Megashor provides shoring for Basgoiti Viaduct Construction a complex and programme time sensitive project.
Constructed as a key link on the Arrasate to Eskoriatza section of the new Vitoria to Eibar motorway, located near the town of Mondragón in Guipúzcoa, the smallest Spanish province in the Basque region of Northern Spain, the 391 metre Basagoiti Viaduct has been formed using RMD Kwikform Ibérica’s heavy duty 1000 kN Megashor shoring equipment.
Completed in September 2008, the 12 month project, undertaken for primary contractor UTE Laurena by a joint venture between four Spanish construction firms, (Dragados, Moyua, Obras Subterraneas and Geotunel) is well under way. The 12 metre wide box shaped viaduct now supports a total of 2 lanes of traffic on the new 47 Km long motorway.
Designed by a specialist team of six engineers from RMD Kwikform Ibérica, the formwork and falsework solution for the construction of the viaduct involved the hire of a total of 1,800 tonnes of equipment, including a combination of RMD Kwikform’s world leading Megashor 1,000 kN heavy duty steel shoring, Superslim soldiers, R700 girders, Kwikstage shoring and T200 timber beams.
Due to the complexity and length of the viaduct, measuring some 391 metres, the RMD Kwikform Ibérica engineering team has worked throughout the three phases of construction to support the RMD Kwikform Ibérica erection teams on-site. In order to overcome some of the technical challenges, the engineering team developed new special pyramid shaped header parts and adjustable Superslim beams, that were manufactured specifically for the project.
These additional parts enabled the team to design a unique system that allowed two key parts of the formwork, the Megashor beams and R700 Girders, to be connected together safely and swiftly, at the required angles for the support structure to allow the viaduct to be cast in-situ.
Commenting on the technical issues of the project, one of RMD Kwikform Ibérica’s senior engineers, Andrés Rodríguez, said “Due to the density of the reinforcement in the piers, the client decided to concrete the piers with self compacting concrete. The difficulty with using this type of concrete is the increased pressure it places on the formwork system used. It was for this reason that we formed a specialist engineering team for the project and increased the tolerances of our design.
Preventing Concrete Leakage
“Having worked with this type of concrete before, we recognized that the key challenge was to eliminate the possibility of leakage into the formwork that could be caused by the increases in pressure. It was here that the strength and interconnectivity between our Megashor and Superslim soldier products was so important, as we were able to create a very strong interlinking formwork system that could dissipate pressures effectively.
“With three V-shaped piers required for the complete construction of the viaduct, a total of eight special pyramid shaped header parts were manufactured. This enabled each ‘arm’ of each pier to be angled at the required 45º, whilst spanning the required length of 32m. In order to meet the increased pressures and tolerances needed for the formwork system, the design and construction of each ‘arm’ took the form of a solid shaft (5.5m wide and between 1.8m and 2.2m thick). By interconnecting each of the arms with the formwork structure, a solid, strong and structurally sound system was developed.
Dealing with difficult terrain
Having worked on a number of bridge and viaduct projects with similar terrain issues, RMD Kwikform Ibérica engineers opted for a tried and tested support structure, using R700 steel girders supported by Megashor towers, positioned on concrete blocks at dedicated intervals. Due to the added weight pressures exerted by the solid ‘arms’ and self compacting concrete, this shoring support system was further strengthened by reinforcing the girders, using additional Megashor beams.
Andrés: “By using additional equipment like the Megashor beams to help reinforce the girders we were able to create a formwork system that could absorb the high traction the girders were submitted too. In this case the Megashor beam was attached to the lower chord of the girder, providing the support required.”
Combating the effects of concrete
“After we solved this issue we needed to combat the effects of concrete on the piers themselves. Here we used the specially designed steel pyramid shaped headers fixed on top of the Megashor towers to support the piers, whilst the deck was being laid and struck. Because the viaduct was constructed in three phases, each about a third of the overall length, all ‘arms’ including the first ‘arm’ had to be supported.
“This was achieved by using two Megashor towers and a pyramid shaped header as supports until the second part of the decking was concreted, therefore removing the additional pressures on the formwork system and maintaining its overall stability.”
With all of the piers and foundations for the viaduct constructed first before the deck construction phase began, RMD Kwikform Ibérica engineers had to find a way of safely transmitting the large horizontal push made by the formwork system to the girders. Andrés: “Reaching up to 4,800kN or 480 tons, this horizontal push would in most cases have simply been transmitted to the ground or the foundation of the piers, but because the foundations and piers had already been constructed, it was impossible to transmit the load in this fashion, without causing structural damage.”
“Faced with this dilemma, our team decided to use the in-built strength of the solid ‘arms’ to balance the load of each ‘arm’ with the load of the opposite ‘arm’. In order to achieve this we placed six special steel Dywidag beams, measuring 47mm in diameter into the key support section of the R700 girders, located on the shoe of the pier.”
Using a combination of R700 girders and additional formwork, RMD Kwikform Ibérica engineers were able to design two block structures, which were placed on each side of the pyramid shaped header to support it whilst concrete was poured. Once the concrete was poured these blocks could then be removed, leaving the header to support the concreted arm. The blocks were then re-used for the same process on each of the three piers.
The final technical challenge facing the RMD Kwikform Ibérica team was the variable thickness of the decking design. This was overcome by redesigning RMD Kwikform Ibérica’s most popular fixed steel beam Superslim soldier into an adjustable telescopic product. This made the erection of the deck support formwork much simpler, lighter and faster, allowing the project to be kept on schedule for a 2009 opening.
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