When the Norwegian Public Roads Administration asked the design-build team of Sweco, PNC, Armando Rito Engenharia and Isachsen to deliver a 643-meter-long concrete box-girder bridge completely in 3D, designers with Armando Rito were initially a bit skeptical. In the firm’s home country of Portugal, it had used building information modeling on some projects, “but not in terms of bridges, and not this advanced,” says Tiago Vieira, the firm’s design team leader. “Norway is more advanced regarding this type of methodology than other countries.”
Rising to the challenge, team members working across Europe are using parametric algorithmic design principles and data-sharing in Tekla Structures as the only official documentation and repository of information needed to build the Randselva bridge. Project officials say it is the longest bridge in the world to be built entirely 3D to date.
The bridge, which spans a river of the same name, sits on six piers ranging in height from 5 m to 42 m. It is located in the town of Hønefoss, some 60 kilometers northwest of Norway’s capital, Oslo, and carries the E16 highway, which originates in Sweden.
Oystein Ulvestad, a specialist with Sweco, says Norway embraced the idea of model-based project delivery a few years ago. “We’ve done it for about 20 or 30 smaller structures before,” he says. When the client stated a desire to build the Randselva Bridge this way, “We said, ‘let’s go headlong into the future and do this.”
The two-lane curving bridge’s single lanes gently curve through a deep valley over the river and forests, some 55 m above ground level at the bridge’s highest point. Based on a cast-in-place concrete box-girder design and the balanced cantilever method, the bridge has over 200,000 sections of rebar contained within concrete that is added in 200 separate pour phases, with more than 200 post-tensioning cable anchors.
“The bridge has some special local requirements that we had to solve,” says Vieira. “On the east side, there is a very significant geotechnical condition—80-meter deposits of sand, which is not common in Norway.” The condition called for piles up to 30 m long.
The west side’s geology consists of black shale. There, foundations include 1.5-m-dia concrete piles in sand, 1.5-m-dia concrete piles to bedrock, 230-mm-dia steel core piles and shallow foundations with a footing. “We have a big river to cross, a railway and existing roads,” adds Vieira.
The longest free span is almost 200 m long, says Rasmus Sainmaa, designer with Sweco. “Usually we would use a lot of timber falsework,” he says. “But this bridge is being built with moveable scaffolding” for the 60-m-long side spans. The balanced cantilever method is being used for the bridge’s 194-m-long main span.
“The biggest challenge is that there is just more of everything,” says Ulvestad. “On a large bridge, you have a lot of tendons. They tend to clash with everything else.”
Each object in the Randselva Bridge model carries some 50 information attributes. Some 95% of this information was transferred to the contractor via open-source files. As Tekla Structures labels all reinforcement according to its pour phase, the contractor can extract bar bending lists from the files whenever needed. At the same time, automatic clash detection ensures that the design is buildable.
On-site workers are equipped with tablets for accessing the BIM on the go, or they can view it on larger computer screens housed inside portable shipping containers, according to a case study report published online by Trimble. Within the online collaboration platform, Trimble Connect, the on-site team can communicate with the 3D modelers and other stakeholders whenever issues arise. To ensure that 3D knowledge is shared among everyone, on-site crew members with computer skills are teamed up with those used to working in the more traditional drawing-based project delivery.
Working entirely in 3D allows field workers to use Trimble SiteVision, an outdoor augmented-reality (AR) system to situate and “see” the 3D model at true-to-life scale on site.
The Randselva design team is also using Trimble SiteVision AR. Back in the office, it allows them to place a virtual version of the next building sequence on top of what has already been done. At Randselva, the AR technology is being used to plan and install pipes and reinforcement, as well as to control scaffolding and pile positions.
These visualizations came in handy as designs evolved. “The main challenge was not only the geotechnical [conditions] but the client wanted the possibility of reducing the deck height,” says Vieira. Revisions to the design reduced the deck height to 13 m from 20 m and increased the number of spans to seven, from six. The original cantilever length was reduced to 127 m from 175 m.
Sigmund Log, head of verification for the Directorate of Public Roads, the approval oversight agency on behalf of the Norwegian Public Roads Administration, explains that Norway implemented a regulation allowing for BIM on project designs in 2015. “That regulation wasn’t touched for a time,” he tells ENR. That changed in 2017 when a project owner wanted to use BIM and galvanized the agency to develop standards for approving models as well as design.
“We needed to adapt and develop a detailing model at the same level as drawings,” Log told Gabriel Neves, Tekla bridge structures manager, in a YouTube interview last November. “All the information developed needed to be incorporated into the model.”
In 2020, the agency approved about 300 projects a year, with about 100 of them based on models, Log says. “At some point I hope it all comes in by model. The framework was put in place and it just built up.”
The agency also now has the ability to export its comments directly back into the live model, he notes.
The bridge’s designers used Grasshopper scripts and Rhino for preliminary design, says Sainmaa. In the aforementioned YouTube interview, he said “the function allows you to write a data file and connect multiple scripts together. We had five people working at the same time on our own scripts. For example, I am in charge of the superstructure. Everyone else needed the geometry data.” He added, “You can only reach a certain level of information in a drawing until it’s so full of stuff” that it becomes saturated and unusable. “BIM has no limitations on how much info you can put into it.”
Sainmaa notes that while Sweco had experience with 3D modeling bridges in the Nordic countries, “they were never as complex” as the Randselva Bridge. Moreover, the design-build team for this project included a contractor, designer and suppliers who were not as experienced with paperless, 3D delivery of a large civil infrastructure project.
Wiktor Rybus, BIM/VDC coordinator with PNC, says that the contractor was willing to take the plunge for this project. “We wanted to try. Drawing-less projects for buildings have been developed for quite a while. But there is a big demand for bridges in Scandinavia—[with] so many islands … we wanted to go drawing-less so as not to stay behind in the market.”
Not only did contracting crews have to learn how to collaborate with designers through the model, but so did suppliers. “They had to internally design equipment based on the 3D model, so the fast way was to create a ready view of the model for them,” Rybus says. Using Solibri software, suppliers could view cross-sections and measurements, check the information or make their own models, he says.
Despite the mandate to go fully 3D, the team didn’t completely avoid drawings, Rybus adds. For some field workers, “we sent a team of engineers to show them how the software works. They created 2D drawings on site and printed out screenshots from the model.”
Construction of the bridge’s superstructure is well underway, with 300,000 elements in the model, says Oystein. “When you model an object, you also get a set of data, such as volume, materials, etcetera,” he says. “On site, companies don’t need all that data at once. We export data into different files” as needed. For example, one file may be just for rebar or for formwork. “It limits the file sizes, and gets the right data to the right people at the right time.” The model facilitates more accurate customized materials deliveries, Oystein adds. “If it’s a drawing, I have to decide what information is needed on site. It can be wrong, or too much information.”
Working with constant bridge geometry changes along the alignment, “it would have been devastating if we made major changes too late,” says Sainmaa. “My work included deciphering some of the sketches, and transforming the design idea into a process.”
Parametric modeling allowed for a high level of development of detail regarding how components are manufactured and installed, Sainmaa adds. “The rebar are generated parametrically and tied together.” As for the post-tensioning cables, “instead of just creating them based on sketches, I returned critical information on their geometries … if we were working with drawings, it would be the contractor’s job to create the geometry, and then you can have surprises.”
Rybus notes that crews in the field with tablets or smartphones can send pictures of issues to be attached to the cloud-based model via Trimble Connect. “Or you can create a to-do issue just by clicking on the object [within the model],” he says.
While the culture of favoring 2D drawings is still well entrenched in the civil infrastructure world, project officials say the Randselva Bridge will serve as a virtual and symbolic connection to a paperless future. “We are already proposing to clients to start working like this,” says Vieira. “We saw that a lot of questions that arise on site are solved in the model. Technology is moving forward fast. I believe that in the next few years this way of working will happen in every country.”
Log says that major project agencies in Norway have already made it mandatory to use model-based project delivery, with explanations required if companies still want to use drawings. “This is changing the way we work and how we collaborate with each other,” he says.
Tekla’s Neves says the turning point may have already passed. “This bridge will be recorded in the history books as a game-changer.”
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