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Civil Engineering/Thickness of PT Slab

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Expert: - 4/2/2010


Question
Hi Arshad,

Thank you for your answer on the economics of PT V RC system for long span.

Even though my sense tells me this correct also, my engineers tells me otherwise after they have carried out an analysis using the PT design software "Adapt".  From Adapt, PT is shown to be more economical.  I am however new to the design of PT and I do not have much experience in this respect in the design so I am at a loss.

Have we missed out anything critical in the design?  We are located in a region requiring us to design for seismic loads, does this make a difference to the thickness of the slab.  I am aware vibration is critical but will it be critical for my case where a slab thickness of 225mm is considered with drop panels.

Our loads are also comparatively heavy with SDL=4.4kPa and LL=5kPa and 8kPa.  Span between column being 10m.

Your opinion on this would be of great value.

Thanks and best regards,

Marcus

Answer
Hi Marcus,

If your Adapt design is showing thickness and rebar, you also ned to take account of the costs of the strands and the actual prestressing or post-tensiong activities/costs.

If your building is high-rise, and seismic loading is significant, then flat slabs cannot contribute much to lateral stiffness. However, if you use down-stand beams framing from core walls to columns, then you can use a very efficient dual system for lateral stiffness. Also, if the RC leads to lighter self-weight, that will reduce seismic loading. Possibly these two aspects could sway the decision between the two options?

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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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