Safety renovations for the Statue of Liberty.
When Keast & Hood, Structural Engineers were contacted one day in April 2009 and asked to be at the Statue of Liberty the following Monday, the authors had yet to learn what to expect. What followed was a four-year journey that would take them to nearly every interior corner of the iconic National Monument and UNESCO World Heritage Site. That journey, with a design team led by Mills + Schnoering Architects working under the auspices of the National Park Service, resulted in significant life-safety improvements to the Monument as described in the June 2014 Structure article Designing Life Safety Renovations for the Statue of Liberty.
That article focused on the recently completed interior renovations to improve life safety and egress from the Monument’s pedestal and surrounding 200-year-old fort. In this article, we delve deeper into the history and structural details of the Monument.
Fort Wood
Before the Statue of Liberty on Liberty Island, there was Fort Wood on Bedloe’s (alt. Bedloo’s) Island, named for Isaac Bedloo, a former burgher of New Amsterdam whom the English granted the land after they captured the area in 1664. After changing hands several times, the island was conveyed first to the City of New York, then to the State of New York and ultimately, in 1800, to the United States Government. In 1806, as part of a larger effort to improve the defenses of New York Harbor, construction of a “star fort of masonry having a stone magazine, with barracks of brick, and a brick arsenal” was begun. The work was completed in 1811 and, in 1814, renamed Fort Wood for Lieutenant Colonel Eleazer Derby Wood, an 1806 graduate of the US Military Academy who died in 1814 in the siege of Fort Erie, one of the last battles of the War of 1812.
Fort Wood was manned throughout the War of 1812, although it never came under attack. The fort was fortified, improved, and repaired continuously in the period between 1814 and 1884. The result of those improvements is the fort as we see it today from the outside: an imposing, monumental structure with a commanding presence as seen from the surrounding New York Harbor. That presence is due, in large part, to its steep scarp (the front of the rampart or outer fort wall) faced with massive units of ashlar-cut grey/blue granite rising 30 feet from the surrounding grade. The 3′-0 granite facing was added to the rubble masonry of the scarp of the Fort in 1844. The granite and rubble were bonded with concrete.
Through the mid-1800s, the Fort’s use evolved. It was used alternately as a Corps of Artillery garrison, ordinance depot, quartermaster depot, hospital, and recruiting station. That period was one of international peace, and, despite the continuous improvements, military activity at the Fort gradually diminished.
In 1877, President Grant signed a joint Congressional resolution that authorized the President to make suitable provisions to accommodate the impending gift of a Statue from France on either Bedloe’s or the adjacent Governors Island. At that point, the remaining four officers and 32 men promptly moved out of Fort Wood, and the Fort’s military history ended.
Genesis Of The Monument
As most Americans know, the Statue of Liberty was a gift from France. The concept of the gift evolved in the late 1860s amid a group of French intellectuals enamored with the United States Constitution, its guaranteed rights and liberties, and the fact that its principles and ideals had recently survived the test of the American Civil War. The original idea was for the Statue to be presented to the United States in 1876, the centenary of the Declaration of Independence. It was another decade until the Statue was completed and opened on Bedloe’s Island.
In the early 1870s, the Franco-American Union was established to arrange for the Statue’s funding, creation, and installation. The French Committee was responsible for the Statue itself, while the American Committee was responsible for the pedestal and its siting. By the end of 1877, the US Government had officially selected Bedloe’s Island for the Monument’s location. The American Committee decided to locate the Monument within Fort Wood so that the Fort would appear to form the pedestal’s base.
The Pedestal
In 1881 the American Committee selected French-trained American Architect Richard Morris Hunt to design the pedestal of the Statue while US Army General Charles P. Stone was already at work designing the foundations.
True to the Committee’s intentions, Hunt and Stone produced a three-part design:
Below Grade Foundation: Approximately 90 feet square and 15 feet thick foundation of poured concrete akin to a modern mat foundation. At the time of pedestal construction, the original parade ground inside of and below the terreplein was still there, and this portion of the foundation topped out at the parade ground level. The parade ground was later backfilled up to the terreplein level.
Above Grade Foundation: Formed, cast-in-place concrete in the shape of a truncated pyramid, tapering from approximately 70 feet square to 40 feet square at its top – 60 feet above the parade ground. This pedestal section was originally a solid concrete mass except for a 10′-0 × 10′-0 shaft at its center and an access tunnel on one side. The shaft was later enlarged on one side by demolishing concrete to make more interior space for an internal stair starting at the base.
Pedestal Proper: Approximately 38 feet square (outside dimension), granite-clad, cast-in-place concrete, rising approximately 85 feet from the top of the above-grade foundation to the base of the Statue. This pedestal section originally had an interior open shaft of approximately 25 feet square. Multiple sets of 50-inch-deep wrought iron girders traverse the pedestal proper. One set of girders at the top of the pedestal support the corner columns of the central pylon of the Statue. Another set, approximately 50 feet lower, is connected to the upper girders with wrought-iron eye bars and embedded in the pedestal walls. These lower girders resist uplift due to the overturning moment of the Statue under wind loading by engaging the weight of the pedestal. At various times, the pedestal girders have been referred to as “Eiffel Girders.” We expect that, at a minimum, Eiffel would have stipulated the forces to be resisted by the girders. Whether the girders were actually designed by Eiffel or an American engineer on the pedestal design team is unknown. It is known that the girders were fabricated by the Keystone Bridge Company in Pittsburgh, PA.
The Statue
French sculptor Frederic Auguste Bartholdi was well-known within the circle of intellectuals who first discussed the idea of the Statue of Liberty in the late 1860s. By 1870, Bartholdi was at work designing the statue of “Liberty Enlightening the World,” and by 1876, a team of French artisans and craftsmen began constructing the Statue in Bartholdi’s workshop in Paris.
For the design of the Statue’s structure, Bartholdi, in 1875, first consulted with the well-known French architect and engineer Eugène-Emmanuel Viollet-le-Duc. In that era, a metal-skinned statue would commonly have had an interior masonry structure. However, Viollet-le-Duc proposed a stability system of compartments filled with sand from the base to the hip and an iron armature above the hips.
When Viollet-le-Duc died in 1879, the engineering work was passed to the company of Gustav Eiffel, already known for his mastery of aerodynamics and light structural latticework in the design of a series of elegantly proportioned railway bridges in France. (It wasn’t until the World’s Fair of 1889 in Paris that he did the Eiffel Tower).
Eiffel veered away from Viollet-le-Duc’s sand-filled compartments and designed an all-iron structure. Four central angle-iron columns, each with unequal legs measuring 28 × 24 inches, extend from the Statue’s base to the shoulders’ height, leaning inward as they ascend. The columns are laced together with smaller iron angles and form a vertically-cantilevered box truss or pylon – similar to a modern high-voltage electrical transmission tower. The central pylon measures approximately 7 × 6 feet at its top and 16 × 13 feet at its base. From this central pylon, a series of orthogonal and diagonal struts and ties are cantilevered to support the flat, wrought-iron armature to which the exterior, 3/32” thick copper skin of the Statue was connected. The four main columns of the pylon land on the girders spanning the top of the pedestal.
The original design called for the bare concrete section of the foundation from the terreplein up to the third-level to be hidden beneath a planted berm traversed by monumental stairs to the third-level doorways on each side of the pedestal. For the first 20 years of the Monument’s life, the concrete foundation was exposed, and public access to the pedestal was via exterior wood stairs to doorways on the third level. The berm and one set of permanent stairs were not completed until
about 1907.
American Museum of Immigration (1960s)
In 1955, after decades of discussion about the lack of interpretive content at the Statue of Liberty and, separately, discussions about locating an immigration museum in Manhattan, the American Museum of Immigration, Inc. (AMI) was chartered by New York State at the base of the Statue of Liberty.
The design called for the museum to be located beneath the terreplein in the space between the tiered upper foundation of the pedestal and the exterior walls of Fort Wood. The parade ground of the original Fort had been filled in up to the level of the terreplein in 1907. This fill had to be removed to the level of the fort’s original parade ground in order to make way for the museum. Sadly, all remnants of the original fort structures within its walls were demolished and removed as well. The one surviving structure from the interior of the fort was the south sally port.
The AMI structure consists of cast-in-place concrete walls and pan joist floor systems with spread footing foundations. Expansion joints at the four corners of the pedestal divide the AMI into four structurally-independent sections, and some slab sections bear on the stepped pedestal foundation. Construction of the AMI began in 1961 and was completed in 1972.
Centennial Restoration (1980s)
In the early 1980s, plans formed within the US Government to restore the Statue of Liberty National Monument to celebrate the 1986 centennial of the Statue’s opening. The New York architectural firm of Swanke Hayden Connell (now defunct), in association with the firm of French-born, New York-based architect Thierry W. Despont, was engaged to lead a multi-discipline consultant team to design and document the planned repairs and improvements to both the Statue and its pedestal. Ammann & Whitney (subsequently part of the Louis Berger Group and now WSP) served as the structural engineer for the project and worked with the French engineering and industrial research firm Cetim and Lehigh University for materials testing, fatigue modeling, and other advanced material science analyses. Lehrer/McGovern (subsequently Lehrer McGovern Bovis and now Lend Lease) served as the construction manager.
Photo courtesy of Keast & Hood.
Generally speaking, the work included the following:
- Replacing the wrought-iron flat-bar armature to which the copper skin is connected. After extensive analysis and material testing, Type 316L stainless steel was selected to replace the wrought iron bars. Extensive galvanic corrosion had resulted in significant section loss in the bars, and the iron bolts at the splices in the bars had corroded and failed. Stainless steel bars were made to match the dimensions of the original iron bars, and then custom bent to match the shape of the bar it was replacing. In all, approximately 1,800 bars were replaced.
- Evaluation of and localized improvements to the main structure. This work included blast cleaning and zinc-rich and epoxy coating of both the central pylon and the secondary angle strut and tie system that connects the skin’s armature to the central pylon. Also included in this work was strengthening the connection of the structure for the right arm to the central pylon. When the Statue was first assembled in Paris and presented to the United States ambassador to France on July 4, 1884, the arm’s position was altered, resulting in a deviation from Eiffel’s design. Some reinforcing of this joint was completed in the 1930s when the Statue was still under the control of the U.S. War Department. However, in the 1980s, the engineering team determined that additional improvements to the arm-to-pylon linkage were needed.
- In addition to reconnecting the copper skin to the new, stainless steel armature bars, cleaning and numerous repairs to both the interior and exterior of the copper skin, including the replacement of the spikes of the crown, were completed.
- Replacement of the stairs and elevator within the pedestal; repairs and modifications to the double-helix stair within the Statue.
- By the 1980s, the original torch was in poor condition. The windows of the flame enabled the electric lights within to make the flame glow at night and were not watertight. As a result, both the copper skin and the iron armature of the entire torch assembly were severely damaged. The restoration team decided they had no choice but to replace the torch. In lieu of the cladding perforated with windows enabling lights to shine from within, which was not part of the original design but, rather, a modification made in the U.S. in the days before the Statue’s 1886 opening, the team decided to replace the torch entirely and follow the original design. The original torch was removed, and a new torch was fabricated on-site at the base of the Monument. The work was completed by a team of French artisans using the same process of hammering copper sheets into wooden molds, known as repousse, that was used by Bartholdi’s team in the initial fabrication of the Statue. The flame was then covered in gold leaf and lit externally to enable it to shine at night.
Life Safety Improvements 2009–2013
In the aftermath of the attacks on the World Trade Center and the Pentagon on September 11, 2001, access to the Statue of Liberty National Monument was significantly curtailed. After several studies on visitor safety, a series of short-term improvements allowed the pedestal to reopen to the 6th level promenade in August of 2004, but the Statue remained closed. In the spring of 2009, the Park Service engaged Mills and Schnoering Architects, Keast & Hood Structural Engineers, and Kalimex Construction to design and install code-compliant modifications to the handrails on the 118 feet tall double-helix stairs within the Statue in 67 days, enabling its reopening in July of 2009.
Six months later, Park Service representatives and a much larger team of design professionals, still led by Mills + Schnoering Architects, embarked on a larger project to improve accessibility and safety at the Monument. At that time, the majority of the pedestal’s interior was essentially one large, open volume 25 feet × 25 feet × 85 feet high with stairs attached to the walls as they wound their way up. In the pedestal foundation was a narrowed opening 17 feet × 17 feet. Studies had concluded that, in the event of an incendiary incident near the base of the pedestal, that volume could act like a chimney, drawing smoke up through it and making egress challenging for visitors near the top. The primary challenge to the design team: find a way to insert two separate, fire rated, pressurized stairs and an elevator into this volume while avoiding the large, Statue hold-down girders and the narrowed shaft opening in the foundation, fondly described as the “pinch point” during the project.
The complex, three-dimensional puzzle was solved by using Building Information Modeling (BIM) at a time when the technology was still in its early adoption period. By working in three dimensions, the design team achieved a high level of coordination and clash prevention in what was an unusually complex three-dimensional space. Relying on that modern-day advantage just increased our awe for the team that envisioned, designed, and built the Monument 125 years earlier – long before such modern “necessities”, like the computer, were even imagined.
A Monument for all Generations
In the words of the United Nations Educational, Scientific and Cultural Organization (UNESCO), whose mission includes the promotion of international cooperation in education, sciences, culture, and communication, the Statue of Liberty is one of the greatest technical achievements of the 19th century. Further, it is recognized as a bridge between art and engineering. It endures as a highly potent symbol – inspiring contemplation, debate, and protest – of ideals such as liberty, peace, human rights, abolition of slavery, democracy, and opportunity.
The value of this international treasure can and will be its enduring ability to motivate humankind to subscribe to its core principles of freedom, mutual respect, peace, and justice. On an entirely different plane, it can and should serve as both example of and motivation for overcoming obstacles in the pursuit of engineering achievement.■
Reference
Summary Structural History of Fort Wood, Thomas M. Pitkin (1956)
Acknowledgements
In developing this article, the authors drew extensively on the following documents:
Fort Wood Historic Structure Report, Statue of Liberty National Monument, John G. Waite Associates, Architects for the National Park Service, 2009
Liberty Enlightening the World, The Statue of Liberty National Monument, John G. Waite Associates, Architects for the National Park Service, 2011