The new hall of Würth's Finnish branch relies on a sleek construction of columns and beams. However, the design of the beams as arched trusses in Kerto-S proved to be anything but trivial and adds a new variant for roof supporting structures to modern timber engineering.

One of Würth's most strategically important logistics centres is located near Riihimäki, around 70 km north of Helsinki. The branch was founded in 1975. From there, Würth supplies a wide range of products to end consumers as well as to 200 branches and shops throughout Finland. Due to continuous growth, the branch has been continuously expanded and modernised throughout its 30-year history. In order to meet this continuing trend and the changing business requirements, the Würth Center in 2021 received a supplementary new building to present its special range of the so-called ASSY screw, which is considered the company's key component in timber construction.

For this purpose, the client wanted the new “Würth Center ASSY” to be an engineered timber construction. As a result, it now combines state-of-the-art timber construction know-how and uses the fastening solutions of the extensive ASSY product family.

Complex geometry for seemingly simple solution

The external appearance of the new hall does not initially suggest an extraordinary building structure. The cuboid with a glass façade on one of its front sides first reveals its surprising wooden structure on the inside. The arched trusses of the roof structure are particularly striking. They have numerous special features that merit closer examination, as does the overall structure with regard to load transfer.

The overall structure consists of beams on two columns in a row, with the beams designed as arched trusses. The arched trusses may appear to the layman to be arch-shaped lattice girders of a special design because of the inserted vertical bars, but they are not. It is true that the initial goal was to construct a truss.

However, after numerous designs for truss variants, the structural engineers abandoned this and looked for a more practical geometry. This eventually resulted in the arch truss with vertical bars. And because the client's representatives in Finland also liked the beam shape, the structural engineers developed the arched truss further, right down to the details. The latter raised numerous questions that had to be answered.

For the supporting structure, the building dimensions were specified as just under 58 m long, 23 m wide and 10 m high. This not only fixed the span for the arch trusses at 22.50 m, but also their truss height at around 2.80 m at the lowest point of the arch.

It also quickly became clear that the arches could not be made of glulam due to the required transverse compressive strengths - especially at the support, where the transverse compressive strength in the chord of the arch would not have been sufficient at an angle to the direction of the grain - but that Kerto was the material of choice. This was also a good solution, as Kerto is a tradition in Finland.

Dipl.-Ing. (FH) Susanne Jacob-Freitag, Karlsruhe

New Würth Center hall (mikado-online.de)