The Arc Majeur, engineering at the service of art

    Since this Tuesday, the monumental work of Bernar Venet wraps the E411 at Lavaux-Ste-Anne, offering motorists an unmissable landmark in the landscape. The assembly operations, carefully planned, went off without a hitch. Among the many stakeholders and partners in this project, supported by the John Cockerill Foundation, our teams carried out a comprehensive mission of stability and design assistance.

    Since 2005, our teams have studied a dozen works by Bernar Venet. L’Arc Majeur is a continuation of the partnerships that greisch has led since its inception with various artists such as Florence Freson, Emile Desmedt, Jean Glibert or Arne Quinze. Indeed, an artist does not commit himself alone on the path of design. If creative thinking is entirely attributable to it, certain constraints arise during this journey; that’s when the engineer comes in.

    Stability, resistance to the effects of wind and earthquakes, overall coherence of the structure … all elements that contribute to the durability of the works. The role of our teams is therefore important to ensure their sustainability while preserving their authenticity.

    A monumental work

    In the case of the Major Arc, the structure must withstand its own weight of steel -140 tons for the great arc and 40 tons for the small- but also the effects of the wind. It is calculated to withstand gusts of up to 200 km / h. In addition, to counter the effects of wind and avoid steel fatigue, the large bow is equipped with a Dynamic Tuned Shock Absorber (A.D.A) placed at its top. This serves to counteract and dampen the oscillations of the arc. This device, which is essential for the stability of the structure, has been the subject of special studies at Greisch in partnership with ULiège (Windlab) and V2I monitoring, and was manufactured by GERB.

    The principle of such a device is to place a mass, here 1500 kg, which will move where the movements of the primary structure are maximum. It is designed in such a way that its vibration frequency is the same as that of the structure. Its movement will counteract and dampen the oscillations of the arc thanks to shock absorbers fixed to this mass. This makes it possible to transfer some of the kinetic energy of the structure to the damper, to greatly reduce vibrations and thus the risk of fatigue.

    The big bow consists of 3 sections of about twenty meters each. These were transported on site by exceptional road convoy and assembled to each other using concealed flanges inside the caissons. A peripheral weld will then be made at the junctions in order to permanently assemble the different sections. The small bow was conveyed in one piece completely completed.

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