Keywords: formwork, health and safety, falls from height, maturity method, safety system, finite elements.

In building work there is always a risk of workers falling [1] when operations are being carried out at height. The risk is greatest when the formwork is being put in place before the concrete is poured to create the main building supports. In order to minimize the risk of falls, the company Encofrados J. Alsina S.A. [2] has developed a special safety device.

The Alsina safety system (with the trade name "Alsipercha") is based on a moving telescopic support fixed within a metal holder sunk into the upper section of the columns and provides the worker engaged in constructing the formwork with a set of safety points and lines to which he can attach his safety belt or harness to give him protection in the event of a fall.

The Polytechnic University of Valencia in collaboration with Encofrados J. Alsina SA developed the application of the product and determined in a numerical and experimental study the necessary conditions required for the concrete forming the column, so that the device can be used to provide total safety for the workers and guarantee the integrity of the columns.

The system consists of a foldable steel support and a sliding section which brakes when it senses a sudden acceleration. The system is installed as follows:

• A conical tube, used to anchor the system, is inserted into the early age concrete of the column.
• When the concrete of the column has reached the required strength the safety system is placed in position within the metal holder.
• The worker then attaches his harness to the system and can work in complete safety.

Full scale columns were constructed in an experimental study with the aim of determining the age when the system could be installed in the supports so it could withstand the weight of the workers engaged in the system in the case of a fall. A numerical work was carried out using the commercial software ANSYS [3] to extrapolate the results obtained from the full scale columns (0.30x0.30 m cross section) to different types of cross sections (0.15x0.40 m and 0.25x0.25 m). A first step was to validate the numerical model using the results obtained for the experimental tests and then to adjust the Young's modulus for the concrete to be used in the other types of columns.

A maturity study [4] was used to establish the necessary age of the concrete of the columns according to the mean ambient temperature so the column could withstand the safety system and the fall of a worker safely.

1

Bomel Limited, "Improving health and safety in construction. Phase 1. Data collection, review and structuring", Contract Research Report 387/2001 for the Health and Safety Executive, Norwich, 2001.

2

www.alsina.com

3

ANSYS Inc. ANSYS theory reference 9.0. 2004.

4

Freiesleben Hansen P., Pedersen E.J., "Maleinstrument til kontrol of betons haerdning", Nordisk, Betong Vol. 1, 21-25, 1977.

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