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Hidden HSS Base Plate Detail

Hidden HSS Base Plate Detail

Hidden HSS Base Plate Detail

Every so often, I'm asked to provide a hidden connection detail for an HSS column bearing on a suspended CIP slab/column. I give it some thought, root around this forum some, and come to the conclusion that the columns will need to be field welded to embed plates. I yearn for a craftier solution but always come up empty handed.

Over lunch today, I came up with something (attached detail). It preserves the following beneficial features of typical base plate connections:

1) The column should be as initially plumb-able as with a typical base plate detail.
2) The column orientation should be able to be field adjusted later in the erection program to suit floor construction etc.
3) The column should be sufficiently moment connected to the slab to satisfy OSHA requirements.

One feature that has not been preserved, however is economy. My detail is complicated and involves a boat load of pieces and operations. So my questions for the group are:

1) Is this detail so complicated that, given the choice, erectors would prefer to field weld the columns directly to the embed plates?

2) Got any ideas for improving the detail?



The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Hidden HSS Base Plate Detail

If I am understanding this correctly they need to field weld either way so why bother with something complicated and convoluted..

RE: Hidden HSS Base Plate Detail

See points one and two in the OP Jayrod. Those are the areas where I'm trying to improve upon the usual detail.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Hidden HSS Base Plate Detail

One improvement would be to have some developed rebar coming out of the bottom of the couplers I suppose.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Hidden HSS Base Plate Detail

I assume the column has no lateral shear at base, just vertical axial load. What if you welded a foot plate to the bottom of the column the same size as the column. The foot plate would have four bolt holes. The column would have four access holes, one per side, to get to the bolts. The embed plate would have four bolts matching the holes in the foot plate. The holes in the foot plate would be oversized to allow for adjustment of the column axis. Use leveling nuts under the column. Once the column is plumb and oriented, use grout between the foot plate and embed plate.

RE: Hidden HSS Base Plate Detail

Thanks for the feedback vmirat. The column doesn't take any serious shear but some nominal capacity in the out of page direction is a solid idea. In most cases, I think that I could get away with welding the connection plates to the outside of the column. In that scenario, I could put a plate on all four sides and sleep easier with regard to shear.

Your proposal may in fact be a better option for my current situation. I'm hoping to develop a solution that would apply to a fairly broad range of HSS sizes however (as small as 6" perhaps). The internal bolts would start to get pretty crowded with smaller HSS sizes. Also, depending on the spatial requirements, your detail might require a grout bed with vertical sides. I've never been quite clear on whether or not that's okay.

With your detail, one could probably get away with a single access hole, right? Also, would there still be a need for an embedded plate? It seems as thought it's only purpose would perhaps be as a template for the anchor rods.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Hidden HSS Base Plate Detail

I've done this kind of thing with HSS4x4x1/4 columns with just one bolt inside and one access hole. If you use less than four bolts, and it's a primary column, the contractor would have to use bracing to meet OSHA.

I get straight sided grout under base plates all the time. The contractors like to use form blocks on the side of the plate. I have no problem with it. I actually perfer the look.

A single access hole could be used if it is large enough for a wrench.

The embed plate is there to distribute the load to the concrete. You had originally stated that this was for a hidden connection. If the foot plate is enough to distribute the load to the concrete, then you could do away with the embed plate.

The foot plate needs to be designed a little differently than a traditional base plate because it is acting as a plate simply supported on all edges with a uniform load on the entire surface from the grout. Rourke has formulaes for that.

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