shear wall stiffness modifiers

[monchie]

Hello,

I came across on how to adjust SM of shear walls,pls. see below;
"Typically I initially assign a 1.0 factor to f11, f22, and f12 along with a 0.01 factor to m11, m22, and m12 (so that the shearwall essentially has no out of plane stiffness and acts as a classical in-plane only resisting element). I then run the model and check axial stresses against the modulus of rupture to see if the assumption that the wall is uncracked (f11,f22,f12 = 1.0) was correct. For those portions of the wall that are cracked, I reassign with the lower 0.7 crack factor to f11,f22, and f12.”

My questions above are the following;
1. “I then run the model and check axial stresses against the modulus of rupture to see if the assumption that the wall is uncracked (f11,f22,f12 = 1.0) was correct. “
1.1 How will I do this in ETABS? How will I know if the wall is cracked or uncracked?
1.2 What values I will use in checking axial stresses(Load Cases or Load Combination)?
1.3 Where can I find the values for “modulus of rupture”?

 

[Agent666]

1.1 check the moment at which the wall section cracks (for example when the Tensile Strength at the extreme tension fibre is exceeded).

1.2 usually whatever the gravity part of the seismic load case is for your code. For example in my local code it's G+0.3Q (plus lateral seismic load).

1.3 should be covered in whatever concrete code you are working to. Usually it's something like 0.5 sqrt(f'c) or similar (0.5 might vary depending on code)

The 0.7 factor you quote is often a fudge/average, and will in reality vary either depending on code, level of axial load and the reinforcement ratio.

 

[AbhiCrux]

Hi. The code I use has a modulus of rupture as 0.7*sqrt(f'c).

Now I have a shear wall modeled in ETABS, which has a f'c of 30 Mpa, so modulus of rupture = 3.83 Mpa.

To check if the shear wall is cracked/uncracked, what is the shell stress that i need to check in ETABS?

If I am right, it should be S22? If the shell stresses in S22 crosses 3.83 Mpa, the shear wall section is cracked.

Please correct me if am wrong.

 

[Trenno]

AbhiCrux, yes you're correct. You may need to refine your mesh to increase the accuracy of where you deem the wall to be cracked.