Ultra High Performance Fiber Reinforced Concrete (UHPFRC) has a outstanding tensile hardening behaviour after a crack develops, which gives ductility to structures. Existing shear strength model for fiber reinforced concrete is entirely based on crack opening behavior(mode I) which comes from flexural-shear failure, not considering shear-slip behavior(mode II). To find out the mode I and mode II behavior on a crack in UHPFRC simultaneously, maximum shear strength of cracked UHPFRC is investigated from twenty-four push-off test results. The shear stress on a crack is derived as variable of initial crack width and fiber volume ratio. Test results show that shear slippage is proportional to crack opening, which leads to relationship between shear transfer strength and crack width. Based on the test results a hypothesis is proposed for the physical mechanics of shear transfer in UHPFRC by tensile hardening behavior in stead of aggregate interlocking in reinforced concrete. Shear transfer strength based on tensile hardening behavior in UHPFRC is suggested and this suggestion was verified by comparing direct tensile test results and push-off test results.

Abstract
 1. 서론
 2. 실험체 설계
  2.1 재료 강도
  2.2 실험 변수 및 계획
 3. 실험결과
  3.1 평균전단강도-전단슬립 관계
  3.2 평균전단강도-균열폭 관계
  3.3 전단슬립-균열폭 관계
 4. 균열폭에 따른 최대전단강도
  4.1 보통콘크리트에서 균열폭에 따른 최대전단강도
  4.2 UHPFRC의 균열폭에 따른 최대전단강도
  4.3 UHPFRC의 전단강도식 제안
 5. 결론
 감사의 글
 References

• 이지형(서울대학교 공과대학 건축학과, 박사과정) | Lee, Ji-Hyung
• 홍성걸(서울대학교 공과대학 건축학과, 공학박사) | Hong, Sung-Gul 교신저자