The Palais des Congrès extension to the 1,000-bedroom Hotel Concorde La Fayette in Paris is a very imposing and complex piece of modern architecture. It was also a very demanding constructional engineering project. Designed by one of France's leading architects, Christian de Portzampark, it was built by a joint venture between construction groups SNSH and Bouygues, using formwork designed and supplied by RMD KWIKFORM.

The extension stands 28.7 metres high and is a huge inverted cone. It is elliptical on plan measuring 11.5 metres by 7.5 metres at its base, sloping outwards at an angle of 60 degrees to 36.0 metres by 24.0 metres. Construction called for 138 RMD KWIKFORM Super Slim Soldier shoring frames, each of which was set at a different vertical angle and varied significantly in both size and geometry.

Either side of the cone is a ten-metre high perimeter sloping façade that runs 80 metres in one direction and 40 metres in the other. It shares a common viewing gallery with the inverted cone, 11.5 meters above base level and extending some 11 metres from the face of the structure.

Both the cone and the façade walls are faced in 125mm thick decorative precast concrete panels. Those used on the cone are wedge-shaped and curved and typically measure 2.8 metres wide at the top, 1.2 metres wide at the bottom and are 3.2 metres high. Each is made to fit just one precise location, to a tolerance of plus-or-minus 1mm, so formwork accuracy was critical throughout the project.

The main task for the formwork was to provide temporary shoring support for these external precast concrete panels while the in-situ concrete inner skin was being poured and cured. And because the extension was being built over the hotel's basement car park – which was operational throughout the construction of the extension – the load from the formwork was transferred to the foundations five-stories below the new building,

The cone was constructed in two phases. Phase One, which took the outer wall to the level of the first main floor, was 11.53 metres high. Phase Two added a further 17.12 metres and went from first floor to roof level. There were smaller intermediate slabs that were cast on site.

Being a busy city-centre site, space was at a premium, so as one formwork frame was stripped, another was built to new geometry. This was made possible by using jigs that were engraved into a specially laid level concrete slab.

To add to their stability while being craned into position, the larger Phase Two frames were constructed in two sections that were roughly equal in height. However, they were assembled in one jig as one frame to ensure the specified plus-or-minus 1mm tolerance. They were then separated into two sections, to be re-connected once hoisted into their final position.

Construction of the façade called for 68 identical support frames that were moved in sections as work proceeded. As each pour cured, the formwork was hydraulically jacked up and slid to its new position.

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