The crowning achievement on the Wilshire Grand project will be the Crown Sail and Spire that set atop the roof of the building. By any measure the crown sail and spire are a building unto themselves.

Typically, engineers place structures over rigid bases that are 10x stiffer than the structure above. This allows the structure to be designed as if on a rigid base. With the Wilshire Grand project, engineers set a stiff structure on top of a flexible one. This resulted in a sail and spire with very high seismic design requirements from upper mode effects produced by the supporting 73-story building. …