Nonlinear FEM Analysis Research Articles

Nonlinear FEM Analysis of Experimentally Tested Flat Slabs with Openings

Experimental programs focused on the issues related to the flat slabs still attract the attention of the scientists around the world. At the Central Laboratories of STU in Bratislava, together 8 fragments of the flat slabs were tested, focusing on the influence of the openings on the punching resistance. The two reference specimens were without openings and the others had two symmetrically placed openings. The openings were moved from the face of the column in multiples of the effective depth (0d, 1d, 2d). For the assessment of the tests, the models introduced in the relevant standards and codes were applied. The experimental results were also used for NFEM model calibration. The paper will deal with comparison of the theoretical and experimental results as well as with non-linear analysis that was performed in the ATENA FEM program, with the goal to obtain the most realistic behaviour of the flat slabs with openings. The material properties used in the analysis were obtained from the laboratory tests.

SEMI-COMPOSITE STRUCTURES FOR SEWER RENOVATION

In the composite pipe construction method defined in the Japan Sewage Works Association's Design and Construction Guidelines for Sewer Pipe Rehabilitation, a liner pipe is constructed inside an existing sewer and the annular space behind the liner is filled with cementitious grout under pressure to form a highly integrated structure. The Guidelines for sewer renovation in Japan define a composite pipe as a composite structure that requires complete integration between liner materials and an existing pipe. However, in general, owing to the refinement of the small and enclosed working space inside sewers and the significant extension of the pipe to be renovated, mechanical shear connectors are not used to rigidly connect a renovation layer with an existing pipe. To fully explore the advantages of the composite pipe method in sewer renovation while maintaining safe design, a semi-composite structure has been applied in the renovation design of aging sewers using nonlinear FEM analysis for more than 50 sewers (over a total length of 300 km), primarily in big cities in Japan. This paper focuses on the mechanics of the structure.

Evaluation of puncture resistance force of microneedle by nonlinear FEM analysis and experimental validation

Evaluation of puncture resistance force of microneedle by nonlinear FEM analysis and experimental validation

Effects of compaction on soil undrained shear strength deteriorating during undrained cyclic loading and controlling seismic stability of embankment

Effects of compaction on the undrained shear strength of saturated earth-fill dam materials are presented. Poorly and well compacted saturated soils may exhibit undrained shear strengths, respectively, significantly lower and higher than corresponding drained shear strength and this trend is amplified as the undrained strength deteriorates by preceding undrained cyclic loading. These features are implemented in a new simplified seismic analysis to evaluate residual deformation of earth-fill dams. The analysis consists of: 1) a modified Newmark sliding block analysis; and 2) a pseudo-static non-linear FEM analysis, both formulated in a unified framework based on the cumulative damage concept, total stress earthquake response analysis and a direct total stress modelling of undrained monotonic and cyclic stress-strain behaviours obtained by triaxial tests. The analysis simulates very well the collapse of an earth-fill dam by the 2011 Off the Pacific Coast of Tohoku Earthquake, Japan, and indicates a substantially higher seismic stability under the same conditions of the newly restored dam completed in 2017. Paramount effects of soil compaction on the seismic stability of earth-filled dam are demonstrated.

Nonlinear FEM Analysis on Composite Beams with Web Opening Under Negative Bending Moment

Nonlinear FEM Analysis on Composite Beams with Web Opening Under Negative Bending Moment

Influence of boundary conditions and load eccentricity on strength of cold-formed lipped channel columns

The ultimate buckling strength of axially loaded cold-formed lipped channel columns is studied. Variations of boundary conditions and eccentricities of the applied load are considered. The strength is calculated by a geometrically and materially nonlinear FEM analysis. Numerical study is carried out for two columns previously analysed under fixed boundary conditions and centroidal load. Geometrical imperfections in the shapes of eigenmodes of the corresponding linearized buckling problem are assumed. For comparing the imperfections their sizes are set to a uniform level of an energy measure. Particularly the worst eigenmode imperfection is determined for each studied design case. By the corresponding lowest collapse loads the effects of varying boundary conditions and load eccentricities on the ultimate buckling strength of the columns are shown.

Elastoplastic nonlinear FEM analysis of FGM shells of Cosserat type

The paper is a continuation of [1] where the formulation of the elastic constitutive law for functionally graded materials (FGM) on the grounds of nonlinear 6-parameter shell theory with the 6th parameter (the drilling degree of freedom) was presented. Here the formulation is extended to the elasto-plastic range. The material law is based on J2 Cosserat plasticity and employs the well-known Tamura-Tomota-Ozawa (TTO) [2] mixture model with additional formulae for Cosserat material parameters. Formulation is verified by solving a set of demanding analyses of plates, curved and multi-branched shells, including geometry, thickness and material distribution variation parameter analyses.

Ultimate strength formulation of stiffened panels under in-plane compression or tension with cracking damage

The aim of the present study is to develop closed-form formulations for predicting the ultimate compressive and tensional strength of stiffened steel panels with crack damages. First, a numerical database is generated. This database includes the ultimate strength levels of stiffened steel panels with cracks subjected to axial compressive or tensile loads. It was carried out with a series of nonlinear FEM analyses by varying the size of crack damage. In the following sections, regression analysis is used for deriving the empirical formulations. The results of the present paper can be used for the reliability and risk assessment of structures, including stiffened steel panels with cracks.

Comparison of experimental research and nonlinear advanced FEM analysis of load capacity and deformability of slender HSC columns in bi-axial bending

The paper compares results of own experimental research of sixteen reinforced concrete columns made of HSC in bi-axial bending with advanced three-dimensional FEM analysis. Computational analysis with application of TNO DIANA v.9.4 system and pre and post processor MIDAS FX+ was conducted. The analysis was used mostly to check a compatibility of the conducted research with the advanced 3D numerical model and to prove a usefulness of applied numerical model in calculation of load-bearing capacity of bi-axially bending columns. Mechanical properties of concrete and reinforcing steel were assumed based on the results of material tests.

Shear Resisting Mechanism and Shear Strength Equation for Sandwich Beams

The aim of this study is to eliminate the limitation of existing shear design equations and to establish a complete set of rational as well as computationally efficient shear design equations. On this goal, a macro physical model, based on 2D nonlinear FEM analysis, for both open and full sandwich beams are developed which can clearly demostrate the contributions of different parts of the sandwich beam in resisting shear force. The proposed model also shows a satisfactory correlation between the experimental and the analytical results. A series of analytical specimens in connection with experimental one are analyzed by engaging a 2D-FEM program and a complete set of shear strength equations are derived with the help of that proposed shear resisting model. The equations for full sandwich beam show a good agreement with experimental and analytical results, whereas equations for open sandwich beam require further investigation to increase their level of accuracy and are not presented here.

Simulation of microneedle puncture by nonlinear FEM analysis

Simulation of microneedle puncture by nonlinear FEM analysis

Performance of RC Beams with Embedded Steel Trusses Using Nonlinear FEM Analysis

The current study investigates the shear performance of reinforced concrete (RC) beams with embedded steel trusses at small shear span to depth ratios a/d using nonlinear finite element (FE) model. Twenty‐one (FE) models have been built using ABAQUS software to investigate the effect of different a/d ratios and web reinforcement on the shear performance and failure load of RC beams with embedded steel trusses. This research focuses on obtaining failure loads, failure modes, crack propagation, and midspan deflection from the developed FE models. The numerical results indicated that, using RC beams with embedded truss with different a/d ratios increased significantly the ultimate shear strength compared with the common RC beams. Furthermore, the numerical results confirmed that embedment of steel trusses in RC beams would significantly improve the structural behavior of RC beams at different a/d ratios. In addition, the results indicated that the shear reinforcement has a small effect on failure and midspan deflection of RC beams with embedded angle trusses at different a/d ratios.

Non-Linear FEM Analysis of Integral Bridges Transition Area

The transition area of bridges is non-homogeneous solid, which consists of soil embankment, transition slab and roadway layers. These transition area elements consist of various materials with different properties. Besides the imposed loads, behavior of these areas is significantly affected by uneven settlement between the bridge abutment and soil embankment. In case of integral bridges horizontal movements of a bridge caused mostly by temperature and ongoing rheological phenomena in concrete have to be taken into account. This leads to abutment deformation in combination with time dependent soil consolidation it results in varying earth pressure over the bridges lifetime together with cyclic horizontal movements of the pavement resulting in its cracks and excessive deformations. In this paper, comparison of different approaches to finite element analysis of transition areas is presented. First analysis was performed using area elements to represent the bridge structure, and volume elements to represent embankment, while second analysis was performed in more conservative way using spring based method proposed by Křížek[3], as representation of the surrounding soil. Results obtained via both methods are compared with each other as well as with data obtained from experimental measurment of a transition area conducted in Switzerland [1].

Effect of grid size on fatigue life calculations of a dental implant

The aim of this paper was to evaluate the effect of grid size on the fatigue life calculations of a dental implant by conducting a non-linear contact FEM analysis. A Nobel – Biocare (Replace – Select) implant was chosen and modelled in CATIA after retrieving accurate dimensions from SEM. The mandibular bone was modelled using MIMICS software. Static and dynamic simulation was then conducted on the final assembly using ANSYS which is a commercially available FEA software package. It was observed that variation in grid size leads to significant variation in the life of the dental implant. Hence for an accurate estimation of fatigue life of the dental implant the mean of the range of values must be considered

Structural Rehabilitation Analyses for a Romanian Cultural Heritage Building Located in Seismic Area

Structural rehabilitation, especially of historical monuments, is a difficult and widely treated subject in order to achieve a better insight regarding their seismic response. In Romania, a lot of historical monuments that require rehabilitation due to seismic actions are encountered. This paper aims to assess the effects of structural retrofitting on a historical monument located in Botoşani County, which withstood during its life cycle important earthquakes. The 20th century monument is located in a seismic active area of North – Eastern Romania, at a distance less than 300 km from Vrancea region where the epicenter of major earthquakes for the Eastern Europe is situated. Two hypotheses for the FE model of the structure were considered, namely with and without the rehabilitation solution. Nonlinear FEM analyses were performed in computer software environments. Using specific modeling tools of the computer program it is intended to simulate linear behaviour of masonry and global response of the structure. Comparisons between the two models were made. The results are used to validate the rehabilitation solution also consisting a source of information for its effects during structural lifetime cycle of the historical church.

Evaluation of puncture resistance force of microneedle by nonlinear FEM analysis

Evaluation of puncture resistance force of microneedle by nonlinear FEM analysis

Designing of Cylindrical Concrete Tanks with Regard to Buckling and Second Order Effects

Structural designing of reinforced concrete structures consists in determination of the cross section height and amount of the vertical and horizontal reinforcement on the basis of the internal forces. These forces are not determined correctly without considering the structure deformation. It means that the geometric type nonlinearity should be regarded at least. In the case of compression the buckling and the so called “second order effects” should be taken into account. The EC2-1-1 code gives the general rules for such effects, but they are described in details only for columns and buildings. Therefore the aim of this paper is to formulate recommendations which will be useful for reinforced concrete cylindrical tanks for liquids and particulate solids compressed vertically (meridional compression) and horizontally (hoop compression). These recommendations are formulated on the basis of nonlinear FEM analysis, which is preceded by analysis of expressions describing the critical stress of cylinders, formulated by theory of elasticity.

Tolerances of imperfections and strength of cold-formed lipped channel column

The paper addresses the ultimate buckling strength of thin-gauge axially loaded lipped channel columns with initial geometrical imperfections related to execution tolerances. For computational modelling of the column strength respecting the tolerance limits a deterministic method employing geometrical and material nonlinear FEM analysis with imperfections (GMNIA) is suggested. The imperfections are assumed in the shapes of eigenmodes of the corresponding linearized buckling problem and their combinations. For comparing their influence on the column strength, the imperfections are normalized by the energy measure. The comparison is carried out on the top energy measure level limited by execution tolerances. Referring to published experimental work three cross-sections and several column lengths are considered in a numerical study. Summarizing the numerical results and abilities of the energy measure to facilitate the treatment, guidance for the use of FEM GMNIA in the estimation of the column least strength is suggested.

Geometrically nonlinear FEM analysis of FGM shells based on neutral physical surface approach in 6-parameter shell theory

The paper presents the formulation of the elastic constitutive law for functionally graded materials (FGM) on the grounds of nonlinear 6-parameter shell theory with the 6th parameter being the drilling degree of freedom. The material law is derived by through-the-thickness integration of the Cosserat plane stress equations. The constitutive equations are formulated with respect to the neutral physical surface. The influence of the power-law exponent, micropolar characteristic length is evaluated in geometrically nonlinear FEM analyses. The results obtained with the neutral physical surface approach are compared with those computed with the middle surface approach. The influence of choice of the reference surface is observed especially in nonlinear stability analysis.

A User Defined Material Model for the Simulation of Impact Induced Damage in Composite

Low velocity impacts induce concurring failure phenomena in unidirectional fiber reinforced composites. Hence a refined methodology able to predict the different failure modes and their interaction is mandatory to correctly predict the damage onset and evolution. Indeed, intra-laminar damage and inter-laminar damage often take place concurrently, causing a significant strength reduction up to composite structure collapse. In this paper, a numerical study is proposed which, by means of non-linear explicit FEM analysis, aims to completely characterize the composite reinforced laminates damage under low velocity impacts by introducing a user defined material model in the FEM code ABAQUS. The proposed 3-D numerical investigation allowed to obtain an exhaustive insight on the different phases of the impact event considering the damage formation and evolution.