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I accidentally came across these useful case studies, which, I would like to share. You can use them if you are working on a commercial or residential building retrofitting project. These case studies provide insight about seismic retrofitting and also on analytical methods, that are used for building assessment. I would also like to give due credit to people who are involved in these studies. All these studies were performed under a US-Pakistani Joint Cooperation Project. The details for the project are. 6-Storey Mixed Use Building in Karachi.pdf 10-Storey Office Building in Karachi.pdf RS-4 Storey Academic Building in Karachi.pdf Five Storey Residential Apartment.docx

See the code e.g. UBC-97 to calculate amplification factor Ax. Max Ax = 3.0. This Ax you will multiply by 5% (0.05) and input in response spectrum cases/static earthquake cases. To calculate Ax, you need maximum and average story displacements at CM. You can export this data from ETABS Tables to EXCEL for static earthquake cases (Don't use spectrum cases for this). Once in EXCEL, you will see column named 'Ratio'. This will be Max/Avg displacement. Sort this out to find values more than 1.2. These are the locations you need to amplify torsion. After checking which stories you need to amplify torsion in, use the amplified torsion value for e in response spectra cases.

And while doing so you need to check the torsion for building plan also, Wall location should be carefully decided.

See ,from your post what I understood is that you are providing one shear wall along X-axis. And I mean that instead of giving that one BIG shear wall give 2-3 at different locations in that same along x-axis. (location shall be decided considering the architectural restraints).

Very good discussion indeed. I would like to add one more point, it is not necessary to add only one shear wall in x-direction and get larger dimensions of it. Instead you can add multiple (2-3 based on your lateral stiffness required). This could share the forces and hence reducing dimensions and make your client happy. 🙂

Please check ASCE 7-05, Chapter-12.

Hello, Well as you said as per dimensions of the plot that X direction is smaller, it becomes necessary to add shear walls in X direction as it is critical in that direction during seismic analysis. Regarding the system you have asked you can provide core wall around the lift and staircase and columns, however you have to see which zone the plot is located. if it is till zone 2B then i think this system is acceptable as you can have high response reduction factor value. Also even if you are using walls you can reduce the size of walls in terms of thickness as well as length as you go to higher stories. This reduction also should be done in a reasonable manner. There is also another system of haunch girders which could be economical and can be used in zone 3 or 4. There are many systems also like frame tube system or shear wall frame system etc. which could be economical. Thankyou, Regards, Areeb Ahmed.

ASD is an older method that is still practised by a lot of mechanical engineers to size pressure vessels and tanks. However, for structural engineering, everywhere, LRFD is used. Here is a detailed answer I read once somewhere on the internet and saved it as it was very interesting.