Steel Construction Vol 40 no 6 - International Steel Structures | Page 13

SAISC PROJECTS
rooftop garden in the cylindrical tower above. To accommodate
ZSFGH’s ambitious program and the significant amount of
overhead utilities typically required in a hospital, steel moment
frames were selected in lieu of braced frames or shear walls, as
the lateral resistance system to create more space for an efficient
health-care floor layout. The moment frame beams are W27 and
W36 sections, and the moment frame columns consist of W27
and W36 wide-flange columns and flanged cruciform columns
for orthogonal moment frames. High-strength steel plate (65-ksi)
is used for built-up wide-flange columns at selected locations for
increased capacity.

sunshade fins are also visible from the rooftop terrace garden,
which is open to the public.

Constructability was a central focus when designing the steel
details of the new hospital, exemplified by the steel column base
detail. Cruciform-shaped steel column bases are placed above
the isolators to resist the offset between the superstructure
and the isolators that occurs when the isolators undergo large
displacement. The cruciform column bases are shop-welded
and delivered to the site as modular assemblies, which enhanced
installation and saved time in the construction schedule. In
addition, splices of the beams adjoining to the cruciform
assemblies are field-bolted moment connections – not welded – in
order to eliminate the self-straining stresses due to weld shrinkage
that would impose on the structure.

Heart of gold

In the X-ray, radiology, resuscitation and operating rooms – where
the overhead ceiling spaces are the busiest – a steel overheadequipment-support modular grid supports all of the overhead
medical equipment such as lights and booms. The modular grid is
composed of horizontal HSS4×3 and HSS3×3 sections forming an
orthogonal grid, which is hung from the floor beams above through
unistrut drops. Unistrut bracing provides lateral stiffness for the
support grid, and this modular grid facilitated the coordination and
installation of utility runs, ductwork and equipment supports in
these vital rooms.

A steel halo sculpture – a 35-ft-diameter ring cantilevered off of
two 16-ft-tall columns – stands prominently at the groundlevel
entry of the hospital campus. The halo is built from 14-in.-diameter
stainless steel pipe sections, with the ring and elbows fabricated
to fit the architect’s curved geometry design. On the opposite
side of the campus, a trussed pedestrian bridge with exposed
HSS6×6 provides the important pathway between the new hospital
building and the original medical facility at the second floor.

The material-saving base isolation system is one of the sustainable
design features expected to earn the hospital a LEED Gold
certification. Other green features include the use of building
materials containing at least 30% recycled content, including
steel, ceiling tiles, porcelain tiles, terrazzo flooring and Forest
Stewardship Council-certified wood. The hospital also features
full-height curtain walls that use low-emissivity glass and insulation
to protect against heat gain, as well as window shades and room
lighting fixtures that are automatically adjusted based on sunlight
levels as detected by photovoltaic sensors.
Financed by an $887.4 million voter approved bond, as well as a
record number of significant donations, ZSFGH is a city lifeline that,
according to Mayor Ed Lee,“represents San Francisco’s values at
their best, and demonstrates that our city is a leader in innovation
and compassion… for creating a world-class, seismically safe,
technologically advanced and sustainably built hospital for all San
Franciscans” – truly the beating heart of a vibrant city.

Exposed steel
A number of exposed structural steel components are featured
on the hospital campus. A vertical fin sunshade structure, built
from HSS8×8 steel sections, was placed on the south- and westfacing facades of the podium structure. The sunshade elements are
oriented according to the path of the sun and are painted in bright
white. Expressive steel canopies at the top of the curved facade’s

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BELOW LEFT: The cruciform-shaped steel column base was shop-welded, while
the moment connections to the adjoining beams were field-bolted to eliminate
selfstraining stresses due to weld shrinkage.
BELOW RIGHT: The steel-framed superstructure is relatively lightweight and
reduces demands on the base isolators and foundations.

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Steel Construction Vol. 40 No. 6 2016 11