Nonlinear Numerical Analysis Research Articles

Stiffening material impact on the work of thin-walled element

The subject of research is a numerical analysis of a thin-walled plate with a cut-out and stiffening, made of laminate and subjected to axial compression. The plate was made of a carbon-epoxy composite - a laminate consisting of eight symmetrically oriented plies. The scope of the research included a linear and nonlinear numerical analysis using Finite Element Method (FEM). The main objective of the study was to investigate behaviour of the considered plate made of various stiffening materials, under quasi-static compression to achieve Tsai-Wu criterion. The numerical analysis was conducted with the Abaqus, commercial FEM software package.

Experimental and Nonlinear Numerical Analysis of Precast Concrete Column Splices with High-Yield Metal Plates

AbstractThe aim of this study was to present the use of detachable laminated high-yield metal plates for precast concrete column splices. The structural behavior of precast concrete column connecti...

Instability-driven oscillations of elastic microfilaments.

Cilia and flagella are highly conserved slender organelles that exhibit a variety of rhythmic beating patterns from non-planar cone-like motions to planar wave-like deformations. Although their internal structure, composed of a microtubule-based axoneme driven by dynein motors, is known, the mechanism responsible for these beating patterns remains elusive. Existing theories suggest that the dynein activity is dynamically regulated, via a geometric feedback from the cilium's mechanical deformation to the dynein force. An alternative, open-loop mechanism based on a 'flutter' instability was recently proven to lead to planar oscillations of elastic filaments under follower forces. Here, we show that an elastic filament in viscous fluid, clamped at one end and acted on by an external distribution of compressive axial forces, exhibits a Hopf bifurcation that leads to non-planar spinning of the buckled filament at a locked curvature. We also show the existence of a second bifurcation, at larger force values, that induces a transition from non-planar spinning to planar wave-like oscillations. We elucidate the nature of these instabilities using a combination of nonlinear numerical analysis, linear stability theory and low-order bead-spring models. Our results show that, away from the transition thresholds, these beating patterns are robust to perturbations in the distribution of axial forces and in the filament configuration. These findings support the theory that an open-loop, instability-driven mechanism could explain both the sustained oscillations and the wide variety of periodic beating patterns observed in cilia and flagella.

Failure mechanism of joint waterproofing in precast segmental tunnel linings

Water leakage is a major issue for shield tunnels in both the construction and operational stages. The practical solution in industry with relation to the prevention of groundwater penetration is to implement ethylene-propylene-diene monomer (EPDM) gaskets at tunnel joints. Although a few past research has focused on joint waterproof performance, this paper proposes a sealant mechanism based on the finite element analysis. A conceptual model is first established to identify sealant behavior of gasketed joint subjected to lateral water pressurization. A nonlinear finite element model is developed to simulate the gasket-in-groove sealant behavior, and the performance of the model is validated with experimental data. Results of the nonlinear numerical analyses (incorporating a hyperelastic constitutive model of the gasket, complex contact properties, and large deformation) demonstrate the failure mechanism of joint waterproofing. Emphasis is placed on quantifying the effects of joint opening, joint offset and joint rotation on waterproof capacity. The computed results indicate that joint waterproofing capacity significantly decreases with increasing joint opening or joint rotation. The waterproofing capacity varies under different joint offset scenarios because of change of contact interfaces. For the prototype tunnel, it is suggested to control a 6.42 mm joint opening, a 0.0505 rad positive joint rotation or a 0.0141 rad negative joint rotation to maintain its waterproofness.

Integration of reverse engineering and non-linear numerical analysis for the seismic assessment of historical adobe buildings

Abstract This paper aims at presenting a methodology that integrates reverse engineering tools with a combination of advanced and simplified analytical methods to perform predictive analysis of the structural behavior of historical adobe buildings under seismic loads. This methodology proposes the joint use of terrestrial laser scanner and photogrammetry to obtain accurate geometrical models. The methodology also proposes the in-situ measurement of structural system properties through experimental modal tests. All the collected information is used to create representative Finite Element models which are then considered for performing predictive non-linear analyses and identifying the most probable collapse mechanisms. Limit analysis method is finally used to complement the analysis and to assess the structural performance of the adobe building under study considering different seismic scenarios. The methodology proposed in this paper is validated in the church of San Juan Bautista de Huaro, located in Cusco, Peru. This church was built in the 16th century and is known for its impressive mural paintings covering the entire indoor surface of the church. The results of the seismic assessment methodology proposed in this paper allowed to estimate the global behavior and possible damage patterns in the church during seismic events, showing that the most probable failure mechanisms would be the global rocking of the facade and the partial collapse of tympanum of the facade. The application of this methodology also allowed defining the performance levels of this church when facing different seismic scenarios. The results showed that the church should stay in a safe state until occasional earthquakes with a return period of 72 years. However, the results also indicate that rare earthquakes (return period of 475 years) will produce an unsafe structural condition with partial collapses of structural elements.

Equivalent linear computation of response spectra for liquefiable sites: The spectral interpolation method

A simplified methodology is presented for the computation of elastic response spectra at liquefiable sites, based on the widely used equivalent linear site response analysis method. The target response spectrum is obtained by frequency dependent interpolation between the response spectra for “non-liquefied” and for “liquefied” ground, the former computed for the native soil properties, without excess pore pressure buildup, and the latter for the properties of the liquefied soil. Apart from the structural frequency, the interpolation coefficient is also related to the factor of safety against liquefaction. In this way, the proposed methodology takes indirectly into account the initial segment of the seismic excitation time-history, until the onset of liquefaction, which is of cornerstone importance for the overall ground response at sites with low and moderate liquefaction potential. Results of parametric nonlinear numerical analyses and three field case studies are used to calibrate the methodology and evaluate its accuracy. In addition, the potential of the proposed methodology for defining code-oriented design spectra for liquefiable sites is examined.

Seismic behavior study on a space double-layer lattice structure with a lower supporting structure

Severe damage, such as support failure, global buckling of members, local buckling of members, fracture of members, dislocation at the end of members, and failure of bolted connections, were observed in space double-layer lattice structures following the Lushan earthquake (China, 2013, M 7.0). To study the seismic behavior of the space double-layer lattice structure with a lower supporting structure, a series of shaking table tests were conducted. A nonlinear numerical analysis was performed on the damage of the structure, in which the material parameters were obtained from material tests of the steel member. The numerical results were compared with the experimental results, and the difference between the test and the numerical simulation was presented and discussed. The validity and accuracy of the proposed numerical model used for predicting the structural damage was verified by the experimental results, which indicates that the modeling and analytical method was applicable for the analysis of the space double-layer lattice structure.

Influence of pitting corrosion on the bending capacity of thin-walled circular tubes

Thin-walled circular tubes (TWCTs) have been extensively used in space lattice structures and other industrial areas. Corrosion is inevitable for steel structures with regard to its service life, and it will remarkably reduce the loading capacity and critically threaten the structural safety. The present work aims to investigate the influence of pitting corrosion on the bending capacity of TWCT. A series of nonlinear numerical analyses was conducted to investigate the influences of corrosion pit shape, specification, corrosion thickness, diameter, and thickness of TWCT on bending capacity. Corrosion was simulated by reducing the thickness of shell element. Random corrosion distribution was generated, and its influence on bending capacity was estimated. The method for generating a random corrosion would provide a reference for the analysis of other structures with corrosion.

A rolling resistance estimate using nonlinear finite element numerical analysis of a full three-dimensional tyre model

In accordance with the worldwide trend for developing energy-efficient vehicles and meeting environmental regulations, there exists a large potential for decreasing energy losses due to tyre rolling resistance and significantly reduce fuel consumption and greenhouse gas emissions and also improve tyre tread durability. To achieve a quantitative estimate of tyre rolling resistance force, in the present paper, we carry out rolling resistance modelling in order to introduce a comprehensive relation for predicting rolling resistance force variations with speed taking into account the most influential parameters. To accomplish this goal, full three-dimensional finite element modelling of a visco-hyperelastic inflated rubber tyre under the deformation of vertical loading is performed and validated by making use of available test data. Free rolling simulations are performed and rolling resistance diagrams at various vehicle speeds and inflation pressures are extracted by analysing the results. According to the simulation results, a general formula is suggested to predict the tyre rolling resistance force in terms of the influential factors such as velocity, inflation pressure and tyre load. Results obtained using the proposed equation compared with recorded coast down test data clearly indicate excellent agreement between the results, confirming the validity of the relation. The presented solution can be built into models for comprehensive techno-economic evaluation of vehicle performance and fuel economy where changes in velocity, load and inflation pressure can be considered.

Analysis of the influence of column reinforcement anchorage length in a concrete two-pile cap

Abstract This paper describes the parametric analysis applied to assess the influence of column anchorage-reinforcement length on concrete two-pile caps under uniform compression. The non-linear numerical analysis was conducted with the bi-dimensional elements of ATENA 2D software, considering perfect adherence between steel and concrete. Simulation was based on the experimental reference model by Munhoz [1], which was the parameter adopted to validate the numerical modeling. From the validated model, four different anchorage reinforcement lengths were adopted, 34,0 cm, 20,0 cm, 10,0 cm e 3,0 cm, in order to compare pile caps behavior after these changes. Pile cap simulations presented similar behavior, i.e., column anchorage reinforcement length is not a preponderant factor for the internal mechanisms that regulate the function of these elements.

Significance of Rayleigh damping in nonlinear numerical seismic analysis of tunnels

There is no convincing approach to determine the soil viscous damping in the time-history dynamic analysis of tunnels due to the forms and inherent limitations of viscous damping. The users determine viscous damping with a certain degree of arbitrariness that increases the uncertainties of numerical predictions, which has not previously been considered and quantified. Therefore, in this study, the commonly used Rayleigh formulation is considered and its impacts on the nonlinear seismic behavior of tunnels combined with the Mohr-Coulomb failure criterion are investigated through a two-dimensional finite difference code. Potential problems of the improper use of damping parameters are demonstrated through a simple case. After that, four approaches of modeling damping proposed in previous studies are compared to account for the input motions, the intensities, and the target damping ratios. Numerical results reveal that the target damping ratios and the damping determination approaches have an important influence on the tunnel response analyses. The additional Rayleigh damping leads to a reduction of the time step. It is shown that the difference caused by various damping determination approaches generally decreases with the target damping ratio (ξtar) decreases or the intensity of input motion (PGA) increases.

Simplified HYMOD non-linear simulations of a full-scale multistory retrofitted RC structure that undergoes multiple cyclic excitations – An infill RC wall retrofitting study

Having the ability to assess the earthquake resistance of retrofitted reinforced concrete (RC) structures through accurate and objective nonlinear cyclic analysis is of great importance for both scientists and professional Civil Engineers. Full-scale RC structure simulations under ultimate limit state cyclic loading conditions through the use of 3D detail modeling techniques, is currently one of the most challenging modeling tasks that any research or commercial software can undertake. The excessive computational demand and the numerical instabilities that occur when dealing with this type of cyclic nonlinear numerical analysis, make this modeling approach impractical. The simplified hybrid modeling (HYMOD) approach is adopted in this work, which overcomes the above numerical limitations and it is used herein to illustrate the capabilities of the method in capturing the experimental results of a full-scale 4-storey RC building that was retrofitted with RC infill walls and carbon fiber reinforced polymer jacketing. This work has the aim to investigate the importance of numerically accounting for the damage that has developed at the concrete and steel domains during the analysis of problems that foresee consecutive cyclic loading tests. Based on the numerical findings, it was concluded that the proposed modeling approach was able to accurately capture the experimental data and predict the capacity degradation of the building specimen. Furthermore, the proposed method was used to numerically investigate different retrofitting configurations that foresaw the use of infill RC walls. The numerical experiments performed in this work demonstrate that the proposed modeling approach provides with the ability to study the cyclic mechanical behavior of full-scale RC structures under ultimate limit state conditions, thus paves the way in performing additional parametric investigations in determining the optimum retrofitting design of RC structures by using different types of interventions.

Strength Analysis on Brace Structure for Semi-Submersible in Consideration of Wave Slamming

Slamming on bracings of column stabilized units shall be considered as a possible limiting criterion under transit condition based on the requirements in DNV-OS-C103. However, the wave slamming loads under survival condition were ignored for the strength analysis of the brace structures in many semi-submersible projects. In this paper, a method of strength analysis of brace structure is proposed based on the reconstruction and extrapolation of numerical model. The full-scale mooring system, the wind, wave and current loads can be considered simultaneously. Firstly, the model tests of the semi-submersible platform in wind tunnel and wave tanker have been carried out. Secondly, the numerical models of the platform are reconstructed and extrapolated based on the results of model tests. Then, a nonlinear numerical analysis has been conducted to study the wave slamming load on brace in semi-submersible platform through the reconstructed and extrapolated numerical model. For the randomness of wave load, ten subcases under each condition have been carried out. The value of the 90% Gumble distribution values of the ten subcases are used. Finally, the strength on brace structure has been analyzed considering the wave slamming. The wave slamming loads have been compared between the survival condition and transit condition with the method. The results indicate that wave slamming under survival condition is more critical than that under transit condition. Meanwhile, the wave slamming is significant to the structural strength of the brace. It should be overall considered in the strength analysis of the brace structure.

Metal Foam-Filled Tubes as Plastic Dissipaters in Earthquake-Resistant Steel Buildings

The aim of this paper is to investigate whether metal-foam-made devices can be effective to dissipate seismic energy in buildings during strong earthquakes. To this purpose, non-linear numerical analyses of concentrically braced steel buildings under recorded ground motions have been carried out, while some experimental tests on metal-foam specimens and metal-foam-filled tubes have been performed. Foam-based devices are assumed to be inserted within the diagonal braces of the considered steel frame to dissipate energy by plastic deformation during strong earthquakes. To apply the experimental data, a scaled numerical model of the prototype building has been implemented by means of the similitude theory and the Buckingham Π theorem. The results of the study provide a preliminary assessment of the potential of metal foam-based dissipaters to reduce the seismic effects in civil structures.

Over-Wrapping of the Aortic Wall with an Elastic Extra-Aortic Wrap Results in Luminal Creasing.

Elastic extra-aortic wrapping is a potential non-pharmacological way to improve aortic compliance and treat isolated systolic hypertension associated with a stiffened aorta. We aimed to use computer simulations to re-evaluate whether there is aortic shape distortion in aortic wrapping to achieve greater elasticity of the wrapped aortic segment. Non-linear transient numerical analysis based on an idealized hyper-elastic single-layered aorta model was performed to simulate the force/displacement regimes of external aortic wrapping. Pressure-displacement relationships were used to establish model aortic wall distensibilities of 4.3 and 5.5 (10−3 mmHg−1). A physiological pulsatile lumen pressure was employed to estimate the potential improvements in aortic distensibility by compression forces representing elastic aortic wrapping. In the less distensible model of the aortic wall there was increased systolic expansion in the wrapped segment. We found a risk of creasing of the aortic luminal wall with wrapping. Sufficient unloading of a thick and elastic aortic wall to induce increased compliance, as observed in elastic wrapping, is associated with the potential risk of over compression and folding (creasing) inside the lumen.

More adequate seismic design force pattern for yielding structures considering structural and ground motion uncertainties effects

SummaryIn the present paper, a new algorithm to achieve optimum lateral load pattern for inelastic steel shear‐building structures is proposed and the efficiency of the proposed algorithm in terms of convergence speed and stability is investigated. Then, by conducting this algorithm on 28,800 elastic and inelastic steel shear‐building structures having different dynamic characteristics subjected to 40 design compatible earthquakes, a new seismic force pattern incorporating higher modes effect is proposed, and the adequacy of the proposed load pattern is parametrically investigated on the basis of the concepts of structural weight and dissipated energy and cumulative damage index. Through conducting numerous nonlinear dynamic analyses, the effects of uncertainties in story shear strength, structural fundamental period, and damping ratio by using the Monte Carlo simulation are parametrically investigated. Result indicates that optimum structures are in general more sensitive to the random variation of fundamental period and story lateral strength, whereas up to 40% of damping ratio variation does not affect the seismic performance of the optimum design frames. Finally, compared with recently proposed optimum structures without consideration of higher modes and code‐complaint design structures, the proposed mean optimum designed buildings of this study exhibit up to 42% less cumulative damage under the design earthquakes.

Assessment of the bending capacity of welded hollow spherical joints with pit corrosion

Welded hollow spherical joints (WHSJs) are widely used in space lattice structures. Corrosion is inevitable for WHSJs during service, and this phenomenon will significantly reduce loading capacity and seriously threaten the structural safety. Pit corrosion is a typical corrosion type for steel structures. In this study, nonlinear numerical analyses were conducted to investigate the influence of several parameters on the bending capacity of a WHSJ. A numerical model of the WHSJ with random pit corrosion was proposed to investigate the mechanical behavior of the corroded WHSJ. Results indicated that the moment capacity of the WHSJ with random corrosion pits was normally distributed. A probabilistic distribution model of the corroded WHSJ was proposed. The failure probability could be deduced based on the formulae of the upper and lower bounds of the moment capacity.

Elevated slabs made of hybrid reinforced concrete: Proposal of a new design approach in flexure

When designing fiber‐reinforced concrete (FRC) structures, one of the basic design issues is represented by the choice of a proper combination of fibers and conventional reinforcement that allows to obtain the best structural performance with the minimum amount of materials. The combination of rebars and fibers in the concrete matrix is generally known as Hybrid Reinforced Concrete (HRC). HRC represents a feasible solution in many structures; among these, slabs are gaining an increasing interest among practitioners. In fact, slabs are the most widespread structural elements in common practice as they are typically used to construct slabs on ground (industrial floors or foundations), slabs on piles (foundations) or elevated slabs. This paper focuses on the flexural design of FRC elevated slabs by using the most recent design provisions reported in the fib Model Code 2010. A simplified design procedure based on a consolidated design practice is proposed. Emphasis is given to the use of HRC to minimize the total reinforcement (fibers + rebars) in order to get practical and economic advantages during construction (ie, construction time and costs reduction). In more detail, a procedure for proportioning the hybrid reinforcement and then verifying the structural safety will be presented and discussed. Numerical nonlinear finite element analyses will be carried out to assess the effectiveness of the proposed design method.

Nonlinear Analysis of Stability and Unbalanced Response on Spherical Spiral-Grooved Gas Bearings

ABSTRACTThis study conducts a nonlinear numerical analysis of the stability and the unbalance response of spherical spiral-grooved bearings (SSGBs) using a nonlinear orbit simulation method. This method is more accurate than the linear method, especially at high bearing loads. Parametric analyses are also performed with respect to nominal clearance and groove depth to optimize groove parameters. Shaft trajectories reflect the nonlinear characters of SSGBs when mass unbalance increases. Fast Fourier transform analyses of rotor orbit responses facilitate identification of the subsynchronous whirling and unbalance response in rotor vibration behavior. Results show that optimum dimensionless groove depths vary for different nominal clearances or rotational speeds. The static performance and stability characteristics of spherical bearings can be significantly influenced by the spiral grooves on the journal surface.

Dynamic in-plane transversal normal stresses in the concrete face of CFRD

Severe earthquakes can induce damages to Concrete Face Rockfill Dams (CFRDs) such as concrete cracking and joint’s water stops distressing where high in-plane transversal normal stresses develop. Although these damages rarely jeopardize the dam safety, they cause large water reservoir leakages that hinder the dam functioning. This issue can be addressed using well know numerical methods; however, given the wide range of parameters involved, it would seem appropriate to develop a simple yet reliable procedure to get a close understanding how their interaction affects the CFRD’s overall behavior. Accordingly, once the physics of the problem is better understood one can proceed to perform a detailed design of the various components of the dam. To this end an easy-to-use procedure that accounts for the dam height effects, valley narrowness, valley slopes, width of concrete slabs and seismic excitation characteristics was developed. The procedure is the dynamic complement of a method recently developed to evaluate in-plane transversal normal stresses in the concrete face of CFRD’s due to dam reservoir filling [1]. Using these two procedures in a sequential manner, it is possible to define the concrete slab in-plane normal stresses induced by the reservoir filling and the action of orthogonal horizontal seismic excitations acting at the same time upstream-downstream and cross river. Both procedures were developed from a data base generated using nonlinear static and dynamic three-dimensional numerical analyses on the same group of CFRD’s. Then, the results were interpreted with the Buckingham Pi theorem and various relationships were developed. In the above reference, the method to evaluate the concrete face in-plane transversal normal stresses caused by the first reservoir filling was reported. In this paper, the seismic procedure is first developed and then through an example the whole method (dam construction, reservoir filling plus seismic loading) of analysis is assessed.