Products and solutions Jul 2, 2009 11:30 AM
Wrapping up St. Stephen’s
For over ten years now, the scaffold structures required for this have been the responsibility of the working and protective scaffold specialists of ThyssenKrupp Xervon Austria. Most recently, working on behalf of the Cathedral Building Office, they have clad the 25 meter long and 34 meter tall scaffold on the west facade as well as scaffolding two sides of the roughly 136 meter tall, slim south tower with 65 metric tons of materials up to a height of 50 meters. As for most applications on the outer facade, the one meter wide scaffolds are again creating a solid platform for sandblasting and stonemason work.
“The scaffolds with a demanded live load of three kN/m² had to be designed to give the restorers trouble-free access to all parts of the building and their ornamentation,” explains Johann Szlavich, in charge of Working Scaffolds at Xervon Austria. The additional task on this assignment involved discharging high wind loads, as all the scaffolds were erected with cladding that molds itself tightly around the building’s geometry and displays a full-scale image of the building surfaces it conceals. As a result, the onlooker is not immediately aware of the visually obstructive scaffolds in front of parts of the building. For the scaffold erector, however, this means that the tie forces that have to be discharged into the historic building are several times greater. With cladding, the entire surface area is exposed to the wind as opposed to only 25 percent in the case of unclad scaffolds.
To scaffold the tower and facade, it is modular scaffolds that have been exclusively used. While being capable of withstanding high loads, they are also versatile. In the course of restoration work, it will occasionally be necessary to locally modify the scaffolds to allow for the replacement of individual sections of masonry. What adds to the difficulty is that the scaffolders have only limited scope for tying because of the lavishly ornamented facades. This calls for plenty of creativity and know-how.
The same applies to the support surface for the scaffold, which, because of the shortage of space around churches, often demands special solutions from the scaffold erector. At St. Stephen’s Cathedral, for example, the roofs of buildings immediately abutting the two sides of the south tower severely limit the area available as support for the scaffolds on the ground. The technically ingenious solution involves creating a grid-like platform of rolled section girders that rests on the tower’s buttresses. This way a sufficiently large support surface is created for the scaffold, and the loads are safely discharged into the building.
“So that challenging scaffold erection on the ‘Steffl’ proceeds swiftly and smoothly, we always place a lot of emphasis on upstream detailed planning and job scheduling”, says scaffold expert Johann Szlavich, explaining the services that have now been successfully performed for many years. It is not only a question of coming up with technically intelligent solutions. No less important are intricate logistics, Szlavich stresses, because failure in this area can quickly bring operations to a standstill. The scaffold materials are driven from the depot to Stephansplatz (cathedral square) in precisely predetermined batches and put to immediate use as there is no storage space around this tourist attraction.
“Because of the demanding nature of our ‘Steffl’, we only use employees with many years of experience,” says Szlavich, explaining the line-up of his cathedral team. After all, it is not only a matter of protecting the public during ongoing work. It is no less important to protect the building from damage. This is the reason why the last stage in the restoration project, the dismantling of the final scaffolds, calls for undivided attention so that no part of the freshly restored facade is damaged in the process. However, this won’t be happening for a while yet. Not until 2011 will the recently commenced restoration work on the west facade and south tower be completed.