A modular approach gives Despe the Contract of the Year Award

Urban demolition invariably throws up a number of immediate challenges that have to be overcome by contractors, especially in Europe’s heavily congested and built-up city centres. This was the case for Italian contractor Despe when it won the contract to bring down the 22 storey UAP Tour that was located right in the centre of the French city of Lyon.

The contract required the removal of the structure, located adjacent to an important marketplace and an Exhibition Centre that had to remain open and unaffected during the demolition. This meant that there had to be no noise or pollution during the work, which also had to be carried out with the minimum of dust and vibration possible. And as if that was not enough, there could be no disruption to the road traffic that uses the roads close to the foot of the tower.

The above requirements created a challenge – explosive demolition was obviously not an option and the tower was too tall for the use of high reach excavators, even if there was sufficient space for such equipment to work in. At first glance, cladding the building in scaffolding and then carrying out demolition floor by floor was the only viable option. However, the time required for such an operation was a major drawback for the client Bouygues.

Italian flair?

Despe is well known for its often innovative approach to the demolition tasks it undertakes, and it certainly proved the point on this contract. While endorsing the floor-by-floor approach for the removal of the structure, Despe added its own flair to the project by proposing an alternative to scaffolding – a three level working platform that entirely sealed the areas of the building being worked on to prevent any debris from falling to the site below and protected the workforce from the worst of the elements. An important part of the design was the fact that the platform could also hydraulically ‘climb’ down the building as work progressed.

The concept sufficiently impressed Despe’s customer for them to agree to the proposal and what has now become known as TopdownWay was transferred from a concept into reality – a modular frame structure that accommodates three working decks that is assembled by crane. Once in place, it seals itself to the structure to allow work to be carried out on three floors at the same time. It has been CE certified to the IMQ Institute’s machinery, Low Voltage and Electromagnetic Compatibility directives. The three decks are supported by 12 hydraulic pistons controlled by a single PLC that allows the system (in the UAP Tower’s case weighing 300 tonnes) to be lowered by one floor level by a single operator in 10 minutes.

Its first outing, the UAP Tower, was a 78 m (256 ft) tall structure of 22 floors – 2 basement floors, three for car parking, one for restaurants and 17 office floors. TopdownWay was used to remove the top 17 floors of the building.

The tower crane that was used to assemble the structure – a challenge it itself at 80 m (263 ft) above the ground – was also used to lift a variety of machines onto the tower to carry out the actual demolition. This included a Doosan 470, two Cats (a 340 and a 330), a Volvo 140, two Kaiser machines and six mini excavators. Despe worked a single nine hour shift for five days a week, with a maximum workforce on site at peak of 16 (the average was 10). Work began on the project in early October 2011, with the final site clearance being completed at the end of May, 2012.

Soft strip was carried out by workers on the lowest level of the platform, with windows being removed by workers on the middle level. Mechanical demolition was carried out by the machines and personnel working on the top level. This three-strand approach resulted in the UAP Tower being brought down at a rate of two floors per week.

Time of the essence

In all, Despe estimated that it took half the time to assemble the machine than it would to fully scaffold and enclose the structure, and the working sequence also dramatically reduced the actual demolition time required. Also, the company has been left with a system that it can deploy on other, similar projects. Despe’s managing director Stefano Panseri told D&Ri that the system can be used on almost any height multi-storey of regular footprint (square, rectangular or triangular). The need to crane the system into place for assembly is the major criteria for the system’s use.

The judges that assessed the Contract of the Year criteria deemed the demolition of the UAP Tower using TopdownWay as being the outstanding entry for this Award and were unanimous in this decision. The innovative thinking, engineering excellence and textbook project management displayed by Despe during the project were the primary factors in their reaching this conclusion. The result is a worthy winner indeed!