In connection with the design and construction of One World Trade Center, the newest addition to the New York City skyline in the wake of the tragic events of 9/11, city planners are currently carrying out construction on one of the most ambitious transportation center projects in the city’s history.
When completed, the World Trade Center Transportation Hub will connect city visitors to a variety of transit lines as well each tower of the World Trade Center.
The WTC Hub poses demanding surveying project
Particularly notable from a construction standpoint are the building’s unique exterior elements. The strikingly distinct wing-like design of the aboveground portion of The Hub, referred to as the “Oculus,” is comprised of massive steel spires set next to one another to form a unique skeletal pattern.
When completed, this structure will serve as the main concourse, allowing pedestrians to connect with several transit systems easily.
Unlike traditional building plans, the unique design of The Hub called for large, oddly shaped spires to be lifted and placed into position directly next to one another. As such, survey crews were required to make extremely precise measurements to ensure each element fit virtually perfectly within the arrangement. Specifically, this meant achieving an error range of 1 millimeter.
Reflective targets provided surveyors with a means of attaining this level of precision while also providing a way to easily install the targets onto the elements themselves.
Difficult drilling surfaces make reflective targets a viable alternative
Typically, a construction project like this one calls on survey teams to use a carefully adjusted system of prisms to correctly measure the placement of various construction elements to ensure a consistently precise alignment. Unfortunately for survey teams working on The Hub, this involved drilling into the super hardened steel beams being used on the project.
As we’ve outlined earlier, reflective target systems are able to go where traditional prism systems cannot. Target systems, unlike prisms, are light enough to allow the survey teams to use glue when securing them to construction elements rather than drilling directly into their surfaces.
Prisms on the other hand, require both a time and energy commitment on the part of survey and construction teams to drill and thread a hole suitable to screw in the connection unit holding the prism in place.
Finding the task too arduous and sometimes impossible, surveyors began using a combination of both flat and angled reflective target units to position construction elements using much less time and energy. The ability to forgo drilling completely meant surveyors could use reflective target devices on virtually any surface the project called for.
Project’s chief surveyor surprised with targets’ accuracy and ease
With prism systems posing too many issues to be a viable option, The Hub’s chief surveyor transitioned to a reflective marker system in hopes of finding a solution to the problems associated with the prisms’ shortcomings.
After seeing the capabilities of the reflective markers in terms of positioning and accuracy, surveyors were pleased to find the targets’ crosshairs such an easy and accurate way to align the targets relative to one another to achieve a degree of accuracy demanded by such a large significant construction project.
The World Trade Center Transportation Hub is just one example of the versatility and survey accuracy achievable with reflective targets when projects require measurement tools exceeding the capabilities of traditional prism systems. While prisms still provide surveyors with an extremely effective way to accomplish precise measurements, reflective targets can provide a less expensive and equally accurate method for getting exact results.
To learn more about Berntsen's variety of survey marking products, visit the Smart Targets, Datums & Reflectors product page or request a catalog.