Bearing Capacity Model Research Articles

The axial compression mechanical performance of CFRP-confined fully replaced nonnatural coal gangue aggregate columns after freeze[sbnd]thaw cycles

With the continuous mining of coal worldwide, the accumulation of coal gangue, a byproduct of coal production, has increasingly posed severe environmental challenges. To mitigate the environmental pollution caused by coal gangue, this paper proposes the use of processed coal gangue as a replacement for coarse aggregates in concrete. Additionally, carbon fiber-reinforced polymers (CFRP) are employed to confine these square concrete columns, with the aim of expanding the application of nonnatural coal gangue concrete in freezethaw environments. Taking the number of CFRP layers, number of freezethaw cycles, and concrete strength grade as variables, a total of 54 samples were designed. Experimental and theoretical analyses were conducted to investigate the mechanical behavior of CFRP-confined fully replaced nonnatural coal gangue aggregate (FNCGA) columns. The specific conclusions are as follows: (1) Under a freezethaw environment, the stressstrain behavior of the CFRP-confined FNCGA columns undergoes three stages: an elastic ascending stage, a plastic descending stage, and a plastic ascending stage. (2) When the number of freezethaw cycles increases from 100 to 300, the Poisson's ratio of the elastic stage of the sample exhibiting an upward trend. (3) For the three-layer CFRP confined sample, the volumetric strain is positive (in compression), and the bearing capacity of the sample exceeds that of the unconfined concrete by approximately 10%. (4) Compared with existing models and experimental results, the bearing capacity and stressstrain model proposed in this study have greater accuracy, enabling better simulation of the mechanical performance of CFRP-confined FNCGA columns.

Load-bearing characteristics of surface conductor in deepwater gas hydrate formations

The surface conductor is the first structural casing in deepwater natural gas hydrate (NGH) development, bearing the top load while suspending the casings of various layers. NGH decomposition leads to formation settlement, changing the mechanical properties of the formation and reducing the bearing capacity of the surface conductor, threatening the safety and stability of the wellhead. Understanding the bearing characteristics of the surface conductor in the hydrate formation can guide the safe drilling operation in the field. By introducing the negative skin friction theory of pile foundations and based on conventional bearing capacity models, a method for calculating the bearing capacity of surface conductors in NGH formations was developed. Using an NGH drilling simulation apparatus, the accuracy of the bearing capacity theoretical model was verified, empirical coefficients under different conditions were obtained, and the influence of soil parameters, hydrate saturation, and decomposition temperature on the bearing capacity of surface conductors was quantified. The results indicated that compared to clay, sandy soils have higher porosity and significantly weakened strength after the decomposition of NGH; when the hydrate saturation in the formation is 20%, the reduction in bearing capacity of the surface conductor in sand exceeds 30%, and in clay soils, it decreases by 25% after complete decomposition of NGH; as the hydrate saturation increases, the reduction in the bearing capacity of surface conductors after decomposition becomes more significant. Verified through Experimentation, the error of the hydrate-bearing strata-bearing capacity model is around 10%. For short-term test production operations of NGH in water, the design depth for surface conductors is around 100 meters. These research results can provide a scientific theoretical basis for the design of conductor depth below the mud， and reduce operational risks.

Research on the mechanism of impact of vibrational loads on the bearing capacity of drilling surface conductor

The surface conductor is the first structural pipe in the development of deep-water oil and gas resources, bearing the top load and suspending various casing layers. Vibrational loads can cause soil structural damage and increase pore pressure, reducing the bearing capacity of the surface conductor and threatening the safety and stability of the subsea wellhead. Based on the vertical force analysis of the surface conductor and considering the impact of vibrational loads on soil strength, a model for the vertical bearing capacity of the surface conductor was established. Utilizing the dynamic Winkler model for pile foundation horizontal dynamic response, the surface conductor was simplified as a bending beam subjected to harmonic vibration, and a control equation for lateral deformation of the surface conductor was established. The effects of vibration load amplitude and frequency on the vertical bearing capacity of surface conductors were analyzed through simulation experiments, resulting in an equivalent bearing capacity coefficient for surface conductors ranging from 0.88 to 0.97. Combining the engineering data from a deep-water block in the South China Sea, the reliability of the theoretical calculation model was validated. The analysis indicates that the maximum bending moment of the surface conductor is approximately 6m below the mudline; low-frequency(0.05Hz–0.2Hz) vibrational loads can reduce the ultimate bearing capacity of the surface conductor by 3%–11%, with the effect gradually diminishing over time. This research provides a theoretical basis for the design of surface conductor in deep-water oil and gas wells.

Influence of bolt preload of anchors on bond-slip behavior of fiber fabric-steel interface

Bond-slip behavior is a common failure mode in steel structures reinforced with fiber fabric. Premature debonding of the fiber fabric significantly impacts the effectiveness of steel structure reinforcement. In this study, a gripping anchor is proposed to enhance the reliability of the interface between fiber fabric and steel plates. Experimental investigations were conducted to analyze the influence of anchor bolt preload on the double shear joint between fiber fabric and steel plates. 41 specimens were prepared and tested to explore the effects of parameters such as bolt preload, anchor position, number and type of fiber fabric layers, and bond length on load-bearing capacity. Comparative analyses were conducted on failure modes, ultimate loads, and stress-strain distributions of the specimens. Experimental results indicate that the position of the anchor has a minimal impact on the ultimate bearing capacity of the specimen. However, anchors positioned closer to the joint end exhibit lower ductility upon failure. A novel predictive model was developed to characterize the bond-slip behavior of preload applied to carbon fiber fabric and steel plates. The theoretical model of the ultimate bearing capacity in the yield stage fits well with the experimental results of specimens with three layers of carbon fiber fabric, with a difference range of 0.34 % to 14.97 % compared to actual results. This indicates that the model has high accuracy in predicting stress-strain and bearing capacity.

Time-variant reliability analysis of corroded suspender of suspension bridge based on data-driven

The suspender of a suspension bridge is susceptible to corrosion due to environment, material, load, and other factors, which leads to the reduction of its bearing capacity with time, thus adversely affecting the safety and durability of the suspension bridge. Time-variant reliability analysis can consider the time-variant characteristics and uncertainties of each variable, and can better reveal the degradation of corrosion suspender resistance with time. However, due to the complex and highly nonlinear characteristics of the stress situation, the functional function of the suspender is often implicit, and the traditional time-variant reliability analysis method cannot be directly solved. To solve the problem of the implicit function of the suspender, An Adaptive Support Vector Regression with Extreme Response Surface (ASVR-ERS) method was proposed, and it was applied to the time-variant reliability analysis of corroded suspender of a suspension bridge. According to the corrosion characteristics of steel wire in suspenders, a hybrid constitutive model for calculating the ultimate bearing capacity of corroded suspenders was proposed. Furthermore, the time-variant reliability and residual life of corroded suspenders of a self-anchored suspension bridge were systematically studied. The results show that: Compared with the existing methods, the ASVR-ERS method can use fewer training samples to achieve higher computational accuracy. When calculating the ultimate bearing capacity of a corrosion suspender, the phenomenon of ductility degradation caused by steel wire corrosion in the suspender cannot be ignored, and the mixed constitutive model of the ultimate bearing capacity of a corrosion suspender is more reasonable. When the service time of the bridge is the same, the reliability of the suspender in the middle span of the main span is the smallest, and the reliability of the suspender in the full bridge gradually decreases from the bridge tower position to the middle span direction and the side span direction. The decrease rate of suspender reliability is the fastest at the beginning of corrosion and gradually slows down with the deepening of the corrosion degree. When the sheath has the minimum damage and the maximum circumferential damage and reaches life, the suspender section loss rate is between 10 % and 15 %. Compared with improving the safety factor of the suspender, delaying the breakage time of the sheath can improve the life expectancy of the suspender more obviously.

Experimental Investigation of a Novel CFRP-Steel Composite Tube-Confined Seawater-Sea Sand Concrete Intermediate Long Column

In order to fully utilize sea sand in offshore engineering, a novel carbon fiber-reinforced polymer (CFRP)-steel composite tube-confined seawater-sea sand concrete (FCTSSC) column structure has been developed. This study conducts experimental investigations on FCTSSC intermediate long columns for the first time. It investigates the failure modes and the impact of the external CFRP layers number on the axial compression performance. The results reveal that the FCTSSC intermediate long column specimens exhibit the failure modes of global buckling and localized steel tube bulging. After CFRP restriction, the ultimate load bearing capacity of the specimens increased from 12.51% to 20.87%. The ultimate load bearing capacity, its enhancement percentage, and peak lateral deformation are all positively correlated with the external CFRP layers number. Finally, a summary and assessment were conducted on the applicability and accuracy of the existing load bearing capacity models, providing a reference for subsequent research.

Study on the mechanism of soil erosion by submerged water jet vertical scouring in cohesive soils

The water jet trenching technique is widely used in the burial of submarine pipelines. However, its application in cohesive soils often leads to complexity in trench morphology and challenges in predicting trench dimensions due to unclear soil erosion mechanisms. These issues significantly impact pipeline burials. To investigate the soil erosion mechanism of water jet trenching in cohesive soils, two-dimensional physical simulation experiments of submerged vertical water jet erosion were conducted. The influence of jet pressure, impingement height, and nozzle diameter on the shape of the scour hole was analyzed. The erosion damage patterns of water jets on cohesive soils were studied, and a theoretical model for the development of scour holes was established. The study revealed that when the jet velocity reaches 1000 m/s and the nozzle diameter reaches 1 mm, a contracted neck forms at the upper part of the scour hole. The appearance of the contracted neck is due to excessive jet impact energy causing impact shear failure in the soil. The effective height and width of the contracted neck increase with jet pressure and nozzle diameter and decrease with impingement height. Based on Prandtl's bearing capacity model, a model for predicting impact shear failure in cohesive soils was established, and a predictive formula for the effective height and diameter of the neck was proposed. Experimental validation confirmed the accuracy of the predictive formula. These findings provide theoretical support for the application of water jet trenching techniques in cohesive seabed soils.

Evaluation Model for Bearing Capacity of Grouting Sleeves Based on Conventional Material Parameters

The existing bearing capacity model for grouting sleeves is synthesized in this study. Utilizing the principles of thick-walled cylinders in elastic mechanics, a comprehensive ultimate bearing capacity model for grouting sleeves is developed using conventional material parameters. To validate the efficacy of the model, 18 steel bar grouting sleeves of varying anchor lengths, steel bar diameters, and designs were tested. The outcomes indicate minimal errors in the computational results and demonstrate superior applicability when juxtaposed with established grouting sleeve bearing capacity formulas.

Compressive behavior of seawater and sea sand concrete-filled FRP-steel composite multi-tube hollow columns

To further explore sustainable development in high-performance marine engineering structures, this study introduced a new approach - a hybrid structural member called the seawater and sea sand concrete (SWSSC)-filled fiber-reinforced polymer (FRP)-steel composite multi-tube hollow column (S-MTHC). The S-MTHC consists of double-walled FRP-steel composite tubes filled with SWSSC, along with several small-diameter SWSSC-filled FRP tubes (known as SSFFTs). Monotonic axial compression tests were conducted on the S-MTHCs, and a bearing capacity model was established. The test results demonstrated that the presence of FRP-steel composite tubes and SSFFTs significantly improved the axial compressive behavior of S-MTHCs. Increasing the number of external FRP layers or SSFFTs enhanced the strength and ductility of the hybrid column. The influence of increasing concrete strength or FRP tube thickness in SSFFTs, however, was relatively negligible. Additionally, specimens with carbon FRP (CFRP) tubes in SSFFTs exhibited higher bearing capacity while maintaining similar ductility.

Challenges in the measurement of cross-shore geotechnical characteristics of sandy beach surface sediments

Geotechnical properties of surficial beach sediments affect beach erosion and shoreline changes. This study sets out to measure relative density, moisture content, friction angle, and shear strength of sandy beach surface sediments from dune to swash zone towards the goal of assessing their importance in sandy beach morphodynamics. Methods of sediment sampling, a conductivity based moisture probe, field penetrometers, and a field vane shear were deployed to collect data at the sandy Atlantic-side beach in Duck, North Carolina. The tools used were assessed based on their operability in the beach environment and data quality, and results are discussed in the context of beach morphodynamics. A digital field vane shear provided an efficient and direct method of measuring shear strength, but the difficulty of computing stresses on the failure plane, which is necessary to validate the results, ultimately reduced the usability of this instrument. The results from three penetrometers were compared to a partially-saturated bearing capacity model, where a portable free-fall penetrometer yielded the best fit. However, a modified velocity-dependent strain rate correction factor (K=0.31vi) was required to convert dynamic sediment resistance to a quasi-static resistance for the partially saturated sands. A small-scale digital push in penetrometer also achieved a positive correlation when compared to moisture content, but the small tip diameter (5 mm) coupled with the grain size at the beach (0.35 mm) raised concerns about the ability to derive an accurate measure of strength. It was determined that estimating strength parameter using a partially saturated bearing capacity model was appropriate for water contents less than 25% by volume, or anywhere in the crosshore above the swash to the dune. Relative density and moisture content were found to be closely linked, with partial saturation resulting in samples that featured negative relative densities up to −40%.

Experimental study on flexural behavior and bending capacity prediction of Q550E steel beams within corroded shear span

An experimental study is carried out to investigate the degradation behavior of Q550E HPS steel beams with corroded shear span. At first, tensile tests of 15 pieces of steel are undertaken to obtain the degradation law of mechanical property parameters. Four steel beams with different corrosion damage levels in shear span are designed by electrochemical accelerated corrosion. The flexural loading tests of corroded steel beams are conducted, and the mechanical response of local corrosion to steel beams behavior is discussed. The necessity of lateral bracing is discussed theoretically. Considering the constitutive model affected by corrosion and the role of stiffeners, a predictive model of bending bearing capacity is proposed. The results show that the increasing corrosion damage will cause the failure position to move from mid-span to shear span, and the failure mode will shift from mid-span compressive flange buckling to bending-shear buckling, and finally appear web buckling. Corrosion damage level higher than 10% will lead to insufficient strain development. The proposed model can predict the flexural capacity and deflection well. Compared with the test results, the bearing capacity and deflection of corroded HPS beams are predicted by the nonlinear iterative method with high accuracy.

Research on calculation model for ultimate bearing capacity of tensile type anchor cables and the shape of internal fracture surface in anchorage segment

AbstractThe generalized model and parameter equation for the internal fracture surface of tensile type anchor cable anchorage section are constructed, and the calculation model of ultimate bearing capacity is derived based on the principle of limit equilibrium. The shape of the internal fracture surface in the anchorage section and the expression of its parameter equation are experimentally studied, and the variation law of the parameter equation and fracture range with the diameter of the anchor cable and confining pressure is analyzed. The parameter equation is substituted into the calculation model to realize the calculation and verification of the model. Through theoretical derivation, a calculation model of ultimate bearing capacity of anchor cable is obtained, which comprehensively considers the average shear strength of anchorage section, the shape of fracture surface, fracture range and confining pressure. The tests show that according to the magnitude of the confining pressure on the anchorage section, the internal fracture surface takes on two shapes: cylindrical and trumpet‐shaped, the parameter equation of trumpet‐shaped fracture surface obeys logarithmic distribution approximately. The coefficient a decreases with the increase of confining pressure but increases with the increase of anchor cable diameter, the constant b increases with the increase of confining pressure but decreases with the increase of anchor cable diameter. The ranges of horizontal and vertical fracture decrease with the increase of confining pressure, and increase with the increase of anchor cable diameter. The deviations between the theoretical calculation and the experimental results are less than 6.5%.

Limiting physical properties of Technosols formed by the Fundão dam failure, Minas Gerais, Brazil

ABSTRACT Physical properties of the Technosols formed by the tailings deposition may constitute a physical barrier that limits water movement and plant development due to the properties received from those sediments. This study aimed to evaluate the physical quality of the Technosols formed by the deposition of sediments displaced by the Fundão Dam failure, Mariana, Minas Gerais State, Brazil, based on the evaluation of physical properties and Load Bearing Capacity Models (LBCM). For that, three areas under different vegetation types were selected: eucalyptus (Euc), forest with human-assisted revegetation (RF), and forest with native vegetation (NF). Three sampling subareas were demarcated in each area: non-impacted areas (Ni), and Technosols formed in directly impacted areas (Di), and partially impacted areas (Pi). Undisturbed samples were collected in two layers and subjected to the uniaxial compression test after equilibration at five matric potentials. Soil compression curves and LBCM were determined. Soil bulk density (BD), total porosity (TP), organic matter (OM), granulometry, and particle density (PD) were also determined. Clay content was less significant, and the silt and very fine sand content was significantly higher in the Technosols, generating an increase in BD and reduction in TP. Technosols generally exhibited greater load-bearing capacity due to higher pre-consolidation pressure values attained by these soils due to the lower clay and OM contents. High resistance of these soils is one limitation for revegetation of the areas evaluated, being necessary management practices to improve physical properties of the Technosols.

Experimental study on performance of reinforced concrete short columns repaired and strengthened with Basalt fiber ultra-high-performance concrete (BF-UHPC)

To explore the reinforcement effectiveness of basalt fiber UHPC repair materials on concrete structures, this study designed four types of wrapping materials for C40 concrete short columns (inner columns), and formed four types of composite short columns. Axial compression tests were conducted on these specimens to analyze the effects of wrapping material type, wrapping material thickness, and protective layer thickness on bearing capacity. Additionally, a model for axial compressive bearing capacity of short column specimens, based on the Mander model and relevant parameter modifications, was established. The results show that: (1) All designed short column specimens showed brittle failure in the experiment, and the brittle failure phenomenon during the experiment is like that of ordinary concrete short columns constrained by stirrups. (2) The type of wrapping material and the thickness of the wrapping layer are important factors affecting the axial compressive bearing capacity of the entire short column. (3) Adding an appropriate amount of basalt fiber and nano-silica significantly enhances the reinforcing and repairing capabilities of the repair material, thereby improving the load-bearing capacity of the repaired concrete columns. (4) Based on the Mander model and the correction of correlation coefficients, a model for axial compressive bearing capacity of short column specimens was established.

Bending resistance mechanism of prestressed ultra-high performance concrete - reinforced concrete beam based on a full-scale experiment

Ultra-High Performance Concrete (UHPC) is a new type of engineering material with high compressive strength, high tensile strength, and high fracture toughness. Its bending failure mechanism is different from that of traditional concrete beams, which requires a new computational model to describe the bending failure phenomena of the prestressed ultra-high performance concrete - reinforced concrete (UHPC-RC) beam without web reinforcement. Therefore, this paper, through full-scale tests on a 30m prestressed UHPC-RC beam without web reinforcement, captures unique bending failure phenomena, including initial cracking, development of local cracks, and rupture of prestressed steel strands. Considering the tension-compression constitutive relationship of UHPC material, an innovative computational model for bending bearing capacity is proposed. Based on this model, a study on the minimum reinforcement ratio of full prestressed-ordinary steel bars is conducted. The results show that in the bending failure of the prestressed UHPC-RC beam without web reinforcement, excessive tensile strain of steel strands will occur at the local crack location. At this time, the structure does not satisfy the assumption of plane sections, and the introduction of the calculation model of the limit state of external prestressed tendons can effectively match this model, which is highly consistent with the experimental results. The minimum reinforcement ratio of full prestressed-ordinary steel bars is revised to the auxiliary reinforcement ratio of full prestressed-ordinary steel bars, quantifying the minimum reinforcement requirements of ordinary steel bars. The research results of this paper can provide reference for the next step of theoretical research.

Shear Bearing Capacity Prediction of Steel-Fiber-Reinforced High-Strength Concrete Corbels on Modified Compression Field Theory

In order to analyze the shear mechanism of the steel-fiber high-strength concrete corbels, a calculation model for the shear bearing capacity of steel-fiber-reinforced high-strength concrete corbels was proposed based on the modified compression field theory. Considering the existence of residual tensile stress in steel-fiber-reinforced concrete at crack locations, the cracked steel-fiber-reinforced concrete was treated as a continuous material. The constitutive relation of cracked steel-fiber-reinforced concrete and the local stress equilibrium equation were modified. It was compared with the results of 34 steel-fiber high-strength concrete corbels, including those in this paper. The predicted results were compared with the experimental values and the predictions of the Fattuhi model, Campione model, and Russo model to validate the rationality of the proposed model. The results revealed that the mean value between the experimental values and the predicted results of the proposed model is 1.104, with a variance of 0.003, showing good agreement. The proposed model can accurately predict the shear bearing capacity of steel-fiber-reinforced high-strength concrete corbels.

Effects of prestressing wire corrosion on the load response law and bearing capacity of PCCP

The corrosion of prestressed steel wires plays a crucial role in the failure of prestressed concrete cylinder pipes (PCCP). To explore the load-bearing response of prestressed steel wire corroded PCCP and the impact of prestressed steel wire corrosion on the load-bearing capacity of PCCP, a high-precision finite element model of buried PCCP with prestressed steel wire corrosion was established, and a bearing test was conducted based on this model. The results show that the corrosion of prestressed steel wires has the greatest impact on the mortar protective layer and outer core concrete, and the corrosion point at the waist of the pipe is the most detrimental to the pipeline. In addition, as the degree of corrosion of the steel wire increases, the mortar protective layer and outer core concrete at the corrosion point first crack under the action of compressive stress and internal water pressure. Finally, it was verified that the constructed bearing capacity model of PCCP with different corrosion points had high accuracy and could be used to predict the bearing capacity of corroded pipelines. This article can provide theoretical support for the structural safety monitoring and repair of PCCP in service.

Calculation method of deep-water surface conductor bearing capacity based on jetting operation parameters

The surface conductor bears the weight of the Christmas tree, a blowout preventer (BOP), and casings from various layers, and is subject to immense force. It is also affected by the coupling effect of the drilling platform and wellhead load for a long time. The accurate characterization of its bearing capacity is an important guarantee for the safety of deepwater drilling operations. Through the analysis of the installation process, mechanical characteristics, and the theoretical bearing capacity model of the surface conductor, three important stages of jet drilling, lifting up jet string, and running jet string are selected. Carry out the jet operation parameters and vertical force analysis for each stage, reveal the relationship between jet operation parameters and vertical friction of the surface conductor, and establish the real-time bearing capacity calculation model of the surface conductor of each stage. From the operation efficiency and economy, an analysis method of bearing capacity based on an actively pressing downward experiment is established when the well is located in a new block or a shallow block with complex geology. The coefficient of each model is corrected by the known well data, and the adaptability of the bearing capacity checking methods in different stages is evaluated. The results show that the calculation accuracy of the surface conductor bearing capacity model based on jetting operation parameters is more than 85%, and the error is reduced by 20% compared with the conventional model. The calculation accuracy is higher when the calculation is based on the upper friction parameter or lower friction parameter. The calculation method of deep-water surface conductor bearing capacity based on jetting operation parameters has been successfully applied in most deep wells in the South China Sea in recent two years and has become an important method for deep-water surface conductor design, which ensures the stability of the wellhead of deep-water oil and gas wells.

Experimental study on reinforced concrete small-eccentricity compressive column after acid rain corrosion

Six groups of reinforced concrete (RC) columns were designed to investigate the impact of acid-rain corrosion on the eccentric-compression performance of RC columns. The pH, SO42− concentration, and corrosion time were designed as the experimental parameters. The influence of acid-rain corrosion on the acidification depth, spalling thickness, compressive strength, bearing capacity, and deformation capacity of the specimens under eccentric load were analyzed. The results demonstrated that the acidification depth and spalling thickness of concrete increased with corrosion time and were related to the pH and SO42− concentration of acid rain. The rebound-based compressive strength and the ultimate load of RC columns increased first and then decreased with corrosion time. In addition, the macroscopic behavior and mechanical performance of concrete after acid-rain corrosion were revealed by the observed microphase and micro-morphology with XRD and SEM. Finally, a bearing capacity model of RC eccentric compression column after acid-rain corrosion was established.

Experimental and nonlinear analytical of the flexural performance of timber-filled steel tubular composite beams

Steel-timber composite structures present excellent and stable engineering performance. This study presents a novel timber-filled steel tubular composite beam consisting of cold-formed thin-walled rectangular steel and timber.Eleven timber-filled steel tubular composite beams were prepared with various section parameters. A four-point bending test was conducted to evaluate the flexural behaviour of the beams. The failure mode, deflection deformation, and load-carrying capacity were analysed based on the test phenomena and data; the influences of the various parameters on the flexural behaviour were explored.Finally, a simplified mechanical model for flexural bearing capacity was established based on the assumption of plane section and the ideal elastic-plastic.The results show that compared to the timber-filled steel tubular composite beams with composite connection combined the shear screw and the epoxy resin viscose, the beam with a simple epoxy resin adhesive connection has high bearing capacity and deformation performance. The screws have little effect on the bearing capacity and bending stiffness of the composite beam, but can effectively improve the residual bearing capacity of the beam.