Shear Strength of UHPFRC Beams Without Stirrups: Fracture Mechanics Approach

Abstract

Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) has outstanding capacity in post-cracking phase with residual tensile strength and a large tensile strain. The stress redistribution after dispersed crack formation enhances shear strength of UHPFRC I-beams. This paper investigates in-plane shear behavior in the web of UHPFRC I-beams without stirrups of varying shear span ratio and beam depths. And this study proposes a new parameter to relate the stress redistribution capacity at material level and structural performance as structural level in terms of characteristic length. From the test results, all specimens for shear strength were found to fail by critical crack localization in the diagonal crack zones. The tensile behavior of UHPFRC at material level is necessary to understand UHPFRC structural behavior which fails by crack localization. Thereby fracture mechanics approach may lead to more reasonable explanation. Characteristic length representing a hardening tensile behavior of UHPFRC is defined as one of representative parameters for fracture behavior. In this paper the effective length of concrete tension strut in diagonal crack zone is suggested as a characteristic length for structural element with a new brittleness factor. The shear strength equation for UHPFRC beam without stirrup is proposed using the lower bound approach with the brittleness factor based on fracture mechanics.