Punch. Shear at Perimeter Col with Spandrel Beam
Punch. Shear at Perimeter Col with Spandrel Beam
(OP)
I am relatively inexperienced with concrete slab design, and had a few punching shear issues to get worked out that are outside of the cookie cutter examples found in the ACI. Note that this is my first Slab design and I am working under a supervising engineer who has a lot of experience in concrete design, but who doesn't always explain things where I can understand.
Anyways, I have a 12" slab framing into 16"x20" perimeter concrete columns and there is a concrete spandrel beam that is 22" deep and 32" wide (6" each side of concrete column). If I were to check the column for punching shear with moment transfer, the critical section is not a standard ACI shape since it has two different d's (ie. 10" on one edge and 19" on other two edges), and this calculation seems very difficult on this shape. My supervisor had some ideas for approximating what the punching shear capacity, looking at a 12" slab shape and a constant thickness 22" thick slab shape, and interpolating between the two.
However, I am not sure even punching shear is an applicable check in this instance. Section 11.12.6 of the "Notes on the ACI 318-99" (pg 18-11) states that moment transfer isn't critical when beams frame into the columns, as those beams provide alternate ways for the moment to get transfered into the column. With this, I am thinking that the spandrel beams provide torsional restraint of the concrete slab, and all of the moment transfer is spread uniformly across the entire bay. With this method of transfering the load, I would think that you could simply design the shear reinforcement in the spandrel beam for combined shear and torsion. Am I looking at this correct? Are there referenced standards that I should read to help me with punching shear with moment transfer problems?
Thanks for any guidance provided. Note that the example described above is the simple case that I have to work out, and there are other cases that I need to review which are more difficult to explain here, but any guidance provided in regards to torsion/shear in the spandrel beam will help me out with those issues.
Anyways, I have a 12" slab framing into 16"x20" perimeter concrete columns and there is a concrete spandrel beam that is 22" deep and 32" wide (6" each side of concrete column). If I were to check the column for punching shear with moment transfer, the critical section is not a standard ACI shape since it has two different d's (ie. 10" on one edge and 19" on other two edges), and this calculation seems very difficult on this shape. My supervisor had some ideas for approximating what the punching shear capacity, looking at a 12" slab shape and a constant thickness 22" thick slab shape, and interpolating between the two.
However, I am not sure even punching shear is an applicable check in this instance. Section 11.12.6 of the "Notes on the ACI 318-99" (pg 18-11) states that moment transfer isn't critical when beams frame into the columns, as those beams provide alternate ways for the moment to get transfered into the column. With this, I am thinking that the spandrel beams provide torsional restraint of the concrete slab, and all of the moment transfer is spread uniformly across the entire bay. With this method of transfering the load, I would think that you could simply design the shear reinforcement in the spandrel beam for combined shear and torsion. Am I looking at this correct? Are there referenced standards that I should read to help me with punching shear with moment transfer problems?
Thanks for any guidance provided. Note that the example described above is the simple case that I have to work out, and there are other cases that I need to review which are more difficult to explain here, but any guidance provided in regards to torsion/shear in the spandrel beam will help me out with those issues.






RE: Punch. Shear at Perimeter Col with Spandrel Beam
RE: Punch. Shear at Perimeter Col with Spandrel Beam
RE: Punch. Shear at Perimeter Col with Spandrel Beam
You should talk to your supervising engineer and explain that the stiffness of the edge beams is such that punching shear is not a consideration but that there is torsion in the beams... approximately 1/2 the moment going into the columns. You can ask him how he proportions the torsion... this affects the design of columns also. Some engineers use 1/2 the column stiffness, permitting it to crack as well as the compression load has an effect on Ec that is normally not considered. Ec is not linear.
You might consider the system as elastic using a live load that is realistic to determine torsion and moments into columns. There's a whole pile of things to consider and since this is one of your first projects, it's best to have some guidance at the start...
Dik
RE: Punch. Shear at Perimeter Col with Spandrel Beam
RE: Punch. Shear at Perimeter Col with Spandrel Beam
RE: Punch. Shear at Perimeter Col with Spandrel Beam
RE: Punch. Shear at Perimeter Col with Spandrel Beam