huangyhg

concrete beam to wall connection
i am currently working on a parking slab replacement project in canada. the parking slab is covered with asphalt and serves as surface parking for a hotel. below the slab is an under ground parking garage. the slab is a one-way slab spanning approximately 20ft. between beams cast monolithicly with the slab forming t-beams. the slab is supported at each end by concrete foundation walls and there are 4 interior t-beams. the t-beams span approximately 26ft. between columns. the t-beams are supported at each end by concrete foundation walls and there are 4 interior columns. the slab, beams and columns are being replaced and walls are remaining.
my question involves the t-beam connection to the wall. can an adequate connection be established between the new t-beam and existing concrete foundation wall to assume continuous construction and therefore analysis of the beam/column/wall as a concrete single-storey frame? i am finding that i need a negative moment to develop at the beam to wall (end connection) in order to reduce negative moments at the first interior column and as a result reduce the moments in the first interior column (note, that there is not much room for negative moment development over a 12" wall).
new and existing members are as follows:
9" thick slab
19.5" deep t-beam with 24" wide web
12"x24" column (h = 7ft.)
12" thick existing foundation wall.
any help would be greatly appreciated.
gmf
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you don't say why the floor is being replaced. is it as a result of corrosion of steel, concrete failure or simply a change in geometry?
if the existing wall reinforcement is carefully preserved during demolition of the floor and the concrete in the wall is deemed sound, you should be able to develop some continuity between the new beams and the existing wall. it might be a good idea, however to limit the end restraint of the beam to wl^2/24.

ba
why are you getting a negative moment in the interior columns? besides the minimum moment required in 10.12.3.2, i'm not seeing it. model the beams as continuous over the columns and the column as a pinned support. i suspect that is the way the original design was done.
the floor is being replaced due to severe corrosion of the reinforcing steel over a majority of the slab and beams.
gmf

exam and try to figure out if the original wall and the t beam were casted by one pour, or there was a construction joint below the t beam.
for the latter case, demo the wall to the construction joint with a width = 2*horiz bar development length + bw, then rebuid with the preserved bars.
for the former, on top of the width mentioned above, i would demo the wall below further to at least one development length of the wall bar.
watch out for bonding development along the new-existing concrete interfaces.
i have designed my beams as continuous over my interior columns and the column as a pinned support. i am now wondering how to adequately detail my column to beam connection to make sure i have a pinned support. any additional help would be greatly appreciated.
gmf
you can't have an ideal pin like roller support, it's just a matter of design. if there is no difference in spans, you should not worry about. otherwise you are attracting moment in columns to make it pin to idealize your assumption.

i would normally make a rigid connection between the beam and the column and design the column to take whatever bending develops. it is difficult to detail a "pinned" connection at this point. if a pinn is desired, i would probably use separate straight dowels between the column and beam located at the cg of the column.
i would not count on the wall to restrain the beam for negative moment but would add top bars in the beam if any incidental negative moment did develop.
i have never done that before. however, here is an idea.
cast the column with a steel plate at the beam-column interface. the plate shall equipped with anchor studs on both top & bottom to transfer the horizontal shear at the interface, yet allow the beam to under go small rotation. the important thing is some type of flexible sealant shall be used to conceal the plate, and protect the upper edges of the column from spalling.

i have seen some highway bridge details where they used straight dowels and exp jt material around the perimeter of the column to create a semi-pin condition.
just because you model the beam as pinned at the columns, you don't have to build it that way.
if the negative moment at the first column is too high, just make the beam wider. you don't have to rebuild to the same profile as the original structure.

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