Investigation of steel fibre pullout and modeling of bridging behaviour in SFRC

By adding fibres to concrete mix the objective is to bridge discrete cracks providing for some control to the fracture process and increase the fracture energy. Fibres become active mainly when cracking starts and deformation of the fibre occurs. Pullout tests with four types of fibres with different orientation, embedment lengths, and concrete strengths are performed to simulate the bridging process. Fibre pullout behaviour is analysed for relatively small slippage displacement to keep it close to real designing situations. The test results show significant effect of fibre type on pullout behaviour, nevertheless the effect is intangible on fibres inclined at 30 degrees or more. An effective displacement is introduced, derived from experimental force-slip curves, when fibre becomes involved in bridging. Based on the effective displacement and simplified average force-slip curves a numerical model is proposed to analyse the tensile stresses transferred by fibres crossing a crack