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Proceedings fib Symposium PRAGUE 2011 ISBN 978-80-87158-29-6 Session XXX: YYY

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LAS LLAMAS ARCH BRIDGE (SANTANDER, SPAIN)

Juan José Arenas de Pablo

Guillermo Capellán Miguel

Miguel Sacristán Montesinos

Santiago Guerra Soto

Abstract

Las Llamas’ Bridge is settled in Santander (Spain) and crosses over the Atlantic Park, a green area of great ecological and landscape interest, giving access to the University from the main entrance road to the city. The bridge has a main span between abutments of 102 m. The designed bridge is an arch with intermediate deck typology. The slender centre arch crosses 7.8 high over the deck in a length of 60 m, continuing beneath the deck with two straight inclined legs reaching its bearings in plastic hinges 81.6 m apart. The inclined legs continue underground until they reach its foundation on the exiting rock bed 9 m below. The bridge has been designed in high strength, self compacting white concrete C-60. The connection between arch and deck is materialized by means of stainless steel rod hangers. The deck is organized in a central box girder 5.8 m wide and 2.25 m deep, with two lateral cantilevers, which are conceived as inclined precast slabs 9 m large with openings with light projectors to illuminate the green area under the bridge. Lateral sidewalks are paved with composite wood decking. Central reservation passing through the arch end openings holds a bicycle path.

Keywords: Urban bridge, Intermediate arch, white concrete, high strength, self compacting.

1 Las Llamas Bridge design

Now under construction this new bridge is to be finished by March 2010 in the city of Santander, in the north of Spain. Las Llamas Bridge is designed by Arenas & Asociados engineering firm, who is responsible too of the Project Management on construction site for this bridge owned by Santander City Hall.

fib Symposium PRAGUE 2011 Proceedings Session XXX: YYY ISBN 978-80-87158-29-6

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Project Data Owner: Santander City Hall

Project authors: Juan José Arenas, Guillermo Capellán (Arenas & Asociados)

Structural team engineers: Santiago Guerra Soto, Miguel Sacristán Montesinos, Pablo Alfonso, Shihe She (Arenas & Asociados)

Date of the Project: August 2008 Contractor: Isolux Corsan Date of erection: Due to March 2010

Project Management: Guillermo Capellán, Miguel Sacristán, Raquel Sobrino (Arenas & Asociados)

Contractor Team: José Manuel Peña, Ángel de Cos, Roberto Rodríguez

This white high strength concrete arch bridge has an overall length and a single span of 102 m between abutments and end foundations of the arches in the rock bed. The designed bridge can be classified as an arch with intermediate deck typology as seen on Fig. 1. The arch flies over the deck in a central length of 60 m, continuing beneath the deck with straight inclined legs reaching its supports in concrete plastic hinges. The longitudinal separation between the plastic hinges is 81.6 m. The inclined legs continue underground until they reach their support in the rock bed 8 to 9 m underground, for a total span length of 102 m. Key points of the structure are its slenderness, the use of the intermediate arch solution for a 102 m span urban structure, and the use of new materials as with self compacting high strength concrete.

Fig. 1 Rendered view of the finished Arch Bridge of las Llamas

The new bridge connects the University Campus and the main access route to Santander’s

coastline, and flies over The Atlantic Park of las Llamas, one new large green area of the city with great architectural, environmental and landscape interest and values.

The deck is organized in a central box girder with two lateral cantilevers. The central box girder is 5.8 m wide and 2.25 m deep. The cantilevers, conceived as inclined precast slabs, are as large as 9 m and have skylights with light projectors to illuminate the ground level under the bridge. These lights will generate an interesting play of light and shadows during the night in the park. On the inclined slabs and by means of conventional precast slabs it is materialized the deck slab, of 25 cm thick. The sidewalks, which pavement has been projected in technological wood composite decking, are located in the exterior side of the cantilevers; whereas the central reservation, in which the arch is opened forming a vault with an opening in each end, will give service to the bicycle path giving access to most parts of the city.


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Fig. 2 Interior rendered view of las Llamas bridge, with lateral sidewalks and central bicycle path.

From the functional point of view, A deck 23.6 m wide gives service to two roadways 6.5 m

wide; a central reservation of 5.2 m, which includes the arch structure and the bicycle path of 3 m, and the lateral pedestrian sidewalks 2.7 m wide, as seen on Fig. 2.

The arch is a unique piece centred on the bridge and it is opened towards two sloping inclined legs placed under the deck. The depth of the arch is an increasing from the key section down to the take-offs, varying between 72 cm and 120 cm. The deck hangs of the arch by means of 18 pairs of hangers of stainless steel bars arranged every 2.4 m. The maximum height of the arch is of approximately 7.8 m over the deck.

The design of this urban bridge is conditioned by its architectural and environmental

integration on the landscape of the existing large Atlantic Park. Intermediate arch typology is chosen because of its reduced height. A large span is needed in order to keep clear space below. Lighting on the bridge and below is integrated within the structure, including inferior lights through the cantilever openings illuminating the Park area underneath during night time, as seen on Fig. 3.

Fig. 3 Night view below las Llamas bridge, lighting through cantilever openings.


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Fig. 4 Elevation of the intermediate Arch bridge and its foundation on the rock bed.

2 Structural behaviour

The group formed by the central arch and inferior inclined legs founded on the bed rock behaves as a single intermediate arch resting on the ground against which it pushes. The arch has a total span of 102 m, and two hinges materialized as concrete plastic hinges 81.6 m apart, as seen on Fig. 4. The deck’s main girder hangs from the arch in 60 m through stainless steel rod ties every 2.4 m, and it has two side spans of 21 m. The intermediate arch, box girder and hangers form the main longitudinal structure, while in transversal direction cantilevers are formed by inclined precast slabs of 2.4x 9m and a top concrete slab transversally prestressed with four 32 mm bars every 2.4 m, following the typical section seen on Fig. 5. Longitudinal prestress of the concrete box girder is formed by 12 tendons of 19 0.6” units, as seen on Fig. 6.

Fig. 5 Typical section with box girder and precast cantilevers and external view of the arch and inclined legs.


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3 Technology and Innovation

This bridge is located in the proximity to Engineering school in which Professor Arenas imparted his bridge classes. This is seen as an opportunity to carry out innovative solutions in the structure as well as new materials and technologies. Singular structural solutions and erection procedures are needed in order to fulfil the desired design chosen. The use of white self compacting high strength concrete is an innovating challenge required by the geometry and efforts of the arch, together with the density of reinforcement bars. Other singular elements are the concrete plastic hinges, also called Freyssinet hinges. New materials and solutions are used as composite decking of technological wood in sidewalks or stainless steel hangers. Pretensions procedure of the hangers and longituninal prestress tendons, together with progressive drop of the falsework is specially designed to avoid surcharges in any of the elements of the falsework or the structure, and to obtain the desired geometry and tension forces in the arch and hangers.

Fig. 6 Postension tendons in the prestressed concrete box girder. The precast cantilever elements are a larger version of those already used in the bridge over the Tormes river in Salamanca by Arenas & Asociados, as seen on Fig. 7 & 8. Having both constructive and aesthetical advantages, and allowing to reduce selfweight over the falsework and temporary foundations.

Fig. 7and 8 Precast cantilever elements in the Bridge over the Tormes river in Salamanca.


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4 Erection procedure

Fig. 9and 10 Photographs of the steel sheet piling and the micro pile wall on each abutment. In order to build foundations on the bed rock 9 m underground and buried inclined legs, a steel sheet piling and micro pile wall are needed on abutments for direct foundation excavation, as seen on Fig. 9 & 10. The steel sheet piling is 11 m high with 3 levels of temporary steel frames to contain the walls during excavation. Micro pile wall has also 3 levels of ground anchorages which are tensioned as the excavation moves down. The central box girder and inclined legs are built over framed falsework. Falsework is founded on provisional driven precast piles. Inclined legs are poured first, as seen on Fig. 11, and over them the central box girder is materialised in two phases.

Fig. 11 Falsework and formwork for the central girder during construction.

Once the central girder is finished, the arch is erected using falsework supported by the girder

over its temporary falsework towers, as seen on Fig. 12 & 13. It is not until the hangers are placed and tensioned to their initial force and the longitudinal pretension is partially stressed that the falsework can be removed.

Precast inclined cantilevers are placed with provisional supports until transversal prestress bars are placed. The upper slab is poured over precast slabs supported by cantilevers. Prestressing of the transversal bars completes the bridge structure. Finishings include pavement, composite decking in sidewalks, lighting, glass balustrades and every element needed to open the bridge to the traffic.


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Fig. 12 General View of the construction site

Fig. 13 Arch centering and white concrete box girder

5 Conclusions

The design of this urban bridge is conditioned by its architectural and environmental integration on the landscape of the existing large Atlantic Park, as seen on Fig. 14. Intermediate arch typology is chosen because of its reduced height, to ease its integration in the right scale and to avoid unnecessary monumentality, as seen on Fig. 15. A large span is needed in order to keep clear space below, as the Park continues under the bridge. Singular structural solutions and erection procedures are needed in order to fulfil the desired design. The use of white self compacting high strength concrete is an innovating challenge for this bridge in the proximity to Engineering school in which Professor Arenas imparted his classes. This new bridge will be named after Professor Arenas in recognition to his career as a bridge designer and structural engineer.

Fig. 14 Integration of las Llamas bridge in the Atlantic Park green area.


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Fig. 15 General rendered views of las Llamas Bridge.

References

[1] Juan Jose Arenas de P.: Caminos en el aire (Paths in the air) (2 Volums). ISBN for volume 1: 84-380-0222-6. ISBN for volume 2: 84-380-0223-4. 2007

[2] J. Torres, A.J. Santamaría, J.J. Arenas, J. Diaz del Valle, D. Lorenzo.: Arcos. Antifunicularidad (Arches. Antifunicularity). University of Cantabria, 1988.

Prof. Juan José Arenas de Pablo, C.Eng. President

Arenas & Asociados, S.L. Hernán Cortés, 19, 1º Dcha. E-39003 Santander SPAIN

+34 942 319 960 +34 942 319 961 ☺ [email protected] URL www.arenasing.com

Guillermo Capellán Miguel, C.Eng. Technical Director



Miguel Sacristán Montesinos, C.Eng. Project Coordinator



Santiago Guerra Soto, C.Eng. Project Manager



las llamas long paper2 revisado2

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