Civil Engineering/Error in RSA


Spec X & Y = 0
Spec X & Y = 0  
Dear Mr. Khan,

I am having a problem in the seismic analysis of a tower I am modelling on ETABS. Actually I want to do a dynamic analysis of the building so I am using the Response Spectrum Analysis. However the summary results show that the analysis was not done correctly. In fact the earthquake forces of the dynamic analysis shown in the attached picture as "SPECX" and "SPECY" are equal to 0. I guess the modes are not being taken into consideration although I am making sure the number of modes I am setting is big enough to reach 90% of the total mass.

Thank you for your time,

Hi Farid,

It is difficult to say why you have this problem. Check these

1. Have you defined the EQX and EQY parameters and done the static EQ analysis first?
2. have you defined the mass source?
3. have you defined the RSA functions and the RSA load cases?

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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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