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C ~ October 29, 1999 Billy Wasson, Projed Coor~dinator Marion County Courthouse 100 High Street NE Salem, Oregon 97301 and John Whittington, Project Coorclinator Salem Area Mass Transit District 3140 Del Webb Avenue NE Salem, Oregon 97303-4165 Kim Arbuckle, AIA Alan E Cos[ic, AIA Walter E Bensman, Jr., AIA Clayton Vorse, AIA Mark M Fos[er, AIA Leonard Lodder, AIA Richard S Rothweiler, AIA ARBUCKLE COSTIC ARCHITECTS, INC. 363 State Street Salem, OR 97301-3533 503/581-4114 Fax: 503/581-3655 E-Maii: acarchQopen.org RE: Transit Mall Wear Surtace on Elevated Strudural Deck over Parking Garage. courtnouse Square Project No. 9828 Dear Billy and John: The project program includes an elevated stnadural deck over underground parking covering the entire site. Parts of this elevated deck form the ground floor of the office building as well as a future north pad development area. The remainder of this site consists of paved pedestrian plazas and transit mall drive through and parlcing lanes. In assessing the technical issues posed to the design team, by this program, the following issues emerged: - Designing and specifying a reliable deck waterproofing system for the project was a key issue for the Development Team, particulariy because there are many examples of system failures, (including pefiaps the most visible one at the Civic Center in Salem). - The traffic bearing surtace for the transit mall needed to withstand the dynamic loads imposed by a fleet of buses operating on a fifteen to thirty minute pulse. Our search for solutions included consideration of both single track and two track approaches. A single track ~ approach would have involved a combination waterproofing system and wear surtace in a single product application. A finro track approach involves the consideration of two different applications and/or produds, each of which solves separate problems. The single track approach, an idea which resurtaced in recent construdion team meetings, had been ruled out previously because of a relatively short servlce life between resurtacing and the lack of examples with the severity of wear posed by the transit mall. While moving to a two track approach improved the potential quality of the final solution, it eliminated the single source produd responsibility which would have been desirable. The original solution arrived at by the team consisted of two components: A thick, flexible waterproofing system designed to bridge and fill irregularities in the strudural slab, including minor shrinkage cracks which may develop in the near future. A high strength 3" concrete wear surtace designed to proted the flexible waterproofing system and absorb the dynamic loading imposed by bus tra~c. Since the wear surface was not designed to divert 100~ of the surtace water, a drainage layer separated the wear slab from the waterproofing membrane. C