HSS under baseplate to transfer shear 3

[WWTEng]

I am working on baseplate with very large moments and shear forces. The columns are W14s. I intend to use a heavier (wider) W14 as a baseplate to convert the moment to up/down force at each end of the baseplate. I think I can I resolve the moment this way but to transfer the shear I was planning on using a HSS welded to the baseplate.

Has anyone used a WF base plate with a welded HSS?

Thanks.

 

[slickdeals]

Are you planning to weld the smaller W14 to the top flange of the bigger W14 and weld a HSS to the bottom flange?

If you are already using a W14 as a base plate, can't you weld an end plate on either side or use headed studs on the web to transfer the shear?

Where are you attaching the anchor bolts? Can you post a sketch your intended concept?

 

[hokie66]

I haven't used a detail as described, but see no reason why an HSS of appropriate size would not be appropriate as a shear lug.

 

[ToadJones]

First guy I worked for used HSS shear lugs on on the mill building projects we did.
It made for a simple block-out in the foundation forming and made grouting the lug simpler as well.

 

[WWTEng]

Slick,

Attached is what I am thinking of doing. Its still an ongoing thought, so I am not sure what I'll end up with eventually.

 

[WWTEng]

Currently I am trying to come up with a way to encase the WF base plate in concrete. I don't want to leave it exposed to soil.

 

[ToadJones]

I'd be inclined to gusset the W14 col to W14 baseplate other wise the base is only as rigid as the w14's and it will provide more length for weld and maybe make welds easier.
You probably also want stiffeners in the W14 base where the bolts go and I'd run those bolts through both flanges, not just the bottom flange.

 

[SAIL3]

using a HSS section certainly makes it more convenient re conc pocket.....may have to check local buckling of HSS walls depending on magnitude of shear...also may end up with cavity inside HSS section after grouting which should not cause any problem that I can think of right now....I usually use flat pl shear lugs to avoid the above extra checks on HSS wall capacities....welding an end pl on the HSS section would strengthen it if there is a problem.....

 

[Archie264]

Would it be worth cutting one or two holes into the HSS to help avoid the cavity Sail3 mentioned? As long as they don't overly weaken the HSS in the process. Or am I over-thinking this?

 

[ToadJones]

you can drill a grout hole in the bottom flange of the bottom W14 to fill the inside of the HSS

 

[WWTEng]

SAIL, Toad, Archie...thanks for the input. I am going to post the "final" sketch sometime today but for FYI, I am going to call out a 1/4" setting plate. Shear lug will be welded to the setting plate and set. plate will have a 3" dia hole over the lug to facilitate flow of grout. And then I am going to call out a weld between the setting plate and the base plate for shear transfer.

I am showing stiffener plates near the anchor bolts and intend to move the top of the anchor bolt above the top flange so that its easier to connect.

 

[SAIL3]

anytime I get involved in a non-std conn I have to ensure that all load paths are checked....not knowing the the magnitude of the loads I would still suspect that the moment in the shear lug does not have a viable conn to the W14....first a 1/4"pl setting pl seems way lite to me....the transfer of the bending stresses in the side wall of the HSS paralell to shear direction to the W14 has to be reacted by the tip of the outstanding fla of the W14 which is way to flexible, unless you design the HSS and it's conn as just being reacted at it's comp and tension fla....with the need for vert web stiffeners on the horiz W14 etc and perhaps other reinforcements you might be better off going back to a typical col base pl arrangement...that is where I would tend to go...interesting concept, though....

 

[swearingen]

Since you're using W14's everywhere else, why not use one as the lug? Then grouting from the top or sides works just as well and you'll still have the same size pocket as you would for the HSS.


-5^2 = -25 ;-)

http://www.eng-tips.com/supportus.cfm

 

[hokie66]

I agree with SAIL3 that 1/4" just sounds too thin for the leveling plate in this situation.

 

[ToadJones]

After reading through this again, I agree with others...no way you can use a 1/4" setting plate with a lug welded to it. I am pretty certain that when you check the rupture strength of the 1/4" setting plate welds to the HSS you're going to have issues.

 

[WWTEng]

Thanks all. I actually don't even want to use a setting plate but I can see how not using a setting plate could create issues in terms of constructability. I agree that 1/4" in this situation would be too thin, I think I'll start my analysis with a setting plate that is at least as thick as the beam flange and go from there.

 

[paddingtongreen]

Without knowing the details of loading, I would prefer to use a thick plate instead of the W14. I would try using gussets from special depth W14 T shapes or larger, with the flanges going diagonally from the connection to the column flange to the baseplate. I would try to sink the whole thing in the concrete to provide shear resistance, if not I would try two keys, one at the bottom of each gusset flange, near the bolt groups. I would not use HSS for the keys, with wide flanges you can get both flanges working without special and difficult to QA, grouting arrangements.

I don't like leveling or setting plates, I like to shim and plumb the column before grouting. I've seen some nasty gaps when a leveling plate is off level to the maximum allowable and the column base is off to the maximum allowable in the opposite direction.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[ToadJones]

I always prefer leveling plates.
When done properly and set using the proper equipment the leveling plates can be set & grouted prior to the columns even showing up on site.
You can even place center/column line marks on the leveling plate ahead of time to match up with the columns.
If all is done properly/carefully, the column erection goes very quickly and with no where near the effort of grouting and shimming afterward.

 

[paddingtongreen]

I think we've disagreed about this before.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[DCBII]

I've used a pipe shear lugs before. They work great. I left a couple grouting holes in the base plate to eliminate the "cavity" problem. The difficult part is the weld between the lug and the base plate. We use CJP welds and it was hard for the fabricator to get backing inside the pipe. I'd recommend fillet or PJP welds if you can get the required strength out of them.

Looking at your detail, it seems like you may get a lot of rotation in this moment connection before you develop the design moment. I think it will behave more like a pin long before any significant moment is transferred. Are you having issues with traditional fixed bases?