kickers serve? Are they for reducing the effective length of the column? If so, it is likely that they didn't design much fat into them so you should be extra careful with your capacity calculations.

Good luck!

 

[hokie66]

The longest span won't know the difference, as long as the connection is made adequate. The beam which cantilevers should have its bottom flange braced at the column. I assume the knee braces are for lateral stability, so they just need to be moved as you have shown. As larscious said, the column will take more load.

 

[CTW]

Thanks for the replies.

The top flange can't be welded very easily due to a continuous bent plate welded to the top flange. It's possible, but it seemed to be more work than necessary.

The suggestions on flange stability and local buckling are duly noted and will be considered.

As far as I can tell, the knee braces are there for lateral stability. The columns are currently anchored to a thick, moderately reinforced floor slab. The column reactions are not very high, even with the column relocated.

 

[chicopee]

I would explore the possibility of increasing the size of the splice plates on both sides of the webs as well as adding additional splice plates on the bottom and top flanges of the beams.

 

[hokie66]

No need to make the flanges continuous unless deflection is a problem. The deflection will increase because of the cantilever.

 

[larsacious]

I would not add splice plates to the flanges. That will make the beams continuous and then you will need to worry about the unbraced length of the bottom flange as a result of the negative moment.

 

[csd72]

larsacious,

You still have that problem due to the cantilever moment.

CTW,

My only concern would be if those diagonal kickers were there for lateral stability in which cace having a hinge between the column and the kicker may compromise the way this acts.

I would also think that there would be a much larger load on the kicker from strain compatability.

 

[larsacious]

csd72: I agree except the negative moment should be much smaller with the cantilever than with the continuous beam.