Reaching new heights in creating a more resilient, safer, and sustainable urban landscape
by Henry Prenger, Lafarge North America
Photo courtesy of The Durst Organization
Resisting time and natural disasters and reducing environmental impacts are major challenges for cities. Over the next decade, cities will change substantially, as a significant share of our population and economic activity will be concentrated along urban coastal areas prone to natural disasters.
New York City has always faced climate risks, including nor’easters, coastal storms, hurricanes, tornadoes, and storm surges. The tropical storm force winds of Hurricane Irene in 2011 resulted in at least ten fatalities and produced heavy damage over much of the city, and Superstorm Sandy took the lives of 53 residents, destroyed thousands of buildings, and caused $19 billion in damages and lost economic activity. Tornadoes also have been whipping the city more frequently since 2007. These weather events affect every New Yorker, and as our climate changes, they will become more frequent and severe. Following the devastation caused by Hurricane Sandy, New York released a $20 billion plan to invest in resilience measures and improved building codes to protect the city’s infrastructure.
Rising a symbolic 1,776 feet above the iconic skyline of Manhattan and standing as the tallest skyscraper in the Western Hemisphere, One World Trade Center is setting a new standard for more resilient, safer, and more sustainable urban landscapes. Monumental in scale, this landmark 104-story tower features 3,500,000 square feet of space that will accommodate activities vital to the nation’s economy.
Taking advantage of innovative construction materials, SOM Architects designed One World Trade Center to be the safest and most environmentally friendly commercial building in the world. The structure includes a massive cast-in-place, reinforced concrete inner core that runs the full height of the tower—an extra-strong backbone that provides support for gravitational loads as well as resistance to wind and seismic forces. The concrete core walls measure three feet thick or more above ground and up to twice that below grade. Higher up, the concrete core walls slim down to two feet thick.
The 200,000 cubic yards of concrete used in the tower’s superstructure—with a strength that has never been used on such a scale in building construction—was custom-designed to ensure high levels of durability, constructability, and sustainability. Supporting columns on the first 40 floors were made from 12,000- to 14,000-psi self-consolidating concrete and the upper floors with 8,600–10,000-psi mix designs. To meet the compressive strength requirements, the design and engineering team relied on a highly specialized concrete mix that included Lafarge Portland I/II and NewCem® slag cements, as well as other supplementary cementitious materials. Engineered for high strength and long-term durability, NewCem slag cement helps achieve greater strength potential and helps control shrinkage, creep, and cracking in mass concrete structures.
High-strength concrete was the ideal material for meeting the high-priority safety requirements for One World Trade Center because key supporting members—such as elevator and stair enclosures—often relied upon to resist wind, seismic and other impact forces, are designed with an extra measure of durability and resilience. The concrete also made a strong contribution to the building’s LEED® Gold rating. Besides being virtually fireproof, concrete is produced locally and creates excellent thermal and sound barriers. NewCem slag cement also contributed to the tower’s sustainable design, as it saves virgin raw materials, consumes less energy and uses a recyclable by-product of the steel-making process that might otherwise be disposed of in landfills.