The behavior of concrete‐filled steel tube (CFST) columns subjected to axial compression was experimentally investigated in this paper. Two kinds of columns, including CFST columns with foundation and columns without foundation, were tested. Columns of pure concrete and concrete with reinforcing bars as well as two steel tube thicknesses were considered. The experimental results showed that the CFST column with reinforcing bars has a higher bearing capacity, more effective plastic behavior, and greater toughness, and the elastoplastic boundary point occurs when the load is approximately 0.4–0.5 times of the ultimate bearing capacity. The change of rock‐socketed depth and the presence of steel tube will affect the ultimate bearing capacity of rock‐socketed pile. The bearing capacities of the rock‐socketed CFST columns are lower than those of rock‐socketed columns without a steel tube under a vertical load; besides, the greater the rock‐socketed depth, the greater the bearing capacity of the rock‐socketed piles. In addition, a numerical comparison between the ultimate load and the theoretical value calculated from the relevant specifications shows that the ultimate load is generally considerably greater than the theoretical calculation results.

Digital twin technology significantly enhances construction site management efficiency; however, dynamically reconstructing site activities presents a considerable challenge. This study introduces a methodology that leverages camera data for the 3D reconstruction of construction site activities. The methodology was initiated using 3D scanning to meticulously reconstruct the construction scene and dynamic elements, forming a model base. It further integrates deep learning algorithms to precisely identify static and dynamic elements in obstructed environments. An enhanced semi-global block-matching algorithm was then applied to derive depth information from the imagery, facilitating accurate element localization. Finally, a near-real-time projection method was introduced that utilizes the spatial relationships among elements to dynamically incorporate models into a 3D base, enabling a multi-perspective view of site activities. Validated by simulated construction site experiments, this methodology showcased an impressive reconstruction accuracy reaching up to 95%, this underscores its significant potential in enhancing the efficiency of creating a dynamic digital twin model.

Hydropower dams are subjected to soft water penetration during their service lives. Concrete deterioration due to calcium leaching will decrease the durability of concrete and affect dam safety. The long-term performance of concrete dams due to calcium leaching should be evaluated and predicted accurately to complete reinforcement work in a timely manner. In this paper, a methodology that combined microscopic tests and numerical analysis to evaluate the long-term performance of dam concrete due to calcium leaching is proposed. The current state of concrete is evaluated by analyzing the components of sediments and seepage water through microscopic and spectroscopic tests, such as X-ray photoelectron spectroscopy, scanning electron microscopy, and inductively coupled plasma mass spectrometry. The long-term degradation of concrete was predicted by utilizing a multi-scale model of calcium leaching, which considered the micro-pore structure of cement hydrates flux with time. The simulated results using this calcium leaching model showed a good agreement with other experiments. Finally, a real case study including field inspection was performed and the long-term durability of dam concrete was predicted through microscopic tests and finite element analysis method. It implies that the proposed method could provide calculation and theoretical basis for the durability analysis of concrete dams due to calcium leaching.

In this study, a three‐dimensional finite element model was established to simulate the dynamic response of a large‐scale steel‐reinforced concrete composite high‐pile wharf with a rock‐socketed steel sheath. The model is based on the second phase of the Chongqing Orchard Harbor structure project in conjunction with the project “Research on the mechanism of interface damage and energy dissipation of the structure of the large‐scale steel‐reinforced concrete composite high‐pile wharf in inland waters.” The stiffness of frame wharf is studied from the perspective of modal and transient dynamic analysis of structural dynamics. The distribution of the low‐order modal frequency is more uniform. With the increase of the order, the modal frequency of the structure shows a periodical jump. The overall stiffness of the frame structure is larger with the steel sheath, and the longitudinal stiffness is less than the transverse stiffness. Under the action of transverse impact load, the members and joints of the steel‐concrete structure exhibit synchronous mechanical response characteristics in the time domain. The peak values of displacement and stress of the structural joints occur 0.05 s after the peak value of the load‐time history, and the peak value of reverse response of force occurs at 2.3 s, which is markedly smaller than the peak value of the response of load direction. Reducing the local positional stiffness of the load point is beneficial to improve the stress of the entire structure. The weak links of the frame structure appear at the joints of the members. Because of the hoop action of the steel sheath, the stress of the reinforced concrete pile core is more uniform. The peak value of the equivalent stress of the steel sheath member is generally larger than that of the reinforced concrete pile core, and the stress is highly concentrated at the joints of the steel tube longitudinal and transverse braces.

The findings of an experimental study that was undertaken to investigate the performance of concrete‐filled steel tubular members subjected to lateral loads are reported in this study. Columns of pure concrete, concrete with reinforcing bars, and two steel tube thicknesses were considered. Two different tests were conducted in this study. One test is used to research the performance of steel tube‐reinforced concrete model piles under a lateral loading. The other test is used to research the effect of the depth of rock embedment for piles embedded in a foundation to simulate actual engineering applications in an experimental study. According to these test results, a detailed analysis was carried out on the relationships, such as the stress‐strain and load‐displacement relationships for the specimen. These tests show that the steel tube thickness and steel bars will significantly enhance the lateral bearing capacity and rigidity of the composite components. Additionally, the ultimate bending moment formula of a steel tube‐reinforced concrete pile is deduced. The comparison of the calculated results with the experimental results shows that this formula is applicable for this type of pile foundation.

To investigate the mechanical properties of dowel action under fatigue loads, 3 reinforced concrete specimens with different bar diameters (12 mm, 20 mm, and 25 mm) were subjected to the fatigue loading and were designed to investigate the attenuation character of dowel action and the fatigue failure modes. The load transfer mechanism of the bond was analyzed based on the 3D relative motions between reinforcing bars and subgrade concrete. Fatigue damage effects were considered in the model. A deterioration coefficient based on the deformation path was defined to represent the accumulation of fatigue damage. Verification of the model was conducted by comparing the analysis results with experimental data obtained in this study and from the literature, and satisfactory agreement was obtained.