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Products and solutions, 2008-02-18, 03:32 PM

St. Stephen's Cathedral, Vienna

The Viennese love their "Steffl", as the Stephansdom or St. Stephen's Cathedral is affectionately known. Only reluctantly do they tolerate the scaffolding of the Gothic building, which has been the landmark of this City on the Danube for the last 500 years. The Gothic sandstone monument calls for continuous maintenance and restoration, and the spire of the 137 meter tall south tower is currently undergoing an overhaul. A 57 meter tall scaffold encloses the slim structure and gives the stone masons a safe basis for their restoration work.

The working scaffold experts of ThyssenKrupp Xervon, Maria Lanzendorf, have been regularly scaffolding parts of the cathedral for the last ten years. "It is our endeavor to do a perfect job of work throughout – from professional planning and job scheduling through to execution," explains Johann Szlavich, in charge of Working Scaffolds in Austria. To scaffold the cathedral, he only assigns erectors with many years of experience because of the unusual challenges associated with such a project. It all starts with the logistics. The scaffold materials are driven by truck to the cathedral square, where they are put to immediate use because of the total lack of storage space here. For the scaffolding around the spire, for instance, about 70 metric tons of materials had to be delivered, raised to the right level in small batches as needed, and then immediately assembled.

Szlavich does the mental arithmetic: "Assuming 10 kilos per scaffold component, this amounts to 7,000 components that have to pass through several hands – shifted, deposited temporarily, erected and dismantled several times." The scaffolding of the spire starts at a height of 80 meters and ends at 137 meters. At the bottom, octagonal level, each side is 3.5 meters long. The circular scaffolding above tapers from an average of 10 meters to only 6 meters at the top. The required scaffold materials were raised by two existing elevators for people/goods and an existing scaffold access tower to height of only 80 meters. Here on a projecting structure the scaffolders erected a new passenger/goods elevator that ends at a height of 120 meters. The remaining 17 meters have to be negotiated on foot. It wasn't possible to continue the elevator to the top because the tying loads would have been too much for the slim spire. The scaffold discharges additional horizontal forces into the spire as it is. For safety's sake, the team of ThyssenKrupp Xervon Austria suggested at the planning stage that the cathedral maintenance department have the effects of scaffolding on the spire checked by an external structural engineer.

Safety first

All the scaffold components are fastened firmly so that they are capable of withstanding storms during their several years of service. No part must be allowed to fall even during erection and dismantling. This demand for complete safety had top priority for the cathedral maintenance department. The cathedral, after all, is a major tourist destination, attracting over 2 million visitors per year – imagine the consequences if a bystander were hit by pieces of scaffolding! "And the stone masons of course have to have an absolutely safe and ergonomic workplace on the scaffold," adds Johann Szlavich, explaining the company's aspirations for the scaffold structure. At the planning stage, each lift of scaffold was tailored by CAD to the shape of the spire. The detailed drawings cover all eventualities during erection and ensure rapid progress – supported by a meticulously accurate delivery plan for materials. "We go through this procedure for every job, even for technically straightforward scaffolding projects. Professional, detailed job scheduling always pays off in the long run," Szlavich confidently continues. It not only permits a precise list of components, but is also essential for a coherent logistics system so that there are no holdups in the work process.

In the choice of the scaffold system employed, the working scaffold experts consulted with the stone masons of the maintenance department. In the course of these jointly completely projects, the design engineers and users have developed an efficient working relationship. Johann Szlavich sums up the collectively gathered scaffolding experience: "A modular scaffold system is best-suited to the stone masons' work." With this type of scaffold, a deck can be removed ad hoc if, say, a large block of stone has to be lowered. Frame scaffolds will not permit this as the deck also serves as bracing and is necessary for structural reasons. The Austrian working scaffold experts opted for the Modex modular scaffold system from Hünnebeck (Ratingen, Germany). The spire has been scaffolded with it since April 2007. The extensive restoration project is expected to take two to three years.

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