Advanced Three-dimensional Finite Element Research Articles

Unraveling mechanisms and failures of stray current corrosion in urban Subway adjacent pipeline networks through statistical insights and 3D simulation

The escalating expansion of urban subway systems in recent years has accentuated the issue of stray current corrosion within pipeline networks, emerging as a critical concern for urban safety. This paper delves into the intricate interplay between these phenomena, employing data-driven statistical analyses to elucidate the coupling characteristics between subway lines and the occurrence of failures in adjacent buried pipelines. An advanced three-dimensional finite element model was developed for stray current corrosion in pipelines, seamlessly integrating empirical data and physics-based modeling, which is to uncover the spatial nuances and multifaceted impacts on subway pipeline corrosion from both macro and micro perspectives under varying influencing factors. The study unveils a pronounced geographical and functional affinity between urban subway networks and metallic pipeline networks. The coupling attributes between subway systems and pipelines, such as distance, angle, and pipeline-specific characteristics including material and age, assume pivotal roles. The results further emphasize the hierarchical order of influence, with stray current intensity holding the greatest sway, followed by the distance between subway and pipelines, the angle between them, and soil resistivity. This paper offers a comprehensive investigation of the interrelationships and influential factors between subway systems and adjacent pipelines. It contributes to the mitigation and management of stray current corrosion in pipelines induced by nearby rail transit, thereby enhancing the resilience of both subway and pipeline networks within urban areas.

Modelling and Multi-Objective Optimisation of Finger Joints: Improving Flexural Performance and Minimising Wood Waste

The wood industry faces the dual requirements of improving the quality of timber products and minimising waste during the manufacturing process. The finger joint, which is an end-to-end joining method for timber boards, is one of the most important aspects of engineering wood products. This study presents a numerical and optimisation investigation of the effects of finger-joint design parameters on the flexural behaviour of finger-jointed timber beams. A numerical model based on advanced three-dimensional finite element analysis was developed to model the behaviour of finger-jointed beams. Using the validated finite element (FE) model and automated parameterisation, a parametric study was conducted to assess the impact of each design parameter of the finger joint, including finger length, tip thickness, and the number of finger joints. The results indicate that the number of fingers and finger length significantly influence the maximum load capacity, while the tip thickness has a marginal effect on performance. This study identifies a design threshold of five fingers and a 14 mm finger length for achieving efficient, high-performance finger-joint designs. In addition, the multi-objective modified firefly algorithm (MOMFA) was proposed to maximise the finger joint resistance while simultaneously minimising the material waste. The optimisation shows that there will be a significant amount of wood waste when using traditional single-objective optimisation that only focuses on structural performance. In contrast, the proposed method achieves comparable load capacity while significantly reducing waste (up to 53.31%) during the joining process. The automated finite element modelling framework and holistic optimisation developed in this study can be used to design and optimise engineering wood products for construction applications.

A deep dive into the static force transmission of the human masticatory system and its biomechanical effects on the temporomandibular joint

ObjectiveThis study aims to investigate the biomechanical behavior and reveal the force transmission patterns of the human masticatory system through advanced three-dimensional finite element (FE) models. MethodsThe FE model was constructed according to the medical images of a healthy male adult. It contains full skull structures, detailed temporomandibular joints (TMJs) with discs, complete dentitions, masticatory muscles, and related ligaments. Several static bite scenarios were simulated to demonstrate the effects of bite positions and muscle force recruitments on the force transmission patterns. ResultsMolar occlusal surfaces are the primary force transmission region for clenching. Sensitivity analysis demonstrated that the stiffness of the bite substance would not alter the force transmission patterns but could affect the maximum contact stresses on the discs and the occlusal surfaces. During the unilateral clenching tasks, the high-stress region on the discal surfaces shifted ipsilaterally. The presence or absence of the molar cushions would significantly affect the biomechanical response of the masticatory system. SignificanceFE analysis is an effective way of investigating biomechanical responses involving complicated interactions. Enriching the static analysis of the masticatory system with a detailed model can help understand better how the forces were transmitted and the significance of TMJs during the clenching process.

Testing and modeling clay behavior subjected to high strain rate loading in a tunneling problem

Complex numerical simulations of tunnels are often used to model effects of high strain rate surface loads. Most of this modeling ignores soil's strength dependency on strain rate to lessen the complexity. A series of Split Hopkinson Pressure Bar (SHPB) tests emulates the high strain rate compression occurring in blast events, for Nile Silty Clay (NSC) samples. The Cowper Symonds parameters are calibrated to SHPB test results and are used in advanced three-dimensional finite element analysis of a benchmark tunnel problem using Abaqus/Explicit software. The shallow tunnel in NSC formation is subjected to a blast event at the ground surface simulated by the CONWEP algorithm. The Smoothed Particle Hydrodynamic (SPH) mesh-free technique captures the crater formed due to the explosion. Results from the benchmark problem show that including the strain rate dependency in the analysis leads to a significant reduction in the calculated tunnel liner straining actions and deformations.

Structural testing and numerical modelling of T-joints between cold-formed S690 circular hollow sections under brace in-plane bending

This paper presents a comprehensive investigation into the structural behaviour of T-joints between high strength S690 cold-formed circular hollow sections (CFCHS) under brace in-plane bending, and deformation characteristics of these T-joints under both monotonic and cyclic actions are examined experimentally and simulated numerically. These T-joints between S690 CFCHS were found to deform with a high level of resistances and ductility under both monotonic and cyclic actions.Through an integrated numerical modelling approach developed by the authors, advanced three-dimensional finite element models of CFCHS with solid elements were established. With a proper definition of weld collars at the brace/chord junctions of the T-joints between S690 CFCHS with different diameters and thicknesses, these models were readily adopted to perform a heat transfer analysis, a thermomechanical analysis and a structural analysis sequentially with compatible element types and meshes. Hence, the effects of the welding-induced residual stresses at the welded brace/chord junctions onto the structural behaviour of these T-joints were readily assessed. Consequently, these advanced models are demonstrated to be able to predict rationally deformation characteristics of these T-joints between S690 CFCHS under monotonic and cyclic actions of brace in-plane bending with a high degree of structural accuracy.

Cyclic response of column to foundation connections of reinforced concrete precast structures: Numerical and experimental comparisons

The cyclic response of a column to foundation connection system, based on the mechanical connection between steel shoes embedded into the column base and protruding steel bolts anchored into the foundation, is experimentally and numerically examined in this paper. The hysteretic behaviour and the global collapse mechanism of the connections are studied through three full-scale specimens subjected to a constant axial load and to a quasi-static cyclic horizontal top displacement history at increasing drift levels. Additionally, advanced three-dimensional finite element models, including non-linearity in material and geometry, are developed and calibrated in order to analyze and capture the local experimental response of the connections. Due to the lack of information and guidelines on the subject, the aim of this research is to evaluate the seismic performances of the system in order to evaluate the real response of the welded connection between steel shoes and reinforcing bars.

Dynamic response of flexible rockfall barriers with different block shapes

Flexible rockfall barriers are commonly constructed on steep hillsides to mitigate rockfall. The evaluation of the dynamic response of proprietary flexible rockfall barriers is conventionally performed using full-scale field tests by dropping a block onto the barriers in accordance with the European test standard ETAG 027. The block typically has a spherical or polyhedral shape and cannot reproduce more complex rockfall scenarios encountered in the field. Little attention has been paid to the effects of the block shape on the impact force and structural response. This paper aims to quantitatively reveal the influence of the block shape on the dynamic response of flexible rockfall barriers. First, an ellipsoidal model is established to approximately simulate the block, and the sphericity is employed as the representative index of the block’s shape. A full-scale test on a typical flexible barrier system is carried out and then used to calibrate an advanced three-dimensional finite element model. Finally, the dynamic responses of flexible rockfall barriers are analyzed and discussed, focusing on the effects of the block’s shape. The numerical results show that the sphericity will obviously influence the maximum elongation of flexible barriers, the peak impact force, the peak force of the upslope anchor cable, the peak force of the lower main support cable, the axial peak force of the post, and the peak shear force at the post foundation. The assumption of spherical or polyhedral blocks in the test standard could lead to the defensive failure of flexible rockfall barriers in some impact scenarios.

Numerical simulation of responses of flexible rockfall barriers under impact loading at different positions

Flexible rockfall barriers have been widely used to mitigate rockfalls and protect residential buildings, railroads and highways from such natural hazard. Evaluation of the performance of flexible rockfall barriers are conventionally conducted using the full-scale impact tests in accordance with European guideline ETAG 027, in which the impact position is specified at the centre of the middle functional module. However, the trajectory of a rockfall in real case is random such that the impact position is unknown. The influence of different impact locations has not been reported in literature. In this paper, a full-scale test on a typical flexible barrier system is carried out and then used to calibrate an advanced three-dimensional finite element model, which is proposed for parametric study for the investigation of dynamic response of a typical flexible rockfall barrier under impacts at different positions. The numerical results show that the impact location will influence the residual height and maximum elongation of the flexible barrier. Although the impact position slightly affects the peak forces of support ropes, it will significantly influence the peak forces of the upslope anchor ropes and lead to unsafe anchor design. The proposed model can accurately predict the behaviour of flexible barriers and help designers to consider more practical conditions which are not specified in ETAG 027.

A numerical study on indentation properties of cortical bone tissue: influence of anisotropy.

The purpose of this study is to investigate the effect of anisotropy of cortical bone tissue on measurement of properties such as direction-dependent moduli and hardness. An advanced three-dimensional finite element model of microindentation was developed. Different modelling schemes were considered to account for anisotropy of elastic or/and plastic regimes. The elastic anisotropic behaviour was modelled employing an elasticity tensor, and Hill's criteria were used to represent the direction-dependent post-yield behaviour. The Oliver-Pharr method was used in the data analysis. A decrease in the value of the transverse elasticity modulus resulted in the increased material's indentation modulus measured in the longitudinal direction and a decreased one in the transverse direction, while they were insensitive to the anisotropy in post-elastic regime. On the other hand, an increase in plastic anisotropy led to a decrease in measured hardness for both directions, but by a larger amount in the transverse one. The size effect phenomenon was found to be also sensitive to anisotropy. The undertaken analysis suggests that the Oliver-Pharr method is a useful tool for first-order approximations in the analysis of mechanical properties of anisotropic materials similar to cortical bone, but not necessarily for the materials with low hardening reserves in the plastic regime.

Announcement: Remote Sensing 2017 Best Guest Editor Award

Announcement: Remote Sensing 2017 Best Guest Editor Award

Advanced Three-Dimensional Finite Element Modeling of a Slow Landslide through the Exploitation of DInSAR Measurements and in Situ Surveys

In this paper, we propose an advanced methodology to perform three-dimensional (3D) Finite Element (FE) modeling to investigate the kinematical evolution of a slow landslide phenomenon. Our approach benefits from the effective integration of the available geological, geotechnical and satellite datasets to perform an accurate simulation of the landslide process. More specifically, we fully exploit the capability of the advanced Differential Synthetic Aperture Radar Interferometry (DInSAR) technique referred to as the Small BAseline Subset (SBAS) approach to provide spatially dense surface displacement information. Subsequently, we analyze the physical behavior characterizing the observed landslide phenomenon by means of an inverse analysis based on an optimization procedure. We focus on the Ivancich landslide phenomenon, which affects a residential area outside the historical center of the town of Assisi (Central Italy). Thanks to the large amount of available information, we have selected this area as a representative case study highlighting the capability of advanced 3D FE modeling to perform effective risk analyses of slow landslide processes and accurate urban development planning. In particular, the FE modeling is constrained by using the data from 7 litho-stratigraphic cross-sections and 62 stratigraphic boreholes; and the optimization procedure is carried out using the SBAS-DInSAR retrieved results by processing 39 SAR images collected by the Cosmo-SkyMed (CSK) constellation in the 2009–2012 time span. The achieved results allow us to explore the spatial and temporal evolution of the slow-moving phenomenon and via comparison with the geomorphological data, to derive a synoptic view of the kinematical activity of the urban area affected by the Ivancich landslide.

Available rotation capacity of composite beams with high-strength materials under sagging moment

Using high-strength (HS) materials in steel–concrete composite beams is an efficient approach to reduce the self-weight and to improve the sustainability benefits of such members. Due to a lack of precise knowledge of the ductility of composite beams beyond their first yield as a result of the non-linear response of their constituent materials, a comprehensive investigation is reported herein to quantify the available rotation capacity of composite beams using HS materials when subjected to sagging bending. An advanced three-dimensional finite element model is utilised to calculate the end rotation of single-point-loaded simply-supported composite beams. The model has demonstrated to be adequate and reliable in terms of predicting the flexural strength and load–deflection response by comparisons with numerous experimental results reported elsewhere. As many as 1380 beams with various strengths of steel and concrete as well as a wide range of the degree of shear connection and geometries are modelled, and both solid slabs and composite slabs using profiled steel decking are incorporated. Analyses of this body of data indicate that the depth of the neutral axis is the most essential parameter for determining the available sagging rotation capacity, of which an increased value leads to a lower rotation capacity. The yield strength of the steel also has noticeable effects with higher values resulting in poorer rotation performance. The available rotation capacity is also sensitive to the span-to-depth ratio of the beams. In addition, the effects of varying cross-sectional geometries, different patterns of shear connector distributions as well as of geometric imperfections and residual stresses are clarified, which are shown to be slight and can therefore be ignored. Finally, a non-linear empirical equation is developed to predict the available rotation capacity of composite beams using HS materials, which covers the range of numerical data with satisfactory consistency. The outcomes provide an important basis for evaluating the ductility of composite beams by comparing with the required rotation capacity.

Evaluation of Effects of Variations in Aggregate Base Layer Properties on Flexible Pavement Performance

This paper aims to evaluate flexible pavement responses and performance affected by variations in the aggregate base layer properties. An advanced three-dimensional finite element (FE) model was developed to capture the nonlinear cross-anisotropic behavior of granular material. The FE model characterized the hot-mix asphalt layer as a viscoelastic material and used moving load to predict time- and temperature-dependent pavement responses under different temperatures (25°C and 45°C). Two asphalt pavement sections with different asphalt layer thicknesses (3 and 5 in.) were analyzed, considering variations in aggregate properties. The response changes in the asphalt layer, aggregate base layer, and subgrade depended on the interaction between viscoelastic asphalt layer and stress-dependent aggregate base layer. Fatigue cracking and subgrade rutting were more affected by changes of aggregate base layer properties among different failure mechanisms in each pavement layer. The coefficient of curvature and complex maximum dry density served as the contributing parameters most affecting fatigue cracking potential, especially for the relatively thinner asphalt pavement at the higher temperature. However, the moisture content ratio affected the subgrade rutting potential more than other parameters did. These conclusions serve as the basis for selecting optimum aggregate properties for pavement design and developing a performance-related specification for quality control and quality assurance in pavement construction.

Airfield Flexible Pavement Responses under Heavy Aircraft and High Tire Pressure Loading

This paper investigates airfield flexible pavement responses under heavy aircraft and high tire pressure loading considering the realistic aircraft tire–pavement interaction. An advanced three-dimensional finite element model was developed; it characterized the hot-mix asphalt layer as a viscoelastic material and used implicit dynamic analysis to predict time-and temperature-dependent pavement responses under various loading conditions. The tire loadings were simulated as moving loads having uniform and nonuniform contact stress distributions. To illustrate the effect of moving load, stationary loading analysis was conducted with the equivalent modulus determined from the middepth pulse time under moving loading. Two temperature profiles were considered in the analysis, as compared with the constant temperature profile using the average temperature. The pavement responses in the asphalt layer (tensile, compressive, and shear strains) under different loading conditions were calculated and analyzed in terms of pavement failure mechanisms. The results emphasized the importance of considering nonuniform contact stresses and moving load in airfield pavement analysis. On the contrary, applying the average temperature profile in summer was a conservative approach for predicting fatigue cracking potential but underestimated rutting or near-surface cracking potential in the airfield pavement. The rut depths in the asphalt layer were predicted by using mechanistic–empirical performance models and compared with the measurements from the full-scale test. The results suggested that specific calibration parameters should be developed to provide accurate prediction of rut depth for airfield pavements.

Finite Element-Based Design of Grouted Connections with Shear Keys for Offshore Wind Turbines

Unexpected settlements in grouted connections caused concern in the offshore wind power industry. A grouted connection connects the transition piece of the tubular turbine tower to the monopile foundation by an annulus filled with high-strength grout. On several wind turbines, the transition piece has moved several centimetres downwards. Since the discovery of this serious problem, the generally applied codes for the design of grouted connections are under revision, and alternative solutions are investigated. Shear keys on the steel surfaces increase the capacity of the connection significantly. The paper discusses various approaches to finite element modelling of grouted connections with shear keys. For the design and the corresponding certifying process, advanced three-dimensional finite element models have been developed by the authors. The models consider the complex interface behaviour between steel and grout, the nonlinear material behaviour, and the detailed geometry of the shear keys. The results of the analysis are compared with laboratory tests on small-scale grouted connections and show good agreement. Furthermore, a comparison is made with recently published design guides.

Analytical model for the bond-slip behaviour of corroded ribbed reinforcement

Corrosion of reinforcement affects the bond mechanism between reinforcement and concrete, and thus the anchorage. Reliable models describing this are needed especially for assessment of the load-carrying capacity of existing structures. This paper presents an analytical one-dimensional model for bond-slip response of corroded reinforcement. The proposed model is an extension of the bond-slip model given in the CEB-FIP Model Code 1990, and is practically applicable for structural analyses to determine the load-carrying capacity of corroded structures. Furthermore, the anchorage length needed to anchor the yield force is calculated from the bond slip, using the one-dimensional bond-slip differential equation. Results of the proposed model are compared with experimental results as well as results from an advanced three-dimensional finite element model. The suggested model is shown to give results that are consistent with the physical behaviour.