Fort Jefferson

Fort Jefferson, located in the remote Dry Tortugas National Park seventy miles from Key West, is one of the largest brick masonry structures in the western hemisphere. The mid-1800s masonry and coral concrete structure was constructed over a period of 30 years and exemplifies the military architecture and civil engineering of its era, when the United States was building dozens of forts under a coastal defense strategy known as the Third System. The National Park Service (NPS) began managing Fort Jefferson in 1935.

Over the subsequent decades, the fort’s saltwater environment resulted in corrosion and expansion of the embedded iron shutters at the small wall openings used to fire canons. The movement of the iron in turn caused significant damage along the scarp wall; major sections of brick and mortar fell into the surrounding moat.

Responding to a perceived need for emergency stabilization, Silman conducted a program of archival research, testing, analyses, and monitoring to assess the structural behavior of the fort. As part of this work, Silman developed a comprehensive model of the casemates along Front 3 from archival documents and targeted field measurement. The model was used to define the loads imposed on the deteriorated structure and was critical to guiding the analyses and communicating repair solutions.

Silman determined that emergency stabilization of the brick scarp wall was not necessary, allowing efforts to be directed towards targeted permanent repairs. This assessment also provided a framework for understanding and preserving other Third System fortifications.

The most recent phase of work on the fort, completed in 2013, entailed removal and rebuilding of critical areas of the scarp wall, including replacing the corroded shutters with non-ferrous material.

Silman is also working on the design of repairs for the Tortuga Harbor Light, an iconic hexagonal cast-and-wrought-iron lighthouse, built in 1876.