On Wednesday evening, the Storebælt Bridge had to be closed at around 19:00 due to a collision alert. Fortunately, the bridge opened again after a few minutes.
If an incident had taken place, however, the Storebælt Bridge is capable of withstanding any impact from the largest of vessels.
”Based on risk analyses carried out during the design phase, the bridge is designed to withstand collisions with very large ships. When significant changes in maritime traffic occur, we conduct a new risk evalution. We did so in 2012 when we recalculated whether the Storebælt Bridge’s pylons could also withstand collisions with the largest container ships in the world, which had begun to sail through Storebælt at that time,” explains Leif Vincentsen, Senior Consultant at Sund & Bælt and former Technical Director.
The pylons are designed for ships of 250,000 DWT (deadweight tonnage). The ship that triggered the alarm on that Wednesday was far smaller and only about 1800 DWT. There was, therefore, no risk of damage to the pylon. That the alarm was raised and the bridge was closed was because the approach spans – i.e. the piece between the anchor block and the abutment – are only designed to handle collisions with smaller vessels. It was specifically the risk of hitting an approach span that triggered the alarm and caused the barriers to descend preventing motorists from being on that part of the bridge. .
”In this specific case, such a small ship would probably not have done any serious damage to the bridge. But the procedure prevents vehicles driving on to a possibly damaged part of the bridge with the risk of them landing up in the sea,” explains Leif Vincentsen.
”Drivers may wonder about being stopped in the middle of the bridge, but it’s in order to prevent them from continuing on to that part of the East Bridge between land and the anchor blocks, which is the most vulnerable. That section on the high bridge – from anchor block to anchor block – is, in fact, the safest place to be in the event of a collision.
Is it dangerous for motorists?
Shipping in Storebælt is monitored from Naval Station Korsør via VTS – Vessel Traffic Service Storebælt. VTS keeps track on vessels that have run off course, makes contact with them and raises an alarm should contact not be established. When the alarm is raised, traffic on the Storebælt Bridge is brought to a halt.
”There’s no need for drivers to be worried about such incidents. In the first place, they happen very rarely and secondly, we close the bridge to traffic in good time. We have four barriers on the bridge, which we can use to control and channel traffic back and forth to areas where it’s safe to be when an alarm has been raised. The barrier system was introduced following an accident on Tjörn Bridge in Sweden in January 1980, when a ship collided with a bridge which collapsed and sent seven vehicles into the sea,” explains Leif Vincentsen, who points out that barrier testing is part of the ongoing safety procedures on the Storebælt Bridge.
In 2005, the ship, Karen Danielsen, sailed into the West Bridge and became wedged. Although this caused a hole in the concrete, this had no practical significance for the bridge’s stability or resistance. The bridge was subsequently closed for five hours.
This was the fifth time for the VTS alarm to be raised due to a risk of collision at the East Bridge since it opened 18 years ago.
Read more about the East Bridge and how it can withstand a collision in the book entitled ‘East Bridge’.