MODELING OF FRACTURE OF STEEL FIBER REINFORCED SELF-COMPACTING CONCRETE

Abstract

In this paper, a simple, effective and constitutive size dependent finite element based tri-linear model for cohesive fracture of steel fiber reinforced self-compacting concrete (SFRSCC) with two kink points for mode-I fracture is proposed. The co-ordinates of the first kink point is size independent and calculated directly from the geometry of the model whereas for second one the horizontal ordinate is hypothesized to crack tip opening displacement  (CTOD_c) of concrete and vertical ordinates is dependent on size of beam. Experimentally, the 3 geometrically similar sizes 100x240x1100,100x120x550 and 100x60x275mm as per RILEM are used for the tests under 3 point bending. The fracture parameters (total fracture energy, initial fracture energy, , critical stress intensity factor and fracture process zone length ) used to link the fracture model are determined by various nonlinear(NLFM) fracture models. The two parameter fracture model, size effect model are based on effective elastic crack approach and work of fracture and crack band model are based on fictitious crack approach. The fracture zone of the model has small aggregate bridging zone and large fiber bridging zone. Since the simulated monotonic load (P) v/s crack mouth opening displacement (CMOD) curves perfectly fit with that of experimental curves, a tri-linear model can be predicted by finite element based ATENA software. Unlike for plain concrete, the total fracture energy CT0D_c increases with decrease in size of SFRSCC beams. Hence there is no size effect but noticeable only for large size SFRSCC beams.
The toughness properties such as toughness index, toughness ratio determined as per ASTM C 1018 and ductility ratio increases with decrease in size of beams. Empirical formula established for all these quantities are useful for the design of beams based on toughness and ductility respectively.