📋 Tender Overview
The manufacture of the steel structure of the Kirjalansalmi bridge began at the beginning of September 2023 in Oulu. The completion and installation of the steel structure according to schedule is a critical phase for the completion of the new Kirjalansalmi bridge.
The manufacture of the custom-made steel structure started on 5.9.2023 at Steel Group Pohjanmaa Oy's workshop in Oulu. Material orders have been placed since the summer, and material has been arriving at the workshop for the main materials since August. The production of the first blocks has just begun, and the first steel structures will be delivered to the bridge construction site in Pargas in December 2023. Engineering production will continue until May 2024.
"The steel structure has been designed for a long time by many different professional groups. In addition to the manufacturing process, we have of course also had to take into account how the steel structure can be put in place, i.e. what requirements the transfer places on the auxiliary supports on which the steel structure is pushed. We follow a strict process in terms of planning and reviewing plans to ensure a high-quality and sustainable end result for at least a hundred years," says Project Manager Janne Wikström from the Finnish Transport Infrastructure Agency.
Production of the steel structure will start in full swing in November 2023
The completion of the steel structure is one of the most critical phases in terms of the project schedule, as it sets the pace for other construction. Its installation is a long-term work phase, the completion of which is a prerequisite for starting the next, also long-term, work phases.
"We are currently doing subassemblies at the workshop. We are still waiting for some material deliveries, and production of the steel structure will start in earnest after mid-November. As a project, the manufacture of a steel structure is of a unique size, the likes of which are not often carried out in Finland. The production consumes 3,300,000 kilos of steel," says Henrik Kiviniemi, CEO of Steel Group Pohjanmaa Oy.
The transfer of the steel structure will begin in February 2024
The Kirjalansalmi bridge is a composite cable-stayed bridge with a reinforced concrete deck and a continuous concrete beam bridge with tension for the result bridge. The steel structure is made of structural steel, i.e. an iron-based alloy.
The steel structure of the Kirjalansalmi bridge consists of 20 sections. The block has two main beams and a certain number of crossbars and rope crossbars. The parts of the block are delivered to the site as these parts and are assembled into blocks on site. The structures are delivered on site on a just-in-time basis.
The assembly of steel structures begins on the Pargas side at support T4 (see picture), where the steel structures in the support area are installed on top of the auxiliary supports in the bridge formwork. The steel structure between T1 and T3 is assembled at the end of Kaarina in a so-called steel structure. on a mounting platform called the launch bed and steel structure are pushed (jacked) from support T1 to support T3 on three separate occasions. The jacking speed is six meters per hour. A total of 14 blocks form a whole that extends all the way to the pylon of the bridge support T3. The first push installation is carried out in February, the second in April and the third in May.
Once the section between supports T1-T3 has been placed from the direction of Kaarina to the pylon of bridge support T3, the movement of the steel structure changes from horizontal to vertical. The remainder, i.e. the section between the bridge support T3 and the result bridge at the end of Pargas (T3-T4), will be lifted from the work bridge into place.
Designing a challenging bridge project
The Kirjalansalmi bridge site is a challenging construction environment, which has also affected the work of bridge designers.
"Bridges are always designed and built to last, and so is the Kirjalansalmi bridge. Its service life will be at least 100 years. Technical design is, of course, guided by industry guidelines and standards, for example in terms of load and materials, but we also take into account road safety, road maintenance, costs, surrounding settlements and the appearance of the bridge, among other things. The Kirjalansalmi bridge is a complex and large project. The location of the bridge also poses its own challenges: the water depth of the strait is very large and the embankments are steep. There is little space for construction and, for example, for working with machinery, which has had to be taken into account in the design. In addition, the construction schedule is tight, and planning and construction are partly intertwined. Fortunately, the different parties involved in the project are committed to facing the challenges with honor," says Chief Designer Sami Niemelä from WSP Finland, a built environment design and consulting company. WSP Finland was involved in drawing up the general plan for the project, and is also acting as a bridge designer for the Kirjalansalmi bridge.
