Three-dimensional Finite Element Program Research Articles

Minimum Shear Reinforcement for Reactive Powder Concrete Beams

The aim of this research was to determine the minimal requirements for shear reinforcement for reactive powder concrete (RPC) rectangular cross-sectional beams with a compressive strength of 157 MPa and a steel fiber volume content of 2.0% that remained constant for all the tested beams. Additionally, the recommendations of KCI-2012 and AFGC-2013 for the design of RPC beams as well as the shear design requirements of ACI 314-2014 when applied to RPC beams were studied. Utilizing a three-dimensional finite element program, a computational model was designed for forecasting the deformations and shear strength of the examined RPC beams. Both the shear-span-to-depth relationship (a/d) and the minimal reinforcement web ratio, represented by the distance between stirrups and the diameter of the stirrup bars, are the key study parameters in this regard. According to this study’s experimental findings, increasing the given reinforcement of the web ratio has little influence on both the ultimate shear strength as well as the diagonal cracking strength of the beams. Additionally, the findings demonstrated that the ACI 318-2014 maximum stirrup spacing requirement of 0.5 d can safely be extended to 0.75 d for beams that are relatively short. Compared to what ACI 318-2014 mandates, the suggestions of AFGC-2013 and KCI-2012 are more cautious and safe. According to the AFGC-2013 criteria, the mean proportion of Vfb to projected Vu,AFGC is roughly 58.3%, whereas the mean proportion of vs. and Vc is just 41.7%. The deformation response and ultimate shear strength of the examined RPC beams were well predicted by the designed model using finite elements when metal fibers were taken into account.

The flexural behavior and efficiency of RC beams strengthened with SNSM bars under the effect of several end conditions and material properties

In this paper, twelve strengthened, and one un-strengthened reinforced concrete (RC) beams were experimentally and numerically investigated in flexure. The strengthened RC beams were upgraded with steel or glass fiber reinforced polymer (GFRP) in the form of side-near surface mounted (SNSM) reinforcement. The tested parameters were the SNSM bar diameter, adhesive materials, SNSM end conditions, and materials of strengthening bars. The three-dimensional elastic-plastic finite element program (ABAQUS) was utilized to simulate numerically the tested beams in the experimental program. Finally, a parametric study was numerically conducted to show the effect of different parameters of the SNSM technique on the flexural response of the strengthened beams. The experimental findings demonstrated that the RC beams strengthened with SNSM steel bars generally had higher load capacity than those strengthened with GFRP. Bent ends of the SNSM steel bars were more efficient than in SNSM GFRP bars or end anchorage by GFRP sheets. The load-carrying capacity enhancement for strengthened beams with SNSM steel bars (10 and 12 mm in diameter) having end anchorage (wrapped by CFRP sheets) was 212.6% and 234.7% compared to the unstrengthened beam. In contrast, the enhancement decreased from 184.5 to 145% and 160.5 to 158.3% as the bond material changed from epoxy to grout for the beams strengthened by 10 mm and 12 mm diameters of SNSM steel bars, respectively. The numerical and experimental findings were in close agreement.

Performance of NSM and EB methods on the flexural capacity of the RC beams strengthened with reinforced HSC layers

The near-surface mounted (NSM), in which strips or rods are fixed by an adhesive in slits formed inside the concrete cover, and the externally bonding (EB), in which the reinforcement is glued to the concrete surface, are well-known strengthening methods. In the present work, an experimental and numerical study was carried out on reinforced concrete (RC) beams strengthened with NSM and EB-reinforced high-strength concrete (RHSC) layers. The RHSC layers were reinforced by steel or glass fiber reinforced polymer (GFRP) rods and bonded to the RC beams without and with a concrete cover. Seven specimens were cast and loaded in flexure up to failure to investigate the effect of RHSC layer position and reinforcement on the RC beams' efficiency. The three-dimensional finite element program (ABAQUS) verified the experimental results numerically. Also, a parametric study was numerically performed to examine the factors affecting the flexural performance of the strengthened RC beams using NSM and EB RHSC layers. The strengthened beams by NSM steel RHSC layers increased the load capacity by 147.9% compared to the control beam (CB). Changing the RHSC layer reinforcement from steel to GFRP bars enhanced the load's efficiencies from 147.9% to 172.0% compared to the CB. Decreasing the width and reinforcing area of the RHSC layer decreased the beam load capacity by about 17.5 %. Due to their longer bending arms, the EB RHSC layers showed lower load capacity than the NSM ones, which accelerated the EB RHSC failure. When the carbon fiber-reinforced polymer bars were utilized to reinforce the HSC layers, the strengthened beams showed higher load efficiency than those strengthened with HSC layers reinforced by GFRP rods.

A Review of the Computational Investigation of Three-Dimensional Transient Magneto-Thermal Coupling Characteristics of Electromagnetic Railgun Armature and Rail in High-Speed Sliding Electrical Contact

In order to investigate the dynamic process of electromagnetic field distribution, temperature change and the deformation during the launching process of electromagnetic railgun. It is necessary to conduct a three-dimensional coupled electromagnetic-temperature-structure analysis of the rail and armature, which requires the establishment of the corresponding multi-physics field model and the use of appropriate software and algorithms to complete the relevant simulation calculation and solution results. Based on this, this paper summarizes the current domestic and foreign research methods for multi-physics field characteristics under sliding electrical contact conditions, analyses the advantages and disadvantages of each method, and focuses on the updates of the three-dimensional finite element program EMAP3D based on Lagrangian description and the advantages of multi-field coupling. Finally, several considerations and operable spaces for multi-physics field coupling simulation are summarized to provide technical support for subsequent studies on multi-physics field characteristics for high-speed sliding electrical contact condition.

Numerical study on pile group efficiency for piles embedded in cohesive and cohesionless soils

This paper aims to study the efficiency of pile groups with various numbers of piles and pile spacing. Axial loading tests on pile groups and also single piles were simulated using a three-dimensional finite element program to obtain the load-settlement curve and the ultimate bearing capacity of the piles which was later used to estimate the pile group efficiency. In this study, the piles were embedded in cohesive and cohesionless soils. The stress-strain responses of the soils and the concrete pile and pile cap were simulated using the Mohr-Coulomb and the linear elastic models, respectively. The numerical-based pile group efficiencies were then compared to those computed using the published formulas. To verify the findings, a series of parametric studies on pile groups embedded in stratified soil was performed where the parameters of the soils were derived based on a back analysis on a case study of a single pile axial loading test in South Jakarta. The results show that the axial pile group efficiency in cohesive soil would be less than or equal to one, whereas in cohesionless soil would be more than or equal to one, especially at pile spacing more than three times the pile diameter. Meanwhile, similar results as found in cohesionless soil were obtained for the stratified soil case.

Mechanical Behavior Analysis of Excavation and Retaining Piles in Gravel Formation along Adjacent Railways: A Comparative 3D FEM Study with Monitoring Data

Carrying out underground excavation work with retaining pile supports adjacent to a running railway is a risky and cautious job. To evaluate the safety and practicability of underground excavation, a three-dimensional finite element program was developed and used in this study to simulate and analyze the mechanical behavior of the gravel layer in response to excavation to serve as the design for retaining piles as supports. Monitoring instruments (such as inclinometers and subsidence observation points on railway track surfaces) were installed during construction to provide immediate monitoring of the excavation area and information for safety assessments. The calculation process in the numerical analysis included the execution of programs such as pre-processing, central calculation, and post-processing, as well as the simulation of construction steps, such as the initial stress of gravel layer, railway vehicle load, layered excavation, and support installation. By comparing the results of 3D finite element analysis with monitoring data, it was found that the construction method of excavating the gravel layer near the adjacent railway and supporting it with retaining piles provides a reliable engineering technology. The results of the comparative analysis were all within a safe range and showed a consistent trend.

Behavior of Waste Glass Powder in Concrete Deep Beams with Web Openings

Waste Glass Powder (WGP) could be used as a cement replacement additive to manufacture concrete and solving the problem of environmental pollution. The experimental program was made up of ten simply supported reinforced High-Strength Concrete (HSC) deep beams tested under static loadings. Five beams were with WGP, while the other five beams were without WGP. Eight beams had web openings while two reference beams were without openings. The principal studied parameters were the effect of using WGP, and the location and size of web openings. Using the three-dimensional finite element computer program ABAQUS, a numerical simulation for comparing the shear strength and behavior of tested deep beams has been suggested. The comparison between experimental failure loads of studied beams with that estimated by the Strut-and-Tie model was carried out. Three codes of practice were used to make this comparison: the American Concrete Institute (ACI 318-19), the New Zealand Code (NZS-06), and the Japan Society of Civil Engineering (JSCE-07). The results showed that using WGP in similar deep beams with web openings enhances the cracking shear strength (by about 17–25%) and the ultimate shear strength (by about 12–41%). The improvement in the ultimate failure load could be attributed to the developed concrete microstructures caused by WGP’s very fine grains, producing further gel, and decreasing the number of voids in the concrete matrix. The suggested finite element simulation accurately predicts the behavior of HSC deep beams with and without WGP beams and with web openings.

Development of framework of the predictive performance-engineered mix design procedure for asphalt mixtures

ABSTRACT This paper presents a new asphalt mixture design framework for predictive performance-engineered mix design (PEMD) and the theory and procedures that underlie the proposed design method. This method allows pavement engineers to determine an optimized mix design based on the predicted pavement/mixture performance for all possible combinations of a given set of component materials (i.e. aggregate and binder) in the design space. The proposed PEMD process is based on the ‘performance-volumetrics relationship’ (PVR) concept. The calibration of the PVR is based on the mixture performance predicted from FlexPAVETM, a three-dimensional finite element program that performs viscoelastic analysis under moving loads, using the material properties of the asphalt mixture in question at widely spaced volumetric conditions. Three mixtures of different nominal maximum aggregate sizes and binder types are used to demonstrate the proposed PEMD process. Finally, the predicted performance results obtained from different design approaches are compared.

Study on the implementation of reinforced concrete target in PELE with hood

In order to analyze the influence of the material and shape of the hood of the medium-caliber PELE warhead on the damage effect of the reinforced concrete wall with PELE projectile, the three-dimensional nonlinear dynamic finite element program LS-DYNA was used to numerically simulate the penetration of the PELE projectile with the hood of different shapes and materials into the 0.25 thick thin reinforced concrete wall target at various velocities. The results show that under the same conditions, the hollow cone shaped phenolic resin hood can achieve better damage effect of reinforced concrete wall. Chinese map classification number: TP391.9 Document identification code: A

MATHEMATICAL MODELING OF THE PROCESS OF POSSIBLE DAMAGE TO NPP PIPELINES DUE TO THEIER LOCAL EROSION AND CORROSION SINKING

The article is devoted to computer modeling of the process of possible damage to the pipelines of nuclear power plants that received local thinning of the walls.The geometric features of pipelines are essential not only for assessing the intensity of erosion and corrosion of a metal, but also for the final strength assessment, in particular, when calculating local thinning of the walls of pipelines. The accuracy of forecasts of the life of pipeline structures directly depends on the ability to evaluate the strength of pipeline elements that have received local thinning, especially if these elements themselves have a complex shape. Such elements include elbows, nozzles, adapters (transitions), shells. All of these elements are thin-walled structures of complex shape. Computer modeling of the process of crack formation and growth requires solving several problems. A review and critical analysis of the available experimental information on the growth rates of cracks in specific structural materials and in the environment that is characteristic of given operating conditions is required. An assessment of the crack growth rate is impossible without determining the stresses and strains in the shell structure of complex spatial geometry. The development of routine criteria for crack growth and their attachment to a stress-strain state calculation program is the next task. To solve these problems, a complex of three-dimensional finite element methodologies and programs based on the theory of thick shells has been created. The article presents some results of calculating the stress-strain state of adapters and the growth of cracks in them.

Redevelopment of Artificial Neural Networks for Predicting the Response of Bonded Concrete Overlays of Asphalt for use in a Faulting Prediction Model

Transverse joint faulting is a common distress in bonded concrete overlays of asphalt pavements (BCOAs), also known as whitetopping. However, to date, there is no predictive faulting model available for these structures. Therefore, the intended research is to develop a predictive faulting model for BCOAs. In addition, it is important to be able to account for conditions unique to BCOA when characterizing the response in a faulting prediction model. To address this, computational models were developed using a three-dimensional finite element program, ABAQUS, to accurately predict the response of these structures. These models account for different depths of joint activation, as well as full and partial bonding between the concrete overlay and existing asphalt pavement. The models were validated with falling weight deflectometer (FWD) data from existing field sections at the Minnesota Road Research Facility (MnROAD) as well as at the University of California Pavement Research Center (UCPRC). A fractional factorial analysis was executed using the computational models to generate a database to be used in the development of the predictive models. The predictive models, based on artificial neural networks (ANNs), are used to rapidly estimate the structural response at the joint in BCOA to environmental and traffic loads so that these responses can be incorporated into the design process. The structural response obtained using the ANNs is related to damage using the differential energy concept. Future work includes the implementation of the ANNs developed in this study into a faulting prediction model for designing BCOA.

Parametric study of CFST columns by numerical mock-up

This paper offers the material constitutive numerical mock up on CFST columns exposed to an axial compression load. The three-dimensional nonlinear finite element program used in this study is ABAQUS and the results are related with experimental results obtained from previous researchers. It is clear that, the proposed FE model is in good agreement with experimental results and it is pertinent to note that the FE results are design conservative. Further, parametric study on CFST columns were conducted using the proposed material mock-up by varying grade of concrete core, grade of steel tube, type of infill concrete, thickness of steel tube, diameter of column and height of column in CFST column specimen. All the parameters considered in the study has a noteworthy influence on axial compressive strength of CFST column and such influencing parameters are discussed elaborately in this paper.

Deep-Seated Slope Stability Analysis and Development of Simplistic FOS Evaluation Models for Stone Column-Supported Embankments

Inclusion of stone columns in the underlain soft soil is one of the most prominent methods for improving the stability of embankments. The stone columns are encased with a geosynthetic material to further enhance the stability. The influence of this partial replacement of weak foundation soil with stone columns on the performance of embankments needs to be quantified. In this study, performance of ordinary stone column (OSC) and geosynthetic-encased stone column (GESC)–supported embankments is carried out using a three-dimensional finite element programme (PLAXIS3D). A parametric study was conducted to quantify the influence of various factors viz. spacing to diameter ratio (S/D), stiffness of encasement, cohesion of soil, friction angle of stone column and friction angle of embankment on the factor of safety against deep-seated failure. The results show that encasing the stone columns enhances the stability of embankments. Decreasing the column spacing (S/D) enhances the stability, reduces the excess pore pressure development and average settlement. Increase in geotextile encasement stiffness, cohesion of underlain soft soil, friction angle of stone column and friction angle of embankment improves the performance of embankments and also reduces the average settlement of the ground under embankment. Results of the parametric study were used to develop two types of data-driven models viz. multiple linear regression (MLR) and artificial neural networks (ANN) to simplify the evaluation of the factor of safety (FOS) of embankments. Among the two approaches, ANNs were able to predict the factor of safety values more accurately.

Effect of Cavities from Gypsum Dissolution on Bearing Capacity of Soil under Square Footing

This study deals with cavities under square footing which resulted from gypsum dissolving due to water flow in gypseous soil. This process leads to collapse of soil structure and progressive compression. A model was developed for governing the mass-transport to assess the variation of gypsum content of the soil during dissolution by ground water flow then cavity formation was adopted. A general three-dimensional finite element program (PLAXIS 3D) was selected for numerical analysis method to generate the solution. The study included a number of variables and their effect on bearing capacity of gypseous soil such as (gypsum content, cavity volume and location). The cavity was represented as axis and plane cavity which has square section. The results show that the most dangerous case is found when the cavity locates at the center of footing base (Z/B = 0), where the bearing capacity decreased by (14, 37, and 69%) for (20, 30, and 40%) gypsum dissolving ratio respectively. Also, the bearing capacity decreased when the cavity volume increases due to increasing dissolution ratio. The effect of cavity became disappear after (Z/B = 4). While, when using plane cavity, there was no cavity at center of footing base (Z/B = 0) because it considered as a hole not cavity. When using plane cavity, the bearing capacity decreased by (28, 43, and 53%) for (20, 30, and 40%) dissolving ratio respectively when (Z/B=1). The effect of cavity on the bearing capacity would be disappear as the distance from footing center increase until it became disappear at (Z/B = 6 m). The plane cavity is more dangerous than axis cavity.

Estimation of Bearing Capacity Dropping Due to Cavities from Gypseous Soils Melting

The presence of gypsum in the soil will cause problems if the source of freshwater is available and permeable soil permitting significant movement of water is to take place. The solubility of gypsum by excess water from irrigation or localized leak into the gypseous soil may cause cavity formation. In this research, a model was developed for governing the mass-transport to assess the variation of gypsum content of the soil during dissolution. A general three-dimensional finite element program (PLAXIS tunnel) was selected for the numerical analysis method to generate the solution. Parameters that affect the bearing capacity of a square footing represented by the gypsum content, the cavity volume, and the location of the cavity which represent by three offset distances from the footing center to the cavity center (x, y, and z), where (X) represents the horizontal distance, (Y) represents the vertical (depth) distance, and (Z) represents the diagonal distance. The main results show that the cavity location found to be the most parameter that affects the bearing capacity ratio (BCR). The minimum values are found when the cavity locates at the center of the footing base, and the lowest one (0.211) when the gypsum dissolved equal to 40%, also there is no effect of the cavity location when the ratio of (X/B) and (Z/B) exceed (3.0) for any depth and when the gypsum dissolved less than 10%. For high gypsum dissolution (more than 30%), the dimensionless ratios (X/B), (Z/B), and (Y/B) of the cavity must be more than 5.0.

An investigation on tunnel deformation behavior of expressway tunnels

The magnitude and distribution of tunnel deformation were widely discussed topics in tunnel engineering. In this paper, a three-dimensional (3D) finite element program was used for the analysis of various horseshoe-shaped opening expressway tunnels under different geologies. Two rock material models — Mohr-Coulomb and Hoek-Brown were executed in the process of analyses; and the results show that the magnitude and distribution of tunnel deformation were close by these two models. The tunnel deformation behaviors were relevant to many factors such as cross-sections and geological conditions; but the geology was the major factor to the normalized longitudinal deformation profile (LDP). If the time-dependent factors were neglected, the maximum displacements were located at the distance of 3 to 4 tunnel diameters behind the excavation face. The ratios of displacement at the excavation face to the maximum displacement were around 1/3 to 1/2. In general, the weaker the rock mass, the larger the ratio. The displacements in front of the excavation face were decreased with the increasement of distance. At the distance of 1.0 to 1.5 tunnel diameter, the displacements were reduced to one-tenth of the maximum displacement.

Generalized viscoelastic model for laminated beams using hierarchical finite elements

The formulation of an enriched hierarchical one-dimensional finite element suitable to analyze the rheological behavior of thick arbitrarily laminated beams is presented. The formulation is based on the Equivalent Single Layer (ESL) theory and was developed to allow the use of any high-order beam shear deformation theory (HBST) in a unified approach. A generalized Maxwell model was implemented to analyze the time-dependent behavior of the composite. The finite element employs local Lagrange and Hermitian support functions enriched with orthogonal Gram-Schmidt polynomials and is free of shear locking. The enriched macro elements can be used with very coarse meshes and the precision can be controlled without generating a new mesh. The formulation has been validated with numerical examples of symmetric and non-symmetric laminated beams using the three-dimensional finite element program PLCD.

The Effect of the Length and Distribution of Implants for Fixed Prosthetic Reconstructions in the Atrophic Posterior Maxilla: A Finite Element Analysis.

In this study, different prosthetic designs that could be applied instead of advanced surgical techniques in atrophic maxilla were evaluated with finite element analysis. Atrophic posterior maxilla was modeled using computer tomography images and four models were prepared as follows: Model 1 (M1), two implants supporting a three-unit distal cantilever prosthesis; Model 2 (M2), two implants supporting a three-unit conventional fixed partial denture; Model 3 (M3), three implants supporting three connected crowns; and Model 4 (M4), two implants supporting two connected crowns. Implants 4 mm in width and 8 mm or 13 mm in length were used. A linear three-dimensional finite element programme was used for analysis. The maximum principle stress (tensile) and minimum principle stress (compressive) were used to display stress in cortical and cancellous bones. The von Mises criteria were used to evaluate the stress on the implants. M1 was found to be the most risky model. The short dental arch case (M4) revealed the lowest stresses among the models but is not recommended when one more implant can be placed because of the bending forces that could occur at the mesial implant. In M2 and M3, the distal implants were placed bicortically between the crestal and sinus cortical plates, causing a fall of the stresses because of the bicortical stability of these implants.

Recommendation of Suitable Loading Waveforms and Wavelength Equations for Dynamic Modulus Based on Measured Wheel Loads

Dynamic modulus is a key parameter in the pavement structure design and analysis. A haversine loading waveform is the most widely recommended waveform in the laboratory to obtain the dynamic modulus of asphalt mixtures by test protocols, which may not completely represent all field loading conditions. The aim of this study is to investigate the suitable vertical compressive stress pulse waveforms at different depths under different pavement structures and to obtain the best fitting waveforms by using the least squares method. Specifically, the vertical compressive stress of different pavement structures was calculated by utilizing a three-dimensional finite element program incorporating with the measured wheel loads. The results revealed that the vertical stress pulse waveforms at different depths in asphalt layer were different within different pavement structure combinations. Generally, the square waveform fitted the vertical stress pulse waveform better for the shallow depth of the surface layer. The haversine waveform became more suitable while the depth increased. The bell waveform was better when the depth went deeper (i.e., 10 cm). In addition, the method of choosing waveforms at different depths of different pavement structures was provided, and the equation of calculating wavelength was recommended. Moreover, dynamic modulus under different loading waveforms were analysed through laboratory test, and the process for obtaining dynamic modulus of asphalt layer in any depth was presented.

Seismic Fragility Analysis of High Earth-Rockfill Dams considering the Number of Ground Motion Records

This study analyzes the impact of the number of ground motions on the seismic fragility of a high earth-rockfill dam and the estimation of reasonable fragility parameters based on a sufficient number of earthquake records. In this paper, the vertical deformation is obtained using the three-dimensional finite element program DYNE3WAC combined with the Pastor–Zienkiewicz–Chan model and Biot dynamic consolidation theory. The relative seismic settlement rate is considered the damage index for the seismic fragility analysis of the dam. The fragility curves of the high earth-rockfill dam are determined by the multiple stripe analysis (MSA) method. A set of seismic waves is chosen based on the spectrum in the Chinese hydraulic structure seismic code. With an increasing number of earthquake records, the coefficients of variation (COV) of the mean and standard deviation (STD) of the relative seismic settlement rate decrease and tend to stabilize when the number of earthquake records reaches 34. The estimated fragility parameters θ and β are constant when the number of earthquake records exceeds 34. The requisite number of earthquake records for an accurate fragility estimation is determined by analyzing the lower and upper confidence intervals for the estimated θ and β. The 95% and 90% confidence interval can accurately estimate the fragility of a high earth-rockfill dam when the number of ground motion records reaches 36 and 32, respectively. The results of the fragility analysis demonstrate that the DYNE3WAC program and MSA method can provide an effective basis for determining fragility curves. Furthermore, the sensitivity analysis of earthquake records is essential for assessing the seismic fragility of high earth-rockfill dams.