Caterpillar tracks will soon be making their way through the centre of Helsinki. New lifting capacity is required for the library construction site, and a new lattice boom crawler with rigging will see to that. In mid-December, a route was cleared for the new crane.
‘Lattice boom cranes are not seen on building construction sites every day, We need this 300-tonne Havator with rigging because it can move from place to place while carrying a load. We have to dismantle our tower crane to make room for the steel arcs’, explains Tero Seppänen (right), YIT’s senior site manager.
A team from Normek Oy has already arrived at the site for the erection of the steel arcs. Alongside Seppänen, the site map and the route for the new monster is being studied by Normek’s site manager Markku Roininen (left) and YIT’s site engineer Unto Miettinen.
For the time being, the tower crane has been joined by the wheel-mounted car hoist shown in the front of the picture, which took care of lifting the northern stairway shaft and the wall moulds for the movie theatre in December. The car hoist is supported by adjustable legs, which makes it unsuitable for the erection phase of the steel arcs.
The three northern shafts were worked on during the end of the year. This picture shows the tower crane lowering a wall mould into shaft three, in which both a lift shaft and a staircase will be built. The scaffolding is being built up as the moulds for the concrete castings are put in place. The tower crane is to be dismantled during the second week of January.
YIT has cleared the construction site and expanded it. The site is now intersected by a clear route for the new monster of a crane. A new gateway has been opened at the southern end of the plot, in front of Sanomatalo, and the site fence has been moved out to the west towards Kansalaistori. This additional space will be necessary as the parts for the steel arcs that will later on support the entire library arrive in January, along with their temporary supports.
Steel arcs arrive in batches during the night
The arrival of the support structures for the arc solution has been scheduled for the first week of January. Even though this delivery will only cover the supports and not the arcs themselves, the parts will be massive, reaching 10 metres in height. A total of ten support structures will be set up at the joints of the actual steel arcs that will then support the library.
According to the schedule, the parts for the actual arcs will be delivered in week 3. The parts for both steel arcs will be delivered in one batch. The delivery is therefore so big that its transportation is scheduled for a quiet time of day.
‘One part for one arc weighs over 85,000 kilos. With the delivery truck weighing 100 tonnes, its progress is slow and every turn takes a lot of time. On main roads, such a delivery causes a lot of disruption, and it can only be delivered in the centre of Helsinki in the middle of the night. The delivery will be coming from Normek’s facilities in Oulu. The vehicle cannot manage tight curves, and the only route with sufficient space is from behind the old storehouse,’ Seppänen explains.
‘The support structures will be completed as far as possible in early January. This will allow us to get the first pieces of the arcs in their places soon after they arrive. Even though the arcs now seem like the most impressive parts on the site, the fact is that erecting them is quite simple, and the challenges will only begin after that phase’, site engineer Unto Miettinen says.
The traverse steel gratings that will support the frame of the upper floors will be supported by the steel arcs when they are in place. The western arc is more sturdy than the eastern one, because it will bear a higher load. In comparison, the eastern gate could almost be called petite. The structure is new for YIT, but the cooperation partner for the phase, Normek, has already erected a similar arc structure in Helsinki.
The maker of the arcs also erected Isoisänsilta (‘Grandfather’s bridge’)
The Isoisänsilta bridge, which opened for bicycle and pedestrian traffic between Kalasatama and Mustikkamaa in September, was also erected by Normek. Unlike the library, however, the bridge did not include any structures that would need to be supported.
‘The library has a harsher structure’, says Normek’s site manager Markku Roininen, adding that the location in the centre of the city creates a bigger challenge.
The same installers who gained experience in the bridge project were available for this erection, bringing continuity to the installations for Normek. It may be surprising that only 2–4 installers are needed, compared to a total of eight welders.
The first parts of the arcs will be put into place at the southern end of the site. Roininen doesn’t foresee any problems with attaching the ends of the arcs to the steel casings that wait for them. Normek made the casings and arcs, and the parts were manufactured in Oulu exactly to measure.
The safety precautions on the site have been increased. Electric gates were installed on the fence, and everyone must be identified on their way in as well as out. YIT’s village of yellow containers already has three floors, because since the excavation phase, the number of people has increased by 20. A total of 57 experts in various fields now work on the site.