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Civil Engineering/estimate:how to optimise steel rebar

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Question
Im am a young engineer about to enter the industry of constructin residential houses.

My question is regarding estimating steel bars.

Usually as i understood, if a footing for example requires 10-3.00m bars,and if the standard bar size is 6.00m, we can easily compute the no. of required bars for say all of the footings. But my problem is in excesses, since not all designed bar sizes are acutually "exact". To elaborate: of 20mm bar needs only a length of 3.9m,and the standard size of bars is 6.00m,then there is an excess of 2.1m. If the structure doesn't really need that much 20mm bars, what happens to those excesses? do they become waste?which would just turn as losses for the company..

Suppose there is a given design, is there a systematic way of estimating to reduce these "excesses" to zero wastes? kind regards

Answer
Hi Nords,

Your questions are very relavant for the sake of optimisation and economy. The normal length of rebar is 12m, but you could also assume 6m.

The best way to economise is to use full lengths of rebar when detailing, or fractions of that, so that the wastage is minimised. But even if there are off-cuts, sometimes these can be used for making links (for smaller diameters), or as spacers (between large diameter bundled bars in beams), so if the contractor is clever he can keep wastage to a minimum.  

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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: 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.

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 •2013: IEK International Conference, Kisumu, Kenya

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 2010)

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