Impact of loading rate and elevated temperatures on the pull-out behaviour of inclined hooked-end steel fibres embedded in normal and high-strength concrete

The coupled effects of loading rate, fibre inclination, and post-fire exposure on the pull-out behaviour of steel fibre reinforced concrete (SFRC) remain insufficiently quantified. This study experimentally investigates the pull-out response of hooked-end steel fibres embedded in normal and high-strength concretes under quasi-static, intermediate (seismic), and impact loading, before and after thermal exposure up to 600°C. Single-fibre tests were conducted over inclination angles from 0° to 60° and slip rates from 0.018 to 1800 mm/s, generating a comprehensive dataset of 120 tests. Results show pronounced rate sensitivity, progressive bond degradation beyond 400°C, and strong inclination effects, with high angles inducing severe spalling and strength loss, particularly in high-strength concrete. Based on these findings, a unified analytical model is proposed incorporating snubbing, rate-dependent amplification, thermal degradation, and high-angle damage. The model accurately predicts peak pull-out loads across all loading regimes, providing a robust framework for SFRC assessment under combined impact and post-fire loading.