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• Peeling forces in friction stir composite joints are not enough to overcome the binding forces. • Higher stiffness of composite joints resulted in a rigid body rotation due to secondary bending. • The failure mechanism exhibited a brittle behaviour with crack nucleation at the highly strained region. • A relationship between tension, bending and mechanical performance of the joint was obtained. • The development of secondary bending moment acts as main catalyst of the failure mechanism. Friction stir composite joints between an aluminum alloy (AA6082-T6) and reinforced polymer (NorylTM GFN2) were studied regarding their failure characteristics. A comprehensive analysis on the mechanical behaviour of the joints was carried out, assessing the resulting deformed shape, the associated strain field and the observed failure modes using a digital image correlation (DIC) system and comparing with a finite elements method (FEM) model. The numerical model evidenced a good fitness to the experimental results since both the displacements and strain fields were found to be very similar. Both numerical and experimental strain fields in the longitudinal direction exhibited a localized spot of highly strained material, clearly indicating the nucleation site. Since secondary bending occurs in structural elements under tension due to geometrical and stiffness asymmetries, as is the case of overlap composite joints, a bending stress is induced, increasing the local stress compared to the nominal tension stress values. The ultimate tensile stress of the joints was found to range between 60.2 and 70.4 MPa, leading to an average joint efficiency of 82.6 %. The bending factor (k b) at the failure region was found to be 2.0, which means that the bending stress accounts for 2/3 of the total stress, acting as main failure catalyst. [ABSTRACT FROM AUTHOR]

• Previous studies have lacked comparative research on tunnel failure analysis under oblique-slip fault conditions. • Under the action of fault displacement, tunnels undergo shear and bending failures. • Oblique-slip faults cause more severe damage to tunnels, with more cracks and a wider range of damage. • The displacement mode of active faults is the key factor determining the final failure mode of tunnels. To deeply study and compare the failure characteristics of tunnels under strike-slip and oblique-slip active faults, with the engineering background of a railway tunnel in western China crossing both strike-slip and oblique-slip active faults, two sets of large-scale indoor model tests with a geometric similarity ratio of 1:35 were conducted. The fissure development patterns and strain trends of the tunnel under the movement of both types of faults were monitored and analyzed. Meanwhile, a three-dimensional model of tunnel-rock-fault interaction was established using ABAQUS finite element analysis software to determine the variation patterns of bending moments and shear forces of the tunnel under the movement of both types of faults. The results showed that under the movement of strike-slip and oblique-slip active faults, circumferential bending fissures appear at the right waist of the hanging wall and the left waist of the footwall of the tunnel, and shear oblique fissures appear at the vault of the fault fracture zone. Among them, the number of cracks, the range of tunnel cracking and the degree of crack damage under the condition of the oblique-slip fault are obviously more serious than those under the condition of the strike-slip fault. Under the dislocation of the oblique-slip fault, a large area of broken zone appears in the vault of the fault fracture zone, the lining falls off, the steel bar is exposed, and there is an obvious uplift phenomenon. The right waist of the tunnel's hanging wall mainly experiences tension while the left waist experiences compression, whereas on the hanging wall, the right waist experiences compression while the left waist experiences tension. Under the fault movement, the maximum bending moment value mainly occurs at a distance of 10 m from the fault fracture zone on both the hanging wall and the footwall, with the bending moment values at the fault fracture zone nearly approaching zero. The maximum shear force value occurs at the fault fracture zone. Under the movement of both types of faults, the failure mode of the tunnel is mainly characterized by bending failure of the hanging wall and the footwall and shear failure at the fault fracture zone. Compared to strike-slip active faults, the development of fissures in tunnels under oblique-slip active faults is more severe, with larger bending moment and shear force values, and a wider range of tunnel failure. These results can provide theoretical and technical experience for future similar projects. [ABSTRACT FROM AUTHOR]

• The wooden drum-tower exhibits poor ductility, and the premature withdrawal of tenon-mortise joints in components adjacent to the failure zone is a triggering factor for the collapse of the structure. • After component failure, the structure undergoes internal force redistribution. The beam in the failure zone is forced to bear tension, bending, and torsion simultaneously, leading to the failure of the tenon-mortise joints. At the moment of mortise-tenon joints failure, the columns within the failure zone gradually tilt under the influence of gravity, eventually leading to progressive collapse. • The failure of mortise-tenon joints in the failure zone is characterized by compression deformation of the tenon in the transverse direction and splitting of the mortise edges. Non-collapsed structure tilts as a whole, with slight detachment of tenon heads and uplift of column bases. The drum-tower belongs to the category of towering structures, and the overall collapse is a common accident in such structures. In order to study the anti-collapse performance of drum-towers, this research used the bottom floor of a wooden drum-tower in the southwest China as a prototype, designing and producing a 1/3 scale structural model. The sudden-column-removal (SCR) method was employed to simulate the structural collapse process, observe collapse characteristics, and analyze the dynamic response of the structure. A finite element model was established, and on the basis of verifying its accuracy, a parameter expansion analysis was conducted. The study indicates that the ductility of wooden drum-towers is relatively poor, and the pulling out of mortise- tenon joints in adjacent components in the failure area is a primary factor for the progressive collapse of the structure. Due to the redistribution of internal forces, the load-bearing status of beams in the failure area changes, experiencing tension, bending moment, and torsion simultaneously, leading to the pulling out, compression, and splitting of mortise-tenon joints. After the failure of these joints, the structure undergoes progressive collapse under the influence of gravity. The dimensions of mortise-tenon joints and the friction coefficient have a significant impact on the anti-collapse performance of the structure. Larger dimensions and friction coefficients result in slower structural damage and more stable structural response. Among these factors, increasing the depth of mortise-tenon joints has the most significant effect. [ABSTRACT FROM AUTHOR]

• The impact test results of the scaled model corresponding to the finite element model were used to verify the accuracy of the adopted material models and contact relationships. • Based on the spatial complexity of urban overpasses, the dynamic responses and failure mode of the full-bridge model under non-bottom impact were numerically simulated. • Four comparative models were established to study the effect of the bridge model parameters on impact responses. Urban viaducts are likely to be subjected to non-ground-level vehicle collisions during their service life period. However, current research primarily focus on vehicle impacts on the bottom of bridge piers. In this research, a full-bridge scale model impact test was conducted to validate the accuracy of the finite element (FE) model. Then, LS-DYNA is used to establish refined vehicle-bridge collision FE models. The dynamic responses and failure mode of the pier impacted by the non-bottom vehicle are investigated. Besides, the effects of bridge structure spatial stiffness, superstructure mass, and double-column structure on the impact responses of bridges are analyzed. The results show that vehicle collisions are characterized by a continuous impact action involving multiple components. The damage to the full bridge model is concentrated in the directly impacted double-column pier, where the head-on column sustains three-point bending damage, the indirectly impacted column sustains bending damage at the top and bottom, and the cover beam sustains tensile shear damage. The non-bottom impact significantly increases displacements and bending moments of the pier while causing a substantial decrease in bottom shear. The impact responses of the pier are greatly influenced by the superstructure mass and double-column structure, while the spatial stiffness of the bridge has minimal affection. [ABSTRACT FROM AUTHOR]

• The nonuniform fault displacement, fault zone width, and nonlinear soil-tunnel interaction are considered in this model. • This model agrees well with the numerical results, the error of bending moment is 0.8%, and the error of shear force is 4.6%. • The effect of fault displacement, fault zone width, and the maximum fault displacement ratio on tunnel response are analyzed. • The failure evolution process of the tunnel under reverse fault dislocation is revealed in detail. Tunnels subjected to reverse fault dislocation undergo severe structural damage, and their mechanical response and failure characteristics play a key role in seismic fortification efforts. This paper investigates the mechanical responses and failure characteristics exhibited by tunnels subjected to reverse faulting using theoretical analysis and numerical simulations. A theoretical model is established for analysing the bending moment, shear force, and safety factor of the tunnels under reverse fault dislocation. The nonuniform fault displacement, fault zone width, and nonlinear soil-tunnel interaction is applied in the proposed theoretical model, significantly improving the analysis accuracy and range of applicability. The corresponding numerical simulation based on the XFEM (extended finite element method) is carried out, and the proposed theoretical model is verified by the numerical results. The theoretical results demonstrate excellent agreement with the numerical results when nonuniform fault displacement is considered. A parametric analysis is presented in which the effects of the maximum fault displacement, fault zone width, and ratio of the maximum fault displacement of the footwall to the hanging wall are investigated. The results show that the ultimate fault displacement for compression-bending failure of the tunnel subjected to reverse fault dislocation is estimated to be approximately 30 cm, while the ultimate displacement for shear failure stands at 20 cm. Variations in the fault displacement ratio yield alterations in the distribution pattern and peak values of internal forces, together with shifts in the potential failure ranges of the footwall and hanging wall. Additionally, an initial crack emerged on the tunnel crown near the fault plane, followed by a second crack on the tunnel invert. Upon reaching a fault displacement of approximately 40 cm, the crack fully traverses the entire tunnel lining. [ABSTRACT FROM AUTHOR]

• Established experimental method for composite pre-tightened tooth connections under bending and tension coupling load. • Based on the USDFLD subroutine, a finite element model of progressive failure of composite pre-tightened tooth connections is developed. • The analysis of the failure process of composite pre-tightened tooth connections under bending and tension coupling load. With the application of composite pre-tightened tooth joint in engineering practice, relevant studies have found that in actual structures, the joints are subjected not only to axial tension but also to bending and tension coupling force. Therefore, to analyse the load mechanism and progressive failure process of the joint under bending-tension coupling, a experiment loading method for joint structure was first designed in this paper, and axial-tension and bending-tension coupling experiments of single and double teeth were carried out by this method. Then, a three-dimensional model of progressive failure based on the USDFLD subroutine and Tsai-Wu failure criterion is established based on the experiment condition, and finally, the progressive failure process of the joint in the case of bending-tension coupling is analysed by verifying the correctness of the finite element simulation. The study revealed that the top surface of the composite tooth is subjected to the combined effects of tension stress from the bending moment and tension stress from the axial force at the same time, so the joint damage starts at the top surface and the stress state at the top surface of the composite tooth needs to be considered. [ABSTRACT FROM AUTHOR]

• Develop a Python-based interface program from LS-DYNA model to Blender 3D solid model. • Develop element merging technique during mapping and suggest the determination of the connection constraints in PE model. • The developed FEM-PE method able to track accurate nonlinear dynamic response and collapse mode of RC structures. • Two column removals rather than a single column removal able to cause progressive collapse of a seismically designed frame. • Propagated collapse mode is observed due to column failure with excessive torsion and large bending moment. High-fidelity collapse process and reasonable debris accumulation and distribution after collapse are very critical to carry out post-disaster investigations and show why collapse happens. Moreover, previous researches on progressive collapse is more concerned with structural behavior in resisting collapse and pays little attention to the dynamic response after collapse criterion is reached. Therefore, a hybrid numerical framework is developed through combining the advantages of the finite element method (FEM) and the physics engine (PE), which provides new ideas for studying the full collapse process of structures. In this paper, based on previous work, such hybrid framework is further developed with efforts on element merging technique in the model mapping process from a FE model to a PE model and determination of connection constraints in the PE model. Then, a new Python-based interface program is developed to integrate the FE model using LS-DYNA and the PE model using Blender 3D. The accuracy of FEM-PE framework is verified by a collapse test of a flat plate structure, and an RC frame structure is designed for studying full process of progressive collapse. Results show that FEM-PE simulation can achieve accurate nonlinear structure behavior at small deformation and high-fidelity collapse at large deformation. To obtain reasonable debris accumulation, a single beam, column and slab should be meshed with the element number no more than 3, 2 and 3 × 3 in PE models, respectively. For a seismically designed RC frame structure, a single column removal scenario cannot initiate the collapse, but the simultaneous removal of a corner and a neighouring penultimate column generates the propagated collapse mode. [ABSTRACT FROM AUTHOR]

• An improved XFEM is proposed to calculate the load- and corrosion-induced cracks. • A new energy conversion equation is constructed to improve calculation accuracy. • A high-order function is used to optimize calculation efficiency. • The relation between segment cracks and bending deflection is investigated. Load- and corrosion-induced cracks are generated in the segment concrete of a shield tunnel during the operation period, and will reduce the bending performance of the tunnel segment. In this paper, an improved extended finite element method (XFEM) is proposed for calculating the cracks of a segment under the effects of an external load and reinforcement corrosion. A new fracture energy conversion equation is constructed to improve the calculation accuracy and is verified by a full-scale test, and a high-order function of the crack diffusion coefficient is used to optimise the calculation efficiency of the crack propagation. The characteristics of the corrosion-induced cracks of the segment and its relationship with the segment bending deflection are investigated based on the improved XFEM. The numerical calculation results show that: (1) the morphology of the tunnel segment corrosion-induced cracks can be described as multiple connected ellipses; (2) the span length and angle of the corrosion-induced cracks are affected by the load-induced cracks on the surface of the segment, and an increase in the bending moment will enlarge the crack span length and reduce the crack angle; and (3) when the corrosion time reaches 9 years, the deflection of the segment is increased by 24% to 58% from that of a non-corroded segment under bending moments of 220 kN·m to 260 kN·m, respectively. The relevant results can provide a theoretical basis for the analysis and treatment of shield tunnel structural diseases. [ABSTRACT FROM AUTHOR]

This paper describes the fatigue failure of a rotary dryer in a chemical plant. The process conditions required the dryer to be rotated continuously at a speed of about two and half revolutions per minute. The shell structure of this large drum is formed by combining segmented shell parts using bolted ring flange joints. Because of the gross weight of the dryer in operation time, each joint was subjected to bending moment. In the first two years in service, micro cracks were occurred by fatigue. The failure was analyzed using the fatigue curves given in ASME Boiler and Pressure Vessel Code Section VIII Division 2 and EN 13445 Unfired Pressure Vessels Part 3 Codes. Finally, flange joints were removed from the drum and new cylindrical parts adapted to the drum using butt welding after reaching better results in FEM and fatigue calculation. [ABSTRACT FROM AUTHOR]

• A self-deforming structure was designed by introducing the shape memory polymer actuators. • The suitable shape and size of the actuators were determined by selecting the minimal damage and the maximum recovery bending moment. • The feasibility of the proposed method was verified for designing the self-deforming structure. Materials with shape memory effect (SME) can be used as the actuators of self-deforming structures, but the existing ways to design and select actuators with SME are complicated. In this work, an efficient and easy idea was proposed to select the shape memory polyurethane (SMPU) actuator with different designed shapes and sizes. First, the mechanical and shape memory experiments of SMPU were performed to obtain the basic mechanical and shape memory properties. Then, a self-deforming structure was designed by introducing the SMPU actuators with different shapes and sizes. Next, to select the optimal structural SMPU actuators, the finite element analysis was carried out by simulating the self-deforming process. Finally, based on the criteria of the minimal unrecoverable strain and maximum recovery bending moment, two kinds of actuators were chosen to drive the designed self-deforming structure cooperatively. Comparing the simulated and experimental self-deforming process, the feasibility of this method was verified. This work plays a guide in designing and selecting the actuators for self-deforming structures. [ABSTRACT FROM AUTHOR]

Highlights: [•] Revealed that bending moment is the cause of thread gluing at the HDD exit side. [•] A 3D drill pipe thread FEM model was established which could load combining loads. [•] Put forward some improvement measures and successfully used in HDD. [•] Proposed the beveled shoulder thread which could strongly withstand bending load. [ABSTRACT FROM AUTHOR]

• Structural analysis of collapsed roof flat slab using Linear finite element analysis (LFEA) and Non-linear finite element analysis (NFLEA) • Assessment of punching capacity using design equations from Eurocode 2 and Critical shear crack theory (CSCT) with LFEA. • Application of the NFLEA with CSCT for the assessment of the punching capacity of slab-column connections in collapsed flat slab. • Considering of membrane forces on the prediction of punching capacity of slab-column connections in collapsed flat slab. The article deals with failure analysis of collapsed parking garage building due to punching shear failure of the roof slab. Overloading of the roof slab-column connections led to the progressive collapse of the five-story building. The reason of the failure is known however, answer how the structure could withstand such a high level of overloading for 8 months when the ratio of design values of shear force vs. punching capacity βV Ed / V Rd reached a value of 3.9 provides the article. The design equations for prediction punching capacity, e.g. the EC2 or ACI 318–19 model, are empirical models calibrated using results of the tests carried out on isolated slab specimens. Therefore, they do not allow take into account the favourable effect of membrane forces and redistribution of bending moments in continuous flat slabs. Application of the Critical Shear Crack Theory (CSCT) in combination with non-linear finite element analysis has shown actual punching shear capacity of the system. [ABSTRACT FROM AUTHOR]

• Failure analysis of a natural gas pipeline that ruptured during a landslide was carried out. • Pipeline rupture was due to the high shear demand on a girth weld in a fabricated bend. • The high shear demand occurred because the bend was located within the anchor length. • Fabricated bends should be avoided where landslide-induced axial force is large. • The anchor length formula in the PRCI guidelines is unconservative. • In the landslide region, the pipe has experienced a maximum longitudinal strain of 3.60% without rupture. This paper presents the results of failure analysis of a 16-in. natural gas pipeline that ruptured due to ground movement caused by a 40 m wide landslide. The rupture occurred at a girth weld in the middle of a double bend located 120 m from the center of the landslide. The Finite Element Analysis (FEA) method was used to evaluate the response of the pipeline to the ground displacement. The pipeline and the surrounding soil were simulated by the Winkler-type beam-on-spring model and nonlinear static analyses were carried out to establish the root cause of the failure. The results of the analyses indicated that the ground movement was primarily resisted by the membrane action of the pipeline. The pipe axial force due to the membrane action extended well beyond the landslide zone and encompassed the bend region. The axial force at the bend location caused high local shear and bending moment in the bend region. Assessment of the state of stresses on three girth welds in the bend region indicated that the rupture was mainly due to the high shear demand on the girth weld in the middle of the bend. This study indicates that fabricated bends are vulnerable if they are placed within a critical length of the pipeline where the landslide-induced axial force is substantial. To reduce the risk of pipe rupture in pipelines crossing a potential landslide, fabricated bends should be avoided along this critical length. The critical length of a pipeline crossing a potential landslide includes the landslide zone and the anchor length on either side of the landslide. This study also indicates that the anchor length calculated by the relevant equation in the PRCI guidelines may underestimate the actual anchor length. [ABSTRACT FROM AUTHOR]

• A finite element model of wheel-mounted brake disc bolts is established and validated. • The high-speed EMU operation speed affects the load variation in the brake disc bolt. • Many small loads are exerted on the bolts because of the track excitations. • The amplitude and direction of the bending moment along the bolt are inconsistent. The reliability of brake disc bolts is crucial to the operational safety of high-speed electrical multi-units (EMUs). It is of great significance to investigate the bolt loads to ensure the bolt service life. A theoretical analysis is completed according to the jointed structure and the service condition of the bolts. By establishing a finite element model of the wheel-rail contact, the bolt loads of the wheel-mounted brake disc under high-speed rotation are simulated. A field experiment is implemented to obtain the dynamic loads of wheel-mounted brake disc bolts of a Chinese high-speed train based on a load test technique. The tested bolt loads include the tensile force, radial bending moment and circumferential bending moment. The simulation results are compared with the field test data. It validates the finite element model. The results indicate that the bolt loads are closely related to the operation speed of the high-speed EMU. The theoretical calculation method and the finite element method both prove that the amplitude and the direction of the radial bending moment along the bolt are inconsistent. The extrema of the radial bending moments appear in the left, middle and right cross-sections. The radial bending moment at the left cross-section is larger than that at the right cross-section because of the asymmetry of the wheel structure. [ABSTRACT FROM AUTHOR]

The extrusion and scraping action of rocks at the bottom of buried pipelines can lead to dent and scratch defects. Beside internal pressure, the pipelines should also bear other forms of loads during its operation, such as bending moment and axial force. The combination of internal pressure and these loads can make the pipe easy to damage. In order to study the influence of bending and axial loads on the limit internal pressure of dent-scratch pipelines, large numbers of finite element calculations are carried out in this paper. Through the comparison with experimental results, a failure criterion is proposed for finite element analysis (FEA). It is found in actual buried pipelines during pipe inspection that the existed maximum bending strain is equal to 0.4%. Take the bending moment which leads to the axial strain of 0.4% as the reference moment. A series of finite element calculations are conducted to analyze the influence of various bending loads on the limit internal pressure of pipelines with dent-scratch defects. In addition, the effect of axial compression loads on the limit internal pressure is also studied by FEA. According to the finite element results, it is concluded that both axial load and bending moment can decrease the limit internal pressure compared to one subjected to internal pressure only. Moreover, the tendency of the impact is approximately linear. Finally, an expression of limit internal pressure with respect to pipe material, pipe and defect dimensions and the magnitude of axial force is fitted, which provides a strong guidance for the safety assessment of the defective pipelines. • The effect of axial force on the limit internal pressure of dent-scratch pipelines is analyzed. • The effect of bending moment on the limit internal pressure of dent-scratch pipelines is analyzed. • The predictive formula of the limit internal pressure is modified by considering the combination action of complex loads. [ABSTRACT FROM AUTHOR]