Flexural behavior of shield tunnel segmental linings incorporating hybrid fiber high-strength ECC: Experimental and theoretical investigation

High-strength engineered cementitious composite (HS-ECC) shows great potential for improving the flexural performance and crack control of shield tunnel segment linings. This study experimentally and theoretically investigates the flexural behavior of HS-ECC segments reinforced with polyethylene (PE) fibers and steel (ST) fibers, focusing on the effects of longitudinal reinforcement ratio, fiber content, and hybrid fiber ratio. Flexural tests were conducted on HS-ECC and conventional reinforced concrete (RC) segments to analyze failure modes, crack propagation, and flexural behavior. The results indicate that HS-ECC segments exhibit distributed micro-cracking with narrower crack widths and more uniform crack spacing compared with RC segments, effectively delaying crack localization and flexural failure. At a constant reinforcement ratio, increasing the PE fiber content resulted in a denser crack distribution and improved crack control. Compared with RC segments, HS-ECC segments showed significantly higher flexural performance at both serviceability and ultimate limit states. Notably, even with a 30% reduction in reinforcement ratio, the ultimate flexural capacity of HS-ECC segments exceeded that of RC segments by 6.6%. An increase in PE fiber content substantially improved flexural performance, resulting in increases of up to 28.9%, 39.3%, and 42.8% in the cracking, yield, and ultimate loads, respectively. Furthermore, a mesoscopic tensile constitutive model of HS-ECC was developed, and a theoretical method for predicting the flexural response of HS-ECC segments was proposed and validated against experimental results. These findings provide valuable insights into the flexural failure mechanisms of hybrid fiber HS-ECC segments and support their application in shield tunnel linings.