Simplified Finite Element Model Research Articles

Experimental and numerical investigations of the impact resistance of socket and pocket connections for precast bridge columns

This study investigates the dynamic performance of precast bridge columns under pendulum impact testing, including socket connection, pocket connection, and cast-in-place (CIP) columns. The study focuses on comparing the impact behavior of CIP and precast columns regarding failure modes, impact force-time, and deflection-time histories. Furthermore, the mechanism by which the socket or pocket connection configurations affect the impact resistance of the precast columns is discussed. The results indicate that the development of cracks in the precast and CIP columns is consistent under the same impact conditions. Notably, the shear resistance mechanisms and failure modes vary significantly at the bottom of the two columns. For the precast specimens, substantial local damage occurs at the connections with consecutive impacts. Specifically, punching shear failure is observed at the pocket connections, whereas the connection sections of the socket columns may pull out from the grooves. Local damage to the column-footing connections reduces the global stiffness of precast columns, leading to higher deformation, greater residual displacements, and lower impact forces than those of CIP columns. A simplified finite element modelling method is proposed to simulate the characteristics of precast column connections, and its accuracy is verified using the test results. The numerical findings show that increasing the friction coefficient at the connection interface promotes the formation of diagonal compression struts within the connection, effectively resisting impact loads and preventing excessive shear stress produced by sliding at the interface. Furthermore, amplifying the minimum embedment depth of the socket-connected precast column to 1.0 D is recommended to ensure safe performance under impact loading.

Passive Shunted Piezoelectric Systems for Vibration Control of Wind Turbine Towers: A Feasibility Study

Many countries have a variety of offshore and onshore wind turbines that face extreme aging challenges. Issues with harmful vibrations that must be minimized are addressed in this paper. A new method of wind turbine tower vibration control using piezoelectricity and shunt circuits is proposed in this paper. The passive vibration control method is shown to improve the tower’s structural performance under various environmental loads, like wind and seismic excitations. To examine the effectiveness of the suggested shunted piezoelectric system, a simple surrogate finite element model of a wind turbine tower is considered, and various investigations at the second eigenfrequency are carried out. An alternative way of modeling the studied structure is considered and the results demonstrate better performance. The advantages of setting up structural damping systems for decreasing tower vibrational loads and boosting their structural stability and resilience against extreme events are highlighted throughout this work.

A Gaussian process approach for rapid evaluation of skin tension

Skin tension plays a pivotal role in clinical settings, it affects scarring, wound healing and skin necrosis. Despite its importance, there is no widely accepted method for assessing in vivo skin tension or its natural pre-stretch. This study aims to utilise modern machine learning (ML) methods to develop a model that uses non-invasive measurements of surface wave speed to predict clinically useful skin properties such as stress and natural pre-stretch. A large dataset consisting of simulated wave propagation experiments was created using a simplified two-dimensional finite element (FE) model. Using this dataset, a sensitivity analysis was performed, highlighting the effect of the material parameters and material model on the Rayleigh and supersonic shear wave speeds. Then, a Gaussian process regression model was trained to solve the ill-posed inverse problem of predicting stress and pre-stretch of skin using measurements of surface wave speed. This model had good predictive performance (R2 = 0.9570) and it was possible to interpolate simplified parametric equations to calculate the stress and pre-stretch. To demonstrate that wave speed measurements could be obtained cheaply and easily, a simple experiment was devised to obtain wave speed measurements from synthetic skin at different values of pre-stretch. These experimental wave speeds agree well with the FE simulations, and a model trained solely on the FE data provided accurate predictions of synthetic skin stiffness. Both the simulated and experimental results provide further evidence that elastic wave measurements coupled with ML models are a viable non-invasive method to determine in vivo skin tension. Statement of significanceTo prevent unfavourable patient outcomes from reconstructive surgery, it is necessary to determine relevant subject-specific skin properties. For example, during a skin graft, it is necessary to estimate the pre-stretch of the skin to account for shrinkage upon excision. Existing methods are invasive or rely on the experience of the clinician. Our work aims to present an innovative framework to non-invasively determine in vivo material properties using the speed of a surface wave travelling through the skin. Our findings have implications for the planning of surgical procedures and provides further motivation for the use of elastic wave measurements to determine in vivo material properties.

A Numerical Model for the Scour Effect on the Bearing Capacity of an Offshore Wind Turbine with a Five-Bucket Jacket Foundation

As offshore wind farms move into deeper waters and the capacity of offshore wind turbines (OWTs) increases, a new type of OWT foundation needs to be developed. In this study, a new type of five-bucket jacket foundation (FBJF) was proposed based on the broad application of a multi-bucket jacket foundation (MBJF) in offshore wind farms. The soil around the OWT foundation is subject to scour due to the complex marine environment. To investigate the effects of scouring on the FBJF, a series of local-scour simplified finite-element models of the FBJF were established using ABAQUS, and the effects of scouring depth and the extent on the bearing capacity of the FBJF with the monotonic load were analyzed. Then, the failure envelopes of the FBJF under combined loading were obtained using the fixed-displacement ratio method, and the effects of various scour conditions on the failure envelopes were compared. The results indicate that the failure envelope profile contracts inward, and the bearing capacity decreases with the increasing scouring depth and extent. Furthermore, the failure envelopes of the FBJF under different vertical loads were calculated, and the FV-FH-FM failure envelopes of the FBJF were obtained through interpolation. Finally, the effects of different scour conditions on the FV-FH-FM failure envelopes of the FBJF were analyzed. The results show that the FV-FH-FM failure envelopes of the FBJF have similar profiles and follow the same trend under different scour conditions.

Parameter identification procedure for hysteretic shear-resistant properties of beech wood dowels

To evaluate the shear-resistant behavior of wooden dowels used in Blockhaus shear walls under cyclic load, 19 specimens under ten groups of conditions were prepared and tested. The failure modes, hysteresis curves, mechanical properties, stiffness degradations, and energy dissipation capacities of the specimens were studied. The test results showed that with the increase in the number of dowels, the initial stiffness and peak load of the specimens increased greatly. The diameter of the dowels had little influence on the mechanical properties of the specimens. Furthermore, the test findings demonstrated that the pretension load between the walls greatly enhanced the initial stiffness and energy dissipation capacity of specimens. A simplified finite element model was established in Opensees. Considering the effect of material variability, the parameters of single dowel shear spring and friction spring were identified by Genetic Algorithm with modified objective function in Matlab. The identified parameters were applied to the finite element model of the multi-dowel specimens. The simulation results were in good agreement with the test results, and the validity of the numerical model and parameter identification method was verified.

Investigation on the bending deformation of laser peen forming with a simplified eigenstrain-based finite element model

Investigation on the bending deformation of laser peen forming with a simplified eigenstrain-based finite element model

Combining X-ray micro-CT and microscopy-based images of two lianas species to derive structural, mechanical and functional relationships

This paper presents a biomechanical study of stems of two liana species, Clematis vitalba and Vitis vinifera, investigates the mechanical performance of these two liana species and attempts to enhance the understanding of structure–function relationships. The investigation involved mechanical testing of whole plant stems, supplemented by X-ray micro-CT (X-ray computed tomography at micron voxel size) imaging and 2D microscopic images of stained cross sections of the plant stems, to derive structure–function relationships with potential for application in bioinspired composite materials. The micro-CT images were compared to the microscopic images of stained cross sections, in order to show benefits and potential drawbacks of the X-ray micro-CT method with respect to traditional methods. The high-resolution 3D imaging capacity of micro-CT is exploited to explain the structural functionality derived from the mechanical testing. A simple finite element model is developed based on the plant topology derived by the micro-CT images and proved accurate enough to model the plant’s mechanical behaviour and assess the influence of their structural differences. The two plants exhibit different to each other physical and mechanical properties (density, strength and stiffness) due to their common growth form. Anatomical cross-sectional observation and X-ray micro-CT provide complementary information. The first method allows the identification of the lignified parts, supposedly more resistant mechanically, of these structures, while the second one provides a full 3D model of the structure, admittedly less detailed but providing the spatial distribution of density contrasts supposed to be important in the mechanical properties of the plant. The proposed methodological approach opens new perspectives to better understand the mechanical behaviour of the complex structure of plants and to draw inspiration from it in structural engineering.

Verification of a Simplified Design Method for Timber–Concrete Composite Structures with Metal Web Timber Joists

This study presents a comprehensive analysis of a simplified design methodology for timber–concrete composite roof and floor structures employing metal web beams, also known as posi-joisted beams, easi-joist, or open web joists, validated through both laboratory experiments and finite element (FE) method analyses. The proposed method integrates the transformed section method and the γ-method, as outlined in Annex B of EN1995-1-1 for mechanically jointed beams. The investigation focuses on roof and floor structures featuring posi-joisted beams, oriented strand board (OSB) sheets connected by screws, and a layer of concrete bonded to the OSB sheets using epoxy glue and granite chips. Two groups, each consisting of four specimens, were prepared for the laboratory experiments. Each specimen comprised two posi-joisted beams, 1390 mm long, connected by OSB/3 boards measuring 400 mm in width and 18 mm in thickness. The beams had a cross-sectional depth of 253 mm, corresponding to beams of grade PS10, with top and bottom chords made from solid timber (95 mm × 65 mm). Bracing members with cross-sections of 100 mm × 45 mm were used to join the bottom chords of the beams. A layer of self-levelling mass SakretBAM, 50 mm thick, was bonded to the OSB/3 boards using SicaDur 31 epoxy glue and granite chips (16–32 mm). The specimens underwent three-point bending tests under static loads, and FE modelling, conducted using Ansys R2 2022 software, was employed for both experimental groups. A comparative analysis of results obtained from the simplified design method, FE simulations, and experimental data revealed that the simplified method accurately predicted maximum vertical displacements of the roof fragment, including posi-joisted beams, with precision up to 11.6% and 23.10% in the presence and absence of a concrete layer, respectively. The deviation between normal stresses in the chords of the beams obtained through the simplified method and FE modelling was found to be 7.69%. These findings demonstrate the effectiveness and reliability of the proposed design methodology for timber–concrete composite roofs with posi-joisted beams.

An Improved Decoupled Finite Element Analysis Method of Ultra-Large Offshore Wind Turbine Subjected to Combined Wind–Wave Actions

Abstract Owing to the simplification of the wind turbine, it is difficult to accurately simulate the interaction between the rotor system and the supporting structure using the decoupling finite element method. Therefore, when using this method for safety assessment and dynamic response research of the offshore wind turbine (OWT), there is a deviation between the simulation result and the real response of the OWT. In this study, an improved decoupled finite element analysis method is proposed based on a theoretical derivation. A simplified finite element model of a 10 MW jacket OWT with an equivalent substructure was established, and the dynamic response of the OWT under wind and waves was studied. By comparing the results of the fully coupled analysis method and the traditional finite element method, the applicability of the traditional finite element analysis method to the dynamic analysis of an OWT under typical winds and waves is discussed. The limitations of using the traditional finite element method to study or evaluate an OWT complex dynamic system were revealed, and the effectiveness and applicability of the improved method proposed in this study were qualitatively and quantitatively verified. Subsequently, based on the proposed improved decoupled finite element analysis method, a numerical calculation corresponding to a fully coupled test was performed. Compared with the numerical results obtained by the traditional finite element method, the improved decoupled finite element method proposed in this study obtained more consistent results with the fully coupled test.

Reliable design rules for cold-formed ferritic stainless steel closed built-up beams

In the companion paper, test results were presented to explore the flexural performance of cold-formed ferritic stainless steel (FSS) closed built-up beams. Each specimen was fabricated by joining two lipped channels in a face-to-face configuration and securing them with spot welds at intermediate points along the beam span. Sectional aspect ratio, compression flange’s sectional slenderness and moment gradient were the key parameters varied to explore their influence on the flexural response of such members through tests. The current paper establishes a simplified finite element (FE) model of cold-formed FSS closed built-up beams and verifies it against the test results. Further, an extensive parametric study is carried out using the validated FE model to generate a large pool of data points. A wider database comprising of test results, numerical results obtained from this study and numerical results available in the companion paper were used to critically examine the adequacy of the current Australian Specifications (AS/NZ), American Standard (SEI/ASCE-8), European Code (EN 1993-1-4), Modified Eurocode approach suggested by Gardner and Theofanous, and Direct Strength Method (DSM) in North American Specification (AISI-S100: 2016), Modified DSM approach proposed by the authors in the literature and Continuous Strength Method (CSM) for cold-formed steel (CFS) flexural members. This makes the current study the first to extensively assess the accuracy of the various design guidelines available in the codes and other relevant literature, which explicitly highlighted their grave limitations. Accordingly, through suitable modifications and recommendations, new design rules are proposed to reliably and safely predict the flexural capacity of cold-formed FSS closed built-up beams.

Efficiency of timber-concrete composite floors with discrete perfobond connections: A numerical study

To evaluate the behaviour of a single timber-concrete composite (TCC) T-beam, a simplified 2D finite element (FE) model in Abaqus is developed and validated using experimental tests and the Gamma method given in Annex B of EN 1995–1-1. The shear connection used in the beam consist of perfobond connectors, which are adhesively bonded to the timber beam. In the developed model, beam and shell finite elements have been used to simulate/reproduce the timber beam and the concrete slab, respectively. These have then been connected using connector elements which incorporate the mechanical behaviour of the tested shear connections, obtained in a previous research. After the successful validation of the FE model, this is used to further analyse different parameters such as: i) different number of connections (varying from 8 to 20), ii) different types of loading (point load, distributed load and line load), iii) different concrete slab widths and iv) connection models with elastic perfectly plastic behaviour applied to TCC T-beam and a 5 m by 5 m floor system. The results of the conducted study provide an in-depth understanding of the effect and impact of the investigated parameters which can support a future optimisation of the structural solution. Moreover, the results show that the use of a simplified 2D model can support designers to overcome the limitations of analytical approaches, such as the Gamma method, to analyse large spacing and to take benefit of bidirectional effects (load sharing) if analysed as a whole instead of a single T-beam.

Model verification and vibration analysis of the four-disk hollow flexible shaft rotor system

Rotor unbalances failure due to various factors such as manufacturing defects, mounting errors, and material inhomogeneity is inevitable, and will be aggravated by bearing pulse displacement excitation caused by maneuvering flight. Therefore, the purpose of this paper is to study the vibration of the rotor system under disk unbalance forces and bearing pulse displacement excitation. Firstly, the differential equation of motion for four-disk flexible hollow shaft rotor system modeling with a simple finite element model(SFEM) is established by the Lagrangian method in non-inertial systems, and the shaft is modeled using Timoshenko beam theory. Then, the dynamic characteristics of the four-disk flexible hollow shaft rotor are analyzed and compared with the 3D finite element model(3D FEM) to verify the accuracy of the model. To analyze the effects of different disk unbalanced positions and pulse displacement excitation on the vibration characteristics of the rotor, the characteristic vector method and the Runge–Kutta method are used to obtain the steady-state solution and the transient solution, respectively. In addition, the simulation results show that suitable in-shaft damping has a stable effect on the rotor during the start-up. Disk2 and Disk3 are more sensitive to synchronous harmonic excitation and pulse displacement excitation than Disk1 and Disk4. The research of this paper provides an important basis for vibration monitoring and control, and vibration transmission analysis of aero-engine rotor system.

Seismic behaviour of self-centring hybrid steel frames equipped with SMA plates under mainshock–aftershock sequences

This paper focuses on the mechanical behaviour, seismic application in steel frame connections and steel structure of shape memory alloy (SMA) plates. This study commenced by examining the hysteretic response of SMA plates subjected to cyclic tension tests, considering two different loading paths. Subsequently, a self-centring steel frame connection equipped with SMA plates and washers (SC-PW) was examined via quasi-static cyclic loading tests, and comparatively satisfactory self-centring behaviour was observed. However, the degradation of the initial stiffness of the SC-PW due to an initial imperfection was observed. An improvement strategy was proposed to overcome the degradation of the hysteretic behaviour (e.g., initial stiffness) of the SC-PW. Disc springs with a larger stiffness and preloads were introduced to overcome the degradation of the initial stiffness of the SC-PW, and the validation was confirmed via detailed finite element (FE) analyses. To improve the computation efficiency, a simplified FE model was developed to reproduce the hysteretic responses of the connection. Based on the simplified FE model, a six-storey prototype structure, i.e., a self-centring hybrid steel frame (SCHSF), equipped with the improved connection was developed, and the structural dynamic responses were investigated via nonlinear response history analyses, where mainshock–aftershock sequences were considered. The influence of the SMA material properties on the seismic behaviour of the prototype structure was investigated.

Simplified numerical model development for sophisticated analysis of lightweight-concrete encased cold-formed steel compressed column-end joints and panels

Since cold-formed steel (CFS) members are prone to complex buckling phenomena; that decrease their structural capability, many strengthening trends have been developed so far. One of these methods has been proposed as a new structural system comprising cold-formed steel (CFS) elements encased in polystyrene aggregate concrete (PAC). In this research, a simplified finite element model has been developed using ANSYS software, where a geometrically and materially nonlinear analysis with imperfections (GMNI) was used to solve the problem of PAC-encased CFS connections and panels subjected to compression. Each model was validated against available test results from literature. The full detailed volume-contact element-based model of concrete was replaced by spring elements perpendicular to the plate’s plane with equivalent properties, where a specific formula was set to define the stiffness of springs. A parametric study was performed to investigate in which range this stiffness has an impact on the ultimate load of the examined members. Additionally, different geometric imperfection amplitudes were implemented to test the real imperfection values. Finally, a failure mode-based equivalent geometrical imperfection amplitude was proposed to anticipate the design resistance of PAC-encased connections and panels.

Seismic behavior of a novel liftable connection for modular steel buildings: Experimental and numerical studies

Modular steel buildings (MSBs) have achieved considerable popularity in multi-to-high rise constructions due to the favorable mechanical characteristic, eco-friendliness, cost-effectiveness, and enhanced construction efficiency. As the critical part of MSBs, the inter-module connection has an important influence on determining the seismic performance of MSBs. This study presented an experimental-numerical investigation on an innovative fully prefabricated liftable connection (FPLC) for MSBs. To study the seismic performance of the FPLC, quasi-static tests were conducted on four full-scale specimens. The seismic behavior of the specimens, including failure mode, hysteretic response, strength and stiffness degradation, deformation characteristic, etc. was evaluated and compared in detail. The effect of the section of the twin-beams, the dog-bone weakening of the beam and the connecting method between the corner fitting and twin-beams on the seismic behavior of the FPLC was revealed. Moreover, the feasibility for seismic application of the FPLC was evaluated according to Chinese code GB 50,011–2010 and Eurocode 3 Part 1–8. The results indicated that the proposed FPLC met the limit of elastic and elastic-plastic inter-story drift ratios required by GB 50,011–2010. According to Eurocode 3 Part 1–8, the FPLC with welded beams should be classified as “semi-rigid” connections, while the FPLC, whose beams were connected to the column walls by the steel angles and bolts, was classified as a “pinned” connection. Then, a refined finite element model (FEM) was developed and verified by the test results. Furthermore, the verified FEM was utilized to analyze the distribution of the equivalent plastic strain, the stress variation path, and the yielding area of the twin-beams to further reveal the energy dissipation and damage mechanism of the FPLC. Finally, a simplified FEM was established and the comparison with the test results proved its reliability and efficiency. The present study will contribute to provide a comprehensive understanding on seismic performance and design of the inter-module connection for MSBs.

The Material Heterogeneity Effect on the Local Resistance of Pultruded GFRP Columns.

Pultruded GFRP (glass fiber-reinforced polymer) materials are widely used in structural engineering because of their lightweight, corrosion immunity, and electromagnetic transparency. However, the design of load-bearing components facing substantial compressive stresses, e.g., columns, must be more stringent than steel structures due to excessive deformability, material heterogeneity, and vulnerability to stress concentration. This manuscript investigates the failure performance of locally produced GFRP materials, focusing on the material heterogeneity effect on the mechanical resistance of a support joint of a pultruded tubular GFRP column. This experimental campaign employs relatively short rectangular profile fragments to isolate the support behavior and verify a simplified numerical finite element model, which neglects the nonlinearity of GFRP material. This work determines the material failure mechanisms behind the mechanical performance of pultruded profiles subjected to longitudinal compression for various column lengths.

Climate Change Impact on Corrosion of Reinforced Concrete Bridges and Their Seismic Performance

As a consequence of climate change impact, a significant variation in terms of temperature, atmospheric humidity, and carbon dioxide concentration levels is happening. This condition leads to several negative effects on the safety and the life cycle of existing concrete structures, such as the increase in the rate of material degradation, due to corrosion phenomena. In fact, the presence of carbonation and corrosion phenomena significantly influence the load-bearing capacity of existing reinforced concrete (RC) structures, under both static and dynamic loads. Among the wide range of existing RC constructions, bridges stand out for their importance. Furthermore, as structures directly exposed to the weather effects, they are more susceptible to these phenomena. In this paper, the influence of corrosion on existing RC motorway viaducts’ seismic behavior, considering the impact of climate change, is investigated, by means of an efficient procedure based on the implementation of 3D simplified finite element models and the use of analytical relations to obtain the amount of reduction in the steel reinforcement area as a function of the age of the bridge and of the different corrosion scenarios analyzed. Several scenarios for the expected variations in CO2 concentrations, temperature, and relative humidity are evaluated, considering that most of the viaducts present in the Italian motorway network were built between the 1960s and the 1970s. The results obtained using the projection of climate change impacts are compared with those calculated considering the corrosion scenarios resulting from the DuraCrete research project, to understand if the evolution of climate change leads to worse scenarios than those previously assessed.

Comparative study on the dynamic responses of monopile and jacket-supported offshore wind turbines considering the pile-soil interaction in transitional waters

In this study, simplified finite element models for monopile and jacket offshore wind turbines, referred to as MOWT and JOWT, respectively, were established for dynamic response analysis using the X-SEA program, based on the National Renewable Energy Laboratory's 5 MW OWT model. First, using five design constraints, an optimization design was conducted for the substructures and foundations of both MOWT and JOWT located in transitional waters to ensure a fair comparison of the dynamic performances of the two structures. Next, putting special attention to the natural frequency, tower top displacement and member stress, two kinds of OWT models with fixed and flexible bases subjected to combined wind, wave and current loads were analyzed using the pile-soil interaction module of X-SEA to further explore the influence of the foundation flexibility on dynamic responses. Subsequently, a parametric study was conducted to evaluate the sensitivity of the dynamic responses to the changes in environmental conditions, soil properties and pile embedded lengths. Finally, a comparison of the dynamic performances, parameter sensitivities, and total masses of the MOWT and JOWT was performed to determine the optimal fixed OWT support structure for the 50 m water depth of the southwest sea area of South Korea.

Research on rapid calculation method of wind turbine blade strain for digital twin

Digital twin (DT) technology provides unlimited possibilities for remote intelligent operation and maintenance of wind turbine blade (WTB) in operation. However, the urgent demand for high accuracy and real-time performance limit the engineering applications of this technology. This article presents a novel rapid calculation method of WTB strain, which aims to break the technical difficulties of real-time calculation in digital twin and realize synchronous mapping of WTB health status. Firstly, the load acting on the WTB is simplified according to the equivalent conversion theory. Then, a simplified finite element model, namely mechanism calculation model, of WTB is built based on mechanics. The multi-fidelity surrogate model is innovatively adopted to calibrate the results of the mechanism calculation via a small amount of data measured via sensors on the WTB. Based on the calibrated results, a unique strain field estimation model is built to provide more comprehensive information about WTB. Finally, the proposed method is verified via an experiment about WTB strain measurement and numerical simulation. The results demonstrate a considerable advancement in real-time performance with approximately 1444× compared to the traditional finite element method. The shortest elapsed time is 0.91s. Moreover, the minimum relative error is 0.11 % and the average relative error is less than 0.76 %.

The mechanical behaviour of a slip joint for an offshore wind turbine: First monitoring and modelling results

This study aims at shedding light on the mechanical behaviour of a prototype monopile–wind turbine tower connection, constituted by a slip joint. Selected examples of data set recorded during a long term monitoring campaign are illustrated and discussed. The data set encompass axial and hoop stresses measured over the slip joint area, relative displacements of the slip joint with respect to the monopile and acceleration levels recorded above the slip joint. In parallel, an ideal and simplified Finite Element model (FEM) of the slip joint is developed, in order to interpret the observed experimental data. Experiments first highlight the relevance of modelling the manufacturing imperfections of the overlapping steel sections. Subsequently, both experiments and FEM show that states of prestress need to be accounted for. Such prestress states first originate from the installation process, and subsequently from further loading events, triggering settlements of the slip joint. Finally, experiments and FEM showcase the force transfer mechanisms from the upper part to the lower part of the slip joint.