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The seismic retrofitting of the County of Placer/Foresthill Road Bridge included replacing the gusset plates at the bolted connection points on the structure. Newly fabricated connection plates were prepared in the steel fabrication shop by abrasive blast cleaning and applying an inorganic zinc-rich primer. Existing connection plates were removed and the surfaces beneath abrasive blast cleaned and primed on-site with an organic (epoxy) zinc-rich primer. The connections were slip-critical. The coating manufacturer did not have historical test data to demonstrate the slip coefficient classification of the inorganic zinc primer bolted to the organic zinc primer. Further, in order to maintain the project schedule, the contractor proposed to bolt the new connection plates in place reasonably soon after application of the field-applied organic zinc primer. To address both of these concerns, a novel testing program was undertaken to determine when the field-applied organic zinc primer was dried sufficiently to be mated to the shop-applied inorganic zinc in a bolted connection and provide resistance to slip once bolted. This paper describes the engineered approach, the experimental design and the results of the slip coefficient testing.
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