Existing Concrete Beam Fix
Existing Concrete Beam Fix
(OP)
I have an existing concrete beam, and it is over stressed in shear, but not moment for the new load.
I have a very limited depth, so I was going to attach to the bottom of the beam with a WT and say that the shear would all be carried by the WT.
Is this acceptable? I was going to try to make the section composite, but the shear flow I get is way to high for any kind of post-installed anchors.
I cannot connect to the sides of the existing beam because there are cast-in-place joists framing into it.
If I assume that the beams act separately than the load would all go to the concrete beam and it would not work. I was thinking about it from a limit state approach. i have more shear strength (using the two sections) than applied so it is ok.
I have a very limited depth, so I was going to attach to the bottom of the beam with a WT and say that the shear would all be carried by the WT.
Is this acceptable? I was going to try to make the section composite, but the shear flow I get is way to high for any kind of post-installed anchors.
I cannot connect to the sides of the existing beam because there are cast-in-place joists framing into it.
If I assume that the beams act separately than the load would all go to the concrete beam and it would not work. I was thinking about it from a limit state approach. i have more shear strength (using the two sections) than applied so it is ok.






RE: Existing Concrete Beam Fix
There was a good tread on this subject recently. Please do a search, and if you can't find it, post again and I'll see if I can't dig it up.
Basically there are other options.
Good luck,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
RE: Existing Concrete Beam Fix
Provide wedges along the length to ensure that transfer of load occurs.
RE: Existing Concrete Beam Fix
RE: Existing Concrete Beam Fix
RE: Existing Concrete Beam Fix
BA
RE: Existing Concrete Beam Fix
RE: Existing Concrete Beam Fix
The concrete beam is 12" x 15" with 3 #8 top and bottom, but it only has #2 Hoops at 24" c/c, so there is practically no shear reinforcing. I checked the beam for the change in load, and it works for moment but not shear.
Also, the architect is only moving the column below not the column above, so now I have a transfer condition which makes matters even worse. I do not the deflection in the beam to adversely effect the roof beam above because one of the support columns is settling to much.
The new spans are 12 and 14.5 feet and the orginial spans are 16 and 10.5 feet. They are carrying an office load. the orginial design is supposed to carry the same load according to the copy of the building code i have from original construction.
Yes the whole thing does not bode well, but that is what I am stuck with.
RE: Existing Concrete Beam Fix
I would also be concerned about where the laps of the top and bottom bars are in relation to your new column position.
RE: Existing Concrete Beam Fix
The joists are 10" deep and spaced at 2'8" c/c
RE: Existing Concrete Beam Fix
RE: Existing Concrete Beam Fix
Mike McCann
MMC Engineering
RE: Existing Concrete Beam Fix
Just one of many options.
RE: Existing Concrete Beam Fix
BA
RE: Existing Concrete Beam Fix
RE: Existing Concrete Beam Fix
RE: Existing Concrete Beam Fix
Prestressing the steel fixes that.
RE: Existing Concrete Beam Fix
I would worry about continuity of the top bars over the new column. The 12' span will still work as a concrete beam, unless you intend to reinforce it as well. Is the upper column supporting another floor?
If you can develop the reactions at the columns and predeflect the steel beam to carry at least the dead load, the steel beam solution should work.
RE: Existing Concrete Beam Fix
I am not worried about splice too much, from what the drawings show there is no splice over the columns, I think that there is only one splice along the length of the beam and it does not occur near the area I am working in.
The load can be transfered but I have to bottom cope the beam and weld a plate to get the bolts I need.
RE: Existing Concrete Beam Fix
This should insure that the steel beam will be the primary load carrying member and the concrete beam will only act as a filler.
RE: Existing Concrete Beam Fix