2 WAY CONCRETE SLAB WITH REINFORCING 45 DEGREES TO AXIS OF GRID
2 WAY CONCRETE SLAB WITH REINFORCING 45 DEGREES TO AXIS OF GRID
(OP)
Has anyone come across a 2 way concrete slab system with drop panels at the columns but the reinforcing of the concrete slab is 45 degrees from the axis of the column grid and not the typical perpendicular direction? We are going to be renovating the entire existing building. They want to change the use of the building and therefore are going to be putting all kinds of new plumbing penetrations through slab. They are asking where they can place these penetrations (best locations)? Also I have to analyze the building for seismic/wind lateral loading and based on what I saw in the field and the as builts the only thing I think that is holding this structure up is the slab and columns. Therefore I was going to look at the building as concrete moment frames.
So I would like to know how to come up with capacities for the slab system and how to take in account the new penetrations?
So I would like to know how to come up with capacities for the slab system and how to take in account the new penetrations?






RE: 2 WAY CONCRETE SLAB WITH REINFORCING 45 DEGREES TO AXIS OF GRID
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: 2 WAY CONCRETE SLAB WITH REINFORCING 45 DEGREES TO AXIS OF GRID
Just need to make sure the amount of steel passing through a given design cross section (with arbitrary orientation) satisfies the bending moment (Mx, My AND Mxy).
On second thought: why can't you simply disregard the grid lines and take strips @ the 45 deg angle?
RE: 2 WAY CONCRETE SLAB WITH REINFORCING 45 DEGREES TO AXIS OF GRID
Flat slab moment frames are not very efficient at the best of times. Any chance of introducing some shear walls?
Just curious, how old is the building and where is it located?
RE: 2 WAY CONCRETE SLAB WITH REINFORCING 45 DEGREES TO AXIS OF GRID
KootK (Structural)1 Jul 15 04:32
Any chance the rebar might be radial, like this: Link?
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: 2 WAY CONCRETE SLAB WITH REINFORCING 45 DEGREES TO AXIS OF GRID
Trenno (Structural)1 Jul 15 05:25
Principle bending moments in flat plates almost never follow traditional X/Y strips, yet your reinforcement almost always does.
Just need to make sure the amount of steel passing through a given design cross section (with arbitrary orientation) satisfies the bending moment (Mx, My AND Mxy).
On second thought: why can't you simply disregard the grid lines and take strips @ the 45 deg angle?
RE: 2 WAY CONCRETE SLAB WITH REINFORCING 45 DEGREES TO AXIS OF GRID
Any chance this was a C.A.P. Turner system?
http://www.mbjeng.com/wp-content/uploads/2011/03/N...
There are several antiquated two-way systems that it might have followed that might make your life easier if you can find the information on them.
RE: 2 WAY CONCRETE SLAB WITH REINFORCING 45 DEGREES TO AXIS OF GRID
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: 2 WAY CONCRETE SLAB WITH REINFORCING 45 DEGREES TO AXIS OF GRID
KootK (Structural)1 Jul 15 13:41
Age and location of the building would be very useful parameters here.
RE: 2 WAY CONCRETE SLAB WITH REINFORCING 45 DEGREES TO AXIS OF GRID
njlutzwe (Structural)1 Jul 15 13:19
Rweave,
Any chance this was a C.A.P. Turner system?
http://www.mbjeng.com/wp-content/uploads/2011/03/N...
There are several antiquated two-way systems that it might have followed that might make your life easier if you can find the information on them.
RE: 2 WAY CONCRETE SLAB WITH REINFORCING 45 DEGREES TO AXIS OF GRID
I have used that approach several times and I believe it is discussed in Park's, "Reinforced Concrete Slabs" book.
John Klein, P.E., M.L.S.E.
www.johnkleinpe.com
RE: 2 WAY CONCRETE SLAB WITH REINFORCING 45 DEGREES TO AXIS OF GRID
Nichols' total static moment concept of wl2/8 was fought by many, including distinguished professors.
I think the ACI-318 provision of 85% of the total static moment stayed in the code until 1963 or 1971! Long live Newtonian mechanics!
RE: 2 WAY CONCRETE SLAB WITH REINFORCING 45 DEGREES TO AXIS OF GRID
http://www.fib-international.org/practitioners-gui...
RE: 2 WAY CONCRETE SLAB WITH REINFORCING 45 DEGREES TO AXIS OF GRID
The reinforcement can be at any angle. The principal stress will be at different angles at every point on the slab so we cannot put the reinforcement in at the principal stress angle, so we normally use the angle that is easiest to build, orthogonal and perpendicular to the slab edges, and resolve the moments to suit in each direction.
I once had a square slab that was shown as 11.3m * 5.7 perpendicular to the edges. But if you rotate everything 45 degrees, it was actually an 8m * 8M grid, but with 45 degree sloping sides! You could design it either way, but an 8m flat plate suited much better than an 11.3 * 5.7m beam and slab arrangement.