Cap plates on columns for beam bearing - are they required?

[EngDM]

I've been doing a little digging to see if cap plates are strictly required to pick up W beams bearing on an HSS (round or square) but haven't been able to come to a clear cut concensus. For a rock socketed round HSS at this site the refusal depths are all over the place, and the site is in such a remote place, that we want to make this as simple to construct as possible. My immediate thought was to just weld to the underside of our steel beam floor, which avoids any cap plate welding (so effectively eliminating half of the welding), but I can't seem to find any information saying NOT to do this. As long as the beam has been checked for web crippling, which we have added stiffeners for, is there any other considerations? All lateral loads are transfered to battered piles elsewhere along the perimeter, so for all intents and purposes this is a strictly axial/bearing condition.

FYI - connection has to be a welded connection, otherwise any bolt holes in the beam flange would need to be site drilled which for obvious reasons we would rather not do.

 

[KootK]

I don't feel that having cap plates is mandatory. Depending on how the geometry plans out, your beam bottom flange may perform a similar function.

As long as the beam has been checked for web crippling, which we have added stiffeners for, is there any other considerations?

You basically need to check the same thing on the other side of the joint: crippling etc of the pile. Two paths:

1) Design the beam bottom flange as the distribution that the cap plate would otherwise be.

2) Assume that the pile walls are loaded in a concentrated fashion beneath the beam webs and design the pile walls for that.

 

[DrZoidberWoop]

One of the other benefits of cap plates, in conjunction with shims/filler plates, is that they can be milled to the required thickness to ensure proper bearing/load-transfer if significant variances in post/column height are discovered during a survey.

 

[KootK]

It will also behoove one to be realistic about the tolerances involved in pile placement.

 

[EngDM]

I don't feel that having cap plates is mandatory. Depending on how the geometry plans out, your beam bottom flange may perform a similar function.



You basically need to check the same thing on the other side of the joint: crippling etc of the pile. Two paths:

1) Design the beam bottom flange as the distribution that the cap plate would otherwise be.

2) Assume that the pile walls are loaded in a concentrated fashion beneath the beam webs and design the pile walls for that.

For 2) is there anything in CSA for a method of analyzing this? Not something I am familiar with, typically just assume the cruciform transfers it to the bearing point, but I can visualize the high stress concentration below this loaded area.

 

[KootK]

For 2) is there anything in CSA for a method of analyzing this? Not something I am familiar with, typically just assume the cruciform transfers it to the bearing point, but I can visualize the high stress concentration below this loaded area.

Not sure. I usually go straight to the AISC design guide on HSS connections for this kind thing. Most of that was developed by Dr. Packer at the University of Toronto anyhow.

 

[ANE91]

For a rock socketed round HSS at this site the refusal depths are all over the place

Off topic, but was a drivability study performed in advance?

 

[EngDM]

Not sure. I usually go straight to the AISC design guide on HSS connections for this kind thing. Most of that was developed by Dr. Packer at the University of Toronto anyhow.

Only reason I ask is because the web crippling/bearing procedure for CSA and AISC are vastly different.

 

[EngDM]

Off topic, but was a drivability study performed in advance?

Not sure. We aren't doing the piles just providing loads, but I believe we are responsible for speccing the cap plate. It's down to bedrock which is 1-2m below grade, I think they core it out to get some meaningful penetration.

 

[BulbTheBuilder]

I personally don't think column cap is mandatory, but it is mostly preferred for fabrication purposes. Assuming you have cap plate with bolts installed, you have some stability or support as erection is going on. You also get some flexibility in the joint (pinned joint) as opposed to welded with the column now bending with overrun beam due to rigidity which you have already accounted for (local beam checks). You might also want to check your column for the additional moment.

But if we can weld tubes to WF for trusses, why can't we weld the beams and columns? I see no problem.

 

[KootK]

Only reason I ask is because the web crippling/bearing procedure for CSA and AISC are vastly different.

Way back in 2007, I received carte blanche from CISC to use AISC for anything not covered in CISC. I've kind of extended that to now using AISC for anything where I feel that CISC does not cover it as well as AISC. Naughty me. I feel that one of the nifty feature of Newtonian physics is that it is ostensibly agnostic to geography.