How BIM is changing setting-out on site
Building information modelling or “BIM” for short, is the next evolution in technology that is revolutionising the construction industry, and setting-out on site is one process that is instantly improved by BIM. Surveyors no longer need to rely on printed plans, tape measures and plumb lines to translate designs to the field. Instead, BIM software combined with the latest hardware now brings the precision of 3D models from the office to the field, saving time and money. This case study introduces the solutions available to do exactly that, highlighting the reduction in rework and productivity gains available to today’s surveyor on site.
In the complex design-build-operate (DBO) lifecycle of any major construction project today, “build” is where contractors are under the most pressure to deliver. They need solutions that will work within their business structures and processes, and to leverage technology that won’t distract them from their core competency of building.
Fig. 1: Trimble Westminster, Westmoor Drive, Colorado.
Trimble Westminster project
This development represents Trimble’s strategic initiative to grow its Colorado operations and houses teams representing machine control, geospatial, building construction, MEP, monitoring and others. Phase 1 of the project was an 11 600 m2 office building on a 6 ha site (Fig. 1). Trimble leases over 40 buildings across the US but this is the first building that Trimble helped design, manage the construction of, operate from and own. They have been in the building since May 2013 but were able to showcase many of Trimble’s technologies during the planning, design and construction phases, and capture many of the processes and metrics.
Traditional setting-out issues
A question I have heard on many construction sites is “Why would we need a robotic total station if we have tape measures? We’ve been building without them for the last 50 years”. Most workers on a job site know how to use a tape measure, string line, plumb bob or level, but what many of them don’t realise is that tape measures can actually give false measurements.
These false measurements can be due to many factors including deflections over uneven surfaces such as dirt or materials in the way, temperature variations causing the steel tape to shrink or stretch, or the pressure applied when pulling on longer measuring tapes.
Other issues arise just from misreading the tape measure or by inaccurate addition or subtraction of dimensions from drawings, especially in the US when there are numerous fractions of an inch. More importantly for today’s highly litigious construction market or for the more sophisticated BIM projects, there is no record of measurement with a tape measure.
Robotic total station setting-out
With a robotic total station, we are now able to create points directly in a 3D model or 2D drawings, wirelessly transmit them to the robotic total station for setting-out, and then take as-built records of these measurements back into the model.
Fig. 2: Setting-out with Tekla software and robotic total station.
The fact is now that almost all contract drawings are produced in 2D electronic formats such as AutoCAD or 3D electronic modelling software such as SketchUp, Tekla or Revit. As every project is constantly changing, the most up to date information is contained within these models or 2D electronic files. Handing a worker a set of printed drawings or even a tablet with PDF drawings will not always ensure they have the latest set of changes to incorporate that day.
Within SketchUp and Tekla, or Trimble Point Creator for AutoCAD and Revit, you are now able to create setting-out points directly within the latest 2D or 3D version of the project. On the Trimble Westminster project, setting-out points within a Tekla model ensured the engineers and contractors were coordinating anchor bolts, reinforcing bars and even formwork to 100% accuracy (Fig. 2).
We are now in the middle of a dramatic paradigm shift within the architectural, engineering and especially the construction industry. Only ten years ago, very few projects had electronic drawings, let alone MEP coordination, robotic total station setting-out or laser scanning verification. With developments in processor speed and software, we are now able to coordinate numerous models simultaneously, compare versions of 2D drawings or 3D models for changes, and visualise the construction sequence/schedule before we even create setting-out points.
As every item on a construction project has to be laid out by some method, we can now incorporate this process into a separate item within the 5D estimate, and show setting-out in the 4D schedule as the critical path and quality control process.
Return on investment
ROI calculators are useful tools for modelling the financial benefits of these modern setting-out solutions versus traditional methods. Trimble’s tool which can be found at http://roi.bimtofield.com/e is a great working example (Fig. 3). You can plug in your job information into the ROI calculator and there is also some sample data which shows a doubling in setting-out productivity over the older mechanical total stations and substantially more productivity over the use of manual tape measures and levels.
What many people forget is the fact that every item on site needs to be set out, from excavation to interior wall, with either a tape measure or a robotic total station. This means there is a direct cost every time a worker pulls out a tape measure that is usually hidden in the construction estimate or job cost. However, with a robotic total station, you are able to set up almost anywhere and perform site layout faster with one-person operation (Fig. 4). This saves the considerable cost of a second person either on the end of a tape measure or as the rod man for a mechanical total station. There are no delays for hand signals or trying to communicate with the rod man via hand held radios or cell phones.
Fig. 3: Construction setting-out ROI calculator example (US).
Many times, the rod man may not be the most skilled or experienced worker on the jobsite and may not understand the importance or accuracy required for the point being set out. With robotic total stations, the setting-out foreman is at the point of installation, seeing actual jobsite conditions along with the latest background files or model information and can pass that information back and forth to the office wirelessly.
Doing 500 setting-out points per week for a typical tape measure and builder’s level crew is pretty productive. Even with the more traditional mechanical total stations, when laying out interiors in large curvilinear buildings, achieving over 200 points in a day is very good.
Now with robotic total stations, we are able to get over 400 points per day with a one man crew instead of 200 points with a two man crew. You can see through the ROI Calculator that a robotic total station can pay for itself within a single project and still provide tremendous labour savings. Also, if you have multiple projects per year for your setting-out team, the savings can be very significant over a five year period.
During the Westminster office project, Trimble tracked the expenditures and metrics associated with the robotic total station setting-out. With traditional methods they would have utilised at least two people for roughly four months in total to set out foundations, anchor bolts, gridlines for the steel, interior and exterior walls, and control gridlines for other trades.
Fig. 4: One person operation of a robotic total station.
The main contractor JE Dunn conducted studies and found that even very small issues resulted in over $2500 (R36 750) in costs on a project when you start to account for the foreman and worker’s time to find the issue, the project manager and assistant’s time to raise the paperwork, and then more management time to incorporate the issues onto the drawings and ensure the subcontractors and other workers in the field correct the issue appropriately.
For example if a set of anchor bolts were off by 2 cm and the base plate needed to be slotted to fit the in-place bolts, this would easily cost the general contractor over $2500 (R36 750) in extra management time to get approval through the structural engineer. This doesn’t include any subcontractor costs if they didn’t find the issue until they started erecting steel.
A larger issue such as pouring a pile cap too high or too low, or installing a door opening in a concrete core wall in the wrong location could result in costs of over $25 000 (R367 500). Even if the surveyors had set out everything perfectly, you would still have the costs of a QA/QC engineer and/or BIM specialist to check the onsite as-built situation versus the design models. The traditional method also would not include delays in the project schedule.
Foundations and concrete works
A single setting-out foreman used the Trimble robotic total station to lay out each of the 83 piles with four offsets each. The centreline method was used to position anchor bolts before, during and after pours while the concrete was still wet to make sure they were perfectly located.
Every corner of the structural concrete cores were marked and even the door openings were marked prior to the re-bar installation to ensure proper clearances were maintained. A 100% accurate placement for every anchor bolt and embed location was actually achieved and this reduced structural related RFI’s by at least 50%.
For future projects, the as-built locations of any post-tensioning cables could be scanned and accurately recorded with the robotic total station to ensure they are not cored or drilled through later.
Steel and edge angle setting-out
After checking to ensure all of the anchor bolts and embeds were correct after backfill, grid intersections or offsets at each column location and benchmarks at every floor were set out. This allowed for quick installation of the permanent stairs and steel structure prior to decking installation. In fact, the steel structure went up twice as fast as originally scheduled and allowed the steel erector to brace and install safety rails and miscellaneous metalwork early.
It was decided that more traditional methods using tape measures would be used in some areas of the site in order to be able to make comparisons with the more modern automated technology. When edge angles along the perimeter of the building and at openings were checked with the robotic total station, a few issues were indeed found due to bad tape measurements.
Trimble Vision Technology
One of the many benefits of Trimble’s RTS 773 robotic total station is the ability to remotely control the instrument, as well as see and measure through a live video feed on the Trimble Tablet within the Trimble Field Link software. This is Trimble’s patented Vision Technology. This allows the operator to easily locate and mark out points in the field. Using this Augmented Reality Layout, as it’s often referred to, within the model viewer on the Trimble Tablet, you can actually see the model superimposed directly over the real site work, and create setting-points on the fly where you need them (Fig. 5).
This exciting new technology only became available after the Westminster project had started, so was only used to check some of the final column positions. They were found to be within 4 mm of the final design and construction model.
Fig. 5: Trimble Vision Technology.
Interior setting-out competition
After setting-out all of the interior and exterior walls on the first three floors of the building, Trimble and JE Dunn conducted a setting-out competition on the fourth floor. A best team utilising traditional 2D plans, tape measures, chalk lines and squares was put together to race JE Dunn’s robotic total station. JE Dunn’s hardware operator produced 200 points in the half-day that it took the manual team to lay out 100 points.
In the end, the latest modern technology helped set out two thirds of the building within the same timeframe as the team using the manual traditional methods laid out one third. The manual team also missed numerous dimensions that weren’t on the drawings, they laid out items incorrectly as they referenced the wrong “typical” plan for several rooms, and they did not have any information on window, soffits or openings that were already in the model.
Typically, the architect won’t show all the dimensions on the 2D plans as this adds too much clutter. So on a normal project, the framing subcontractor would have to stop production, submit a RFI and then wait for one to two weeks to get the answer back and then check to see if it works. However, with 3D model based design, the 2D drawings are automatically created directly from the model, and then accurate setting-out points are exported directly to the robotic total station, so there are no missing dimensions.
Fig. 6: Floor flatness verification.
Although JE Dunn did spend time modelling the stud walls in Tekla and then creating the points within the model, the manual setting-out crew also spent quite a bit of time going through the drawings and preparing a cheat sheet for dimensions and layout to help increase their productivity.
Floor flatness and interior plan modules
One of the new developments with the Trimble Field Link controller for the robotic total stations is the Surfaces Module where you can utilise the robotic total station almost as a laser scanner. The Field Link software can be programmed to take a snapshot on the slab or ground surface at a certain interval using Direct Reflex Scanning (Fig. 6).
Direct Reflex uses a laser beam to take a direct measurement off a vertical surface or difficult to reach area without a prism. This function can be controlled through the scope of the robotic total station or through the hand-held controller remotely. These robotic total stations can be controlled in a fluid, real-time movement directly on the tablet with the Dynamic Joystick drag and point feature.
You can then check the elevation variations against a benchmark or model elevation to create contour lines and then get a PDF Surface Report showing areas and volumes of fill or grinding that needs to be done to get a flat floor surface. This is especially handy in hospital projects with vinyl flooring, warehouses or other facilities requiring super flat floors for high-tech equipment or robotics.
Quality assurance and control
Utilising the reporting and camera features with the Trimble Field Link controller you can create daily layout summaries, deviation reports, field reports with photos, descriptions and exact coordinates of any issues. You can also take as-built snapshots of everything that has been built so far and bring them back into the final design and construction models for an absolutely accurate model update before hand over to the owner.
Fig. 7: Flow of BIM model data in the design-build-operate project lifecycle.
Additional benefits of these latest in-field controllers include checking and controlling site logistics, utilities, concrete levels post and during pours, and embeds and anchor bolt positions prior to the steel fabrication to eliminate costly on-site repairs. Mechanical, electrical and plumbing trade items can easily be checked with accurate positions documented pre-pour to ensure everything is where it should be within the wall cavities or chase areas before ceilings are fitted.
Utilising these latest hardware technologies on site means guaranteed dimensions to allow for pre-fabrication of bathroom or plant room assemblies, exterior panels and glazing systems. With safety of the building in mind, you can even monitor movement, of say, the temporary works, any shoring props, the adjacent buildings, or even the current building under construction.
Benefits for the general contractor
Modern construction layout tools, such as a robotic total station, are capable of great things on a construction site. Whether advancing your company’s adoption of BIM by using construction layout tools to extend the BIM workflow into the field, improving the quality control process, or increasing efficiency, there have already been many successes globally, supporting a strong business case for investment in this technology. General contractors can really benefit from the ability to reduce rework, utilise staff more efficiently and get a quick return on their investment. MEP contractors using this technology to site hangers, sleeves, anchors etc, before or after concrete pours, have the added security of documented layout data against the original building design or model.
With these construction layout tools, on-site crews not only have up to date coordinated models, but as-built setting-out points are easily documented and sent to the office, reducing one-sided conversations. Additional benefits include reduced risk and hence insurance rates, less rework, less RFIs, reduced general costs of being on site longer, a better quality product and better relationships.
Why does this matter to an owner?
We often hear from many owners and even designers that BIM and the new integrated construction technologies are for the general contractors to worry about. They believe that the contractor is the only one who benefits by producing a better quality project in a shorter amount of time and therefore it increases their profits. Some contractors will typically try to charge more for the increased coordination efforts as it can initially cost more for the additional management of this BIM process, while some owners believe they should not have to pay more for the same end product – a building.
However, what these owners do not realise is that the ones who benefit the most are in fact themselves, in many cases, the final operators of the building. Because soaring costs of managing construction projects and the facilities management that follows are the biggest challenges that owners, managers and occupiers face, boosting efficiencies in every phase of building design, construction and operation is critical.
With construction technology from suppliers like Trimble, this is now possible through accuracy and intelligence at every stage of the entire plan-design-build-operate lifecycle. Insurance companies are saying that a contractor’s utilisation of BIM is a better forecaster of risk. Shorter schedules mean that the property owner can expect occupancy sooner, and more accurate as-built information allows for more informed decision making on changes during construction or for future remodelling of the building.
Continuity of process
With the growing implementation of BIM in today’s design-build-operate lifecycle, as well as mobile project management of data, it is important that all stakeholders become more aware of maintaining the consistent flow of data between the office and the field (Fig. 7). With the continual flow of intelligent data, project teams can ensure that a consistent level of continuity of processes is maintained. This leads to a greater level of analysis and critical decision making to ensure that high-level project performance is maintained. With intelligent positioning, it’s now easier to ensure that the original design intent is maintained, but also that critical data is captured and shared during the project.
Whether we like it or not, BIM is the next evolution in technology that is already revolutionising the construction industry, and setting-out on site is one process that is instantly improved by BIM. General contractors and surveyors no longer need to rely on printed plans, tape measures and string lines to translate designs to the field. Instead, BIM software combined with latest BIM compliant hardware now brings the precision of 3D models from the office to the field, ensuring accuracy is not lost and significant time and money is saved, as proven on Trimble’s Westminster project.
Acknowledgements
Content within this paper is republished with thanks to, and with permission from Mark Sawyer, Bryan Williams and Ian Warner of Trimble’s GC/CM Division, Westminster, Colorado.
This paper was presented at Geomatics Indaba 2016 and is republished here with permission.
Contact Sean Dane, Optron, Tel 031 566-6221, sdane@optron.com
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