Roller shutter joints are being replaced by modern modular expansion joints on the New Lillebaelt Bridge in Denmark, reports Winfried Ollendiek
In recent years, increasingly frequent repairs have been required on the roller-shutter joints of the New Lillebaelt Bridge. Additionally, a rise in the level of noise being emitted by the joints as traffic passed over them signalled that they were reaching the end of their lives. As a result, the Danish Road Authority decided to dismantle the existing roller-shutter joints and replace them with new modern modular expansion joints.
When it was built in the 1970s the New Lillebaelt Bridge ranked among the 20 longest suspension bridges in the world. The bridge, of 1,700m total length, has a 600m span between the pylons. Built during the period from 1965 to 1970, it connects the regions of Jyzlland and Fynn and is one of the main links between Germany and the Danish capital of Copenhagen.
Modular expansion joints were considered to be best suited to the demanding environment of this bridge due to their capacity to absorb very large movements - more than 2m movement is possible - the fact that they are 100% waterproof and also their flexibility, which allows three-dimensional translation and rotational movements.
Danish steel construction company Bladt Industries won the contract to dismantle the existing roller-shutter joints and install the new modular expansion joints, as well as carrying out construction work on the underside of the bridge at the pylons. Swiss specialist Mageba was commissioned to deliver and install the new modular expansion joints. Mageba had already carried out renovation work on large bridges in Denmark with the Faro Bridge retrofit, where old joints had been replaced by modular expansion joints with a movement capacity of up to 880mm. The company also provided bearings and expansion joints for the Oresund Bridge and the Storebaelt West Bridge.
In the course of the Lillebaelt Bridge renovation project, six new modular expansion joints will be installed to replace the old roller-shutter joints; two type LR4, with a movement capacity of 320mm; two type LR7, with a movement capacity of 560mm and two type LR16, with a movement capacity of 1,280mm. This will give the bridge a total longitudinal movement capacity of 4,320mm through all of the carriageway joints. The LR4 modular expansion joints connect the abutments and the bridge and the LR7s and LR16s are located on either side of the two pylons. The large gaps taken up by the old roller-shutter joints were bridged by a special steel structure, which will allow easy access for checking and maintenance of the new expansion joints in the future.
The bridge joints are being replaced in two phases - the work on the northern carriageway has just been carried out, while the southern carriageway is scheduled for summer 2003 - hence the joints for each carriageway are being produced and installed as separate units. This approach will be advantageous for future maintenance and exchange of the waterproof sealing components. A cover panel between the two bridge deck carriageways will ensure that the expansion joint is totally watertight.
A number of challenges relating to the special characteristics of the New Lillebaelt Bridge had to be overcome by Mageba during the design, production and installation phases.
Firstly, the thermal expansion of the bridge interacts with the movement caused by traffic and strong winds. Because of the heavy loads and forces and the slender construction style, the movements are not only extraordinarily large for the length of the bridge, but also take place comparatively quickly. Movements between the pylons and the main bridge can exceed 50mm within just 15 to 20 seconds. Components had to be specially adapted to allow for these extraordinary movements.
Tight time pressure was imposed on the development and production of the new expansion joints with delivery of the static calculations and the first expansion joints due only three months after signing the contract. Nevertheless, all the joints were delivered to the site within the required time frame.
The installation process posed significant difficulties as the bridge was under traffic, and moved considerably at the connection points while the new expansion joints were being fitted. Special support elements were manufactured to aid the installation process.
Because the existing steel construction differs by up to 20mm on both the horizontal and vertical axes, the new expansion joints had to be designed to compensate for the differing dimensions. To achieve this, Mageba developed and manufactured a flexible system for fitting the new carriageway joints to the existing steel construction.
First phase of the installation on the northern half of the bridge has been successfully completed and the bridge is currently open to traffic again. The distinct contrast between the new modular expansion joints and the old roller-shutter joints can be seen as they now lay directly beside one another. The new Mageba modular expansion joints belong to the so-called 'fourth generation' of modular expansion joints.
In summer 2003 renovation on the southern half of the bridge is due to be completed, restoring safe travelling conditions to the bridge for the next several decades with significantly reduced noise levels.
In essence almost all older bridges can be retrofitted with new, modern modular expansion joints, and both steel bridges like the New Lillebaelt Bridge as well as concrete bridges are suitable for such renovation. The new modular expansion joints are waterproof, require little maintenance, are quiet and can absorb movements and rotations around all three axes.
Mageba also offers additional sinusoidal plates, which can be fitted to the top surface of the lamellas. This increases riding comfort as well as reducing noise to a level superior to that of a finger joint whilst still retaining the distinct advantages of the lamella joint, being able to move and rotate in all three dimensions.
Winfried Ollendiek is project manager at Mageba (Switzerland).
