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Civil Engineering/raft foundation design

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Expert: Arshad Khan - 5/4/2007


Question
Dear Mr.Arshad
I am an undergraduate student studying civil engineering in the UK.I have a task I'd like your help with.
It is supposed to design a raft foundation (in fact it is more of a ground floor slab) to retain two flour silo's of total weight 70 tons on an industrial road where loading and unloading of heavy vehicles takes place all the time.The slab is of 36 square meters area,  to be filled with reinforced concrete ,what is the recommended depth that should make the slab capable of retaining the imposed loads ?
Thanks a lot for aid
Best Regards

Answer
Hi Hachem,

This is a problem of soil-structure interaction, whereby the strength/thickness of the slab is dependant on the ground conditions. Assuming that the supporting ground is good and that you provide compacted hardcore for the top, say 300mm, then the slab of 36m2, say 6m by 6m would need to be roughly 600mm thick, with top and bottom rebar each way- without doing calculations, I would reckon the rebar would need to be about T20 or T25 at 200mm spacing.

However, as I said, a lot depends on the supporting strata and also on the pattern of loading on the slab.

I hope that helps!

Kind regards,

Arshad

Civil Engineering

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Arshad Khan

Expertise

I can answer any questions to do with 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: 35 years in Construction and consultancy in the UK, Kenya, Tanzania, Uganda, Ethiopia, Eritrea, South Africa, Somalia, Austria, Bahrain 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 .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 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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