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The 720 m Verrieres viaduct features a radius curve of 1800 m and has five supporting piers (P1 - P5), two large abutments and a bridge deck - which will be ‘pushed’ across the completed piers from one side of the valley. An impressive element of the Verrieres viaduct will be its supporting piers, particularly the two central piers P2 and P3 which will both be 140 m high. To enhance the aesthetic appearance of the viaduct it has been designed such that all its piers have the same cross section at any given elevation.
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Two sets of Doka self-climbing formwork totalling 750 m2 have been supplied for the project’s main joint venture contractor comprising Spie Batignolles, Razel, SOGEA, Dodin Sud and Victor Buyck.
Piers P1, P4 and P5 are all conical in shape over their complete height, as are the top sections of P2 and P3. Where these two piers differ however is for the first 50 m with a parabola profile. Whilst certainly pleasing to the eye, according to Herwig Steininger, General Manager of Doka France, the design posed a few headaches for the formwork designer.
“It was this complexity of design, working within a tight schedule with minimal production losses, and limited manpower that made the project so demanding and one of the most difficult to date,“ added Mr. Steininger.
In order for the finished concrete to follow the parabolic profile, a formwork system was required where individual panels could be connected and packed securely to the overall support system. Designing the overall system at its headquarters in Amstetten, Austria, Doka incorporated as much preassembled componentry as possible, to ensure that both formwork systems could be adapted as quickly as possible. This was achieved by pre-planning all the changes required for the subsequent climb upwards.
Herwig Steininger confirms, “The design process was extremely complex in order to ensure simple use of the system on-site“.
According to project director Vincent Preysass, Doka undertook to guarantee lifting sections on the conical elements in three days. “In practice,“ he adds, “we have been achieving average cycles of just two days with a work force manpower of only nine people“.
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