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Civil Engineering/Moment Redistribution

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Expert: - 9/17/2011


Question
Sir, At last floor column have more monents. can you please explain me about Moment Redistribution?

Thanks,
Sirisha.

Answer
Hi Sirisha,

Moment re-distribution occurs when you have high support (hogging) moments in beams and low span (sagging) moments at or near midspans. This then causes some cracking in the concrete at the supports (both elastic as well as long term creep/plastic), whilst at the same time the rebar strains (elongates). This has the effect of reducing the beam section stiffness at the supports and a reduced internal moment. In order for the beam to remain statically stable, the additional moment shifts (re-distributes) to the span. Codes usually limit the maximum re-distribution to between 15-25% of support moment.

Once the beam moments are re-distributed, obviously that would also reduce the moments at the tops of the supporting columns, unless the beams are continuous over internal columns, in which case the reduction of moments at tops of columns would be minimal.

Moment re-distribution should only be applied to moments caused by garvity loading, not due to lateral wind or seismic loading.

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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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