Decagon slab
Decagon slab
(OP)
A slab is supported by blockwork in the shape of a decagon with a "radius" of 5.5 metres. The slab cantilevers out another 1.5 metres on all sides. There is a stud wall running through the middle which can accommodate internal columns. (please see attached)
Instead of designing the slab with radial and circumferential reinforcement, can it be designed orthogonally by simply taking 1 metre strips spanning over the 2 rows of beams and blockwork, and then adding additional top reinforcement local to the cantilevers - which would make the backspans act as a two-way slab in some areas..
Thoughts?
Instead of designing the slab with radial and circumferential reinforcement, can it be designed orthogonally by simply taking 1 metre strips spanning over the 2 rows of beams and blockwork, and then adding additional top reinforcement local to the cantilevers - which would make the backspans act as a two-way slab in some areas..
Thoughts?






RE: Decagon slab
Dik
RE: Decagon slab
R13.6.2.5 — If a supporting member does not have a
rectangular cross section or if the sides of the rectangle are
not parallel to the spans, it is to be treated as a square support having the same area, as illustrated in Fig. R13.6.2.5.
In Russia building design you!
RE: Decagon slab
RE: Decagon slab
In Russia building design you!
RE: Decagon slab
For the cantilevers, I would add top steel normal to the wall, carrying it an equal distance to the inside. Temperature steel in the cantilevers would be parallel to the wall, i.e. circumferential. Two or three circumferential tie bars could be added to control the flying ends of the cantilever reinforcement.
BA
RE: Decagon slab
RE: Decagon slab
RE: Decagon slab
Hokie's idea appeals too. Perhaps it is the simplest.
BA
RE: Decagon slab
What I am describing is closer to the classical concept of reinforcing for tensile stress in shells considered as membranes, you deal with the tensile stress, and one trick to do that is to use rebar that shows equal capacity in every direction, as 2 equal orthogonal reinforcements at whatever vector in the shell does (omiting the small difference in capacity due to different cover in the 2 layers). We do the same here, but for flexure, and to start we use a model with the actual geometry, not one equivalent as per the ACI quote.
So, practically you read the tensile principal stress at the point in the face where the tension is tensile, and then there you simply imagine a elastic setup for the stresses that give you a moment per unit length, that needs be covered by the capacity of the mesh in one direction (and as well, and then, the other, since equal).
This results for many situations quite practical, starting from the point from higher stresses, you may find you only need the basic mesh plus another superimposed (or better, parallel) mesh to get a rational reinforcement, sometimes two superimposed (or better, parallel) meshes.
So by using just the scalar value of the biggest tensile stress at the face, the equal capacity mesh allows you to disregard the orientation of the principal stress. It is more applicable than it looks in that you adapt to the equal value contour plan of the principal stresses, so there having more tensile stress in one direction than the other can be reasonably dealt with. It also gives you excellent (at least qualitative) appraisal of where the reinforcement is needed.
I may also add that I have used such reinforcement scheme (as main, but not only device for design) in maybe tens of thousands of square meters of slab without no problem whatsoever. No wonder since it puts reinforcement where needed.
RE: Decagon slab
with no problem whatsoever.
RE: Decagon slab
In Russia building design you!
RE: Decagon slab
BA
RE: Decagon slab
In Russia building design you!