Some 200 remains of amphitheatres of the immense Empire!

The mast anchors of the velums are sometimes so well preserved that we can know exactly their number and their section: 240 holes of 45 x 55 cm for the Colosseum, 120 of 30 cm in diameter for the arenas of Nîmes.

See on the Internet: Listing Roman amphitheaters

The photographs on the lower left are those of the top and the below one of the 120 receptacles of masts 30 cm in diameter implanted once at the top of the arena of Nîmes.
Most of the amphitheatres are not as well preserved as those pictures above, Colosseum, Nîmes, El Djem, Pula, Arles .... That of Pompeii, protected by the ashes of Vesuvius, deserves special mention on the grounds that a period painting was found representing him covered with a velum.

Velum representations Romans since the 19th

Rare pen drawings of 1876 and 1888, presumably inspired by the discovery, in 1869, of the famous painting of the amphitheater of Pompeii at the time of its splendor. representations whimsical velums, without any demonstration of feasibility. Why vertical strings in front of the audience? Question without reply.

Images from No. 83 (2003) of the journal "Historia". A representation of velum even more fantastic than previous ones ! Its inclination to the outside leaves the notables of the first rows in full sun. Without reason we kept the useless strings verticals in front of the spectators.

675/5000 Representation of 1996. The notoriety of the French archaeologist who defended it, and no doubt initiated it, gave it a wide broadcast in magazines and documentary films. It results from his " "a priori" as sealing holes in large stones, found at the foot of the Colosseum, were used to fix maneuvering winches velum. 240 2 x 50 m canvas strips are supposed to wrap unroll on drums maneuvered from the square. 480 strings of 50 m long in front of the facade, parvis cluttered with 240 winches, «faseyages Noisy canvases and ropes under the slightest breeze ... and no resemblance to the velum of Pompeii's painting.

This fairly recent representation is the result of the archaeologist German Rainer Graeft, no less famous than French. Celebrity which also allowed wide distribution in magazines and various films : The photo opposite is from "Gladiator". Point is not needed to have strong notions of physics and resistance of materials to understand that this concept is unrealistic, except to protect ardours of the sun as the plebs of the highest tribunes. Would the emperor and his relatives have appreciated?

Velum concept of the engineer of Arts et Métiers René Chambon. The following pages do not hide anything from its proof of feasibility, supported by the validation of its calculations by Bureau Veritas and a modeling of Dassault Systèmes, a world leader in advanced software.

  • - velum of the same look as that of the period painting on the amphitheater of Pompeii.
  • - without hanging ropes and bulky winches around the building.
  • - of an easy initial Installation, with the strength of the arms, without crane and without scaffolding.

Here is dear Emile Zola how we could draw the velum above the colisee

We must first install 240 mats

At the top of a building as tall as a building modern 15 floors, 2m more than the Stade de France). The size of the holes (45 x 55 cm) receiving them suggests that each of them weighed at least 1500 Kgf. Calculations of the second tab demonstrate that the said sections are adequate for masts in front of bear the weight of a velum as big as 3 to 4 football fields. The image illustrates how they could be hoisted by means of a winch on the ground. Sealing holes on some heavy stones, found near the monument, suggests that they served as a basis to winches, their weight, estimated at 2000 Kgf, opposing the effort of tearing induced by the weight of the mast.

Then you have to hoist the central ring

This one, a hemp rope of about 80 mm (or metal chain) is spread on the ground of the arena, equipped with its halyard pulleys, his arms and his halyards. Through the stands ends of the two strands of these are mounted and rolled up on a winch previously fixed on the upper platform. Point There is no need to maneuver as many men as winches: alone can support 2, 3, 4, 6, 8, 10, 12, 24, the flexibility of the ring allowing to lift, step by step, only one about half a meter high. When the ring is at the elevation required, here for a height difference of 14 m, the arms (in brown) hang down. The mass share to be raised by each double halyard being 25 Kg (ring + pulley + additive mass) the effort required of the winch varies from 30 to 100 kgf approximately, from the beginning to the end of the operation. With a ratio of 3 to 4 a single man enough!

The drawing below shows the hanging of the arms at the top masts. The lower strand of halyard is then released from the winch and hangs to the ground.

The whole of the trussed canvas (in red) is placed on the entertained. The lower strands of the halyards are then easily passed in the rings carrying canvas, then wound on the winch of platform. Those at the lower ends of the canvas are then immobilized on the strands of halyards. All that's left is to operate the winches to hoist the velum as shown. . The share of mass to be lifted by each strand of halyard being 30 kg (a canvas rectangle of 2 x 50m) the effort required of the winch is a higher than previously, from about 40 to 120 kgf, from the beginning to the the end of the operation. Again a small number of men at the maneuver can suffice.

Some adjustments of the halyards are enough now to obtain a tight troussage of the canvas in front of the platform winches. The Figure 3 below provides a better view of the canvas completely folded. It then holds in a section of 75 x 75 cm, although inferior to that of one of the men represented at the foot of the monument !

How could we then unfold and fold it?

Figure 1 : The canvas (in red) is carried by about thirty small rings that can circulate on the lower strand of a halyard (in blue), excluding: - from the lowest, fixed on the rope. - from the highest, immobilized at a fixed point in the platform. The halyard moves around a pulley attached to the ring central and winch drum T on the platform. The central ring is carried by a series of arms (in brown) attached to the tops of the masts.

Figure 2 : Winch rotation in the direction of the need began to fold the canvas back to its low end.

Figure 3 : All the canvas was trussed near the winch T on a height of about 75 cm for 1.5 m wide canvas rings and the same width (30 rings of 1 cm thick). Both strands of halyard have only one weak tension.

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