Bond of epoxy-coated reinforcement under repeated loading

Douglas Bruce Cleary, Purdue University

Abstract

Epoxy-coatings applied to reinforcement are known to reduce the bond strength of the reinforcement. Twenty-three beams with splices placed in a constant moment region were subjected to repeated loading and then tested to failure to compare the service and ultimate load behavior of beams with coated and uncoated reinforcement. The repeated loading consisted of one million or five million cycles in the service load range. Use of epoxy-coated reinforcement reduced the formation load of splitting cracks by 9%. More flexural cracks were present in beams with uncoated reinforcement however the average crack width was larger with epoxy-coated reinforcement. Deflections of beams with coated bars were larger than of beams with uncoated bars. The differences in crack widths and deflections between beams with coated and uncoated bars were reduced with increasing number of applied loads. At loads above 6 kips, reinforcement stresses were 12% higher at crack locations in beams with coated bars than in beams with uncoated bars. The average reinforcement stress along the length of reinforcement between two flexural cracks was 6% greater with epoxy-coated reinforcement. The failure bond stress ratios ranged from 0.82 to 0.96 with an average of 0.88. Solution of the differential equation of bond revealed larger reinforcement slip with epoxy-coated reinforcement. The bond stress-slip relationship was steeper for uncoated bars than for epoxy-coated bars. Differences in the behavior of beams with coated and uncoated reinforcement under service and at ultimate load are attributed to a larger friction component of the bond mechanism with uncoated reinforcement. This component is reduced but not eliminated by repeated loading.

Degree

Ph.D.

Advisors

Ramirez, Purdue University.

Subject Area

Civil engineering

COinS