Effectiveness and response of replacing web reinforcements with steel fibers reinforced in shear for non-stirrup UHPC beams

Abstract

This paper reports the shear behavior of non-stirrup ultra-high performance concrete (UHPC) beams to fully use the high strengths of UHPC. A total of nine simply-supported beams were entailed based on steel fiber contents (0%, 1%, 2%, and 3%), equivalent stirrup ratios (0.6%, 0.8%, and 1.1%), and shear span-to-depth ratios (1.0, 2.0 and 3.0). Test results indicate that the failure loads of specimens using steel fibers achieved about 1.5, 2.5, and 3.75 times the specimens with equivalent stirrups. Also, the shear cracking loads increased by 100%, 200%, and 250%; meanwhile 20% higher global stiffness was found relative to the specimens using stirrups. Note that the longitudinal crack along the tensile reinforcements at the shear span-to-depth ratio of 1.0 led to the anchorage failure whereby the used straight steel fibers and reduced interlock and/or friction along the shear crack enabled greater fiber-composite strain hardening. Additionally, replacing stirrups with steel fibers could decrease the maximum crack width from 0.04 to 0.01 mm despite carrying twice the cracking load. These findings demonstrated that substituting steel fibers for stirrups could improve the structural both service and ultimate performance. In closing, too-conservative predictions from the current codes warranted a rational theoretical method.