Efficiency and economy in precast concrete construction is driven by repetition, standardization and minimum number of pieces. Optimum bay sizes are most commonly based upon the width of the standard double tee module being used. A garage manufactured by a precaster utilizing 12' wide double tees would optimally use 36' or 48' bays while a garage constructed with 15' wide double tees would implement 30' or 45' bays. Precasters in the project region should be consulted to determine available modules.
PCI's Parking Structures: Recommended Practice for Design and Construction recommends a minimum 1% slope be maintained throughout a garage. Camber is generally not used as a drainage mechanism. Careful consideration should be given to product tolerances and camber of double tees when establishing drainage slopes
The recommended precast panel to panel joint width for architectural projects is 3/4". This is the minimum nominal joint width needed to adequately account for production and erection tolerances and still maintain an effective minimum joint width that can be caulked. A 30' long spandrel panel is allowed, per PCI tolerances up to a 1/4" variation in length. Keep in mind that of 3/8" is the minimum width that caulk suppliers will warrant. It is also important that the joint between precast panels and window frames also maintain the same nominal joint width.
Cracking in double tee flanges is occasionally encountered on newly erected parking garages. This is commonly the result of torsional stresses developed during loading, transporting or erection of the member. Similarly, this may occur when a double tee is "warped" in its final position to allow for proper drainage. This type of cracking does not jeopardize the structural integrity of the double tee. To avoid long-term durability problems, these cracks should be filled with an approved sealant or epoxy. Epoxy repairs should be covered with a cementitious material to limit UV exposure.