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Civil Engineering/Concrete Strength

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Expert: - 1/7/2010


Question
Top five floors of a 11 story building are to be removed / demolished, what would be its effect on remaining building (concrete strength). Hammer men are using hammers of 11 kg from a man height of say 6 ft, surface area of hammer striking concrete is 3"x3" = 9 sq.in. The grids are 18'x18' with column size of 2'x2'.  
What could be the force / stress produced due to hammer %26 its resultant effect on concrete, bond, steel. Can we work it out mathematically.  

Answer
Hi Saeed,

As all the live-loading for the upper 5 storeys will not be in place, the columns/shear walls below level 6 should have ample spare capacity to support the loading due to hammering- so long as large pieces of debris is not allowed to fall on to the floor below.

There are formulae to work out the impact loading you refer to, but this is outside my expertise.

I would suggest that you carefully examine the columns and walls below the last demolished floor for any signs of concrete spalling/cracking. If there is none, the structure should be safe.  

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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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