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Posted by Geoff Weisenberger on October 1, 2007 at 9:15 AM.
I am president of a national engineering firm that specializes in parking structure design and restoration. With offices in many geographic regions, we are very aware that different exposure conditions exist on concrete slabs and structural frames in various areas of the country. However, we believe the AISC map of durability regions shown in the article “Are You Next?” (September 2006, p. 35) and also included in Steel Design Guide 18: Steel Framed Open Deck Parking Structures in Figure 2-1 is overly simplistic. The AISC map has only three durability regions:
Region A applies to the majority of the United States; it covers the southern two-thirds of the country and the West Coast.
Region B applies to the northern one-third of the country, but excludes most of Washington and Oregon.
Region C applies to areas within one-half mile of a salt water body.
This regionalization lumps areas subject to harsher exposure conditions (e.g., Colorado, Kansas, Missouri, Kentucky, Virginia, and much of Illinois, Indiana, Ohio, West Virginia, and Delaware) into the same durability design category as dry and warm weather states such as New Mexico and Florida. We believe this is unrealistic. Durability design considerations for structures exposed to snow, ice, and the use of de-icing salts can not be ignored. We’ve restored many deteriorated parking structures in these states that succumbed to the harsh exposure conditions. AISC Region A is too varying in atmospheric exposure conditions for the purposes of defining a single, one-size-fits-all durability design strategy.
We highly recommend that AISC adopt by reference the durability zone map included in ACI 362, Design of Parking Structures published by the American Concrete Institute. This map more reasonably depicts the country divided into four regions. Also, the industry does not benefit from having two separate maps apply to the design of parking structures—one for the concrete and one for a steel frame.
Gary Cudney, P.E., President, Carl Walker, Inc., Kalamazoo, Mich.