Experimental study on shear behavior of externally prestressed ultra-high performance concrete beams without stirrups

In order to study the shear behavior of ultra-high performance concrete (UHPC) beams without stirrups, 9 externally prestressed UHPC beams without stirrups were fabricated. The experimental parameters included the level of prestress, shear span-to-depth ratio, longitudinal reinforcement ratio and volume fraction of steel fibers. Four-point loading method was used to obtain the failure patterns, cracking strength and ultimate strength. The results show that the non-prestressed UHPC beam under the shear span-to-depth ratio of 1.0 suffers from flexural failure. However, the flexural resistance of the normal section of UHPC beam is strengthened by a prestressing tension of 25% ultimate strength of the strands, resulting in an increase of the flexural moment by 157% and turning into a shear failure. Compared with non-prestressed UHPC beam, the cracking loads of UHPC beams tensioned by 25% prestress and 40% prestress increase by 1.2 times and 2.6 times, respectively, which effectively inhibit the formation of cracks. The UHPC beams with 40% prestress under shear span-to-depth ratio of 1.0 and 1.5 fail in shear. However, when the shear span-to-depth ratio increases to 2.0, the UHPC beam suffers from a flexural failure, which leads to concrete crushing in the compression zone. The formulae of the codes underestimate the shear capacity of the externally prestressed UHPC beams, since the average ratios of the experimental shear capacity to the calculated one of the inclined section are 2.28 and 3.21, respectively.