More support structures for the arches

The installation plan of the most extraordinaire solution of the new library, the steel arches supporting the building, has been given more detail. Erection of this unique internal bridge requires a few more support structures, which means that the installation process has been delayed a little from the original schedule.

“The loads of the arch structure are very great. The original idea was that during the installation phase, the arches will be supported directly to the existing floor. However, more specific calculations proved that in addition to the vertical supports, the arch load should also be distributed with a horizontal grid that transfers the load to the footing structure. The horizontal grid will be introduced as a new solution,” says Tero Seppänen, YIT’s senior site manager.

During the installation phase, the arches will be supported with vertical and horizontal transmission grids. The horizontal grids required by the updated installation plan will be the first structures to arrive at the worksite before the arches, so the logistics plan was also updated. The support structures will not be removed until the arches have been welded into one structure and tensioned.

“The first grid delivery will arrive during the night at the turn of January and February, during week five, and the next during week six. The deliveries mean night shifts for the unloaders, as the loads will be delivered between midnight and four am. The first installations of the arches will begin sometime before mid-February,” says Tero Seppänen.

Finnish construction ethics dictate that safety is not to be compromised in order to make the work go faster, not even when the deadline is approaching. The change in the design proves how important it is to supervise how theory and practise come together and adapt the plans as the situation requires.

While the transverse support grids have been manufactured in Oulu at Normek Oy factories, the on-site workers have assembled a tracked lattice boom crane, Havator, for installing the arch structure. It was delivered in several pieces from Äänekoski, from the worksite of Metsä Group’s bio-product plant. The wide wheelbase of the tracks takes up a lot of space, and very large steel elements will be delivered to the site, which means that the worksite had to be extended further. Since the fence was moved in December, it has been moved again towards the west and the Parliament House. The arches will be transported to Helsinki in 12 separate pieces. Each delivery carries two pieces, so, in total, there will be six deliveries.

Lifting the arches requires detailed plans

When one part of an individual arch weighs more than 85,000 kilos, the process ahead will be a heavy jigsaw puzzle that requires careful preparations. In addition to the lifting and installation plans, detailed occupational safety plans are needed. All of this has kept YIT’s worksite manager and occupational safety manager Mansoor Ardam busy. He acts as YIT’s supervisor during the steel frame’s installation.

“Success is based on careful planning. The arches and grids are a challenge, but we will proceed in bits and pieces, one matter at a time and in accordance with the plans approved by the structural engineer. The work will be paused, if we notice a safety risk. It is important to react in time during the implementation phase, so that the support towers can hold, lifts succeed and everyone can go home safe and sound after the workday. Motivation is strong, and even if the project is complex, it does not have to be complicated.”

Mansoor Ardam has construction work in his blood. He says that his grandfather was a major contractor in the Afghan state. Mansoor came to Finland in 2005, and in 2012 he graduated as a civil engineer from the Häme University of Applied Sciences. Currently, he is studying for a degree in Master of Engineering in an Industrial Management degree programme in English. He will graduate in May.

“Large projects are already familiar to me. I’ve been in part of the construction projects of HKL’s metro depot in Roihuvuori and Otaniemi metro station. Both were successful, transferred over with zero errors.”

First shafts about to be completed

The construction of lift and stair shafts has progressed on schedule, and the cast-in-situ works of the three first shafts are almost complete. At the beginning of February, the work for the fourth shaft can be started.

The first shaft in the northern end of the building will be around 20 metres high. It reaches through the entire building, from the cellar level to the third floor. The eaves height of the building itself is 23 metres. Next to the shaft, part of the movie theatre wall and the shape of its space can already be seen. The actual building construction will also start from the north end: the first steel pillars and grids will be erected in February.

It is easy to watch the shafts being built, but a lot is also going on below the ground, for example, in the process of covering the concrete vault seen in front of shaft number three. Temporary heating was installed for the basement, as masonry works were started in the premises. During the masonry works of the basement’s partition walls, channels for ventilation and electric system pipes will also be made. ARE was selected as the building system contractor that will manage heating, water, ventilation, electricity and automation works.

When the lattice boom crane’s chains start to lift up the pieces of steel, they can also be seen from far outside the worksite. The crane will see some action as the winter starts to turn towards spring.

 

 

Text and pictures: Liisa Joensuu/Tmi Magic Words

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