Civil Engineering/Punching Shear

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Expert: - 6/8/2011


Question
QUESTION: Dear Sir,

I will be grateful if you answer me my question?

Does the addition of Piles to raft reduces effect of Punching shear? My design requires almost 50% of only loads from columns to be bared by raft and rest will be done by piles.

Thank You
Sajeev

ANSWER: Hi Sajeev,

I am not sure if I have understood your question correctly, but whether you have piles or not, it will make little difference to the raft punching shear around a column, unless that column happens to be vertically aligned above a pile or a cluster of piles.

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

QUESTION: The foundation is Piled-Raft.I have in my foundation 7.5m bored-piles evenly distributed to whole raft at the spacing of 5'-0". So Beneath the columns, either there is pile aligned vertically or at its close proximity. I am getting 3'-0" thickness of raft when i check punching shear for Raft alone.

Hope you understand my question and my sincere respect to you sir for your kind prompt response..

Thank You

Sajeev

Answer
Hi Sajeev,

With the dimensions you have indicated, if the column is right in the centre of 4 piles, then you are at the limit and will have to consider punching shear. If part of your zone of influence (at say 45 degrees down from footprint of column, between top of raft and bottom of raft) falls over any piles, then you can deduct that proportion of the axial load from your punching shear calculation.

Hope you understand.

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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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