BIM (building information modeling) is certainly a common buzzword in the construction industry. A simple Internet search uncovers multiple articles that discuss how this application is used in both design and construction. However, BIM is only one piece that contributes to the overall process of virtual design and construction (VDC).
The goal of VDC is to use multiple 3D technologies, both software and hardware, to improve not only the process of design and construction but also to promote communication and collaboration among all members of a project team during all phases of the construction process. Collaboration is paramount to the success of any project — saving time and money, strengthening relationships, and reducing the errors and conflicts that affect quality, safety and profitability.
Many mechanical-electrical-plumbing contractors understand the benefit of using BIM to create their spool sheets. What is less understood, however, is the use of 3D field technology and how it can connect both BIM and VDC methods to the activity of building in the field.
3D field layout
Once the process of design is complete, the 3D MEP coordination model has been signed off and the detailing of the mechanical fabrication model has taken place in the office, how do you extend the benefit of using 3D models with the team in the field? One popular solution used by MEP contractors is through layout technology using robotic total stations.
Robotic total stations are precise measurement instruments that have evolved from surveying applications into sophisticated time-saving, remote-controlled, building layout tools. They work by creating an optical line-of-sight from the device to the target using a prism and a laser measurement, and are capable of providing accuracy of 2mm from up to 700m away.
The technology has been adapted to fit the needs of MEP contractors by providing simplified workflows and easy-to-use software interfaces. The benefit of this technology is that the construction model is now accessible to the craft worker installing pipe or ductwork, ensuring that onsite tasks can be done more quickly with precision.
Let’s walk through a typical project layout workflow to demonstrate these benefits. The process begins with the creation of layout drawings, typically provided from a modeling team in the office or, in some cases, developed by the same crew that will do the layout in the field. They are typically developed from a fully coordinated 3D model. Layout points are identified in the model and represent locations that the MEP contractor will need to accurately locate and mark in the field.
The layout points are created using software and indicate the X, Y and Z positions of the point and any attributes, or system information, associated with that location. Layout drawings are then produced. The layout points and the 3D model are transferred to the field and loaded on to a controller, typically a rugged tablet that operates the robotic total station. The field layout crew will set up the robotic total station on the jobsite and, as a field point is laid out and staked in the field, the point immediately becomes an as-built record of the installed condition.
When field layout is complete, the as-built information is then exported from the robotic total station and sent back in to the 3D model to update it with the current jobsite conditions. Any deviations between the design intent location and the staked or built condition are immediately identified, providing true round-trip collaboration between the office and field teams.
Mechanical contractor U.S. Engineering Co., based in Kansas City, Mo., realized the benefits of 3D field layout in helping to drive efficiency and accuracy at a recent hospital renovation project in Joplin, Mo. Soon after St. John’s Mercy Regional Medical Center was destroyed by a massive tornado May 22, 2011, plans were launched for its replacement. The new 875,000-sq.-ft. Mercy Hospital Joplin, designed to withstand the next powerful tornado, included beds for surgical, critical care, women’s and children’s services, behavioral health and rehabilitation.
The bottom three floors of the structure included hospital space along with a seven-story patient/owner and a four-story clinic tower rising above the hospital space. The facility also incorporates heavy-duty mechanical, plumbing and electrical systems, including the necessary components for fuel storage, air supply and return, chilled water, condenser water, HVAC and plumbing, as well as piping for the tunnel between the hospital and the utility plant.
Using 3D models, U.S. Engineering completed the design of the mechanical and plumbing systems, and located in excess of 78,000 points for sleeves, embeds, floor penetrations, drains and hanger supports. The points located on the first and second floors of the hospital main building exceeded 38,000 points. The third floor, which is common to both towers, had roughly 10,000 points. The six-story patient tower added another 22,000 points and the three-story clinic tower another 8,000 points.
U.S. Engineering also used the Trimble Point Creator for CAD and Revit and Trimble Field Link for MEP connection to verify as-constructed conditions with the architectural floor plan.
Jeff Kiblen was U.S. Engineering’s project manager of fabrication and 3D coordination oversight for the mechanical and plumbing systems on the project. “Any inaccuracy, especially with sleeve layouts in walls for plumbing, would have created significant fit problems,” he says. “We needed to be within 1/4 in. or 1/2 in. because of the density of ceiling spaces and tight coordination with all the other systems. Thus far, we’ve realized incredible accuracy thanks to our 3D model-to-field workflow.”
Understanding the ‘as-is’ condition
3D scanning is gaining momentum within the MEP community. How can scanning help the MEP contractor? Renovation and adaptive re-use projects require accurate drawings of the “as-is” condition and documentation to work from. This level of information often does not exist or the drawings available do not represent the actual condition built in the field.
To create drawings, manual measure-ments can be taken of a space; however, this process is both time-consuming and prone to human error. Scanning is a fast and accurate way to collect large amounts of measurement data that can be modeled and used in design and construction. The registered point cloud also can be applied to 3D model coordination. By overlaying the point cloud model with the design model, project teams can visually check for conflicts between existing and new conditions.
As building owners become more sophisticated with their BIM requirements on projects, scanning provides the solution to address both quality assurance/quality control needs and create accurate documentation of installed systems. Information can be given to building owners as either point cloud data or 3D-modeled objects that can be added to facilities management models.
There are three steps that make up the basic scanning workflow: scan, register and detail. The first step places a scanning instrument in the field to collect measurements of individual points using a laser. The technology is similar to the measurements taken by a robotic total station where points are recorded with an X, Y and Z value. Where the robotic total station captures individual measurement points, the 3D scanner collects millions of measurements within a matter of minutes.
Once measured, these points resemble a cloud and provide an accurate 3D representation of the area scanned. In typical applications, multiple scans are made by placing the instrument in different locations so measurement data is collected from various angles. The multiple scans increase the accuracy of the data. When all measurements of an area have been taken, the next step of the scanning process is to register the data.
During the scanning process, two types of targets are placed in the area to be scanned. These objects are either free-standing spheres or checkerboard targets attached to a surface. The targets help to align the multiple scans into one composite model by linking common targets found in each individual image. A minimum of three common targets in each individual scan is needed. Software that is designed to register point cloud data can then detect these common targets to automatically “stitch” together the individual scans into one composite 3D point cloud model.
The detection of targets also can be done manually using the point cloud software. In addition to the targets, common elements found in each scan can be identified to register the data. Once registered, the composite 3D point cloud model can be either exported to other applications or detailed using modeling software.
The last step in the scanning workflow is to detail the registered 3D point cloud data. Using scanning software, individual elements of the point cloud data can be isolated and 3D objects can be modeled from the information. An entire model can be created using the registered data. The 3D representation can then be used to detail or supplement an existing building information model or understand how new elements will connect to existing conditions.
These two examples of 3D technology illustrate how BIM and VDC methods are being connected to the activity of building in the field through the use of hardware applications. Robotic total stations connect the 3D model with the field installation crew, ensuring accurate placement of model elements with the real-world conditions of the field. 3D scanning supplements the model by adding accurate measurement data with the “as-is” condition either through a point cloud or modeled elements. These technologies are being adopted by the MEP industry to increase accuracy, efficiency and use the BIM to link the office with the field.
This article was originally titled “Collaboration with 3D technology” in the May 2015 print edition of Plumbing & Mechanical.
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