Sophisticated Finite Element Analysis Research Articles

Over-sampling for data augmentation in data-driven models for the shear strength prediction of RC membranes

Complex reinforced concrete (RC) structures are generally assessed as a group of individual membrane elements subjected to in-plane combined stresses; however, an accurate prediction of the shear strength of such elements is still a complex task. In addition, the limited availability of experimental data of RC panels, which also presents an unbalanced statistical distribution towards lower strength values, limits the development of data-driven models. Thus, it is crucial to explore data augmentation techniques with a view to supporting the development of more accurate and generalizable predictive models in structural engineering. This paper evaluates over-sampling techniques for data augmentation and their use in the creation of an explainable, data-driven model for the shear strength prediction of RC panels. A dataset of 195 experimental tests of RC panels under different loading conditions is initially collected. Five over-sampling techniques are implemented to extend the original dataset and to reduce the imbalance. Three ensemble models (Random Forest, AdaBoost, and XGBoost) are trained with each of the generated datasets. It is observed that all the over-sampling techniques produced predictive models with better performance than the original dataset; however, the results show that by applying the Random Over-Sampling (ROS) the performance metrics of the model can significantly increase (around 39% for some metrics) compared to the model with the original dataset, without any overfitting issues. This strategy allowed to develop an accurate XGBoost model (with a value of R2 = 0.97 for the testing set). The explainability of the final predictive model (XGBoost model obtained from ROS) is evaluated using the SHAP (SHapley Additive exPlanations) analysis. The proposed predictive model outperformed traditional mechanics-based models (improvement of approximately 27% over SMCS and 33% over MCFT for some performance metrics) and with a more controlled error distribution over the range of variables. The proposed model was also more accurate (mean prediction ratio of 0.98) than sophisticated finite element analysis (mean prediction ratio of 0.84) for six specimens of the original dataset.

FE and probabilistic analysis for rubber life estimation considering cracking energy density as a fatigue predictor

This article suggests an engineering design for developing the probabilistic Wöhler diagram of rubber parts. The presented methodology includes multiaxial fatigue study as well as probabilistic fatigue calculation based on Wöhler diagrams. This approach is basically built on the Cracking Energy Density (CED) criterion. This is achieved by combining sophisticated Finite Element Analysis (FEA) with Monte Carlo simulation (MCS). To this end, a 3D-FEA numerical model is produced for several loading cases by means of the commercial software ABAQUS.

Tornado-affected safety assessment of tower cranes outer-attached to super high-rise buildings in construction

To fully address the safety concern of construction tower cranes outer-attached to super high-rise buildings in tornado wind fields, the safety envelopes of cranes under various scenarios are constructed. To more precisely obtain the time history of wind forces applied on the building-crane system in a tornado environment, the working conditions of cranes and the feature of the tornado field are considered in the development of various spatio-temporal computational fluid dynamics (CFD) models. To avoid sophisticated finite element analysis of the main building, the modified generalized flexural-shear model (FSM-MS) is used to estimate the along-wind and across-wind displacement response of main building and the response at the connection support of the tower crane. To reproduce possible failure modes of tower cranes as many as possible, the similar concept of incremental dynamic analysis was adopted to generate the safety envelopes of outer-attached tower cranes in various normal and typical abnormal scenarios. By this, whether a tower crane of concern is safe or not can be efficiently assessed by the ultimate wind velocity obtained from the envelope corresponding to certain working conditions. The feasibility of the safety assessment procedure has been systematically demonstrated on three case super high-rise buildings. The ultimate reference wind velocity of the tower crane was observed to be more sensitive to slewing angle. And, more attention should be paid to the issues of overloading and stiffness reduction of connection supports. The outcome from this concern has definitely enriched the framework of construction safety control management.

A Semi-Analytical Model for the Heat Generation during Hybrid Metal Extrusion and Bonding (HYB).

Hybrid Metal Extrusion and Bonding (HYB) is a novel solid-state welding method for metals and alloys that utilises continuous extrusion as a technique to enable aluminium filler metal additions. In the present study, a new semi-analytical model for the heat generation during aluminium butt welding is presented. As a starting point, the classical Rosenthal thin plate solution for the pseudo-steady-state temperature distribution around a fully penetrating line source is invoked. Then, the associated heat generation is calculated by considering the individual contributions from the tip of the rotating pin, the pin shoulder, and the filler metal additions on the net power input. In a calibrated form, the model yields thermal efficiency factors that are in close agreement with those obtained from more sophisticated finite element analyses but with considerably less computational effort.

An Analysis Tool for the Installation of Submarine Cables in an S-Lay Configuration Including “In and Out of Water” Cable Segments

Today, the offshore oil and gas and wind power industry is a heavily regulated segment, and current standards have established restrictions which yield a very limited weather window for submarine cable installations due to experience with cable failure in bad weather. There are two main limiting factors in current practice during cable installation of an S-lay configuration: the design criterion for the minimum allowable radius of curvature in the touch down point and the avoidance of axial compression in the touch down zone. Accurate assessment of the cable integrity during offshore installation has drawn great attention and is related to the existing available analysis and design tools. The main purpose of this paper is to develop and propose a quick and easy custom-made analysis tool, which is able to export similar results as sophisticated finite element analysis software. The developed tool utilizes analytical equations of a catenary-type submarine structure extended to account for varying cross-sections with different weights and/or stiffnesses, as is the real practice. A comparative study is presented in this paper to evaluate the significance for the modeling of the “out of water” cable segment required for accurate safety factor quantification during a laying operation. The efficiency and accuracy of the proposed tool are proven through a validation study comparing the results and the computational effort and time with commercial finite element analysis software. The analysis error in the case of not modeling the “out of water” cable part is significant, especially in shallow water areas, which proves the importance of using the proposed analysis tool.

Determination of Model Parameters for the Hardening Soil Model

The Hardening Soil model, an elasto-plastic second-order hyperbolic isotropic hardening model, in Plaxis has seen many applications in finite element analysis of various earth structures. This technical note presents a protocol for determination of the model parameters of the Hardening Soil model from a set of triaxial compression tests. The technical note also describes details about how to determine the Mohr-Coulomb strength parameters c and ϕ for well-compacted fills (with and without cohesion), of which the failure envelopes are typically curved. The motivation for preparing this technical note came from a study on analysis of field-scale soil–geosynthetic composites in which the soil model and model parameters deduced from triaxial tests were able to predict with very good accuracy “all” measured results of five field-scale soil–geosynthetic composites under increasing applied vertical loads up to 1000 kPa (approximately five times the load level commonly used in design of reinforced soil bridge abutments). The model parameters were determined by a well-defined protocol. The protocol should be of value to researchers and engineers who use the soil model for sophisticated finite element analysis and design of earth structures.

Nonlinear finite-element-analysis and design of steel-concrete composite ring (SCCR) joints

Conventional steel-plates-strengthened-composite ring (SPSC) joints are extensively used in composite structures to connect concrete-filled tubular (CFT) columns and reinforced concrete (RC) beams. However, the refinancing-bars of the adjacent beams require on-site welding to the steel strengthened plates of the SPSC joint, which, regarding workmanship, is difficult and time-consuming. Recently, a new type of joint, the steel-concrete-composite-ring (SCCR) joint, has been proposed as a substitute for the SPSC joint since it has been successfully used in several construction projects in Hong Kong. An SCCR joint consists of a steel tube, a concrete ring beam with reinforcements in both the radial and hoop directions, and shear studs. This research develops a sophisticated Finite-Element (FE) modelling method for SCCR joints, where the dominant factors affecting the joint's behaviors are considered, such as the explicit simulation of the complex reinforced bar details and shear studs, the cracking and crushing of concrete, the yielding of reinforced bars, and the contact behaviors between the steel tube and the concrete. From the FE analysis results, four possible failure modes are identified. Parametric studies are sequentially conducted in regard to these modes, yielding corresponding design eqs. A design procedure developed through the proposed equations is illustrated with a flowchart. Finally, a real-world example project is presented and further validated by sophisticated FE analysis.

Evaluation of eddy current damper for vibration control of a frame structure

In this study, an eddy current damper (ECD) prototype model is presented. The ECD consists of three principal components: Neodymium Iron Boron (NdFeB) permanent magnets, a copper plate (conductive material) and an aluminium frame. The magnets have a rectangular design, and can be assembled with magnetic pole projection in either alternative or unidirectional orientations and in two orthogonal directions. The key merit of this type of ECD is its non-contact characteristic; thus there is a complete absence of mechanical friction. This study examines the use of this prototype damper when applied to suppress structural vibration in multi-storey frame structure. To effectively estimate the damping performance of the ECD, simple analytical calculations involving both infinite and finite boundaries are proposed and illustrated in this paper. These can be compared against the results of more sophisticated finite element analysis (FEA). The conductive material can be defined to move in two orthogonal directions. Therefore, based on the four magnet configurations and two directions of motion of conductive material, a total of eight models were created for analysis and validated by the proposed designed formule. It was found that analysis based on the method of images provides a satisfactory estimation of the damping force, similar to that estimated using the FE model. This study also includes experimental testing of a prototype ECD applied to suppress vibration within a six-storey aluminium frame structure. This testing shows that the prototype ECD is able to provide a significant level of damping with performance comparable to that of an ideal conventional linear viscous damper.

Analysis of the jet pipe electro-hydraulic servo valve with finite element methods

The dynamic characteristics analysis about the jet pipe electro-hydraulic servo valve based on experience and mathematical derivation was difficult and not so precise. So we have analysed the armature feedback components, torque motor and jet pipe receiver in electrohydraulic servo valve by sophisticated finite element analysis tools respectively and have got physical meaning data on these parts. Then the data were fitted by Matlab and the mathematical relationships among them were calculated. We have done the dynamic multi-physical fields’ Simulink co-simulation using above mathematical relationship, and have got the input-output relationship of the overall valve, the frequency response and step response. This work can show the actual working condition accurately. At the same time, we have considered the materials and the impact of the critical design dimensions in the finite element analysis process. It provides some new ideas to the overall design of jet pipe electro-hydraulic servo valve.

Retaining wall behaviour in Dublin's estuarine deposits, Ireland

Practising engineers in the Dublin, Ireland, area have much experience in dealing with the boulder clay which underlies much of the city. However, significant deposits of estuarine soils, some of them soft, exist along the east side of the city and in particular in Dublin docklands. Some construction difficulties have previously been encountered in these materials and significant developments, including a large tunnel project, are planned in the area overlying these deposits. Few published data exist on retaining wall schemes in the deposits. Data from nine sites, including three detailed case histories, are presented which confirm that construction of deep propped excavations and cantilever walls up to 7·5 m are feasible in these deposits and can perform well. A key issue is the soil that is located at excavation level and competent deposits here are essential to prevent large displacements or possible instability. The resulting movement will also be sensitive to the overall system stiffness. There seems to be scope for more efficient future design, including more use of cantilever walls, particularly for temporary works purposes. Beam-on-spring type computer analyses tend to give conservative results for these deposits and more sophisticated finite-element analyses may be warranted for future schemes.

50 years ago in CORR: Biomechanics of hip prostheses. Duncan C. McKeever, MD CORR 1961;19:187-199.

“The fact that a device or a procedure is successful some of the time, most of the time, or even all of the time, does not prove that it is mechanically and physiologically correct.” Thus began Duncan McKeever in his article on, “The Biomechanics of Hip Prostheses,” published in CORR in 1961 [7]. This “axiom” remains true today. Surgeons have recognized the importance of mechanical conditions, and have attempted to explain why implants work and why they fail since the advent of implants and artificial joints in the 1890s [4, 5]. Haboush [6], in explaining the rationale for what was perhaps the first contemporary arthroplasty using cement (1953), designed his implant using mechanical principles. Charnley [2, 3] performed extensive mechanical experiments while developing his arthroplasty. McKeever outlined four mechanical principles in designing a hip prosthesis (presuming it has a stem): (1) the components of stress should have a constant direction; (2) there must be an optimal relation between the maximal stress and the cross-sectional area; (3) the total stress must be transferred at a single level; (4) the range of stress must be within the range of functional adaptation of the bone (Fig. 6). These are undoubtedly sound principles, but the problem was – and is – determining stress histories in an accurate comprehensive, and meaningful way. Today, stresses throughout a complex structure, such as a bone-implant construct, can be estimated using increasingly sophisticated finite element analyses, but these analyses do not account for the dynamic nature of the stresses nor the manner in which bone adapts to the constantly changing stresses during function [1]. Further, the precise nature of the stress transfer varies from patient to patient, and more generic estimates of that transfer may not apply. Fig. 6 McKeever’s illustration shows the four principles he outlined in his text and the additional point about where the “total stress” is transferred to bone. In fact, stress transfer will occur throughout the interface, depending upon ... McKeever did not have the ability to estimate the stresses at his disposal, but he commented, “The stem of the prosthesis should act only as a directional device only, and none of the stress should be transmitted through it.” He presumed all of the stress would be transferred at the point of maximal contact (Fig. 6). We now know this is not the case. Because of the uncertainties of stress transfer and bone response, empiricism has always played a role in the development of arthroplasties. Implants may be designed on a sound theoretical basis, but may not account for all in vivo conditions or unanticipated responses or reactions; thus, it is hard to predict whether a given arthroplasty will be durable, and much of the advances have occurred through trial and error. McKeever concluded, “Our salvation in many of the more serious problems of bone surgery lies within the field of mechanics and structural design as related to physiology. To think along these lines will avoid some of the complications and some of the failures.” In a strict sense, he was correct, but 50 years later, we still do not adequately understand the details of bone adaptation in general or in specific individuals to design an implant that will be durable in all patients.

An analytical model for evaluation of compaction-induced stresses in a reinforced soil mass

When an earth fill is subject to loading and subsequent unloading, it will bring about an increase in the lateral stress, provided that there is sufficient constraint to lateral deformation of the soil mass. The increase in lateral stress is commonly known as the "residual" or "lock-in" lateral stress. The residual stress resulted from compaction operation, which involves a series of loading and unloading onto a soil mass, is referred to as "compaction-induced stress" (CIS). The CIS will increase the stiffness and strength of the soil mass, and is an important factor to be considered in the behavior of compacted soil. A number of studies have been conducted on the CIS in an unreinforced soil mass. With a reinforced soil, the CIS is likely to be much more pronounced because there is a higher degree of constraint to lateral deformation in a reinforced soil mass due to soil-reinforcement friction. An analytical model, referred to as the CIS model, is developed for evaluation of compaction-induced stress in a reinforced soil mass. Correlations for determination of model parameters are given so that the parameters can be estimated through reinforcement spacing and stiffness, and common soil parameters, such as the angle of internal friction (Φ), and overconsolidation ratio (OCR). In addition, the stress paths of typical fill compaction operation are discussed, including compaction with a plant moving toward and away from a section under consideration, and compaction with multiple passes. The CIS model presented in this paper is found to give CIS values very close to those obtained from sophisticated finite element analysis of a 6-m high GRS mass under different values of compaction pressure. The CIS in the reinforced soil mass is significant under compaction pressures typically used in actual fill compaction.

Deformation analysis of reinforced soil retaining walls—simplistic versus sophisticated finite element analyses

Over the last two decades, different kinds of modular block have been increasingly used in the geogrid-reinforced soil retaining walls. The simulation of such wall behavior, which involves interactions between different structural components and backfill soils, requires a rigorous numerical procedure. Finite element is usually a preferred method, but this procedure, especially the soil constitutive models, is of different degrees of sophistication. It is always an issue of how simple or sophisticated should an analysis be conducted in replicating the actual behavior. In this article, a full-scale test wall was used to validate simplistic and sophisticated finite element analyses. Different types of finite element and material models were used in the two kinds of analysis to differentiate the level of simplicity or sophistication. The results obtained from stress-deformation analyses are presented and compared. It is shown that for wall construction that involves static loading conditions, simplistic nonlinear elastic and sophisticated elastoplastic analyses produced close and acceptable results.

Eddy current heating in large salient pole generators

PurposeThe purpose of the paper is to investigate pole face heating in large, salient pole generators and establish a modelling procedure for accurate rotor pole heat loss computation using finite element analysis.Design/methodology/approachFinite element‐based simulations of the dynamic electromagnetic problem in an idealized 60 Hz, six‐pole, three‐phase generator were carried out, including coupling to three‐dimensional finite element thermal analysis.FindingsThe effect of trailing pole face heating was effectively demonstrated. Accurate estimates of the ventilation and convective cooling were shown to be particularly important.Research limitations/implicationsAccurate heat transfer values could only be obtained using a very sophisticated model in a computational fluid dynamics analysis software package. The complexity of the stator end winding alone makes this a daunting challenge, without the inclusion of the rotation effects and stator cooling ducts. At this stage, it was deemed more useful to use the thermal analysis to observe trends.Practical implicationsThree‐dimensional effects are significant and require modelling. However, obtaining steady state behaviour using a 3D analysis is probably not viable yet. The synchronous operating conditions were obtained from a two‐dimensional analysis and used as the initial conditions for a full 3D analysis.Originality/valueThe paper has helped to enhance the understanding of pole face heat loss in large salient pole synchronous generators, fully examining the mechanisms causing the heating. A complete procedure to achieve this task in a realistic time frame using sophisticated finite element analysis tools has been proposed.

A simple way to model wires used in ring fixators: Analysis of the wire stiffness effect on overall fixator stiffness

The Ilizarov fixator has become widely used in the treatment of complex trauma and deformity correction in the United Kingdom over the last few decades. As such, it has been widely researched. Within this fixator, the characteristic fine wires are the weakest and most flexible component. The wires allow interfragmentary micromotion, which is believed to be beneficial to bone healing. In this paper, a novel and simple numerical model of the stiffness and deflection of the wires when the fixator is subject to axial and torsional loading is presented. A range of wire lengths and pretensions are analysed, and the results compared to the findings of other researchers, with generally good agreement. This indicates that fixator stiffness can be determined simply and without recourse to sophisticated finite element analyses or extensive physical testing. In addition, the model is used to predict the contribution of the wires to the overall stiffness of the fixator.

GALLOPING OF BUNDLE CONDUCTOR

A useful design tool is developed for a bundle conductor of an electrical transmission line by using a three-degree-of-freedom hybrid model. The model is adaptable because it incorporates numerical mode shapes determined by numerically employing the finite element technique to form relevant matrices. On the other hand, it is quite computationally efficient because analytical expressions are used to investigate the initiation and steady state amplitudes of galloping. The model accommodates interactions of the vertical, horizontal and torsional movements, non-linear aerodynamic loads, a non-uniform ice geometry, distributed and discrete galloping control devices, and a variation of the wind along a span. By neglecting the sub-span motions between the conductors, a bundle is modelled as an equivalent single conductor so that the initiation conditions for galloping, periodic and quasi-periodic states and their stability conditions are considered by taking advantage of previous achievements for a single conductor. Numerical examples are presented to assess the accuracy of the results obtained from the model in comparison with analogous data from a more sophisticated finite element analysis. Parametric studies are reported for limit cycle amplitudes with variations of the critical wind speed, wind speed above the critical wind speed, static tension and span length.

Flexural Capacity of Pressurized Steel Pipe

This paper describes the experimental and theoretical behavior of two large-scale pressurized pipes tested with a sleeve fully welded to the midspan of each specimen. Each specimen was subjected to an internal pressure, a constant axial load and lateral deformation of a four-point bend test to simulate the flexural behavior of a buried pipeline. The only test parameter was the length of the sleeve needed for pipe repair; one specimen had a sleeve length equal to one pipe diameter, and the second specimen had a sleeve that was two pipe diameters in length. Flexural deformations were imposed on each test specimen until clear failure occurred. For both specimens, failure occurred by local wall buckling of the carrier pipe adjacent to the sleeve region. A simple theoretical model is discussed to predict the flexural capacity of pipes subjected to these load conditions. This analytical method was developed to enable a quick computation of the inelastic flexural strength of the pipe, and to enable a check of the output from a more sophisticated finite element analysis. Reasonably good agreement was found between the theoretical and the experimental flexural capacity of the pressurized pipe. Analytical results demonstrated that the Tresca yield criterion conservatively estimated the inelastic flexural strength of the pressurized pipe. It was also found that, when using the Tresca criterion to describe the inelastic behavior of the pipes tested in this research program, local inelastic wall buckling was initiated at a displacement ductility of about 3.

SIMPLIFIED EVALUATION OF EARTHQUAKE-INDUCED PERMANENT DISPLACEMENTS OF SHALLOW FOUNDATIONS

The earthquake response of shallow foundations is studied by a simple method that incorporates nonlinear behaviour at the soil-foundation interface and, unlike other simplified approaches, directly takes into account the coupling between the soil-foundation system and the superstructure. The proposed model consists of a four degrees-of-freedom (dof) oscillator, namely one dof for the superstructure and three for the foundation, and introduces nonlinear effects in the calculation of soil reactions through a failure criterion and plastic flow-rule calibrated through previous experimental work. Comparing the results of an application to granular soils with those of more sophisticated finite element analyses, a satisfactory agreement is found, suggesting that the main features of this complicated nonlinear problem can be captured without resorting to an accurate description of the soil behaviour.

New approximate formulae in the torsion problem

This Note describes the development of new approximate formula for torsional rigidity of beams with simply connected cross-sections. The formulae are not dependent on a ‘thin-section’ assumption and can be applied to cross-sections with many ‘corners’ and many ‘ends’. The formulae give values for torsional rigidity with accuracies which compare well with those achieved using a sophisticated finite element analysis.