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Civil Engineering/Dynamic-Diaphragm Eccentricity

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Expert: - 12/4/2009


Question
QUESTION: Dear Arshad Khan,
I hope that you are fine and keeping good.
When i perform static analysis i define 4 type of seismic load cases
EQX + 5% ecc in Y
EQX - 5% ecc in Y
EQY + 5% ecc in X
EQY + 5% ecc in X

When doing a dynamic analysis do i also need to define 4 response spectrum cases like static analysis with + and - eccentricities or it is sufficient to define 2 ??????

I did a tutorial in which the author has defined only 2 thats why i am asking.. I dont have a good understaning of dynamic behaviour of structure.

Thanks in advance

Best Regards,
Muhammad Umar



ANSWER: Hi Muhammad,

Yes, 2 cases (in X and Y direction) in dynamic analysis are fine as each one covers both -ve and +ve direction responses.

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

QUESTION: Thank you for your reply..
Sir, I have one more question.. When i checked story shears I had Shear in Y due to EQX loading and value was significant..
now,
to check my building for orthogonal effects what is the procedure.. I think I need to define a load combination
1EQX + 0.3EQY
1EQY + 0.3EQX
Am i right.. and I believe only columns and shearwalls (if any) need to be analyzed and designed for orthogonal effects.
I havent done it before... please advice..

Best Regards,  

Answer
Hi Muhammad,

Yes, that is correct, but also ensure you have the negative direction load combinations. As for which elements contribute, this depends on your structral system- for example if you have a moment resisting frame system or a dual system, then the beams will also be contributing to lateral stiffness/seismic effects.

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Arshad Khan

Expertise

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.

Experience

Employment history: 36 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.

Organizations
.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)

Publications
•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

Education/Credentials
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 date)

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