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Civil Engineering/Scaling response spectrum base shear



Dear Sir,

Hope you are well.

I would like to state that i am working on building design in which there are 6 levels below ground and 39 levels above ground.
i have define story range for static base shear calculation as roof to ground floor level ( excluding the basements).

Now i have to scale response spectrum base shear to static base shear. Base shear for SPECX case is different at ground floor level foundation level.

Which level response spectrum base shear should scale with static base shear?


With Kind Regards

Junaid Ahsan Khattak

Hi Junaid,

In the case such as yours, it is prudent to define the base for static earthquake at bottom of basement 1, rather than at GFL, as that takes account of possibly lower passive resistance of soil near the surface. Then I would suggest you proceed as follows:

1. Define supports at bottom of basment 1 and run the model for static and dynamic forces and scale as normal.

2. Then remove the supports at bottom of basement 1 and re-run the analysis.

Also, if the bottom 4-5 basements are going to be cast in soft rock, then you could insert lateral supports (with free vertical movement) at all the floor levels below say basment 2 level, as that will correctly simulate actual behaviour- otherwise your lateral sway (and forces) from lateral loading will be for a 45 story building rather than a 39 storey building.

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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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