Photo courtesy of Deb Nystrom (CC)
Earlier this month, the newly constructed World Trade Center Transportation Hub in lower Manhattan partially opened to the public with plans to be fully operational later this year.
Since its initial design plans were unveiled over ten years ago, the Hub’s grand concourse––commonly called “The Oculus,” has drawn the attention of the surveying community for the unique challenges posed by its twisting, rib cage-like design.
We first discussed the Hub’s demanding surveying needs while construction was still in progress in 2013. Two years later, we’re revisiting how surveyors were able to overcome these challenges and what tools might prove useful for completing similarly unusual or difficult projects in the future.
The “smart” angle survey target
As explained in our original article, the Hub is designed to connect New York City’s transit system beneath ground while providing street-level access above ground.
This above ground component is a massive circular structure comprised of steel spires set next to each other in series.
The close-knit arrangement of these spires demanded incredible precision to ensure proper alignment––oftentimes allowing error ranges of just one millimeter.
Add to this the impenetrable steel surface of the spires themselves, and the problem facing surveyors was clear.
Engineers looked to innovative reflective and construction survey targets for a solution. Rothbucher Systeme’s smart angle survey targets––high visibility, 90º angled control monuments––offered a way to achieve extreme precision and high visibility in specialized measurement conditions without drilling into hardened steel.
Rothbucher Systeme’s reflective angle targets (the RS80 and RS90) feature a unique “roof,” protecting the reflective tape when pushing the target into new concrete and shotcrete.
Construction angle targets (the RS100), which are used as an accurate, highly visible benchmark, were used extensively throughout the Hub’s construction. All three target types are easy to attach, and the temperature and UV resistant marker bodies stay in place permanently, saving time and effort every time a horizontal or vertical reference point is needed.
These light, robust survey targets proved so useful, the project’s chief surveyor transitioned from prisms to reflective markers to avoid drilling altogether.
Other uses for smart angle survey targets
While the Hub offers a high-profile example of smart reflective survey targets in use on-site, the value of highly accurate, lightweight survey targets can be realized in typical surveying projects too, including:
Bridge and tunnel construction
RS90 being used in Rotterdam Metro
Setups that are impossible to sight with typical reference points
RS90 being used in hard-to-sight location
Facades & Corners
RS80 being used as a corner solution
Other typical uses include backsights, check shots elevation references and monitoring situations where precision is needed without significant setup delays. Rothbucher Systeme’s Reflective and Construction Angle Targets are perfect for placing permanent measurement points for additions and conversions, alignment of machines, production lines and material handling technology.
Learn more about Berntsen's survey marking products by visiting the Smart Targets, Datums & Reflectors product page or request a catalog.