limit resisting section of columns/walls

[ramihabchi]

hi,
I need to know if it is possible to make just a part of a column resist loading instead of the whole cross section?which dispotion enable me to do it?.reference would be appreciated.
Also i am wondering if same thing could be done in shear walls,from another perspective ofcourse,due to formation of shear hinges the part of the wall unable to resist shear will make the other part resist it by itself.am I right?

 

[johnie134]

Yes you a right. The simlest scenario related to what you say is a concrete beam section under pure bending, where only the part under compression is considered.

 

[ramihabchi]

To avoid miss understanding please find attached the clarification of the questions

 

[ramihabchi]

2nd picture for wall

 

[r13]

Pic 1 - I don't know how you going to load the column, what is on top, shape...?
Pic 2 - If the floor ends on the ledge, the upper wall will not have much shear other than inertia force during earthquake, and wind (for exterior wall). If you don't provide reinforcement, how a hinge could form? It will just crack and fall.

 

[r13]

If the column on pic 1 is a gravity only element, then it is possible to avoid load get into areas 2 & 3 by leaving a gap on top and bottom of these element to the floors above and below, so they are acting like added weight to the column. You have to make sure the buckling stress is not reached on the column core (area 1), and still need to provide ties to tie all parts together. But I wonder why you want to do this?

 

[ramihabchi]

@retired13 for wall I assumed that shear stresses in the wall will make the left part attain plastic range,and before it ashieve failure it would have released the stresses into the right part of the wall because at plastic range where displacements are not restrained anymore the stiffness of the right part will do the job and therefore resist by itself the shear loading.correct me if I am wrong.
As for column it is a general question.It also help me understand if I could prevent the left part of the wall from resisting compression.thank you.

 

[r13]

Plasticity will only occur in ductile material, such as metals; plastic design is based on the full cross section has stressed beyond yield, along with large deformation. Does concrete posses such property and behavior, you need to examine your concept on plastic behaviors.

 

[johnie134]

get a software for arbitrary structural cross section analysis to do that in seconds!

 

[BAretired]

In the case of the column, there is no way to prevent parts 2 and 3 from taking compression.

In the case of the stepped wall, there is no way to prevent Part 2 from taking shear in accordance with its shearing stiffness. Part 1 can be designed to take all of the shear, but Part 2 will be displaced accordingly and will likely crack; cracks may be ameliorated somewhat by adding a modicum of reinforcement.

BA

 

[r13]

Yes, BA is correct, if the parts of the column are casted in one pour. However, it is possible to make parts 2 & 3 as architectural columns without sharing the axial load. But I wouldn't want to discuss it further for it's an unconventional application.

 

[dhengr]

Ramihabchi:
It seems to me that you should be able to accomplish what you want, but it is a bit unorthodox. And, your problem and reasons for this need are not well defined/explained. For the column, I would put a piece of 1x4 pine board, wrapped in plastic, in the bottom of the form and at the top of the pour at each of the small areas 2 & 3, to form a conc. void under these areas. Then, remove the plastic covered wood when stripping the forms, and fill the void with backer-rod and caulk. You should still not ignore that these small conc. areas will see some stresses/loads away from the voids at the top and bot., and provide some reinforcing accordingly. For the walls, cast the two wall sections with a wide control joint btwn. then and caulk it so the two sections can move semi-independently. The two wall sections will still take lateral loads in proportion to their relative lateral stiffness. But, the drastic change in section and any difference in strength/stress/movement, will at least be separated. This is just a slight variation on what I believe has been mentioned above.

 

[ramihabchi]

Does the minimum reinforcement given for walls in codes,example in aci 21.9.2 0.25%,guarantee a ductile behavior of wall?if so,providing minimum reinforcement in the left part will do the job.

 

[BAretired]

Does the minimum reinforcement given for walls in codes,example in aci 21.9.2 0.25%,guarantee a ductile behavior of wall?if so,providing minimum reinforcement in the left part will do the job.

Concrete is not a ductile material, so minimum reinforcement cannot guarantee ductility, but will help to reduce crack width by spreading the cracks out (more cracks of lesser width).

BA