The system combines upper and lower cables with varying tensions that are jacked apart and connected by rigid vertical struts.

First developed for the Utica Memorial Auditorium, which was completed in 1960, Lev Zetlin's bicycle wheel system has helped to shape the design of other tensile structures, among them the New York State Pavilion, Madison Square Garden, the Seoul Olympic Gymnastics Arena, Tropicana Field, and the Georgia Dome.

In the early 1990s, the FLEX code was diversified into a family: NLFlex (blast), EMFlex (electromagnetic waves), and PZFlex (sonar and ultrasound).

Thornton Tomasetti staff were the first engineers on the site on September 11,[citation needed] and started work that afternoon.

The firm assisted in rescue, demolition and clean-up, advising on structural issues that required resolution as part of the recovery effort.

Working with engineer of record Evergreen Consulting, Thornton Tomasetti established an efficient steel-based dual structural system and solved wind behavior problems with distinctive double stair-step corners.

In response, the firm conducted damage assessment in three states related to structural and architectural integrity, HVAC, electrical, plumbing and fire protection equipment and systems.

Weidlinger Associates was a U.S.-based structural engineering firm that designed and rehabilitated buildings, bridges, and infrastructure and provided special services in applied science, forensics, and physical security.