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Civil Engineering/ETABS modelling - Differential settlement

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Expert: - 10/10/2010


Question
Salam,
When you have tall tower, it is obvious that the columns will be subjected to the differential settlement due to axial shortening ( creep, shrinkage, elastic).
Due to this, whether etabs will take into the account of this settlement or manually, we have to assign the settlement in each columns at every floors? please clarify.
Or if we do the sequence analysis, does it consider the differential settlement?

Answer
Hi Firdows,

ETABS will only take account of instantaneous elastic shortening, so for any buildings above about 30 storeys you will need to do other calculations to ascertain long term shortening due to creep and shrinkage.

By doing staged construction analysis, you will arrive at a more accurate estimate of elastic shortening due to vertical load, as that takes account of correction of cast levels at each level(or at every 5 or 10 levels), so that you can then further refine by ascertaining the effects of long term creep and shrinkage. There are some papers/books written about this such as by Mark Fintel- see below:

http://openlibrary.org/books/OL2556632M/Column_shortening_in_tall_structures

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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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