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Civil Engineering/clear-span load capacity

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Expert: - 4/30/2009


Question
Mr. Khan,
I am the owner of an older home which has had several upgrades performed over the years. I am now wanting to re-do my basement. The current support configuration uses 8 inch square wood beams braced/supported by the concrete floor on one end and the foundation at the other. This involves 2 sections, one on either side of an existing stairwell which is located approximately in the center of the structure. I would like to be able to install a spiral staircase and eliminate the bracing to floor in order to open up the floor space and gain more useable area. The distance between the foundation footings is about 24 ft.  The square footage of the single story living space above the basement is 1100 sq. ft. The existing beams and bracing appear to have been put in place in order to support the floor joists when the stairwell was cut in and added.  Originally, this structure did not sit on a basement.   The home was moved and sat on a different foundation which has a basement.  I would like to jack up and replace what is currently in use with 2 clear span sections of steel beam, each section being about 24 ft in length with each end supported by the foundation. Is this a feasible option? What size and style of beam would be proper to consider for this task? Thank you for any input you may provide to my question.

Answer
Hi Jim,

What you are proposing is feasible, but you will really need a local structural engineer to study the details (especially foundations) and advise you- this is too complex a problem to advise you over this forum, I regret to say.

The I-beams will need to be about 20-24 inchs deep to limit deflections over the span length of 24 feet.

The following website will give you load capacities of I-sections:

http://www.toolbase.org/Design-Construction-Guides/Exterior-Walls/steel-beam-col...

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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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