This presentation is part of the 2017 3D Digital Documentation Summit.
Combining hands-on inspection, nondestructive evaluation, and drone-based data acquisition in the investigation of the Soldiers’ and Sailors’ Memorial Monument
Recent investigative work at the Soldiers’ and Sailors’ Memorial Monument leveraged a variety of digital documentation technologies, including direct-to-digital conditions documentation, nondestructive evaluation, and data acquisition by drone in order to allow the project team to fully understand existing conditions and failure mechanisms. Challenges included limited means of access for personnel, in-complete as-built drawings, and data acquisition and management for a structure in need of extensive evaluation to determine the extent of restoration. Additionally, the project team worked to limit the impacts of “downtime” for a public monument in a busy city park.
The Soldiers’ and Sailors’ Memorial Monument is located within Manhattan’s Riverside Park. It was dedicated on Memorial Day, 1902, as a monument to Union Army soldiers and sailors who served in the Civil War. Architects Charles and Arthur Stoughton won the design competition for the monument, with an entry based on the Choragic Monument of Lysicrates in Athens, Greece. Rising 96 feet above the surrounding plaza, the monument consists of a tall cylindrical base, a rusticated drum ringed by Corinthian columns, an ornamental entablature, and a low conical roof. The exterior is clad in white marble with a granite water table. The marble-clad interior space features a tiled dome with an oculus opening to a second dome, both constructed by the Guastavino Fireproof Construction Company.
The last major repairs to the monument were undertaken in 1962. The exterior masonry is currently in poor to fair condition, with widespread spalling and cracking of the masonry, mortar loss, failed Dutchman repairs, and failures of the sheet metal roof and flashings.
Working with the New York City Department of Parks and Recreation and architect Perkins Eastman, Leslie E. Robertson Associates (LERA) retained Vertical Access LLC (VA) and GB Geotechnics (GBG) to inspect the exterior of the monument. VA performed a hands-on and close-visual inspection using industrial rope access, documenting conditions using TPAS, the Tablet PC Annotation System, linking photographic documentation and quantitative data within a single AutoCAD drawing. VA assisted GBG with lift access in order to acquire infrared imagery of the monument exterior, and VA provided rigging and guiding for GBG rope access technicians performing ground penetrating radar and ultrasonic pulse velocity testing of the drum.
Vertical Access was also asked to perform a visual and infrared investigation of the monument interior using its Unmanned Aerial Vehicle (UAV, or drone). There is currently no means in place for personnel to access the interior space between the two domes. In order to avoid the erection of pipe scaffolding at the interior, which would be better suited for a full restoration program in the future, VA’s solution was to fly a lightweight quadcopter through the 5’-diameter oculus in the lower dome, providing video and infrared footage of the interior finishes. VA used a DJI Phantom 4 quadcopter mounted with a GoPro Hero 3+ (?) for video capture and a FLIR Vue Pro thermal camera designed for UAV applications. Conditions observed during the drone investigation were recorded in AutoCAD using TPAS. A live-feed video downlink allowed multiple project team members to observe the conditions in real time and to direct the drone pilot to areas of interest. The project team was also able to schedule the drone investigation immediately following several days of rain for the best opportunity to see thermal differences in the materials due to water infiltration.
The data gathered at the exterior and interior of the monument is being used by LERA for a full restoration condition assessment with scoping recommendations to determine a comprehensive cost estimate that facilitates New York City’s Department of Parks and Recreation fund raising for the eventual restoration of the Memorial. In addition, LERA utilized the data obtained to develop a 3D geometry model of the Monument using Rhinoceros to assist with quantity determination and structural analysis. The Rhino model geometry was manipulated with scripting within the Grasshopper platform to create an accurate finite element analytical model for further verification of the Monument’s performance under deteriorated conditions. The team is currently investigating the use of virtual reality to explore better communication of actual conditions and proposed remediation of improved access to the Memorial as well as improving future restoration investigative and descriptive tools with the use of 3D drone video capabilities.
Douglas P. González is an Associate Partner at LERA. With over 25 years of experience as a Structural Engineer, Doug has developed the design of new structures and renovations for a wide array of healthcare, government and cultural projects. In addition to his expertise in healthcare, cultural and civic facilities, as well as adaptive reuse and historic preservation, he serves as President of the Structural Engineers Association of New York (SEAoNY), having previously served as Secretary and Director. Doug holds a Master of Science from Cornell University and a Bachelor of Engineering from The Cooper Union in New York City.
Kristen Olson is an architectural historian with Vertical Access and a SPRAT-certified Level II industrial rope access lead technician. Kristen has worked on investigation and documentation projects including McKim Mead and White’s Manhattan Municipal Building, the Chapel at the United States Naval Academy and the historic campus of Harvard Medical School. She is actively involved in the continued development of the TPAS direct-to-digital documentation system and the production of drawings from video captured using unmanned aerial systems. Kristen has a Bachelor of Arts degree in Art from Colby College and a Master of Arts in Historic Preservation from Cornell University.