Friction between elements

There may be a requirement to know the coefficient of friction between elements in contact, for example precast units resting on a concrete corbel or structural steel members on a concrete support. Values are not included in design codes such as BS 8110 and Eurocode 2. However, there is some guidance in the BS EN 12812: 2004, Falsework – Performance requirements and general design. Informative Annex A suggests friction coefficients for various combinations of materials (based on research work in Germany) as follows: Concrete/concrete maximum 1.0 minimum 0.5 Steel/mortar bed maximum 1.0 minimum 0.5 Steel/concrete maximum 0.4 minimum 0.3 Wood/concrete maximum 1.0 minimum 0.8

Work at Birmingham University, published by Pallett et al in CONCRETE in 2002 would appear to suggest significantly lower values, as follows: Concrete/concrete 0.4 Steel (plain, unrusted)/cast concrete 0.1 Steel (plain, unrusted)/trowelled concrete 0.5 Timber (perpendicular to grain)/concrete 0.7

The Authors note that these are the lowest values they measured in their tests but suggest that the values may be reduced by conditions on site. When a lateral force is to be transmitted between two components a factor of safety of at least 2.0 should be applied.

Further reading: Pallett, P., Gorst, N., Clark, L. and Thomas, D. Friction resistance in temporary works materials, CONCRETE, Volume 36, Number 6, June 2002, pp. 12, 14 & 15. Note that copies of CONCRETE articles (in pdf format) can be down loaded from the Members’ Area of the Concrete Society web site.

Acknowledgement: The Concrete Society

The information contained in this nugget has been provided by The Concrete Society technical staff.

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