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Civil Engineering/Point Load in One Way Slab

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Expert: - 10/4/2006


Question
Hi,

I search a theorical approach to design a point load in a one way slab.

Suppose I got a one way slab supported by steel joist at each five feet. If I got at midspan a concentrated load of 3 kips on an area of 4 inches by 4 inches. To calculate the flexural capacity of my one way slab, was is the width that I can pick to compute my Inertial moment ? Personnaly, I know that I can pick 4 inches because at less 4 inches width will work again the load. But, I want to know if I can pick more than 4 inches for the width because logically more than that width will work again this load.

If I can pick more, what is the width in that case that I can take. Some engineers say to me to start at the load and to return to the joist with an angle of 45 degree. In that case, that means I will got a width of 60".

5 ft = 60 in
Point Load at Mid Span = 30 in
Point Load of 4 x 4 inches than we got a 28 inches free distance to the joist.
45 degree of Each Corner Give 28 inches.
Than 28 inches X 2 + 4 inches = 60 inches.

Thank you for trying to help me !

Jim

Answer
Hi Jimmy,

The rule of thumb for this is that you use a width of slab equal to one fifth of the span, so in your case it will be 1 foot or 12 inches. You could increase that to 16 inches to take account of the width of the load.

This will give you a conservative (safe) result. If you need to optimise, then you will have to use 3D finite element analysis.

I hope that helps!

Kind regards,

Arshad

Civil Engineering

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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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