A Paris landmark is soon to be shrouded in a massive temporary structure at the start of a major restoration project. NCE reports.
Work has just started on the first phase of a massive project to renovate the Panthéon in Paris. It is one of the city’s most recognisable landmarks, and an expression of France’s national pride. The full project, being undertaken by Centre des Monuments Nationaux, is set to take around 10 years, and could cost up to €100M (£83M).
The Panthéon was built between 1758 and 1790, and originally conceived by architect Jacques-Germain Soufflot as a church dedicated to Paris patron saint Geneviève. However, the revolution of 1789 changed the prevailing mood, and the building instead became a temple to the new republican nation.
It is the final resting place of many French cultural, scientific and national heroes, including Jean Jacques Rousseau, Emile Zola, Voltaire, Alexandre Dumas, Victor Hugo, André Malraux, Marie Curie and French Resistance hero Jean Moulin. It is visited by around 700,000 people a year.
The building is neo-classical in style and it boasts an 82m high dome that was made possible by the inclusion of iron reinforcing bars set into the masonry. At the time of construction it was the tallest building in Paris, a record it held until 1889 when it was beaten by Gustave Eiffel’s famous tower.
But the innovative construction method is partly responsible for the Panthéon’s need for repair, as water ingress has rusted the ironwork, and caused the stone cladding to swell and split.
“Obtaining the permits necessary to truck in and install this kind of equipment in the heart of Paris was no easy thing”
Stéphane Yorgui, Ponticelli Frères
Phase one of the restoration - valued at around €19M (€16M) and set to take around 18 months - involves repairing the building’s dome and the colonnaded stonework that supports it. The base of the dome will be rejointed and replaced with new stone and ironwork, and the dome’s lead roofing will be replaced.
Where possible, the original ironwork will be stabilised and treated to prevent further decay, while the dome’s glasswork and the lantern will be replaced to improve the interior lighting.
Subsequent phases will focus on the building’s internal colonnade, its vaults, internal and external walls and the stone base slab.
Preparing for the first phase has involved installing some substantial temporary works that have been designed in a way that ensures no load is transferred into the fragile building.
French scaffolding specialist Entrepose Échafaudages has designed a temporary roof to cover the entire dome and lantern that sits on a 315t base, made up of a reinforced hoop encircling the colonnaded drum at the base of the dome.
This hoop is supported by four legs, each 37m high, which take the load of the temporary structure into the ground where they are anchored by 17m deep micropiles.
One of the legs will also serve as the base for a 96m high tower crane that will be used throughout the restoration project.
To assemble the scaffolding, main contractor Ponticelli Frères brought in a Terex AC 700 all terrain mobile crane, equipped with a 42m luffing jib and 140t of counterweight.
“Obtaining the permits necessary to truck in and install this kind of equipment in the heart of Paris was no easy thing. But it turned out to be the best option for this type of project,” explains Ponticelli project engineer Stéphane Yorgui.
The entire lift took four weeks, with the largest of the structural elements measuring 20m by 20m in size and weighing 42t.
As the crane was working all around the Panthéon, the crane operator had to reposition it for every lift.
This was a major consideration when choosing which crane configuration to use, as the time required to partially dismantle the crane each time it was repositioned would have a big impact on the overall project schedule. With the chosen configuration, Ponticelli’s team needed only to remove 80t of counterweight to move the crane, and it was possible to transport the AC 700 fully rigged within the site.