Welding robots are a common sight in engineering workshops, but not so much at construction sites. It’s no surprise then, that this mechanical marvel is turning heads at the construction site of the new library. The new electricity-powered addition to the construction crew is isn’t much of a conversationalist, but compensates for such shortcomings by being unbeatable when it comes to accurately welding seams.
The robot will be lending its talents to the construction of the library’s load-bearing steel bridge, and more precisely to the welding of the four units that make up the bridge’s housing structures, which arrived at the site in July. The robot will be welding together two of the pieces at the north end of the bridge, and the other two at the south end.
“There’s a piece of steel between the two halves of the housing structure, which is used to join them together. The seams to be welded are subject to strict quality and precision requirements. The robot can keep welding the seams repeatedly while maintaining a uniform level of quality”, says Site Manager Kyösti Kontio, while showing the reel of welding wire that is fed to the robot’s welding head.
In late August, the work focused on the housing structure at the southern end of the bridge. The robot moves along the surface of the two halves of the housing structure while welding the thick piece of steel between them over and over again. In the photo above the robot is taking a break; during operation it’s guided by a team of experts from the same Normek factory where the elements that make up the housing structure were made. As surprising as it may sound to a layman, the welding will take several weeks.
“The problem is that welding produces a lot of heat, which causes the elements to deform. It’s very difficult to predict how the pieces will move as a result of the heat. We use a jack tensed between the halves of the housing structure to compensate for the movement as needed”, Kyösti Kontio explains.
The welding of the north end housing structure is already complete, and the temporary lattice used to support the footing can soon be dismantled. The reason why the two halves of the housing structures were not welded together at the factory is their size; as complete units they would have been simply too large and heavy to transport and mount.
The walls of the library’s basement need to be thoroughly waterproofed, as the basement lies below the groundwater level. Because of this the walls are fitted with as many as five layers of waterproofing, which is more than at any construction site that Kyösti Kontio has ever worked at before. In the photo above, waterproofing is underway at the western end of the excavation site. After this the walls will also be outfitted with a layer of thermal insulation.
At the northern end of the construction site, thermal insulation has already been installed, and the ditch has been filled with sand, which is tamped down layer by layer. The area in the lower right-hand corner of the photo will become one of the building’s stairwells. The metallic objects in the background are formwork towers, which were used to construct the basement ceiling. The towers are being stored here for a while, after which they will be used at the south end of the construction site.
The construction of the basement ceiling requires various types of formwork. The upright formwork towers are topped with horizontal formwork units, similar to how you would place a table top on a set of legs. These kinds of formwork units are constantly arriving at the site, as the size of the area that needs to be covered is approximately 1,700 square metres.
Here the formwork panels delivered by truck are being installed for the casting of the loading area ceiling. The concrete will be cast on top of the yellow panels, which will keep it in place while it’s still wet. Once the concrete has dried and the ceiling can hold its own weight, the panels will be removed. The holes visible in the walls of the loading area are intended to accommodate various building services.
Concreting of vertical structures complete
Concreting is proceeding well at the construction site, as all the vertical structures of the basement, meaning the exterior walls, partition walls, pillars and lift shafts, have already been completed.
At the northern end of the construction site, a sizeable portion of the basement ceiling, covering an area of approximately 800 square metres, has also already been cast. The ceiling will also serve as the floor of the library building’s cinema. The spaces below will house technical facilities as well as facilities related to the library’s restaurant, such as freezers and cold storage rooms, as well as storage and office spaces. These facilities are needed as the library is set to include a high-quality restaurant. The restaurant’s employees will have direct access to the cold and dry storage rooms in the basement via a dedicated lift.
The library building will be exposed to considerable structural loads, which has been taken into account in the casting of the building’s lift shafts. The lift shafts need to especially strong, because of which they were cast from high-strength concrete, which has a compressive strength of 7,000 tonnes per square metre. This lift shaft, which was cast in late August, required nearly 80 cubic metres of concrete.
The southern end of the library does not have a basement. Here work is underway on the floor level of the library’s ground floor. The insulating boards shown above may look like they’re made of stone, but they are actually made of insulating material that will be covered with concrete. On the right workers are preparing tension wires for concrete casting.
The very southern tip of the construction site houses a stairwell constructed in anticipation of the planned city centre tunnel. If constructed, the tunnel will go under the library at Sanomatalo. The stairwell is intended to serve as an emergency exit in case of accidents inside the tunnel. As you can see from the photo above, the walls of the stairwell are already in place. The metal shafts jutting out of the walls are rock anchors, which provide added support for the structure. The photo is actually quite historic, as the Parliament House can still be seen in the background, covered with a printed wrap due to renovations. Once the library rises higher, the Parliament House will no longer be visible behind the construction site from the Töölönlahdenkatu side.