© Kruunusillat, Helsingin kaupunki, WSP, Knight Architects
A consortium formed by Kreate and YIT selected Ramboll as the construction designer for the project. The bridge will shorten the distance from the islands of Laajasalo to the city centre, thereby making it easier to travel the distance by bike or even on foot.
“Every time a tram passes over the bridge, a fatigue cycle that affects the resistance of the steel occurs, but this bridge will last 200 years. It is twice as long as the usual 100,” says Ilkka Ojala, Chief Designer from Ramboll. Long service life in the quality and durability properties of the concrete is also considered. “Much attention is paid to details. If a component cannot last 200 years, it will be replaced.”
A bridge only for public transportation, pedestrians and cyclists
The completed Kruunuvuori Bridge will be special in many ways. It will be the only bridge in the world of this size that caters only for public transport, pedestrians and cyclists. The bridge will be the longest and tallest in Finland, and the central pylon of the suspension bridge will be 135 metres tall and built on a rock at the point where the rock rises close to sea level.
The concrete deck of the bridge rests on large steel girders with spans the maximum length of 260 metres. The maximum height for boats going under the bridge is 20 metres. The whole structure will require about 6 million kilograms of steel.
Large blocks put in place by sea crane
WSP Finland designed the basic solution for the Kruunuvuori Bridge, which is currently being modified by the contractor. Originally, the deck structure of the bridge was to be installed at the main openings supported by diagonal cables using the cantilever method. However, the construction schedule will be accelerated by installing the deck in large blocks.
“The sea crane will install about a dozen 60-metre-long steel blocks, each weighing about 300,000 kilos on temporary supports,” Ojala says. The weight of one block is equal to about 200 cars. Due to the change in construction method, all steel structures on the deck will be re-dimensioned. “It requires a lot of work, but the most important thing is to build the bridge in a way that minimises risks. After all, conditions in the open sea are exceptionally demanding.” Ojala continues.
Innovative data modelling process shortens design time
Due to the tight schedule, design automation has been enhanced, while a parametric workflow enables the design and data modelling processes to occur simultaneously. Algorithms were used to create dependencies between different components, allowing automatic updates of changes throughout the model. “Our approach is similar to programming. The entire geometry of the bridge is encoded, making it easy to change data on the fly as the plans are refined,” says Ojala.
The dimensioning of the steel structures of the deck and engineering design will continue until next summer when installations will begin on site. This autumn, dredging and other preparatory work are being carried out in the Korkeasaari area. “We are currently working with the bridge calculations , and the first engineering drawings will go into production later this year. The bridge will open to the public in 2026,” Ojala concludes.