Nonlinear Finite Element Model Research Articles

Nonlocal nonlinear higher-order finite element model for static bending of curved nanobeams including graphene platelets reinforcement

The aim of this work is concerned with the nonlocal nonlinear bending characteristics of non-classical isotropic and composite curved beams based on graphene platelets reinforcement, viz., nano size/micro beams. The size-dependant effect prominent in micro/nanobeams is incorporated in the formulation based on the nonlocal theory using size-dependent continuum approach. The proposed structural model includes both moderately large displacement and rotations, respectively. The system governing equations are established in terms of displacement functions using the principle of virtual work statements. A three-noded shear deformable curved beam finite element using a higher-order sinusoidal function based beam theory is employed; the solutions are obtained by adopting direct iterative procedure. The efficacy of the model is tested against the analytical studies available for the nano-size beams. A detailed analysis is made to highlight the influence of various design variables like thickness ratio, curvature of beam, nonlocal parameter, and the support conditions on the nonlinear bending behavior of curved nano/micro-size beams.

Seismic behavior of reduced beam section joints considering concrete floor effect

SummaryThis study investigates the seismic impact of concrete floors on reduced beam section beam‐to‐column joints through four quasi‐static cyclic tests. We examine mechanical properties, failure modes, and processes against specific criteria. Additionally, we analyze hysteretic response, energy dissipation, stiffness, capacity, and stress–strain mechanisms. Moreover, the ABAQUS platform was used to reproduce the specimen nonlinear finite element model to compare and analyze the test results. The results showed that the specimens exhibit excellent energy dissipation capacity and ductility (with a coefficient of 5.00); the column‐bar connection characteristics affect the maximum capacity and plastic hinge behavior in the reduced beam area. The reduced section of beam's upper flange could not improve the overall seismic performance of the joint. The observed failure sequence is as follows: concrete floor cracking, beam flange yielding, reinforcement fracture, lower flange yielding in the reduced beam area, and overall joint failure. This sequence confirms that the joint fulfills the design criteria of a “strong column‐weak beam” by achieving the target of plastic hinge outward movement.

A Dynamical Model for the Control of a Guyed Tensegrity Beam Under Large Displacements

Abstract Most studies regarding models of tensegrity systems miss the possibility of large static deformations or provide elaborate and lengthy solutions to determine the system dynamics. Contrarily, this work presents a straightforward methodology to find the dynamic characteristics of a guyed tensegrity beam structure, allowing the application of vibration control strategies in conditions of large deformations. The methodology is based on a low-order, adaptive, nonlinear finite element model with pre-stressed components. The method is applied to numerical and experimental models of a class 2 tensegrity structure with a high length-to-width aspect ratio. Image processing and accelerometer data are combined to extract the experimental natural frequencies of the structure, which are compared to numerical results. Prony’s method is applied to estimate damping, and a numerical control strategy is employed using the dynamical model of the structure.

The effect on punching shear failure in centrally loaded ground-supported concrete slabs for different aspects like slab thickness, size and the position of reinforcement bar, and the strength of concrete using a validated FE model

The effect of slab thickness, presence of reinforcement and concrete strength on punching shear capacity of the ground-supported concrete slabs (GSCS) is an important issue in Industrial Ground-supported slab construction. In this study, a three-dimensional nonlinear finite element (FE) model for GSCS was validated with three experimental results from literature and used to assess those effects. A Concrete damaged plasticity model in ABAQUS2020 software with a suitable simulation technique and the theory-based material property was adopted. The results of FE models and predictions of the Technical Report34 (TR34) of the Concrete Society were compared with the experimental results. The average FE predicted/Experimental punching shear capacity ratio was 0.93 with a 0.06 standard deviation and the average TR34 predicted/Experimental punching shear capacity ratio was 1.01 with 0.06 standard deviation. However, the average TR34 predicted/FE predicted punching shear capacity ratio was 1.08 with a 0.13 standard deviation. TR34 prediction was little bit liberal. The results of 72 FE models were compared with the TR34 prediction. The average TR34 predicted/FE predicted punching shear capacity ratio is 1.17 with a 0.21 standard deviation. TR34 prediction was liberal compared to FE prediction. The study showed that the effects of an increase of Slab thickness, Concrete strength, and reinforcement were positive in both FE and TR34 predictions, whereas TR34 predictions were conservative up to a certain slab thickness around 115–130mm for concrete grade 20–40 MPa. As concrete strength and thickness increase, TR34 predictions become more liberal. The bottom layer reinforcement provides greater strength, however, TR34 was unable to predict that.

Finite Element Analysis of the Influence of Implant Tilting and the Direction of Loading on the Displacement and Micromotion of Immediately Loaded Implants

ABSTRACT Objectives: To investigate the outcome of the loading direction and implant tilting on the micromotion and displacement of immediately placed implants with finite element analysis (FEA). Materials and Method: Eight blocks of synthetic bone were created. Eight screw-type implants were inserted, four axially and four slanted, each measuring 11 mm in length and 4.5 mm in diameter. The axial implants and the tilted implants were distally inclined by 30°. The top of the abutment was subjected to 180 N vertical and mesiodistal oblique (45° angle) loads, and the displacement of the abutment was measured. The abutment displacement and micromotion were estimated, and nonlinear finite element models simulating the in vitro experiment were built. In vitro studies and FEA data on abutment displacement were compared, and the reliability of the finite element model was assessed. Result: Under oblique stress, abutment displacement was larger than under axial loading, and it was also greater for tilted implants than for axial implants. The consistency of the in vitro and FEA data was satisfactory. Under vertical stress, the highest micromotion values in the axial and tilted implants were extremely near Conclusion: Under mesiodistal oblique stress, tilted implants may have a smaller maximum amount of micromotion than axial implants. The loading direction had a significant impact on the highest micromotion values. The abutment displacement values were not reflected in the maximum micromotion measurements.

Investigation of the displacement-based seismic performance of geogrid earth-retaining walls using three-dimensional finite element modeling

This study evaluates the earthquake-induced movement of geogrid earth-retaining (GER) walls. A thorough investigation was conducted on a GER wall model, utilizing a comprehensive finite element (FE) analysis. This research focuses on investigating and designing hollow prefabricated concrete panels and conventional gravity-type stone masonry GER walls. It also displays comparative studies such as the displacement of the wall, deflection of the wall, lateral pressure of the wall, settlement of the backfill reinforcement, vertical pressure of the backfill, lateral pressure of the backfill, vertical settlement of the foundation, and settlements of soil layers across the height and acceleration of the walls of the GER walls. The FE simulations used a three-dimensional (3D) nonlinear dynamic FE model of full-scale GER walls. The seismic performance of models has also been examined in terms of wall height. It was found that the seismic motion significantly impacts the height of the GER walls. In addition, the validity of the proposed study model was assessed by comparing it to the conventional reinforcement concrete and gravity-type GRE wall and ASSHTO guidelines using finite element (FE) simulation results. Based on the findings, the hollow prefabricated concrete panels were the most practical alternative due to their lower deflection and displacement. Based on the observation, it was also found that the hollow prefabricated GER wall is the most viable option, as the settlement and lateral pressure in the former type are high.

Effects of boundary conditions on RC beams subjected to accidental thermal load in nuclear power plants

Reinforced concrete (RC) beams in nuclear safety related structures should be designed for accidental thermal gradient combined with mechanical loads. Design capacity and structural behavior of those beams are affected by constraint boundary conditions at beam ends. In design approaches widely used in nuclear power plants (NPPs), it is commonly assumed that the thermal curvature of a RC member is fully constrained while axial constraint condition is often not specified. In this paper, RC beams with various constraint boundary conditions that are subjected to accidental thermal gradient combined with mechanical loads are studied using both experimental tests and nonlinear finite element (NLFE) models. Both rotational and axial stiffness ratios at boundary and their effects on thermal moments and ultimate flexural capacity of RC beam are evaluated. Results shows that the assumption of a fully constrained rotational boundary condition is practically accurate for most RC beams in NPPs subjected to thermal gradient. On the other hand, results also show that axial constraint boundary condition has considerable influence on both thermal moment and usable design flexural strength thus neglecting its effect may lead to insufficient design of RC beam. In addition, this study established relationship between axial constrain stiffness ratio and thermal moment, as well as relationship between axial constrain stiffness ratio and usable design flexural strength for different accidental temperature gradients and reinforcement ratios. That information can be used for correction of thermal moment and usable design flexural strength in design practice.

Numerical investigation of the influence of transverse welds on the strength of aluminum alloy I - shaped members – beams

The weldability of high strength aluminum alloys is an important consideration when designing aluminum structures. While these alloys do suffer significant strength loss in the weld heat affected zone (HAZ), available design codes are often overly conservative in their guidelines regarding the design of welded aluminum members. This paper presents a numerical investigation of the effect of reduced strength in the HAZ adjacent to a transverse weld in simply-supported aluminum alloy beams subject to concentrated end moments. Nonlinear finite element (FE) models were developed, validated, and applied in a parametric study of non-welded and transversely welded 6061-T6 flexural members with an I-shaped cross section. The FE model included initial geometric imperfections and material nonlinearities in both the HAZ and the base material. The parametric study examined 400 unique beam cases defined by the combination of four factors, including slenderness ratio or unbraced length, weld location along the beam span, post-yield material stiffness model, and loading case or resulting moment gradient. The FE results were subsequently compared with capacities predicted by the Aluminum Association’s Specification for Aluminum Structures, with proposed modifications to SAS also provided. A similar study on columns is presented in a companion paper within this issue.

Seismic performance and estimation of flexural bearing capacity of prefabricated engineered cementitious composite shell–reinforced concrete composite column with grouted sleeve connection

Engineered cementitious composites (ECCs) have excellent crack control capacity and pseudo-strain-hardening behaviour. They can be used to improve the damage-tolerant capacity of vulnerable parts of structures. To improve the seismic performance of a traditional prefabricated column connected with grouted sleeves (GSs), an innovative prefabricated ECC shell–reinforced concrete (RC) composite column with GSs (ECC–PRC–GSs) is proposed in this paper. Then, three-dimensional nonlinear finite element models of the ECC–PRC–GSs are established and validated with previous experimental results. Subsequently, parametric analysis of the ECC–PRC–GSs is systematically performed to assess the seismic performance of ECC–PRC–GSs. Notably, certain important design suggestions for the ECC–PRC–GSs are proposed. Finally, a theoretical model is developed to predict the flexural bearing capacity of ECC–PRC–GSs based on the strain compatibility and force equilibrium conditions. The effectiveness of the model is verified through finite element analysis and experimental results.

Numerical analysis and optimization of CFRP buckle arrestors in subsea pipelines

This research investigates the collapse mechanisms and crossover pressure capacity of carbon fiber-reinforced polymer (CFRP) buckle arrestors in subsea pipelines. A nonlinear three-dimensional finite element (FE) model was formulated using ANSYS framework, incorporating a nonlinear geometric algorithm to simulate the collapse and crossover failures. The study underscored a good agreement between the FE model predictions, experimental observations done by the author, and previous research outcomes. Two principal crossover modes; flattening and U-shape modes were identified, though initiated similarly, differ in progression, attributed to the arrestor's attributes. The arrestor thickness ratio (h/t) emerged as a significant determinant of arresting efficiency, particularly impactful when h/t ≥ 1.5. An inverse relationship between σyp/σuc and PX/PP was identified. Furthermore, specific geometric parameters, like h/t and L/D, delineate the predominant crossover mode. Finally, new empirical expressions including the geometric and material parameters are proposed to predict the crossover pressure (PX) for each crossover mode, separately. Also, the findings suggest that CFRP arrestors, especially those with configurations of L = 1.5D and h = 3t, can offer optimum resilience to external pressure.

Numerical investigation of the influence of transverse welds on the strength of aluminum alloy I-shaped members – Columns

This paper presents a numerical investigation, using finite element analysis, of the effects of transverse welds on the structural behavior of aluminum-alloy compression members. A non-linear finite element (FE) model was developed, and validated using experimental tests, to simulate the behavior of 6061-T6 aluminum-alloy columns with an I-shaped AW6×4.03 section geometry. The FE model included different material properties for the heat-affected zone (HAZ) that occurs in the proximity of the weld and the remaining base material, and incorporated both geometric and material nonlinearities. A parametric study of 80 columns with and without transverse welds was conducted, which investigated ten unbraced lengths, three weld centerline locations along the member length, and two types of post-yield material stiffness models, including elastic-perfectly plastic and strain hardening materials. The FE results provide clear evidence of the significance of the HAZ strength reduction on the load carrying capacity of welded aluminum-alloy columns. Numerical results were compared with those obtained using the provisions within the Aluminum Association’s Specification for Aluminum Structures, and they were used to develop proposed modifications to these provisions, which can remove the degree conservatism observed. A similar study on beams is presented in a companion paper.

Fatigue assessment of CFST joints using the effective notch stress approach

Compared to tubular joints formed by hollow steel sections, concrete-filled steel tubular (CFST) joints exhibit more complicated failure modes and mechanism under fatigue load due to the nonlinear material confinement and the associated stress redistribution. For a reliable fatigue design of such composite tubular joints, these complexities need to be fully addressed and reasonably quantified, which necessitates an accurate approach for assessing their fatigue performance. The effective notch stress approach is widely recognized in fatigue design for its applicability and efficiency in evaluating the fatigue strength since it can rationally account for the effects of geometric configurations and welding defects on the fatigue performance. However, it has not been widely adopted in the assessment of CFST joints due to the high costs involved in modelling and computing. In this paper, a refined nonlinear finite element model is established, which facilitates the acquisition of reliable notch stress values. Subsequently, a statistical analysis is conducted on the available fatigue data of CFST joints, employing the computed notch stress to yield an S–N curve. A comparative evaluation on the results obtained from the nominal stress approach, the hot-spot stress approach and the effective notch stress approach testifies the superior accuracy of the last in assessing the fatigue strength of CFST joints.

Mechanical safety prediction of a battery-pack system under low speed frontal impact via machine learning

In response to nonrenewable energy consumption and environmental pollution, the development of electric vehicles has accelerated. The safety of electric vehicles has garnered considerable attention. There are numerous incalculable foreign objects on the road that may collide with or scratch the battery-pack’s frontal, resulting in battery-pack system damage or even explosion. This poses a significant risk to the safety of passengers and drivers. In this paper, a diversity of mechanical safety prediction models for battery-pack systems are proposed. These models support data-driven structural optimization of the battery-pack system by utilizing the numerical results of the bottom shell deformation. These simulation-based prediction models combine response surface method and machine learning algorithms. First, a nonlinear finite element model of the battery-pack system is established. The efficacy of the model is verified using constrained modal analysis in a variety of commercial software packages. Second, the collision simulations are executed and the data in various collision conditions are collected. Different sample sizes are used to develop various response surface models and machine learning models. The machine learning algorithms adopt support vector machine, Gaussian process regression, and neural network models. Third, the prediction accuracy of multiple prediction models is investigated according to error functions. The results show that the neural network model can predict the most accurate deformation under the condition of low speed frontal impact. The prediction average absolute percentage error of the neural network model is only 0.34% within the design domain, and only 2.54% outside the design domain. The proposed prediction model can be used for reliable design of the battery-pack system in electric vehicles. It also can be employed to design the early warning system of the battery-packs.

Nonlinear finite element analysis of steel fiber reinforced concrete beams subjected to impact loads

Steel fiber reinforced concrete, compared to the conventional concrete; is a composite building material that performs much better in terms of parameters such as ductility, energy absorption capacity, fracture toughness, fatigue resistance, and the use of steel fiber reinforced concrete (SFRC) in structures has become widespread. In this study, a nonlinear finite element model (FEM) has been developed that can represent the behavior of beams produced by using steel fiber concrete subjected to impact load. For this purpose, a finite element model of beam series produced with fiber-reinforced concrete obtained from the literature was created. The ABAQUS package program was used to create models simulating the behavior. Numerical results showed that the model could successfully capture the experimental results of beams selected from the literature. In addition to simulation, a parametric study was also performed to investigate the effect of stirrups, reinforcement ratio, and drop height on the behavior of SFRC beams under impact loads. The results of the parametric study showed that increasing the fiber ratio and reinforcement ratio positively affected the behavior of SFRC beams in terms of displacement recovery.Steel fiber reinforced concrete, compared to the conventional concrete; is a composite building material that performs much better in terms of parameters such as ductility, energy absorption capacity, fracture toughness, fatigue resistance, and the use of steel fiber reinforced concrete (SFRC) in structures has become widespread. In this study, a nonlinear finite element model (FEM) has been developed that can represent the behavior of beams produced by using steel fiber concrete subjected to impact load. For this purpose, a finite element model of beam series produced with fiber-reinforced concrete obtained from the literature was created. The ABAQUS package program was used to create models simulating the behavior. Numerical results showed that the model could successfully capture the experimental results of beams selected from the literature. In addition to simulation, a parametric study was also performed to investigate the effect of stirrups, reinforcement ratio, and drop height on the behavior of SFRC beams under impact loads. The results of the parametric study showed that increasing the fiber ratio and reinforcement ratio positively affected the behavior of SFRC beams in terms of displacement recovery.

Seismic analysis of buildings with basements

This research work analyzes how seismic waves affect buildings with basements that are usually studied independently: In surface structures the inertial forces originated by the movement of their base and in subway structures the deformations due to ground motion are considered. The building located in the city of Quito with twelve elevated floors and five subfloors is studied using nonlinear finite element modeling, considering that the subsoil depends on seismic excitations in a dynamic soil-basement-structure set, for which it is modeled together with its geotechnical components. The superstructure is integrated to the infrastructure and a time-history analysis is included with the most representative earthquakes can affect the building. The present investigation has three basic components: seismic, geotechnical, and structural, which are merged by means of specialized 3D structural engineering programs. In the seismic component, local and regional information about tectonic faults within Ecuador is collected; the building is then located on a seismic risk map and the magnitudes, types, and other parameters of the site where the building is located are determined. Using the results of the Earthquake Risk Assessment Project for the city of Quito (TREQ) and the Pacific Earthquake Engineering Research Center (PEER) database, three relevant seismic events are chosen for the time-history analysis that meet the seismic risk data for the building. For the geotechnical soil component, the geotechnical parameters of the original design of the building foundation, stratigraphy, and characteristics of soil solids, among others, are used. The structural component considers the type of material, geometry, dimensions, joints between elements and others of the original design for both basements and superstructure. The connection of these three components is carried out using Midas Gen and Midas GTS NX. The results of deformations as a function of time are compared with similar standards, studies, and investigations.

Biomechanical effects of endplate sagittal coverage change on cervical disc replacement: a finite element analysis.

In recent years, the number of artificial cervical disc replacements has increased, and paravertebral ectopic ossification is a common complication. Although the exact mechanism is not clear, some studies suggest that it is related to the concentration of tissue stress caused by incomplete coverage of the trailing edge of the endplate. Therefore, this study performed a quantitative analysis to compare the biomechanical effects of different sagittal distances at the posterior edge of the endplate of the upper and lower prosthesis on the cervical spine and to explore the mechanical response of incomplete coverage of the posterior edge of the endplate on the paravertebral tissues. A C2-C7 nonlinear finite element model of the cervical spine was established and validated. Based on the cervical spine model, cervical disc replacement surgery models were constructed with different distances of sagittal distance at the posterior edge of the upper prosthetic endplate (0, 1, 2, 3mm, respectively) and sagittal distance at the posterior edge of the lower prosthetic endplate (1, 2, 3mm, respectively). Each model was subjected to the same 1Nm torque and 73.6N driven compressive load. Range of motion (ROM), intervertebral disc pressure (IDP), facet joint force (FJF), and endplate stress were measured at the cervical surgical and other segments. Compared to the intact cervical spine model, the sagittal distance of the posterior edge of the prosthesis endplate at different distances increased the stress on the intervertebral disc and the capsular joint in the adjacent vertebral body segments to different degrees, especially in extension. In different directions of motion, the posterior margin sagittal distance of the posterior edge of the endplate of the lower prosthesis has a greater mechanical influence on the cervical spine compared to the posterior margin sagittal distance of the posterior edge of the endplate of the upper prosthesis. Compared with the intact model, the biomechanical parameters (ROM, FJF, endplate stress) of the C5-C6 segment increased the most when the sagittal distance of the posterior edge of the endplate of the upper prosthesis was 3mm. Compared with the intact model, the maximum intervertebral disc stress of C4-C5 and C6-C7 was 0.57MPa and 0.53MPa, respectively, when the sagittal distance of the posterior edge of the upper prosthetic endplate was 3mm. After the sagittal distance of the posterior edge of the prosthetic endplate was completely covered, the mechanical influence of the entire cervical spine was low. The sagittal distance at the posterior edge of the endplate of different sizes changed the motion pattern and load distribution of the implanted segment to some extent. When the sagittal distance between the prosthesis and the upper endplate was greater than or equal to 3mm, the mechanical indices of the implanted segment increased significantly, increasing the risk of local tissue injury, especially during extension motion. Compared to the sagittal distance at the posterior edge of the endplate of the lower prosthesis, increasing the sagittal distance at the posterior edge of the endplate of the upper prosthesis has a greater effect on the mechanics of the cervical spine.

Diaphragm effect of unreinforced historical masonry vaults

In historical masonry structures, and particularly in churches, vaults have a fundamental role in bearing the vertical loads of floors and roofs. However, in past earthquakes they have proved vulnerable, representing a source of fragility under horizontal loading. In addition, the global seismic behavior of masonry structures is strongly affected by the stiffness of flooring elements (diaphragm effect), which, when sufficient, allows for transfer of horizontal actions to stiffer wall working in-plane.In this paper, the diaphragm effect of historical masonry vaults under horizontal loads is investigated numerically. A parametric nonlinear Finite Element model of a cross vault is subjected to in-plane shear actions on two supports to evaluate the response and damage during an earthquake. This work is preparatory for future physical testing activities on scaled prototypes to be performed within a broader research project, aimed at the enhancement and exploitation of artistic and cultural heritage.

Nonlinear isogeometric analysis of axially functionally graded graphene platelet-reinforced composite curved beams

The linear and nonlinear isogeometric finite element models of an axially functionally graded graphene platelet-reinforced composite (AFG-GPLRC) curved beam are established within the framework of the third-order shear deformation beam theory (TSDT) and von-Kármán’s nonlinear geometric relation. The AFG-GPLRC curved beams can be seen as composite structures in which the graphene platelets (GPLs) are continuously distributed in the matrix along the length direction of the curved beam according to different patterns. The modified Halpin-Tsai parallel model and the rule of mixture are implemented to predict the effective Young’s modulus and mass density as well as Poisson’s ratio, respectively. Hamilton's principle, TSDT, and von-Kármán’s strain-displacement relation are combined to derive the governing partial differential equation of motion and corresponding boundary conditions. Furthermore, the Non-Uniform Rational B-splines (NURBS)-based isogeometric analysis (IGA) approach together with a direct iterative technique are utilized to solve the nonlinear governing equation. The accuracy and efficiency of the proposed IGA framework are confirmed by comparing corresponding numerical solutions with other available results. The parametric investigations, such as the curved beam’s geometric parameters, boundary conditions, and GPL’s distribution patterns, on the nonlinear bending and vibration responses of the AFG-GPLRC curved beams are carried out by some illustrative examples.

A computationally efficient procedure for calibrating model parameters of multiple specimens

Model calibration can be a very intensive and time-consuming task, especially when dealing with non-linear and large finite element models. The computational effort further increases when multiple specimens have to be calibrated. This is typical of laboratory experiments where several specimens made with the same and/or different constituent materials are tested. This paper proposes a calibration procedure aimed at reducing the computational effort of multiple specimen model calibration. The calibration procedure combines the robustness of a surrogate-assisted evolutionary algorithm with the exploitation of a database collecting the results of the previously calibrated specimens. In this research, the proposed procedure is applied to the calibration of the parameters of a cohesive crack model for fiber-reinforced concrete specimens. The benefit of the proposed procedure is shown by comparing the results with those obtained from the same calibration method but without accounting for the previous results in the calibration of a new specimen.

Shell buckling of suction buckets for offshore wind turbines considering imperfection and soil parameter sensitivity

Suction buckets or suction caissons in combination with jackets as substructures have become a prominent foundation solution for offshore wind turbines. These large shell structures with relatively thin walls are installed by pumping out the water inside the structure, which creates a pressure difference and thus a downward force. The circumferential compression on the cylindrical shell causes a risk of shell buckling. The prediction of the buckling capacity of such large cylindrical shells is challenging, since it depends significantly on the initial geometric imperfections resulting from the manufacturing process and on the boundary conditions imposed by the surrounding soil. Previous work on suction buckets revealed that the choice of a representative imperfection form and amplitude is very challenging and the buckling pressure is sensitive to soil modeling choices. In this work, various imperfection forms and amplitudes as well as different soil parameters are applied to geometrically and materially nonlinear finite element models and the buckling capacities are determined. The novelties in this contribution are in evaluating and comparing the effects of global and local imperfections in form of sinusoidal eigenmodes and weld depressions for an unstiffened cylindrical shell under hydrostatic compression. The results suggest that global imperfections are more detrimental than local imperfections and further, a new approach based on sorting eigenmode imperfections depending on the wave number to identify the most unfavorable eigenmode-affine imperfection pattern is developed. Additionally, this study is the first to show that the inclusion of soil plasticity and contact effects has a significant impact on the buckling pressure.