THE PROBLEM

We were approached by a number of engineers throughout the country with regards to a problem they were experiencing with the operation of their barriers featuring hinged skirts. The problem was that the barrier struts forming the skirt were distorting due to internal stresses during their normal operation. An illustration of the problem is shown in the pictures below.

This distortion prevents the barriers from closing and opening properly and, when severe enough, can allow either children or animals easy access to a live line. In addition, vandalism accounts for a high number of broken struts.

The next problem to be tackled was the easy removal and installation of a strut on the GWE barrier. At present the removal of these struts can be extremely time consuming and there is also a risk of damage to the upper channel of the barrier as the strut has to be forced out in order to turn it through 90o for removal. Pressure has to be applied to the upper channel to separate it to allow the strut head to move away from the barrier which is a delicate operation.

THE SOLUTION

As both the barrier and skirt operation is basically very simple, moving from the vertical to the horizontal and back, it was fair to assume that the stresses causing the struts to bend were simple as well. At some point in the movement up and down, the struts had to be experiencing a compression that finally resulted in them deforming. The obvious answer was to allow some movement within the strut that would compensate for this and therefore prevent the deformation.

The design features a telescopic strut that involves two tubes, one of which moves inside the second one, and is connected by a spring (see drawings SL/1003 and SL/1004). The strut is designed to be of such a length that once installed the spring would be under sufficient tension that should the strut need to move up to a distance of 2cm no distortion would occur. The tubing and fixing barrel at either end of the strut are manufactured from P.V.C which has a di-electric strength of 39kv/mm and a surface resistivity of 1013 ohms which makes it electrically safe to use.