If one wants to construct a building, one often requires an official permit. A prerequisite for this are usually static calculations, also known as stability approvals or simply statics. While simple or subordinate construction projects often require only a simple proof of stability, special proofs of stability which must be approved by a second, independent body are required for buildings in public areas as well as for commercial or larger buildings. Especially concerning construction law, however, the building regulations and other legal requirements of the federal states and municipalities often differ significantly from one another and change over time. In North Rhine-Westphalia, for example, roofing for bicycle parking spaces with a roof area of up to 100 square metres is currently not subject to approval; but everywhere else in Germany it is.
For customers commissioning a canopy system to be used as a waiting hall, bicycle parking space or smoker’s shelter, the static calculations required will delay the delivery process by up to three weeks. Add to that the time required for their review which can take months; depending on the capacity of the testing engineering office or the testing body. Statics and their testing are also a cost factor: for waiting halls, they account for an average of around 30 percent of the actual construction costs.
One for all: type static calculations
Time and costs that can be easily avoided: statics for standard structures can be created independently of the building application and be approved by an independent institute. These type approvals or type static calculations then apply nationwide. If a building permit is applied for, the issuing authority only has to check, on the basis of the type statics, whether the building requested matches with them. Usually just a formality.
Although type static calculations are practical, their importance had declined in recent years. Experts cite several reasons for this: many builders and builder/owners want increasingly custom design and construction while simultaneously the effort required for the type static calculations is always increasing. Finally, there are only a few organisations that carry out the independent type static tests; namely the State Office for Construction and Transport in Thuringia, the State Trade Office Baden-Württemberg, the State Trade Institute of Bavaria, and the German Institute for Construction Technology DIBt in Berlin.
On the safe side
Yet, what is meant by statics and how does a structural engineer work? The aim of the statics of building structures is to ensure their safety and reliability. The forces acting on a structure and their mutual effects are calculated in order to determine possible hazards.
The basis for every structural calculation is the determination of the framework conditions. Roofing systems, for example, have various profiles and material thicknesses, different materials used, dimensions and a building grid, structures, materials for the fillings, such as a sheet metal roof or glass side panels. In their interaction, these elements must always safely carry all arising loads and withstand the various external forces.
Since these loads are location-dependent, acceptable limits are set for wind and snow load type static calculations. There are many factors to consider: in the North German lowlands, for example, since 1980 we have seen increased snow load requirements. Accordingly, the permitted snow load here is determined as 2.3 times that of normal. Wind loads, on the other hand, are dependent on terrain structures such as the surrounding buildings and are also height-dependent.
In his calculations, the structural engineer also has to consider the way in which the waiting hall system, for example, is fastened. Finally, evidence of the quality of the production, as well as constant checks on, for example, the welding procedures used and the necessary qualifications are required.
The static requirements for a building are nowadays consistently ensured by standards; the same applies to the permissible types of calculation, for materials and fastening systems. For a waiting hall, between 20 and 30 of these standards must be observed and fulfilled. Nonetheless, the end-customer need not be concerned about their compliance. Another advantage for the customer is that compliance with the standard limits influences his liability. Anyone who has done everything right is automatically on the safe side and also benefits from the guaranteed, high-quality production.
The demand for type static calculations is increasing again, and these are also increasingly being asked for where no certified statics are required under building law. For companies the aspect of quality assurance certainly plays a role here.
Type testing ex factory
The numerous advantages were reasons enough for WSM – Walter Solbach Metallbau GmbH – to have the State Trade Institute Bayern (LGA) execute a type approval for variants of its popular Cologne shelter system. The present test certificates are valid for halls of up to 4195 mm wide and 2165 mm deep and allow complete freedom of design.
The Cologne and Mannheim model series are designed according to type testing for snow (Sk = 1.9 kN/m²) and wind loads. The characteristic Sk value in the snowiest zones (3) in Germany is greater than or equal to 1.10 kN/m². The constructions are also approved for wind load zones I – III and thus approved throughout German federal territory. Only a few places near the coast and other extreme locations are excluded.
The Cologne type shelter has a flat roof made of weatherproof ribbed sheet metal. Its load-bearing frame construction consists of galvanized steel square-profile tubes which are coated with freely selectable colours (RAL). The shelter system includes foot plates for bolting to the ground and wall elements made of toughened safety glass. The Mannheim model is also enclosed with weatherproof ribbed sheet metal. As with the Cologne variant, an integrated drain also carries rainwater through the frame construction and spouts divert it close to ground level. Side elements, such as opaque corrugated iron walls, can be customised. A wide variety of panels, including trapezoidal sheeting, aluminium corrugated sheet, toughened safety glass, trellis or wood are available. The Cologne and Mannheim shelter systems each have LGA-tested type statics and are delivered key-ready by WSM. As a result, assembly times as well as interruptions due to set-up time are considerably reduced. Due to their welded construction, both systems can be easily dismantled even after years of use and re-installed at other locations.
Good advice is – gratis
Who requires a stability certificate for which building and what effort can be reckoned with can be found out from the building regulations of the federal states and municipalities. These are very different and are constantly evolving. “We therefore recommend our customers to submit a general construction request to the relevant authorities for new projects which will provide clarity,” explains Christian Mortsiefer from WSM. “Our customers, however, also receive initial free information and all-round support from planning via approval up to installation”.
Conclusion: Builders often save time and money with type static calculations. Even if no independent static approval is required, it remains good to know that the building was carefully produced and tested, and that nothing can go wrong in terms of statics and quality.