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Civil Engineering/Dual System in ETABS


QUESTION: Hello Sir,

I have designed a building G+13 storeys with shear wall and beam column framing. I used R for seismic loads 5.5.

Now I need to check if this structure fulfills the requirements of Dual system which is the Moment Frame is able to resist at least 25% of the required shear force and the rest is resisted by the shear walls.

If this is the case, can I change the 'R' to 6.5 and rerun the analysis.

Thank you so much for your help on the matter.


Hasnain Khan

ANSWER: Hi Hasnain,

Yes, you can but you will need to do some special seismic detailing for the frames in order to achieve the increased ductility.

---------- FOLLOW-UP ----------


I would like to know how we can check the total base shear and then the shear resisted by columns in order to check if the structure can be designed as a Dual System.

In the meantime, I'll check what the codes say about detailing these.

Thanks for your prompt reply.

ANSWER: Hi Hasnain,

When exporting base reactions for the earthquake cases, first select all the supports (cores + columns) and then compare that with the reactions for the columns alone. Ensure that there are no basement walls that may interfere with the distribution of base shears.

---------- FOLLOW-UP ----------

QUESTION: Mr. Arshad,

I'm relatively new to the workflow of ETABS, and if you can kindly direct me exactly where to look for base reactions for earthquake cases, (of walls  + columns and columns alone), I really really am thankful of your help so far.

Hi Hasnain,

I am afraid there are no shortcuts to learning all the features of ETABS, but if you use the help menu within ETABS as well as the manuals/cocumentation, you will learn a lot. Also visit the CSI website and there are watch and learn videos as well as FAQ's etc.

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Arshad Khan


I can answer any questions to do with civil and structural engineering consultancy and construction industry in East Africa and the Middle East, and specifically with the analysis and design of reinforced concrete structures. My particular expertise is in the aseismic design and optimisation of tall buildings.


Employment history: 40 years in Construction and consultancy in the UK, Kenya, Tanzania, Uganda, Ethiopia, Eritrea, South Africa, Somalia, Zambia, Austria, Bahrain, Kuwait, Doha and the U.A.E.

.Fellow of Institution of Structural Engineers (UK) .Fellow of Institution of Civil Engineers(UK) .Member of the Institution of Engineers, Kenya .Registered Engineer, ERB, Kenya .Member of the Architectural Association of Kenya (Engineers Chapter) .Chartered Engineer (UK)

•1984: International Conference on the Art and Practice of Structural Design, London •1994: 3rd Int. Kerensky Conference in Structural Engineering, Singapore •2008: International Conference on High-Rise Towers, Abu Dhabi •2013: IEK International Conference, Kisumu, Kenya

BSc, 1st Class Hons, in Building Engineering, University of Bath, UK MSc in Concrete Structures and Technology, University of London. Diploma of Imperial College, UK.

Awards and Honors
•Science Congress Special Award (for 2-seater Hovercraft - 1968) •Institution of Civil Engineers Award for outstanding performance at Bath University (1975) •Concrete Society Postgraduate study Bursary Award (1976) •Consular Representative for British High Commission, Nairobi. (1995 to 1998) •Examiner for Institution of Civil Engineers Professional Interviews, Nairobi. (1997 to 1998) •Branch Representative in Vienna for PI assessment for Inst. of Struct. Engrs. (1999 to 2010)

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