740 Heinz Avenue
An award-winning case study in the efficacy, cost efficiency, and replicability of BRB mast frames.
The first major application of the BRB mast-frame system and designed to be a state-of-the-art life sciences building, 740 Heinz is clad in precast concrete behind brick veneer. The building has a footprint of approximately 136 feet north–south by 192 feet east–west, for a total of 110,000 gsf. The floor framing system consists of steel beams and girders supporting concrete-filled metal deck. Framing is supported by steel columns spaced at approximately 32 feet on center in both directions.
The seismic lateral-force resisting system consists of two BRB mast frames in each direction: in the transverse, the frames are located next to the building’s stair cores; in the longitudinal, they are installed at the perimeter façade line.
Each BRB mast frame comprises yielding BRBs connected to a vertically oriented truss-like mast; a true pinned-base connection joins the frame and base. The structure was designed according to the provisions of the 2010 CBC; the frames were designed using an R of 7. Seismic analysis relied on a conventional code modal response-spectrum method. The base connection, anchorage, braced-frame pile caps, and piles were designed to resist omega-level forces. The BRB mast frame’s vertical-truss configuration is a key aspect of the design, as it is able to redistribute lateral loads between levels, eliminating soft-story mechanisms. The BRB mast-frame system relies on capacity design principles to ensure that inelastic mechanisms will form predictably and reliably.
The BRB mast frame has equal-capacity BRBs at all levels. In contrast, a conventional code-designed braced frame, based on a prescribed triangular lateral-force distribution, typically has the strongest BRBs at the base and the weakest at the top.
The inherent redundancy of the system allows for fewer braced frames. Employing BRB mast frames at 740 Heinz allowed the number of required frames to be cut from 7 conventional BRB frames down to 4 BRB mast frames; the total number of BRB elements was reduced from 56 to 16. Moreover, because the BRB mast frames were easily located next to the building’s two stair cores and at the perimeter façade, they did not impinge on the architectural space plan. Lastly, this lateral system saved the project $360,000 in construction costs when compared to a conventional BRB-frame system.
In short, this system holds a great deal of promise for the future: it is a cost-efficient, nonproprietary, and simple high-performance system that can be designed in any number of possible configurations, making it an ideal lateral system for any steel braced-frame building.
2016 NCSEA Excellence in Structural Engineering Awards, Outstanding Project
2016 SEAOC Excellence in Structural Engineering, Award of Excellence for New Construction, Small Project