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Civil Engineering/ribbed(hollow block) slab

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Expert: - 8/31/2007


Question
QUESTION: we are constructing a cast in situ ribbed (hollow block)slab in ethiopia for an occupation of a small hospital(g+1).we use stirups for shear resistance (8mm bar) 'u' shaped and tied with the stirrups from adjecent ribs.if we dont use wire mesh for the slab topping of 6cm,would the tied legs of stirrups be sufficient for preventing cracks.


ANSWER: Hi Belete,

No, it is best to have the mesh in the topping, otherwise the stirrups will not work and also you will get cracks in the topping.

Hope that helps!

Kind regards,

Arshad

---------- FOLLOW-UP ----------

QUESTION: thank you for responding but i would like to know if you think damage would be serious if the wire mesh is not used .
and if it is what may be done to remedy if the slabis casted without the mesh.(the slab we are talking about is the 1st floor slab and the roof slab)
ANSWER: Without knowing the loading and the support conditions it is difficult to comment further. Remedial measures would include scabbling the surface, drilling and grouting in dowels and then insertinga  mesh and casting a further topping of say 40-50mm, assuming this does not exceed the laod capacity of the system.

Kind regards,

Arshad

---------- FOLLOW-UP ----------

QUESTION: thanks for the response.let me clarify on the loading&support conditions.we have a panel of 6m*5m supported on the four sides with simple support.the loading can be taken a maximum of 12kN/m2 factored load.
with this loading ,do you think that excessive cracking occurs so as to have a visible effect on the flooring tiles
to be used (which may be terrazo tiles).

Answer
hi Belete,

Again, without knowing the actual ribe tension rebar and the deflection criteria, it is difficult to comment. However, based on simoly supported conditions, the topping should be in compression, so maybe cracking will not be a problem. However, at each of the four corners you will have some tension/torsional effects, so may there may be minor crack on top, but structurally it should be Ok.

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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