VIDEO - Spanish viaduct uses RMD's Megashor towers for support

RMD Kwikform Iberica has provided an innovative launching system to deliver a viaduct in the Cadagua valley near Bilbao, Spain. Richard High reports.

RMD's Spanish subsidiary, RMD Kwikform Iberica, has supplied its Megashor towers, including the world's tallest, to support four pillars up to 50 m high, as two twin-steel bodied viaducts were pushed across the Cadagua valley.

The project is part of the Cadagua Link on the new 36 km-long Supersur Bilbao by-pass, which will be operated as a toll road.

One of the most difficult projects on the tollway's route, the new viaduct across the deep Cadagua valley was constructed by UTE Enlace del Cadagua, (a joint venture between Spanish construction specialists Sacyr and Exbasa). It is in fact two 50 m-high viaducts with two lanes in each direction.

RMD's Megashor towers were used to support the viaduct's Y-shaped concrete pylons during the viaduct's launch. While the slim concrete pylons were more than capable of supporting the weight of the deck once it was installed, they were not able to withstand the large horizontal loads they would be subjected to as the viaduct sections were pushed over them.

RMD's Spanish engineers provided a method of supporting the viaducts, using the pillars without affecting their structural integrity, by designing and constructing a number of specialist Megashor towers that provided flexible support.

Engineering know-how

"Due to the steep inclines on both the south and north sections of the crossing, which lead down to the Cadagua river, and on the east side also incorporate two busy train lines linking Bilbao with Santander and Balmaseda, the more traditional method of viaduct construction using in-situ or precast concrete sections supported by falsework was not possible," explained RMD Kwikform Iberica engineer Alberto Aldama.

"Similarly, the use of the push technique normally relies on very large and rigid concrete pillars, especially at such great heights. So with slimmer and therefore less rigid pillars, a new and more innovative method of supporting the construction was required.

"This involved the fabrication of two steel structures for each viaduct, welded together on the north side in several 20 m-long sections. They were then pushed across the valley, over our Megashor towers which embraced the pillars.

"A critical element," added Mr Aldama, "was the protection of the pillars for each viaduct, which were positioned at set intervals across the valley."

Starting out from abutments at the north side of the valley the overall span to the abutments on the other south side is 430 m, with four Y-shaped bridge pylons for both viaducts requiring Megashor tower support.

Vertical loads

The pylons were formed with vertical Megashor beams and horizontal Superslim beams tied together, with extra support provided by specially fabricated large bracing plates. Each pylon was designed to support vertical loads of up to 800 tonnes and horizontal loads of 50 tonnes, which were produced by pushing the bridge deck onto two jacks on top of each tower.

In total six towers were erected, two measuring 50 m, two of 45 m, one of 20 m and one of 43 m.

"The greatest challenge to overcome was the design of the 50 m-high towers, a record for RMD Kwikform," said Mr Aldama, "that could support the great loads of the pushed bridge decks."

"There was also the added difficulty of the movement of the pillars, as they could fissure and sway over 400 mm at the top. We therefore had to make our towers especially rigid so that apart from supporting the high loads, they could avoid the swaying of the pillars and prevent any damage occurring.

"In order to withstand the forces and maintain rigidity, we had to combine a total of six Megashor legs together to form the tower. This was achieved by using specially designed bracing plates that were positioned at set intervals on both sides of the tower.

"We also designed some special parts for the tops of the towers, which allowed them to be tied to the pile, 'embracing' it with Superslim soldiers," he explained.

Safety

With safety and accuracy a key element to the overall design, in order to ensure the jacks that pushed the decks at the top of the towers were correctly adjusted, they had to be handled manually, which involved the construction crew working at a maximum height of 50 m-plus.

To ensure the crews safety, and to stop work tools and other smaller peices of equipment falling into the valley floor below, RMD designed special platforms using plywood boards over T200 beams on top of Superslim soldiers. These were placed around the tops of the pillars and accessed using ladders and intermediate platforms attached to the Megashor legs.

In total 660 tonnes of RMD equipment was used, including 1000kN per leg Megashor towers, steel Superslim beams, standard steel beams and bracing plates.

RMD's role at the project finished last month (April) and the viaduct is due to be officially completed in June.