The picture above – courtesy of Irfan Haider of the Central Park Conservancy – shows the realization of another of our designs for small rustic structures in the park. Again, Shaquana Lovell took the lead for OSE.
In this case, the design of the log structure was not the main structural problem. The logs of the umbrella shelter are relatively large compared to their spans, even with the cantilevered edges, so detailing the connections between the round and irregularly-shaped pieces was more challenging than analyzing them. The big structural issue, and any engineers reading this are already way ahead of me, is the foundation. The Belvedere Summer House has six columns, which means that they can be analyzed and designed as pin-ended, which is the default for wood. The umbrella has one column and relying on those little diagonals at that base – which were put there to hold up the bench – would require that their connections to the central column be quite a bit stronger than ordinary wood connections.
The solution to cantilevering the column was related to a condition that the photo does not show: the soil at this (low) hilltop location is quite thin, with bedrock close by. By pinning a concrete footing to the bedrock, we had a piece of new structure that was strong enough to serve as a base to connect that central log column in order to resist the lateral wind moment.
In short, the visible structure is very nice, but our best work here is hidden underground. C’est la vie.
