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Civil Engineering/Cracking tests on high rise shear walls

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Expert: - 5/30/2011


Question
QUESTION: Dear sir,
I would like to ask that what are the industry tests peformed on high rise core shear walls of a tall building (400m)..if it is found during construction that the wall is facing cracking problems. How to check the width, depth of the already produced cracks.
Thanks

ANSWER: Hi Rana,

I would suggest that you first check the design and construction details, and if both these are OK the chances are that the cracks you are seeing are surface cracks due to poor curing techniques.

However, if you do need to investigate further, the best method is to extract some cores from the wall (75 to 100mm diameter) and have them tested for compressive strength (just to verify design strength) and you can take some cores over the cracks too to establish depth of cracks.

Other methods are by using radiographic (X-ray) equipment, which can be quite expensive.

A cheaper option is to use UPV equipment (Ultrasonic Pulse Velocity) which can give an indication of cracks, voids, etc in concrete.

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

QUESTION: Dear Sir,
We in the design office have checked the design of shear walls and it is ok. We have also got a crack testing report from site and it is found that the in a long main shear wall at level 1 (construction is done upto this level till now) there is a crack region of about 1 m high by 1.5 m wide with crack widths from  0.5mm to 3mm and depth upto 1.2m in 2.5m thick walls. and there were no course aggregates found in the cracked region.

Answer
Hi Rana,

You did not tell me that the walls were 2.5m thick! This sounds very much like a heat-of-hydration early-age cracking problem and you should cease any further casting until measures are taken to prevent it happening again.

There are some very special design and construction requirements for such thick structures (something that I am well experienced in, but which I cannot go into full detail over this forum.)

I suggest you seek some expert assistance to help you on site, as the nature of cracks you mention are quite serious!

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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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