Bresle viaduct – Wikipedia
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The Bresle viaduct Allows the French highway A29 to cross the Bresle valley north of Aumale, and connects Hauts-de-France and Normandy.
With a length of 755 m, the viaduct allows you to pass over the Coastal River La Bresle valley [ first ] . Only a fifth of the bridge is Picard and the approximately normandy four-fifths are [ 2 ] .
The work was carried out as part of a “design-realization” competition with constraints of implantation of support and respect for the environment because the work is in a Natura 2000 zone launched by the company D ‘Sanef motorway with the project manager Scetauroute. Five teams participated in the competition.
The competition was won by the Razel company associated with the architectural firm AOA architects with a proposal for a concrete structure, a single concrete concrete apron of 19.64 m width 2 × 2 lanes of traffic and a height of 4 m . The proposed solution is inspired by the Scardon viaduct.
The bridge is in right alignment [ 3 ] . The longitudinal profile of the apron has a constant slope of 1.5%. The company has chosen to carry it out according to the longitudinal pushing method [ 4 ] By choosing compatible litters with this method and having the best compromise between the constraints of implantation of the batteries, of ratio height of the deck with respect to the ground (maximum: 38 m ) / scope and economic imperative. Current spans have a maximum range of 61.20 m , the last two spans before accosting on the abutments have 57.80 ranges m and 44.20 m . The apron has a central box of 4 m height with two souls of 0.35 m thick and tilted bracons [ 5 ] Starting from the intersection of the axis of each soul with the lower slab (or slab) of the box and going to support the upper Hourdis. This solution made it possible to have a mechanical yield [ 6 ] 0.62.
- – Concrete volume: 7,700 m 3
- – Deck surface: 14,800 m 2
- – Average thickness of the apron: 0.46 m
The total weight of the deck pushed, in the last pushing phase, is 19,800 t . The apron was pushed by going up. The pushing force necessary for the displacement of the apron corresponds to that necessary to exceed the resistance due to the friction of the apron on its temporary sliding supports placed on each battery and corruption, on the prefabrication area as well as the influence of the slope longitudinal. We generally consider the following friction coefficients:
- – Sliding support: 3 ± 2% [ 7 ]
- – Prefabrication area: 15 ± 5%
When the effects of friction can be unfavorable with regard to security, for example when you push an apron when you go down, it is prudent to take a coefficient of zero friction on the support devices. The friction coefficients are important at the start of the pushing to decrease as soon as the trip started until you are almost zero. It has therefore already happened that a deck pushed when descending moves without being exercised. In this case, it is necessary to hold it back.
The support surfaces of the sliding supports are not horizontal but have the slope of the apron. They generate a component opposing the advancement of the apron equal to the longitudinal slope of the deck multiplied by the vertical reaction.
The apron was prestressed longitudinally by prestressing cables 27T15 external to the concrete, placed inside the box and 12T15 ripped cables interior with concrete, stretched after the end of the pushing. During the pushing, an antagonistic prestressing is put in place which is dismantled after the push. The Hourdis is prestressed transversely by 4T15 cables.
In total, the average prestressing ratio compared to the volume of concrete of the apron is to 21 kg/m 3 :
- – Definitive longitudinal prestressing: 162,000 kg
- – prestressing longitudinal antagonistic: 167,000 kg
- – Transversal prestressing: 68,700 kg
The apron was carried out on a prefabrication area placed at the back of the low -cutting in sections with a length of 30.60 m each made in three phases:
- Realization of the lower Hourdis and two souls to the underside of the lower Hourdis, giving a section in U,
- realization of the upper Hourdis with the establishment of side bracons,
- Longitudinal and longitudinal prestressing of the section front section and installation of part of the equipment of the superstructure.
The realization of the U and Upper Hourdis section is broken down into formwork, reinforcement, concreting and formwork phases. The bracons are supposed to be fully compressed. They are simply sealed in their lower part and linked in the superior to the Hourdis by reinforcements.
At the end of the pushing, the apron is common support by support to allow the dismantling of the temporary sliding supports and set up the final supports.
At the bottom of the valley, the land is swampy. Each battery is based on foundations of 4 piles of diameter 1.60 m having depths between 15 m and 33 m. The architect has chosen to make a single and flexible single -shaped barrel batteries of oblong section which evade in mind to take up the support devices placed in the right of souls.
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Notes and references [ modifier | Modifier and code ]
- Bresle viaduct On Structurae, accessed June 3, 2009.
- SFIC, ‘ A29 Bresle viaduct: a light and environmentally friendly structure » (consulted the )
- Right alignment = The plane layout of the highway defining the apron axis is a right in projection on a horizontal plane.
- Planet TP: the implementation of the deck by pushing
- Bracons are compressed parts in support of a slab.
- Mechanical yield is the relationship between the inertia of the box and the product of its section and the two distances of its center of gravity to the extrados and the intrados of the apron. In theory, the maximum yield is 1 for a box not having lower and upper slabs. For a rectangular section, this mechanical yield is equal to 0.33.
- These friction coefficient figures depend on the design of sliding supports and the products used. The given values correspond to a neopre-téflon support sliding on stainless steel turntables of mirror polished quality with appropriate sliding products.
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