The Future of Layout, Part 1
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.
How things are currently done
Traditionally, layout of AEC services has always been completed by a team armed with the building drawings, a tape measure and sometimes a piece of string! Height or elevation is measured with a level, and a theodolite is used to measure angles. This team works from a reference point of known location and elevation to plot where certain building services need to be placed. Obvious examples are HVAC, pipework and cable trays. Unfortunately, this system doesn’t work particularly well with complex buildings, buildings with curved walls, buildings with prefabricated materials, or coordinated models. Which doesn’t leave much else! ‘Errors and omissions are so common that special contingencies are allocated for construction budgets and separate insurance policies are required to address the repercussions from these mistakes’1. However, many contractors still love a tape measure and string, despite all the additional work and risk involved.
Why is this a problem?
Inaccuracy is probably the most fundamental problem with this traditional approach. It requires multiple people doing repetitive manual work, largely by eye, and in reference to a drawing in a different scale. The margin for error is huge and can be seen in every action: » Ensuring the reference point is right » Making sure the tape measure doesn’t move » Making sure the string doesn’t move on arcs » Ensuring the theodolite is level » Making sure the degree in which you’re measuring is exact However, there are potentially serious consequences to every small mistake, some of which may even affect the profitability of the job. When working from a design or 3D model, especially one that includes precise measurements used in the prefabrication of components, missing an angle, or layout position, by only a narrow margin could mean that systems will not fit when the time comes to install them in the field. Similarly, incorrect layout could result in clashes with other building elements or services. This could be problematic for project scheduling, as well as profitability. Remedial work involves large volumes of wasted materials, labor and time (and therefore money).
It’s also inefficient:
Site layout using manual methods takes a very long time. The people doing it often know about the consequences of inaccuracies, so they will use extra time to ensure they don’t make any errors. This can cause delays to the install of other services, as well as generating extra labor costs from the prolonged activity of the layout team. When changes need to be made, methods of recording the reason for a change (obstruction etc.) and evidence (photographs etc.) are added to any design drawings they are working from. These reasons are sometimes reported to the design team to amend the drawings or model; at other times, these records are filed separately for the purposes of managing construction liability. As a result, it takes a long time for this information to be reflected in the designs, if at all, which means other contractors won’t see the changes until its’ too late.