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Civil Engineering/stair supporting beam construction

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Expert: - 12/7/2009


Question
QUESTION: Dear Arshad Khan

The question I had was on the procedure of the construction of the beam supporting the intermediate landing of a beam. The procedure that has been done till now is as follows. First they fix the reinforcements of the columns and beams. The part I do not approve of is that the columns are filled with concrete first to a height of 2.9meters. This is done while the reinforcements of the stair beam are hanging out from the midheight of the column. Then the beam is casted with concrete after the formwork and reinfocement of the stairs are complted, which could be three or four days later. What I want to understand is if there could be aproblem at the joints?

Thank you

ANSWER: Hi Tesfaye,

This is a perfectly acceptable sequence of construction. All you need to do is prepare the face of the column against which the stair beam will be cast, by scabbling the surface (to expose aggregate) and to to apply a cement slurry just before casting the stair beam.

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stair beam construction
stair beam constructio  
QUESTION: I would like to thank you for your quick response. There is this one thingI would like for you clarify. And it is if the beam casted after scrabbing and adding cement slurry is as strong as the monolithically casted beam, specially at its joint. This I am very skeptic because of the high amount of shear force.
Further I have attached an image to clarify this.

Thanks

Answer
Hi Tesfaye,

I principle your gut feeling is correct, but in practice the method I have mentioned is commonly used and is adequate for shear so long as aggregate is exposed and the surface prepared. If you want a more positive connection, you can ask that a say 25-40mm deep recess be formed within the concrete cover of the column (by using say a block of expanded polystyrene, stuck to the column formwork) which can be removed before scabbling the recessed surface and casting the stairs beam.

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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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