Comparison for Solid Concrete-filled Circular Steel Tubes Load-carrying Capacities in Frame Structures Basing on Chinese codes

Under the influence of material defects, structural grooving, environmental corrosion, and other factors in engineering, concrete-filled steel tubes incur local defects on their external surfaces that affect their structural integrity and service life. This work conducts axial compression tests on 10 grooving-damaged square hollow concrete-filled steel tube (SHCFST) columns to investigate the effect of grooving damage on their axial compressive ultimate bearing capacity and the effect of steel tubes on concrete confinement. It explores the effects of three parameters, namely, the length of grooves, presence of slots in internal and external steel tubes, and orientation of grooves, on structural static performance. This study analyzes the loading, failure mechanisms, and axial compressive ultimate bearing capacity of grooving-damaged SHCFST columns. Results indicate that grooving weakens the steel tube’s confinement effect on the concrete core, reducing the axial compressive ultimate bearing capacity of specimens. On the basis of this experimental research, a method for calculating the axial compressive ultimate bearing capacity and axial compressive stiffness of grooving-damaged SHCFST columns is proposed. The calculation results closely align with experimental outcomes, providing valuable insights for related scientific research and engineering applications.

Performance of stirrup-confined concrete-filled steel tubular stub columns under axial loading: A further investigation

A reliability analysis of the axial compressive load bearing capacity of postfire reinforced concrete (RC) columns strengthened with carbon fiber reinforced polymer (CFRP) sheets was presented. A 3D finite element (FE) model was built for heat transfer analysis using software ABAQUS. Based on the temperature distribution obtained from the FE analysis, the residual axial compressive load bearing capacity of RC columns was worked out using the section method. Formulas for calculating the residual axial compressive load bearing capacity of the columns after fire exposure and the axial compressive load bearing capacity of postfire columns retrofitted with CFRP sheets were developed. Then the Monte Carlo method was used to analyze the reliability of the axial compressive load bearing capacity of the RC columns retrofitted with CFRP sheets using a code developed in MATLAB. The effects of fire exposure time, load ratio, number of CFRP layers, concrete cover thickness, and longitudinal reinforcement ratio on the reliability of the axial compressive load bearing capacity of the columns after fire were investigated. The results show that within 60 minutes of fire exposure time, the reliability index of the RC columns after retrofitting with two layers of CFRPs can meet the requirements of Chinese code GB 50068 (GB 2001) for safety level II. This method is effective and accurate for the reliability analysis of the axial load bearing capacity of postfire reinforced concrete columns retrofitted with CFRP.

Axial compressive behavior of corroded double-steel-plate composite shear wall with binding bars

Elliptical concrete-filled steel tubes (CFST) are structural elements where concrete is embedded in an elliptical steel tube, offering significant advantages such as effective axial compression resistance. These structures are widely applied in civil engineering and critical infrastructure like airport terminals and bridges. While most CFST research focuses on circular and rectangular cross-sections, there is limited study on elliptical CFST. The emergence of neural networks offers a novel approach to calculate the compressive capacity of elliptical CFST. Neural networks can learn from sample data without predefined assumptions, uncovering nonlinear relationships between the data and results. Furthermore, they can predict new variables, overcoming the constraints of traditional experimental and finite element methods. This paper proposes an advanced calculation method to quickly and accurately assess the axial compressive bearing capacity of elliptical CFST short columns. The model integrates neural network capabilities with unified strength theory, simulating the bearing capacity of elliptical CFST stub columns. Through simulation training, the method is validated for calculating the compressive performance of elliptical CFST. The findings demonstrate that this approach not only enhances computational efficiency but also provides a reliable and optimized tool for structural evaluation. The calculation efficiency of the compressive capacity of elliptical CFST based on a neural network is increased by about 23.7%.

To study the axial compression performance of high-strength recycled concrete columns with built-in square steel tubes, ABAQUS software was used to model and analyze two existing test specimens, verifying the accuracy of the model. On the basis of a reliable model, parameter analysis was conducted on 13 specimens, with variable parameters including square steel tube thickness, square steel tube strength, and slenderness ratio. The results showed that the established finite element model exhibited longitudinal reinforcement buckling and steel tube tearing deformation consistent with the experimental results, and the height of the load axial displacement curve was consistent. The average error of the ultimate bearing capacity was within 5%; The increase in steel tube thickness has little effect on the axial compression bearing capacity and stiffness, while the increase in steel tube yield strength has a significant impact on the axial compression bearing capacity and residual bearing capacity; With the increase of slenderness ratio, the axial compression stiffness and ultimate bearing capacity of composite columns are obviously degraded. A numerical calculation method between the axial compression stability coefficient and slenderness ratio is fitted, which can be used as a reference for the design of composite columns.

Successful experimental and theoretical studies have promoted fiber-reinforced polymer (FRP) as an innovative strengthening material for metal columns in structural engineering, highlighting the necessity for an effective and reliable calculation method for such strengthened members. Here, based on existing experimental data, an advanced method using an artificial neural network (ANN) is developed to predict the axial compression bearing capacity (ACBC) of FRP-strengthened hollow section metal (FSHM) columns, where FRP strengthening includes wrapping/bonding FRP sheets/laminates; this method considers realistic conditions, incorporates a variety of parameters, and produces accurate and fast predictions. First, a multilayer perceptron (MLP) neural network was applied. By studying the optimization algorithm, learning rate, hidden vector and activation function, an optimal ANN model was established, which yielded better predictive accuracies and safety than existing calculation methods. Using the validated model, an prediction program was developed that promptly generated predictions of ACBC with a high reliability. Finally, a sensitivity analysis was performed to further assess the effects of key parameters on the behavior of FSHM columns to provide practical recommendations for their design.

Oil and its derivatives such as gasoline, gasoil and ‎kerosene are the main sources of energy in the transport and industry sectors, and also the most common ‎soil contaminants. Oil contamination of the soils as a serious geoenvironmental problem not only affects soil quality ‎but also changes its geotechnical properties. Any changes in the geotechnical properties of the soils affect the axial bearing capacity of pile. The main objective of the current study is to determine the effects of various concentrations of different oil ‎products, as well as different soil relative densities, and thickness of the contaminated sand layer on the load–displacement (axial compressive) behaviour of two ‎instrumented, close-ended steel pipe piles with different diameters and slenderness ratios implemented in an oil-contaminated sandy soil through physical modelling. Tests results were compared with the CFEM ‎analytical method of calculating pile axial bearing capacities. Results showed that increasing the percentage of the oil in the soil reduces the values of net total, toe and shaft bearing ‎capacity of the pile. The type of the oil had a remarkable effect on the bearing capacities of the pile. The higher the kinematic ‎viscosity, the lower the amount of bearing capacities. ‎Comparing the measured and predicted values of bearing capacity based on modified CFEM ‎method concluded that, although a good agreement can be seen between the results of shaft capacity, the ‎CFEM method with modified bearing capacity factors could not predict the effects of oil contamination ‎on the toe bearing capacities of piles precisely.

Axial compressive performance of ultra-high performance concrete-filled steel tube stub columns at different concrete age

Axial performance of concrete-filled GFRP tube columns jacketed by outer stainless steel tube and sandwiched concrete

Cold-formed steel framing walls with infilled lightweight FGD gypsum Part II: Axial compression tests

Interface bonding conditions between concrete and steel materials play key roles in ensuring the composite effect and load-carrying capacity of concrete-steel composite structures such as concrete-filled steel tube (CFST) members in practice. A method using both surface wave and electromechanical impedance (EMI) measurement for detecting the existence and the location of inaccessible interface debonding defects between the concrete core and steel tube in CFST members using piezoelectric lead zirconate titanate (PZT) patches as actuators and sensors is proposed. A rectangular CFST specimen with two artificially mimicked interface debonding defects was experimentally verified using PZT patches as the actuator and sensor. By comparing the surface wave measurement of PZT sensors at different surface wave travelling paths under both a continuous sinusoidal signal and a 10-period sinusoidal windowed signal, three potential interface debonding defects are quickly identified. Furthermore, the accurate locations of the three detected potential interface debonding defects are determined with the help of EMI measurements from a number of additional PZT sensors around the three potential interface debonding defects. Finally, the accuracy of the proposed interface debonding detection method is verified with a destructive observation by removing the local steel tube at the three detected interface debonding locations. The observation results show that the three detected interface debonding defects are two mimicked interface debonding defects, and an unexpected debonding defect occurred spontaneously due to concrete shrinkage in the past one and a half years before conducting the test. Results in this study indicate that the proposed method can be an efficient and accurate approach for the detection of unknown interface debonding defects in existing CFST members.

A new type of square concrete-filled steel tubular (SCFST) column is proposed, which is characterized by transverse stiffened bars inside the steel tube to improve the effective constraint performance of the concrete core. The experiment of this kind of composite material under axial compression was carried out. The results showed that the bearing capacity of the SCFST column reinforced by internal transverse stiffened bars increased by 4.5%-15% than that of the ordinary SCFST column. The transverse strain is smaller than the SCFST column. As the diameter of the reinforcement increases and decreases the spacing of bars, the axial load bearing capacity increased. The transverse strain of the member decreased obviously. It is noted that the confinement performance of the concrete core of this type was improved to some extent. At the same time, based on the unified theory, the simplified calculation formula of axial compression bearing capacity is derived.

Behavior of ultra-high-performance concrete (UHPC) encased concrete-filled steel tubular (CFST) stub columns under axial compression

Based on unified strength theory solution of thickness cylinder, according to the introducing concrete strength reduction factor and equivalent restriction factor, this paper deduced the axial compressive bearing capacity formula of concrete-filled double skin steel tubular columns of octagon section. Compared the results of the paper with the experiment results，both coincide in good condition. The results show that the theoretical formula are correct and viable. The theoretical formula is expected to provide a theoretical foundation to the research of concrete-filled double skin steel tubular columns of octagon section.And it provides references for the engineering design.