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Civil Engineering/sizing structural materials of a deck

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Expert: - 9/29/2008


Question
Hello dear Expert,

In order to use rainwater collected from my roof for household and garden purposes, I need to store it.  That's where the difficulties show up!
The idea is to store it (up to 10m3) in a PVC textile bladder (sold in these parts (France)) which is to be positionned under the rectangular, wooden deck I want to build; it  will then have to span over this 4*5*0,8m bladder.
My question is: how to size the structure of this 4*8m deck so it will behave like a deck rather than an elastic trampoline? Let's say deflection should be less than 1cm at its center. All wood? Steel H- or I-beam + wood? What sizes
-the deck is to be anchored on my concrete house along its length, and on cinder-block "pillars" along the other sides
-its height above the natural ground (quite tough schist) is 1m or less
-I expect max load 20people around dinner table (2T over a 6m2 table).

Thank you very much for any pointers help in this problem


Answer
Hi Joel,

Due to liability reasons, I cannot perform a design for you but merely give advice.

I would imagine that for a 4m by 5m deck (or is it 4x8m?- if it's 8m, then the main beams should span the shorter distance-i.e. 4m), you could use timber beams with timber planking for the deck. To control deflection, you need to have the main beams at least 250-300mm deep for the 4m span(by possibly 75mm wide) and at a possible spacing of between 600- 900mm and with the timber decking of some 30-40mm thickness.

This is based purely on my engineering judgment without doing any calculations. I would suggest you seek some advice from a local contractor as well about cost of materials, as steel beams would be smaller but may be more expensive.  

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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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