Vibration isolation

mageba’s expertise in developing detailed vibration isolation solutions for buildings is demonstrated by an ongoing project in the Swiss Alps – protecting a transportation hub’s users from vibrations from a gondola-type cable car ropeway

Although not traditionally a core product area for mageba – alongside bearings and expansion joints for bridges and buildings, for example – the field of vibration isolation for buildings is one in which we continue to expand our capabilities. Developing a range of products to meet diverse vibration isolation and noise insulation needs is just the first step in most cases; generally, a detailed project-specific technical analysis and design is required to determine how the selected product should be applied to meet a building’s varied conditions and requirements.

In the case of the new transportation hub building currently being built in the town of Fiesch in the Swiss Alps, a solution based on one of mageba’s VIBRAX®DAMP range of vibration isolation bearing mats was proposed. The hub combines the valley station of a new gondola-type cable car with a Matterhorn-Gotthard railway station and a bus depot, with a number of businesses sharing the building. The various sources of vibrations affecting the building – most significantly from the cable car’s ropeway – would be expected to cause significant disruption to building use. In particular, the noise resulting from these vibrations would typically be a cause of considerable discomfort and annoyance.

To overcome this challenge, and thereby also comply with local building construction regulations relating to noise protection, a comprehensive analysis had to be undertaken, with a detailed design process to determine the different needs of the walls and slabs that should protect the building’s noise- and vibration-sensitive areas. It was established, for example, that an elastic separation with a tuning frequency of ≤ 25 Hz was required in order to adequately reduce vibrations from the ropeway (these typically having a much higher frequency, in the range 80 to 120 Hz).

Vibration isolation mats of type VIBRAX®DAMP were selected for use – a range of bearing mats of rubber granulate bound by PU elastomer. These can typically be used for loads of between 0.05 and 2.0 N/mm2, to achieve natural frequencies of 15 Hz or higher. The bearing mats were installed on the sub-base (lean concrete) beneath the building’s foundation slab, and a similar solution was implemented to prevent horizontal transmission of noise and vibrations through selected external basement walls.

The specific characteristics of the VIBRAX®DAMP mats required at each location were determined by mageba, resulting from an analysis of characteristic ground pressures (as determined by the building’s structural engineer), in such a way that the differential deflection between connecting parts of the building would not be significant. In determining the natural frequency of the bearings in each area, the dependence of dynamic stiffness on load had to be considered, as had the amplitude and frequency of the excitations and the bearings’ long-term behaviour.

Since mageba was already involved in the project early on, all design and execution details could be defined at an early stage, enabling the supply and installation processes to be implemented smoothly, maximising the quality of the final solution. As a result, the building’s users will be able to enjoy the use of this fine new building in a way befitting its location in this idyllic Alpine setting. 

Building designer: SPI Schmidhalter Partner Ingenieure AG
Contractor: Volken Group
Building owner: Aletsch Bahnen AG

Artist’s impression of the transportation hub building, currently being constructed in the Swiss Alps (Image: ©Aletsch Bahnen AG)

The quality of the vibration isolation solution must be matched by the quality of the subsurface on which it is installed, with a high degree of evenness required

VIBRAX®DAMP as installed in accordance with a detailed design plan, with gaps between mats avoided and all joints sealed using adhesive tape

Plastic sheeting was then used to further protect against the ingress of concrete into the joints between sections of matting, since such concrete would bridge across the isolation matting, transmitting structure-borne noise