Whereas if you modify m11 or m22, you will have D*(0.7*t)^3/12 or W*(0.7*t)^3/12 as stated by ETABS manual. This means that for a wall WxDxt (length x depth x thickness), for f11=0.7 you will have an inertia of 0.7*t*D^3/12, and for f22=0.7 an inertia of 0.7*txW^3/12. The m11, m22 and m12 modifiers are essentially equivalent to modification factors on the thickness3 of the shell element."įor what I understood, if you modify f11 you are modifying the thickness (only for stiffness calculation) of the wall for the face perpendicular to axis 1, whilst when modify f22 you are modifying the thickness of the wall for the face perpendicular to axis 2.
Descargar etabs 9.7.4 manual#
RE: ETABS 9.7.4 - Wall stiffness modifiersĪccording to ETABS manual and ATKINS manual, " The f11, f22 and f12 modifiers are essentially equivalent to modification factors on the thickness of the shell element. You would modify vertical stiffness (F11) for spandrels/beams in shear walls because the vertical section is what is resisting the bending moment. You would modify horizontal stiffness (F22) for piers in shear walls because the horizontal section is what is resisting the bending moment. To accomplish this, you'll need to modify the axial stiffness factors of the shell element.
Descargar etabs 9.7.4 crack#
You'd be more interested in making sure crack factors are applied to rotation about the X axis, because those are the forces the shear wall will primarily be resisting. Which isn't really what you're interested in because your shear wall isn't typically used to resist forces out-of-plane. If your shell element is in the YZ plane with X pointing out from the plane of the shell, M11 and M22 (bending modifiers for the shell element) will affect bending about Y and Z axes.
Descargar etabs 9.7.4 cracked#
I will often apply them anyways because if your wall is cracked in plane, it'll be cracked for out of plane as well and I don't want to be attracting more moment than I should (even though it's not much). M11 and M22 are out of plane bending moments.
RE: ETABS 9.7.4 - Wall stiffness modifiers chekre (Structural) 26 May 13 05:42
So, to take into account cracking for shear should I modify f12? and what is the value? 0.7 uncracked and 0.35 cracked?Īnd for out of plane shear v13= v23 should I use 1 because the shear within the thickness is neglectible (that’s why ETABS doesn’t allow me to change it)?įurthermore, just thing if I decide to use a membrane element, which means m11= m22=0, what should be the values for the other parameters? what do you usually use, and where/how did you get them? And what about m12=?Īnd what about f11= f22=? I believe I should use 1 to account elastic shortening correctly. Is it a mistake or am I missing something?Īccording to ACI318 and ATKINS I should I use m11= m22=0.7. If F11& F22 are axial forces, why in CSI website Link is stated that f11 controls EI? EI is obviously related to bending (so to m11&m22), whereas f11=f22 control EA (axial behavior), and f12 controls GA (in plane shear behavior). Shear v23 modifier (supposed to be out-of plane shear)Īnd in CSI Analysis Reference manual at p.144 is specified that F11& F22 are axial forces along axis 1&2, F12 is shear within plane 1-2, M11& M22 are bending moments out of plane, and M12 is torsional moment, and V13& V23 are transverse shear out of plane, according with what I have written above. Shear v13 modifier (supposed to be out-of plane shear) Membrane f12 modifier (supposed to be in-plane shear)īending m11 modifier (supposed to be bending moment about axis 1)īending m22 modifier (supposed to be bending moment about axis 2)īending m12 modifier (supposed to be torsional moment about axis 3) Membrane f22 modifier (supposed to be axial force along axis 2) Membrane f11 modifier (supposed to be axial force along axis 1) In wall's ETABS table is required to specify: I read a lot about stiffness modifiers for shear walls (CSI website, ATKINS manual, Eng-Tips forum threads.), but I have some doubts about what they report because they say different things, and they look different to what is required by ETABS.
Hi everybody, please help me cause I'm getting frustrated with all these different explanations!
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