Wasel, the heavy load logistics experts from Bergheim, Germany, impressed everyone concerned with their professionalism during a difficult crane job on Cologne Cathedral in July. One of the two enormous hanging scaffolds on the north tower of the cathedral had to be dis-mantled at a height of roughly 100 meters. To do this, Wasel erected its biggest and most powerful mobile crane, a Liebherr LTM 1750-9.1, to its maximum hook height of 154 meters. Not an everyday crane job, since there were quite a few logistical and static engineering challenges involved.
This was the second time that the crane service provider had to remove scaffold from Cologne Cathedral. Six years ago, a Liebherr LTM 1500-8.1 mobile crane carried out a similar job on the west facade of the building. However, because of the position of the scaffold considerably less effort was involved at that time. But with this job, it was a completely different matter.
Apart from the fact that the aluminium scaffold, which was completed in 2004 after two years of manual work, had to be removed in three sections from the cathedral tower at a height of 100 meters, the boom radius was almost the same for each section. What was, from a technical lift-ing aspect, the much better location for the crane on the pedestrian area on the south side of the cathedral was ruled out from the start. The plans for the underground car park below the area were lost in mud when the Cologne City Archive collapsed in 2009. Because of this, it was impossible to examine the static engineering drawings or to make special static engineering calculations to erect the crane.
However, the much lower railway station forecourt, which was also further away from the build-ing, created serious obstacles for those involved in the project. For example, the underground railway station below the area where the crane was to be erected required a complicated search for points where the concrete foundations for the large crane’s supports could be poured. On top of this, the enormous number of pedestrians in front of the station also had to be considered.
On the crane side, Jürgen Oprée, Technical Manager at Wasel, was responsible for the organization and sequence of the work at the World Heritage cultural site. For two years he was in contact with the cathedral administration and with a dozen departments, authorities, and institutions in the city that were also involved. But finally, on a Sunday morning at the end of July, the Liebherr LTM 1750 9.1 mobile crane rolled up to the station forecourt. This was the first time since it had been delivered to Wasel in March that the 9-axle mobile crane was to be used with full boom extension and 91-metre luffing jib.
Assembly at the difficult area
“In the run-up to this job, the assembly gave us some headaches”
Jürgen Oprée: “We had to consider station evacuation plans in our assembly schedules and also had to keep the escape and rescue routes free at all times. As well as all this, we were given a very tight time window for the set-up work.” As one of the busiest railways stations in Germany, Cologne Central Station is frequented by about 280,000 passengers each day. Because of this, the crane crew were allowed to block the areas of the station forecourt needed to assemble the boom only at night. Another difficulty was that the area was much too small to assemble the lattice boom to its full length flat on the ground. Only 90 meters was available. The boom had to be assembled in a suspended position. The lack of space also demanded optimum planning by the suppliers of the required parts so that they were delivered “just in time”.
But the meticulous planning of the project paid off. Less than eight hours after the mobile crane had moved into position the basic crane was equipped with supports, telescopic boom guys and telescopic boom extension, including pivot section and ballast. The area for the suspended assembly of the lattice jib was blocked off from 10 pm. Assembly of the lattice section with a Liebherr LTM 1095-5.1 mobile crane required full deployment and intense concentration from the Wasel team the whole night through. But by early morning the impressive 160 meter boom soared into Cologne’s summer sky next to the cathedral towers.
Watched by a large number of spectators – many crane fans from all over Germany and the Netherlands had also made the pil-grimage to Cologne – the largest crane job in the history of Cologne Cathedral started. The most protracted part of the action was fastening the elements to the special cross beam and separating the sections of scaffold from the basic construction. Each time it took almost an hour before the scaffolders, who were secured with climbing harnesses, radioed through the command for crane driver Michael Michatz to lift the section that they had separated.
The enormous aluminum elements then began moving imperceptibly slowly. Through the precise interaction between the crane driver and the guides on the tower the roughly seven meter wide and 33 meter high scaffold was moved carefully past century old finials and weathered angel figures. “When we were threading the rear scaffold out, in some cases we had just 15 centimeters be-tween the load and the cathedral,” said Jürgen Oprée, describing the difficult space conditions during the lift. The Liebherr crane maneuvered the bulky load between the towers, over the top of the northern side aisles and past the tower to finally deposit it in front of the main entrance with the help of an LTM 1070-4.2.
The final lift was already completed by early afternoon, which was much earlier than planned. The actual crane job had taken just about four hours. If the seven scaffolders from the cathedral workshop had dismantled the scaffold manually, it would have been a long, drawn out undertaking. “We would have needed about six months,” explained the master builder of the cathedral Michael Hauck, who was very relieved and satisfied that the job had been completed.
“Just a few years ago a job like this wouldn’t have been possible in this manner,”
Matthias Wasel, who together with his brother Thomas manages the Bergheim company, was also satisfied that the crane job on the World Heritage cultural site was completed successfully. Like Wasel, Jürgen Oprée was also on site almost continuously day and night. Because the job went so smoothly, the coordinator of this complex job was able to relax after the stress of the previous few days. “Just a few years ago a job like this wouldn’t have been possible in this manner,” explained Oprée. “From a technical aspect, maybe, but certainly not within these short times. And probably another crane would have also caused problems in terms of the support pressure. The LTM1750-9.1 was ideal for this job on the cathedral.”