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Civil Engineering/Earthquake Drift Limits

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Expert: - 1/18/2012


Question
QUESTION: Dear Sir,
IN ASCE - 2005 commentary, the drift combination is defined for WIND as D+0.5L+0.7W (0.7W to reduce from 50 yr to 10yr return period for serviceability). I want to ask what combination we will use if there is also EARTHQUAKE. We will still multiply E with 0.7 to get the same combination for drift?

ANSWER: Hi Waseem,

No, earthquake loading is usually unfactored, so you can not reduce for that, However for serviceability drift limits, you can reduce by a factor related to the R value used for ductility- this aspect is covered in the codes

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

QUESTION: Thank you so much sir for information. Can you also please mention that factor by which we can reduce the E and after reducing E, in which combination i will put this reduced E? D+0.5L+(Reduction Factor)*E ??

Answer
Hi Waseem,

Normally you do not apply the reduction factor in the combo, but look at the output drifts and then apply appropriate factors to see if they fall within limits. The factors depends on some variables- please refer to UBC-97 clause 1630.10 and also the website below:

http://www.structuremag.org/article.aspx?articleID=756

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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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