Steel Column to Concrete Column Detail - Bars welded to underside of Base Plate

[Rainbowtrout]

This is my first time doing this type of details and I want to bounce it around a bit. I have steel columns coming down to a concrete column. I am welding bars to the underside of base plate. The bars will be hooked at the other ends. The concrete columns will have vertical reinforcements hooked at top.

I know how important pictures are. SO I attached one.

My question:
Will the forces in steel column successfully transfer to vertical reinforcement in the column below? Max Mu is around 130 k ft w 110 k compression.

I am open to other ideas too.

 

[shaneelliss]

I think the idea in general is ok, but you have to make sure you have developed your 1" bars enough into the concrete to have a safe connection. I don't know anything about the properties of the concrete you are specifying, the size of the vertical bars in your concrete columns, or if there are seismic loads on the system, but putting those things aside, you need to make sure that not only do your baseplate bars have enough development length, but also that the length of the column vertical bars above the breakout cone has enough length or the concrete will likely fail in breakout or some other method before your desigm moment is reached.

Also, with hooks on the baseplate bars and hooks on the column vertical bars, you just want to make sure there is enough physical space to get it all in there. I would personally also add more column ties in that area.

 

[msquared48]

The "4 - #4 ties" note is confusing to me. How are these to be spaced and exactly where are the other three?

I agree with the comment above on additional ties too.

Mike McCann, PE, SE (WA)

 

[azcats]

I echo shaneelliss' concerns about development. I'd be tempted to use nelson stud or headed bolt type anchorage for the plate and embed it so the failure cone intersects the vertical column reinforcing below it's development length.

Similar discussion here. Link

 

[KootK]

My thoughts:

1) Is there an architectural requirement to avoid an exposed base plate? If not, go with a conventional anchor bolt arrangement. Welding to an embedded plate is possible but contractors don't care for it. It's more difficult to plumb the columns.

2) There's a pretty good chance that you'll find the embed plate tilted 5-10 degrees after the concrete dries, making it tough to get a good 1/4" fillet weld on it. If aesthetics allow it, consider transferring your base reaction through side plates shipped loose and welded to the faces of the column.

3) Plan for your embed to be shifted up to 1.5" from it's intended location. Design for the added eccentricity and bending in the embed plate.

4) As others have suggested, consider using some form of headed anchor rather than rebar. The only problem that rebar solves is side face blowout which ought not be a problem based on your sketch. Other than that, reinforcing bars are just anchor bolts that develop very slowly.

5) Joint analysis and detailing will also be complicated by the fact that you may have appreciable, additive moments coming into the joint from beam #2. You may need substantial flexural corner bars passing from the exterior of the column into the top of the beam.

6) if you decide to stick with hooked rebar, I'd turn all of the column vert hooks inward and all of the weld plate hooks outward as that will suit the flow of compression forces in the joint.

Is your moment in the plane of your sketch or out of the page? Is it reversible? Will it be accompanied by an appreciable shear? Is it your intent to keep the anchor rods out of the column pour? We can get more specific with more detail.


I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.