One WTC Cable Net Walls

Each of the four cable net walls on the facade of New York City’s One WTC (World Trade Center) stands at over sixty feet tall, providing a grand entrance to the tallest building in North America. The challenge was to develop a sixty-foot tall glass structure for each wall that appeared to be floating, all while providing maximum blast security. This proved to be no small feat to achieve, but our team excelled with the innovate use of high strength stainless steel.

In the end, the sixty-foot tall glass walls are supported on all sides by two- inch thick stainless-steel jamb plates up to six feet wide. A two-way grid of pre-tensioned cables supported by the perimeter jamb plates support spider fittings which in turn support the laminated panes of tempered glass. The perimeter jamb plates resemble a “picture frame” around the cable net, providing an architecturally exposed structure for the cables and glass.

Facade Engineering Design

The architectural constraints, coupled with the large blast pressures, required a dynamic multiple degree of freedom (MDOF) analysis. McLaren used ETABS to perform a 3-dimensional dynamic analysis of the jamb and canopy structure using time-history functions to account for the dynamic effect of the blast loading.

The exposed structure required tolerances of less than one quarter that is typically allowed for steel construction. Coupled with the fact that nearly all connections must be hidden, constructability became a key part in our design. The tolerances were so strict, that the connections of the members had to be designed to account for temperature differences between the indoor temperature at the shop and the outdoor temperature at the site.

Most structures of this complexity and level of tolerance are prototyped, tested and revised accordingly, sometimes involving several iterations. With the scheduled completion date of the building quickly approaching, there was no choice but to get it right the first time, leaving no margin for error. From the spider fittings made in Germany, to the high strength stainless steel bolts, nearly every piece of the structure was a custom designed and fabricated piece. McLaren’s attention to detail and experience with large scale, fast track, architectural structures provided a constructible design true to their original intent.