Axial compression of steel base plate supported over steel beams

[camel7]

Hi

I am working on A steel column which is supported on a steel beam. The steel column is having compression load of 550KN with no moments. For designing the base plate do I need to check for the base plate thickness? When I calculate baseplate thickness based on equation tmin = L* SQRT (2 PU/(0.9FY BN) the thickness comes quite big and I dont see a reason why I need to provide thicker plate is it fair enough to use just use a nominal 12mm or 10 mm plates?
hope to hear from you guys...
cheers
camel

 

[dhengr]

Camel7:
Think about how you get the compressive load from the column into the beam, as a concentrated loading on the beam. If the webs of the column and beam are in line up, then you already have a bearing load transfer in that area. Then you put stiffeners about the same size as the column flanges btwn. the beam flanges and welded to the beam flanges and the beam web to transfer the column flange loads into the beam web. You might not have to run the stiffeners all the way down to the bottom flange of the beam, and you might want to cope the corners where they meet the beam flange/web radius; then you design the welds for those bearing and shear stresses. And, the base plate can be fairly nominal, holding the two together.

You tell us what you would do if the column was oriented with its web perpendicular to the beam web.

 

[delagina]

550KN is 123Kips. Dont know why you prefer to only use 12mm using "engineering judgement."

 

[BAretired]

I agree with dhengr. Use stiffeners to match the column flanges above. Then the baseplate thickness doesn't really matter.

BA

 

[camel7]

Thanks all, Thats what I am planning to do .....
cheers
camel7

 

[slickdeals]

@dhengr:

For column web perpendicular to beam web, I can think of the following two options.
1. Weld 2 plates (parallel to column web), connecting the flanges (each side). This creates a closed box for a height (h=weld length needed to transfer compression). Then use detail similar to web parallel (2 beam stiffeners each side).
2. Weld a WT equal to column weight, each side of beam web.
a. If beam flange width < column width, add flange extension plates (CJP).

I am sure there are other ways of doing this.

 

[graybeach]

Will you mill the bottom of the column and the tops of the stiffeners to bear or design the fillet welds to transmit the full 550 kN?

 

[dhengr]

I would at least saw cut the column section, so I got a good true, square bearing end. But, look at the mill tolerances for W shapes and you’ll see that the beam flange can screw this up. This detail requires some special attention to fit-up out in the fab. shop, maybe even straightening the flg. a bit for good bearing and fit-up. We milled large/heavy column sections (larger W14's, heavy built-up sections, etc.), I don’t remember off the top of my head what the size or design criteria was for requiring milling. We finally got a larger saw on our beam line (about a 6-7' dia. circular blade, with machine tool teeth) which operated much like a milling tool. Then we didn’t have to mill rolled shapes any longer.

Slick’s first approach seems a little busy, I’d opt for his second solution. And, I’d mill order the column long enough so that while I had it on the beam line, I’d cut the col. to length and then make a second cut which would fit from flg. to flg. on the beam. I’d rip this short piece to make my own WT’s. I’d clip its web for the radius at the flg./web on the beam. If the col. has a ‘d dim.’ greater than the beam ‘bf dim.’, I’d cope the top webs so that the WT’s fit up and around the beam flg. and to meet the col. flange, at the top of the beam. I think the OP said there wasn’t much col. moment, so you might not need CJP welds on the col. flgs. to the WT flgs. Obviously, these welds must be designed for the actual conditions. The prep. on the col. section and the WT’s would be done in the shop and the WT’s would be shop welded to the beam. There is considerable fab. savings if the WT’s can be cut short of needing fit-up at the beam bot. flg. too. Fitting a stiffener to the web and the inside of both flgs. is a difficult process, to be avoided if possible. The entire col. load is transferred to the beam web through web to web shear welds and direct bearing btwn. the webs. In this case that direct bearing area may only be (2 x k1)^2. The beam flgs. really can’t take much of the col. load, they are just too flexible as cantilevers in bending, when compared to the web to web shear welds.