Finite Element Model Results Research Articles

New Methods for Predicting Strain Demand of Arctic Gas Pipelines across Permafrost under Frost Heave Displacement

With increasing gas resource development in the Arctic region, gas pipeline installations in permafrost regions are becoming important. Frost heave of pipeline foundation soils may occur when a chilled gas pipeline passes through unfrozen areas with frost-susceptible soils. The stress and strain behaviors caused by the differential frost heave will directly affect the safety of the pipeline. A nonlinear finite element model (FEM) computing the mechanical responses of the buried gas pipeline subjected to frost heave load was established and successfully validated with the results of a large-scale indoor pipe-soil interaction experiment carried out in Caen in France. Utilizing C# language and object-oriented visual programming techniques, a new customized parametric strain calculation software was developed. The effects of pipe diameter, pipe wall thickness, pipe internal pressure, and peak soil resistance on the longitudinal strain of X60, X70, and X80 steel pipes have been investigated quantitatively. For the first time, a fitting semiempirical equation and trained backpropagation neural network (BPNN) for predicting pipeline strain demand subjected to frost heave load were proposed based on 2688 groups of FEM results. The comparison results have proved their high accuracy and lower running time cost. The proposed new methods can be applied in the strain-based pipeline design and safety evaluation of pipelines in service. It is in the hope of supplementing existing theory and identifying new approaches for arctic gas pipeline installations.

Mechanics of tubes composed of interlocking building blocks

Topologically interlocking material (TIM) systems are composed of convex polyhedral units placed such that building blocks restrict each other’s movement. Here, TIM tubes are considered as rolled monolayers of such assemblies. The deformation response of these assembled tubes under diametrical loading is considered. This investigation employs experiments on additively manufactured physical realizations and finite element analysis with contact interactions. The internal load transfer in topologically interlocking tubes is rationalized through inspection of the distribution of minimum principal stress. A thrust-line (TL) model for the deformation of topologically interlocking tubes is established. The model approximates the deformation behavior of the assembled tubes as the response of a collection of Mises trusses aligned with paths of maximum load transfer in the system. The predictions obtained with the TL-model are in good agreement with results of finite element models. Accounting for sliding between building blocks in the TL-model yields a predicted response more similar to experimental results with additively manufactured tubes.

Experimental investigation of steel built-up beam-columns composed of tracks and channels cold-formed sections

In this paper, a built-up column of novel cold-formed cross-section that composed of four elements is investigated. The proposed built-up column is suitable for carrying axial, uni-axial, and bi-axial loading. The web of the new cross-section is composed of back-to-back track sections while the flanges of the cross-section are two lipped channels connected to the web using interconnectors. Elements comprising the cross-section are assembled and connected by enough interconnector bolts depending on the column built-up configurations. The interconnector spacing is varied among specimen cross-section and column length. In the present study, series of axially, uni-axially, and bi-axially compression columns were tested experimentally. Eleven specimens with various cross-section aspect ratios as well as different overall slenderness ratios were tested. Numerical finite element model that accounts for both material and geometrical nonlinearities was developed using ‘ABAQUS’ software to analyze the tested columns. A good agreement was achieved between the experimental test and the finite element model results. Experimental test results revealed that for axially loaded columns with small, medium, and high slenderness ratios, the failure modes were local buckling, local-flexural buckling, and flexural-distortional buckling; respectively. On the other hand, for uni-axially loaded columns having small, medium, and high slenderness ratios, the failure modes were local buckling, interaction between local and lateral-torsional buckling as well as lateral-torsional buckling; respectively. Furthermore, for bi-axially loaded columns, the failure mode was lateral-torsional buckling.

An improved mesh stiffness calculation model for cracked helical gear pair with spatial crack propagation path

As one of the most common failure modes for helical gear system, the gear crack in helical gear pair is studied, the improved spatial crack propagation paths are modelled for helical gear pair based on helical gear crack failure mode in actual working condition, in the direction along tooth width, the crack initiates in one end face of gear, and it propagates to tooth addendum or opposite end of the gear, meanwhile, along crack depth direction, the crack propagation path is modelled into straight line or curved line. Furthermore, the limiting line, to characterize the crack effect, is simulated as straight line or curved line. Unlike previous studies, the transverse and axial gear foundation stiffness are modified due to gear crack. In addition to transverse and axial gear tooth stiffness. Based on the improved mesh stiffness calculation method for cracked helical gear pair, the influence of crack parameters and crack types on the time varying mesh stiffness of helical gear pair are studied, and the analytical calculated results are validated against the simulated results of FE (finite-element) models.

Non-linear finite element model established on pectoralis major muscle to investigate large breast motions of senior women for bra design

This paper presents a three-dimensional nonlinear biomechanical finite element model to simulate elderly breast deformation under arm abduction. The finite element model was constructed based on complex anatomical structures that consist of the soft tissues including torso, breast, pectoralis major muscle, and rigid bones including humerus, sternum, clavicle and ribs. The elderly breast was defined as material nonlinearity and geometric nonlinearity. The computational model can simulate and illustrate the deformation of soft tissues during arm abduction from 30° to 90°. The finite element model was validated by motion data. The Young’s modulus for the clavicular portion and the sternocostal portion of the pectoralis major muscle was characterized as 0.1 MPa and 0.08 MPa, respectively. Besides this, the finite element model presented here features the musculoskeletal system for breast deformation and reveals the synergistic relationship between the breast and the pectoralis major muscle. A questionnaire was conducted to analyze the importance of purchasing factors and the discomfort positions in a sports bra from the perspective of senior women. Combined with the finite element model results, this study provides a promising basis for the design of sports bras in an ergonomic way.

Flexural behaviour of circular reinforced concrete columns strengthened by glass fibre reinforced polymer wrapping system

The use of prefabricated glass fibre reinforced polymer (GFRP) wrapping systems in retrofitting reinforced concrete (RC) columns has emerged to enhance the overall axial performance. However, the effect of these systems on columns subjected to bending is still limited although the flexural loading on columns in real life is inevitable. This paper presents experimental, numerical, and theoretical investigations on the flexural behaviour of circular RC columns strengthened by a GFRP wrapping system. A total of eight columns were prepared and tested under three point bending to determine the contribution of the GFRP wrapping system to the overall flexural performance. The annulus between the RC columns and the GFRP wraps was filled with epoxy or cementitious grout to ensure transfer and distribution of stresses. The load-midspan deflection responses and failure modes were presented and evaluated. Furthermore, a nonlinear finite element modelling (FEM) was conducted using ABAQUS software to simulate the performance of unwrapped and GFRP-wrapped columns under flexural loading. A theoretical analysis was also developed using the basic beam theory to obtain the flexural capacity of the tested columns and compare it with experimental and FEM results. A parametric analysis was carried out to assess the effect of varying the thickness of GFRP and infill, as well as the loading mode, on the flexural behaviour of RC columns. The results of experimental tests demonstrated that GFRP-wrapped columns with epoxy infills significantly enhanced the flexural load capacity whereas columns with grout infills showed a prominent enhancement in ductility and energy absorption. The results of FEM and theoretical analyses were in good agreement with experimental results. The results of the developed theoretical model were found to have a good correlation with the results of the parametric investigation. Overall, the GFRP wrapping system implemented in this study is an effective repair technique for structural RC columns subjected to flexural loading. The proposed theoretical model can be used by the practising engineers to design a composite repair system for deteriorated reinforced concrete columns.

Operating regime investigational study of steel-reinforced concrete superstructure flexible pin stops of the existing road bridge

In the article, the author published the full-scale experiment results on an existing steel-reinforced concrete road bridge, carried out to determine the actual parameters of the operation regime of the interconnection elements — flexible pin stops. This work was carried out as part of the author's dissertation research in the field of improving methods for testing the elements' endurance of the steel-reinforced concrete superstructures interconnection and is a development of the previously conducted comprehensive comparative analysis of existing models for testing endurance. The article gives a detailed description of the conditions for conducting and methods of a two-stage experiment, which includes short-term and long-term parts, as well as a detailed description used for processing experimental data for each of the stages. Based on the results of the experiment's short-term part, when compared with the results of finite element modeling of the operation of the stops, the possibility of using existing computational models to describe the actual model operation was confirmed. Also, within the framework of the short-term part, according to the conducted dynamic tests results with the moving load passage through the threshold, the presence of a significant dynamic component of the resulting forces in the interconnection stops was revealed. During the second long-term part of the experiment, a continuous recording of stresses in the interconnection elements from the passage of an unregulated traffic flow over the bridge was made. The article presents both direct survey data (tensograms) and the results of their further processing in terms of damage accumulation analysis; also, the accumulated damages values from actual traffic loads are compared with the expected values in the calculation according to some design standards. Intermediate conclusions based on the experiment results are formed and directions for future work within the scope of this study are indicated.

Models and design procedure for cross-laminated bamboo rocking walls

To conduct a comprehensive parametric and limit state study of Cross-Laminated Bamboo (CLB) rocking walls, this study established a finite element model (FEM) and a modified analytical model (MAM) for rocking walls based on tests. The initial prestress, cross-sectional area of the posttensioned rebars, aspect ratio of the CLB wall, and friction force of conventional friction dampers (CFDs) were studied. Parametric analysis showed that the lateral capacity of the rocking wall increased with the initial prestress and cross-sectional area of the posttensioned rebars, while the cross-sectional area of the rebars also led to an increase in the stiffness. A CLB wall with a high aspect ratio has good ductility and low stiffness. The increase in CFD friction force was an effective method to enhance the energy dissipation capacity of the rocking wall. The MAM was proposed based on the limit states and considered the action of the CFDs in the initial stage while modifying the calculation method of shear deformation of the CLB wall. The MAM was verified by the test and FEM results. Design procedure was then developed to ensure the lateral capacity and stiffness of the rocking wall at the collapse prevention (CP) hazard level.

Indirect field-oriented control of twin-screw electromechanical hydrolyzer

Goal. Development of a mathematical model of indirect field-oriented control of a twin-screw electromechanical hydrolyzer. Methodology. The paper presents a mathematical model of Indirect field-oriented control of twin-screw electromechanical hydrolyzer. The mathematical model was developed in the MATLAB / Simulink software environment. The determination of the main parameters of a twin-screw electromechanical hydrolyzer was carried out by developing a finite element model in the Comsol Multiphysics software environment. Results. Based on the results of a mathematical study, graphical dependences of the distribution of magnetic induction in the air gap of a ferromagnetic rotor, a spatial representation of the distribution of magnetic induction on a 3D model of a ferromagnetic rotor of a twin-screw electromechanical hydrolyzer were obtained. The results of finite element modeling were confirmed by a practical study of a mock-up of a ferromagnetic rotor of a twin-screw electromechanical hydrolyzer. By implementing the MATLAB / Simulink model, graphical dependences of the parameters of the ferromagnetic rotor of a twin-screw electromechanical hydrolyzer are obtained under the condition of a stepwise change in the torque and a cyclic change in the angular velocity. Originality. The paper presents an implementation of the method of indirect field-oriented control for controlling the ferromagnetic rotor of a twin-screw electromechanical hydrolyzer. The work takes into account the complex design of the ferromagnetic rotor of a twin-screw electromechanical hydrolyzer. Practical significance. The practical implementation of the results of mathematical modeling makes it possible to achieve effective control of a complex electromechanical system, allows further research to maintain the necessary parameters of the technological process and to develop more complex intelligent control systems in the future.

Quasi-static and dynamic compaction of granular materials: A strain-activated statistical compaction model and its evaluation

The cold die compaction behaviors of granular material are investigated and a strain-activated statistical compaction model is developed to address its deformation mechanisms, namely particle rearrangement and deformation. The compaction equation is explicit in form and only contains four parameters. Its effectiveness is validated with multi-particle finite element simulation and experimental data. The results show that the compaction model can capture the main features of the nominal compression stress–strain curves of 2D/3D granular materials with different initial relative densities. The dependence of the four parameters in the compaction equation on the initial relative density are analyzed and corresponding quantitative statistical relationships are determined, which takes the same form for 2D and 3D granular materials. It is found that the difference in the quantitative statistical relationships between 2D and 3D granular materials cannot be neglected and the result of 3D multi-particle finite element model is more reasonable, which is verified by the existing experimental data of Al powder. Finally, the statistical compaction model can be applied to characterize the dynamic compaction behaviors of granular materials, and the stress behind the shock front and the shock speed predicted by the model agree well with the finite element results.

A peridynamic formulation for nonlocal bone remodelling

Bone remodelling is a complex biomechanical process, which has been studied widely based on the restrictions of local continuum theory. To provide a nonlocal bone remodelling framework, we propose, for the first time, a peridynamic formulation on the macroscale. We illustrate our implementation with a common benchmark test as well as two load cases of the proximal femur. On the one hand, results of our peridynamic model with diminishing nonlocality measure converge to the results of a local finite element model. On the other hand, increasing the neighbourhood size shows to what extent the additional degree of freedom, the nonlocality, can influence the density evolution.

On the Compression Instability during Static and Low-Cycle Fatigue Loadings of AA 5083 Welded Joints: Full-Field and Numerical Analyses

The aim of this scientific work was to evaluate the compression instability effects during static and low-cycle fatigue loadings of AA 5083 welded joints, commonly used in marine structures. Low-cycle fatigue assessment in marine structures is of utmost importance since high levels of plastic deformation can arise in the proximity of high-stress concentration areas. Displacement ratios equal to minus one and zero were used to perform experimental low-cycle fatigue tests. The tests were monitored by means of the Digital Image Correlation technique in order to detect the strain patterns, with particular attention paid to stress concentration areas, indicating that a specimen tends to buckle during high compression loads, for tests with a displacement ratio of minus one. The tests at displacement ratios equal to −1 showed a lowering of the strain–life curve revealing a considerable effect on compression instability. A nonlinear finite element modelling procedure, depending only on hardness measurements, was developed. The hardness measurements were used in order to assess the distinct mechanical properties of the different zones that were included in the finite element model. The finite element model results were compared to the data achieved by means of the digital image correlation technique, demonstrating that hardness measurements can help predict the low-cycle fatigue behaviour of welded joints and consider compression instability phenomena.

Effect of Tie Bars on Axial Compressive Behavior of Round-Ended Rectangular CFST Stub Columns.

Round-ended rectangular concrete-filled steel tube (RRCFST) columns are prone to local buckling that are close to straight steel plates when used as piers of a bridge and affect its long-term use. In order to solve this problem, tie bars were used in this research to stiffen RRCFST columns. Eleven specimens with tie bars and three specimens without tie bars were tested to analyze influences of cross-sectional aspect ratio, longitudinal spacing, limb numbers and diameter of the tie bar on failure model, confined effect, bearing capacity and ductility of RRCFST stub columns. Finite element models (FEM) with different concrete constitutive models for rectangular and circle parts were established and validated to reveal the mechanism of the constrained effect of tie bars. Experimental and FEM results show that the local buckling scope was decreased and gradually moved to middle height with decreased longitudinal spacings tie bars. The addition of tie bars in RRCFST columns with large aspect ratios slightly enhanced the ultimate bearing capacity, the diameter of tie bars changing from 8 mm to 12 mm greatly enhanced displacement and energy ductility by 58.4% and 85.1%, respectively. However, more tie bars (e.g., two or three limbs) utilization could not further improve the bearing capacity and failure mode. While, the tie bars had very limited contribution to bearing capacity and ductility for RRCFST columns with small aspect ratios, because the outer steel tubes already individually provided for enough confinement on inner concrete. By considering different concrete confined models for rectangular and round-ended parts, an analytical model was proposed and validated to predict the ultimate bearing load for RRCFST stub columns with tie bars.

Structural performance and design of stainless steel SHS-concrete‑carbon steel CHS double-skin stub columns

Concrete-filled double-skin steel tube (CFDST) with outer stainless steel square hollow section (SHS) and inner carbon steel circular hollow section (CHS) is introduced in this paper. The square-shaped section provides easier connection with other structural elements and the utilization of the three different materials (stainless steel, concrete and carbon steel) contributes to the advantages of their combined strength, corrosion resistance and economy. This paper reports a finite element (FE) analysis and the FE models are developed with consideration of geometric imperfection and stainless steel's non-linear material property. To validate the models, a comparison of the results of FE models and experiments is performed on the basis of ultimate section capacities, load deformation histories and failure modes. Parametric study is then carried out for the analysis of structural performance of CFDST stub columns, especially on interaction stresses between concrete and steel tubes, load deformation histories and stress distribution of each component. The failure modes and their corresponding ultimate limit states have been thoroughly discussed for the four typical types of CFDST stub column. In addition, the current international design codes including Eurocode 4, AISC and AIC are assessed with the generated ultimate section capacities from FE models. It is observed that ACI provides better predictions as compared to other codes. At last, the new design equation is proposed to predict the ultimate section capacity of the CFDST stub column which shows very good agreement with the FE analysis results.

Analysis of exterior beam-column joints under varying column axial load and code comparisons

This paper presents a finite element (FE) study of beam-column joints subjected to cyclic loading. This study is primarily dependent on investigating the shear behavior of joints under the influence of different column axial load ratios. Wherefore, a total range of the column axial load ratios, whether in tension or compression has been considered. This paper proposes a two-dimensional (2D) FE model that considers material non-linearity. The proposed FE model was verified with experimental results from literature that tested varying column axial load ratios and different failure modes. The examination among experiential and numerical outcomes demonstrated that the FE model can reenact the conduct of beam-column joints and can catch the different failure modes with acceptable accuracy. A parametric study was established using the proposed FE model and strut-and-tie (ST) model of Pauletta to assess the Eurocode joint shear strength equations. For this purpose, four specimens were designed according to Eurocode recommendations while two other specimens were designed to satisfy all of the Eurocode recommendations except for the required joint confinement. An interaction diagram was introduced for each specimen to express the behavior under varying column axial load ratios. The results of the comparison between Eurocode, FE model, and ST model showed some differences in calculating the joint shear strength capacity, especially under column tension loads. Furthermore, this paper proposed new design equations based on Eurocode equations taking into account the column axial load effect. These proposed equations worked to increase the accuracy in calculating the joint shear strength capacity. Proposed equations were compared to the FE model results and other experimental results available in the literature. The comparison showed that the differences with the FE model decreased and that the proposed equations had better accuracy at different tension and compression loads than the Eurocode.

Optimization of the Curved Metal Damper to Improve Structural Energy Dissipation Capacity

Structural curved metal dampers are implemented in various applications to mitigate the damages at a specific area efficiently. A stable and saturated hysteretic behavior for the in-plane direction is dependent on the shape of a curved-shaped damper. However, it has been experimentally shown that the hysteretic behavior in the conventional curved-shaped damper is unstable, mainly as a result of bi-directional deformations. Therefore, it is necessary to conduct shape optimization for curved dampers to enhance their hysteretic behavior and energy dissipation capability. In this study, the finite element (FE) model built in ABAQUS, is utilized to obtain optimal shape for the curved-shaped damper. The effectiveness of the model is checked by comparisons of the FE model and experimental results. The parameters for the optimization include the curved length and shape of the damper, and the improved approach is conducted by investigating the curved sections. In addition, the design parameters are represented by B-spline curves (to ensure enhanced system performance), regression analysis is implemented to derive optimization formulations considering energy dissipation, constitutive material model, and cumulative plastic strain. Results determine that the energy dissipation capacity of the curved steel damper could be improved by 32% using shape optimization techniques compared to the conventional dampers. Ultimately, the study proposes simple optimal shapes for further implementations in practical designs.

Operational modal analysis and finite element model updating of a 230 m tall tower

Dynamic response levels are critical for tall and slender civil structures. Studying the dynamic behavior of large civil structures with finite element modeling techniques requires detailed and accurate modeling of structural geometry, material properties, member fixities, connection types, and accompanying assumptions. Still, the finite element model results are approximations that could be away from representing the actual structural behavior. Structures are dynamically tested at their operational conditions to validate the finite element model results. This paper presents Operational Modal Analysis (OMA) and finite element model updating of a tall structure located in the West Bay area of Doha (Qatar). The structure is a reinforced concrete building with shear wall cores situated towards the center of the building plan, which was constructed between 2012 and 2016. With 53 stories above the ground and two stories below ground, the 230 m (755 ft) tall building is being used for residential and hotel purposes. For the finite element model updating and calibration tasks presented in this paper, the authors intentionally introduced drastic model changes for the first two model updates so that the results from the first two attempts guide how to proceed with a more reasonable update for the third calibration of the finite element model. While this is a non-standard technique that represents a specific condition where the initial attempts on the finite element model are very crude approximations, it is a systematized demonstration of how to operate when the structural parameters are sparse or uncertain for modeling purposes. While in theory, the finite element model updates can always be fine-tuned in a way to further decrease the error between the measured and predicted OMA results, in this paper, the authors predominantly focused on the presentation of three finite element model updates to demonstrate the way they have improved the modal assurance criteria plots and lowered the average absolute errors by visiting two drastic and then one moderate finite element model updates. The material presented here in this paper is arguably the first published work on large-scale dynamic testing of a civil structure in the State of Qatar.

In-process detection of cutting forces and cutting temperature signals in cryogenic assisted turning of titanium alloys: An analytical approach and experimental study

In-process detection of cutting forces, temperature, roughness, wear etc. during machining of titanium alloys are very important. The Finite element (FE) analysis plays an important role in monitoring and detection of machining responses. It offers a high accuracy in modeling of dry cutting processes and its performance in modeling of cryogenic machining process is a matter of interest. In this context, current investigation focuses on the dry turning and LN2/CO2 cooling assisted turning process of commonly used Ti6Al4V alloy. It is very useful material in the biomedical sector, and the simulation of cutting forces and cutting temperature via finite element method (FEM) has been performed. In addition, the simulation results are validated with experimental work. The results show that the deviations between FE modeling and experimental results for the cutting temperature are the average of 5.54%, 5.18% and 8.42% for the dry, LN2 and CO2 cooling conditions, respectively. On the other hand, the deviations from FE modeling and cutting force test results were 3.74%, 3.358%, and 3.03% under dry, LN2 and CO2 cooling conditions, respectively.

Nonlinear Numerical and Analytical Assessment of the Shear Strength of RC and SFRC Beams Externally Strengthened with CFRP Sheets

This study investigates numerically utilizing nonlinear finite element (ANSYS software) and analytically the shear response of the Reinforced Concrete (RC) beams. Different beams are considered in the current study, such as RC, steel fibre reinforced concrete (SFRC) without web reinforcement, and RC externally reinforced in the shear zone with carbon fibre reinforced polymer (CFRP) sheets. Nonlinear finite element model (FEM) is designed to simulate the performance of the designed beams. The results of FEM are compared to experimental measurements and standard design codes (ACI 440.2R‐17, FIB 14, CNR‐DT200, and ACI 318‐19). According to the experimental approach and nonlinear finite element, the enhancement in the load carrying capacity of SFRC beam due to CFRP strengthening decreases with a volume fraction of steel fibres of 2%. However, the effect of CFRP strengthening on the shear behaviour of RC beams was observed in increased load carrying and ultimate deflection capacities as a result of the CFRP strengthening. The results show that CFRP has a significant contribution to shear strength. At each load increment, the created model accurately reproduced the initial and progressive crack patterns. A comparison of nonlinear finite element and analytical models was conducted using the codes ACI 440.2R‐17, FIB 14, CNR‐DT200, and ACI 318‐19. Numerically, the FEM results showed a high agreement with ACI 440.2R‐17 standard code, with correlation approach to 99%. The comparison experimental load capacity of beams to FEM and ACI 440.2R‐17 shows that the FEM can be significantly used to estimate the shear strength of beams in the X‐Y directions with simulating different scenarios of CFRP and SFRC characteristics. The discrepancy between the nonlinear FEA and the theoretical predictions from the ACI 440.2R‐17 code is less than 1%, from the FIB14 code is less than 2%, from the CNR‐DT200 code is less than 15%, and from the ACI 318‐19 code is less than 30%. The ultimate load capacity evaluated based on ACI 440.2R‐17 code provision shows a good agreement with the experimental data as compared to the others’ code provision. The results of the finite element analysis and analytical models were in good agreement with the experimental results. The most significant advantage of finite element analysis over experimental approaches was that it can aid in the investigation of different output results that cannot be measured experimentally, such as shear stress in the XY direction throughout the beam strengthened in shear with different CFRP properties and steel fibre reinforced concrete (SFRC).

Prediction of reinforced concrete structures behavior using finite element method

In this paper the results of finite element modelling of bended reinforced concrete elements before and after reinforcing by carbon-fibre plastics under static loading are presented. Numerical results were performed taking into account non-linear behaviour of rebar and deformation of concrete with further cracking. A comparative analysis between obtained experimental results and calculated ones was performed and their well-enough matches were shown. Prediction of reinforced concrete structures behavior using finite element method was performed.