Civil Engineering/mat foundation

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Expert: - 1/11/2011


Question
sir,
How to consider the soil -raft/mat interaction as the soil is not a linear material?what about the column loads acting on the raft?that we have to take as equivalent load or moment and force at centre?Is a mat foundation, assuming to be square,is an axisymmetric element or plain strain?

Answer
Hi Rekha,

You can model the matt/raft sitting on springs (stiffness determined from ground investigations) at regular intervals and then do a 3-D FEA analysis using STAAD or SAFE or ANSYS, etc. Then you will need to do an upper-bound and lower-bound analysis, using different stiffnesses to arrive at the envelope moments and shears to design the concrete for the rebar.

The columns gravity loading can be applied as a patch load, over an area equivalent to half the zone of punching shear- in other words the footprint of the column plus additional area around the column equvalent to half the depth of the raft. The moments can eb applied at the centroid of the column, at a node point in the raft elements.

Check out this site:

http://rapiddigger.com/raft-foundation-design-example/  

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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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