Abstract

Tutankhamun Sami Sharif

Fiber pull-out process is the main micro-mechanism that governs post-cracking behaviour of short steel fiber reinforced concrete structural beams. A detailed analysis of the fiber pull-out process provides understanding about the role of different micro-mechanisms involved in the pull-out process and leads to conclusions about the optimal fiber shape as well as the optimal properties of the matrix. Different steel fiber shapes involve different micro-mechanisms in the pull-out process. Initially fibers and the surrounding concrete matrix deform elastically. The linear elastic behaviour of the fiber-matrix system is interrupted by interface debonding which occurs due to overall weak bonding between the concrete matrix and the surface of the steel fiber. Shear crack propagates and the interface debonding continues untill whole length of the fiber has parted from the surronding concrete matrix. At that point the further applied pull-out load is resisted only by friction forces resulting from fiber sliding out of the concrete matrix. In some cases, if steel fibers have sophisticated form (e.g., end hooks or corrugated form) , much of the pull-out resistance can be achieved from straightening of the fibers. Straightening of steel fibers can only be possible if the surrounding concrete matrix has sufficiently enough strength to resist stress concentration at fiber edges. If surrounding concrete matrix is weak, the stress concentration causes failure of the brittle matrix and no pull-out resistance is obtained. Concrete matrix failure (spalling) is more likely to happen for cases with larger fiber diameters. This paper introduces experimental study relevant to impact of fiber shape on mechanical behavior of steel fiber in fiber reinforced concrete FRC using three femouse steel fiber types and different cases of embedded length into concrete matrix