Shear failures and bearing capacity analysis of UHPC beams at low temperatures: Experiment and formulation

The application of ultra-high performance concrete (UHPC) is a potentially effective solution to improve the shear ductility of beam, which has been increasingly apply in cryogenic engineering. To study the shear behaviors of UHPC beams at low temperatures and predict the shear capacity, the low-temperature shear failures of different types of beams at different temperatures (20 degrees C to-90 degrees C) were tested and discussed regarding failure modes, load-deflection curves, maximum shear crack widths, characteristic shear strengths and ductility. The effectiveness of steel fibers and stirrups in mitigating brittle shear failure of UHPC beams at low temperatures was analysed comparatively. Test results show that the nominal cracking strength and ultimate shear strength of the beams increased significantly with dropping temperature, presenting a cryogenic enhancing effect. However, the ductility decreased significantly and the maximum shear crack was widened as the temperature drops, presenting a low-temperature brittle failure characteristic. The incorporation of steel fibers was a more effective method to reduce the maximum shear crack width and improve cracking strength, while the stirrups were better for enhancing ultimate shear strength and improving ductility of cryogenic UHPC beam. Besides, the applicability of existing code formulas for predicting the shear capacity of UHPC beams at low temperatures was evaluated with test results. Finally, based on the test results of different types of beams, an improved formula with quantitatively considering the low-temperature effect on shear contribution by concrete, stirrups and steel fibers on the shear capacity of UHPC beams was proposed and verified. The present study can offer effective reference for the code revision and promote the application of UHPC in infrastructure construction in cold regions.