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Expert: - 1/8/2005


Question
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Followup To
Question -
Hi
I am Stephanie, a first year university student (not enrolled in engineering though). I came across recently a civil engineering problem, and as I know nothing of the field did not know how to answer it. I was hoping you'd be able to help me find the answer, and how I would go about it.
I even asked before you a friend in engineering and he wasn't even that far advanced to answer it. By the way this is NOT for any assignemnt. I just found this on a website and am curious to how you get the answer.
There was a steel beam 50 feet long. There was a 6000 pound weight in the center of the beam. Assume the modulus of elasticity is 29,000,000 pounds per square inch, the moment of inertia is 850 inches^4, the beam has simple pin connections at either end, and all loads other than the weight of the crew are disregarded.
How much will the beam deflect?

Hope you can help. Thank you very much!:)
Answer -
Hi Stephanie,

This one is easy as pie!

The deflection formula for a simply supported beam with pin supports is: PL^3/48EI

Where P= load, L=span (raised to the power 3 i.e.cubed, or LxLxL), all divided by 48 times E=modulus and I= moment of inertia.

Hope that helps!

Kind regards,

Arshad

Hi Again.
Thank you very much for explaining, but I still am a bit confused.
Would the formula with the numbers in the question I gave be...
(6000)(50^3)/(48)(29000000) (850^4)?
I am confused about the statement, 850 inches^4.
If you could please help me again with this, otherwise I understand, I am just having trouble putting the equation together.
Thanks.
Stephanie

Answer
Hi Stephanie,

Yes, you have the calculation correct, except that you have to have consistent units, so first convert the 50 feet to 600 inches, and then you do not raise 850 to the power of 4. The answer is 1.0953 inch deflection. If you are not sure of a formula, check the units to see that the ones above the line divided by the ones below the line results in the correct units for the expected answer- in this case the resulting unit should be inches.

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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