Different Base shear in each direction in ETABS for ELF system

WAAM · Apr 22, 2021

Hi Guys,

How Could you match Base shear in each direction in ETABS for equivalent lateral force system? here is a screen shot of etabs model. my base shear is different in each direction. I am only using one Lateral force system and that is concrete shear wall with R=5. the Base Shear should be the same in both directions.

JoshPlumSE · Apr 22, 2021

What's the period in each direction?

ASCE-7 has eqn 12.8-2 which is NOT dependent of T:
Cs = Sds*I / R

However, you also have eqn's 12.8-3 and 12.8-4:
Cs = Sd1*I / (T*R)
Cs = Sd1*TL*I / (R*T^2)

So, period can certainly come in to play. At least with the US codes. If you're not using ASCE-7, you should tell us what code you're using.

WAAM · Apr 22, 2021

I am Using ASCE 7-16. See the attached Seismic loading screen shot. Eq. 12.8-3 and Eq. 12.8-4 doesn't Control. THE PROGRAM IS USING A PERIOD OF 0.306 SEC. IN ONE DIRECTION AND 0.692 SEC IN THE OPPOSITE DIRECTION. BUT THE PERIOD SHOULD BE THE SAME FOR BOTH DIRECTION. IT SHOULD BE CALCULATED FROM THIS EQUATION Ta =Ct*hn^x. ISNT IT?

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Different Base shear in each direction in ETABS for ELF system

WAAM

Structural

JoshPlumSE

Structural

WAAM

Structural

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