Girona landmark opens to traffic
, May 26, 2015
Girona landmark opens to traffic
A new steel bridge over the Ter River in Girona, north east Spain, was opened to traffic at the end of March. Construction of the crossing had been delayed by the financial crisis, but now the city, which is 100km north of Barcelona, is home to a new landmark.
Girona is a popular destination for tourists, and recent population growth has led to the creation of new residential and industrial areas. The Spanish Ministry of Public Works signed an agreement in 2003 with the Municipality of Girona to build a new bridge over the Ter River and consultant Pedelta won the 2005 competition to design the bridge. Dragados was awarded the contract to build the bridge, which began at the end of 2010, but the US$25 million project was subsequently delayed due to cutbacks in public spending, and has only just been completed.
The key design challenge was to achieve an appropriate landmark quality in this special setting, within a very tight budget. The design, which follows the aesthetic philosophy of ‘complex simplicity’, is a contemporary interpretation of a classic kingpost truss, scaled and proportioned to fit the landscape. The design minimised the amount of materials and used weathering steel for a long service life and minimal maintenance.
The bridge has a nine-span, continuous deck with a total length of 485m and is almost 20m wide, accommodating four traffic lanes, a central median and two walkways, with lanes for bicycles on each side.
The three central spans are steel and the three approach spans on each side are concrete. The main span over the Ter River is a 120m-long king post truss with curved diagonal members suspending the central part of the deck. This splits into two branches over the side spans to create two gateways.
The deck has a constant 2.1m depth; its cross-section is a 7.4m-wide steel box girder with a curved soffit and ribs at 4m centres and concrete deck slab on top. Double composite action has been used in the intermediate supports of the three central steel spans to reduce the thickness of the steel plates and increase ductility. The 17.5m-high ‘towers’ have a hexagonal, concrete-filled steel cross-section while the curved diagonal members of the main spans have a triangular cross-section 1.4m wide with a constant depth of 2m in the main span and a smooth variable depth in the two adjacent spans.
Pedelta was asked to provide construction engineering services to the contractor during construction, and had to adapt the design and approve the different erection and assembly procedures. In some cases, it was necessary to update the pre-cambers and redesign structural details. The approach spans are made of cast-in-place, post-tensioned concrete and were built with a traditional span-by-span procedure on falsework.
The steel box girder was assembled from 20 different segments, some of which were assembled on site in pairs and lifted to their final positions on temporary supports. The steel girder and cantilever ribs were field-welded. Upon the completion of the steel box girder, the lower concrete slab inside the box at the negative bending moment regions was cast in place. Afterwards the segments of the posts were lifted, assembled and partially filled with concrete. Erection continued with the installation of the curved diagonal members. These components were split into six segments in the central span and were installed using temporary props on top of the box girder to allow for alignment.
After the central curved steel ties had been correctly placed and welded, the rest of the segments were lifted using four temporary supports for each lateral curved steel element. While the tied members were being welded, partial-depth precast panels were installed to allow for the casting of the top slab. Steel subcontractors were Ascamon and Urssa.