by Frederike Berg
Maximum installation heights with modular façade scaffolds
Modular facade scaffolding is an efficient implementation of current safety standards such as TRBS 2121. With this type of scaffolding, for example, the next working level is assembled from the level below, even before the scaffold deck is fitted.
In an interview with Scafom-rux Germany Technical Manager, Jochen Gebauer, German scaffolding magazine DER GERÜSTBAUER talked about the topic of maximum erection heights for modular façade scaffolds.
DER GERÜSTBAUER: Mr. Gebauer, with the modern modular façade scaffolds, one question always comes up: "What is the maximum assembly height compared to conventional frame systems?”
Jochen Gebauer: The maximum installation height is a somewhat unrealistic figure, as it is only needed in a very few cases. But be that as it may: For frame scaffolds such as Scafom-rux SUPER or similar, a maximum height of 100 m is assumed. In the case of today's modular facade scaffolding, this height is much lower, because the statics are completely different. The offset standard joints at a height of 1 m alone make these scaffolds significantly "softer" across all manufacturers. The reason for this is that the joints are not welded, as in the case of scaffolding frames, but must be treated mathematically as if they were hinges. For our SUPER-RS scaffolding system, the maximum calculated height is 84 m for a 2-plank construction. But here we already reach the limits of the validity of the maximum height, because it only applies to the ideal case of anchoring every 2 metres.
DER GERÜSTBAUER: That is unlikely to be practical?
Jochen Gebauer: Exactly. This only works with a smooth façade without windows, which would be hard to find in reality. So it makes no sense. So I question the validity of the maximum height.
DER GERÜSTBAUER: Up to what height is the practicality given?
Jochen Gebauer: When anchored every 4 m, the maximum height of SUPER-RS is 56 m. In terms of load-bearing capacity, the scaffolding standards themselves could certainly be loaded much higher, but there are horizontal displacements, e.g. at the standard joints, which must not exceed certain tolerances. So it is not a static problem, but an increasing stability problem from a certain height - and this is the case with all modular facade scaffolding. This may sound a little dramatic, but we always build in a safety margin of 1.65 to make sure there's enough to spare. So, yes, with the SUPER-RS you are standing on a very practical and stable scaffold with a height of 56 metres! In fact, with the erection height of up to 24 m used by the DIBT for scaffold approvals - the so-called standard configuration - the SUPER-RS does not need to be stabilised by cross diagonals at the lowest level of the scaffold, as is the case with other systems.
DER GERÜSTBAUER: What adjustments did your engineering department make to ensure the stability of your modular façade scaffold?
Jochen Gebauer: First of all, we have been able to reduce the wall thickness of the uprights for the SUPER- RS compared to the RINGSCAFF modular scaffolding system in order to make the whole system significantly lighter. Then, by moulding the lower ends of the standards, we ensured that the standard tube connector, which users are familiar with from most market-relevant scaffolding systems, can continue to be used with the best possible fit. In this way, we have ensured upward and downward compatibility.
DER GERÜSTBAUER: What do you mean by "moulding"?
Jochen Gebauer: Scafom-rux did not go for the simple solution of making the tube connector thicker in order to connect the thinner-walled standards securely. Rather we moulded our thinner-walled uprights at the bottom, in other words "pressed them tighter", so that they fit onto the standard tube connector. This way they remain compatible with existing scaffolding systems.
A quick digression: In the case of the tube connector, the contact area of the lower tube on which the upper tube rests is decisive for the load-bearing capacity. This is called compressive force transmission. It is important how well the compression force is transferred from the upper standard to the lower standard. This is determined by accredited institutes via tests and checked by the DIBT. The optimization of the compressive force already starts in production. During the final pressing of the lower ends, our standards are pressed into the exact right shape – i.e. with maximum locating surface on the standard below. Normally this production step can result in a deformation of the lower cut surface. A careless production would spoil the values for compressive force and bending moment and result in significantly lower maximum heights. Therefore, a look at the approvals of the market participants for these values already says a lot about the quality of a scaffolding system. The permissible compressive force for SUPER-RS is 103 kN.
Competitors are sometimes in the two-figure range and have to upgrade the scaffolding much earlier. Our decision to keep the standard tube connector and focus on the precision production of the lower end of the standards pays off not only in terms of better statics, but also in terms of material stock for users. Thanks to the compatibility of the tube connectors, users can continue to use their "old" scaffolding systems.
For example, pedestrian tunnels or similar, where the substructure could be made of RINGSCAFF and the superstructure of SUPER-RS. Or you can use modular scaffolding at intermediate heights to adapt to the object to be scaffolded. SUPER-RS expands the possibilities.
DER GERÜSTBAUER: Mr Gebauer, that was a lot of technology. How would you sum up what you have just said?
Jochen Gebauer: With SUPER-RS you can build very high because of the large bearing surface for compressive loads. And it can be further stabilised by offset post and beam construction. For heights up to 24 m, no diagonals need to be installed in the lower layer, unlike competing systems. And the tube connector remains compatible with the standards.
DER GERÜSTBAUER: Thank you very much for this interview!
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