3D modelling has been used on the construction of the three-span Doro viaduct in Norway, to help overcome the challenging terrain and programme demands.
RMD Kwikform engineers used the technology to construct formwork and shoring to support a 93m long, 750m³ single deck pour.
Measuring just 9.5m wide, the single carriageway, post-tension Doro viaduct forms an important part of the large realignment of the E39 Harangen-Høgkjølen route in the Trondheim region of Norway. Constructed for the Norwegian Public Roads Administration, the formwork and shoring for the project has been supplied to specialist concrete contractor Sobstad AS by local formwork expert equipment supplier, Hansmark AS.
Having worked with Hansmark AS on several smaller bridge projects, the RMD Kwikform engineering team was able to combine existing stocks of Rapidshor shoring and Superslim soldiers, with their heavy duty Megashor shoring and R700 trusses, for the viaduct scheme.
With the need to ensure Sobstad could complete the single pour in the month of August, the RMD Kwikform team had to make sure the right amount of equipment was shipped to site in Norway, for the commencement of erection works in March.
CAD model of viaduct
In order to achieve this, a 3D CAD model of the viaduct was created using information received from the site. This enabled detailed design drawings to be produced, allowing accurate erection of the equipment, with automatic equipment take-offs.
With a total of three spans requiring shoring support, measuring 29m, 35m and 29m respectively, the main engineering challenge was to span an existing river running through the Doro valley. Fortunately the width of the river only required a clear span falsework solution for one of the three viaduct spans.
To support this first 29m span, RMD Kwikform designed a clear-span solution using five pairs of 25m long R700 trusses, each weighing 11t. One end of the trusses was supported by a six legged Megashor tower which was mounted on the pier base, and the other end sat directly on a foundation near the abutment. Loadings from the trusses were transferred to the Megashor tower by an 11.5m-long header beam supporter by three 3m distribution beams.
The five R700 trusses were then craned into position, with steel Superslim soldiers then mounted on top of the trusses. A partial access platform was installed on top of the trusses to allow for the installation of a Rapidshor steel shoring birdcage arrangement, some 3.5m tall. By combining Rapidshor U heads at the base and top of the legs with bracing supports, the birdcage style shoring structure was then able to support another layer of Superslim soldier beams and timber secondary beams for the bridge deck soffit.
One continuous pour
With the additional second and third spans supported by Rapidshor birdcage arrangements from the ground, varying in height from 8m up to 14m, the viaduct with its 4.2% deck incline could be cast in just one continuous pour.
Odd Inge Fremo, from Hansmark AS said: “The whole site was very exposed and so the solution we came up with needed to not only support the loadings pressures from the single concrete pour, it also needed to be robust enough to cope with high winds. With the truss arrangement we wanted to minimise the amount of equipment needed onsite, whilst being able to pre-assemble units next to the structure.
“With the Megashor tower we were able to lift sections into place, sequencing the build and similarly, because the R700 trusses were kept under the capacity of our site crane, we were able to simply manoeuvre them into place with minimal effort.
“With the use of guide plates on the main header beam, when it came to extraction, the site team were able to simply move the trusses to one side, swinging them out safely using the crane. This saved both time and money.”
RMD Kwikform also engineered Rapidshor access towers used to construct bridge piers that would eventually support the viaduct.
Adam Fixter, RMD Kwikform business development manager, said: “Prior to the Doro viaduct project we had supported Hansmark AS with Rapidshor solutions for the construction of the smaller Hallstein and Graven bridges on the same highway improvement programme.
“So when it came to helping them tender for the much larger Doro viaduct, we were well placed to combine existing equipment stock from previous projects with the additional heavy-duty shoring equipment required. This reduced the overall cost of the project, making the RMD Kwikform and Hansmark AS solution both competitive and achievable in the tight timescale.”