September 1, 2010
Building information modeling might seem more like a theory or concept to the average mechanical, electrical or plumbing contractor. But a Nebraska HVAC contractor recently began converting BIM theory into practice with the help of some hardware and software tools designed just for that purpose.
In May 2010, Art Push & Sons in Omaha, Neb., purchased a robotic total station and 3-D computer-aided drafting software from Get the Point LLC, a Larkspur, Colo.-based Sokkia dealer. The total station hardware and CAD software were combined to dramatically increase the precision and efficiency of marking and installing mechanical fixtures during building construction.
By July, the company was using the system on its third project. Due to tight scheduling, Mike Centarri, job foreman for Art Push & Sons, had one day to locate and mark locations for hangers, elbows and takeoffs for a pair of 160-foot-long air ducts on either side of a wall inside a 16,000-square-foot commercial building near Omaha. Centarri was fully aware that one worker marking 141 locations in a day was not possible using conventional layout methods, including marking distances and angles on a CAD drawing and transferring them to the building structure using a tape measure.
“Under the old way, we would use the scale rule and the tape measure on our hands and knees,” Centarri said. “We would have to come off of different points on walls, columns and structures in the building and transfer them onto the floor and measure our distances for every set of hangers. At that point we would either plumb bob or use a laser plumb bob to get a point to install a hanger - that was pretty much the old process simplified.”
The process would typically require one worker for the scaling and another for marking points.
“This ductwork would probably have taken two guys three full days, whereas this won’t be a full day of work,” said Centarri. “I’d say the new way will take a total of six hours versus a 40-hour week doing it the old way.”
The savings on a relatively uncomplicated project such as this would be about 80 percent, Centarri estimated. Moreover, a typical building would get finished more quickly and the owner could begin generating cash flow from the facility. Another advantage is a reduction in physical and mental stress, he added.
But the main advantage of using BIM is increased precision, which translates to more efficient work. Increasingly, buildings are designed with features such as recessed lighting and radius walls, crowding more fixtures into smaller spaces. Precisely locating so many utilities becomes even more challenging in medical buildings - a segment in which Art Push & Sons generates about half of its business - and schools. In a hospital, ductwork is typically located near other utilities like sprinkler systems and large quantities of electrical conduit powering bright lighting and information systems, so precise location is crucial, Centarri pointed out.
Art Push & Sons is familiar with the discrepancies that emerge between paper and an actual structure. Building a model from an official survey and then marking fixture points using a control point as a reference can accommodate ever-tighter tolerances and eliminate rework.
New processInstead of crawling around on his hands and knees to mark locations, Centarri stayed on his feet and set up three system components. First, he deployed a tripod, set a Sokkia SRX total station on top, turned the power on, and leveled it. Next, he set up a Sokkia ATP1 prism on a tripod and located it over one of two control points on the floor, having received the coordinates via text on his smart phone. Then he opened up the project folder on a Windows-based Sokkia SHC2500 handheld data collector and referenced data points for the ductwork fixtures. The coordinates were entered into the unit via a flash drive; the unit is also Bluetooth-enabled to allow remote data entry.
Using a prism pole, he also mounted a Sokkia RC-PR4 controller equipped with a 360-degree prism that allows communication between the total station and the prism for the purpose of locating and marking data points.
The total station shot an infrared laser beam to the back-sight prism, which reflected the beam back to the total station - a procedure that allows the total station to orient itself within the building structure by triangulating the device’s exact location. With its precise location determined, the total station communicated via Bluetooth to the handheld device and indicated where Centarri was to set the RC-PR4 prism pole. Guided by the data in the handheld unit, the RC-PR4 pole determined the location of layout points based on the information from the BIM file. Centarri repeatedly checked for the next layout point on the handheld unit, which guided him to the layout point with a red laser beam, then marked the location for Art Push & Sons’ installation crew.
Having already used the robotic layout system on a public works building and to lay out a hospital operating room, Art Push & Sons had quickly gained an appreciation for working with even greater precision than before.
“We know we are in the right spot. We are where the drawings show us to be,” Centarri said.
Todd Push, vice president and head of project estimation for Art Push & Sons, noted the importance of all contractors using the same control point on a given project.
“As long as everybody is using the same control point, there shouldn’t be an issue of accuracy,” he said. “Where your problem could come in is if somebody decides they want to use different control points. If everybody is using different points but everybody starts at the same spot, we should be OK.”
Eventually, general contractors should realize that using the same control points will benefit subcontractors on the entire project, Push added.
“I think there’s going to come a time when they start the building and establish a control point as a benchmark outside and then we’ll probably get to the point where they move the point into the building on the first floor at a certain column line,” he said. “The other issue that’s going to have to be dealt with is, on remodel projects, somehow, somebody - it’s probably going to come down to the general - is going to have to decide what point they’re going to use inside of a 50-year-old building.”
Still, “Putting up hangers takes a lot of time and effort,” he said. “With this system, as long as you have the right control point to begin with, your hangers are going to be accurate. Someone may come to us and say that our ductwork is off by 6 inches and we can ask, ‘Well, what are you measuring from?’”
Nick Push, project manager, has noticed a trend toward radius walls in medical buildings, but the new system can still allow Art Push & Sons to maintain its own scheduling.
“To be able to accurately locate our ducts in those walls ahead of time, we don’t have to wait for the wall contractor to lay out the radius,” Push said. “We can know where our sleeve is and we can get to work.”
Todd Push added that the station will put pieces into the right place no matter what the angle is.
“What’s nice about the total station is that it doesn’t care if you’re setting the sleeve in a radius wall or a wall with a weird angle. It doesn’t care,” he said. “It’s going to put it in the right spot.”
Centarri said that it is also possible to take readings on slight changes to a structure, make a drawing, and save it to the flash drive for the CAD designers back at the office to make revisions.
Project teamUsing these tools for a new site layout process has a definite upside, but the consensus at Art Push & Sons is that, ideally, every contractor would use them on a given project.
“By the time you actually go on the project to start installing the ductwork, you have a lot of work done already,” said Todd Push. “The installation becomes more of, I don’t want to say a secondary process, but in a sense, it almost is because by using the system, the 3-D CAD beforehand, you’re taking a lot of the guesswork out of it. You can be in front of or at least alongside everybody else.”
Nick Push sees the total station as revolutionizing the sheet metal industry.
“I look at it as doing for the field projects what the plasma table did for the shop,” he said. “Once we made that connection and figured out what it would accomplish for us, it drove us to start using this system. But the biggest problem we’re having is that we ask the general for control points and they look at us like a deer in the headlights. They say, ‘We can snap a line on the ground.’ That’s not what I’m talking about.”
This article was supplied by Sokkia Corp., an international manufacturer of measuring systems, and dealer Get the Point LLC, (800) 385-7131.