Early-Age Behavior of Wide-Deck PK Concrete Box Girders Considering Spatially Non-Uniform Material Properties

This study investigates early-age cracking in the inclined bottom slabs of a 37.6 m wide PK-section concrete box girder during winter cantilever construction. A numerical method considering non-uniform material property development based on equivalent age was established. The method was validated by synchronous temperature and strain monitoring. The validated program was then used to analyze cracking causes and optimization measures. Results indicated that 3 days after casting, the maximum difference in equivalent age exceeded 7 days. Differences in elastic modulus and strength reached 30% and 34%, respectively, showing significant material non-uniformity. The restraint from completed segments was the primary cause of cracking. The total stress at the crack location was 5.5 MPa, with a 95% cracking probability. The ratio of thermal to shrinkage stress was 3.6:1. In summer, both total stress and strength increased, resulting in a similar cracking probability. Reducing the placing temperature decreased thermal stress by 0.13 MPa/°C in both seasons but had little effect on shrinkage. A 3 °C reduction lowered the cracking probability by 5–15%. Adding prestressed tendons to the bottom slab reduced total stress to 3.2 MPa and cracking probability to 37%, significantly mitigating cracking risk.