Steel Frame extension on existing RC Frame

[kellez]

Hi everyone,

1) I want to design a 2-storey steel frame extension on an existing concrete frame.
2) The two beams that run parallel to the concrete beams will need to be anchored to the beams (to connect the two structures)
3) The floor will be a composite metal deck.
4) The composite floor will need to be anchored to the existing RC frame with starter bars connected to the composite floor reinforcement bars.
5) Seismic loads need to be considered in the design

My question is. Since the two structures need to be connected to each other (due to seismic loading) and have a composite behavior what is the best way to connect the steel column shown below, to the existing RC Column?

 

[HTURKAK]

2) The two beams that run parallel to the concrete beams will need to be anchored to the beams (to connect the two structures)OK
3) The floor will be a composite metal deck.OK

4) The composite floor will need to be anchored to the existing RC frame with starter bars connected to the composite floor reinforcement bars. OK
5) Seismic loads need to be considered in the design OK


The best way probably not to use the steel columns adjacent to existing RC columns. Just use one steel column at the corner..
Try this model before adding new columns and new foundations .

 

[dik]

Do you need to use columns adjacent to the concrete ones? Can you use Channels? with shear fin plates for attachment?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[kellez]

The best way probably not to use the steel columns adjacent to existing RC columns. Just use one steel column at the corner..
Try this model before adding new columns and new foundations

I did think of using only one column, which is possible and straight forward but for peace of mind, i will be a lot more confident if i didnt rely at all on the existing structure.

Do you need to use columns adjacent to the concrete ones? Can you use Channels? with shear fin plates for attachment?

Actually it doesnt have to be a column, i think a channel should work just fine, i didnt mention this but for the two beams that need to be connected to the RC beams i am using a UPN which is similar to a channel.

So, your suggestion is to use fin plates welded on the open side of the steel channel? And the main beam connected on the fins?

 

[dik]

Yup... that's likely the way I would have done it...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

UPN, a European channel... had to look it up.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[kellez]

I have worked a bit more on the 3d model in order to understand how this can be put together and here is what I have come up with. Some of my questions now are:

1) Not sure how the IPE270 (picture 1) can be bolted since there are stiffeners for the UPN both at the top and bottom therefore the bolts cannot be reached. Maybe one stiffener shall be installed after the beam has been bolted but the welding on the stiffener will only be on one side.

or the beam shall not be bolted but welded on site.

2) As you can see from the second picture the UPN column is fixed on the existing RC column with anchor bolts. I have never tried this before therefore I am not exactly sure what to expect. Any thoughts on this are welcomed

3) And on the 3rd picture as you can see I have added a baseplate for the UPN in order to treat it as a column.

4) And my last question is: how feasible is this since a UPN is much weaker than a universal column along the y-axis/weak axis.

 

[phamENG]

1) If those stiffeners are required, then you'll need to either weld the beam or use blind bolts.

2) My concern here is the column ties. Drill in the wrong place and you can cut right through them. I would suggest giving a maximum spacing and having the column scanned to be able to avoid the rebar.

3) Do you want the load going to the new footing or into the old column? If the new footing, I would suggest making holes in the channel vertical slotted holes. If into the column, then I question why you don't just anchor the beam end plate directly to the existing column.

4) Sure, but you're anchoring it to the existing column. That will stiffen the week axis considerably.

 

[kellez]

1) If those stiffeners are required, then you'll need to either weld the beam or use blind bolts.

2) My concern here is the column ties. Drill in the wrong place and you can cut right through them. I would suggest giving a maximum spacing and having the column scanned to be able to avoid the rebar.

3) Do you want the load going to the new footing or into the old column? If the new footing, I would suggest making holes in the channel vertical slotted holes. If into the column, then I question why you don't just anchor the beam end plate directly to the existing column.

4) Sure, but you're anchoring it to the existing column. That will stiffen the week axis considerably.

1) The reason for including the stiffeners is that I don't want to drill at the beam-column joint (to anchor the UPN) of the existing RC frame because that point is congested with steel reinforcement. therefore I will use blind bolts, they seem perfect for the job.

2) Yes I will have to scan the existing column to locate the steel ties and avoid them.

3) The reason I don't want to anchor the beam end plate directly to the existing column is again due to the fact that the concrete connection is congested with steel reinforcement, and since the new connection will need to be seismically designed it will require at least 10 bolts anchored inside the existing column, which I think would be impossible to achieve at that location.

My thinking is that I don't want to add any new loads on the existing RC frame without adding any additional strengthening. Therefore by anchoring the UPN on the existing RC Column, I am actually transferring the load to the RC column but I am also strengthening the RC column with the UPN.

Next, since I want the UPN to resist horizontal loadings (in the case of an earthquake) and provide strengthening to the existing RC column, I will have to connect it to the footing.

4) Yes you are right the weak axis would be considerably stiffened.

What would be a good software to be able to analyze such a connection between the existing RC Column and UPN?

I think i need to start analyzing different configurations in order to decide on the final connection.

 

[phamENG]

Software? Not sure. I usually do this sort of thing by hand, but I haven't had to do it for a significant seismic load before. Different codes address that differently, so I will defer to somebody more familiar the requirements you'll need to satisfy.

 

[kellez]

Not to completely design this with a software, I mean to check how this connection will behave by using a FEM software like abaqus or solidworks. ofcourse everything needs to be checked by hand calculations.