Plate in RISA and reinforcement for it 2

[whymrg]

I modeled shear wall with openings in RISA as number of concrete plates. I got results as plate forces and stresses.

How can I determine required reinforcement based on this information?

Thanks for help.

 

[ishvaaag]

For your application you will be getting mostly uniform stresses along the thickness of the plates. The concern, as long the concrete is capable enough to stand the standing compressions, is to of course provide enough rebar to meet any tensile stresses present in the plates in the worse condition.

Hence, first locate the areas where you have such tensile stresses, in both horizontal and vertical directions. There you have to place -and in duly form beyond anchor- rebar enough to meet the tensile forces. To ascertain what is the rebar requirement, you must integrate along the thickness and width (or height) the stresses, then you have the force. Sigma x and sigma y give you this. Give also a look to the shear stresses, tau xy; if the stresses are as small as to be easily taken by the concrete, add nothing. But if tau xy cannot be assumed be resisted by the shear strength of the concrete itself, you may either integrate them along a section to give in the same way a shear requirement, that you can reinforce usually as a beam, or you can directly reinforce for the shear stress in place using shear-friction (or shearing surface) concepts. Of course being integral concrete you may be quite confident on the friction factor, between the biggest in the various tables.
So add whatever the shear stresses considerations has produced.

If you had followed in its direction the principal stresses for reinforcement, only the tensile rebars -that may be needed anyway in the 2 orthogonal directions if both principal stresses are tensile- would be needed and no shear consideration (other than any mandated in the codes) would be required. But since you are considering its tensorial equivalent in the xy directions, the shear stresses components needs be also considered.

This said, one needs not to forget in the procedure the usual understandings of the trade. That is, you preferably detail the links as recommended for shearwalls with holes, and of course try to provide regularity in the reinforcement, plus check you meet the minimum geometrical requirements for the kind of structure.

 

[JAE]

RISA also provides output of Mx, My, and Mxy which are bending moments about the axes in the plane of the plate elements.

What you do, is set up your model to ensure that your local x and y axis all are oriented in the same directions. Get your graphical output (colored contours) for the three moments.

The design moment is the factored moment Mx + Mxy in one direction and My + Mxy in the other.

 

[fleisher]

If you are going so far with a computer software, you should think of purchasing one that can give you an estimate of the reinforcement as well. Our copy of RISA does not do concrete design. We use STAAD and/or SAP to do that. Shear walls are relatively simple (as long as you don't have to consider seismic), but still, it might be worth taking a look at it.

 

[ishvaaag]

JAE

for the particular case of a shear wall it won't have very significant flexure of any of the component plates. Hence reinforcing using the moments won't represent properly the rebar needs. I directed my answer to the stresses that may be significant to the case.

Your comment more readily applies to models where the plates are components of slabs mainly subject to loads orthogonal to the plane of the plate, where bending is very significant, i.e., mats, floors or roofs. But loads for shear walls use to come in the plane of the shear-wall.