We’re currently working on a team that is creating a Historic Structures Report for Castle Clinton. Our concern, obviously, is the structure of the old fort. But for us, part of analyzing the current structural conditions is looking at the load history of the building. It’s current state is roughly similar to how it was during its brief life as an actual fort: it’s a ring wall, open at the top. In its later incarnations in the 1800s as Castle Garden, first as a theater and then as the New York immigration station it had a low, vaguely dome-like roof supported on the exterior wall and some rather spindly interior columns. Later still, as the New York Aquarium, it had upper stories added above the original entrance-side wall and a new truss roof, again supported on the outer walls and interior columns. The main circular roof as Castle Garden and as the Aquarium were at least partly the same structure and at least partly altered.
What does this mean in terms of load and current analysis? The load on the original walls and foundations increased gradually for the first 140 years of the building’s existence, and then dropped back down to approximately the starting level. It is entirely possible that now, in our investigation, we are seeing damage that is the result of loading that no longer exists and which will not realistically exist again. A fair amount of our work is sorting damage that is the result of current conditions (which must be both repaired and prevented from recurring) from damage that is the result of past conditions (which simply needs repair).
A time machine would help, but document research is the next best thing.
