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About Arshad Khan
Expertise
I can answer any questions to do with 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: 33 years in Construction and consultancy in UK, Kenya, Tanzania, Uganda, Ethiopia, Eritrea, South Africa, Somalia, Austria, Bahrain and the U.A.E.

Organizations: Fellow of Institution of Structural Engineers (UK), Fellow of Institution of Civil Engineers(UK),Registered Engineer Kenya, Chartered Engineer (UK)

Publications: Proceedings of 2 International Conferences; Education: BSc, MSc, D.I.C.

You are here: Experts > Science > Civil Engineering > Civil Engineering > Relation between the thickness of a wall and its length

Civil Engineering - Relation between the thickness of a wall and its length

Expert: Arshad Khan - 11/2/2009

Question
If I consider a dam that is 10 meters in height then the pressure at the bottom of the dam will be around 98kN/m2. The material I select to build the wall should have a compressive? strength exceeding this pressure.

Now what I don't know is how the the length of wall influences its thickness. That is what other forces are acting on it?

Also am I right to say that the pressure on the wall is compressive rather than tensile as it is towards it? I am confused because the the pressure of the water is resisted by the bond formed by the wall with the ground at the bottom.

Thank You.

Answer
Hi John,

This depends on which type of dam wall you are designing- an arch dam or a gravity dam or a cantilever dam. In the former, the concrete wall arches in a horizontal plane against the sides of the valley(and can also arch across the vertical plane to make it a double-arched dam), and all forces are more or less compressive across the section of the wall. Of course you also need to cater for the shear stresses.

If the dam is gravity, then more or less all concrete remains in compression and stability is provided by self-weight resisting over-turning and sliding.

If the dam is cantilever, then there will be compression on the dry side and tension on the wet side, so you will need rebar to resist the latter. Sliding will be resisted by anchorage into a deep foundation block. You will also need to cater for the shear stress.

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