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Civil Engineering/construction crane counterweighting

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Expert: - 4/20/2005


Question
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Followup To
Question -
Construction cranes seem to all have a big "box" hanging from their back ends-- is this the counterweight?  It never seems to move, so how do the cranes compensate for loads of varying weights?  Are there other moveable weights not so visible from the ground?  Does the cab get moved to compensate for the weight on the boom?
Answer -
Hi Bruce,

Yes, that is the counterweight and it is calibrated to balance the median of the max and minimum load at the boom end. The intermediate loads are taken by the tower in bending, which is why normally these towers are braced against the building as they rise with construction.

There are some more sophisticatd cranes that do have sliding counterweights as well.

Hope that helps!

Kind regards,

Arshad

Hi, Arshad,
    Thanks for your quick response.  I am talking about the big cranes that appear to be free-standing some distance from the building, sometimes nearly the length of the boom arm away from the building.  I want to know just HOW the counterweight works.  If the box/counterweight does not move, then how can it be calibrated to compensate for a load?  I'd think that to counterweight some of those huge beams they would have to have a huge weight in there.  And if they DO have a huge weight in there, why doesn't the whole thing fall over when they are NOT lifting a load?   
        Regards,
         Bruce

Answer
Hi Bruce,

Well you are quite right- such cranes would topple over if they did not have travelling counterweights (or a cable stay at the back which is connected back down to the base).

So I reckon the ones you are talking about must be ones as described in the website below.


http://www.towercrane.com/K-10000_tower_crane_10_00.htm

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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