Steel column to concrete beam connection confusion

[hitch22]

Hello folks,

I am trying to design a steel column to concrete beam connection and since I have never done this I am very unsure as to how to do this. Here is the background of the problem:

1. A steel column is to be installed between two existing concrete beams as shown in Figure 1. The purpose is to support the top beam as it could be over stressed in the future.

2. Since the steel column is to inserted in between two existing beams it does not make sense to me to simply weld a base plate on each end of the column (i.e. there is a constructability problem). I cannot assume the steel column will fit perfectly between the beams.

a. Therefore, I propose welding one base plate to one end of the steel column (Figure 2).
b. The other end will be bolt connected as shown in Figure 3. I am thinking of using an angle connected to the base plate and connected to the column web. The angle would be bolt connected to both the base plate and the column flange. The purpose of the connection is to allow some flexibility during construction. The column can be field drilled.

3. The load is almost entirely vertical.

4. The W section has plenty of capacity.

I have attached a sketch to illustrate the situation.The sketch correctly oriented is in page 2.

Any help would be greatly appreciated. If you could tell me what you would do (or consider) or if you could guide me to a source it would be great.

Thanking you in advance.

 

[hokie66]

I couldn't open your file. Things which I would consider include: 1) Strength of the bottom beam. 2) Do you want to preload the bottom beam by jacking some of the load in? Doing that could conceivably crack the top of the upper beam. May not matter, but consider. 3) Why not make the column slightly short with end plates and use grout to fill the gap? 4) After installation, the two beams will share the load in proportion to their stiffness.

 

[hitch22]

Thanks hokie66.

I was already planning on using grout but not to fill the gap. I will consider that option today.

I have attached the sketch once more as a PDF.

 

[Quanski]

The column should be slightly shorter and leveled as required by adjusting leveling nuts of the base anchor. Once leveled and proper contact is achieved at the top, the gap btw the base plate and the footing should be grouted as required. shoring and jacking of the beam is required for temp load relief to allow installation and proper curing of grout.

 

[BAretired]

I agree with hokie, but I would use steel shims to fill the gaps before grouting. If you want to jack a little load into the lower beam, that can easily be done on site.

BA

 

[hitch22]

Well I am afraid of filling in the gap with grouting because the grout layer might be too thick.

I have drawings of the beams, but they are too high for me to climb up and actually measure. Because of this I am afraid the column will not fit exactly.

If the column is made shorter and I don't specify the grout thickness the workers might have to make a 4" thick grout layer for example.

Would this grout thickness not change the local behaviour? For example, the rebar clearance was assumed to have a certain value, but because of this thick grout my assumption is no longer valid.


Does the grout idea still seem practical to you?​

 

[hitch22]

Also, I have reviewed my calculations using 2 angles as shown in the attachment and I think my idea won't work. Although the angles are satisfactory for now, I don't think they will be enough for additional loads. Right now the angle thickness is almost 11 mm. The thickest L angle I can obtain is 13 mm.

 

[BAretired]

Put a cap plate on the column and a couple of vertical side plates aligning with each face of the beam. Provide Hilti anchors through side plates into existing beam.

Shove the column up to meet the underside of beam (you might want to put a neoprene filler on the plate for better bearing). Jack the column to put a slight compression in it, then fill the three or four inch space below the base plate with steel packing and grout.

It might be better to turn the column 90 degrees so that its flanges are parallel to the beam.





BA

 

[hokie66]

Leave the measurement to the fabricator. He has to have some access scaffolding or similar for erection of the column, so he can use that for measuring before fabrication. But if you truly can't get a good measurement, use shim plates as BA suggested. Have them made the same dimensions as the base plate, of several thicknesses if necessary.