Segment Model Test of CFST Arch Rib for Bridge Construction

Literature Overview

The paper by Shao Xudong, Cheng Shangfeng, and Li Lifeng, published in the Journal of Chang'an University (Natural Science Edition) (2003, Vol. 23, No. 4, pp. 34-37), presents the results of a 1:5 scale segment model test of the main arch ring for the Maocaojie Bridge. This research is particularly significant because it addresses the long-term behavior of concrete-filled steel tubular (CFST) arch ribs, specifically focusing on the effects of concrete creep on internal force redistribution. The test simulated the construction process of the full-scale bridge and measured the stress distribution in the arch crown segment under various loading conditions. The research provides valuable insights into the construction methodology and long-term performance of large-span CFST arch bridges.

Test Configuration and Methodology

The 1:5 scale model test was designed to replicate the construction sequence and loading conditions of the full-scale Maocaojie Bridge. The test setup included:

Stress Distribution Results

The test measured the stress distribution in the arch crown segment under various loading conditions corresponding to different construction stages. The results showed good agreement between the measured stresses and theoretical predictions, validating the theoretical models used for the design of the full-scale bridge.

The stress distribution revealed several important characteristics:

1. Non-uniform stress distribution: The stress in the CFST arch rib was not uniformly distributed across the cross-section. The steel tube and the concrete core experienced different stress levels depending on the loading condition and the construction stage.
2. Construction stage effects: The stress state at the end of each construction stage differed from the final stress state after all stages were completed. This is because the concrete in later-constructed segments has not yet experienced the full duration of creep, leading to time-dependent internal force redistribution.
3. Steel-concrete interaction: The interaction between the steel tube and the concrete core was effective in most loading conditions, but the degree of interaction varied with the construction stage and the magnitude of applied loads.

Creep Effects on Internal Force Redistribution

One of the most important findings of this research is the quantification of concrete creep effects on internal force redistribution in the CFST arch rib. The researchers tracked the creep behavior over an extended period and observed:

The creep effects were found to be particularly significant in the arch crown segment, where the internal forces are most sensitive to changes in the relative stiffness of the steel tube and concrete core. As the concrete creeps, its stiffness decreases relative to the steel tube, causing a progressive transfer of load from the concrete to the steel tube. This redistribution can lead to increased stresses in the steel tube, which is a critical consideration for the long-term design of CFST arch ribs.

Engineering Practice Implications

From a steel pipe manufacturing and bridge construction perspective, this research has several important implications:

• Construction sequence optimization: The construction sequence of the CFST arch rib segments should be planned to minimize the differential creep effects between segments. Segments constructed earlier will experience more creep, leading to different stress states compared to later-constructed segments.
• Steel tube stress monitoring: The steel tube in the arch rib should be monitored for stress levels during and after construction, particularly in the arch crown region where creep effects are most pronounced. Excessive stress in the steel tube could indicate premature failure.
• Concrete quality control: The quality of the concrete used in the arch rib is critical for controlling creep effects. Higher-quality concrete with lower water-cement ratio will exhibit less creep, resulting in more stable long-term performance.
• Temporary support design: The temporary supports used during construction must be designed to accommodate the time-dependent changes in internal forces due to concrete creep. Premature removal of temporary supports can lead to excessive stresses in the arch rib.

Study Insights

This research provides valuable experimental evidence for the design and construction of large-span CFST arch bridges. The quantification of creep effects on internal force redistribution is particularly important because these effects can significantly influence the long-term performance of the arch rib. The good agreement between the test results and theoretical predictions validates the analytical methods used for the design of the full-scale bridge. For engineers involved in steel pipe fabrication for arch rib applications, the research highlights the importance of selecting appropriate steel grades with adequate long-term strength and fatigue resistance. The findings also emphasize the need for careful planning of the construction sequence and temporary support design to minimize the adverse effects of concrete creep. Engineers should recognize that the long-term performance of CFST arch ribs is fundamentally influenced by the time-dependent behavior of the concrete core, and that proper attention to construction methodology and material quality is essential for achieving the designed structural performance over the service life of the bridge.