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

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 (A), 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 A = 3.67 exhibited flexural failure due to the large A. The stiffness, shear-cracking strength, and shear strength of EPUBs-WS decrease as A 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 pre-stressed UHPC beams is proposed and validated using a database of experimental results reported in the liter-ature. A parametric analysis is performed using 40 available specimens to investigate the effects of compressive strength, A, reinforcement ratio, fiber reinforcing index, and prestressing level on the shear strength of pre-stressed UHPC beams without stirrups. By considering the key parameters, equations for estimating the shear strength are proposed and exhibit good accuracy.