5 - Modern Steel Construction

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28 years of experience
shows that combining a
structural steel frame with
a precast, prestressed
deck creates the most
economical and efficient
system
By Michael J.A. H. Joll iffe, P.E.
Zaldastani Associates in Boston has
a long history of designing longspan
parking facilities. In 1962, the
finn designed its first parking structure, a
precast, prestressed concrete structure as
part of a residential project for Harvard
University. Since that time, the firm has
designed more than 25,000 parking spaces.
But during the past several years,
Zaldastani Associates has been redeveloping
its approach to the structural framing
of open parking structures.
In developing any design, it is imperative
that the parameters to which that design
must respond are clearly defined.
These parameters will reflect not only the
performance of the finished structure or
PARKING STRUCTURES
building, but also the manner in which it
is constructed.
Usually, a principle consideration will
be cost. For a parking facility, additional
parameters relate to the performance of
the structure, including: durability in the
chloride ion environment of the parking
deck; ease and speed of erection; ease of
maintenance; drainage performance; visual
security; and ease of parking. Structural
issues that can affect design include:
the ability of a structure to resist lateral
loads from wind and seismic forces; the
weight of the structure and its effect on the
magnitude of those seismic forces and on
the foundation; and the effect of the large
temperature changes which occur in the
open exposed environment.
During the past 28 years, our experience
shows that the best material for parking
decks is precast concrete, while the
best material for the structural support
system is exposed steel. Precast concrete
has a greater potential for high strength,
high durability than poured-in-place. And
steel which is exposed to view is much
more easily maintained than rebar buried
in concrete that has lost its ability to protect
the steel when its alkaline environment
has been changed by the intrusion of
acidic ion s.
The exterior of the
Bectoll DicklUS01l
Parkll/g FaCl/ity
utilius brick. natural
stone, u..'OOd, copper mId
steel 011 the exterior to
mate" adjacent
hlli/dll/gs. Pilato by
Gcorge E. PClrce
Modern Steel Construction I September-October 1990 I 37