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Civil Engineering/opening in existing flat slab


Dear Sir,
Good Day:
In one of my existing project(2B+G+6+roof),I need to  provide an opening of 1.35mx0.60m in the ground floor slab.(slab thickness 30cm).spacing  between columns are 6.0m and 4.0 m.
opening is coming at 40cm away from the peripheral concrete wall.Is this affect my slab strength.Appreciate for your quick advice.Thanks so much..Regards...

Hi Ravi,

If the opening is only 40cm from an existing RC wall that is supporting the slab, then I do not see how the columns spacing has any bearing on the issue. Depending on the orientation of the opening and the direction of span (main rebar), it may or may not have an adverse impact. You will just need to analyse and see if you need some additional trimmer bars installed (or carbon fiber strengthening around the opening).

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Arshad Khan


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.


Employment history: 40 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.

.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)

•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 •2013: IEK International Conference, Kisumu, Kenya

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 2010)

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