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This paper studies the effects of steel fibre geometry and architecture on the cracking behaviour of steel fibre reinforced concrete (SFRC), with the reinforcements being four types, namely 5DH (Dramix Ò hooked-end), 4DH, 3DH-60 and 3DH-35, of various hooked-end steel fibres at the fibre dosage of 40 and 80 kg/m 3 . The test results show that the addition of steel fibres have little effect on the workability and compressive strength of SFRC, but the ultimate tensile loads, post-cracking behaviour, residual strength and the fracture energy of SFRC are closely related to the shapes of fibres which all increased with increasing fibre content. Results also revealed that the residual tensile strength is significantly influenced by the anchorage strength rather than the number of the fibres counted on the fracture surface. The 5DH steel fibre reinforced concretes have behaved in a manner of multiple crackings and more ductile compared to 3DH and 4DH ones, and the end-hooks of 4DH and 5DH fibres partially deformed in steel fibre reinforced self-compacting concrete (SFR-SCC). In practice, 5DH fibres should be used for reinforcing high or ultra-high performance matrixes to fully utilize their high mechanical anchorage.

A series of uniaxial tensile tests on cylinders made from steel fibre reinforced selfcompacting concrete (SFR-SCC) have been carried out to investigate the influence of fibre geometry and the combined effect of fibre content and distribution on the post-cracking behaviour. Three types of commercially available hooked end fibres (3D (single hooked), 4D double (double hooked) and 5D (triple hooked)) have been used in this study, which are added to the concrete mixture at two fibre dosages (0.5 and 1% by volume). The experiments show that the post-cracking strength increases significantly (P˂ 0.05) with the increase of fibre content for all mixtures. The combination of a unique shaped hook of high tensile strength demonstrates an optimum effect on the failure mode of concrete cylinders in which peak and post-peak strengths are raised. Notably, strain-hardening behaviour is observed only for cylinders reinforced with 5D hooked end fibres. A correlation between number of fibres exposed on fractured surfaces and post-cracking behaviour is established.

This paper represents an analytical model to predict the influence of the fibre geometry on the pull-out behaviour of various geometrical hooked end steel fibres. The model is established based on the concept of a frictional pulley along with two, three and four plastic hinges to simulate the mechanical anchorage effect provided by the hook. The mechanical contribution of the hook is a function of the cold work needed to straighten the fibre during the pull-out. The input parameters used in this model are directly related to geometrical and mechanical properties of each fibre. Model predictions are validated against experimental results for single fibre pull-out tests, and very good agreement is shown.