The initial clamping forces of the high strength bolts depending on the different faying surface conditions drop within 1,000 hours regardless of loading any other external force or loosening of the nut. This study focused on the mathematical model for relaxation confined to creep on coated faying surface after initial clamping. The quantitative equation for estimating long term relaxation was derived from nonlinear regression analysis for relation between the creep strain of coated surface and the elapsed time.

ABSTRACT
 1. 서 론
 2. 시험 및 결과분석
  2.1 시험계획
  2.2 장기축력 결과
 3. 장기축력에 관한 수학적 모델
 4. 결론
 참고 문헌

• 나환선(한국전력공사 전력연구원/책임연구원) | Nah Hwan-Seon
• 이현주(한국전력공사 전력연구원/선임연구원) | Lee Hyeon-Ju