Advanced Finite Element Model Research Articles

Challenges in Modelling Reinforced Concrete Panels Subjected to Blast Load - A Critical Review

Reinforced concrete panels are widely used in modern facilities, and evaluating their blast loading capacity is vital for security-critical assets. Due to the high impulsive nature of blast loads, the response of reinforced concrete panels is characteristically different from that under static or low dynamic load conditions. The failure of individual components often initiates the blast load's destructive effects on the entire structure. The material breach can be caused by stress wave localized effects before the general structural response becomes significant. Numerical methods are one of the key methods for studying the behaviour of reinforced concrete panels under blast load. This paper aims to review the current state of practice in modelling reinforced concrete panels and predicting their blast capacity and failure mechanisms under blast load. The work addresses the research gaps associated with using advanced finite element modelling as compared to test results.

Lateral–torsional buckling resistance of corrugated web girders based on deterministic and stochastic nonlinear analysis

There is no commonly accepted and reliable design method to determine the lateral–torsional buckling (LTB) resistance of steel trapezoidally corrugated web girders. Therefore, the focus of the current paper is on the investigation of this failure mode, detailed evaluation of the structural behavior and determination of the accurate LTB resistance. An advanced finite element (FE) model is developed and validated using the results of laboratory test performed at the Budapest University of Technology and Economics in 2018. Based on the experimental background virtual tests are performed on a simply supported beam subjected by pure bending moment. The effect of the different flange sizes, corrugation layouts, boundary conditions and steel grade including high-strength steel as well, are investigated. Two kinds of parametric studies are performed using (i) deterministic and (ii) stochastic nonlinear analysis. In both cases the imperfections have a key role in the FEM-based resistance calculation. Therefore, the imperfections are considered as initial geometric imperfections and residual stress, and also as equivalent geometric imperfections and their results are compared. The required equivalent geometric imperfection magnitude is determined and proposed in such a way to achieve the same impact as the initial geometric imperfection and residual stresses have. By both the deterministic and stochastic analysis results the required buckling curve of the Eurocode is determined by reliability assessment. The results of the two different analyses are compared and design recommendation is given for reduction factor determination for trapezoidally corrugated web girders. • Advanced finite element model is developed, verified and validated based on own experimental tests specimens. • Imperfection sensitivity study is performed. • Both residual stresses and initial geometric imperfections are considered. • Effects of the corrugated web layout, the boundary conditions and the steel grade are studied. • Deterministic and stochastic nonlinear analyses are performed. • Reliability assessment is performed. • New design method is developed.

Behaviour of CFST Stub Columns Subjected to Pure Compression

Application of concrete-filled steel tubes (CFST) is becoming increasingly prominent in the civil engineering practice. However, the interaction of cross-sectional elements in CFST columns raises a number of questions, which have to be investigated in detail to improve design background and analytical resistance formulae. The aim of the current paper is to examine the structural behaviour of innovative concrete-filled steel tubes using different structural steel grades (S355, S500 and S960) and concrete classes (C30/37 and C60/75). Combination of normal or high strength steel with normal or high-performance concrete is a novel research topic of composite structures resulting in economic and optimal design for distinct civil engineering applications such as buildings, bridges, towers and masts, etc. An advanced finite element model is developed and validated based on previous experimental results found in the international literature in order to investigate the discrepancies in structural behaviour, load-bearing capacity and failure mode of stub columns subjected to pure compression. Validated numerical results are compared to formulae-based resistances and the applicability of standardised design methods are examined. In addition, a novel formula is proposed considering hardening of steel material in accordance with EN 1993-1-5. The developed formula can be used for the economic design of CFST stub columns, combining normal and high strength materials, where elastic shell buckling cannot occur (D/t ≤ 90ε2).

Multi-impact performance of prestressed CFRP-strengthened RC beams using H-typed end anchors

To address the problem of insufficient ductility of traditional Carbon Fibre-reinforced polymer (CFRP) strengthened marine structures and to enhance the application of CFRP in marine engineering, the present study develops novel prestressed CFRP-strengthened RC beams using H-type end anchors with ductility controllable devices. In this device, part of the reinforcement bars are replaced by CFRP, which is prestressed as the structural enhancement material. The CFRP sheet is connected with a tensioned screw, which is used to realize the function of early warning based on a large plastic deformation when the structure is overloaded. Thus, the ductility of the composite structure could be improved based on yielding of the screw rod rather than the fracture failure of the CFRP sheet compared to that with CFRP bonded. This study investigates the flexural static and impact performance of the representative large-scale RC beams strengthened by prestressed CFRP through four-point bending and drop-weight impact. The results show that the H-typed end anchor and raising the prestress level of CFRP not only improve the ultimate resistance and ductility, but also realize the overload warning function under static load. Accordingly, the design still shows advantages in energy consumption and impact resistance through drop-weight impact. An advanced 3D nonlinear finite element model is built to simulate well the multiple impact performance in terms of the failure modes, impact force and displacement history. This study provides a new approach to address design deficiencies with insufficient ductility behaviour while using CFRP as a strengthening material. This prestressing technology is able to utilize the material efficiency of high-strength CFRP and open a new path for CFRP applications in marine civil engineering.

FREEDAM connections: advanced finite element modelling

FREEDAM connections: advanced finite element modelling

Bond-slip model uncertainty quantification and effect on nonlinear behavior simulations of reinforced concrete columns

• Developing a new model for bonding properties based on the dataset compiled from the literature. • Quantifying the uncertainties of bonding properties through Bayesian linear regression. • Significant effect of variations of bonding properties on the nonlinear behavior simulation of RC columns with unhooked steel bars. • Need to consider the pertinent uncertainties of bonding properties in probabilistic dynamic analysis of RC columns. In advanced finite element (FE) modeling of reinforced concrete (RC) structures, realistic bond-slip behavior, i.e., imperfect bonding, at the steel–concrete interface needs to be considered with caution. This paper compiles an experimental database on bond-slip behavior from the literature, evaluates a variety of existing models for predicting bonding properties, and develops a new model to better characterize the bond-slip behavior using the experimental database. Recognizing variations in bonding properties, the authors also quantify the prevailing uncertainties as indicated by experimental data in the new model by Bayesian linear regression. To study the effect of bond-slip model uncertainties on the nonlinear behavior simulations of RC columns under static and dynamic loadings, the recently developed geometrically nonlinear fiber-based frame element capable of capturing bond-slip is used in this study together with a commonly-used bonding stress-slip pattern. To this end, three RC columns are firstly modeled with bonding properties determined from eight existing models and the newly developed one, showing that the simulated behaviors using different models can be different to various degrees. Next, the relative importance of the uncertainty in bonding properties is evaluated with comparison to that of the uncertainties in concrete/steel properties. The results indicate uncertainties associated with bonding properties can significantly alter the nonlinear behavior predictions of RC columns, and thus not negligible, particularly for probabilistic dynamic analysis of RC columns under large intensity excitation levels.

Numerical analysis of composite slim-floor beams

Abstract In this research work existing laboratory tests of slim floor beams with solid monolithic concrete slab were modeled and analyzed using GID and Atena software. After validating the advanced finite element model with the test results of the international literature, structural parameters were analyzed with the aim to study their influence on the load bearing and deformation capacity of the beams. The parameters were related to the geometric of the beam: size of web openings and top concrete cover. With these results conclusion can be noticed that focusing on the optimal arrangement of the geometrical parameters of the composite beam could lead to better structural behavior with more economical solutions.

Non-linear necking behaviour of S275 to S960 structural steels under monotonic tension

• Tensile behaviour in steel is examined with a new definition of the on-set of necking. • Instantaneous diameters are measured accurately to determine true stress–strain curves. • Correction factors η σ and η ε are used to describe non-uniformity within the neck. • The true fracture strains of S275 to S960 steels are determined successfully. • A generalized constitutive model for S275 to S960 steels is developed. For cylindrical coupons of structural steels under tension, gradual reductions in their cross-sections, commonly known as necking, occurred at an elongation that the maximum force is attained. Non-uniform stress and strain distributions in the critical cross-sections of the necking regions have been known for more than 70 years; however, the values of these stresses cannot be directly measured in experiments so far. This paper presents a systematic investigation into the post-necking structural responses of the S275 to S960 steels under monotonic tension forces through the Instantaneous Area (iArea) Method proposed by the authors. In order to examine post-necking deformation characteristics of structural steels up to fracture, a total of 15 standard tensile tests on proportional cylindrical coupons of these steels were carried out carefully to obtain their force–elongation (F – e) curves while precision measurements were made to obtain their instantaneous dimensions. Complementary advanced finite element models are then established to predict non-linear stress and strain distributions at the critical cross-sections of the necking regions. Through a process of successive approximation, a series of correction factors are obtained to allow for the effects of these non-uniform stress and strain distributions respectively onto the post-necking structural responses of the coupons. Hence, the predicted force–elongation (F - e) curves of the coupons are demonstrated to follow the measured curves closely throughout the entire deformation ranges. More importantly, the predicted instantaneous diameters d gi are shown to have a good agreement with the measured values at various deformation stages up to fracture.

Determining adhesion of critical interfaces in microelectronics – A reverse Finite Element Modelling approach based on nanoindentation

State-of-the-art microelectronic devices, especially power semiconductors, are usually exposed to harsh environmental conditions on the one hand, for example large temperature hubs, and to challenging application conditions on the other hand, such as pulsed current applications. Mechanical robustness and reliability have become more and more challenging in recent years. Along with a continuous shrinkage of dimensions, thin film materials are stacked and micro-structured for optimized performance of such devices. Major risks for device reliability can result from loss of adhesion at interfaces of these stacked thin films. Therefore, it is crucial for such devices to feature perfect initial adhesion of the said thin film layers, even after exposure to thermal treatment or in presence of intrinsic stress. In order to validate device robustness, the quality of interface adhesion between isolating and metallization layers should be carefully assessed. A particular focus is set on interfaces between the following, widely employed materials: Cu, Al, WTi, BPSG, SiN etc. Robustness by design at critical interfaces has relied more and more on advanced Finite Element Modelling (FEM) methods in recent years. This includes explicit modelling of adhesion and delamination. Accurate parameters that describe interfacial adhesion – critical adhesion energies in tensile and shear mode – need to be extracted by means of suitable experiments on tailored test vehicles. FEM is able in turn to verify the existing theoretical framework about extracting adhesion energies from experiments, given that the analytical models are often phenomenological and based on simplified assumptions. Experimentally, Nanoindentation on designed multi-layer thin film stacks has proven to be a suitable method to investigate inter-layer adhesion strength on test vehicle basis. We focused on layered stacks of tungsten‑titanium (WTi) and Boron-Phosphorous-Silicate Glass (BPSG) on Silicon substrates. The WTi layer exhibits compressive stress tailored by means of deposition. When an axis-symmetric conical or spherical indenter penetrates the WTi film, buckles around the indenter imprint arise upon loading and may propagate during unloading. Buckle geometry is measured by means of focused ion beam and Scanning Electron Microscopy. Afterwards the critical adhesion energies can be determined by existing analytical models. Combining experimental and simulation methods one may follow a Physics-of-Failure approach and assess the failure mechanisms related to thin film delamination and interface fracture. With experimental results on hand, we implemented an FE model of the same multi-layer system. Initiation and propagation of delamination was modeled by means of a Cohesive Zone Model (CZM) based on a cohesive surface contact approach. The model incorporates elastic-plastic deformation as well as intrinsic stresses of all layers, including the substrate. Following an inverse FEM approach, we reproduced the size of the delaminated area and load-displacement curves of the indenter by recursively readjusting Cohesive Zone parameters. The so-obtained adhesion parameters and modelling can be used elsewhere in delamination risk assessments of industrial semiconductor applications. This approach also gives insight into the accuracy of the formulae used for calculating the total energy release rate and extracting the further relevant parameters without the need to rely on phenomenological assumptions. • Thin film adhesion, • nanoindentation, • inverse Finite Element Modelling, • Cohesive Zone Modelling, • Reliability

Combined compression-bending performance and design of CFST with localised pitting corrosion

This paper presents a comprehensive numerical study on the combined compression-bending performance of concrete-filled steel tubes (CFSTs) considering the commonly seen localised pitting corrosion damage in the marine environment. An advanced finite element modelling technique is utilised to simulate the localised corrosion pits on the outer surface of the steel tube considering its random nature. The differences between the load-moment interaction of CFSTs with uncorroded conditions, uniform corrosion simplification and pitting corrosion are discussed. The analytical results reveal the impact of localised pitting corrosion damage on the combined compression-bending performance of CFSTs can be grouped as the stress concentration around corrosion pits, premature local buckling of steel tubes and the reduction in effective confinement. An extended parametric study illustrates that the confinement factor and the mean pit depth have a considerable impact on the combined compression-bending behaviour of CFSTs with localised pitting corrosion. The feasibility of utilising existing design approaches calculates the load-moment interaction diagrams of locally pitted CFSTs following the DoV-based uniform corrosion simplification is evaluated. On this basis, simplified design methods accounting for the characteristic of pitting corrosion are proposed for estimating the post-corrosion load-bearing capacity of CFSTs under combined compression and bending, and reasonable accuracy is achieved.

Structural design optimization of composite materials drive shafts

Composite materials drive shafts attract particular interest in recent years. Their high strength, light weight and high fatigue and corrosion resistance make them suitable for high specification mechanical and marine applications. In the context of the present work, advanced finite element models that simulate the static and dynamic mechanical behaviour of composite drive shafts are combined with optimization algorithms in order to determine the optimum lay-up of a composite shaft according to the desired specifications. The composite shaft is also combined with metallic flanges and the performance of the combined system is also investigated. The created models facilitate the structural design optimization of composite material drive shafts and constitute the basis for the future implementation of the simulation driven digital twins of composite materials drivetrain systems. • Composite driveshafts have high specific strength, fatigue and corrosion resistance. • Composite driveshafts are fit for high specification power transmission systems. • FEA can accurately simulate the composite materials shafts' mechanical behaviour. • FEA combined with optimization algorithms can determine the shaft's optimum lay-up. • Basis of simulation driven digital twins of composite materials drivetrain systems.

O.I.C.-based design of mono-symmetric I-sections under simple load cases

This paper studies the ultimate resistance of mono-symmetric hot-rolled and welded sections under axial compression, major-axis bending or minor-axis bending as affected by local buckling and material yielding. Following the development of advanced non-linear shell finite element models and their validation against existing test data, extensive non-linear numerical analyses are carried out. Various parameters including two manufacturing types, three steel grades and various section dimensions are considered, to investigate the influence of mono-symmetric levels with various flange widths ratios b1/b2 on section behaviour. The numerical results are then used to assess a proposed extension of the Overall Interaction Concept (O.I.C.) to mono-symmetric I-shaped sections. Systematic comparisons with existing standards – Eurocode 3 and the American Standards – and the proposed O.I.C.-based method prove the new approach to be more consistent, accurate and straightforward.

Structural Fire Risk for Heritage Buildings by the Performance-Based Engineering Format

ABSTRACT This paper discusses and presents an example of fire risk analysis for a case study of an existing heritage building: the Duomo of Modena Cathedral, located in Italy. The main issues related to the application of the fire risk analysis to heritage buildings are discussed in detail, and an ad-hoc procedure is proposed to manage them for the case study. In order to assess the performances of the building in probabilistic terms, the fire risk analysis is conducted by the event-tree method, the fire dynamics are analyzed by numerical thermo-fluid dynamics models, while the structural behavior is investigated by advanced nonlinear thermomechanical finite element models. Results are expressed in terms of risk curves related to a fixed return period, which quantify the occurrence probability of different damage levels induced by fire in the wooden roof of the case study building. This kind of result is fully compatible with probabilistic performance-based engineering frameworks commonly accepted for other hazards (i.e., earthquakes).

Comparative finite element modelling approaches for the seismic vulnerability analysis of historical masonry structures: the case study of the Cathedral of Catanzaro (Italy)

The vulnerability assessment of an ancient cathedral located in Southern Italy is performed by using both conventional and advanced finite element models. The structural safety under both static and seismic loading conditions, also including wind and temperature loadings, is mainly assessed via a response spectrum analysis performed on an accurate 3D global model of the cathedral ad hoc developed. Moreover, additional pushover analyses are conducted using an advanced nonlinear model, for a better understanding of the seismic behaviour of the analysed structure. In particular, an innovative diffuse cohesive interface approach has been adopted and suitably compared with a well-established damage model, also in terms of associated mesh dependency issues. Finally, a critical discussion of the numerical results obtained via all these different models is reported, with the aim of comparing their predictive capabilities in terms of both global and local structural safety.

Finite element model validation for a 14.5 mm armor piercing bullet impact on a multi-layered add-on armor plate

For armor plates testing and evaluation the use of modeling and simulation tools, together with a validated finite element model is a reliable approach in respect to a firing conducted session. The paper presents the validation of an advanced finite element model on the impact between two 14,5 mm armor piercing bullets with a multilayered add-on armor plate made by aluminum alloy, alumina tiles, aramid fabric woven, ultra-high molecular weight polyethylene fiber composite and a steel plate. An 8 mm thick armor steel witness plate was placed at 2 cm behind the add-on plate. The real tests were conducted in a firing range and a chronograph was used to measure the values of the bullet impact velocities. The test results showed that the first bullet penetrates the witness plate and the second bullet only deforms it. A three-dimensional finite element model of the bullet and armor plates was conceived to perform the impact simulations in LS-DYNA. Tensile and compression tests, as well as other scientific methods were employed to establish the strength and failure model parameters for each material. The results of the finite element model follow the experimental ones regarding the yaw angle assumptions that were applied for a simulation scenario.

Free vibration analysis of sandwich composite plate with honeycomb core

The modal analysis of a sandwich composite plate with a honeycomb core is investigated using finite element method. The sandwich composite plate is modelled using ANSYS APDL software program. The literature is used to validate the advanced finite element models. The present sandwich plate model is discretized using four nodded serendipity elements (SHELL181). To characterize the effectiveness of sandwich composite plates with honeycomb core, several parametric investigations are carried out to determine the values of natural frequencies and mode shapes of composite sandwich plates using Block Lanczos scheme. The findings suggest that the thickness of the face sheet and the material of the core has impact on the values of natural frequencies and mode shapes of sandwich composite plates.

Structural testing and numerical modelling of T-joints between cold-formed S690 circular hollow sections under brace in-plane bending

• Six T-joints between S690 CFCHS were tested under brace in-plane bending. • Both monotonic and cyclic actions were applied to these joints. • All joints failed with a fracture in the heat-affected zones of the braces. • An integrated numerical modelling approach was developed to examine these joints. • Heat transfer, thermomechanical and structural analyses were performed. • Residual stresses caused little strength reductions in these T-joints. This paper presents a comprehensive investigation into the structural behaviour of T-joints between high strength S690 cold-formed circular hollow sections (CFCHS) under brace in-plane bending, and deformation characteristics of these T-joints under both monotonic and cyclic actions are examined experimentally and simulated numerically. These T-joints between S690 CFCHS were found to deform with a high level of resistances and ductility under both monotonic and cyclic actions. Through an integrated numerical modelling approach developed by the authors, advanced three-dimensional finite element models of CFCHS with solid elements were established. With a proper definition of weld collars at the brace/chord junctions of the T-joints between S690 CFCHS with different diameters and thicknesses, these models were readily adopted to perform a heat transfer analysis, a thermomechanical analysis and a structural analysis sequentially with compatible element types and meshes. Hence, the effects of the welding-induced residual stresses at the welded brace/chord junctions onto the structural behaviour of these T-joints were readily assessed. Consequently, these advanced models are demonstrated to be able to predict rationally deformation characteristics of these T-joints between S690 CFCHS under monotonic and cyclic actions of brace in-plane bending with a high degree of structural accuracy.

Performance and strength calculation of CFST columns with localized pitting corrosion damage

In recent years, concrete-filled steel tubular (CFST) columns are increasingly used in ocean construction, such as offshore towers and marine platforms. When used in harsh marine environments, the inevitable pitting corrosion poses a crucial threat to the outer surface of CFST and results in stress concentration, early local buckling as well as confinement reduction towards concrete. Relevant study is rarely seen given the complexity in experimental realization and numerical modelling of random pitting corrosion. This study aims to investigate the nonlinear performance of CFST columns with localized pitting corrosion damage. Advanced finite element modelling techniques are developed to simulate the localized corrosion pits with the consideration of its random nature in terms of sizes, depths and distributions. Previous test data are adopted to verify the developed model. The differences between the structural performance of CFST columns under pitting corrosion, uniform corrosion and uncorroded conditions are revealed. Comparison results demonstrate a more severe degradation caused by localized pitting corrosion. Finally, taking the characteristic of pitting corrosion into account, simplified design methods are proposed by modifying the existing methods in the current standards for calculating the post-corrosion strength of CFST columns.

Cardiac mesh morphing method for finite element modeling of heart failure with preserved ejection fraction

Numerical modeling of heart biomechanics can realistically capture morphological variations in diseases and has been helpful in advancing our understanding of the physiology. Subject-specific models require anatomic representation of medical images, and it is desirable to have a consistently repeatable models for any given morphology. In this study, we propose a novel and easily adaptable cardiac reconstruction algorithm by morphing an existing discretized mesh of an advanced finite element (FE) model, to match anatomies acquired from porcine cardiac magnetic resonance imaging (cMRI) scans. The morphing algorithm involves iterative FE simulations with visco-hyperelastic material properties. The living heart porcine model (LHPM) was chosen as the input baseline FE mesh, in order to preserve detailed anatomical features that cannot be captured in routine scans such as myofiber orientations and conduction pathways. The algorithm was demonstrated for the recreation of porcine hearts of a healthy subject and of a subject induced with heart failure with preserved ejection fraction (HFpEF) conditions, where there were substantial hypertrophy and anatomical alterations. We further used the morphed meshes for FE modeling of cardiac contraction and relaxation, thus demonstrating the applicability of the proposed algorithm in producing viable meshes. The results show that our algorithm can recreate the characteristic anatomical changes of cardiac remodeling, including heart muscle thickening, as well as replicate the reduction in ventricular volume. This algorithm allows for the creation of subject-specific models with the same mesh connectivity, thus enabling spatial comparison and analysis of pathologic progress.

Dynamic assessment, FE modelling and parametric updating of a butterfly-arch stress-ribbon pedestrian bridge

The article focuses on the dynamic identification and finite element (FE) modelling of a butterfly-arch stress-ribbon pedestrian bridge in Fuzhou, Fujian, China. The Stochastic Subspace Identification method yields an estimate of the operational modal parameters. A highly synchronous tri-axial wireless sensor network was deployed on the bridge deck to record the structure’s ambient vibration. Eight stable modes in the frequency range 3.59–14.92 Hz were found, associated with prevalent bending and torsional deformations. Four distinct FE models of the bridge with progressive complexity and accuracy were developed to investigate the sensitivity of the modal features to the modelling choices. The FE model characterised by the fittest agreement with the experimental modal parameters was used for the automatic parametric optimisation based on a sensitivity-based algorithm. The stiffness of the springs simulating the soil-structure interaction, the elastic modulus of the concrete deck and the elastic modulus of the tendons were chosen as updating parameters for a total of eight parameters. The effect of non-structural elements (handrails) and prestress on the modal features are also investigated. The final advanced FE model developed can serve as baseline for a long-term monitoring of the bridge during its life-cycle, and also provides some recommendations to practitioners and scholars all over the world for the modelling and analysis of this particular kind of footbridges.