Optimizing the Design of Structures with Unique Site Conditions

摘要

Air rights projects have historically led to creative structural solutions since restrictions are imposed on the placement of vertical load resisting elements and their accompanying foundations. Good examples of this are buildings constructed over the Liverpool Train Station in London: Bishopsgate Exchange House uses a tied arch bridge concept to span the rail yard below and the Broadgate Tower introduces a creative diagonal bracing system that searches for terra firma between the tracks. In Salt Lake City, the current design for a 25-story office tower allows for the insertion of a performing arts facility at its base prohibiting any column above to pass through the facility below. Similarly, a new federal courthouse building is designed with no perimeter columns extending to foundations, eliminating elements that would otherwise be vulnerable to threat. In both cases, these unique site conditions have lead to creative approaches to design and strategies to optimize material use. For both the Salt Lake City and federal courthouse projects, the entire perimeters of the buildings are supported by a three dimensional steel roof hat truss system. The office building is designed as a core-only lateral system using non-prescriptive performance-based design. In addition, six large stainless steel bearings are used to manage loads at the top of the core wall system. For the courthouse building, six large shear wall cores are linked with unbonded braces and the cantilevered trusses are optimized in accordance with principles set forth in the early 1900's by the mathematician John Michell. Construction sequence and load balancing are essential in the design of these structures.