3D scanning science
The all-glass elevator shaft nears completion, as The Carvist Corp. team installs the large glass panels on the steel structure.
When The Carvist Corp., Placentia, Calif., took on the design and installation of a complicated all-glass curtain wall that would enclose a large elevator shaft at the Santa Monica Place mall in California, its biggest challenge was obtaining exact field dimensions of the existing, three-story steel structure.
“We had to enclose the steel structure that was going to be the elevator shaft with glass on all four sides,” says Bill O’Connell, co-owner, The Carvist Corp. “Traditionally, that would require us to send people out to the site, where they would somehow have to draw the structure, noting all of the different bows and twists of the metal.” The all-glass elevator shaft design called for hundreds of glass panels up to 1 5/8 inches thick, measuring up to 80 square feet and weighing 1,110 pounds. The glass panels were to be assembled using point-load spider fittings, leaving no room for mistakes. “We had to find out exactly where the steel was bowing out or twisting in order to design a point-loaded glass system that used brackets attached to the steel to hold the glass in place,” O’Connell says. “Because the elevator enclosure is glass, we couldn’t use shims that you might typically use in a curtain wall, where they are hidden from view. So, we had to figure out exactly where the steel was, relative to the perfectly rectangular glass structure that we were going to put around it. In order to do that the traditional way, we would have had to spend weeks with guys on boom lifts onsite, trying to figure out where the biggest bow was in the steel in order to get the measurements that we needed.”
At the Santa Monica Place mall, Carvist Corp.’s task was to enclose this existing, three-story steel structure with an all-glass elevator shaft, above.
To produce the most accurate field dimensions and reduce the potential for fabrication error, the company invested in a Leica ScanStation 2 and 3D scanning software from Leica GeoSystems, part of Sweden’s Hexagon Group; incorporating its capabilities with existing 3D CAD (computer-aided design) and CAM (computer-aided manufacturing) software.
The Leica Scan Station 2, pictured on a job site above, features powerful laptop control and the ability to conduct full-dome scans using its oscillating mirror with front- and top-window design, according to the Leica GeoSystems Web site, www.leica-geosystems.com.
The Leica ScanStation 2 features a high-resolution, internal digital camera that scans the structure, gathering data based on triangulation of multiple scans. Millions of laser dots canvas the project, enabling the user to see the structure inside and out, and gather accurate field dimensions.
“The scanner allows us to put one guy out there,” O’Connell says. “He sets the [ScanStation 2] up at three or four places around the structure. The camera scans the structure, painting it with little dots of light and storing those dots of light dimensionally correct relative to each other. We are able to take that information and, using AutoCAD, accurately model the structure. [For the Santa Monica project], we were then actually able to tell where the bows and the twists were in the steel. That allowed us to build a perfectly rectangular glass structure around it and determine where the glass brackets had to be at each load-bearing point.”
For the Santa Monica project, the steel structure was scanned using the Leica ScanStation 2. Engineers applied the scan data in 3D CAD and designed the glass panels around the scan data; then they extracted the panels for the CAM process. As a result, every panel was a perfect fit and provided for speedy installation.
Actual scanned image of the complex elevator shaft, above.
Actual scanned elevator shaft. Note the detail of the safety cable, above.
Photograph of scanned image, above.
Describing life before the Leica technology, Project Manager Tim Egan says: “Most of our projects required confirmed field measurements, often holding up projects until such data became available. And while approved building plans are great as a map, they do little to provide exact measurements. … I cannot foresee going back to the old way of handwritten field measurements. With accuracy of 1/10th of an inch at 900 feet, we simply go to our scan data for such information … it’s very accurate.” In the case of the Santa Monica Place mall, “One mistake due to one poor field dimension could have cost us tens of thousands of dollars as there would have been a compounding effect offsetting adjacent panels,” Egan says.