Axial Bending Research Articles

Fatigue strength evaluation of case‐hardened components combining heat‐treatment simulation and probabilistic approaches

AbstractIn order to raise the hardness and strength of the surface layer of mechanical components and induce favorable residual compressive stresses, case‐hardening procedures have become established in the heat treatment of steel. In this work, a calculation concept for the fatigue strength of components that have been case‐hardened through carburizing heat treatment is being developed. The residual stress and the load stresses in complex‐shaped, carburized materials are determined using a finite element (FE) model. The fatigue limit of the components is derived using probabilistic methods and taking into account hardness gradients, residual stresses, and non‐metallic inclusions. The model is validated with available axial bending fatigue test data and then used to predict the rotating bending fatigue limit of samples with various geometries and heat‐treatment conditions. This work demonstrates the capability of combining probabilistic and FE‐based modeling to represent complex interactions between variables that affect the fatigue of heat‐treated components, such as steel cleanliness, notch shape, case‐hardening depth, or loading conditions.

Mechanical Performance of Concrete Segment Lining Structure of Shield Tunneling in Different Strata

There are many problems in the development of urban space in China. Among them, urban tunnels generally pass through many sections with very complicated geological conditions, and the construction will encounter great difficulties, so the mechanical behavior of shield segments in different complex strata is worth discussing. In this paper, the axial force, bending moment and pore water pressure of shield tunnel segments in the soft and hard uneven stratum, clay stratum and fully weathered granite stratum of overlying buildings are studied by establishing a rectangular element mechanical model based on the field test method. The analysis shows that the mechanical properties of shield tunnels in different strata are quite different, but their mechanical properties change stages are the same. The earth pressure on the left and right sides of the test ring is asymmetric in the soft and hard uneven stratum, and the vault pressure is much greater than the vault bottom pressure. The distribution of earth pressure in each position of the segment ring in clay stratum is relatively balanced, and the earth pressure on both sides is relatively small; in the fully weathered granite layer of the overlying building, the segment ring of the test ring is subjected to greater additional stress, and the internal force of the segment is much greater than that without the overlying building. Exploring the similarities and differences of segment stress in these three complex strata can provide an important basis for the design and construction of shield segments in complex strata.

Research on the Influence of Compression and Offset of Cushion Blocks on the Axial Strength of Transformers

The instability of the winding-cushion structure is one of the primary causes of transformer failures. Insulation cushion compression and offset are the predominant forms leading to structural instability. Therefore, this paper, using the SFSZ7-31500/110 transformer as an example, first derives the theoretical formula for mechanical stress calculation. It clarifies the key influencing parameters of the winding-cushion block structure on the axial bending stress of the winding. Subsequently, an electromagnetic force finite element calculation model is established to obtain the axial force distribution in the winding and the distribution of unbalanced displacement during short-circuit processes. Based on the force and offset distribution, a specific cushion block compression and offset test platform is constructed. By setting different cushion block variables, the effects of cushion block unbalanced height and cushion block offset on the winding’s bending elastic modulus are determined. Finally, a simulation model for stress calculation of the winding-cushion block structure is established, revealing the influence pattern of cushion block compression and offset instability on the axial strength of the winding. The results of this study indicate that the greater the uneven cushion block height, the lower the axial strength of the winding. Under the same cushion block offset angle, winding structures with non-uniform cushion block offsets exhibit the worst axial stability. When the offset angles are 30°, 45°, and 60°, the maximum axial bending stress of the winding increases by 1.73%, 3.46%, and 7.82%, respectively. Increasing the offset angle exacerbates the decrease in the axial strength of the winding up to a certain extent. The findings in this study have significant implications for enhancing a transformer’s short-circuit resistance.

Novel corrugated tube–rubber–concrete flexible joint for lining water conveyance tunnels crossing reverse Faults: Numerical analysis of dislocation resistance performance

When water conveyance tunnels cross seismic fault fracture zones, significant deformation may occur, threatening the structural integrity of the tunnel. To resolve this problem, a novel corrugated tube–rubber–concrete flexible joint (CTRCFJ) for improving fault resistance is proposed for the first time. The effectiveness of the CTRCFJ was evaluated using advanced three-dimensional non-linear finite element analysis. The design parameters of the CTRCFJ, including rubber width, corrugated tube interval, and corrugated tube width, were selected based on the distribution of the axial bending moment of the lining structure. An orthogonal test was performed to determine the optimal combination of parameters. The effects of the number of crests, different steel grades, and wall thickness of the corrugated tube on the fracture resistance of the CTRCFJ are investigated. Results show that the CTRCFJ can effectively improve the dislocation resistance performance of composite lining water conveyance tunnels crossing reverse faults by reducing axial compression and bending strain. This study provides a reference for the structural design of composite lining structures that can cross reverse faults.

Mechanical response of concrete pipe rehabilitated by liner under external load: Analytical solution

AbstractUsing pipe lines to rehabilitate concrete drainage pipes is a popular trenchless technique. In this paper, the concrete pipe and liner are equivalent to a symmetrical structural mechanics problem, and the mechanical solution of the composite structure is obtained using the force method. Subsequently, the analytical solutions are compared with the test and finite element results. The distribution law of axial force, bending moment, and shear force of the composite structure are obtained, and the circumferential strain law of the inner and outer surfaces of the host pipe is analyzed. Lastly, the influence of pipe diameter and liner thickness on the bearing capacity of the host pipe is examined. The results indicate that the axial and shear force distribution of the composite structure remains the same for different pipe diameters, as the distribution diagrams of shear and axial force along the circumferential direction coincide. While the elastic modulus and thickness of the liner have no effect on the internal force distribution of the composite structure, they do directly affect the stress state of the host pipe. Additionally, the bottom support causes abrupt changes in the bending moments and strains of the host pipe.

Seismic performance of special-shaped hexagonal concrete filled steel tubes with inner diaphragm plates and shear studs

With the development of the high-rise buildings, the columns with special cross-sectional shapes are frequently adopted for architectural and aesthetic purposes. The concrete filled steel tube (CFST) is a reasonable choice for such requirement due to the characteristics of excellent seismic performances, construction efficiency and strong adaptability to special shapes. This paper focuses on the seismic performance of a special-shaped hexagonal CFST column with an inner diaphragm plate and shear studs adopted in a super high-rise building. Experiments were conducted on five column specimens under axial compressive force and lateral cyclic loading to investigate the influence of various parameters including loading angle, axial compression ratio, shear studs and the type of in-filled concrete. In one of the specimens, the ultra-high performance concrete (UHPC) was used as the in-filled concrete to substitute the conventional normal strength concrete, and the effects on the capacity and ductility of the column were revealed. Then the failure mode, the load-deflection curves, seismic performance indexes and the strain distribution were analyzed. The flexural capacities of the columns were evaluated by the fiber section model, where the failure criterion considering the buckling of steel tube was proposed and the effects of studs were included. Finally, the contribution to axial force and bending moment from outer steel tubes, inner diaphragm plate and in-filled concrete were calculated and compared based on the proposed model. It is found that the fiber section model considering the steel plate buckling and strengthening effects of studs precisely predicted the moment-curvature curves and the flexural capacity of the test specimens. The contribution of the inner diaphragm plate was considerable which could not be neglected.

Experimental and numerical study on the impact performance of concrete-filled high-strength steel tube (CFHSST)

The performance of concrete-filled high-strength steel tubes (CFHSST) under transverse impact was studied through experiments and numerical analysis in this paper. A total of 14 specimens of concrete-filled BG890QL high-strength steel tubes and 8 specimens of concrete-filled Q345B carbon steel tubes were tested using a drop hammer apparatus. Test results showed that CFHSST presents a bending failure under transverse impact and has good impact resistance. However, CFHSST with a higher axial compression or bending resistances show lower impact resistance compared to that of the concrete-filled carbon steel tubes (CFST). This may be due to the relatively lower strain rate effect and the characters of the constitutive relation of the high-strength steel. A finite element analysis (FEA) model was then established to broadly compare the impact resistance of CFHSST and CFST. The finite element analysis shows that the impact resistance of CFHSST members is higher than that of CFST members with the same axial compression resistance and static bending resistance when the impact energy is relatively low. However, with the increase of the impact energy, the impact resistance of CFHSST is gradually lower than that of CFST, showing its potential mechanical shortcomings under extreme hazards compared to the conventional CFST. Finally, based on a parametric analysis, key parameters that may influence the impact resistance of CFHSST are identified.

Približni proračun kružnih AB stupova uz pomoć nomograma

Calculating the reinforcement of circular reinforced concrete (RC) columns involves not only the dual nonlinearity of the geometry and material but also the nonlinearity of the section width. Accurate solutions require iterative calculations. To develop the calculation method manually, the model column method was proposed to compute the second-order effect of the columns, and the strain method was used to calculate the ultimate strength of the sections analytically. The nomograms required to calculate the reinforcing steel content of the columns without iterations were obtained. The nomogram for calculating the section bearing capacity and reinforcing steel has three parameters (axial force, bending moment, and mechanical ratio of the reinforcing steel). Further, the nomogram for calculating the column bearing capacity and reinforcing steel has five parameters (axial force, bending moment, curvature, slenderness ratio, and mechanical ratio of the reinforcing steel), and the relationship between the five parameters can be expressed in a plan, which makes the application convenient. Finally, the calculation results of the nomograph were compared with those of the existing approximate calculation formulas and exact numerical methods, and the accuracy of the nomograms was verified.

Hysteretic performance of thin-walled Q690 high-strength steel H-section beam-columns bent about the weak-axis

High-strength steel has broad application prospects in steel structures as its weight to strength ratio is low, but the reduced ductility limits its application in seismic design. In order to evaluate the application potential of high-strength steel in light steel structures, four Q690 high-strength steel beam–columns with large width to thickness ratios were tested under cyclic loading about the weak axis. The failure mode, ultimate strength, hysteretic curve, stiffness degradation, ductility and energy dissipation capacity of the tested specimens are discussed. Subsequently, a finite element analysis model is established, and an extensive parametric study is carried out using the verified finite element model. The test results show that the failure mode is the local buckling of column base. The hysteretic behavior of the specimens is mainly affected by the axial load ratio and the flange width to thickness ratio. The results of the parametric study show that the extent of development of plasticity in the cross-section is related to the axial load ratio. The calculated ultimate strength of the beam–column shows that Eurocode 3 is conservative for the classification of the beam–column as having a Class 4 cross-section, members with Class 4 cross-sections should in fact be classified as having Class 3 cross-sections. Accordingly, a section classification for a high-strength steel beam–column subjected to weak axis bending is discussed.

Hysteretic behavior of prestressed high-strength bolt joint subject to combined flexure and axial forces for prefabricated prestressed spatial structures

A novel prestressed high-strength bolt (PHSB) joint applied in the prefabricated large-span ridge tube cable dome with annular struts (PLRTCDAS) was proposed. Firstly, the hysteretic behavior of the PHSB joint under combinations of bending moment and axial compression was studied by experiments. Four parameters of the PHSB joint, including the disc thickness, perforated cross plate thickness, perforated angle steel thickness, and outer sleeve height, were considered in the test. The effects of these parameters on the hysteretic curves, skeleton curves, bearing capacity, failure modes, energy dissipation behavior, and ductility were analyzed and discussed in detail. Secondly, a three-dimensional finite element (FE) model of the PHSB joint considering geometric, material, and interaction nonlinearities was established by ABAQUS. The accuracy of FE model was verified by comparing the test and numerical results. Finally, the hysteretic behavior of the PSHB joint under different combinations of axial forces and bending moments was investigated by the proposed FE model. The research indicates that the PHSB joint exhibits perfect energy dissipation capacity and higher ductility. Reducing the perforated angle steel thickness or increasing the outer sleeve height can improve the hysteretic behavior of the PHSB joint without significantly reducing its bearing capacity. The verified FE model is an effective method to simulate PHSB joint hysteretic behavior.

Steel tubes subjected to combined axial compression and bending

The bending response characteristics of ten tubes subjected to axial pre-compressive stresses ranging from 0 to 45 % of the tube wall yielding stress (σr) were investigated experimentally. The tubes had different diameter-to-thickness ratios of 42 and 56 and length-to-diameter ratios of 15 and 20. The results showed up to a 31 % reduction in the bending capacity of tubes when σr increased from 0 to 45 %. Experimental interaction diagrams for axial pre-compression and bending moment capacity were compared with the proposed relationships in different codes, with the results showing a substantial load-bearing capacity of tubes beyond the codes' predictions.

Numerical Analysis of Soft Soil Improvement using Pile at Airport Construction Project

Construction on the soft ground poses an excellent challenge for geotechnical engineers. Several engineering problems such as bearing capacity failure and differential settlement could occur either during or after the construction phase due to high compressibility and low shear strength. Nowadays, a number of soil improvement techniques are available to solve such problems. However, each method has its advantages and disadvantages. In this study, soil improvement analysis using pile were performed with three variations depths so called 12 m, 18 m, and 24 m from the ground level. A finite element simulation has been performed using PLAXIS 2D. The pile has been modeled as plate and Mohr-Coulomb model was used for soil model. The results show that the deeper the pile, the settlement will be decreasing. Moreover, the axial force and bending moment of the pile obtained from the output of PLAXIS 2D were also presented to assess the performance of the soil improvement technique.

THE ROLE OF THE DEAD ZONE IN PREDICTIONS OF TRABECULAR BONE TOPOLOGY AND CONTINUUM LEVEL MECHANICAL PROPERTIES

Abstract1.0 ObjectivesPredictive structural models resulting in a trabecular bone topology closely resembling real bone would be a step toward 3D printing of sympathetic prosthetics. This study modifies an established trabecular bone structural adaptation approach, with the objective of achieving an improved adapted topology, specifically connectivity, compared to CT imaging studies; whilst retaining continuum level mechanical properties consistent with those reported in experimental studies. Strain driven structural adaptation models successfully identify trabecular trajectories, although tend to overpredict connectivity and skew trabecular radii distribution towards the smallest radius included in the adaptation. Radius adaptation of each trabecula is driven by a mechanostat approach with a target strain (1250 µɛ) below which radius is decreased (resorption), and above which radius is increased (apposition). Simulations include a lazy zone, in which neither resorption nor apposition takes place (1000 to 1500 µɛ); and a dead zone (<250 µɛ) in which complete resorption of trabeculae with the smallest included radius takes place. This study assesses the impact of increasing the dead zone threshold from <250 µɛ to <1000 µɛ, the lower limit of the lazy zone.2.0 MethodsIn-silico structural models with an initial connectivity (number of trabeculae connecting at each joint) of 14 were generated using a nearest neighbour approach applied to a random cloud of points. Trabeculae were modelled using circular beams whose radii were adapted in response to normal strains caused by the axial force and bending moments due to a vertical pressure of 1 MPa applied to the top of the lattice, with the bottom of the lattice fixed in the vertical direction. Lattices in which nodes are either able (rigid jointed) or unable (pin jointed) to transmit bending moments were considered. Five virtual samples of each lattice type were used, and each simulation repeated twice: with a dead zone of either <250 µɛ or <1000 µɛ.3.0 ResultsIn pin jointed lattices the increase in dead zone threshold resulted in reduction of predicted Young's Modulus from 580 MPa (95% CI [577 MPa, 583 MPa]) to 408 MPa (95% CI [397 MPa, 419 MPa]) whilst in rigid jointed lattices it increased form 839MPa (95% CI [832 MPa, 846 MPa]) to 933 MPa (95% CI [931 MPa, 936 MPa]). Mean connectivity decreased from 10.2 to 5.8 in pin jointed simulations and from 9.6 to 3.8 in fixed joined simulations. Topological studies of trabecular bone CT images report a mean connectivity of around 3.4. Pin jointed lattice mean radius increased from 33mm to 45mm, and rigid jointed lattice mean radius increased from 33mm to 64mm. Prevalence of smallest included radius beams decreased in both.4.0 ConclusionImproved in-silico representations of trabecular bone can be achieved in structural adaptions by increasing the dead zone threshold and adopting a bending dominated (rigid jointed) lattice structure.Declaration of Interest(b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Functionally graded 3D printed plates for rib fracture fixation

BackgroundDesign freedom offered by additive manufacturing allows for the implementation of functional gradients - where mechanical stiffness is decreased along the length of the implant. It is unclear if such changes will influence failure mechanisms in the context of rib fracture repair. We hypothesized that our novel functionally graded rib implants would be less stiff than controls and decrease occurrence of secondary fracture at implant ends. MethodsFive novel additively manufactured rib implants were tested along with a clinically used Control implant. Fracture reconstructions were modeled with custom synthetic rib bones with a transverse B1 fracture. Ribs were compressed in a cyclic two-point bend test for 360,000 cycles followed by a ramp to failure test. Differences in cyclic stiffness, 3D interfragmentary motions, ramp-to-failure stiffness, maximum load, and work to failure were determined. FindingsThe Control group had lower construct stiffness (0.76 ± 0.28 N/mm), compared to all novel implant designs (means: 1.35–1.61 N/mm, p < 0.05) and rotated significantly more about the bending axis (2.7° ± 1.3°) than the additively manufactured groups (means between 1.2° – 1.6°, p < 0.05). All constructs failed via bone fracture at the most posterior screw hole. Experimental implants were stiffer than Controls, and there were few significant differences between functional gradient groups. InterpretationAdditively manufactured, functionally graded designs have the potential to change the form and function of trauma implants. Here, the impact of functional gradients was limited because implants had small cross-sectional areas.

A semi-analytical model to predict residual stress distribution in thick wall girth weld with narrow gap welding

Benefited by its high efficiency and low cost, the narrow gap welding has been widely used in thick wall pressure equipment. Considering the fact that defects in welded joints inevitable, the safety assessments for welding equipment with residual stress are crucial. However, for the thick-wall equipment using narrow-gap welding, the current safety assessment standards specifying the residual stress distribution are not detailed or missing. In this paper, the through-wall residual stress of thick wall girth welds with narrow gap welding is studied. The stress components (bending stress, membrane stress and self-equilibrating stress) at the evaluation point are obtained by stress decomposition. The effects of the heat input, the wall thickness, the radius thickness ratio and the number of welding passes on residual stress are considered, respectively. The results show that the heat input only affects the distribution of bending stress and membrane stress. The axial and hoop bending stresses decrease with the increase of the wall thickness, and the hoop membrane stress is about 0.75 times material yield strength. With the increase of radius thickness ratio, the bending stress decreases while the hoop membrane stress increases. The stress distribution is fluctuating when the number of welding layers is small, which be expressed by trigonometric function. The distribution model of welding residual stress through the wall thickness is proposed. The stress distribution obtained by the proposed prediction model is in good agreement with the finite element calculation results.

A Small-Deformation Rate-Independent Continuous-Flow Model for Elasto-Plastic Frames Allowing Rapid Fatigue Predictions in Metallic Structures

Fatigue analysis in metallic frame structures can be challenging due to associated computational costs; if localized plasticity is involved, then the approach of three-dimensional (3D) continuum plasticity models for direct computation of stresses will be infeasible for the analysis of cyclic loading that would need to be modeled in medium- to high-cycle fatigue and vibratory fatigue applications. This difficulty is particularly accentuated in architected structures, for which high-resolution 3D finite element analysis (FEA) would be prohibitively expensive. In this work, we propose an alternative approach based on the use of novel elasto-plastic frame model with continuous flow (i.e. no sharp yield function) for modeling 3D frame and lattice structures. Rather than splitting the strains (as is done in classical plasticity) we split the deformation measures, extension, curvature and twist, into elastic and plastic components and postulate a rate type evolution rule for the plastic variables in terms of the stress resultants (axial force, bending moment, and torque). The combination of structural models together with the use of elasto-plastic operator split to solve the resulting boundary value problem allows for much faster determination of localized plasticity than continuum models can provide. The use of a continuous transition from elastic to rate-independent plasticity (as opposed to an abrupt change with classical plasticity models) allows us to capture localized microplasticity and determine resulting fatigue progression using a cycle-count-free, plastic work-based approach, formulated in terms of the curvatures and resultants. We demonstrate that (a) the model is able able to reproduce the response of 3D FEA with very few elements and (b) the model has the ability to rapidly predict the fatigue life under variable amplitude combined loading with relatively few frame elements.

Fatigue strength and impact toughness dependence of powder bed fusion with laser beam-manufactured 316L stainless steel on orientation and layer thickness

Additive manufacturing is an enticing way of producing complex geometries and optimized parts for special applications. Even though the achievable static properties for the printed material are usually good when compared to wrought materials, in many cases dynamic properties are known to be much worse. Often, the quality is sacrificed in respect of printing speed. Furthermore, printed materials have usually anisotropic behavior, caused by the remelting and fast cooling of each deposited layer. This means that the mechanical properties need to be measured in several directions in respect of the printing direction for attaining a more holistic approach to the achieved static and dynamic behavior. As a demonstration, this study focuses on determining the properties of 316L stainless steel-manufactured with laser powder bed fusion. A comprehensive set of samples for various testing methods were manufactured to investigate the effect of the layer thickness and printing orientation on the microstructure, mechanical properties, impact strength, and fatigue life. Fatigue performance of the material was evaluated in both axial and flexural bending comparing as-built and polished surface conditions. Bending fatigue testing revealed that a fatigue limit of 100 MPa at best can be achieved with the as-built surface quality, but with a polished surface and lower layer thickness, it could be doubled. Impact toughness and mechanical strength of the material are heavily dependent on the layer thickness, and while the best results were obtained with the lower layer thickness, the printing orientation can have a detrimental effect on it.

Finite element analysis comparison of Type 42A2 fracture fixed with external titanium alloy locking plate and traditional external fixation frame

BackgroundAt present, not all Type AO/OTA 42A2 open fractures can be treated by external fixation brackets, not to mention the inconvenience of this technique in clinical practice. External titanium alloy locking plates, which are lightweight and easy-to-operate, can be used as an alternative treatment option for such patients. However, there are few reports of finite element biomechanical analysis on the titanium alloy locking plates and fixation brackets being placed on the medial side of the tibial fracture. In this study, the biomechanical properties of titanium alloy locking plates and fixation brackets for treating Type AO/OTA 42A2 fractures were compared by applying the finite element method, and the results provided data support for the clinical application of the external titanium alloy locking plate technique.MethodsType AO/OTA 42A2 fracture models were constructed using CT data of a male volunteer for two external fixation techniques, namely the external titanium alloy locking plate technique and the external fixation bracket technique, according to commonly-used clinical protocols. Then, the four-point bending, axial compression, clockwise rotation and counterclockwise rotation tests under the maximum load were simulated in finite element analysis software. The stress distribution, peak stress and overall tibial displacement data for the two different external fixation techniques were obtained and compared.ResultsIn the four different test conditions (i.e., four-point bending, axial compression, clockwise torsion, counterclockwise torsion) under the maximum load, the two external fixation techniques showed obvious von Mises stress concentration at the contacts between the screw and tibia, between the screw and titanium alloy locking plate, between the self-tapping self-drilling needle and tibia, between the self-tapping self-drilling needle and the external fixation device, as well as around the fracture end and around the cortical bone at the upper and lower ends of the tibia. The peak stress was ranged 26.67–558.77 MPa, all below the yield stress strength of titanium alloy. The peak tibial displacement of the external titanium alloy locking plate model was smaller than that of the fixation bracket model. In terms of structural stability, the external titanium alloy locking plate technique was superior to the external fixation bracket technique.ConclusionsWhen fixing Type AO/OTA 42A2 fractures, external titanium alloy locking plates are not only lightweight and easy-to-operate, but also have better performance in terms of axial compression, bending and torsion resistance. According to the finite element biomechanical analysis, external titanium alloy locking plates are superior to traditional external fixation brackets in treating Type AO/OTA 42A2 fractures and can better meet the needs of clinical application.

Research on the spatial structure of environmental art design based on topology optimization and morphology optimization

Abstract In this paper, firstly, a mathematical model of spatial structure topology optimization is constructed, and sensitivity analysis, approximate model fitting and optimization finding strategy for topology optimization in environmental art design are carried out. Secondly, morphological optimization is carried out from the morphological model of spatial structure and the urban thermal environment through urban environmental art design and morphological optimization. Finally, the optimization of structural morphology is explored under static multiple working conditions and single-objective optimization, considering the dynamic frequency of the structure. The results show that as the optimization proceeds, the total strain energy, axial strain energy and bending strain energy of the space structure increase to 0.45, 0.52 and 0.5 of the initial structure, respectively. At the 9th iteration of optimization, the performance is at its peak. The load-carrying capacity is 1.59 times that of the 35th step and 1.5 times that of the initial structure. The research results of this paper can provide references and guidance for structural design and optimization in the fields of environmental art design and urban planning.

Bearing capacities and failure behaviors of bolt fasten wedge (BFW) active joints used in prestressed internal supports

In this paper, the bearing capacities and failure behaviors of bolt-fastened wedge active joints used in prestressed internal supports are studied. A thorough exploration of the design of the bolt-fastened wedge active joint is elaborated, and an overview, working mechanism, stiffness analysis, parameters, and strength checking are provided. Then, loading tests are conducted on four full-scale specimens. One test is an axial compression test, while the other three tests are performed to analyze the long-axis (Y-axis) eccentricity, short-axis (X-axis) eccentricity, and biaxial (XY-axis) eccentricity. The load–displacement curve, load–strain curve, bending moment-rotation curve, and failure mode of each specimen are obtained. The experimental results show that the samples have good compressive properties and bending resistance. The impact of the X-axis and Y-axis eccentricities on the compressive ultimate bearing capacity is investigated, revealing a significant reduction in the former, while the latter has a minimal effect. Under bidirectional eccentricity, the weakening of the axial bending performance is most apparent. Bidirectional eccentric loads lead to a reduction in the yield load and initial compression stiffness to approximately 90% of those observed under unidirectional eccentricity. Finally, a field test is carried out to compare the constructability and load-holding performances of bolt-fastened wedge active joints with those of commonly used steel wedge active joints. It is demonstrated that the bolt-fastened wedge active joint effectively maintains prestress through bolt fastening, substantially enhancing the safety of foundation pit excavation construction.