Types Of Failure Mechanisms Research Articles

Numerical analysis of downward progressive landslides in long natural slopes with sensitive clay

Landslides occurring in sensitive clay often result in widespread destruction, posing a significant risk to human lives and property due to the substantial decrease in undrained shear strength during deformation. Assessing the consequences of these landslides is challenging and necessitates robust numerical methods to comprehensively investigate their failure mechanisms. While studies have extensively explored upward progressive landslides in sensitive clays, understanding downward progressive cases remains limited. In this study, we utilised the nodal integration-based particle finite element method (N-PFEM) with a nonlinear strain-softening model to analyse downward progressive landslides in sensitive clay on elongated slopes, induced by surcharge loads near the crest. We focused on elucidating the underlying failure mechanisms and evaluating the effects of different soil parameters and strain-softening characteristics. The simulation results revealed the typical pattern for downward landslides, which typically start with a localised failure in proximity to the surcharge loads, followed by a combination of different types of failure mechanisms, including single flow slides, translational progressive landslides, progressive flow slides, and spread failures. Additionally, inclined shear bands occur within spread failures, often adopting distinctive ploughing patterns characterised by triangular shapes. The sensitive clay thickness at the base, the clay strength gradient, the sensitivity, and the softening rate significantly influence the failure mechanisms and the extent of diffused displacement. Remarkably, some of these effects mirror those observed in upward progressive landslides, underscoring the interconnectedness of these phenomena. This study contributes valuable insights into the complex dynamics of sensitive clay landslides, shedding light on the intricate interplay of factors governing their behaviour and progression.

Spinopelvic fixation failure in the adult spinal deformity population: systematic review and meta-analysis.

Despite modern fixation techniques, spinopelvic fixation failure (SPFF) after adult spinal deformity (ASD) surgery ranges from 4.5 to 38.0%, with approximately 50% requiring reoperation. Compared to other well-studied complications after ASD surgery, less is known about the incidence and predictors of SPFF. Given the high rates of SPFF and reoperation needed to treat it, the purpose of this systematic review and meta-analysis was to report the incidence and failure mechanisms of SPF after ASD surgery. The literature search was executed across four databases: Medline via PubMed and Ovid, SPORTDiscus via EBSCO, Cochrane Library via Wiley, and Scopus. Study inclusion criteria were patients undergoing ASD surgery with spinopelvic instrumentation, report rates of SPFF and type of failure mechanism, patients over 18years of age, minimum 1-year follow-up, and cohort or case-control studies. From each study, we collected general demographic information (age, gender, and body mass index), primary/revision, type of ASD, and mode of failure (screw loosening, rod breakage, pseudarthrosis, screw failure, SI joint pain, screw protrusion, set plug dislodgment, and sacral fracture) and recorded the overall rate of SPF as well as failure rate for each type. For the assessment of failure rate, we required a minimum of 12months follow-up with radiographic assessment. Of 206 studies queried, 14 met inclusion criteria comprising 3570 ASD patients who underwent ASD surgery with pelvic instrumentation (mean age 65.5 ± 3.6years). The mean SPFF rate was 22.1% (range 3-41%). Stratification for type of failure resulted in a mean SPFF rate of 23.3% for the pseudarthrosis group; 16.5% for the rod fracture group; 13.5% for the iliac screw loosening group; 7.3% for the SIJ pain group; 6.1% for the iliac screw group; 3.6% for the set plug dislodgement group; 1.1% for the sacral fracture group; and 1% for the iliac screw prominence group. The aggregate rate of SPFF after ASD surgery is 22.1%. The most common mechanisms of failure were pseudarthrosis, rod fracture, and iliac screw loosening. Studies of SPFF remain heterogeneous, and a consistent definition of what constitutes SPFF is needed. This study may enable surgeons to provide patient specific constructs with pelvic fixation constructs to minimize this risk of failure.

Influence of Thermally Aged Underfill on Flip-Chip Packages

Underfill material plays a crucial role in flip-chip package reliability, thus it necessary to accurately understand the mechanical properties. The material itself is nonlinear and is dependent on degree of cure, temperature, strain rate and thermal aging, among others. In this work, two underfill materials were characterized for thermal expansion and viscoelastic properties over a wide temperature range. A second set of each material was thermally aged through flip-chip processing steps and 250 thermal cycles and then characterized. Temperature dependent thermal expansion and timetemperature dependent moduli curves were generated to represent each material type. These material models were then implemented into a nonlinear finite element model of a flip-chip package to evaluate package stress interaction through processing steps and thermal cycling. The influence that each underfill material had with and without thermal aging was analyzed with respect to typical package failure mechanisms.

Bearing Capacity of a Shallow Foundation above the Soil with a Cavity Based on Rigid Plastic Finite Element Method

Based on the Rigid Plastic Finite Element Method (RPFEM), this study investigates the performance of the footing on the soil with a cavity. The RPFEM is used in plane strain conditions and necessitates only a few materials to predict the bearing capacity: the unit weight of the soil, the cohesion, the shear resistance angle, and the dilation angle. Considering diverse soil types, including cohesive and intermediate soils, the findings are presented through dimensionless 2D charts in which the horizontal axis X and vertical axis Y are normalized to parameters R and H, representing the horizontal and vertical dimensions of the plastic mechanism beneath the footing in the absence of the soil cavity. Analyzing geometric factors such as footing width B and cavity characteristics (shape, size, and location), the study reveals that the farther the cavity, the less it impacts the footing performance. The distribution of the normalized bearing capacity across the (X, Y) space elucidates the expansion and variation of the influence zone. Equations incorporating the mentioned geometric parameters and soil shear strengths are proposed and verified with data in the literature. In cohesive soils, the influence zone predominantly extends vertically, following the expansion of the slip surface in no void condition. Conversely, for intermediate soils, the zone of influence exhibits a dependency on the shear resistance angle, resulting in an extension in one direction more than the other. Illustrating typical failure mechanisms, the study delves into detailed discussions to enhance comprehension of how the cavities affect the bearing capacity of the footing.

Review of Numerical Methods for Analyzing the Progressive Collapse of Concrete Structures

Construction accidents have been documented throughout history. One type of failure mechanism is progressive collapse, in which one or more structural components fail suddenly without regard to the cause (attack, anomalous accident). Numerous methods have been employed to simulate the impacts of this phenomenon. Still, they are all predicated on some distinct premises, such as the procedure's independence from the root cause of the first failure or the order in which the pressures are applied. To analyze framed building structures in the event of a column loss caused by an extreme event, this paper evaluates and offers an overview of the numerical analytical tools and approaches that are now available. In the literature, there has been a discussion of the applied element method, the discrete element method, and the finite element method. They were thoroughly discussed and contrasted. This study investigates and ends with challenges that must be resolved in many areas that will be required in the future.

Stability analysis of a vertical excavation reinforced with horizontal nails using three-dimensional finite elements limit analysis

Three-dimensional stability analysis of a vertical excavation, reinforced with grouted horizontal nails, has been carried out by using the three dimensional lower and upper bounds based finite elements limit analysis (FELA) using Optum G3. The nail along with the surrounding grouted cementitious material is assumed to behave as a single monolithic cylindrical block which was assumed to be either rigid or an elasto-plastic material following the Von-Mises yield criterion. The excavation is assumed to fail on account of either an interface shear slippage between nails and surrounding soil mass or on an account of axial tensile rupture of the composite nail material for a few typical cases as well. The soil unit weight has been varied to induce the ultimate shear failure of the soil nailed excavation. The unit weight of the soil mass at which the failure of the nailed wall occurs is termed as γcr. Two different types of boundary conditions along the base of the excavation have been considered. In the first case, the in-situ soil mass behind the excavation is extended below the base as well (Case 1) and in the second case, the excavation is assumed to simply lie on a hard stratum (Case 2). The results have been provided in the form of a non-dimensional stability number N=γcrHc as a function of soil friction angle φ, Sv/H, SH/H, d/H, L/H and m; where H refers to height of the wall, d is diameter of the grouted nail, Sv and SH imply centre to centre vertical and horizontal spacing of the nails, and m is the mobilization factor between grouted nails and adjoining soil mass. The results from the analysis have been found to compare well with the data reported in literature. All the results have been presented in the form of non-dimensional stability charts, which will be useful for design for any given values of height H and cohesion c. From the observed failure mechanisms, an analysis has also been carried out to determine the optimized lengths of nails. The optimized lengths of nails for both Cases 1 and 2 have been also provided. The type of failure mechanism, base or face failure, dictates the optimized lengths of the nails.

Discrete element analysis and analytical method on failure mechanism of retaining structures with narrow granular backfill

AbstractAscertaining failure mechanism is a prerequisite of the derivation for earth pressure against retaining structures. Retaining structures constructed adjacent to existing structures and excavation with narrow backfill have become common in practical engineering. The backfill width has a significant effect on the failure mechanism, requiring further study. In this study, a series of discrete element analyses are conducted to investigate the shear localization in soil mass behind retaining structures with narrow backfill in the active and passive limit states at the grain scale. Furthermore, the distribution characteristic of failure surfaces in soil mass is discussed from three aspects: the development of the failure surface, the state of soil mass behind retaining structures, and the shape of the failure surface. Based on the typical nonlinear failure mechanisms observed in particle rotation contours with various backfill widths and interface friction angles, the failure mechanisms behind retaining structures with narrow spacing are categorized into three types according to the backfill widths. According to the stress characteristics of interfaces under different failure mechanisms, the variational method and Mohr stress circle analysis are adapted to analytically obtain the failure surfaces behind the retaining structure with narrow backfill. Comparisons with results obtained by the discrete element simulation show a reasonable agreement. In addition, a series of parameter studies are conducted to investigate the effect of backfill widths and interface friction angles on the failure mechanism.

A 3D cohesive‐frictional coupled interface model for mesoscale simulation of steel fibre‐reinforced concrete

AbstractA 3D mesoscale finite element modelling approach is developed for simulating complicated damage and fracture behaviour in steel fibre‐reinforced concrete (SFRC) with explicit modelling of fibre–matrix interfaces. In this approach, a new 3D four‐noded cohesive‐frictional coupled interface element is developed to model the nonlinear interfacial bond‐slip behaviour, supplemented by a kinematic multiple‐point‐constraint (kMPC) algorithm to simulate the wrapping effect of the mortar around the fibres. They are implemented as a user‐defined element (UEL) and a user‐defined MPC subroutine in ABAQUS, respectively. Three cohesive‐frictional constitutive relationships are proposed to describe the nonlinear bond‐slip behaviour of different fibre–matrix compositions. The new approach is validated by single fibre pullout tests, direct tensile tests and three‐point bending tests of SFRC specimens with randomly distributed fibres. The results show that the new approach is capable of effectively capturing typical failure mechanisms in SFRC, such as fibre yielding, matrix failure, and fibre–matrix debonding and slipping.

Experimental study on crashworthiness and failure mechanisms of aeronautical multi-fibers hybrid composite corrugated structures with Carbon, Glass, Kevlar

Crashworthiness of aeronautical composite structures can be effectively regulated and controlled by fiber hybridization design, because the structural failure modes are highly sensitive to hybrid parameters. However, the complex failure mechanism is still unclear, resulting in the inability to optimize the fiber hybridization. Hence, this study focuses on crashworthiness and failure mechanisms of aeronautical multi-fiber hybrid composite corrugated structures consisting of carbon, glass, and Kevlar fiber. The composite corrugated structures with single-fiber, double-fiber hybridization and triple-fibers hybridization are prepared by hand lay-up process. The quasi-static axial crushing tests are conducted to evaluate the crashworthiness and failure modes. The experimental results show both the crashworthiness and failure modes are very sensitive to fiber hybridizations with different fiber type and stacking sequence. Both double-fiber hybridization and triple-fibers hybridization can obtain high comprehensive properties including specific properties and cost effectiveness. However, Kevlar fibers placed in inner layers or alternately stacked with other fibers are vulnerable to the buckling-dominated failure mode that is detrimental to energy-absorption. The typical failure mechanisms of proposed hybrid composite corrugated structure are extensively revealed through the corresponding mechanism models. Overall, this study on disclosing complex failure mechanism can guide the optimization of fiber hybridization to improve crashworthiness of hybrid fiber composite corrugated structures.

Seismic Bearing Capacity of Strip Footings Placed Adjacent to Rock Slopes

ABSTRACT The bearing capacity of strip footings placed adjacent to the rock slopes subjected to pseudo-static horizontal earthquake body forces has been investigated by using the upper bound (UB) finite element limit analysis (FELA) in combination with a mesh adaptive strategy. The generalized Hoek–Brown (GHB) failure criterion is applied to describe the strength properties of rock masses, which can be treated as its native form without the smoothing of the yield surface while employing the second-order cone and power cone programming to solve the optimization models. Based on the UB FELA method, the seismic bearing capacity factor is determined considering the effect of different governing parameters, namely the horizontal earthquake acceleration coefficient k h , the normalized slope height H/B, the rock strength ratio σ ci /γB, the geological strength index GSI and the material constant m i . For design purpose, a series of non-dimensional charts are provided, and typical failure mechanisms are also discussed in detail.

Low-cycle fatigue behavior on the tensile region of Hollo-bolted angle connections

This paper presents the results of an experimental program to evaluate the low-cycle fatigue-related characteristics of the tensile region of Hollo-bolted angle connections. A summary of a total of 40 tension tests of equivalent T-stub connections is reported. The geometric parameters vary with the bolt gauge width, the column wall's thickness, the bolt type, and the angle's thickness. Based on the experimental test results, the typical failure mechanisms, the hysteretic load-deformation relationship, and the response characteristics such as degradations of strength and energy dissipation capacity of the connections are examined. It is shown that the bolt gauge width and the angle's thickness have significant influences on the failure mode. Energy-based model is proposed to overcome certain geometric limitations and five commonly used damage models are used to predict the damage behavior of connections. Moreover, the low-cycle fatigue life test results are compared with the codified S–N curves through a transformation of the displacement range into the effective stress range. Furthermore, the cumulative damage mechanism is analyzed and the fatigue life formula is obtained. Finally, the results are evaluated and verified by regression analysis. The 90% confidence level was used to test the availability of the regression equation, and the equivalent level of fatigue strength of the tensile region of angle connections is not less than Category 40 (ΔσC = 40 N/mm2). The EC3, BS7608, and AISC-LRFD-1999 specifications are used to evaluate the low-cycle equivalent fatigue strength, and it is found that there is a certain safety reserve when using Category 36.

Failure Investigation of Braced Excavation in Soft Clays: Case Study on the Collapse of Nicoll Highway

Deep excavation in clay normally causes large soil movement, which may induce basal heave failure. In this study, the three-dimensional finite element analysis with the strength reduction method was employed to evaluate the typical failure mechanism of braced excavation in soft clays. The collapse of Nicoll Highway was selected as a failure case history and further conducted by considering the full elastoplastic structural behavior. The results showed that the computed wall displacements were successfully verified through the observation data. It was also found that the excavation failure was initiated by the yielding of the strut-waler connection, which was similar to that of the field observation. Finally, the proposed finite element model adopted in this study can be used as a design recommendation to evaluate the failure mechanism and further prevent possible braced excavation failure in soft clays.

Slip-Line Solution for the Active Earth Pressure of Narrow and Layered Backfills against Inverted T-Type Retaining Walls Rotating about the Base

In this research, we used a slip-line method for a typical failure mechanism simulated with adaptive finite-element software to investigate the active earth pressure of narrow and layered backfills against inverted T-type retaining walls rotating around the base mode. The slip-line field calculation models for the inverted T-type retaining wall with narrow and layered backfills were established considering the effect of the heel bottom plate and the inverted T-type retaining wall characteristics. Subsequently, the limit equilibrium and finite difference methods were used to solve the stress state of each point. The earth pressure acting on the stem and the second failure surface can be obtained by converting the boundary conditions. The proposed method was verified by comparing its results with those from finite-element limit analysis and existing theoretical solutions. Furthermore, several extensive parametric studies have investigated the effects of backfill width, heel length, and interface strength. The results show that increasing interface strength and decreasing backfill width help reduce the earth pressure against the stem and second failure surface. The change in the length of the heel bottom plate exhibited a dual effect.

Axial compression behaviour of circular concrete-filled double-skin steel tubular columns with bolted shear studs: Numerical investigation and design

The concrete-filled double-skin steel tubular (CFDST) columns have recently attracted significant attention for practical engineering constructions. The axial resistance behaviour of CFSDTs can be greatly enhanced by installing bolted shear studs as pin supports for the outer. This is a companion paper that expands on the authors' work [1]. The previous paper concentrated on full-scale experimental testing to ascertain the influence of bolted shear studs on the axial resistance of CFSDT columns, while this study focused on finite element (FE) analysis and a simplified design approach for such composite structural members. A three-dimensional FE model for predicting the axial behaviour of circular CFDST columns without and with shear studs was developed and validated using the test results of the specimens' typical failure mechanisms and load-displacement responses. The model was then employed to perform structural analysis by comparing the axial load-displacement curve, internal force distribution, longitudinal stress distribution over the sandwiched concrete, and confinement mechanism of a circular column with bolted shear studs with that of its counterpart without bolted shear studs. Parametric studies were carried out to examine the effects of bolt longitudinal spacing, diameter, length, and yield strength. It was found that the spacing of the bolts-to-width (bs/Do) ratio had significant effects on the axial resistance and ductile performance of columns. Also, a bolt spacing corresponding to bs/Do<0.44 was suggested to attain an acceptable ductile performance in practical application. Verification of the design model revealed that it led to satisfactory predictions of the ultimate strengths of circular CFDST columns without and with shear studs.

Multi-layer modelling of masonry structures strengthened through textile-reinforced mortar.

Background Textile-reinforced mortar (TRM) is an innovative strategy for the reduction of the seismic vulnerability of existing masonry buildings consisting in the application on the masonry surface, of a mortar coating with fiber-based grids or textiles embedded. The paper presents the calibration and application of a simplified modelling approach, based on multi-layered elements, for the simulation of existing masonry elements and structures strengthened through TRM. Methods The strengthened masonry is modelled by using 20-nodes brick elements formed by a stacking sequence of layers representing the different material components (the masonry, the mortar coating and the embedded reinforcement). The nonlinear behavior of the materials is considered and calibrated on the basis of experimental characterization tests on individual components available in the literature. The simplified assumption of perfect bond among layers is considered. Results Non-linear static analyses are performed on samples of increasing complexity: elementary panels, structural elements (piers and spandrels) and a pilot building. The results of some tests on TRM strengthened masonry, available in the literature, are considered to assess the model reliability in terms of capacity curves and collapse mode. The model is capable of detecting the typical failure mechanism of both unstrengthened and TRM strengthened masonry, namely the diagonal cracking, the in-plane bending and the out-of-plane bending and is able to detect the activation also of mixed failure modes, that often occur in actual configurations. Conclusions Given the coarse mesh size and the smear plasticization assumption, the model is not suitable for the rigorous reproduction of individual cracks but represents a good compromise between the goal to grasp the structural performances at the wide scale, including failure modes, and the analysis optimization.

Typical Fault Modeling and Vibration Characteristics of the Turbocharger Rotor System

To study the typical failure mechanism (rotor unbalance, rotor friction, and rotor crack) and vibration characteristics of the turbocharger rotor system, a rotor system dynamics simulation model was established by an improved four-node aggregate parameter method. The geometric and physical characteristics of the rotor system under three failure states and its dynamics under operation were analyzed. Thus, a typical failure dynamics simulation model of the rotor system was established. On this basis, the output failure simulation signal was extracted using the Hu invariant moment feature extraction method to analyze the system vibration characteristics under each typical failure state of the rotor system. The results show that the model in this paper can effectively reduce the computational volume and computational time, and the errors of numerical simulation were less than 3%. When an unbalance fault occurred in the rotor system, the shaft trajectory was “0” shaped and the response spectrum was dominated by 1X. When the rotor system was frictional, the shaft trajectory was a slightly concave “8” shape, and the response spectrum was dominated by 0.5X. When the rotor system was cracked, the axial trajectory was a “vortex”, and the response spectrum was dominated by 0.5X. Thus, the study of typical failure mechanism and vibration characteristics of a turbocharger rotor system by simulation calculation is effective and has good research prospects, providing an important technical reference for dynamic analysis and fault diagnosis of the rotor system.

Interplay Between Friction and Cohesion: A Spectrum of Retrogressive Slope Failure

AbstractRetrogressive failures occur in slopes consisting of sensitive materials such as snow or quick clay. They can be triggered by a small disturbance at the slope toe, but can cause propagated failure spreading miles away. Understanding the physical mechanism and predicting the retrogressive failure process are particularly important. Previous studies have discussed the failure criteria, the soil properties or the method of numerical modeling of retrogressive slope failure. However, little attention has been paid to the microscopic failure mechanism, especially relating to various possible failure patterns. In this study, multiscale modeling is incorporated to study the physical mechanism of different retrogressive failure patterns, including earth flow, flowslide and spread failure, within a unified framework. Utilizing multiscale analysis, we found that earth flow failure is related to the shear failure of granular materials. In contrast, the development of macroscopic shear bands is accompanied by tensile failure. As shear and tension failures are typical failure mechanisms of frictional and cohesive materials, it is deduced that friction and cohesion effects play key roles in different retrogressive failure patterns. Therefore, the distributions of attractive and repulsive contact forces are explored and a novel parameter η is proposed to quantify the interplay between friction and cohesion. Further analysis proves that η can capture the effect of friction and cohesion and distinguish different retrogressive failure patterns. Finally, a spectrum of retrogressive failures for a granular slope is established, in which the failure mechanism is explained by the changeable dominant effect, that is, frictional or cohesive in soil.

An extension of Broms’ theory to unsaturated soils

This paper presents an analytical method to predict the horizontal capacity of piles in unsaturated soils. The method extends the well-known Broms approach to account for the combined effect of the groundwater table and the apparent cohesion of the unsaturated soil above it. Similar to the original formulation of Broms, the present method calculates the maximum horizontal force and bending moment that can be sustained by the pile for two different head fixities (i.e. free-head and restrained-head) as a function of non-dimensional parameters that depend on the geometry and flexural resistance of the pile (i.e. yielding moment), the soil resistance and the type of failure mechanism (i.e. short, intermediate or long pile). Compared to Broms’ solution, the method introduces additional non-dimensional parameters that relate the water retention behaviour of the soil to the geometry of the pile. The proposed formulation accurately predicts the lateral capacity of piles as experimentally measured in previous works. Results confirm that consideration of the partially saturated state of the soil above the groundwater table is essential for a reliable estimate of the horizontal capacity of piles.

Variable blank holder pressure by magneto-rheological actuators in deep drawing

Deep drawing is one of the most used processes in industry, whose reliability is closely linked to the possibility of adequate control of the blank holder force (BHF). To avoid typical failure mechanisms, such as wrinkling and tearing, it is necessary to properly adjust the BHF during the process. The paper presents the design of a new blank-holding set-up based on magneto-rheological actuators, which allow a flexible adjustment of the force during the process. A closed-loop control, based on the direct detection of the metal sheet displacement under the blank holder, is implemented to regulate in real-time the actuator's load. The obtained experimental test results show that (i) the presented set-up allows to apply blank holder pressures with an average error less than 5% with respect of the target forces; (ii) the low latency times to allow the force variations, and (iii) the possibility to vary in real-time the blank holder load response during the deep drawing.

Research on Fracture Mechanism and Stability of Slope with Tensile Cracks

Tensile cracks at the crest of slope will attenuate the stability of slope. The aim of this paper is to investigate the computation of safety factors acting on a clay slope when the slip surface consists of tensile crack and shear surface. Based on the theory of limit equilibrium, an analytical solution for safety factors containing three types of failure mechanisms is presented. The optimal crack depth was obtained by using the principle of minimum safety factor. In the solution, effects of parameters such as crack depth, slope angle, height, cohesion, and internal friction angle on slope stability were discussed. By comparing with the results of previous studies, the rationality of the proposed approach was verified. Results show that consideration of tensile cracks lead to a significant reduction in slope stability, and the safety factor decreases by about 10% compared with the slope without cracks. The law of safety factor varying with crack depth indicates that it first decreases as the crack depth is increased and then increases as the crack depth is further increased. Through the parametric analysis, it is found that the safety factor increases with an increase in cohesion and internal friction angle but decreases with the slope angle and height increase. It is important to note that the optimal crack depth does not exceed one-third of the slope height. Moreover, a highway landslide that occurred in the road running across the Yunnan and Tibet Province was investigated to verify the practicality of the present method.