Fine-tuned performance

A new cable-stayed footbridge in Hungary is currently being equipped with tuned mass dampers and spherical bearings that will ensure the structure’s long-term ability to perform well – both structurally and from a serviceability point of view.

Providing pedestrian and cycle access to a new intermodal transportation centre (including a railway station, a bus station and a P+R carpark) in the town of Kaposvár in southwest Hungary, the new cable-stayed bridge has a length of 200 m and is due to be opened later this year. Due to the structure’s long main span and its low structural damping, its designers predicted that significant vibrations would arise in service which could potentially reduce the structure’s service life and would likely affect the comfort of bridge users. Rather than fundamentally changing the bridge’s design to reduce these vibrations, it was decided to overcome the problem by equipping the structure with tuned mass dampers (TMDs) – passive damping systems, consisting of a mass, springs and individual dampers, that lower the natural frequencies of bridges and other structures and thus reduce vibrations in service conditions.

mageba’s Hungarian subsidiary, working in collaboration with KTI Schwingungstechnik GmbH, proposed a solution consisting of two TMDs, each carefully tailored to suit the structure’s unique design with optimally combined mass, frequency and damping variables. The designed mass, in the form of stacked steel plates, is mounted on the springs and equipped with viscous dampers. The TMDs were designed with tuned mass values of 2,800 kg and 3,800 kg respectively. Due to inadequate space for connecting the TMDs to the underside of the bridge superstructure, as would normally be done, they have instead been installed on top of the bridge deck – making them an interesting feature for bridge users and maximising ease of access for the responsible structural engineers.

In addition to the vibration dampers, mageba also provided 10 units of RESTON® SPHERICAL bearings to support the bridge superstructure, each designed for the project with a vertical load capacity of 2,600 kN. With these high-tech components installed to meet the structure’s various needs, the bridge can be expected to perform well, for its owners and for its users, throughout its expected service life.

Designer: Simon Viktória
Architects: Gábor Naszády and Dóra Zsódi
Contractor: SWIETELSKY Magyarország Kft.
Owner: Nemzeti Közútkezelő Zrt.

The new bridge provides access across a railway corridor to an intermodal transportation centre in Kaposvár

View of the underside of the bridge showing how the steel superstructure is supported by bearings on the concrete piers beneath

One of the TMDs as installed on the bridge deck (since clearance beneath the deck was inadequate) – before covering with a plexiglass enclosure for presentation as an interesting bridge feature

Each tuned mass damper was specially designed to suit the structure’s unique requirements, with optimally combined mass, frequency and damping variables

More usually – where clearance allows – TMDs are suspended from the underside of a bridge’s superstructure

Where used to dampen the vibrations of floor slabs etc., TMDs can typically be tailored to fit into suitably designed support beams or the like

Some of the supplied RESTON® SPHERICAL bearings, delivered to site and waiting to be installed

Two of the spherical bearings as installed to support the superstructure, before positioning of the connecting section of the deck