the Huck Institutes of the Life Sciences, in the
MSC’s west wing, for instance, were designed
to vibrate at less than 4,000 millionths of an
inch per second (100 μm/s) under excitation
produced by an individual walking at 75 steps
per minute. The laboratories of the Materials Research Institute,
in the MSC’s north wing, were designed to vibrate at less than
2,000 millionths of an inch per second ( 50 μm/s) under excitation produced by an individual walking at 75 steps per minute.
The velocity limits on these so-called class A laboratories can be
met on framed floors using structural measures that will be discussed below. However, the class E, or “quiet,” laboratories in
the MSC have vibration criteria that are so exacting—125 millionths of an inch per second ( 3 μm/s)—that locating them on
framed floors would have been impractical.
Instead, the MSC’s quiet labs are located on dedicated 2 ft
thick concrete slabs on grade one story below grade. Any vibration traveling horizontally from adjacent equipment and
pedestrians is blocked by neoprene-filled isolation joints located around the slabs, and airborne vibration is blocked by local
walls and roofs supported outside the isolated slabs. In effect,
the quiet labs are buildings within a building. To avoid possible electrical or magnetic interference or interaction from steel
reinforcing bars, nonmagnetic, nonferrous fiber reinforcing
was used to control cracking in the quiet lab slabs as a more
economical but still effective alternative to such traditional
approaches as using plastic rods reinforced with glass fibers.
Yet even with all these measures, there was still one more
potential vibration challenge to consider: roadway vibrations.
Cars, trucks, and regularly scheduled buses on
the streets on the south and east sides of the
site could vibrate the ground enough to affect the quiet labs. To minimize this possibility, the quiet labs are located as far as possible
from those streets, that is, in the northwest corner of the site.
But that decision introduced another concern: would build-ing-based vibrations travel down the superstructure columns
into the foundations and the ground? The giant cantilevers
at the building corner eliminate this possibility by creating a
154 ft square zone that is free of superstructure columns and
forms the dramatic gateway.
At the same time, the cantilevers also created additional
concerns: would runners, skateboarders, or light vehicles passing through the gateway zone excite the ground-floor slab
enough to affect the quiet labs below? To address this issue,
the gateway area directly above the quiet labs features a design created by the project’s landscape architect, the Atlanta
office of Dewberry, that offers winding paths, extensive plantings, and picturesque boulders that weigh as much as 5 tons.
The winding paths force people to slow down and enjoy the
setting, while the mass of planting soil and rocks, which imposes loads of up to 200 psf in some locations, minimizes the
potential movement of the ground-floor framing under footfall excitation. Beneath the landscape architecture, this area is
supported on W 40 × 593 girders that span 81. 7 ft across the
quiet labs and land on plaza columns that are separated by a
sufficient distance from the joints for isolating the slabs of the
The space defined by the intersecting trusses is open to the
sky, allowing daylight to reach
the gateway garden area below.
 Civil Engineering SEPTEMBER 2012