Joint Medical Command Headquarters. Rendering courtesy Gensler, model courtesy James G. Davis Construction.
Thornton Tomasetti performed structural design services for a fast-track renovation of a three-building, 650,000-square-foot office complex. The building systems and finishes in the existing structures – a two-level building constructed in 1954 and two four-story buildings dating to 1960 and 1985 – were upgraded to meet current Class-A office lease standards. The project also involved significant structural modifications to meet seismic design guidelines and progressive collapse resistance requirements of the federal government tenant.
To achieve an efficient seismic performance upgrade for all three buildings, our engineers took advantage of existing lateral-load resisting capacity in the structures and then added a series of new steel braced frames around the building cores. The angles of these braces could be individually “tuned” to provide the precise level of additional stiffness needed to satisfy seismic codes. This design was faster and less expensive than completely replacing the lateral systems.
Federal security codes also required progressive collapse resistance for the four-story buildings that would allow them to withstand the removal of perimeter columns. We created a secondary gravity system by threading new full-height steel columns through the roofs and floors below. These new columns support individual floors and carry loads up to a rooftop transfer beam. This minimally-invasive approach didn’t require façade removal, making it faster and easier to construct than more conventional systems employing column-jacketing and perimeter transfer girders.
Because a tight schedule required the steel to be ordered before the contractor had full access to the building, all design disciplines created detailed building information models, which the contractor combined to “virtually construct” the project. This allowed placement of early material orders and improved overall coordination. The use of BIM on the project sped construction and reduced field issues, helping the project meet its fast-track delivery timeline.
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