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Concrete-filled steel tube (CFST) columns are widely used in civil engineering because of their excellent bearing capacity; however, the reinforcement of CFST columns lacks effective measures. To strengthen CFST columns quickly and effectively, two methods, namely, winding FRP (fiber reinforced polymer) or steel strips, were explored in this work. Two unconfined CFST columns, eight FRP-strengthened CFST columns and four welded steel strip-strengthened CFST columns were manufactured and tested. The failure modes and axial load–strain curves of all specimens under compression load were concluded and compared. The effects of the primary parameters, such as FRP layers (1, 2, 3 and 4 layers) and steel strip thickness (3.0 and 6.0 mm), on the bearing capacity and deformation capacity were also investigated. The ultimate load of CFST columns increased from 28.72 to 64.16% after being confined by FRP with one to four layers. The ultimate load of the welded steel strip-strengthened CFST column with 3.0 mm steel strips and 6.0 mm steel strips increased by 28.46% and 49.82%, respectively, compared with the unconfined CFST column. Thus, the increase in FRP layers and steel strip thickness can markedly improve the compressive behavior of the FRP/welded steel strip-strengthened CFST columns. The cost performance of the two different reinforcement methods also showed that the cost of the welded steel strip-strengthened CFST column is nearly 40% of that of the FRP-strengthened CFST column when the same strengthening effect was obtained, which indicated that the welded steel strip-strengthened CFST column is more cost-efficient than CFST columns confined by FRP. Finally, six existing models for the ultimate load of FRP-strengthened CFST columns were presented and evaluated. From the evaluation results, the Zhang et al.’s model, Lu et al.’s model and Hu et al.’s model for FRP-strengthened CFST columns were shown to provide the best applicability and accuracy. Based on the Mander et al.’s model, a model for the ultimate load of welded steel strip-strengthened CFST columns was proposed and evaluated. The proposed model can accurately predict the ultimate load of welded steel strip-strengthened CFST columns.

This work aimed to investigate the effects of steel tube corrosion on the axial ultimate load-bearing capacity (AULC) of circular thin-walled concrete-filled steel tubular (CFST) members. Circular thin-walled CFST stub column specimens were made of steel tubes with various wall-thicknesses. These CFST column specimens were subjected to an accelerated corrosion test, where the steel tubes were corroded to different degrees of corrosion. Then, these CFST specimens with corroded steel tubes experienced an axial static loading test. Results show that the failure patterns of circular thin-walled CFST stub columns with corroded steel tubes are different from those of the counterpart CFST columns with ordinary wall-thickness steel tubes, which is a typical failure mode of shear bulging with slight local outward buckling. The ultimate strength and plastic deformation capacity of the CFST specimens decreased with the increasing degree of steel corrosion. The failure modes of the specimens still belonged to ductile failure because of the confinement of outer steel tube. The degree of steel tube corrosion, diameter-to-thickness ratio, and confinement coefficient had substantial influences on the AULC and the ultimate compressive strength of circular thin-walled CFST stub columns. A simple AULC prediction model for corroded circular thin-walled CFST stub columns was presented through the regression of the experimental data and parameter analysis.

In the wake of modern construction practice that minimizes the top storey floor area compared to the bottom storey, the inclined columns are inevitable when floating columns are avoided. Hollow tubular steel inclined columns with variable moment-resisting bracings are employed in modern construction to enhance structural performance, especially under lateral loads such as wind and seismic forces. These systems integrate columns' inherent strength and aesthetic appeal with strategically designed bracing to optimize load distribution and overall stability. In this study, inclined column specimens featuring knee-type moment-resisting bracings (conventional, 50 mm, 100 mm, and 150 mm) were investigated experimentally to evaluate the structural performance and identify the impact of varying bracing dimensions on load and displacement characteristics. In addition to this experimental work, an analytical study using the finite element analysis software ABAQUS was performed to simulate the behaviour of these column configurations. The experimental and finite element analysis results revealed that the inclined column member with 80° inclination and 50 mm moment-resisting bracings exhibited superior performance with a maximum ultimate load of 68 kN and 80 kN, respectively. This configuration also demonstrated a minimum displacement, emphasizing its enhanced stability, whereas the other configurations resulted in a minimum load-bearing capacity with maximum displacement, which reduced the structural efficiency. From the analytical study, it was also observed that inclined column members with 50 mm moment-resisting bracings exhibit maximum stresses and rotation angles that provide an ideal balance between strength, stability, and material efficiency compared to all the other members. Thus, a member with 50 mm moment-resisting bracing was considered as the optimum member.

The axial behavior of self-consolidating concrete (SCC) columns confined with engineered cementitious composite (ECC) was investigated through experimental and analytical investigations. Both square and cylindrical-shaped columns were considered in the study. The other variables of the study were the presence or absence of longitudinal reinforcement, the thickness of ECC confinement, and the loading types. The behavior of the columns was evaluated in terms of the axial load-deflection response, strain characteristics, ultimate load-carrying capacity, ductility, energy absorption capacity, and modes of failure. It was found that the ECC confinement significantly increased the ultimate axial load capacity and energy absorption of the SCC columns. The confined columns also exhibited enhanced ductile behavior compared to the corresponding core column under axial loading. The confined concrete strengths predicted by existing analytical models were found to be in satisfactory agreement with the experimentally obtained values. Keywords: axial behavior; confined column; ductility; energy absorption capacity; engineered cementitious composite (ECC); load-deflection response; self-consolidating concrete (SCC); ultimate load capacity.

The ultimate load capacity of extradosed cable-stayed bridges (ECSB) is the basis for structural design and bridge management. The ECSB is a new combination system of both cable- stayed bridges (CSB) and multi-span continuous bridges. It is difficult to predict the ultimate load capacity of ECSB due to its particular form. In this paper, a novel method is presented to predict the ultimate load capacity of ECSB. The procedure of predicting ultimate load capacity consists of two steps. The first is that the ECSB can be equivalent to a multi-span continuous girder with the analogy method; The second is that structural configuration is developed when the live load can form the plastic hinge (PH) and it can determine the load locations using influence lines (IL). Finally, the proposed method is validated with other analytical solutions and numerical results. The results show that the proposed method agrees with previous research findings and the finite element method (FEM). It demonstrates that the proposed method can predict the ultimate load capacity of ECSB.

Determining the bearing capacity or ultimate load of piles for practical pile foundation design is of utmost importance, and it relies on the analysis of load-settlement (Q-S) curves obtained from static load tests. This paper focuses on evaluating the bearing capacity of a long-bored pile, considering cases where the Q-S curve does not reach a critical state. To achieve this, three different approaches are employed using field data from the Q-S curve. These approaches include 3D finite element analysis (3D-FEA) based on back-analysis techniques, extrapolated approximating correlations derived from previous research studies (such as Chin-Kondner, Decourt, Hansen 80% criterion, and Vander Veen), and four newly proposed mathematical functions. The results reveal that the extrapolated curves obtained from the approximating correlations of Chin-Kondner, Decourt, Hansen 80% criterion, Vander Veen, and the four suggested mathematical functions closely approach the Q-S curve, demonstrating an asymptotic behavior. In addition, extrapolation according to four approximating correlations and two mathematical functions (y = ax4 + bx3 + cx2 + dx + e and 1y=a+bx) provides the predicted results of the ultimate load matching the one of the 3D-FEA.

In this paper, we conducted the axial compression test on one improved welded concrete filled L-shaped steel tube (IWCFLST) stub column and two stirrup-enhanced IWCFLST stub columns. The experimental results indicate that the stirrup-enhanced IWCFLST stub columns exhibit better compressive mechanical properties. The stirrups can increase the axial compressive load-bearing capacity by up to 35% and the ductility coefficients by 77%. The impact of the equivalent stirrup ratio on the axial compression mechanical behavior was investigated. Three-dimensional (3D) solid finite element (FE) model of the specimens was constructed by ABAQUS. Parametric analysis was performed and the restriction action of IWCFLST stub column under axial compression was studied. The numerical study revealed the working mechanism of stirrups, steel tubes on concrete, while direct confinement of concrete elevates its axial stress level. Considering the shape and the stirrups, the axial compression ultimate load-bearing capacity design method of the IWCFLST stub column was proposed, providing data support for the promotion and application of special-shaped CFST columns.

China's rapid urbanization intensifies third-party excavation risks to underground gas pipelines, escalating emergency repairs and accident hazards. This study systematically evaluates the mechanical response and safety of buried steel and polyethylene (PE) gas pipelines under excavation loads through integrated numerical simulations and theoretical analysis. A 3D finite element model incorporating soil-pipeline-bucket interactions was developed using ABAQUS to simulate the dynamic response of steel and PE pipelines. Key parameters, including excavation force, bucket tooth number, burial depth, pipe diameter, wall thickness, and internal pressure, were analyzed to evaluate their sensitivity and impact on pipeline integrity. The second-order elastic slope criterion was employed to determine the ultimate load under various excavation conditions, providing a reliable framework for safety assessment. This study provides valuable insights into the safety assessment and integrity management of buried gas pipelines subjected to third-party excavation activities.

The integration of cutting-edge technologies into reinforced concrete (RC) design is reshaping the construction industry, enabling smarter and more sustainable solutions. Among these, machine learning (ML), a subset of artificial intelligence (AI), has emerged as a transformative tool, offering unprecedented accuracy in prediction and optimization. This study investigated the flexural behavior of steel rebar RC beams, focusing on varying concrete compressive strengths via theoretical, experimental and ML analysis. Nine steel rebar RC beams with low (SC20), moderate (SC30) and high (SC40) concrete compressive strength, measuring 150 × 200 × 1100 mm, were produced and subjected to three-point bending tests. An average error of less than 5% was obtained between the theoretical calculations and the experiments of the ultimate load-carrying capacity of reinforced concrete beams. By combining three-point bending experiments with ML-powered prediction models, this research bridges the gap between experimental insights and advanced analytical techniques. A groundbreaking aspect of this work is the deployment of 18 ML regression models using Python’s PyCaret library to predict deflection values with an impressive average accuracy of 95%. Notably, the K Neighbors Regressor and Gradient Boosting Regressor models demonstrated exceptional performance, providing fast, consistent and highly accurate predictions, making them an invaluable tool for structural engineers. The results revealed distinct failure mechanisms: SC30 and SC40 RC beams exhibited ductile flexural cracking, while SC20 RC beams showed brittle shear cracking and failure with sudden collapse.

The usage of carbon fiber–reinforced polymer (CFRP) to strengthen cracked steel structures can effectively improve its bear capacity, so it has been extensively used in recent years. The degradation of interfacial bonding is one of the most important factors affecting the durability of CFRP–steel structures under a freeze–thaw(F–T)/wet–dry (W–D) environment. In this study, epoxy resin adhesive (ERA) dog-bone specimens and CFRP–steel double-lap joints (bonded joints) were prepared. F–T/W–D cycles experiment and tensile tests of the ERA specimens and the bonded joints were also performed. Under F–T/W–D cycles, the main properties of the ERA specimens and the bonded joints were examined. Results indicated that fracture failure occurred in all ERA specimens. The hybrid failure modes of fiber peeling on the surface of CFRP plate and the bonded interface peeling between the CFRP plate and ERA layer primarily occurred in the bonded joints. The failure of both of them can be considered to be brittle, which was unaffected by the F–T/W–D cycles. With increased F–T/W–D cycles, the ultimate load and tensile strength of the ERA specimens initially increased and then decreased, whereas the elastic modulus initially increased and then remained unchanged. The ultimate load of the bonded joints decreased gradually. Based on the relationship between the interfacial bond-slip parameters and the number of F–T/W–D cycles, the bond–slip model of the bonded joints was established. The proposed relationship was validated by comparing with the experimental bond-slip relationships and the predicted relationships under the F–T/W–D cycles.