David Dexter Associates are proud to have worked on the award winning 46m ‘floating’ Vierendeel truss bridge which forms a major part of the £6m Harlech Castle Visitor Centre refurbishment project.
SH Structures appointed consultants David Dexter Associates to develop the concept, which had established the architectural intent, through to a fully designed practical and buildable structure that would meet all the requirements of the performance specification for final approval by Cadw.
Throughout this process there was a continued dialogue between SHS, DDA, Mott MacDonald and Cadw using 3D BIM CAD modelling to explain design proposals and ensure the design developments were acceptable.
To minimise the impact of the views of the distant mountains of Snowdonia the profile of the bridge was reduced by tapering the bottom chords of the trusses and eliminating any diagonal bracing avoiding a potentially more cluttered appearance. The visual lightness of the bridge is also significantly improved by the selection of a stainless steel mesh infill to the parapets. The deck is 2m wide in general however it widens up to 3m above the middle support to provide an area where people can enjoy the views.
Designed to Eurocodes, which have very onerous dynamics performance requirements, meant the bridges dynamic performance required very careful consideration. The columns needed to be very stiff in the transverse direction so an elliptical section was used, which when partly filled with concrete achieved the required result. This choice has the added architectural benefit of the elliptical column being less obtrusive on elevation whilst approximately matching profile of the truss chord.