Shell Stiffness Modifiers
Shell Stiffness Modifiers
(OP)
To All
As per ACI code, the initial stiffness modifiers are to be assingned for wall/slab/column/beam structural elements.
Slab - 0.25 Ig
Wall - 0.70 Ig
Beam - 0.35 Ig
Column - 0.7 Ig
In ETABS
Slab -> Assigned with shell element -> M11, M22 & M12 as 0.25
Wall -> Assigned with shell element -> f11, f22,f12 are related to in-plane forces.
Do we need to apply 0.7 factor to f11, f22 & f12 (axial & shear area) ? M11,M22 & M12 are insignificant since they affect out of plane bending forces.
Please clarify this point.
Thanks
Murali G
As per ACI code, the initial stiffness modifiers are to be assingned for wall/slab/column/beam structural elements.
Slab - 0.25 Ig
Wall - 0.70 Ig
Beam - 0.35 Ig
Column - 0.7 Ig
In ETABS
Slab -> Assigned with shell element -> M11, M22 & M12 as 0.25
Wall -> Assigned with shell element -> f11, f22,f12 are related to in-plane forces.
Do we need to apply 0.7 factor to f11, f22 & f12 (axial & shear area) ? M11,M22 & M12 are insignificant since they affect out of plane bending forces.
Please clarify this point.
Thanks
Murali G





RE: Shell Stiffness Modifiers
RE: Shell Stiffness Modifiers
You are correct. But in shear wall, the be section will undergo cracking due to in-plane moment.
How to assign stiffness modifiers for this condition? f11, f22 & f12 - 0.35Ig. But there are also related to axial stresses.
How to go about?
Thanks
RE: Shell Stiffness Modifiers
RE: Shell Stiffness Modifiers
RE: Shell Stiffness Modifiers
Once you change the m22 modifier, the load is going to be transfered in X direction i.e along local axis 1. Please let me know what is your point here.
Hi WillisV
For serviceability studies, lower factor 0.7 crack factor would be ok. But for ultimate state (design purpose), 0.35 would be appropriate.
Please explain with respect to ACI 10.11.1
Thanks
Murali
RE: Shell Stiffness Modifiers
RE: Shell Stiffness Modifiers