The River Clwyd Viaduct represents the best use of modern concrete techniques in a historically significant and environmentally sensitive location. Great care was taken to maximise the benefits of reinforced-concrete design and technology to create a structure that was economical to build, and will be durable, maintenance-free and visually appealing.
The structure comprises two continuous 430m-long decks of combined precast beams and in-situ reinforced concrete over 11 separate spans. Each span is made up of precast prestressed beams in the central element - where most bending resistance is required - and in-situ cross-head elements above supporting piers, ie the locations of maximum shear. In this way, the effective span range of the precast elements is considerably increased and span/ratio depths of 30 were achieved. This compares favourably with typical values of 17 for simply-supported equivalents. Internally, post- tensioned parapet string courses accentuate the slenderness of the structure while helping to reduce potential for cracking in these areas.
The continuous form of the deck provides significant maintenance benefits by reducing the number of movement joints to just two. The buried deck joints, one at each end of the structure, are designed to accommodate longitudinal movements of up to 75mm, although actual working movement is less than that. Movement at the intermediate pier locations is accommodated by a combination of encastre, pinned and sliding bearing arrangements.
Concerns about the visual impact of the structure, especially in direct contrast with the nearby Medieval stone arch bridge and Edward I's Rhuddlan Castle, were fully addressed and overcome by careful attention to the alignment/form of the viaduct and the use of admixtures to darken the colour of the structural concrete.
OWNER AND IN-HOUSE DESIGNER Denbighshire County Council
MAIN CONTRACTOR Edmund Nuttall
PRECAST PRESTRESSED CONCRETE BEAMS C V Buchan
READY-MIXED CONCRETE arc Premix
CEMENT (SULFATE RESISTING) Castle Cement
PRECAST-CONCRETE PILING Westpile
CONCRETE PUMPING Pochin
POST-TENSIONING psc Freyssinet