Finite Element Analysis Program Research Articles

Performance analysis of a jacked-in single pile and pile group in saturated clay ground

When a pile is installed into saturated clay ground, the “setup” effect may occur due to ground consolidation, which changes pile performance. Although this phenomenon has been observed both in the field and laboratory, its numerical simulation is still challenging. In this work, pile installation effects on the behaviors of jacked-in piles were investigated through three simulation techniques by a three-dimensional finite element analysis program, PLAXIS 3D. A constitutive model called the soft soil creep model was used to describe the soil behavior based on soil parameters obtained from laboratory tests. The behaviors of single piles were first investigated with or without the consolidation process after pile installation to evaluate the pile setup effect. Then, a pile group comprising 4 piles was analyzed using the consolidation process to verify the applicability of the three simulation techniques. The calculated results were compared with the corresponding experimental results. The calculated results using three techniques generally agreed well with the experimental results in terms of initial stiffness and pile shaft resistance. Both the measured and calculated results indicate that ground consolidation caused by pile installation significantly increases the pile bearing capacity and especially, the pile shaft resistance. Therefore, the pile setup effect can be reasonably simulated by the three proposed techniques.

Investigation on the Performance of Partial Penetration Welds in Multicell Concrete Filled Steel Tubes

This paper presents an experimental and analytical investigation on the performance of partial penetration welds used to adjoin steel plates in irregular shaped multicell concrete filled steel tubes. The experimental program of this study is designed based on an actual implementation of such members as mega columns in a super high rise building in China. A total of six specimens are designed with different plate arrangements for the purpose of testing the performance of the partial penetration welds at different locations of the specimen. The designed specimens are tested under different load procedures and directions; this is achieved by placing them in vertical and slantwise manners between two loading plates which impose monotonic and cyclic actions. The failure conditions of each of the tested specimens are presented and discussed in detail and are based on the conclusions drawn from the experimental observations; the partial penetration weld at the corner of the tested specimens is found to be the most vulnerable. To facilitate large scale analysis, a finite element model constructed by the finite element analysis program ABAQUS is verified against experimental results. The evaluation of the stress at the partial penetration welded corner is carried out following an empirical procedure, which is adopted due to the complexity of the problem domain. The adopted procedure consists of two steps: the first one is to initially evaluate the stress based on an existing method in the literature, and the second one is to fit the results of the initial evaluation with the finite element model results based on parametric and regression analysis. After performing regression analysis, a formula to predict the weld stress is concluded, and the results of the proposed equation are found to be satisfactory when compared with the finite element model results.

Determination of representative elementary volume (REV) for jointed rock masses exhibiting scale-dependent behavior: a numerical investigation

Representative elementary volume (REV) is defined as the usual size of a rock mass structure beyond which its mechanical properties are homogenous and isotropic, and its behavior can be modeled using the equivalent continuum approach. Determination of REV is a complex problem in rock engineering due to its definition ambiguity and application area. This study is one of the first attempts to define a REV for jointed rock masses using the equivalent continuum approach. It is aimed to numerically search a ratio between the characteristic size of an engineering structure and pre-existing joint spacing, which are the two most important contributing elements in assessing REV. For this purpose, four hypothetical engineering cases were investigated using the RS2 (Phase2 v. 9.0) finite element (FE) analysis program. An underground circular opening with a constant diameter, an open-pit mine with varying bench heights, a single bench with a constant height, and an underground powerhouse cavern with a known dimension were executed for possible changes in the safety factor and total displacement measurements under several joint spacing values. Different cut-off REVs were calculated for FE models depending on the type of excavation and measurement method. An average REV size of 19.0, ranging between a minimum of 2 for tunnels and a maximum of 48 for slopes, was found in numerical analysis. The calculated sizes of REV were significantly larger than the range of values (5 to 10) commonly reported in the relevant geotechnical literature.

Failure analysis of simple overlap bonding joints and numerical investigation of the adhered tip geometry effect on the joint strength

Abstract This study was carried out in two stages. In the first step, a numerical study was performed to verify the previous experimental study. In accordance with the previous experimental study data, single lap joints models were created using the ANSYS finite element analysis program. Then, nonlinear stress and failure analyses were performed by applying the failure loads obtained in the experimental study. The maximum stress theory was used to find finite element failure loads of the single lap joints models. As a result of the finite element analysis, an approximate 80 % agreement was found between experimental and numerical results. In the second step of the study, in order to increase the bond strength, different overlap end geometry models were produced and peel and shear stresses in the adhesive layer were compared according to the reference model. As a result of the analyses, significant strength increases were calculated according to the reference model. The strength increase in model 3 and model 5 was found to be 80 % and 67 %, respectively, relative to the reference model.

Vehicular impact resistance of highway bridge with seismically-designed UHPC pier

This study strives to numerically explore the performance of highway bridge supported by seismically-designed ultra-high performance concrete (UHPC) piers in resisting heavy truck impact. Firstly, six types of bridge piers are designed with considering two different concrete types (i.e., normal strength concrete (NSC) and UHPC) and three various seismic hazard levels (i.e., earthquake intensities (EI) of 7, 8, and 9) according to Chinese seismic design specifications, and the corresponding refined finite element (FE) models are established and validated by reproducing the tests of drop hammer impacting on reinforced NSC and UHPC members. Based on the well-verified FE models of simply-supported double-pier bent highway bridge and heavy truck, total 54 collision scenarios are carefully designed by referring to the actual accidents, and the vehicle-pier collision analyses are numerically performed by using the nonlinear FE analysis program LS-DYNA. Then, the effects of seismic fortification level and concrete type of impacted pier on the vehicular impact force and dynamic responses of entire bridge structure, as well as the damage and failure modes of both impacted pier and entire bridge are studied. It demonstrates the effectiveness of seismically-designed UHPC pier on improving the vehicle-impact resistance of bridge structure. Besides, more attentions should be paid to the safety of NSC-EI7 and UHPC-EI7 piers and the brittle shear failure in NSC-EI8 piers. Finally, aiming to quantitatively compare the anti-collision performances of entire bridge structure supported by NSC and UHPC piers under the identical seismic fortification intensity, a performance evaluation method of entire bridge structure is proposed based on the residual lateral displacement of the impacted pier. The present work can provide helpful references for the practical applications of UHPC in bridge piers and the on-site feasible evaluation of the residual performance of the post-collision bridge structure.

Efficient form-finding algorithm for freeform grid structures based on inverse hanging method

Grid structures and branching columns have been widely adopted due to their high structural efficiency and novel appearance. High structural efficiency must be achieved through a strict form-finding analysis. Existing algorithms are mainly applicable for grid structures or branching columns only. However, the form-finding of upper grid structures and the lower branching columns are mutually affected. A form-finding algorithm is needed for grid structures supported by branching columns. In the present work, an efficient form-finding algorithm suitable for grid structures is initially proposed, and the feasibility of this algorithm is verified through three examples. Then, the form-finding algorithm for grid structures is integrated with the form-finding algorithm of branching columns. Results indicated that the proposed algorithm can be used for form-finding analysis of various grid structures supported by branching columns. This work was conducted using a general finite element analysis program and can be easily mastered by engineering designers while avoiding tedious programming.

Novel Ring Compression Test Method to Determine the Stress-Strain Relations and Mechanical Properties of Metallic Materials

Although there are methods for testing the stress-strain relation and strength, which are the most fundamental and important properties of metallic materials, their application to small-volume materials and tube components is limited. In this study, based on energy density equivalence, a new dimensionless elastoplastic load-displacement model for compressed metal rings with isotropy and constitutive power law is proposed to describe the relations among the geometric dimensions, Hollomon law parameters, load, and displacement. Furthermore, a novel test method was developed to determine the elastic modulus, stress-strain relation, yield and tensile strength via ring compression test. The universality and accuracy of the method were verified within a wide range of imaginary materials using finite element analysis (FEA), and the results show that the stress-strain curves obtained by this method are consistent with those inputted in the FEA program. Additionally, a series of ring compression tests were performed for seven metallic materials. It was found that the stress-strain curves and mechanical properties predicted by the method agreed with the uniaxial tensile results. With its low material consumption, the ring compression test has the potential to be as an alternative to traditional tensile test when direct tension method is limited.

Damage effect of pile wharf under underwater explosion load

According to the relevant data of reinforced concrete pile test under underwater explosion load in the near-field range of the cooperative company, the corresponding numerical model is established through the explicit finite element analysis program AUTODYN. The accuracy of the required parameters and the calculation method in the numerical simulation process is verified by comparing shock-wave load with reinforced concrete pile damage. Considering the influence of charge quality on the dynamic response and damage mode of reinforced concrete single and group piles, the collapse conditions of the high-pile wharf are analyzed from static and dynamic aspects based on the reinforced concrete pile model of a typical high-pile wharf structure. Results show that the reflected pressure of shock wave is unevenly distributed along the pile with different explosive equivalents, that is, large in the middle and small on both sides. The damage modes of single piles can be divided into bending, bending shear, and shear failures. The study of the continuous collapse condition of piled wharf reveals that the concrete pile and the cap contact part of the first coagulant crushing failure.

Buckling Knockdown Factors of Composite Cylinders under Both Compression and Internal Pressure

The internal pressure of a thin-walled cylindrical structure under axial compression may improve the buckling stability by relieving loads and reducing initial imperfections. In this study, the effect of internal pressure on the buckling knockdown factor is investigated for axially compressed thin-walled composite cylinders with different shell thickness ratios and slenderness ratios. Various shell thickness ratios and slenderness ratios are considered when the buckling knockdown factor is derived for the thin-walled composite cylinders under both axial compression and internal pressure. Nonlinear post-buckling analyses are conducted using the nonlinear finite element analysis program, ABAQUS. The single perturbation load approach is used to represent the geometric initial imperfection of thin-walled composite cylinders. For cases with the axial compressive force only, the buckling knockdown factor decreases as the shell thickness ratio increases or as the slenderness ratio increases. When the internal pressure is considered simultaneously with the axial compressive force, the buckling knockdown factor decreases as the slenderness ratio increases but increases as the shell thickness ratio increases. The buckling knockdown factors considering the internal pressure and axial compressions are higher by 2.67% to 38.98% compared with the knockdown factors considering the axial compressive force only. The results show the significant effect of the internal pressure, particularly for thinner composite cylinders, and that the buckling knockdown factors may be enhanced for all the shell thickness ratios and slenderness ratios considered in this study when the internal pressure is applied to the cylinder.

The Research of Blast Resistant of Reinforcement Concrete Beams in Concrete Structures at Off-site Oil and Gas Plant

In the recent decades, blasts and gas explosions at the off-site of oil and gas plants have increased leading to destruction of important concrete structures, essential equipment and loss of human life. In response, structural engineers have come up with different ways of reinforcing beams of concrete structures using fiber reinforced polymers composite materials to produce blast resistant structures to minimize the impact of the blast loads, due to their unique and individual characteristics like high flexural and shear strength. This paper seeks to research the dynamic behavior, response and performance of reinforce concrete beams strengthened with Carbon Fiber Reinforced Polymer composites when subjected to blast loading. The study aims at proposing a design model of strengthening reinforce concrete beams with Carbon Fiber Reinforced Polymer in supporting concrete structures at off-site oil and gas plants against hydrocarbon explosions. Carbon Fiber Reinforced Polymer composites exhibit higher modulus of elasticity, higher energy absorption capacity, resistant to all forms of alkali and higher tensile strength compared to all other fiber reinforced polymers reinforcements and therefore the need to assess its capacity in protecting concrete structures at oil and gas plants against dynamic loads. The research will be carried out through numerical analysis using the finite element analysis computer program, ANSYS.

Case study on advanced 3D finite element limit analysis of counter-acts installed at Ormen Lange

The design of counter-acts for the Ormen Lange Northern Field Development has previously been considered in other publications. Counter-acts were used to ensure pipeline stability during pipe-lay along route curves. The counter-acts were large diameter steel cylinders installed with self-weight penetration. The in-place design was completed with use of advanced Finite Element Analysis (FEA) program Abaqus and validated in parallel by the finite difference (FD) program, FLAC. This paper will present a comparison of the previous work to advanced 3D Finite Element Limit Analysis (FELA) with use of the software OPTUM G3. 3D FELA is newly developed for geotechnical design. The paper will show the advantage of the FELA which is based on the principles of limit analysis. The counter-act design is particularly complex and given the cylindrical shape with no internal base plate. This will challenge the element types in the FELA model. Further, the soil conditions are amongst the softest clay encountered in Norway further increasing the complexity of the design.

Performance of Enhanced Steel Beam-Column Welded Connections for Seismic Resistance

This paper presents and discusses the development of a numerical model which investigates the enhancement of overall stiffness and stress distribution in welded connections under cyclic loading. The structure under investigation, described in four fully welded T-joint (BCC5) specimens. The four specimens were modeled under different displacement loading using a finite element analysis program Solidworks and Ansys software in conjunction with test data obtained from the University of Lisbon, which was validated with the test results by matching the hysteresis loops, maximum high strain, and maximum stress at the crack location steel joint specimens. The comparison between the analysis and test results showed good agreement and also showed that the maximum strain in the enhanced model is less than the maximum strain on the base model, and the location of maximum strain is moved to the gusset plate rather than the weld zone, therefore the gusset plate makes the joint in the enhanced model more ductile than the joint in the base model. Life cycles to failure for the enhanced model are more than life cycles to failure in the base model. It is therefore found that this has useful applications in the steel construction industry.

Performance of Enhanced Steel Beam-Column Welded Connections for Seismic Resistance

This paper presents and discusses the development of a numerical model which investigates the enhancement of overall stiffness and stress distribution in welded connections under cyclic loading. The structure under investigation, described in four fully welded T-joint (BCC5) specimens. The four specimens were modeled under different displacement loading using a finite element analysis program Solidworks and Ansys software in conjunction with test data obtained from the University of Lisbon, which was validated with the test results by matching the hysteresis loops, maximum high strain, and maximum stress at the crack location steel joint specimens. The comparison between the analysis and test results showed good agreement and also showed that the maximum strain in the enhanced model is less than the maximum strain on the base model, and the location of maximum strain is moved to the gusset plate rather than the weld zone, therefore the gusset plate makes the joint in the enhanced model more ductile than the joint in the base model. Life cycles to failure for the enhanced model are more than life cycles to failure in the base model. It is therefore found that this has useful applications in the steel construction industry.

Quench Induced Eddy Current and Mechanical Stresses in the Bobbin and Thermal Shield of the 1.5 T MRI Magnet System

An actively shielded 1.5 T superconducting MRI magnet is designed for a whole-body clinical scanner. During a quench, its fast-decaying field induces a strong eddy current in all the conductive parts of the cryostat. The eddy current together with the decaying magnetic field generates Lorentz force, which generates stress and deformation in the bobbin structure, thermal shield, and other conductive parts of the cryostat. In this article, we report the analysis of the eddy current distribution induced in the bobbin structure and thermal shield made of various alloys of the MRI magnet system using a finite element analysis program. The net forces on each part of the bobbin structure and the thermal shield and the associated stress distribution, the deformation are analyzed in detail using OPERA-3D software. The eddy-current-induced effects on a few metallic alloys are compared for generating design inputs for the bobbin structure and the thermal shield of the MRI magnet system. We also report the transient behavior of the eddy current in correlation with the decaying current during a quench.

Fire resistance of bi-directionally prestressed concrete under extreme fire loading

Infrastructures such as prestressed concrete containment vessels (PCCVs) and liquid gas storage tanks are constructed as bi-directional prestressed concrete (PSC) structures to ensure outstanding leak-tight storage and shielding performance. However, PSC structures exhibit severe vulnerability to high-temperature fire due to the high-strength concrete used and the application of prestressing (PS) stresses to increase the strength of the structures. The PCCV of a 1400 MW advanced power reactor was selected as the target for study. A scaled-down model of the PCCV outer wall was fabricated and tested to determine its resistance to a standard fire-loading scenario. Furthermore, different PS forces were applied to the specimens to evaluate the effect of concrete confinement on the fire resistance. Test data of temperature distribution, PS force loss and residual strength capacity were obtained. The experimental data were used for calibration of a commercial finite-element simulation program (Midas FEA) for structural fire analysis of real-scale concrete structure and infrastructure. The simulation and test results showed significant similarity and the result trends were accurate.

An impact echo method to detect cavities between railway track slabs and soil foundation

The impact echo technique is one of the most useful non-destructive test methods for determining the thickness of concrete or detecting possible cracks or cavities in the internal parts of a concrete structure without damaging the surface. Many types of unstable conditions in railway tracks, including various modes of irregularities, may occur when cavities are generated directly under a concrete slab track or when a slight open space is made under a loose sleeper. In this study, we developed a nondestructive testing (NDT) system for detecting abnormalities in concrete tracks and performed 3D numerical simulations using the ABAQUS finite element analysis (FEA) program to investigate the impact echo response from a concrete track slab with different sizes of cavities. Sections of concrete slab were simulated as solid body masses under the railway tracks with gaps in the bodies themselves or with cavities existing between the track concrete layer (TCL) and the hydraulically stabilized base (HSB). We investigated the locations and depths of the cavities and gaps in the model concrete slab using the acoustic impact echo response based on the frequency response of the elastic waves generated in the slab. In addition, a Short-time Fourier Transform (STFT) and a wavelet technique were adopted for a time frequency analysis. Our study demonstrated that the impact echo technique developed in this study by FEA and NDT can measure and confirm the location and depth of cavities in concrete slabs.

Numerical Simulation on Dynamic Behavior of Slab–Column Connections Subjected to Blast Loads

Although many studies on the blast-resistant performance of structures have focused mainly on single members such as beams and columns, there is little research on the behavior of joints that are subjected to blast loads. In this study, the structural behavior of a slab–column connection subjected to blast load was investigated using a numerical analysis method. LS-DYNA was used as a finite element analysis program, and in order to improve the accuracy of numerical analysis, mesh size, material model, and simulation method of blast load were determined through preliminary analysis. The effect of different restraints of the joints, depending on the position of the columns in the slab, on the blast resistance performance was investigated. As a result, the highly confined slab-interior column connection showed better behavior than other edge and corner columns. The drop panel installed between the lower column and the slab was effective in improving the blast-resistance performance of the slab–column connection. For a more accurate evaluation of blast resistance performance, it was suggested that various evaluation factors such as ductility ratio, reinforcing stress, and concrete fracture area can be considered along with the support rotation, which is an important evaluation factor suggested by many standards.

Application of Failure Assessment Diagram (FAD) for Steel Welded Connection Based on BS7910 and DNV-RP-108

The failure assessment diagram (FAD) method has been widely accepted to evaluate the extent to which cracks may affect structural safety. The usage of this FAD method has been validated and included in [1]-[3]. The structure under investigation, described in four fully welded T-joint (BCC5) specimens, where these welded joints are a source of stress concentration and defects from which fatigue cracks can grow. The four specimens were modeled under different displacement loading using a finite element analysis program Ansys and SolidWorks software. In this work, the application of a FAD (Lr, Kr) using maximum stress, cumulative stress ranges, and the last half-cycle stress range was investigated. The results are showing that all the points were lying outside the FAD curve except for the BCC5D specimen point was inside FAD when using maximum stress.
 Conclusions made that the cumulative stress gives Lr and Kr are extremely large and hence predict failure too early. With the Crack Tip Opening Displacement (CTOD) of the test specimen assumed to be about 1mm rather than 0.1mm it was found that, if a FAD is to be used to indicate failure, then both Lr and Kr should be based on the maximum stress. It appears that the FAD methodology does help to predict the final failure (which is the usual application in such cases). This represents more effectively the structural behavior and would be more easily used by designers.

Application of Failure Assessment Diagram (FAD) for Steel Welded Connection Based on BS7910 and DNV-RP-108

The failure assessment diagram (FAD) method has been widely accepted to evaluate the extent to which cracks may affect structural safety. The usage of this FAD method has been validated and included in [1]-[3]. The structure under investigation, described in four fully welded T-joint (BCC5) specimens, where these welded joints are a source of stress concentration and defects from which fatigue cracks can grow. The four specimens were modeled under different displacement loading using a finite element analysis program Ansys and SolidWorks software. In this work, the application of a FAD (Lr, Kr) using maximum stress, cumulative stress ranges, and the last half-cycle stress range was investigated. The results are showing that all the points were lying outside the FAD curve except for the BCC5D specimen point was inside FAD when using maximum stress.
 Conclusions made that the cumulative stress gives Lr and Kr are extremely large and hence predict failure too early. With the Crack Tip Opening Displacement (CTOD) of the test specimen assumed to be about 1mm rather than 0.1mm it was found that, if a FAD is to be used to indicate failure, then both Lr and Kr should be based on the maximum stress. It appears that the FAD methodology does help to predict the final failure (which is the usual application in such cases). This represents more effectively the structural behavior and would be more easily used by designers.

Improving expansive clay subgrades using recycled glass: Resilient modulus characteristics and pavement performance

The scarcity of sound soils, especially in urban areas, often forces engineers to construct the pavement on problematic subgrade soils such as expansive clays. The associated cost involved in replacing the existing problematic soil is avoided by adopting treatment techniques. In this study, a type of high plasticity expansive clay was mixed with 10, 20, and 30% sand-size recycled glass (RG) as a non-chemical soil treatment approach. An extensive investigation comprising experimental works, numerical modeling, and pavement performance analysis was undertaken. After determination of the physical properties of clay and RG, resilient modulus characteristics of clay and the three clay-RG mixtures were carried out through an experimental program. Subsequently, the obtained resilient modulus data sets were incorporated into a finite element analysis program in order to analyze the stress-strain response of pavement models founded on clay and RG-treated subgrades. The compressive and tensile strains achieved through the analysis of the pavement models under traffic loads were next used to compare each pavement model with respect to fatigue and rutting performances. The experimental results showed up to a 113% increase in resilient modulus of clay by the addition of 30% RG. The outcomes of the analysis on pavement systems modeled using the experimental input showed a considerable reduction in compressive and tensile strains by treating the clay subgrade with RG. Consequently, the strain reduction exhibited a significant increase in fatigue life and rutting life of pavements founded on RG treated clay subgrades. The outcomes of this research aim to encourage the construction industry to consider the utilization of environmentally clean recycled aggregates, such as RG, for improving subgrades with problematic soils and hence, promote sustainable construction materials and approaches.