BIM plays an important role in legislature dome renovation
A $6.1-million renovation project for the Alberta Legislature dome is expected to take about one year and is slated for a late-2013 completion. Construction should start at the site this fall, shortly after celebrations marking the 100th anniversary of the official opening of the building in September 1912.
Elements of the dome are approaching the end of their shelf life, hence the renovations.
"The existing terracotta on both the major dome and the minor dome above the Legislature chamber has deteriorated," says Lyle Butchart, an area manager for property at Alberta Infrastructure. "The project will include replacing the terracotta on the cupola as well as the terracotta on the main dome."
The deterioration of the terracotta, however, is not yet severe, but the issue of potential water penetration was a major spur to do the work now, says Butchart, who notes that the terracotta has no waterproof membrane. There is only concrete book tile beneath it.
Restoring these elements of the 54-metre-high dome is going to rely heavily on some of the latest 3-D modelling software and methods from the Building Information Modelling (BIM) tool box. "We didn't have an adequate set of drawings with enough detail, so BIM is going to have a role in filling in gaps for the design process," Butchart says.
Planning and design began with consultation and determining what the dome required for restoration and improved waterproofing, with Edmonton-based Building Science Engineering Ltd. (BSE) contracted to run the project.
"BSE designs the anchorage and some other components and sets up the criteria for them," notes Chris Makepeace, a principal at BSE.
HIP Architects, in turn, did much of the modelling and other design work on the project. The use of 3-D BIM not only saved both time and money in the design process, but also played a crucial role in analyzing the existing curved terracotta and tile surfaces, and developing a design that would replicate these elements.
Need for precision
Allan Partridge, a former principal with HIP who is now with Group2 Architecture Engineering Ltd., did much of the design work for the project. He says, "One of the hardest things is to do a 3-D model of curving surfaces. Having [the dome] scanned and developing a BIM was the best way to access how to represent work that needed to be done. This would take into account not only the surface in three dimensions, but also the deformations from age-and the original imperfections that may have been built in. So, with BIM, we can develop an exact profile of what's there and therefore what needs to be done within plus or minus a quarter of an inch. And precision was essential to the dome project."
The structural elements and building components required detail analysis and modelling from outside to inside. Some of the area on the inside of the dome was also scanned to provide a series of control points.
"Once we had enough data to derive control points, we used those control points to measure the rest of the interior using a hand-held laser. This gives you a virtual replica of the interior structure," Partridge says.
Advances in laser scanning technology help the process, as earlier laser-scanning technology was relatively limited, he says.
Without today's laser technology and BIM, the process of developing a model and design based on the original may have had to resort to "stereo-photogrammetry," a process of determining the geometric properties of objects from photographic images. In this case, Partridge says, "Someone with a special camera would have to be up there on a crane."
Older systems of measurements and analysis could take weeks. Instead, BIM, assisted by modern laser scanning, enabled this measurement and analysis to be done in a matter of days.
Most restorations projects today can expect to include the application of some scanning technology. A project in Calgary recently used the same technologies, Partridge notes. He says the scanning, combined with BIM, provided a very comprehensive record of both older and more recently installed building components.
"This allowed us to check and verify the entire structure, whether new or old," he says.
The technology results in lower costs for the recording process and is about 50 per cent less than a traditional manual method, or 20-30 per cent less than photogrammetry. But the savings don't stop there.
"The increasing accuracy is immeasurable in terms of costs of the overall project," he says. "A big advantage is that consultants, contractors, owners, all the way down the supply chain, have access to the same accurate, precise data sets. Just 30 years ago, the whole project could have cost double, and with a high degree of risk, which would have been borne by the owner. Now, we have high fidelity and high predictability, and, therefore, sharply diminished risk."
A key part of the architect's role in the process, he says, was to provide a complete, precise record of the existing structure and details on how the new insulation, membrane and tiles would integrate within the refurbished dome.
Because BIM has advanced so much in the last few years, the silo effect from the various elements-engineering, architectural and so on-are much reduced, with a resulting streamlining of the process.
Says Kyle Bradshaw, an intern architect at HIP: "Before, elements were each in their respective file. Now, all the element sets are in the same file. It makes coordination much easier. So you can easily tell if, say, a stairwell aligns precisely with other elements."
It's anyone's guess what the technology will be like decades from now when the dome is ready for another renovation. But it is clear that BIM is playing a role in this effort to preserve Alberta's history.