Civil Engineering/WIND LOAD DRIFTS

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Expert: - 12/9/2011


Question
QUESTION: Dear sir,
I want to inquire about the drift limits in codes. FOr example in UBC-97, drift limits are based on earthquake design criteria; time period and R factor. My concern is if i have a building where only wind loading occurs, what limitations i will check? I do not have any seismic loads on my structure, only wind.

ANSWER: Hi Waseem,

Wind drift limits are similar to those for seismic, except that there will be no R factors, so you will compare the drifts from service load wind loads with the usual H/500 to H/400 limits set by different codes. The same applies for inter-storey drifts, to prevent distress to cladding and internal partition walls, etc.

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

QUESTION: Dear sir what does it really means?
"PROBABILITY OF 0.05 of being exceeded"?

I am copying text from ASCE commentary

" The load combination with an annual
probability of 0.05 of being exceeded, which can be used for
checking short-term effects..."

Please explain in simple language...Thank You

Answer
Hi Waseem,

This is the usual statistical probability used in most codes- for example the acceptance of 28 days cube strength is also based on the probability that only 5% of the results would fall below the specified strength.

So, it is the same with wind loading- take it as being the acceptable wind loading for normal design purposes, rather than the extreme case where you may want to design for a 1 in 10,000 year wind loading, etc.

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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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