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Home arrow Archives   The American Surveyor     

Scanning a Building in Motion Print E-mail
Written by Angus W. Stocking, PS   
Friday, 10 July 2015

A 3.777Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

Since the earliest days of their implementation by land surveyors, laser scanners have increasingly been used to create high-quality 3D documentations of buildings for use by architects, planners, contractors and other infrastructure professionals, so it would seem that there wouldn't be much new to write about in the world of architectural scanning. But in April 2015, James G. Davis Construction Corporation (DAVIS) of Maryland proved that to be wrong after scanning a four-story, 880-ton brick building in Washington, D.C., and then scanning it again a week later, discovering that the building had moved 34 feet!

This was according to plan, thankfully. The building in question is (or was) at 639 New York Avenue and was built in 1891. It's a historic building in the nation's capital, which of course calls for scrupulous preservation. But the building is also subject to history and is part of a massive downtown development. DAVIS is the general contractor. To work with the rest of the development plans, 639 New York really needed to be beside itself. "The developer has a niche in this area, working with historic properties," DAVIS VicePresident of Integrated Construction Chris Scanlon explains. "In this case, several buildings are affected; on some, just the facade needed to be preserved. But to work with the overall development, two buildings had to be entirely preserved, and moved."

Providing Crucial Insights Early On
The initial scan was routine; just three setups with a Leica ScanStation C10, purchased by DAVIS in 2010. But the detailed information provided was invaluable and could not have been obtained with conventional survey techniques. "For one thing, we learned that the building was even farther over property lines than we thought," says Project Superintendent Doug Bauer. "Four inches of encroachment into public space was known, but the scan showed a bulge in the brick facade that was actually eight inches into public space. Learning about that after the move would have been a big deal."

Historic building encroachment in D.C. is grandfathered in, so the known four inches was fine--ironically, setting the building down in the same encroaching relationship to the property line was a requirement of the move. But if the additional four inches of encroachment had been discovered after the move and blamed on the moving process, DAVIS might well have been required to move the building again... and in the world of big building moves, four inches costs about the same as 34 feet.

DAVIS crews and office staff used the Leica Infinity and Leica Cyclone software solutions to import and manipulate point clouds. One primary analysis tool is heat maps, used to identify deformations from plane. "Within Cyclone, we can easily project planes, from a property line for example, and then generate heat maps that show us deformations relative to that plane," Senior Field Engineer Mike Cumberland explains. "It's a really nice feature and gives us critical information quickly."

This knowledge of a building's deformations can be used to add bracing as needed before a move, to facilitate removal and accurate replacement of building sections, and to account for property line issues, as in the example described above. On this project, heat maps also discovered another deformation in a sidewall, a bulge that could have been a big problem. "We were moving this building 34 feet laterally onto a new pad within a few inches of an existing four-story building," explains Cumberland. "In fact, pilasters on each building were projected to be within two inches of each other--so when we learned that our building's pilasters were out of plumb, leaning more than an inch past vertical, we realized we had a potential issue." But a scan of the neighboring building saved the situation; since that building leaned inward about five inches in the corresponding area of the sidewalls, there would be sufficient space for the buildings to "marry up."

Tracking the Move for Accuracy
During the actual move, DAVIS used a Leica Nova MS50 MultiStation, primarily in robotic mode, to track the building and compare its path to an ideal baseline. "We knew where the building was, from as-builts, and we knew where it needed to be after the move," Bauer says. "And since there are five jacks actually pushing the building, it was possible to make adjustments mid-course." During the event, the initial track of the push would have left the building three inches out of square, but adjustments with the jacks were able to bring it back onto the desired course.

In this case, several prisms were mounted on the moving building and shot periodically. But Cumberland says the process will be done differently next time; "We'll mount prisms for the next move, but this time we'll use the Leica Nova MS50 to track continuously; this should give us even better real-time information."

The move of 639 New York Avenue was the biggest ever attempted in Washington, D.C., but DAVIS will be breaking their own record as early as June 2015, when they move the building currently at 632 L Street as part of the same project. The second move will be bigger in every way; the building itself is taller and weighs more--1,100 tons--and it will be moved farther laterally, about 52.5 feet. And this time the building will also be moved vertically, down precisely five inches, to accommodate a floor level match with new structure.

Scanning Becoming Standard in Construction
"When we formed our Virtual Construction Group six years ago, the investment in the Leica ScanStation C10 was a big leap of faith," says Scanlon. "We did have a couple of use cases, including the Constitution Center [at over one million square feet, the Center is D.C.'s largest privately owned office building], which justified a large portion of the cost, but after that we weren't sure we'd be doing enough scanning to dedicate a crew to it. But in fact, high density surveying quickly became almost standard for us--it's just more efficient, and our field crews caught on quickly."

Scanlon says the same is true for the firm's recent use of the Leica Nova MS50. "Our standard field crews are all able to use the Nova MS50, and there is no shortage of use cases. So gathering scan information is not a problem anymore; our biggest challenge now is processing the information."

As the D.C. building moving projects have shown, contractors are now able to use scanning routinely even on unusual projects. And in this case, heat maps and other specialized information displays were generated quickly enough to make a real difference. Scanlon says that even the information processing is starting to get easier. "Leica's Cyclone has been very useful, and Infinity looks good so far; we're encouraged."

As laser scanners become more common, it can sometimes seem that all their applications have been discovered. But as DAVIS Construction demonstrated by successfully and accurately moving an 880-ton building, surveyors and contractors might just be starting to learn what this remarkable technology is capable of achieving.

Here is a link to a video of the building move: vimeo.com/125509745

Angus W. Stocking, PS, is a licensed land surveyor who has been writing about infrastructure since 2002. For more information about laser scanning solutions, visit www.leica-geosystems.us. For more information about DAVIS Construction, visit davisconstruction.com.

Data Flow Q&A

With Chris Scanlon, vice president of Integrated Construction at Maryland's DAVIS Construction.
What are the basics of your laser scanning data flow, and what options are you exploring? Historically, our workflow was through a single individual in the company that both ran the C10 scanner and had spent a lot of time developing Leica Cyclone expertise. But our goal is to bring HDS capabilities to more folks in the company. We have only just gotten our hands on Leica Infinity, and we still need to explore Leica MultiWorx and CloudWorxs for AutoCAD and Navisworks to see if any of these can provide us the capabilities we need in an easier to use tool. Similarly on the equipment side of things we are looking to expand our abilities to collect point cloud information from the field as part of our regular field engineers' daily process by using equipment like the Nova MS50.

How and when are you using Leica Cyclone? Cyclone is currently used to register and analyze the field data from our C10 scanner. On the building move project, we created a heat map of many of the historic building facades to understand exactly the existing conditions of the buildings.

What other software are you using early in the process to work with point clouds? Have you made changes in this area that are making things more efficient for you? Cyclone is the primary tool for the last five years. We are now overlaying our point clouds when we have outside consultants provide us models from point cloud data, as a quality control methodology.

A 3.777Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

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