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Bridges: From the site to BIM


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April 1, 2015 by JACOB STOLLER

Whoever coined the phrase “measure twice, cut once” would be challenged to come up with an updated version that reflects today’s state of the art measurement technology. Survey equipment found on a growing number of jobsites is so powerful that it is transforming how construction projects are planned, negotiated, and built.

Today, a Laser Imaging Detection and Ranging (LIDAR) device can scan 100,000 points per second within tolerances of a few millimeters, creating a “point cloud” which, with the help of specialized software, can be formed into an accurate 3D model.

Mounted on a drone, LIDAR or photo imaging equipment can be flown around a gravel pit, gathering measurements in 30 minutes that would take a traditional measurement crew an entire week. Global Navigation Satellite System (GNSS), an enhanced version of common GPS systems, has become so accurate that it can be used to plan, build, and inspect road building projects. Finally, robotic Total Stations can import points directly from an electronic 3D model and shoot them via laser onto actual points on a jobsite.

“It’s a really exciting time,” says Toronto-based Don Edgar, technical sales representative for Leica Geosystems. “Every day, there’s something new – not just new technology, but new ways of using it.”

BRIDGING SYSTEMS

For the construction industry, the power of these tools goes far beyond better measurements. They are becoming, essentially, a bridge between Building Information Modeling (BIM) systems and the physical jobsite. It is this magical combination of state-of-the-art measurement and virtual modeling that is changing the game in construction.

“A 3D model is obviously 3D geometry, and it’s accurate,” says Tom Strong, managing director of Virtual Construction Services at Mississauga-based contractor EllisDon. “It’s to scale, and it’s usually tied to the geodetics of the jobsite so it’s oriented correctly. But you can also can generate control points directly from the model, and then lay out those control points in the field. Now you have a way of going from the 3D hypothetical environment to the real world coordinates.”

The exact location of a bolt, for example, can be established in the virtual model before the concrete is poured, allowing an insert to be installed precisely to accommodate it. The process works in reverse as well – a surveyor can scan as-built points in the field, and then compare these against the virtual model.

“It goes both ways,” says Strong. “You pull your coordinates out of the model and lay it out, and you can go in the field and check what’s been installed to be sure it’s in the correct location.”

Strong is also active with the Canada BIM Council (CanBIM), a non-profit association devoted to educating the construction industry BIM technologies and practices. CanBIM hosts several learning events a year across Canada.

The equipment is also allowing professional surveyors to have a much bigger role in construction projects. “Surveying can now mean surveying the pieces of a building,” says Larry Ertl, President of Richmond Hill, Ontario-based Ertl Surveyors. “With piping, for example a surveyor can come in with a LIDAR and map out as-built conditions, and the subcontractor can use that to pre-cut and preassemble all their piping offsite.”

NEW STRATEGIES

On the business side, the new survey technology is accelerating a trend towards better collaboration. “There’s a big difference in the way the industry works now,” says Strong. “Everyone used to work off just blueprints. You’d lay your grids, and everyone would measure off those grids. Now everybody’s working and coordinating in 3D, so we’re getting to a much higher level of detail with coordination to the point where we can pre-determine where all the nuts and bolts and hangers are going in the field. And we’re doing that months and months before we start construction.”

This means that subtrades can plan their pipe hanger locations, for example, before the concrete is poured. “So while we are doing our formwork, the subtrades come in with a Total Station and lay out exactly where those hangers are going to go, and actually put embedded anchors in the correct locations,” says Strong, noting that this prevents uncertainties, delays, and the high expense of drilling into concrete in awkward locations. Essentially, everybody on the construction team wins.

The technology might even spell the end of the adversarial jockeying that used to be typical on jobsites. For example, a subcontractor would typically race to get their piping in early so others would have to work around them, instead of the reverse. In this current model, everybody works to the plan.

“It’s a team sport where everybody develops their precise geometry, and they work out all their details in advance,” says Strong. “Then, when you go to the field, you work the plan.”

Collaboration between all players – architects, engineers, client representatives, contractors, and subcontractors – is also enhanced by the BIM model being available to all partners via web portal, putting everybody on the same page.

PRACTICAL ADVANTAGES

Accurate scanning of site conditions means that more fabrication work can be done in the shop. For example, one of Strong’s early projects with EllisDon was the management of several very intricate stainless steel staircases at the Art Gallery of Ontario in Toronto. Because their BIM model was so accurate, the staircases were built entirely offsite and installed without incident.

As-built records is another huge area. At Calgary Airport, for example, EllisDon used a 3D scanner to map the locations of tubing for in-floor heating covering literally acres of floor area. Previous methods would have used thousands of photographs created by laying a measuring tape on the floor and creating a gridline. Deciphering these photos to determine a safe place to drill, for example, was a tedious and risky task. Today, all the data sits in a CAD or BIM file, easily available to the installer of a ticketing terminal or other late addition. By Strong’s estimate, the approach has saved the airport hundreds of thousands in mitigation costs.

The technology is also highly effective in civil construction. A LIDAR device can be flown on an airplane or drone, or installed on a truck, and used to create a digital terrain model (DTM) that is highly accurate. “If they’re surveying for a new highway or a new lane, they don’t have to close the highways so survey crews can work,” says Ertl. “They just drive along with traffic.”

The resulting 3D model might also allow, for example, a road builder to improve work efficiency over a seven-km segment. “You can optimize your cut and fill patterns based on that LIDAR scan, ultimately,” says Strong, “and that’s a big deal. An inch of earthworks over seven km is a big cost. So if you can optimize that, you can be very competitive.”

GNSS devices can then be mounted onto the earth-moving equipment, giving operators immediate feedback, and Total Stations can help grader operators fine tune jobs down to a few centimeters. “In the past, it might take a grader four or five passes to get it within tolerance,” says Edgar. “Now they can achieve that with one or two passes.”

There are, however, some cautions. The data, if not correctly processed, can be easily misinterpreted. As well, some work may call for traditional survey methods. “The technology is very good for gathering the data and processing it for site conditions,” says Ertl, “but one area where technology doesn’t hel
p is when we have to do a reconstruction of a survey boundary. Now we have to apply legal aspects, and there’s a lot more involved to resolving boundary issues, or re-establishing those boundaries.”

GETTING STARTED

When it comes to embracing the new technology, Strong believes that contractors may not have a choice. As BIM becomes the de facto standard for the industry, surveying equipment will give companies a huge competitive advantage by helping contractors work to a common model with extreme accuracy, reducing time on jobsites, improving the accuracy of offsite work, and preventing re-work.

Ertl notes that the price of many of the tools, such as LIDAR units, has dropped significantly. However, the cost of entry for contractors remains significant. For one, the point clouds produced by LIDAR units are very large and complex, and the data needs to be cleansed and imported properly into a BIM model. “It appears that the software hasn’t really caught up to the hardware yet,” says Ertl. “But it is getting better.” Strong notes that there is a lot of consolidation now in the software industry, and that buyers can expect to see better integration in the near future.

The biggest challenge for contractors, however, is getting people on board who can support this technology. Look to the younger generation, says Strong. “You’ve got a whole generation of young people coming into the industry that are very interested in technology and are driving the use of it,” he says, “and the younger people want to work for progressive firms that use this type of technology.”

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Jacob Stoller is a principal of Toronto-based consultancy StollerStrategies. Send comments to editor@on-sitemag.com


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