1st Place, Exterior
The Helmsley Building at 230 Park Avenue has been described by the New York City Landmarks Preservation Commission as “one of the most recognizable and most admired skyscrapers in New York.” It recently underwent a comprehensive façade restoration program, which included restoring the iconic 3-story columns at the 29th floor and 7-foot-tall terra-cotta bison heads.
Thornton Tomasetti’s Renewal team provided historic preservation and structural renewal services to RXR Realty, the building’s owner, for the project.
“RXR Realty’s portfolio includes many of New York City’s most iconic buildings and we are committed to preserving and revitalizing them,” says RXR Realty Senior Property Manager Gregory S. Brown. “Having been involved with many façade repair projects over the course of my long career in property management, I was both personally and professionally impressed with Thornton Tomasetti’s performance on such a large-scale exterior repair. The intricate and ornate nature of the architecture of 230 Park Avenue made it a very challenging task, but the team rose to meet that challenge very successfully.”
PHOTOS: ALEXANDER SEVERIN PHOTOGRAPHY; BEFORE PHOTOS: Thornton Tomasetti
DISTINCTIVE TERRA COTTA
Completed in 1929, the 1.4 million-square-foot Manhattan tower was the last major work of architects Warren and Wetmore in New York City. It is the skyscraping counterpart to Grand Central Terminal; it was designed by the same architects, for the same client and of the same materials. The 34-story building consists of a low-rise base and a slender tower capped by a pyramidal roof and cupola. It also features ornamentation by American sculptor Edward McCartan, such as its famed Park Avenue clock.
Distinct terra-cotta elements define the façade, including the 32 freestanding, Corinthian columns. At each column, there is a terra-cotta bracket at the 28th floor and a top bracket at the 32nd floor. The 16th-story cornice is populated by a herd of 74 7-foot-tall terra-cotta bison heads, symbolizing the westward extension of the railroad, along with additional iconographic ornamentation representing research, discovery and engineering progress.
The terra-cotta bison heads had cracked due to embedded steel corrosion expansion. Because of their size and intricate elements, it was not feasible to replace the heads, but the design team determined it could remove them intact and have them properly repaired. While not quite brain surgery, the repairs required removing the craniums of 36 of the bison figures, welding steel plates where needed, adding waterproofing, and resetting and repairing the original terra cotta.
A preconstruction survey found large-scale systemic cracking in the terra-cotta brackets that sit directly below the columns at the 28th floor and project 6 feet from the building’s façade. Thornton Tomasetti used nondestructive evaluation techniques, including impact echo, ultrasonic pulse velocity and infrared scanning, to better understand the cause of the cracking. It then developed a finite element model, with data inputs from the preconstruction survey, to analyze the behavior of the cracks. The model revealed a high stress concentration that closely matched the observed diagonal cracking.
The team was then able to implement appropriate, cost-effective repairs, including specially designed 6-foot-long stabilization anchors that relieved the stress concentration, which enabled the preservation of most of the historic terra cotta. Lost sections of terra cotta were recast directly on the building. This solution addressed the underlying cause of deterioration while significantly reducing the project schedule and overall cost.
The project team discovered heavy corrosion of the structural-steel lattice columns within the colossal terra-cotta enclosures and potentially throughout the structure, which was damaging the masonry cladding.
Because the columns were on the north elevation, directly above two major roadways, the project team decided to remove the bottom third of the terra cotta at these columns to access the steel for repairs. Repairs included welding plates in localized areas at the flanges and web of the built-up lattice steel column and at the lacing itself. A high- performance epoxy paint system was then installed on the steel, waterproofing added and augmented moisture management designed to weep the masonry of the column.
To address the steel corrosion, the team installed an impressed current cathodic protection (ICCP) system to arrest the corrosion. The cloud-based ICCP system imparts current into the steel to counteract the electrochemical process of corrosion and transmits monitoring data to the design team. This solution provided significant long-term cost savings over extensive masonry removal and replacement to access the steel.
A FOUNDATION IN BUILDING SCIENCE
Where the team was unable to salvage or repair the terra cotta, such as where the masonry cladding had been demolished to access the underlying steel at the columns, new terra cotta was produced. RXR Realty contracted to purchase new terra cotta early on in the design phase to accommodate the long lead time of the material. The intent was to get into the manufacturing queue as soon as possible, so when the restoration contractor was fully rigged, the new terra cotta would be arriving onsite.
Boston Valley Terra Cotta utilized laser scanning to fast-track the shop-drawing phase and a new hydraulic ram-pressing system, instead of the traditional hand-packing method, to accelerate the fabrication schedule. The faster extrusion process was not possible because of the classical column entasis. The color matching took several rounds of glazing samples to replicate the existing buff terra cotta, which was critical to blend into the remaining two-thirds of the column. This early planning helped to eliminate potential bottlenecks in the schedule and facilitated an early approval of the new terra cotta by the New York City Landmarks Preservation Commission.
Other major work included restoring the crowning cupola at the top of the pyramidal roof, as well as the Park Avenue arch portals. These two City Beautiful Movement features enhance the long vista down Park Avenue that carries vehicular traffic through the base of the building.
The project plan allowed for a significant number of structural-steel repairs without adversely impacting the aesthetic character of the historic masonry. This also provided comprehensive solutions to prevent future steel deterioration.
Systematic terra-cotta repairs included patching, pinning and coatings, as well as reinstallation. The team produced new terra cotta for portions of the colossal columns where the original material could not be preserved. Considerable effort was made to ensure that the new terra cotta matched the original shape, texture, color and glazing sheen.
This project, which was completed in December 2020 and met RXR Realty’s sustainability and preservation goals, sets a precedent for repairing terra cotta and embedded steel in terra cotta with a solid foundation in building science. In an era when it is more common to demolish historic terra cotta due to uncertain repair safety, the project demonstrates that preserving historic fabric is more economical than large-scale replacement.
METAMORPHOSIS AWARD WINNER and ARCHITECT AND ENGINEER: Thornton Tomasetti
PROJECT CLIENT/BUILDING OWNER: RXR Realty
GENERAL CONTRACTOR: Benjamin Maintenance
CATHODIC PROTECTION ENGINEER, MONITORING AND MANAGEMENT: C-Probe
HISTORIC PRESERVATION LIAISON: Higgins Quasebarth & Partners LLC
ROPE ACCESS RIGGER AND CONTRACTOR: STRUCTURAL
NEW TERRA COTTA: Boston Valley Terra Cotta
IMPRESSED CURRENT CATHODIC PROTECTION SYSTEM: C-Probe
TERRA-COTTA, LIMESTONE AND GRANITE PATCHING MORTARS: Edison Coatings
EPOXY PAINT: Tnemec
GROUT-SOCK ANCHOR: Cintec
COPPER FLASHING: Hohmann & Barnard Inc.
RUBBERIZED ASPHALT WATERPROOFING: GCP Applied Technologies