Highest quality all the way to welded joints
The quality of construction is constantly monitored in detail at the Oodi site. Everyday activities include operational and quality monitoring actions and recording the data from them. Everything is based on a quality monitoring plan, which site engineer Ahmed Ibrahim (in the picture) prepared for the central library as the thesis work for his Master’s degree.
‘Digital project management tools and mobile equipment make monitoring and documentation significantly simpler. All of the necessary data can be entered into the system directly on a tablet or phone, and it is available to everyone in real time,’ Ibrahim says.
The most eagerly awaited construction phase, which is the erection of the steel arches that support the entire library, is now ongoing on the site. Welding the parts together also requires precise quality control: the welded seams will be inspected using ultrasound equipment.
Ahmed Ibrahim says that software and cloud-based services are part of construction operations today. Production used to be managed by using files and files of papers, which were then transported from one person to the next, requiring pictures to be scanned and documents printed and sent by post.
‘These days, everyone uses the same software. We can document various observations and measurements, and attach pictures. One person inspects, another approves, and the designer signs everything. This allows us to build faster.’
Ahmed Ibrahim wrote his Master of Engineering thesis on ‘Leadership in quality assurance and creating the conditions – Helsinki Central Library project’. Based on the Finnish Congrid system, he developed a quality management matrix suitable to be used in other YIT sites as well.
Arches under the magnifying glass
As planned, the steel arches that support the library arrived at the site in 12 parts in February. Their erection could be started quickly, as the support structures were already in place.
The north ends of the steel arches were resting on the support grids before mid-February. Their bottom parts are protected by a weather guard tent, inside which they are connected to their housings.
‘The housings were made so well that we had no problems installing the ends of the arches. The bottoms have been welded inside the tents, because welding must be done safe from water, and the protective gases must stay within the welding area. For now, everything has gone well with the erection of the arches,’ says Pasi Parkkinen, Project Leader at Normek Oy.
The steel arches will end up supporting several structures, which means that the securing of the load-bearing capacity of the arches is being monitored particularly carefully. This means, for example, that the welded seams connecting the various parts are inspected dozens of times.
‘At first, the arches are only welded a little, so that the parts are connected, but the full weight of the arches rests on the support structures. One seam needs to be welded about 100 times before the arches are fully in place and the supports can be taken down,’ Parkkinen says.
Around ten people are working on the welding of the arches. Each seam is worked by two people at the same time. A third person is needed who is responsible for the pre-heating of the place to be welded and the additional materials, such as gas and welding wire. Pre-heating is important, because if the area being welded is too cold, the seam will crack.
The arches are welded on the inside, as well as on the outside. The welder has access to the arch housing through a hatch on the side. The piece of arch works like a chimney, letting all the fumes and gases out through its end. The housing is not only for small people: they are approximately two metres in width and height.
Ultrasound imaging for the welded seams
The use of ultrasound in the inspection of welded joints has become more and more common, and it is used on the Oodi site as well. The objective is to have intact seams, which can take the necessary load.
Structural engineers have appointed certain values to the seams, and an external certified institution, Suomen Testauspalvelu Oy, uses ultrasound to ensure the integrity of the seams and that their thickness corresponds to the defined values.
Shafts also support structures
Along with the steel arches, the lift and staircase shafts are also parts of the library’s supporting frame. The third shaft in the middle of the building supports even the steel arches.
The cast-in-situ slab, i.e. the floor, located on the third floor of the third shaft, is connected to the shaft, as well as the steel arches. The slab can be cast between the shaft and the arch structure once the steel arches are in place and the weldings are strong enough. The support grids for the arches are only removed after the cast-in-situ slab is finished.
The staircase landings are being prepared in the first shaft in the northern end. The first two large landings are cast in their places, and the smaller landing slabs are installed as elements. At the turn of March, the stairs themselves will arrive at the site as concrete elements, and their installation can begin.
Site engineer Unto Miettinen preparing coffee with his arm in a sling, and said that construction has already started on the fourth staircase shaft, and its first floor is already completed. The fifth shaft, which will be placed opposite the Sanoma House, is only begun once the steel arches are fully welded and the support structures, which currently block the way of the shaft, are removed. Miettinen pointed out that he isn’t wearing the sling due to an occupational injury, but that the problem lies in an older shoulder injury.
Text and pictures: Liisa Joensuu/Tmi Magic Words