Mechanical strength and ageing of plastic steps

Status:

completed 01/1991

Aims:

Steps (up to a height of 1 m; top step can be stepped on) are mainly made from plastics. As a result of ageing or varying temperatures, the properties of plastic materials are likely to change much more than those of metals. Mechanical strength testing was intended to provide information whether or not and to which extent plastic steps suffer from an intolerable decline in mechanical strength and thus in safety. The project was launched by the BG expert committee for structural engineering.

Activities/Methods:

New and aged steps made from polypropylene and polystyrene were tested in view of their mechanical strength in accordance with DIN 4569 "Steps - Terms, functional sizes, requirements, testing". Some of the tests were conducted at temperatures other than the ambient temperature.

Results:

The investigations showed that ageing and short-term thermal load within a temperature range of -20°C to +40°C does not lead to a significant decline in mechanical strength and therefore does not give reason to expect a sudden breakdown of plastic steps. If the steps are correctly designed, they are so dimensioned that mechanical load is flexibly absorbed. Ageing effects do not have the same effect as in the case of a plastic deformation. Therefore, the lifetime of plastic steps is not limited. Just like ladders and steps made from other materials, plastic steps must be replaced as soon as they are visibly damaged. Cracks, fractures, permanent deformation etc. are some of the criteria for deciding that a plastic step should no longer be used.

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