Shear behavior of externally prestressed ultra-high-performance concrete (UHPC) T-beams without stirrups

Abstract

Externally prestressed ultra-high-performance concrete (UHPC) beams without stirrups (EPUBs-WS) that simplify the reinforcement design and construction procedure are becoming a competitive option in bridge engineering. To investigate the shear behavior of EPUBs-WS, five specimens were designed and tested considering several critical parameters, such as the shear span-to-depth ratio (λ), shear stirrups, and longitudinal reinforcement ratio. The EPUBs-WS exhibits diagonal tension failure as the fibers pull out and the specimen shears off into two parts along the critical diagonal crack. However, the beam with λ = 3.67 exhibited flexural failure due to the large λ. The stiffness, shear-cracking strength, and shear strength of EPUBs-WS decrease as λ increases. Stirrups enhance the shear resistance of EPUBs but result in a more brittle shear failure mode. A higher reinforcement ratio augments the dowel action in EPUBs-WS, which contributes to a ductile shear failure mechanism. The web-shear cracking force accounts for 46% to 87% of the shear capacity, implying that the shear-cracking strength is a significant factor in the design of EPUBs-WS. An equation for predicting the shear-cracking strength of prestressed UHPC beams is proposed and validated using a database of experimental results reported in the literature. A parametric analysis is performed using 40 available specimens to investigate the effects of compressive strength, λ, reinforcement ratio, fiber reinforcing index, and prestressing level on the shear strength of prestressed UHPC beams without stirrups. By considering the key parameters, equations for estimating the shear strength are proposed and exhibit good accuracy.