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There is no lower limit for T but there is an upper limit for Maximum V, so even if the time period calculated by ETABS is significantly lower than Ta, code provisions for maximum base shear would govern and the calculated value of T would be ignored. Similarly, no vertical distribution of force would take place for a small time period hence your design would still be in reasonable FOS limits.

Correct like you said above. Thanks.

The interaction of frame and shear wall would be considered in the first model with full V. Second model is to check frame only. Thanks.

Do you mean "There is no need to use the value of time period that is LESS than Ta" or "NOT LESS than Ta"? As you quoted FEMA 451, it says Ta is lower-bound limit (more conservative for base-shear as T-computed would be higher) CuTa is the upper-bound limit (can be ignored for drift calculations) But, There is no guidance on if T-computed is less than Ta, not even in ETABS manuals. All the documents highlight the upper limit but not the lower one. For example, consider a bearing wall building, (density of walls/floor is large), T-computed is ~ 0.10s, however Ta=0.5s; huge difference. ETABS only checks the upper limit (lets say 1.0s) and not the lower one and selects 0.10 automatically and calculates base shear for this T. However, if I am getting you right or as per; 2009 NEHRP Recommended Seismic Provisions; Chapter 4, page-41, it says; if T-computed is less than Ta, then use Ta. https://www.fema.gov/media-library-data/1393888487069-c071850c3050c34da135376baa478a1b/P-752_Unit4.pdf Please shed some light on this issue.

For the exact quote, Google SK Gosh Associates and start of this quote. The statement reiterates the basis of strength design earthquake design being followed. Read the codes that you are using. They all refer to strength level earthquake forces. Thanks.

Is it from some document? Kindly give reference. I would like to study more about it. thanks.

Kindly explain for what purpose? Because for seismic drift, @Rana Waseem sir has explained only seismic CASE should be used. instead of Ex or Ey with any combination.

Dear waqas, Calculation of Ie for live load only doesn't make sense as live load will always act on the section after the application of dead loads and will act simultaneously with dead loads. Therefore , Ie must be calculated for possible combinations that could be 1.0D,1.0D+0.5L & 1.0D+1.0L as per ACI-435. Detailed calculations of deflection for 1-way NP flexural members as per ACI 435 is shown in attachment.

Here are the SDS and SD1 Values for Islamabad, Karachi, Lahore & Peshaware.

What do the local building authorities follow. If you are in Pakistan, you should go with UBC. Its pretty straight up. Make combos as per the article and use EQx and EQy at 5% default eccentricity. If you have an unsymmetrical building, you will end up with 4 earthquake cases. EQx + 5%y EQx - 5%y EQy + 5%x EQy - 5%x I cant open the link in the above post by Rana, so I cant comment on his post. IBC has a supplement, for different countries where they have given the values of SDs and SD1. I will look up at my documents. If I or Baz find it, we will post it.