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PRECAST PARKING STRUCTURES:


Design Techniques to Prevent Cracks and Connection Failures


BY NED M. CLELAND


structural analysis and on my participation in the design ofmore than 250 parking decks.


P 24


But there’s a caveat. In order to build highly durable and reliable precast struc-


tures, youmust design, construct andmaintain themaccording to principles of good practice. Proper design, construction and maintenance are vital in maximizing the life of double-tee park- ing decks and in slowing deterioration by preventing connection failures and tee-flange cracking.


Recognize regional differences Deterioration of parking structures is caused by structural


volume changes due to shrinkage, creep and annual temperature shifts, as well as by damage from freeze-thaw cycles and corro- sion caused by chloride exposure. Freeze-thaw conditions, the use of deicing salts and the


effects of airborne salt in coastal areas vary greatly by region – as should the design details of individual parking garages. Northern regions require design for snowloads and the use of deicing salts.


FEBRUARY 2010 • PARKING TODAY • www.parkingtoday.com


Figure 1 Double-Tee Surface in a 23-Year-Old Garage in Vienna, VA


RECAST/PRESTRESSEDCONCRETE double-tee parking structures are remarkably durable. I base that assess- ment on more than 30 years’ experi- ence in parking garage design and


Other areasmust include design for seismic conditions.


Specify quality concrete Given that consideration, the first step for parking garage


engineers, designers and owners in creating durable, moisture- and chloride-resistant parking structures is to specify the use of durable concrete. These conditions can easily be obtained with precast/prestressed components manufactured and heat-cured in a factory, but they can be difficult to achieve in the field. The use of high-strength or high-performance concrete (with


high cementitious content, lower water/cement ratio and strengths of 6,000 psi), often containing fly ash or microsilica, can further lower a structure’s permeability and increase its dura- bility. Epoxy-coated steel or high-strength carbon-fiber compos- ites can be used in the flanges to add to this protection of the con- cretemix.


Drainage To prevent water ponding, it’s extremely important to design


for adequate drainage. Floors must have sufficient slope in two directions to bring water to drains at low points. This can be accomplished by tilting the floors both on the tee spans and across the beam spans. To maintain level on a garage perimeter, some warping of the floor is permissible.


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