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Civil Engineering/about slab and secondary beam


sir namaste .iam student from nepal. i like your answer giving technique. Sir we doing a project of multistorey building . and we had design a slab of thickness 320 mm for each floor ( 6m * 6.5m). the question i want to ask is that is this thickness is not more for slab . Is it necessary to put secondary beam or not? please clearify    sir . iam confused.
1.what are the criteria to put secondary beam in building? sir.
thanks sir .

Hi Rajesh.

For a span of 6m x 6.5m, a continuous spanning slab between beams should not be much thicker than 200mm, so your proposed 320mm will be too heavy, especially for a multi-story building.

Secondary beams are used when there is a requirement to reduce the amount of materials (and weight) for a slab- in your case you could reduce the slab thickness to 125-150mm if you introduced secondary beams half-way between your 6.5m span beams.

The disadvantage of secondary beams is that they require additional formwork and so slow down contruction speed and may also hinder free distribution of services (cables, ducts, etc)

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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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