Standard parts used for difficult Norwegian bridge construction
By Chris Sleight12 April 2013
RMD Kwikform supplied Norwegian construction company, Nordang, to approach HEAB Bygstallningar with a falsework system to help construct a new bridge as part of a tricky road realignment programme near Alsesund in western Norway.
The Ljoen Bridge is located some 350 m above a Fjord and the existing road on the steep mountainside often becomes impassable in winter due to ice and the risk of avalanche. The purpose of the project was to re-align the road with a new bridge to straighten a bend and divert it away from the waterfall area.
As part of the Norway project, RMD Kwikform engineers were approached through its customer, HEAB. They were tasked with designing a bridge falsework support system over the mountain side’s fast-flowing waterfall, with its loose and unstable rock.
The design used Megashor heavy duty shoring, R700 girders, Superslim soldiers and specially fabricated items.
The Megashor tower solution was designed to take the concrete loads from the bridge deck into the existing pier pile cap bases, so no additional foundations were needed for the falsework system, saving time and cost. Two Megashor towers, which were 10 m and 4 m high respectively, were founded on the small footprint of the bridge pier pile caps. Raking Megashor members splayed out from specially fabricated nodes on the Megashor towers to support the ends of the header beams.
Mats Nilsson of HEAB said, “The solution they devised used the capabilities of the Megashor system, while recognising the need to keep construction costs as low as possible. With this in mind, RMD Kwikform’s engineers helped us develop a design that would allow the customer to integrate material they already had possession of, into the bridge.”
Between the two header beams at the top of the Megashor towers, a system of Superslim plan bracing was used to transfer the wind forces acting on the bridge falsework into the concrete bridge piers. This solution enabled the partly completed bridge structure to resist the strong winds present in this exposed construction environment, horizontally stabilising the Megashor towers without need for additional temporary bracing members. With vertical loading of approximately 700 tonnes in each Megashor tower, maintaining structural integrity and stability was very important.
Petter Nyberg from project manager Nordang said, “RMD Kwikform provided an extremely high standard of service on this complicated project, including giving us an on-site engineer who assisted with pre-assembly of their equipment. Due to the unique construction environment and terrain, it was important to pre-assemble as much equipment as possible in our site compound area before transporting these modules to the bridge site. The expertise of the RMD Kwikform engineers was essential for this process. They were also able to help us cut construction costs by providing an arrangement of Superslim soldiers for the bridge soffit profile, which dramatically reduced the quantity of timber formwork that would normally be needed for this kind of project.”
R700 girders were delivered as flat packed truss panels to the site compound area, a short distance from the bridge site. Each girder assembly comprised of two rows of truss panels, connected together with shear pins, and braced together with the R700 bracing system. The 8.8 tonne pre-assembled girder modules where then transported to the bridge site and crane lifted into position on top of the Megashor tower header beams.
In Scandinavia, an abundance of timber means that it is a material often used for formwork frames on bridge deck soffits. However, when it came to the Ljoen Bridge deck soffit design, because the crossfall was complex, the RMD Kwikform team came up with an alternative solution to reduce costs and maintain a high level of precision.
Adam Fixter, senior project engineer at RMD Kwikform, said, ”The crossfall of the deck continuously changed along the bridge, meaning that every soffit formwork frame placed on top of the R700 trusses had to be a slightly different dimensions to give the right profile for the deck. The need for precision demanded a frame solution using Superslim Soldiers and specially fabricated struts. The specially fabricated struts varied in length slightly for each soffit frame. These frames were pre-assembled in the site compound area, with the specially fabricated struts delivered in bundles unique to each Superslim frame. Each Superslim frame could then be quickly pre-assembled using pins and R-clips while lying flat, with the specially fabricated struts precisely dictating the geometry. Each Superslim frame was then labelled and transported to the bridge site and easily integrated into the structure.”
The final challenge related to how to recover the formwork and falsework equipment after the concrete had set. The Superslim soffit frames were designed to be easily spilt, and modules of soffit formwork slid out from under the completed bridge deck and lifted clear. The R700 girder modules could then be slid along the extended header beams on top of the Megashor towers. Specially designed shoes between the R700 girders and header beams ensured that the trusses could not fall off the header beams during the sliding operation. Once clear of the completed bridge deck the R700 girders could be lifted off the header beams and stored on top of the deck ready for transported back to the assemble area.