One World Trade Center and HISTAR® steel: slender, safe, and sustainable

Detailed information

One World Trade Center was built on ground zero, the site of the former Twin Towers in Lower Manhattan, and stands at a symbolic 1776 feet (542m) tall including the spire. With its 104 storeys and its slender, tapering triangular form, it shimmers in the light and acknowledges the adjacent memorial as a symbol of renewal and hope.

From a 200-foot (61m) concrete base, the tower ascends sixty-nine storeys. Its edges are chamfered back to form eight isosceles triangles, resulting in a perfect octagon at its centre. It culminates in a square, glass parapet at the crown. The light refracts in its crystalline form like a kaleidoscope, creating a vibrant effect that changes throughout the day.

With a total usable floor area of more than 3 500 000 square feet (325 000 m2), the new tower is composed of offices, a grand public lobby, an observation deck, parking, and broadcast and antennae facilities above grade. The below-grade concourses include approximately 55 000 square feet (5100 m2) of retail space and connect to an extensive transportation network.

Designed by renowned architect David Childs, of Skidmore, Owings and Merrill, LLP, One World Trade Center sets a new level of social responsibility in urban design by incorporating new architectural and environmental standards.

Safe and sustainable

Sustainable design is central to One WTC's development, integrating renewable energy, interior day lighting, reuse of rainwater, and recycled construction debris and materials.

One WTC incorporates advanced life-safety systems that exceed New York City building code requirements. From structural redundancy to dense fireproofing to biochemical filters, it creates a new standard for high-rise buildings. Extra-wide pressurised stairs, multiple backups on emergency lighting, and concrete protection for all sprinklers to ensure optimal firefighter access. Exits are designed to ensure easy evacuation, and all safety systems are encased in the core wall with the enhanced lifts.

Structural design

The tower's structure is designed around a strong, redundant steel frame made of beams and columns. The reinforced concrete core wall system at the centre of the tower acts as the main spine and provides support for gravitational loads as well as resistance to wind and seismic forces.

Together with the robust concrete core, the redundant steel frame lends substantial rigidity and redundancy to the overall building structure while providing column-free interior spans for maximum flexibility. The ductile perimeter moment frame twines around all vertical and sloped perimeters, forming a tube system.

ArcelorMittal steel

ArcelorMittal supplied both structural steel sections and plates for the tower's steel frame. The project features more than 12 500 tonnes of structural shapes, including jumbo columns for the perimeter of the tower's base, which were produced by the company’s mill in Differdange, Luxembourg and sold to the project through efforts led by ArcelorMittal International North America.

These beams and columns, mostly of the W14x16 family, are mainly made of HISTAR® (ASTM A913/913M), an innovative structural steel grade that combines a low alloy content with high strength, good toughness, and superior weldability. These characteristics are achieved by a quenching-and-self-tempering (QST) process at the end of the rolling line, which considerably improves the mechanical and physical properties of the steel shapes.

For steel shapes with flange thickness up to and exceeding 4.9 inches (125 mm), the QST process can help achieve yield strengths up to 40% higher than other steels used in comparable applications. Furthermore, the QST process enables great toughness characteristics even at low temperatures and excellent weldability as many sections do not require preheat before welding, thus simplifying fabrication and construction.

ArcelorMittal Coatesville, US provided 10 000 tn of steel plates that were used for the fabrication of girders supporting the building's foundation, floor support girders, and the construction of the antenna. The plates were also used in the foundation of the underground system beneath the building.