Interlaboratory Variability of Slip Coefficient Testing for Bridge Coatings

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RECOMMENDATIONS

Based on the observations of the participating labs and the data produced by them, this study offers the following suggested changes to the RCSC for appendix A of its Specification for Structural Joints Using High-Strength Bolts:⁽²⁾

• If RCSC maintains the current procedure wherein the slip coefficient is strictly determined as the average of five specimens, it should allow testing agents the ability to test one extra plate and to ignore an outlier data point.
  
  
• RCSC should consider restructuring its requirements for the test apparatus to mandate the use of more than a single slip measurement point during the test. This second point should be placed in a plane such that it can effectively monitor any undesired measurement error caused by specimen rotation or eccentric loading.
  
  
• The test method should be modified such that tolerances are imposed to ensure symmetry of the load train and reduce the eccentricities as much as possible between the jacks and specimen. A ±1/8-inch tolerance is recommended.
  
  
• RSCS should consider eliminating the requirement stating that tests be conducted until 0.05 inch of slip occurs. The test method specifies reporting the maximum load that is observed during the test up through the attainment of a 0.02-inch average slip. Information obtained after 0.02 inch of slip is not explicitly reported in the results. If RSCS wants to keep the existing requirement, it should consider allowing an increase of the rate of loading after 0.02 inch of average slip has been achieved.
  
  
• RCSC should consider redrafting the test method language to focus on using digital data acquisition in lieu of analog X-Y plotters.
  
  
• RCSC should consider eliminating the load and displacement rate limits on the test. In lieu of them, the test method could suggest the maintenance of a rate of loading until 0.02 inch of slip and that the test from start through 0.02 inch of slip should be completed within a fixed timeframe.