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Civil Engineering/design of strip foundations

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Expert: - 11/3/2008


Question
QUESTION: l am an undergraduate student in civil engineering. Al am currently on industrial training , l have been given a task to design a foundation for a double storey town house, my problem is the value of imposed load on the foundation , the building is roughly 6m high with a dead load of 72KN from my calculations and l am doing this manually as part of the learning process. also l need to know a basic idea on how to go about the design.

ANSWER: Hi Noreen,

Without knowing the plan dimenisons, it is difficult to confirm figures, but on average a building weight (total) will be about 15 kN/m2 per floor, so for a 2-storey building plus roof it will be about 15+15+10=40 kN/m2 (unless the ground floor is supported directly on the soil).

So, if you have a foundation supporting say 6 m span of slabs, the total applied laod will be about 40x6=240 kN/m.

So, if the soil can support say 200 kN/m2 as safe bearing capacity, then the strip footing will be 240/200=1.2m wide, and you should make it about 250 to 300mm thick.

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

QUESTION: the dimensions of the slab are 11200 by 8600 the slab thickness is 170 also the slab is resting on the wall therefore l hope you can give me a more accurate estimate. how do l check for the shear.

Answer
Hi Noreen,

Ia m afraid that this still does not give me sufficient info, but based on my previous answer you should be able to work it yourself. Shear can be worked out bt taking the load on one side and dividing by the cross-sectional arear of the member.

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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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