Reliability evaluation of flexural capacity design provision for UHPC beams reinforced with steel rebars/prestressing tendons

Abstract

This study investigated the reliability of the flexural capacity prediction models for ultra-high performance concrete (UHPC) beams in various standards, including the Chinese UHPC Code (draft), Chinese standards JGJ/T 465–2019 and JTG 3362–2018, Swiss standard SIA 2052–2016, and French standard NF P18–710–2016. The research was based on two comprehensive databases of 110 reinforced and 47 prestressed UHPC beams. Correlation analysis of the model errors of the flexural capacity formulae was conducted at first. Then, the reliability of the prediction models was analyzed through Monte Carlo simulation (MCS) and first-order second-moment (FOSM) method, considering the design parameters such as material strength, live-to-dead load ratio, longitudinal reinforcement ratio, and prestressing tendon ratio. The results indicated that the prediction model in Chinese UHPC Code (draft) could accurately predict the flexural capacity of reinforced and prestressed UHPC beams among the five specifications, with the mean model errors of 1.06 and 1.02, respectively. The reliability indexes of Chinese UHPC Code (draft), Swiss standard SIA 2052–2016, and French standard NF P18–710–2016 for both the reinforced and prestressed UHPC beams were significantly higher than the specified value of 4.2 in the Chinese standard. The sensitivity analysis showed that the reliability index increased with the increase of live-to-dead load ratio, but it was not significantly influenced by UHPC compressive strength. In addition, the reliability index decreased as the longitudinal reinforcement ratio and prestressing tendon ratio increased. Material partial factor of flexural resistance of the formula in Chinese UHPC Code (draft) was calibrated, and γc= 1.30 was recommended for UHPC beams for safety.