Refined Finite Element Model Research Articles

Failure assessment and virtual scenario reproduction of the progressive collapse of the FIU bridge

The Florida International University pedestrian bridge in the United States is a two-span prestressed reinforced concrete bridge, which collapsed during its construction in March 2018. In this study, a finite element (FE) numerical simulation is performed to reproduce the virtual scenario of the bridge collapse and examine the cause of this accident. A refined FE model is established on the basis of the concrete plastic damage constitutive relations, and the damage factor is calculated using the Najar damage theory. When the model is combined with the alternative path method, the complete simulation of the structural damage and the collapse process is obtained. Especially, two key features of the structural response process, i.e. the instantaneous image of the collapse behavior and the total time of collapse 1.2 s, are almost identical with that recorded in the video. Simulation results can accurately reproduce the entire collapse process, indicating that the computational strategy used in this study are appropriate. Further investigation on the deformation and failure modes at different times during the collapse process and a discussion on the critical role of key components in the progressive collapse are presented. Analysis results show that the collapse of the structure is caused by the destruction of local nodes; the structural robustness analysis is crucial for the collapse resistance design. Numerical results and conclusions can provide a reference for the cause of bridge collapse accidents. The critical information of the finite element analysis process is presented in detail.

A machine learning approach for magnetic resonance image-based mouse brain modeling and fast computation in controlled cortical impact.

Computational modeling of the brain is crucial for the study of traumatic brain injury. An anatomically accurate model with refined details could provide the most accurate computational results. However, computational models with fine mesh details could take prolonged computation time that impedes the clinical translation of the models. Therefore, a way to construct a model with low computational cost while maintaining a computational accuracy comparable with that of the high-fidelity model is desired. In this study, we constructed magnetic resonance (MR) image-based finite element (FE) models of a mouse brain for simulations of controlled cortical impact. The anatomical details were kept by mapping each image voxel to a corresponding FE mesh element. We constructed a super-resolution neural network that could produce computational results of a refined FE model with a mesh size of 70μm from a coarse FE model with a mesh size of 280μm. The peak signal-to-noise ratio of the reconstructed results was 33.26dB, while the computational speed was increased by 50-fold. This proof-of-concept study showed that using machine learning techniques, MR image-based computational modeling could be applied and evaluated in a timely fashion. This paved ways for fast FE modeling and computation based on MR images. Results also support the potential clinical applications of MR image-based computational modeling of the human brain in a variety of scenarios such as brain impact and intervention.Graphical abstract MR image-based FE models with different mesh sizes were generated for CCI. The training and testing data sets were computed with 5 different impact locations and 3 different impact velocities. High-resolution strain maps were estimated using a SR neural network with greatly reduced computational cost.

Collapse prognosis of a long‐span cable‐stayed bridge based on shake table test and nonlinear model updating

SummaryThe collapse of long‐span cable‐stayed bridges under strong earthquakes will not only result in severe casualties and loss of property but also significantly delay the rehabilitation of the affected area. It is therefore essential to study the failure progress and potential collapse mechanisms of these bridges under strong earthquakes for assisting their inspection and maintenance and helping them survive an earthquake. Collapse simulations in existing studies are commonly conducted with design‐document‐based finite element (FE) models, which usually neglect the actual damage state of the bridges. The influences of modelling uncertainties on the simulated responses cannot be addressed. This study proposes a nonlinear FE model updating‐based collapse prognosis method for long‐span cable‐stayed bridges, which includes (1) a correlated‐updating‐parameter‐based nonlinear FE model updating algorithm, (2) a restarted time history analysis‐based seismic response prediction method and (3) an elemental deactivation‐based collapse simulation algorithm. The shake table test of a scaled Sutong cable‐stayed bridge in China is adopted to illustrate the proposed earthquake‐induced collapse prognosis method. A refined FE model of the bridge is first established and nonlinearly updated using the measurement data. The collapse prognosis of the bridge under a subsequent strong ground motion is then performed based on the updated model. The predicted structural responses and final failure mechanisms are compared with the measured responses and experimental observations with good agreement, indicating that the proposed method is feasible and accurate for evaluating the seismic performance and failure mechanisms of long‐span cable‐stayed bridges.

Numerical Analysis of Working Processes in the Blade Channels of the Highly-Loaded Turbine of a Marine Gas Turbine Engine, Using a Refined Finite Element Model

Numerical Analysis of Working Processes in the Blade Channels of the Highly-Loaded Turbine of a Marine Gas Turbine Engine, Using a Refined Finite Element Model

A novel identification method for obtaining bending moment–curvature relations of wood stems based on digital image correlation and SDOF analysis

Bending moment–curvature relations (M-χ) are useful in many beam modelling approaches. It allows describing in a simple way the mechanical behaviour at the cross-section scale and can be used to model continuous beams as single degree of freedom systems dedicated to perform stochastic analysis. This paper focused on tree mechanical charaterisation and presents an identification method for obtaining bending moment–curvature relationships up to failure from Digital Image Correlation (DIC) and experimental three points bending tests. Due to wood intrinsic variability, the proposed identification method has been validated from a Finite Element (FE) model which aims at simulating precisely the bending response of a cylindrical stem. The refined FE model has been developed based on the geometry and the boundary conditions of the experimentally tested stems. M-χ curves are derived from the FE model and used within a Single Degree Of Freedom (SDOF) approach. At the stem scale, the prediction of the SDOF model (Force-Displacement) is compared to the FE model and lead to a good agreement. Then the approach is used to characterise fresh European beech samples allowing deriving their mechanical properties (longitudinal Young modulus, modulus of elasticity and modulus of rupture).

Use of Refined Finite Element Models for Solving the Contact Thermoalasticity Problem of Gas Turbine Rotors

A refined mathematical model of gas turbine engine rotors using three-dimensional finite elements of a curvilinear form is developed. All the calculations were performed for rotors, which are widely used in power machine building and shipbuilding. The fact is that such components have a constructive heterogeneity that can hardly be correctly explained using well-known finite elements and their shape functions. On the other hand, the mathematical model should be as simple as possible with a view to its wide use in the process of designing a rotor. Therefore, a new refined finite-element mathematical model was developed, consisting of three-dimensional curvilinear hexahedral finite elements. It was used to calculate the displacement field caused by the complex action of the heat flux and contact load at the junction of rotor elements. This approach makes it possible to describe the entire rotor as a superposition of the developed curvilinear finite element models and make the calculation process more correct and compact. To solve this problem, a system of matrix equations was compiled. It is based on the use of energy balance dependences in the mechanical contact interaction of rotor elements, as well as the heat balance under the influence of non-stationary heat flow. When creating a numerical algorithm for solving the problem, the direct decomposition of Cholesky was used. To make the solution more compact, the Sherman scheme was used. All the calculations of displacement and temperature fields were carried out for two widely used types of joints, which are used to create such rotors, namely: joints with clearance and interference.

Numerical investigations on elastic buckling and hysteretic behavior of steel angles assembled buckling-restrained braces

This paper presents a numerical investigation on elastic buckling and hysteretic behavior of a steel angles assembled buckling-restrained brace (SAA-BRB). The SAA-BRB is composed of a cruciform-sectional steel core encased by an external restraining system, which consists of four steel angles connected together by high-strength bolts and spacers. It is found that the SAA-BRB may fail in a global buckling mode or in a local buckling mode. In order to predict the global and local buckling behavior of SAA-BRBs, two design parameters: the restraining ratio and segment restraining ratio are proposed. To determine these two design parameters, a simplified theoretical model of SAA-BRBs and an accurate finite element (FE) model are used to investigate the global and local elastic buckling behaviors of SAA-BRBs. Based on more than 500 FE results, explicit expressions of the restraining ratio and segment restraining ratio are obtained and validated to be sufficiently accurate for practical design applications. In addition, 20 refined FE models considering material and geometrical nonlinearities are used to carry out parametric studies for comprehensively investigating the hysteretic behavior of SAA-BRBs. Finally, the following design recommendations for fix-ended SAA-BRBs are proposed: (1) the restraining ratio should be >2.2 to prevent a SAA-BRB from the global buckling failure, and (2) the segment restraining ratio should be >6.0 to prevent a SAA-BRB from the local buckling failure.

Determination of thermo-elastic parameters for dynamical modeling of 2.5D C/SiC braided composites

An approach on determining elastic parameters and Coefficient of thermal expansion (CTE) of a 2.5-dimensional (2.5D) braided composites is proposed in this paper, by adopting mesoscopic mechanics integrated Finite element (FE) modeling. According to the geometric features of meso-structure, Representative volume cell (RVC) models of composite for predicting thermo-elastic parameters are established. On the basis of the models, homogenized parameter prediction is carried out in three steps: Firstly, equivalent elastic properties is predicted subject to periodic displacement boundary conditions; secondly, the equivalent thermal modulus is determined by using the periodic non-adiabatic temperature boundary conditions; thirdly, using the obtained elastic parameters and thermal modulus to calculate the equivalent coefficient of thermal expansion. A multiscale finite element analysis is conducted: The thermo-elastic parameters of yarn is calculated using the RVC model; subsequently, the equivalent parameters of the yarn are substituted into the RVC of 2.5D braided C/SiC composites, to predict the thermo-elastic parameters. Results indicate that the CTE determined by homogenized parameter prediction of 2.5D C/SiC composites shows good agreements with the experimental results. At last, the refined FE model and the equivalent homogeneous model are employed to verify the effectiveness of the predicted parameters in terms of effective modeling. After the comparative analysis on thermal modal data between refined model and equivalent model, the acquired results demonstrate the effectiveness of the proposed method in determining thermo-elastic parameters.

Subassemblage tests and numerical analyses of buckling-restrained braces under pre-compression

Pre-compression loads are conducted in BRBs if the installation of frames and BRBs are performed simultaneously. In this paper, the load-carrying and energy-dissipating behavior of BRBs under pre-compression are investigated by subassemblage tests and additional finite element (FE) analyses. A total of five specimens were tested, in which two specimens were tested by cyclic pure compression loads and three specimens were tested by hysteresis loads; four of them maintained stable load-carrying behavior during loading process. The load-carrying and energy-dissipating behavior of the specimens were satisfactorily simulated using a refined FE model with a combined isotropic and kinematic hardening rule of the core material, and the compression strength adjustment factor and the stress enhancement coefficient were well predicted by the FE analytical results with a relative error less than 3.0%. The FE analytical results of BRBs with different pre-compression strains are presented, indicating that the pre-compression in a BRB would aggravate the stress enhancement of the core material in both tension and compression, yet it would hardly influence the value of the compression strength adjustment factor.

Assessing the influence of hand-arm posture on mechanical responses of the human hand during drilling operation

Drilling is one of the important metal cutting processes in the industrial sectors. Though there are several research studies exclusively pertaining to drilling mechanism and the implications on materials, there are research voids that pertain to the driller’s hand-arm posture and the corresponding mechanical responses during the process. Considering the vitality of the ergonomics involved, the objective is framed to estimate the stresses acting on the hand while operating handheld drilling machine by different subjects and investigate the effects of various hand-arm postures on the stresses transmitted to the hands. Finger TPS—wireless tactile force sensor device—is employed for measuring the force exerted at the fingers while operating handheld cordless drilling machine. The nature of vibration transmitted to the human hand-arm system is affected by the contact force variation between a vibrating tool handle and the hand. The transmitted vibration will impose the stresses on the anatomical structure of the hand-arm system. In the present study, the dynamic response of a human hand to exert force during drilling task is analysed by three-dimensional finite element (FE) model of the human hand of a normal male. The model is developed from 3D reconstruction of CT scan images using the segmentation software, Mimics. The FE model contains the essential anatomical structures of a human hand. It includes both linear and nonlinear elements to represent rigid and elastic parts of the hand like the bones, tissues etc. Refined FE model is properly meshed, and analysis is carried out using finite element code ABAQUS. Preliminary results of the numerical analysis utilizing the developed model and qualitative evaluation are presented. Stress values are the highest while drilling in the extended forearm with the elbow at an angle of 180° and are followed by drilling objects located at a height above shoulder level.

Seismic damage analysis of the outlet piers of arch dams using the finite element sub-model method

This study aims to analyze seismic damage of reinforced outlet piers of arch dams by the nonlinear finite element (FE) sub-model method. First, the dam–foundation system is modeled and analyzed, in which the effects of infinite foundation, contraction joints, and nonlinear concrete are taken into account. The detailed structures of the outlet pier are then simulated with a refined FE model in the sub-model analysis. In this way the damage mechanism of the plain (unreinforced) outlet pier is analyzed, and the effects of two reinforcement measures (i.e., post-tensioned anchor cables and reinforcing bar) on the dynamic damage to the outlet pier are investigated comprehensively. Results show that the plain pier is damaged severely by strong earthquakes while implementation of post-tensioned anchor cables strengthens the pier effectively. In addition, radiation damping strongly alleviates seismic damage to the piers.

Development and application of a simplified model for the design of a super-tall mega-braced frame-core tube building

Resilience-based earthquake design for next-generation super-tall buildings has become an important trend in earthquake engineering. Due to the complex structural system in super-tall buildings and the extreme computational workload produced when using refined finite element (FE) models to design such buildings, it is rather difficult to efficiently perform a comparison of different design schemes of super-tall buildings and to investigate the advantages and disadvantages of different designs. Here, a simplified nonlinear model is developed and applied to compare two design schemes (i.e., the fully braced scheme and half-braced scheme) of a super-tall mega-braced frame-core tube building, which is an actual engineering project with a total height of approximately 540m. The accuracy of the simplified model is validated through a comparison of the results of modal analyses, static analyses and dynamic time history analyses using the refined FE models. Subsequently, the plastic energy dissipation of different components and the distribution of the total plastic energy dissipation over the height of the two design schemes are compared using the proposed simplified model. The analyses indicate that the fully braced scheme is superior because of its more uniform energy distribution along the building height and the large amount of energy dissipated in the replaceable coupling beams, which enables rapid repair and re-occupancy after an earthquake. In contrast, the potential damage in the half-braced scheme is more concentrated and more severe, and the damage in the core tubes is difficult to repair after an earthquake.

Joints and wood shear walls modelling II: Experimental tests and FE models under seismic loading

This study presents a finite element (FE) model of timber-framed shear walls under seismic loading, which has been validated in Part I under quasi-static loading. In this paper, experimental shake table tests on shear walls are described and some examples of the obtained results are discussed. Then, the refined FE model predictions under dynamic loading are compared to the 11 shake table tests. The final objective of this study is to create a 3D model of timber-framed structures; thus, a simplified FE model is proposed to reproduce the refined FE model predictions at a reasonable computational cost. The calibration method of the simplified model uses the predictions of the refined FE model under quasi-static loading as input. The simplified model is then used for dynamic calculations and its predictions are confronted to the refined FE model ones, in order to validate its behaviour under dynamic loading. Eventually, an efficient method to build the walls of a timber-framed building by coupling simplified FE models is proposed.

A numerical-informational approach for characterising the ductile behaviour of the T-stub component. Part 1: Refined finite element model and test validation

In the component-based method, the ductility characterisation of the tension component plays a primary role in accurately predicting the rotation capacity of the whole connection. In this paper, a refined finite element (FE) model is presented to assess the complete force–displacement response of the T-stub component, from the initial stiffness up to the fracture point. The refined FE model includes a non-linear continuum damage mechanics model that considers the onset of the damage, the damage evolution law, and the component failure. A parametric study was conducted to evaluate the influence of the damage parameters in the overall response of the T-stub component. The numerical results obtained from the refined FE model strongly agree with the experimental results of 18 test specimens. The comparison reveals the proposed FE model’s satisfactory accuracy, with an average fitting error below 9%. This paper constitutes the first part of a comprehensive methodology based on combining FE analysis and soft computing techniques. The ultimate goal of this methodology is to predict the key parameters that define the force–displacement response of the T-stub component.

Finite element modelling of concrete-filled steel stub columns under axial compression

Due to the passive confinement provided by the steel jacket for the concrete core, the behaviour of the concrete in a concrete-filled steel tubular (CFST) column is always very challenging to be accurately modelled. Although considerable efforts have been made in the past to develop finite element (FE) models for CFST columns, these models may not be suitable to be used in some cases, especially when considering the fast development and utilisation of high-strength concrete and/or thin-walled steel tubes in recent times. A wide range of experimental data is collected in this paper and used to develop refined FE models to simulate CFST stub columns under axial compression. The simulation is based on the concrete damaged plasticity material model, where a new strain hardening/softening function is developed for confined concrete and new models are introduced for a few material parameters used in the concrete model. The prediction accuracy from the current model is compared with that of an existing FE model, which has been well established and widely used by many researchers. The comparison indicates that the new model is more versatile and accurate to be used in modelling CFST stub columns, even when high-strength concrete and/or thin-walled tubes are used.

Experimental investigation into the thermoelastic spring-in of curved sandwich panels

An investigation into the thermoelastic spring-in of curved sandwich panels has been conducted. Sandwich panels incorporating solid foam cores and biaxial glass–epoxy skins were manufactured and spring-in measured. The major contributors to spring-in were found to be the thermal expansion and Poisson’s ratio of the foam which were subsequently characterised. Also important was the development of resin rich regions on the surface of the panel. Experimental findings were implemented into a finite element (FE) model developed using 3-dimensional elements in ANSYS. The investigation was extended to panels including a core with machined slots. A refined FE model highlighted the influence of in-plane restraint reduction within the core, as well as the effect of a much thicker resin rich region caused by core segmentation. Results showed good agreement with experiment and provided a good basis for shape prediction of sandwich panels.

Mechanical Analysis of the Anchorage Zone of Pylon for Xinjiang Cable-Stayed Bridge Based on Refined Finite Element Model

The Pylon of Xinjiang Cable-Stayed Bridge has a special geometric form, of which the anchorage zone adopts the steel-concrete composite structure with built-in steel anchorage box. To investigate the mechanical behavior, the refined 3D finite element model has been established with the shear nails of steel anchorage box simulated. The stress conditions of steel anchorage box and concrete under prestressing bar and stayed cable forces have been then studied. The bearing proportion at the anchorage zone for the horizontal component of cable force has been calculated. Results indicate that the overall mechanical performance of the anchorage zone is excel, which can be a reference for designing of similar structure.

Simulation of the structural modifications of a disc brake system to reduce brake squeal

The noise and vibration generated by the braking system in passenger cars are important technical and economic problems in the automotive industry. In recent years, the finite element (FE) method has been found to be a useful tool in predicting the occurrence of noise in a particular brake system during the design stage. This paper presents a more refined FE model of the disc brake corner that includes the wheel hub and steering knuckle. The model is an extension of earlier FE disc brake models. Experimental modal analysis of the disc brake system is initially used to validate the FE model. The unstable frequencies were then predicted by applying a complex eigenvalue analysis to the FE model. Finally, a number of structural modifications are made and simulated to evaluate brake squeal at the design stage. From the predicted results, it is found that the most significant improvements in brake squeal performance could be achieved by using an aluminium metal matrix composite brake rotor, steel calliper, and steel bracket. It is also found that a stiffer friction material with a diagonal slot could reduce the propensity for brake squeal.

Piezoceramic shunted damping concept: testing, modelling and correlation

New laboratory tests are presented for the experimental evaluation and assessment of the piezoceramic shunted damping (PSD) concept for cantilever Aluminium thin (long) beams bonded symmetrically on their upper/lower surfaces with single pairs of small piezoceramic patches. Following these tests outcome, the PSD efficiency measure is proposed to be the so-called modal effective electromechanical coupling coefficient, which is post-processed from free-vibrations analyses under short-circuit and open-circuit electrodes of the patches. For this purpose, the tests are numerically modelled, analysed, and correlated using ABAQUS® commercial finite element (FE) code. Good tests/models correlations were reached after FE models electromechanical updating. This is attributed to the refined FE models in the sense that they have considered realistic and desirable features such as, electrodes equipotentiality, piezoceramic patches poling orientations (same/opposite), and the corresponding (parallel/series) electric wiring (connections).

Numerical modelling of riveted railway bridge connections for fatigue evaluation

Past experience has shown that stringer-to-cross-girder connections in riveted railway bridges are susceptible to fatigue cracking. This fatigue damage is caused by secondary stresses, which develop in the different components of the connection. For this reason, more detailed analysis techniques are needed to capture this type of behaviour. In this paper, a finite element (FE) model of a typical riveted railway bridge is developed by incorporating the detailed local geometry of a stringer-to-cross-girder connection into the global bridge model. Before the development of this model, benchmark FE studies are carried out on a double-lap joint and the results are presented in terms of stress concentration factors and stress gradients. Further verification studies are carried out on a local bridge connection FE model, in terms of its rotational stiffness. After this investigation, a refined FE model of the bridge is analysed under the passage of a freight train. Principal stress histories at different components of the connection are obtained, which are then combined with the plain material S–N curve, in order to identify the most fatigue-critical locations of the connection. These are identified as being the rivet holes and, in some cases, the angle fillet. By considering different rivet clamping stresses and different rivet defect scenarios it is found that the most damaging effects are caused by the presence of clearance between the rivet shank and the hole, and the loss of a rivet. The rivet clamping stress is also found to affect fatigue damage considerably.