More news on the bridge
- Fri 12th Apr 2002
As controversy over the new bridge railings continues we have been provided a copy of the HCC Engineers report on this issue. The report discusses the reasons behind the new parapets and how the chosen system was selected. It also contains links to some photographs of the type of parapet to be used and the alternative that was decided against.
(click 'click here for full story' to see the report and pictures)
Those interested in the issue of the choice of parapets, or the lack of consultation with Hayling residents are encouraged to attend the open meeting at URC Church Hall at 7pm on April 18th.Background
The existing parapets were not designed to take any type of vehicle impact and the rails are badly corroded in places. The strengthening of the parapets has been a high priority of Hampshire County Council but lack of funds has delayed the scheme until now.
During the design process the bridges group was asked to look into the possibility of widening the footways for possible future use by cyclists. This proves possible but required extra strengthening to the deck edge beam. This edge beam strengthening is part of the present works.
Parapets
Modern parapets are designed to retain the vehicle, to absorb the energy gradually and to avoid throwing teh vehicle abruptly back into the traffic flow. The materials for the approved systems are aluminium or steel.
In both systems the posts are designed to fail progressively at their bases as the energy of the moving vehicle is absorbed. In order to avoid serious damage to the bridge on impact, the deck edge must have a strength capacity of at least 1.5 times that of the posts - this ensures that the posts fail before the edge beam fails.
Because of teh less predictable behaviour of aluminium compared with steel the aluminium posts are made with a higher capacity that steel posts. Without major alterations to the substructure it is not possible to cater for the strength requirements of an aluminium post and to widen the footways. Hence the decision was made to use steel parapets.
For the traffic speeds on Langstone there are two available steel systems. Both systems require an extra rail at a height of 1.4m to allow for cyclists.
The first system (which is the cheapest) has four horizontal rails with mesh infill panels on the traffic face. These panels have no mesh between the third and fourth rails. The mesh is specified to prevent children using the rails as a ladder to climb up and to prevent younger children climbing through the rails. This mesh is easily damaged , prone to vandalism and has little aesthetic appeal.
The proposed system has three horizontal rails with vertical infill rails between the bottom two. This system is the more expensive option and tends to be used where teh visual effects are important.
Harbour Views
The present parapets do little to obscure the views of the harbour from car drivers and their passengers. Unfortunately it is not possible to conform with modern standards and maintain the visibility through the parapet. The attached photographs show that substituting the mesh system does not improve the visibility of the harbour.
During the scheme preparation the design staff have been aware that this is a gateway to Hayling Island and as such the aesthetics are very important. Following consultation with a number of councillors and local groups non-standard (and very expensive) lighting columns are included, the pain colour for the columns and parapets were agreed and observations platforms have been added.
Photographs
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