Element Model Of Joint Research Articles

Study of the effect of seismic performance measures on a metro station structure in liquefiable soil

After the concept of ‘resilient city’ was introduced, the anti-seismic and resilience enhancement of underground structures gradually became an important issue in engineering. In this study, a method for enhancing the resilience of a soil–structure system subjected to earthquakes is proposed. First, a water-soil fully coupled numerical model was established to analyse the seismic behaviour and enhancement effect of a station structure subjected to an earthquake in liquefiable ground. In the analysis, an elastoplastic cyclic mobility model was used to describe the soil behaviour, whereas an interface joint element model was used to consider the soil-structure interaction. Subsequently, a non-liquefied clay replacement method was designed, and the effects of the replacement position and thickness on the floating displacement and internal force of the structure were analysed. To fully utilise the cushioning effect of the liquefiable sand and the anti-floating drainage near the station structure, a unilateral drainage diaphragm wall that does not drain in the far-field soil and drains in the near-field soil is proposed around the station structure. Based on the analysis results of different cases considering the soil replacement position, replacement thickness, distance between the unilateral drainage diaphragm wall and station structure, and buried depth of the wall, combined measures of clay replacement with unilateral drainage diaphragm wall were examined. The results show that the combination of the two measures significantly reduced the floating displacement, restrained the additional internal forces of the structure, reduced the time for the structure to reach stability after an earthquake, which is helpful to enhance the ability of self-recovery and improve the seismic resilience of the underground structure.

NUMERICAL STUDY OF REINFORCED CONCRETE PLATES IN THE PRESSURE AREA

Here is the description of fi nite elementmodels of joints between reinforced concrete slab and column, made in the SIMULIA ABAQUS software package. The variable parameters were the ratio of the sides of the column cmax/cmin and the ratio of the side of the column to the eff ective depth c/h0. The calculation is performed in a non-linear formulation. Finite elementmodels showed realistic behavior: a punching shear pyramid was detected. It was found a signifi cant unevenness in the distribution of tangential deformations, as well as the main compressive deformations of the concrete slab near the column. The nature of the formation and development of the punching shear pyramid depends on the value of the ratio of the sides of the column cmax/cmin and the ratio of the side of the column to the eff ective depth slab c/h0.

A finite element model of semi-rigid mortise-and-tenon joint considering glue line and friction coefficient

The aim of this study is to build a new numerical model of a mortise-and-tenon joint based on the finite element method (FEM) considering glue line and friction coefficient to analyze the semi-rigid wood joint. Firstly, the friction coefficient, glue distributions and strengths of the mortise-and-tenon joint were determined by experimental methods. Secondly, these parameters were specified to a T-shaped mortise-and-tenon joint model to build a finite element model of joint by FEM. Finally, both withdrawal and bending load capacity of T-shaped specimens were investigated by experimental and numerical methods. The results showed that the testing methods used to determine the coefficient, distributions and strengths of the glued mortise-and-tenon joint were all effective enough to determine the mechanical properties of the wood mortise-and-tenon joint, and the finite element model of joint can be applied to analyze the semi-rigid mortise-and-tenon joint with consistency beyond 85%. These methods and finite element models will contribute to the analysis of wood products and wood constructions.

A proposed model for nonlinear analysis of RC beam-column joints under seismic loading

Beam-column joints are generally subjected to significant inelastic deformations and considerably contribute to storey drifts under seismic loading. It is vital to consider joint shear deformation and longitudinal bar slip in the finite element simulation, and neglecting these effects will lead to misleading results. A new macro beam-column joint element model was proposed to consider the influence of joint inelastic deformations for interior joint with stirrups. The proposed macro beam-column joint was developed based on the force transfer mechanisms and inelastic response mechanisms, using axial springs representing bar-slip mechanism of longitudinal reinforcement, concrete and reinforcement in the joint core and interface-shear. In the joint core, eight concrete components and eight reinforcement components worked together to contribute to the effect of joint shear deformation. Constitutive relationship was developed to define the response of proposed joint model based on the dimensions, geometric, and material properties. An applicable model was used for simulating strength reduction of confined concrete strut due to joint damage and cyclic load history. Modifications were made to provide a more reasonable simulation of the anchorage zone response. The numerical analysis results were compared with experimental data of six beam-column subassemblages to validate the proposed macro beam-column joint element model. The comparison between the simulated and the test results shows that the proposed joint model is able to simulate the hysteretic response, joint shear strength and joint shear deformation of the beam-column subassemblages. Additionally, the comparison of the simulated results between proposed joint model and available joint model indicates that the proposed joint model is more accurate and efficient.

Efficient 3D boundary element dynamic analysis of discontinuities

In the present study, a nonlinear joint element model with a coupled shear-tensile behavior for multi body boundary element frictional contact problems is presented. The analysis is carried out by discrete crack model using the multi-region 3D boundary element method including material damping. To account for the decay of joint strength parameters at intermediate courses of deformation, the simplified discrete crack joint model (SDCJ) has been used. The nonlinear nature of contact problems demands an iterative technique development to determine the actual contact conditions (opening and sliding with bonding and friction) at arbitrary points of the contact boundaries. Through several analyses, it is demonstrated that the proposed method is robust, as it does not require to solve the whole system simultaneously. As a particular case, the influence of foundation inhomogeneity on the seismic response of concrete arch dam has been studied in order to illustrate the accuracy and efficiency of the present approach in a complicated case.

Rapid, automated imaging of mouse articular cartilage by microCT for early detection of osteoarthritis and finite element modelling of joint mechanics

SummaryObjectiveMouse articular cartilage (AC) is mostly assessed by histopathology and its mechanics is poorly characterised. In this study: (1) we developed non-destructive imaging for quantitative assessment of AC morphology and (2) evaluated the mechanical implications of AC structural changes.MethodsKnee joints obtained from naïve mice and from mice with osteoarthritis (OA) induced by destabilization of medial meniscus (DMM) for 4 and 12 weeks, were imaged by phosphotungstic acid (PTA) contrast enhanced micro-computed tomography (PTA-CT) and scored by conventional histopathology. Our software (Matlab) automatically segmented tibial AC, drew two regions centred on each tibial condyle and evaluated the volumes included. A finite element (FE) model of the whole mouse joint was implemented to evaluate AC mechanics.ResultsOur method achieved rapid, automated analysis of mouse AC (structural parameters in <10 h from knee dissection) and was able to localise AC loss in the central region of the medial tibial condyle. AC thickness decreased by 15% at 4 weeks and 25% at 12 weeks post DMM surgery, whereas histopathology scores were significantly increased only at 12 weeks. FE simulations estimated that AC thinning at early-stages in the DMM model (4 weeks) increases contact pressures (+39%) and Tresca stresses (+43%) in AC.ConclusionPTA-CT imaging is a fast and simple method to assess OA in murine models. Once applied more extensively to confirm its robustness, our approach will be useful for rapidly phenotyping genetically modified mice used for OA research and to improve the current understanding of mouse cartilage mechanics.

Transverse joint aperture simulation of high arch dam based on measured temperature in construction period

Transverse joint aperture is of certain reference value to ensure joint grouting quality and overall safety of high arch dam. A 3D isoparametric joint element model with spherical surface key grooves and finite thickness is used to simulate a transverse joint. A set of program is developed to simulate the transverse joint aperture of Dagangshan high arch dam. Combined with the measured temperatures, the whole developing process of Dagangshan arch dam’s transverse joint aperture is simulated. The real work behavior of transverse joint, thermal and mechanical properties of concrete, pouring process, joint grouting temperature and cantilever height of high arch dam are considered during the simulation. The simulation results show that the lower of the joint grouting temperature, the larger value of transverse joint aperture; the higher of cantilever height during the construction period, the smaller value of transverse joint aperture.

A study on the contraction joint element and damage constitutive model for concrete arch dams

A new contraction joint element model for the interface in different meshes between the arch dam sections is constructed. The study on the elastic-plastic damage constitutive model for concrete, which is applied to multi-axial stresses, is also taken. The models of the dam-foundation-reservoir system for Xingbiling and Jinping concrete arch dams, China are calculated using the proposed contraction joint elements and the elastic-plastic damage constitutive model to verify the proposed models. Results showed that the proposed contraction joint element model has a high precision in simulating the behavior of contraction joints and the elastic-plastic damage constitutive model has a high precision in simulating the behavior of the damage to the concrete.

Seismic behaviour of infilled and pilotis RC frame structures with beam–column joint degradation effect

The influence of the exterior joints capacity deterioration on the local and global failure mechanisms of reinforced concrete structures with infills is investigated. Exterior beam–column joints with reduced capacity is the common case for the majority of RC structures designed according to older design standards. Nevertheless in common practise the response of these regions is typically assumed as rigid. A key parameter of this investigation is the inclusion of the joints strength and stiffness degradation in the study of the seismic performance of the structures. In this direction, a special-purpose rotational spring element that incorporates a special behaviour model is employed for the simulation of the exterior joints’ local response. The spring element has been incorporated in a well-established general program for nonlinear static and dynamic analysis. The effectiveness of the used joint element model has been demonstrated in a previous paper through comparisons with experimental data reported in literature. In this paper an attempt is presented for the investigation of the influence of the exterior joint damage on the seismic behaviour of bare and infilled RC frame structures. Two types of masonry infilled structures are considered: (a) infilled frame and (b) infilled frame without infills at the base storey (pilotis frame). A parametrical study of the overall seismic response using push over analyses and step-by-step analyses is performed. Results in terms of interstorey drifts, base shear, failure mode, ductility requirements and joints rotational requirements demonstrate that neglecting the possible local damage of the exterior joints may lead to erroneous conclusions and unsafe design or seismic behaviour evaluation that subsequently may become critical in some cases. Furthermore the influence of exterior joints degradation has been proven of vital importance for the overall behaviour of pilotis frames.

Modelling exterior beam–column joints for seismic analysis of RC frame structures

AbstractIn common practice, the local response of beam–column joints is not considered for the seismic analysis of multistorey reinforced concrete (RC) frame structures, where these critical regions are typically assumed as rigid. Studies that incorporate the local effect of the joints in the seismic analysis of multistorey RC frame structures are limited. Identifying the main disadvantages of the analytical models that have been proposed so far, a behavioural model is developed for the simulation of the local inelastic response of exterior RC beam–column joints in multistorey RC frame structure. Special attention is given to the description of the main characteristics of the actual seismic response of the joints, including strength and stiffness degradation. The proposed model is incorporated as a rotational spring element in a general program for nonlinear static and dynamic analysis of structures, and a procedure for the evaluation of the required model parameters is also presented. The effectiveness of the proposed joint element model is demonstrated through comparisons with experimental data of 12 RC exterior joints reported in the literature. Moreover, using the proposed element, the influence of the local nonlinear response of RC exterior beam–column joints on the ductility requirements of columns and on the failure mode and overall seismic response of a multistorey RC frame structure is investigated. From the results of these analyses, it is concluded that the modelling of exterior RC joints with reduced capacity as rigid joints can lead to unconservative results and therefore to unsafe design. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Non-linear and failure behaviour of spotwelds: a “global” finite element and experiments in pure and mixed modes I/II

The paper deals with joint element model used in crashworthiness simulations. The first part of the paper is dedicated to the formulation of a new “global” finite element for spotweld modelling. The mechanical behaviour of the joint is elastic–plastic type and damage is taken into account to model the failure of the welded area. The second part of the paper concerns a new experimental procedure for joint strength analysis in pure and mixed modes I/II and for joint model characterisation. Experiment is based on Arcan principle and results are compared to open literature. In the last part of the paper, the parameters of the new joint model are identified using experiments and used for several shapes of spot-welded specimens. The model predicts reasonably the elastic–plastic part of the response but is unable to predict the post-peak response observed especially in the case of pure shear.

A finite element analysis for the stability of drystone masonry retaining walls

The stability of a drystone retaining wall involves large plastic strain, interactions between the wall, backfill and base, the placement process of backfill and the behaviour of joints within a wall. A finite element analysis method for modelling the behaviour of a drystone wall using the finite element code VISAGE is described. The results obtained were compared with those from field trials and discrete element analysis. In the finite element analyses, the same critical stable height was obtained by using an equivalent continuum model for the wall and a joint element model. The deformation behaviour obtained using the joint element model was closer to that observed in the field trials and the discrete element analysis than that obtained using an equivalent continuum model.

A discrete crack joint model for nonlinear dynamic analysis of concrete arch dam

Concrete arch dams are generally constructed of massive plain concrete with almost no tensile resistance. To control tensile forces due to concrete shrinkage, temperature variations and for construction facilitation, arch dams are built in cantilever monoliths separated by vertical contraction joints. Earlier studies show that the modeling of such joints has significant influence on the seismic safety evaluation of arch dams. This fact is due to the tensile and shear failures of joints causing a redistribution of internal forces during and after a big earthquake. In the present study, a nonlinear joint element model with a coupled shear–tensile behavior for realistic finite element analysis of dam–reservoir system is presented. Reservoir upstream radiation, and bottom partial absorption of acoustic waves, as well as water compressibility are considered. The model when applied to simpler cases solved by other workers shows good performances. However, it is much more useful to solve problems not considered so far, e.g., shear keys behavior, joint damages, etc. The model could be employed effectively and conveniently for earthquake safety evaluation of arch dams in highly active seismic regions.

Mechanobiological adaptation of subchondral bone as a function of joint incongruity and loading

Computed tomography (CT) has been employed to determine non-invasively the distribution of subchondral bone density in joints and to evaluate their dominant loading pattern. The objective of this study was to investigate the relationship between subchondral bone adaptation, joint incongruity and loading, in order to determine to what extent the loading conditions and/or geometric configuration can be inferred from the distribution of subchondral density. Finite element models of joints with various degrees of incongruity were designed and a current remodeling theory implemented using the node-based approach. Appropriate combinations of joint incongruity and loading yielded subchondral bone density patterns consistent with experimental findings, specifically a bicentric distribution in the humero-ulnar joint and a monocentric distribution in the humero-radial joint. However, other combinations of incongruity and loading produced similar subchondral density patterns. Both the geometric joint configuration and the loading conditions influence the distribution of subchondral density in such a way that one of these factors must be known a priori to estimate the other. Since subchondral density can be assessed by CT and joint geometry by magnetic resonance imaging, the dominant loading pattern of joints may be potentially derived in the living using these non-invasive imaging methods.

Free vibrations of coupled walls by transfer matrices and finite element modelling of joints

A transfer matrix analysis of coupled shear walls is combined with finite element models for joint flexibility. Every joint is considered as a single rectangular element with a displacement model that is consistent with the kinematic constraints imposed by the adjacent beams. The derivation of the element stiffness is based on plane stress elasticity. The overall problem can be solved for the static and free vibrational response of coupled shear walls on flexible foundations. Assessment of its performance and comparison with simpler models for joint deformation is accomplished through the determination of natural frequencies and modes of vibration for a range of previously tested or analysed specimens. Having established the accuracy of the proposed high-order finite element joint model, the effect of joint flexibility on higher frequencies and modes of vibration is then assessed.

AN AXISYMMETRIC JOINT ELEMENT UNDER NON-AXISYMMETRIC LOADINGS IN SEMI-ANALYTICAL FINITE ELEMENT METHOD

A new axisymmetric joint element model for semi-analytical finite element analysis of axisymmetric bodies subjected to non-axisymmetric loading is proposed. The new joint element model for axisymmetric interface has three degrees of freedom: normal tangential and circumferential directions and describes debonding (normal direction), and slip (tangential and circumferential direction) on the interface. The new joint element model was incorporated into a finite element program and test-case analyses were performed. The results indicate that the new joint element model is useful in the semi-analytical finite element analysis for deeper understanding of stress distributions on the axisymmetric interface.