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Civil Engineering/Mechanical testing of wood

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Expert: - 11/20/2002


Question
Hi there - I'm a second year civil engineering student in Canada, and we recently had a wood lab where we tested wood for different strengths (tensile, cleavage, compressive, shearing and static bending).  I was wondering why the compressive strength is different depending on if the wood is loaded parallel or perpendicular to the grain?  I know that the compression perpendicular is supposed to be 12-18% of the compression parallel, but why is this?  I don't know if you deal with wood at all, but any insight you might have would be much appreciated.

Answer

Hi Emily,

I am not an expert on timber design, but from first principles I would say that the reason the wood has higher compressive (& indeed tensile) strength parallel to the grain is because you can think of the grains as a bundle of straws clamped together. If you pull/push  the bundle parallel to the length, it is fairly strong. However, if you compress the bundle at right angles, it is very soft because the voids within the straws are weak. Timber has similar voids along the grain which carries moisture, etc up the tree trunk, so it is weaker/softer across the grain.

I hope this 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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