Who has never sweated strongly and been sunburnt sitting on benches of a stadium in a hot afternoon? Still today, most of the open-air stadiums are not covered. The only solutions are cap, sunglasses, and sunblock. However, over 2000 years ago, Romans had already designed and built a system spreading and rolling back a cloth, called velum, over benches of amphitheaters.

Even if many manuscripts and paintings prove the reality of the velums, few clues reveal the secret of the spread and roll back mechanism and the installation on the arena walls. In the fall of 2003, Mr. René CHAMBON, retired engineer from “Arts et Métiers”, decided to spend his free time solving this enigma. After many years spent on bibliographic research and watching amphitheater vestiges, this Roman antiquity enthusiast discovered how the Romans could have installed, spread and rolled back a 25000 m² and 8 tons cloth, over the benches of the Roma Coliseum, in order to protect 50000 spectators from the sun.

Reusing his experience in engineering, he built a physical mock-up at reduced scale (1/100) in order to explore his hypothesis on velum installation and proceeded to traditional structural analysis computations in order to determine the materials and dimensions needed to support the velum weight. The results of his works were reported through TV broadcasts, conferences and newspaper articles.

Convinced by his enthusiasm and the quality of his approach, Dassault Systèmes proposed to submit his theory to its design and scientific simulation software, bringing his project to digital mock-up at real scale and from 2D static linear computations to 3D dynamic non-linear computations, better suited to simulate the reality. 

The 3D digital geometry representing the cloth has been generated with CATIA V5. The use of parameters, such as cloth dimensions, the number of cloth segments, or velum inclination angle allows an easy and quick update of the geometry, enabling to switch from the Puy du Fou arena to the Roma Coliseum in a few clicks. This geometrical model is used as support for the 3D mechanical simulation of the velum. This simulation is fully performed with the Abaqus software, the non-linear finite elements analysis solution from SIMULIA.
Special attention was given to the tuning of the mechanical behavior of the cloth and the hoists, the management of the multiple contacts and frictions of this case as well as on the influence of the weight of the system, in order to accurately measure the efforts required on each hoist by the pullers. This important work was a prerequisite for running the numerical simulation. This simulation was computationally intensive, yet feasible on a laptop.

The realistic 3D animation of the cloth and cables strains during the spread and roll back phases, as well as the computation of forces required at any time, achieved to validate that the mechanism imagined by Mr. CHAMBON could indeed work. This simulation also showed that one man’s strength was enough to activate each hoist, even when pullers were not in-synch or if one puller was temporally deficient. The Dassault Systemes fully parameterized model, by allowing rapid variations of the number of hoists, demonstrated that the actual number of hoist masts found on the Coliseum was well dimensioned for the pullers’ strength, even during the critical phase of the roll back where friction and weight are at their max.

The DS 3D fully parameterized model setup for this study can now be used for modern applications of the antic velum, where synthetic cloth and electric engines replace linen, hemp and manpower.

Thus, present could benefit from lessons from the past, making it possible to quickly dimension and build modern arenas. Such facilities could host shows or be a shelter for refugees left homeless after a natural disaster for instance.