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Civil Engineering/Support under plinth beams

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Expert: - 4/19/2010


Question

PB
In the drawings of a G +2 storey school building, it is shown that under the external plinth beams a PCC support of 1:3:6 has been built of width equal to width of plinth beam and depth less than the depth of footing. my questions are
1. that why is this support needed when already the plinth beams are resting column to column?
2. if we are using this arrangement that does this give us the leverage of resting all external plinth beams on this support rather than the columns?
3. has this arrangement something to do with the backfilling?? because I wanted to remove this PCC to cut off some cost

Regards
Saad Younus

Answer
Hi Saad,

If by PCC you mean a 50 to 75mm thick layer of weak concrete, then this is what we call blinding and it is there merely to give a flat surface to place rebar and spacers and formwork so that the beam does not get deformed or contaminated by the soil under the soffit when the concrete is freshly cast and wet. This layer is non-structural and is usually not relied upon for any support for beams that span from pad/column to pad/column, UNLESS the ground is competent enough to support the pressure, without undue settlement..

The only case where you can omit this blinding is when you use pre-cast plinth beams.

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

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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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