„Roofing of Bibracte archeological site“ was quite a small project for Sipral, nevertheless very interesting. The basic concept Paul Andreu, an architect and RFR design office had to work with was to design a light transportable manually assembled construction able to span a big layout area without central columns that could obstruct the ongoing archeological works.
Construction of the whole roof of approximately 22 x 37 m is formed of 11 types of elements welded of 6082T6 aluminum alloy tubes of a strength similar to steel. Basic construction elements are triangular beams (called MING in the project) 3,75 m long, welded of bent tubes and nodes cast in sand forms. Cross arrangement of MINGs, mutually connected only through stainless pins ensures high transverse rigidity and bearing capacity of horizontal construction of the roof.
The roof is born with columns placed only along perimeter. During winter when excavation works are stopped and the roof can be loaded with a thick layer of snow there are also central columns installed.
Since the construction is placed on a protected area of archeological excavations it was not possible to anchor in common foundations. All columns are placed on metal distributing grates that are fixed in their position only with steel tubes driven into the ground. The construction fights with upward pressure and wind effects through loading of these grates with wired baskets filled with stones and rests of amphoras found in the excavations. There are also 12 bags hanging on brackets on opposite sides of the roof. Each of bags is filled with 3,5 tons of excavation soil and have affect on general stability of the construction and together they also ensure perfect stratching of the roof covering fabric.
External surface of the roof construction is covered with white technical fabric providing protection of the excavation space against weather conditions but at the same time let through enough light necessary for the archeological works.
Installation of construction was done by employees of the excavation runner and supervised by a Sipral´s representative. The roof was installed above already open excavation placed in hard-to-access location and the installation had to be done manually from a scaffolding only with help of small technology.
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