FE Results Research Articles

Post-depositional transformations in sedimentary rocks and implications for paleoenvironmental studies: evidence from the Mesoproterozoic (∼1.1 Ga) of the Taoudeni Basin, Mauritania

<h3>ABSTRACT</h3> Recent ⁶⁰Fe results have suggested that the estimated distances of supernovae in the last few million years should be reduced from ∼100 pc to ∼50 pc. Two events or series of events are suggested, one about 2.7 million years to 1.7 million years ago, and another may at 6.5 to 8.7 million years ago. We ask what effects such supernovae are expected to have on the terrestrial atmosphere and biota. Assuming that the Local Bubble was formed before the event being considered, and that the supernova and the Earth were both inside a weak, disordered magnetic field at that time, TeV-PeV cosmic rays at Earth will increase by a factor of a few hundred. Tropospheric ionization will increase proportionately, and the overall muon radiation load on terrestrial organisms will increase by a factor of ∼150. All return to pre-burst levels within 10kyr. In the case of an ordered magnetic field, effects depend strongly on the field orientation. The upper bound in this case is with a largely coherent field aligned along the line of sight to the supernova, in which case TeV-PeV cosmic ray flux increases are ∼10⁴; in the case of a transverse field they are below current levels. We suggest a substantial increase in the extended effects of supernovae on Earth and in the “lethal distance” estimate; more work is needed. This paper is an explicit followup to Thomas et al. (2016). We also here provide more detail on the computational procedures used in both works.

Experimental study on notched concrete beams with externally-bonded CFRP under repeated environmental treatments

• A novel environmental effects in terms of heating, freezing, and humidity. • The bond behaviors under temperature elevation and repeated environmental effects. • Analysis and determination of interfacial shear traction stress and separation. • Numerical simulation under temperature elevation and repeated environmental effects. This paper investigated the influences of the temperature elevation and the repeated environmental effects on the bond behavior of the notched concrete beams with CFRP externally bonded through four-point bending tests. The corresponding numerical model was established and the FE results were compared with the test results. Two failure modes were observed in the test, both of which occurred to be sudden and brittle. The failure mode of the specimens changed from concrete failure to CFRP debonding after the temperature exceeded 150 °C or the cycle number reached 50 times. The ultimate loads of the specimens decreased linearly with the increase of both the temperature and the cyclic number, and the slopes of load-displacement curves in the first phase of the specimens were also reduced by both heating and cycling. Before CFRP debonding, the average maximum interfacial shear stresses at 0–30 mm from the mid-span decreased linearly with the increase of both the temperature and the cyclic number. The average shear traction stresses and the average interface stiffnesses were decreased with the increase of both the temperature and the cyclic number. The results obtained from the FE were similar to that from the test, which confirms the suitability of the FE model in the test conditions.

On the Development of Artificial Neural Network Models of the Critical Moment of Tapered Beams

AbstractThe design of steel structures using elements with non‐uniform geometry is common in practice, both for aesthetic reasons and material optimization. Tapered beams are one of such examples which are widely used. This work is focused on the development of artificial neural networks to predict the critical moment of tapered beams subject to bending moments applied at the extremities since no analytical methods are currently available. Almost 70k data samples were calculated using the Finite Element Method (FEM) with shell elements and were used to train and validate the neural network models. The definition of the data samples was based on a random generation procedure with constrained geometric proportions to reduce their number. The accuracy of the developed model is further illustrated on some particular cases and against the FE results of other authors.Finally, it is demonstrated that neural network models are fast and reliable assessment tools that can be employed during the search of optimal structural solutions in the early design stages.

Design of Steel Columns in Fire using Second‐order Inelastic Analysis with Strain Limits

AbstractIn this paper, a structural steel fire design approach using second‐order inelastic analysis with strain limits is proposed and applied to the design of steel columns in fire. The proposed design approach employs beam finite elements to conduct a second‐order inelastic analysis. Within the proposed method, strain limits are used to account for the effects of local buckling; while global instability, the loss of strength and stiffness and thermal effects are fully considered through second‐order inelastic analysis carried out using beam finite elements. The proposed method is assessed against validated shell FE results. It is observed that the proposed design approach provides consistently accurate and safe capacity predictions for steel columns in fire.

Artificial Neural network-based prediction of SCF at the Intersection of CFST Y-joints

Stress concentration factors (SCFs) are used to quantify the hot-spots stress in tubular joints with circular hollow section for fatigue assessment, which are always obtained by finite element analysis or specimens testing. According to design specifications, complex formulas are recommended to calculate the SCFs at special locations of the intersection lines weld toe of tubular joints for individual load cases. To improve the fatigue performance of the joint, the concrete is filled in the chord to form a concrete-filled steel tube (CFST) joint. The capability of back-propagation neural network-based (BPNN) model in calculation of the SCFs in CFST Y-joints was investigated in this study. Three hundred FE numerical models were investigated to evaluate the effects of changes in different geometrical parameters on the SCFs of CFST Y-joint and the FEA results were used to train and test the neural networks. The nonlinear mapping relationships between the affecting variables and the SCFs distributions were established. Research results showed that SCFs prediction results of CFST Y-joints from BPNN models are close to the FE results, and properly trained and well calibrated BPNN can be reliable alternatives to complicated SCFs equations for predicting SCFs distribution at intersection line of CFST Y-joints.

Bond- and state-based peridynamic analysis in a commercial finite element framework with native elements

This study presents a framework to perform bond-based (BB), ordinary state-based (OSB) and non-ordinary state-based (NOSB) peridynamic (PD) analysis in ANSYS, a commercial software, with native MATRIX27 elements. The PD equilibrium equations as well as the PD form of the traction components are constructed by using these elements and solved within the ANSYS framework through implicit methods. The domain is divided into three regions in order to satisfy the equilibrium equations and to directly impose the displacement and traction boundary conditions without a fictitious layer. The results are free of displacement kinks; thus, removing the unphysical stress concentrations. Also, the displacement predictions maintain the smoothness throughout the domain. Its accuracy is demonstrated by considering isotropic elastic plates subjected to various types of boundary conditions under quasi-static loading conditions. For all combinations of boundary conditions, the displacement predictions agree well with FE results. Failure is introduced gradually through the KILL option in ANSYS.

Finite element modeling of reinforced concrete short columns subjected to shear in two perpendicular directions

PurposeShort columns can cause serious damage when subjected to an earthquake due to their high stiffness with low ductility. These columns can be exposed to multidirectional shear forces, which encouraged this study to investigate the behavior of structural short columns under bi-directional shear.Design/methodology/approachFinite element analysis (FEA) using ABAQUS is conducted and calibrated based on experimental data tested by previous researchers who studied the uni-directional behavior of short columns subjected to cyclic shear displacements. Then, the calibrated column models are further investigated to study the influence of bidirectional cyclic shear. Two scenarios are investigated, namely “simultaneous” and “sequential,” to compare the performance in terms of shear strength reduction.FindingsThe results show that the shear strength reduction significantly appears when 1:1 simultaneous bi-directional cyclic shear is applied. However, the shear reduction is more significant when the sequential scenario is applied. The seismic forces or deformations applied in orthogonal directions should be combined to achieve the maximum seismic response of structures as specified in Federal Emergency Management Agency (FEMA) 356 Standard. Finally, the combinations presented in literature to consider bi-directional shear are investigated. Based on FE results, the effect of applied 1:0.30 bi-directional cyclic shear simultaneously does not result in significant effect on the considered columns properly design for seismic forces.Originality/valueTo investigate the effect of multidirectional shear forces on the shear strength capacity of short columns, the presented effect of multidirectional shear forces in literature to consider bi-directional shear are investigated.

Shear Performance of Corrugated Steel Webs with Local Uniform Defects

Owing to the superior mechanical performance, corrugated steel webs are extensively applied and their shear performance is critical, because of the thin wall. After the steel is corroded and the web is weakened, the problem of shear resistance may become more prominent. The shear performance of corrugated steel webs with local uniform loss was studied to simulate a common corrosion state. Twenty-eight FE models with different defect characteristics, containing defect height and web thickness, are established to simulate corroded corrugated webs. Shear capacity, shear strength, out-of-plane stiffness and bending stiffness are studied. Based on previous studies, the prediction formula is proposed to predict the residual shear strength. Additional FE models are built to validate the reliability. Results indicate that web thickness is the key factor to decide the deformation shape and shear capacity, compared with defect height. Bending stiffness decreases as defect increases. With 62.5% of the initial thickness, the influence of the variation of defect height on the bending stiffness is within 10%. Variation in thickness also affects the sensitivity of shear capacity to corrosion parameters and failure modes. When the thickness exceeds 1.25 mm, about 62.5% of the initial thickness, shear capacity is more sensitive to corrosion height than when the thickness is less than 1.25 mm. The proposed formula is validated and has a good agreement with the FE results, which could help to design the durability of corrugated steel webs and evaluate the performance of existing corrugated steel webs.

The dynamic ultimate strength of stiffened panels under axial impact loading

ABSTRACT The dynamic ultimate compressive strength of stiffened panels under longitudinal compressive impact is studied based on the non-linear finite element method (FEM), and an empirical formula was derived based on the results. Three types of initial deflections are considered in numerical simulation. The FE procedure was validated by comparing with existing formulas and published pieces of literature. The influences of parameters, such as material yield stress, impact duration, impact shape, plate thickness ratio, plate aspect ratio, web height ratio and web thickness ratio, were investigated. The results indicate the impact duration has a significant influence on the non-dimensional dynamic ultimate strength; the geometrical parameters and material yield strength also have a certain effect. While with the same duration, amplitude and impulse, different impact shapes have little influence. The fitting accuracy of the formula was proved by a comparison between the proposed formula and FE results. And its applicability was validated by applying to real ship panels.

Testing, simulation and design of hot-rolled seamless austenitic stainless steel CHS columns

Stainless steel circular hollow section (CHS) members are favoured by architects and structural engineers because of their aesthetics, superior torsional resistance and corrosion resistance. Hot-rolling is one of the typical production processes for producing CHS members. Nevertheless, few research has been carried out concerning the hot-rolled stainless steel CHS members. This paper reports experimental and numerical investigations into hot-rolled seamless stainless steel CHS columns. Flexural buckling tests on eight columns were firstly carried out in the experimental investigation. This was followed by numerical modelling investigation, where the FE models were developed and validated against the test results. The validated FE models were then used to conduct a series of parametric studies to obtain more data covering a wide range of member slenderness and cross-section sizes. Based on test and FE results, three existing design approaches in the Eurocode, Chinese specification and American specification were assessed and discussed. The assessment results show that the three design approaches all provide relatively accurate strength prediction on the whole, but the design approaches in the 1993-1-4 + A2 and ANSI/AISC 370-21both give overestimated strength predictions while design approach in the CECS 410 gives a relatively conservative strength prediction when the column slenderness is small. In view of this, new column design curve has been proposed, with its advantage over the existing design approaches confirmed by quantitative and graphical comparisons.

Study on confinement mechanism of core concrete in steel tubular-corrugated steel plate confined concrete columns

This paper investigated the confinement mechanism of core concrete in steel tubular-corrugated steel plate confined concrete (S-CSC) column. Fourteen S-CSC columns and one CFST column were tested under axial compression, and the corresponding failure modes and load-displacement curves were observed. The strain changes of corrugated steel plate at different positions and square steel tubular were measured. Combined with the test results, the influences of some parameters including the section size, the steel tubular width, the wave height of corrugated steel plate, the thickness of corrugated steel plate and etc. on the strength index of core concrete and the ductility index of the specimens were analyzed. And the confinement mechanism of the core concrete in S-CSC column was studied. It was found that the confinement coefficient ξ which considered the influence of material strength and section size on the confinement effect of core concrete can reflect the confinement mechanism of core concrete effectively. Based on L.-H. Han's model, a constitutive relation for core concrete in S-CSC column by modifying key parameters was proposed and implemented in finite element simulation to predict the mechanical behaviors of axially loaded S-CSC column from the results of the tests. Comparing the test results of S-CSC columns which were described in this paper and the FE results, the satisfactory agreement was observed. Finally, it is verified that the size effect has no effect on the strength index of core concrete in S-CSC column basically.

Numerical and theoretical analysis of FRP reinforced geopolymer concrete beams

The current paper aimed to numerically and theatrically evaluate the flexural performance of polymer bars reinforced geopolymer concrete (FRP-GPC) beams based on applying numerical and theoretical investigations. The numerical study incorporates developing nonlinear finite element models, using ABAQUS software, validated with the data available in the literature. The developed model was then utilised to implement parametric studies for the parameters governing the structural behaviour of FRP-GPC beams, including compressive strength, FRP reinforcement type, shear reinforcement ratio, and shear span-to-depth (a/h) ratio. The results indicated to a reasonable agreement between the FE results and experiments collected from the literature concerning failure mode, failure load, and the load-deflection response. The statistical calculations showed that the mean, standard deviation, and the coefficient of variation between the measured and the FE failure loads are 1.03, 5.4%, and 5.3%, respectively. The FE results indicated that the compressive strength plays a considerable role in the load capacity for the specimens made without any web reinforcement, unlike those supported with web reinforcements. Moreover, the absence of web reinforcement and low a/h ratios resulted in a shear behaviour, which is more likely to be controlled by compressive strength rather than other parameters. The FE results also indicated that the web reinforcement ratio of 0.7% was sufficient to avoid the occurrence of shear failure, and therefore, the increase of the shear reinforcement beyond this level seems to have no considerable impact on the load capacity. Besides, the theoretical study included assessing the Canadian (CSA S806–12) and American (ACI-440–1R-15) codes to evaluate their performance in predicting the loading capacity of FRP-GPC beams investigated in the current study. The findings indicated that both codes provided conservative predictions when they are applied on FRP GPC beams, giving a mean value of 0.66 for the calculated-to-the FE results. Therefore, developing the existing design standards of ACI-440–1R-15 and Canadian CSA S806–12 is strongly recommended to improve the accuracy of applying these codes on FRP GPC beams.

Exact wave propagation analysis of lattice structures based on the dynamic stiffness method and the Wittrick–Williams algorithm

This paper proposes two significant developments of the Wittrick–Williams (W–W) algorithm for an exact wave propagation analysis of lattice structures based on analytical dynamic stiffness (DS) model for each unit cell of the structures. Based on Bloch’s theorem, the combination of both the DS and the W–W algorithm makes the wave propagation analysis exact and efficient in contrast to existing methods such as the finite element method (FEM). Any number or order of natural frequencies can be computed within any desired accuracy from a very small-size DS matrix; and the W–W algorithm ensures that no natural frequency of the structure is missed in the computation. The proposed method is then applied to analyze the band gap characteristics and mode shapes of hexagonal honeycomb lattice structures and the results are validated and contrasted against the FE results. The effects of different primitive unit cell configurations on band diagrams and iso-frequency contours are thoroughly investigated. It is demonstrated that the proposed method gives exact eigenvalues and eigenmodes with the advantage of at least two orders of magnitude in computational efficiency over other methods. This research provides a powerful, reliable analysis and design tool for the wave propagations of lattice structures.

An equivalent mechanism model for kinematic accuracy analysis of harmonic drive

The kinematic accuracy analysis of harmonic drive (HD) is very complex since there is a compliant cup. To explicitly figure out the effects of errors on the kinematic accuracy of HD, an equivalent mechanism in kinematics of HD is proposed, in which a spatial gear-linkage with 3-R, 2-S pin, 1-P and 1-Gear pair is equivalent to the HD with single pair of teeth of flexspline and circular spline. The kinematic model/equations of the mechanism under error condition are established by means of the mechanism topological structure analysis. For multiple tooth pairs’ engagement in HD with load, a similar parallel mechanism with multi-branch of the single tooth pair is then established and a compatibility equation is derived from the identical output motion caused by all branches. With the mechanism model, the kinematic accuracy/transmission error (TE) of HD can be investigated with consideration of errors and deformation caused by load. The TE effects of assembly errors and geometry errors are simulated. The FE analysis and test of a HD are conducted to validate the proposed mechanism model. The FE and test results show good agreement with the simulations’, which indicates that the proposed mechanism model is reasonable and effective.

Ultimate torsional strength assessment of large deck opening stiffened box girder subjected to pitting corrosion

The objective of current paper is to provide an approach for the residual ultimate strength assessment of a large deck opening stiffened box girder with pitting corrosion. Finite element method was used to analysis the bearing capacity of the pitted girder subjected to torsional moment. Nonlinearity of both material and geometry as well initial imperfection were taken into account in the research. A comparing investigation was firstly performed to examine the influences of pitting corrosion and uniform corrosion on the ultimate strength. It was found that the pitting is more detrimental for the same corrosion volume loss. Afterwards, effects of some studied variables including the depth, diameter, density, volume and position related to the pit located on both global and local areas of panel plate were discussed based on a series of numerical computations. According to the presented FE results, the corroded volume loss induced by the pit is an influential parameter leading to approximately linear decrease of the ultimate strength for different distributions. Another valuable finding is that the pit on the side shell which nears the 1/2 bay significantly influences the response characteristics of failure mode and strength. Considering regular/random and global/local distributions, four mathematical formulations were proposed for evaluating the residual strength of large deck opening stiffened pitted box girder.

Effect of Borophene and Graphene on the Elastic Modulus of PEDOT:PSS Film—A Finite Element Study

A finite element method (FEM) was employed to investigate the interaction of borophene nanoplatelets (BNPs) and graphene nanoplatelets (GNPs) on the mechanical properties of Poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) PEDOT:PSS film. A 3D random distribution of the inclusion into the PEDOT:PSS matrix was constructed by developing a 145 × 145 × 145 representative volume element (RVE) with a 4% volume fraction of BNPs and GNPs. In comparison to the pristine PEDOT:PSS, the calculated effective elastic moduli of the BNP-PEDOT:PSS and GNP-PEDOT:PSS nanocomposites exhibited 9.6% and 10.2% improvement, respectively. The predicted FE results were validated by calculating the elastic moduli of the nanocomposites using a modified Halpine-Tsai (H-T) model. The reinforcing effect of the inclusion into the PEDOT:PSS film offers a promising electrode with improved mechanical stability. Consequently, this intriguing result makes the BNP/PEDOT:PSS nanocomposite highly promising for further investigation and application in cutting-edge devices such as touchscreen, thermoelectric, light-emitting diode, electrochemical, photodiode, sensor, solar cell, and electrostatic devices.

Topology optimization design for the lightweight endplate of proton exchange membrane fuel cell stack clamped with bolts

To reduce the mass and improve the uniformity pressure distribution on gas diffusion layer (GDL), a ribbed endplate is proposed as the original model. The endplate is then redesigned using the topology optimization method to maximize its stiffness, minimize the standard deviation of normal displacement of nodes on GDL, and minimize the dual objective parameter. The lightweight endplates are designed based on optimization results, and pressure distribution on GDL of stacks equipped with lightweight endplates is calculated and compared. The weight of endplate is reduced by 14%, and the standard deviation of pressure is reduced by 16.6% at most compared to the original model. A PEMFC stack is composed of 10 unit cells, and the endplate with the best performance is assembled to examine FE results. The experimental data reveal that the trend of pressure distribution and the average pressure along the symmetry axis of tested plane is basically the same with FE results.

Concrete-filled and bare 6082-T6 aluminium alloy tubes under in-plane bending: Experiments, finite element analysis and design recommendations

The application of aluminium alloys in structural engineering is growing owing to their high strength-to-weight ratio, aesthetic appearance and excellent resistance to corrosion. However, the low modulus of elasticity of aluminium poses adverse effects on the flexural response of structural members made of aluminium alloys. In case of tubular members, the performance can be improved with the addition of concrete infill. Research on the flexural response of concrete-filled aluminium alloy tubes is still minimal. This study presents experimental and numerical investigations on the behaviour of concrete-filled and bare 6082-T6 aluminium alloy tubular members under in-plane bending. In total 20 beams, including 10 concrete-filled aluminium alloy tubular (CFAT) and 10 bare aluminium alloy tubular (BAT) specimens, were tested. The specimens comprised of square and rectangular hollow sections and were filled with 25 MPa nominal cylinder compressive strength concrete. The experimental results are reported in terms of failure mode, flexural strength, flexural stiffness, ductility and bending moment versus mid-span deflection curve. Compared to the BAT specimens, the counterpart CFAT specimens have shown remarkably improved flexural strength, stiffness and ductility due to the concrete infill and the improvement is more pronounced for the specimens with thinner sections. Finite element models of BAT and CFAT beams were developed by taking into account the nonlinearities in geometry and material and validated against the experimental data. A parametric study considering a broad range of cross-sections and different concrete grades was conducted based on the validated models. The FE results have shown that the flexural strength of the BAT and CFAT members increases with the increase of cross-sectional aspect ratio, wall thickness and concrete grade. The results obtained from experiments and numerical analysis for BAT members were used to assess the flexural capacity predictions and the applicability of the slenderness limits provided in the European standards. It was demonstrated that the slenderness limits provided by Eurocode 9 are conservative for Class A aluminium sections. Hence, revised Class 1, Class 2 and Class 3 limits are proposed which appear to be better applicable to Class A aluminium alloys. In the absence of design specifications for CFAT flexural members, the design rules for concrete-filled steel tubular flexural members provided by Eurocode 4 were adopted and the material properties of steel were replaced with those of aluminium alloy. It was shown that the proposed design methodology is suitable for the design of CFAT flexural members. Moreover, a slenderness limit for compact sections of CFAT flexural members is proposed based on Eurocode 4 framework.

Effects of corrosion on the strength of self-drilling screw connections in cold-formed steel structures-experiments and finite element modeling

Cold-formed steel (CFS) self-drilling screw connections are popular in construction industry due to rapid fastening and ease of installation. However, the performance of the CFS connections is very critical when they are exposed to corrosive environments such as humid and acidic or chloride-rich environments. The corrosion damage of CFS structures when exposed to these environments can result in significant reduction of mechanical properties, which can affect the safety and durability of such structures. Very limited research is available in the literature to investigate the effect of corrosion on the behaviour of CFS connections. This issue is addressed herein through an experimental investigation. This paper presents a total of 36 new experiments on different types of CFS self-drilling screws (12 and 14 gauge) and steel sheet thickness (2.5 mm). Half of the tests were for corroded specimens and the remaining half were for non-corroded specimens. Further, one to two screws per arrangements connecting the steel sheets having yield strength of 450 MPa, were tested. Screws were immersed for 31 days and the CFS plates were immersed for 8 weeks in corrosion chamber before the tests were conducted. The experimental program was designed to investigate the effect of number of screws on shear strength of corroded specimens. Furthermore, a nonlinear explicit dynamic FE model was developed and validated against the experimental test results. The FE results were in reasonable agreement with the test results, both in terms of connection strength and failure modes.

Artificial neural network assisted numerical quadrature in finite element analysis in mechanics

Finite element analysis (FEA) is a numerical tool that is broadly implemented in solving engineering problems. The Gaussian quadrature rule is commonly used to integrate elemental quantities like stiffness matrices over arbitrarily shaped elements in FEA. The Gaussian quadrature rule is a numerical technique in which the accuracy of numerical integration depends on the number of Gauss quadrature points. A higher number of quadrature points in the Gaussian quadrature rule implies higher accuracy but at the cost of higher computations. Thus, the number of Gauss points directly affects the computational cost and accuracy of the FE results. The main objective of the paper is to develop a deep learning model to predict the optimum number of Gauss points required in three-dimensional FEA utilizing hexahedral elements. In recent times some works have been proposed using deep learning in this direction. The present work further explores new possibilities in the area. In this paper, instead of the coordinates of the hexahedral element, its length and angle between two sides are taken as the input to the model, and the optimum number of Gauss quadrature points are predicted. The performance of the model is evaluated by the accuracy and confusion matrix. The present results are compared and are found to be better than the results available in the literature.