I refer to your news item on the further changes to the design of Stonecutters Bridge by the Arup-Cowi design team (NCE 25 October). As the design competition winning team, we are pleased to see that wind tunnel tests confirmed the external proportions of the tower and our conceptual thinking on wind response.
We are also not surprised to hear that designers need to increase the internal proportions of the tower section following the change from prefabricated cables to larger ducted strand based cables which will significantly increase the governing wind load on the towers.
The competition brief set minimum maintenance and high durability as key criteria. By excluding bridge bearings, as in our original design, maintenance is greatly simplified and bearing movement problems eliminated.
Our solution was structurally and visually simple, with no cross heads or corbels to spoil the clean lines.
Set in the context of the massive towers, constructing the 11m wide elements was considered moderate and lay off the critical path. It also had an added benefit of forming a rigid point from which to begin the cantilever erection of the main span, which has so often proved the most difficult stage in cable stayed bridge construction.
We wait with interest to see what the Arup-Cowi team comes up with for this articulated connection.
Stuart Withycombe, technical director, bridges, Halcrow Group, withycombesi@halcrow. com