Building the Fulton Center Sky Reflector-Net

The construction of a large tensile structure provides an extremely interesting opportunity for close collaboration between designer, fabricator, and installer. The very hands-on process is filled with discovery, as thousands of individual components come together to reveal the true behavior of an installation of this scale.

The net was fabricated in a small rural town in northern Massachusetts by TriPyramid Structures, creator of novel hardware systems for numerous architectural achievements, including the Louvre Pyramid and Apple retail stores worldwide.

It was then assembled offsite in a leased warehouse near TriPyramid’s headquarters. Cable pairs were stitched together at each net node with a connector assembly consisting of 11 hardware components.

The net’s hyperbolic form meant that each panel had to be fabricated to a unique shape and installed in precisely the right place. To facilitate this, each horizontal connector arm was etched with a location reference. The panels were stamped with corresponding references and matched up by installers on the site.

Once put together, the net was raised by crane outside the factory to validate the assembly and resulting form.

It was then packaged for transport to Lower Manhattan, then lifted into place onsite (installation was performed by Enclos).Temporary attachment of the net to the oculus was made with yellow straps that were later replaced with stainless steel tension rods.

Onsite work was performed using a series of boom lifts and a swing stage platform suspended from the oculus. The tie-back rods were installed individually by workers.

Below, workers on the swing stage carry out assembly work at the bottom of the net. The swing stage was used for much of the work, including periodic inspections, tightening, and adjustments by the installer.

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The team used boom lifts to reach the upper regions of the net. The highest portions are nearly 100 feet above street level; the boom lifts were supported by a temporary platform built over the large central opening that allows daylight to pass into the sublevels of the complex. Below, a worker in a boom lift inspects the net following installation of the stainless steel rods that connect it to the oculus.

Because the installation was carried out in a building still under construction, work performed by scores of contractors was carefully coordinated and efforts made to protect the net from the harsh construction site environment. Below, a worker grinds down temporary attachment points from the second floor catwalk.

The final shape of this type of structure relies heavily on the forces imposed by the installer during tensioning and the boundary conditions at the attachment points. The integration of prefabricated infill panels made it critical to achieve the correct final shape — otherwise, the panels wouldn’t fit. The team employed new surveying technologies to capture and analyze the as-built shape of the net during construction.

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Once tensioned, the net was ready to receive the reflective panels. The sequencing of panel installation was heavily influenced by the delicate choreography of up to three boom lifts simultaneously moving within the interior space.

Below, workers installing panels from the swing stage and a nearby boom lift.

Each panel was connected to the stainless steel arms protruding from the four adjacent nodes at the panel corners. Panel attachment was done by hand, from the inside of the net.

Below, a view from the fourth floor mechanical space. The intense reflectivity of the panels as viewed from below is juxtaposed against their alluring transparency when viewed from behind.

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The atmosphere of collaboration pervaded the fabrication and installation processes, with the designer working closely with the contractor to examine the behavior of the installation as it took shape. Technical challenges were solved onsite through discussion and direct interaction with the tensile system.

With panel installation complete, the project team undertook a weeklong assessment of the installation to validate the as-built geometry and ensure proper fit between the panels and the net.

A downward shot shows the temporary floor used to support the boom lifts.

The final product. Installation of the net took the contractor just over three weeks.

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* Sky Reflector-Net (2013), an integrated artwork, is an artist, architect, and engineer collaboration with James Carpenter Design Associates, Grimshaw Architects, and Arup, commissioned by MTA Arts for Transit and Urban Design and the MTA Capital Construction Company.

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