Detail of Steel Column above Concrete flat slab 2

[canstruct]

Hi Guys,

We are designing a mall with concrete flat slab structure supporting steel structure at its top. How we can connect steel column above concrete structure. Architect don't want to expose the base plate and anchor bolts. If we provide a recess of 6" (2" grout+ 1" plate+ 1.5" max for bolts+ 1.5" grout above it) in concrte it means that we are redicing the effective depth of the slab and to me it looks like a bad detail to avoid cracks.
Can somebody can suggest other types of connections which can avoid this problem. Architect don't want to put any cladding around for some leasing issue.

 

[msquared48]

Embed a bearing plate in the slab (with welded nelson studs or rebar on bottom) and field weld the column to it - moment connection here. This will give a flush connection.

Alternate is to attach with four bolts welded to same embedded base plate. Plate on column to be attached is no larger than the maximum dimensions of the column so the bolts end up inside the column.

Mike McCann
McCann Engineering

 

[hokie66]

The detail I use is similar to Mike's, except I use two plates, one on the bottom and one on the top, joined by welded bolts or a steel section. This way, the bottom plate sits directly on the form and is sure to be level and at the right elevation at the top surface.

 

[haynewp]

If it is a tube steel column, another option is to have the embed plate with a short 3 or 4 foot tube post already welded to the plate when it is cast in the slab. The rest of the tube column would then telescope into the stub post with shear tabs welded at the sides.

 

[canstruct]

Thanks Guys,

Two plates will work well, one embedded in concrete and other bolted from inside of the column and it adjust the levelling requirements if any.

We are using W sections. But in case they are HSS, Haynewp suggest telescopic arrangement. How does it works, how could the member inside will be the exactly same or you are suggesting some stiff plate. Plese explain.

Thanks once again.

 

[haynewp]

You can slide, for example, an HSS 3 1/2 x 3 1/2 x 3/16 into an HSS 4x4x3/16 for about 1'-0" or so. A 1/2"x2"x6" tab (for example) is shop welded at the sides of the smaller column which stops the smaller column from sliding further into the larger. Then field weld at the interface of HSS members.

This suggestion was giving an option to avoid having to steady the full height HSS with the crane and weld around the bottom to the embed, but that works too. I mostly have used it in multistory HSS column buildings when changing sizes at floor levels.