The roof structure of the Hemicycle consists of 22 glulam lattice girders arranged radially around a metal core. During an inspection of the ceilings, significant damages were discovered at certain joints. A complete analysis of the existing structure and a check based on current codes revealed a critical sensitivity of the structure to displacement of the supports due to its hyperstaticity. The new distribution of forces within the structure led to stresses being exceeded at certain joints, to the point of failure. Various repair and reinforcement options were studied, leading to the complete doubling of the structure with a steel frame. The glulam beams were completely unloaded using a complex jacking system.
The complexity of the project lay in the contiguity and accessibility of the roof. The entire new structure was installed and loaded without affecting the roofing or the suspended ceilings.