Trubschachen, Switzerland, 2021

Himmelhausmattesteg suspension bridge on a wire rope mesh

An elegant suspension bridge has been crossing the Trub in Trubschachen in the Emmental since spring 2021. The construction of the pedestrian and cycle path bridge is unique: for the first time, a bridge is suspended from a wire rope mesh instead of the usual suspension ropes.

The initial situation
The bridge connects the Trubschacher Himmelhausmatte with the train station. It creates a safe way to school for the local children and closes a gap in the national hiking and cycling network.

The construction
With a slight incline as it crosses the river, the bridge spans a total of 25.8 metres, with the suspended section of the bridge stretching 21.5 metres between the supporting pylons. The bridge joins the road to the neighboring district, with its 2.2 metre width enabling the municipality’s 5 tonne snow-clearing tractor to cross in the winter. The bridge is designed for a payload of 4.0 kN/m2.

Constructed from steel gratings, the bridge deck is supported on four HEA 140 longitudinal steel beams, which in turn are supported by seven transverse beams across the suspended section. The structure is then braced by the Webnet which creates a superelevation sag of 280 millimetres. The design, including the inclination due to the superelevation sag, was developed to allow easy access for people with impaired mobility.

The wire mesh Webnet consists of 3 millimetre stainless steel ropes, with a construction of 6 × 19 + WC, which with sleeves, forms a mesh width of 80 millimeters. The Webnet is connected to 26 millimetre diameter suspension cables, which are 1 x 37 open spiral strand stainless cables, with Jakob Forte turnbuckles fitted at both ends. The suspension cable has a 2.4 metres sag over its 23.7 metres length, which gives an f / l ratio of 1/10. These cables are attached to the pylon heads, together with the Jakob Forte M36 wire ropes and the tie-back cable.

The 5.3 metre high articulated pylons are manufactured from welded hollow sections and support the longitudinal profiles of the bridge girder on their crossbars, these being connected to the pylons by means of bolted joints. In total, the bridge structure, including its gratings, weighs about 12 tonnes and it is anchored into heavy weight concrete.

The construction process
Construction work started in spring 2020. After completion of the foundations, the articulated pylons were positioned in place together with the temporary suspension cables which had already been attached. The girder had been manufactured off-site and transported to Trubschachen in one-piece, where it was lifted into position by pneumatic crane and secured to temporary cables. The suspension bridge was opened in spring 2021.

The bridge is a joint project of the companies Jakob AG, Thuner Bau AG and Kambly SA as well as the municipality of Trubschachen.

Length: 25.75 m, width: 2.20 m, span: 21.40 m
Cable span l: 23.72 m, sag f: 2.41 m (f/l = 1/10)
Pylone height: 5.30 m

Jakob services

Design, planning and calculation: entire structure
Material supply: main cable (Forte ø 26 mm, open spiral strand 1 × 37), tie-back rod (Forte M36), Webnet (ø 3 mm rope, mesh width 80 mm, vertically orientated)
Installation: cable- and mesh structure