Rigid Joint Model Research Articles

Dynamics Modeling of Robot Joints with Asymmetric Load-Dependent Friction

This paper presents a strain wave gear model intended for industrial robots that are operated in both forward drive and backward drive under different load conditions. We show that a simple joint model captures the joint dynamics well at one load, but fails to capture the joint dynamics when the load is changed. Similarly, the simple model cannot capture the efficiency of the joint in both forward drive and backward drive. We propose a tooth model with sliding friction to resolve these issues. This model is simple to simulate and can thus be used for real-time control; the proposed model captures the load dependent friction and difference in efficiency in backward drive and forward drive. We validate the simulation performance of the tooth models on data from a Universal Robots UR10e robot with different payloads which shows an improvement compared to the standard rigid joint model.

Fracture research of adhesive-bonded joints for GFRP laminates under mixed-mode loading condition

Abstract The mixed-mode fracture characterization of adhesively bonded glass fiber-reinforced polymer (GFRP) plate joints is studied based on theoretical and experimental techniques. An improved beam model is used to estimate the compliance and the mixed-mode energy release rate (ERR) for GFRP four-point mixed-mode bending specimens. In this model, the deformation of the upper and lower GFRP plates is mutually independent, and the deformable adhesive is considered to satisfy the displacement compatibility conditions on the bonding interface. The explicit theoretical solutions of the compliance and ERR using the compliance method are reduced. The present theoretical solutions fit well with the finite element solutions by comparison with the rigid joint model. From the critical loads in experiment, the variation in fracture toughness on mixed-mode I/II has been determined by modifying the stiffness of the composite GFRP/GFRP substrate.

Lattice modelling of substandard RC beam-column joints considering localization issues

The strain adjustment for quasi-brittle materials to minimize the mesh size effect and localization issues are investigated by the nonlinear lattice modelling approach for substandard reinforced concrete (RC) beam-column joints (BCJs). The lattice model is generated by implementing the truss analogy for the concrete and reinforcement steel members in RC BCJs. The relevant uniaxial material properties in OpenSees are assigned to the truss members. The reinforcement bond-slip relationship is modelled by zero-length springs attached to steel and concrete elements. The modelling approach is validated by comparing the simulated responses to the experimental behaviour of inadequately detailed RC test specimens. A 3-story 3-bay frame tested with a pseudo-dynamic testing procedure and two substandard RC BCJs tested under quasi-static cyclic loading, one of which contains a slab and an out-of-plane beam, are simulated. To avoid the mesh size effect and localization issues, the strain-based softening function in the uniaxial material property of concrete is adjusted by adopting the crack band approach. Analysis results of the rigid joint model assumption, which does not account for the joint deformation, are also compared with the outcomes of the lattice model. By minimizing the mesh size effect, more realistic results are obtained using the lattice modelling technique with high computational efficiency and less analysis efforts. The model accuracy in reproducing the experimental behaviour and response quantities of prime interest is at a reasonable level for the investigated test specimens.

Accuracy of Seismic Response Evaluation of Two-Dimensional Analysis Model with Rigid Joints for RC Frame Buildings.

Three- or two-dimensional (2D) numerical models are used for the evaluation of the seismic performance of reinforced concrete (RC) buildings. This study examines a 2D numerical model for a specimen used in a full-scale four-story RC shaking-table test and evaluates the accuracy of the seismic response of the 2D numerical model, which is composed of a square fiber section model for the columns, a T-shape fiber section model for the beam and slab, and a rigid joint model for the beam-column joint. A parametric analysis of the effective slab width is performed to analyze its effects on the modal shape and natural period. The results suggest that the primary natural period of the considered model is almost identical to that associated with the experimental results. The applicability of the 2D numerical model for estimating the seismic response of the structure is established. By comparing the results of the seismic analysis and the experiment in the 50% amplitude of the JMA-Kobe wave, which corresponds to slightly exceeding VII on the modified Mercalli intensity scale, the root-mean-square percentage error of the 2D numerical model is 1.03% for the floor acceleration and 4.7% for the inter-story drift. Thus, the analytical model used in this study has sufficient accuracy in evaluating the seismic performance of buildings constructed in regions with a maximum seismic intensity of VII.

A new joint-slippage model for galvanized steel bolted joints with slippage

This paper presents a new joint-slippage model for determining the behavior of galvanized steel bolted joints with slippage based on the joint test results. The influence of the slip coefficient of the friction surface is considered in the new model. Validation of the new joint-slippage model is performed in terms of test results of full-size galvanized latticed steel girders. In addition, by comparison with the conventional rigid joint model and the most representative joint-slippage model – Ungkurupanian’s joint-slippage model, the new joint-slippage model exhibits the best performance according to predicted structural deflection, stiffness and ultimate bearing capacity. The effect of slip coefficient on the behavior of the new joint-slippage model and Ungkurupanian’s joint-slippage model is further discussed through structural response. The new model can be easily embedded into finite element analysis software and has the potential to be used in the design stage for accurately assessing the safety and reliability of galvanized steel structures.

A study on the effect of the deformations in flexiblocks on the behavior of the vehicle axle suspension mechanisms

This work deals with a study on the effect of the deformations in flexiblocks (bushings) on the behavior of the vehicle axle suspension mechanisms. The mechanism in study is a representatiove one for the structural group/class of mono-mobile axle suspension systems, namely the guiding mechanism by five points - on five spheres (so called 5SS). In a previous work, it was established that the rigid joint model for this class of mechanisms does not provide results close to the real flexible bushing model, reason for which the research in this paper is directed towards the identification of a theoretical model of joint which, at a lower complexity than that of the real model, would still provide viable results, in terms of axle guidance accuracy in the spatial movement relative to car body. In this regard, static and kinematic models were developed and analyzed by using the MBS (Multi-Body Systems) software solution ADAMS.

Mode-II fracture behavior evaluation for adhesively bonded pultruded GFRP/steel joint using four-point bending test

The pure mode-II fracture behavior of an adhesively bonded glass fiber reinforced polymer (GFRP)/steel joint was experimentally investigated using a four-point end-notched flexure (4ENF) test. Cracking of the 4ENF specimen initiated and propagated in the adhesive-steel surface. The dominant failure mode observed in all specimens was adhesive-steel interface failure. The compliance of the 4ENF specimen was determined with the rigid joint model and finite element method. The extended global method was employed to obtain a simple analytical solution of the mode-II energy release rate, and the corresponding results were compared with that determined by the virtual crack closure technique (VCCT). The full R-curve for the pure mode-II fracture behavior of an adhesively bonded pultruded GFRP/steel joint was obtained. Then, the VCCT was used to determine the load–displacement curves of the 4ENF specimens for validating the accuracy and applicability of the pure mode-II fracture criteria of the adhesively bonded pultruded GFRP/steel joint.

Evaluasi Level Kinerja Bangunan Gedung Kayu Bertingkat Rendah Akibat Beban Gelombang

Several coastal areas in Indonesia are at risk of moderate to high tsunami disasters, this is related to the condition that Indonesia is located in an earthquake high risk area. At this time there are many buildings located on the coast with a low-rise stilt house system with the main structural system, namely beams and columns using timber materials. The building structure design includes the performance evaluation process, namely strength, stiffness and structural stability. The purpose of this research is to study the evaluation behavior of performance levels, especially the strength and stiffness of low-rise timber buildings, namely the level of structural performance due to gravity and lateral loads, namely sea waves. The research scope is a three-story building with a beam and column frame structure system. Columns are circular and beams have a square cross section. The loads taken into account are gravity and lateral. The strengths discussed are the bending capacity of the beam and the compressive capacity of the column. In order to obtain building behavior that is closer to real conditions, especially in beam-column joints, secondary data is used, namely empirical data on the envelope load-deformation curve of the beam-column joint test results in the laboratory (modeled as link property). Evaluation of structural performance begins with structural analysis using SAP2000 software, to obtain internal forces and building drift. The results show that the use of link properties in beam-column joint joints in the timber building structures shows greater deformation results compared to rigid joint models, this indicates that modeling the structure with beam-column joint joints modeled as link property has an impact on building stiffness. Lower and represents the condition of a timber building with beam-column joint characteristics closer to the actual condition. The existence of a hole size in the column (to insert the beam) which is larger than the cross-sectional size of the beam results in the rotation of the joint not being zero and a slip occurs when the joint works to transmit internal forces.

Rigid-Joint-Model Feedforward with Elastic-Joint-Model Feedback for Motion Control of a 6-DOF Industrial Robot

This paper presents a fast and exact trajectory control scheme for articulated robot arms with elastic joints due to reduction gears. This scheme provides a practical solution for sophisticated motion control of general industrial robots using motor-side measurements only. We previously proposed a torsion-angular velocity feedback (TVFB) scheme for suppressing residual vibration in the tip of a 2-DOF robot arm, using a physically parameterized nonlinear observer. To execute exact trajectory control, we also combined a feedforward scheme based on a rigid-joint model with TVFB, due to the complexity of implementing feedforward based on an elastic-joint model. TVFB suppressed arm-tip vibrations caused by feedforward mismatch between the rigid- and elastic-joint models. In this paper, we extend the scope of the combined scheme to a 6-DOF industrial robot. We implement a real-time controller with complete direct and inverse dynamic models for the feedback and feedforward. The effectiveness of our approach was successfully validated in several experiments.

Simplified assessment of the need for the explicit model of RC beam‐column joints instead of the rigid model

The behaviour of reinforced concrete beam‐column (RCBC) joints may have an important influence on the structural behaviour of unbraced framed structures—this explains why current technical specifications require accounting for their deformation. However, the available numerical models for RCBC joints are rather complex, so that, at the end of the day, these joints are commonly modeled using one of two alternative simplified models: the rigid joint model and the centerline joint model. This calls for the development of “Simplified Classification Criteria”, which are simplified procedures to assess the influence of RCBC joints on the structural behaviour, that is, to determine whether a simplified joint model can be employed in the numerical model of the overall structure without leading to major errors in the analysis. This paper focuses on the possibility of using the rigid joint model. As a starting point for the step‐by‐step development of general classification criteria for RCBC joints we employ the basic simplified classification criterion already existing for steel beam‐column joints.

Buckling analysis of bilayer beam-columns with an asymmetric delamination

A general analytical model is developed to evaluate buckling behavior of a bilayer beam-column with a through-the-width asymmetric delamination under simply supported boundary conditions. Both transverse shear deformation and local deformation at delamination tip are taken into account in the model by considering two sublayers in both delaminated and intact regions as two individual shear deformable ones. Interface continuity conditions, which account for effect of interface normal and shear stresses, are also introduced in the intact regions. Furthermore, the present model is capable of dealing with the case of delamination located arbitrary through thickness and along length of beam-columns. In comparisons with the results of classical Euler-Bernoulli beam model, Timoshenko beam model (rigid joint model) and finite element analysis, better agreements are achieved for the present flexible joint model, which captures local deformation at delamination tip due to consideration of interface normal and shear stress components. Parametric studies are conducted to evaluate influences of sublayer thickness ratio, delamination length, delamination location, specimen length, and material parameters on the critical buckling strain with emphasis on transverse shear deformation and local deformation at delamination tip. The developed model can be used with confidence in buckling analysis of layered structures with an arbitrary delamination through the length and thickness.

Mixed mode fracture characterization of GFRP-concrete bonded interface using four-point asymmetric end-notched flexure test

A combined analytical and experimental study using an asymmetric end-notched flexure specimen under four-point bend loading is conducted to characterize the fracture of glass fiber reinforced polymer (GFRP)-concrete bonded interface. Both the classic composite (rigid joint) and interface deformable (flexible joint) bi-layer beam models are used to calculate the compliance and energy release rate (ERR) of the proposed four-point asymmetric end-notched flexure (4-AENF) specimen. The validity and accuracy of the models are obtained by comparison with the numerical finite element results. The results show that the flexible joint model predicts more accurately the compliance and ERR compared with those of rigid joint model in 4-AENF specimen due to the attribute of crack tip deformation. Moreover, the calculated ERR by the flexible joint model can be reduced to that of the rigid joint one when the specimen is properly sized. Then, the designed 4-AENF specimens are utilized to characterize the fracture toughness of GFRP-concrete bonded interface. To overcome the obstacle of low tensile strength and cracking behavior of concrete and prevent the premature fracture of concrete substrate before debonding of bonded interface takes place, a reduced section scheme is adopted and the steel bars are used to reinforce the concrete substrate beams. An aluminum beam with different thickness is bonded to the thin GFRP layer so as to change the stiffness of the composite GFRP/aluminum substrate, resulting in different fracture mode mixities. The fracture toughness values of GFRP-concrete bonded interface under three different mode ratios are obtained. The proposed 4-AENF specimen and data reduction procedures for interface fracture toughness evaluation can be used to effectively characterize mixed mode and mode-II dominated fracture of hybrid material bonded interface.

Influence of joint modelling on the pushover analysis of a RC frame

In general, conventional analysis and design of reinforced concrete (RC) frame structures overlook the role of beamcolumn (RCBC) joints. Nowadays, the rigid joint model is one of the most common for RCBC joints: the joint is assumed to be rigid (unable to deform) and stronger than the adjacent beams and columns (does not fail before them). This model is popular because (i) the application of the capacity design principles excludes the possibility of the joint failing before the adjacent beams and (ii) many believe that the actual behaviour of RCBC joints designed according to the seismic codes produced mainly after the 1980s can be assumed to be nominally rigid. This study investigates the relevance of the deformation of RCBC joints in a standard pushover analysis at several levels: frame, storey, element and cross-section. Accordingly, a RC frame designed according to preliminary versions of EN 1992-1-1 and EN 1998-1 was analysed, considering the nonlinear behaviour of beams and columns by means of a standard sectional fibre model. Two alternative models were used for the RCBC joints: the rigid model and an explicit component based nonlinear model. The effect of RCBC joints modelling was found to be twofold: (i) the flexibility of the joints substantially increases the frame lateral deformation for a given load (30 to 50%), and (ii) in terms of seismic performance, it was found that joint flexibility (ii-1) appears to have a minor effect on the force and displacement corresponding to the performance point (seismic demand assessed at frame level), but (ii-2) has a major influence on the seismic demand when assessed at storey, element and cross-section levels.

Mode II Fracture of GFRP Laminates Bonded Interfaces under 4-ENF Test

This experiment studies the mode II fracture behavior of an adhesively bonded joint composed of GFRP laminates. A new beam model is presented to calculate the mode II ERR for GFRP bonded 4-ENF specimens. In this model, the deformation of 4-ENF specimens caused by the relative deflection angle between the upper and lower layers and by the bending deformation of the upper and lower layers, respectively, is introduced; the effect of the adhesive layer deformation is presented. The closed-form analytical solutions of compliance and energy release rate based on the crack compliance method are obtained. The high accuracy of present analytical solutions are verified by finite element analysis through bonded GFRP 4-ENF specimens and compared to the rigid joint model and the CBT model. The interfacial crack propagation is numerically simulated using shear fracture toughness determined in this experiment, from which the predicted critical load results are in good agreement with the experimental results. The conclusion indicates that the compliance and ERR can accurately be predicted using the new bonded 4-ENF beam model.

Three-dimensional joint flexibility element for modeling of tubular offshore connections

Intubular jointsofoffshoreplatforms, jointsmay exhibitconsiderableflexibilitysincethematerialsinthechord members near the intersection zone of brace-chord behave as shell-like structures. The resulting flexibility may have sig- nificant effects on the local and overall behavior of offshore platforms. This study describes the derivation of a three-di- mensionaljointflexibilityelement whichisbasedonphysical interpretationofbehaviorofatubularjointupondeformation. Theelementisdevelopedonthebasisofflexibilitymatrixand implemented in a finite element program to account for local joint flexibility effects in numerical models of jacket-type offshore platforms. Results are validated by more sophisti- cated multi-purpose software and compared against conven- tional rigid-joint models which are widely employed in practice. According to the results, the accuracy of response predictionsisimprovedwhentheeffectsofjointflexibilityare considered. This model can be used for predicting more ac- curate response of jacket-type offshore platforms.

On the need for classification criteria for cast in situ RC beam–column joints according to their stiffness

The purpose of this paper is to draw attention to the lack, in current technical specifications, (i) of guidelines on the modelling of cast in situ reinforced concrete beam–column (RCBC) joints and, more specifically, (ii) for a given RCBC joint, of simplified procedures for evaluating if the fully rigid joint model is acceptable or not, having in view its effective stiffness. This is an important issue because, even though it is widely recognized that RCBC joints are a major source of deformation of cast in situ unbraced RC frames, there is no acknowledged simple procedure to assess the relevance of joint flexibility to the overall structural behaviour—as a consequence, the fully rigid joint model is commonly used without any reference to joint stiffness minimum required values. On the other hand, for steel frames, classification criteria for joints according to their stiffness have already been developed. This paper (i) shows that EN 1993-1-8: 2005 simplified classification criteria for steel joints according to their stiffness are inadequate for cast in situ RCBC joints, (ii) develops a modified version of these criteria, appropriate only for very particular conditions, which maintains their basic hypotheses but considers the specificities of RCBC joints and frames and (iii) in agreement with recently published results, concludes that, in some cases, RCBC joints should not be considered nominally rigid and thus their flexibility should be explicitly accounted for in the analysis of unbraced RC frames. The developed simplified classification criteria apply only to very particular cases—some guidance is therefore also provided on the development of general simplified classification criteria for RCBC joints.

Elastic tubular joint element for modelling of multi-brace, uni-planar tubular connections

Traditionally, an analytical model of an offshore structure is composed of beam-column elements rigidly interconnected. However, considerable flexibility exists at the joints where chord outer wall deforms locally, and produces flexibility. In this paper, a new elastic joint element is introduced to consider the local flexibilities for TY- and K-type tubular joints. The element is developed on the basis of flexibility matrix and it is implemented in a finite-element programme to account for local joint flexibility effects in numerical models of steel structures made from tubular members. The element is suitable for modelling of multi-brace, uni-planar tubular joints. The results are validated by more sophisticated model using multi-purpose programmes and compared against conventional rigid-joint models. Based on the results of this study, it is concluded that incorporating the effects of joint flexibility results in more realistic response prediction of offshore structures.

Modeling of Flange Joints for the Nonlinear Dynamic Analysis of Gas Turbine Engine Casings

The finite element analysis of individual components of aircraft engine casings provides high accuracy and a good agreement with the measured response data. However, when these components are assembled, the accuracy of such predictions can significantly deteriorate since models describing stiffness and friction properties of joints are linearized. A full nonlinear analysis of the casing flanges is required to fully include the influence of the bolted joints, model the flexibility in the contact interface, and consider the nonlinear behavior of the contact due to partial slip and separation. In this paper different nonlinear models of casings are investigated with an available nonlinear analysis tool: A parametric study of the contact interface meshes is conducted to identify a satisfying analysis approach. The dynamic flange behavior is analyzed in detail, including effects of the bolt and normal load distribution. A comparison of the introduced nonlinear modeling with more traditional rigid or linear-elastic flange joint models is carried out to evaluate the effect of the nonlinear approach. The study demonstrates the nonlinear nature of a casing flange joint and highlights the need to include them in the analysis. The detailed modeling of the contact interaction of joints gives an insight in the nonlinear contact behavior of flanges of aircraft engine casings, and the predictive capabilities for the nonlinear analysis of gas turbine engines.

Fracture characterization of Carbon fiber-reinforced polymer-concrete bonded interfaces under four-point bending

A combined analytical and experimental approach is presented to characterize both mode-II and mixed mode fracture of Carbon fiber-reinforced polymer-concrete bonded interfaces under four-point bending load, and closed-form solutions of compliance and energy release rate of the mode-II (four-point symmetric end-notched flexure) and mixed (four-point asymmetric end-notched flexure) mode fracture specimens are provided. The transverse shear deformation in each sub-layer of bi-material bonded beams is included by modeling each sub-layer as an individual first order shear deformable beam, and the effect of interface crack tip deformation on the compliance and energy release rate are taken into account by applying the interface deformable bi-layer beam theory (i.e., the flexible joint model). The improved accuracy of the present analytical solutions for both the compliance and energy release rate is illustrated by comparing with the solutions predicted by the conventional rigid joint model and finite element analysis. The fracture of Carbon fiber-reinforced polymer-concrete bonded interface is experimentally evaluated using both the four-point symmetric and asymmetric end-notched flexure specimens, and the corresponding values of critical energy release rates are obtained. Comparisons of the compliance rate-changes and resulting critical energy release rates based on the rigid joint model, the present theoretical model, and numerical finite element analysis demonstrate that the crack tip deformation plays an important role in accurately characterizing the mixed mode fracture toughness of hybrid material bonded interfaces under four-point bending load. The improved solution of energy release rates for the four-point symmetric and asymmetric end-notched flexure specimens by the flexible joint model can be used to effectively characterize hybrid material interface, and the fracture toughness values obtained for the Carbon fiber-reinforced polymer-concrete interface under mode-II and mixed mode loading can be employed to predict the interface fracture load of concrete structures strengthened with composites.

Local Delamination Buckling of Laminated Composite Beams Using Novel Joint Deformation Models

Local delamination buckling formulas for laminated composite beams are derived based on the rigid, semirigid, and flexible joint models with respect to three bilayer beam (i.e., conventional composite, shear-deformable bilayer, and interface-deformable bilayer, respectively) theories. Two local delamination buckling modes (i.e., sublayer delamination buckling and symmetrical delamination buckling) are analyzed and their critical buckling loads based on the three joint models are obtained. A numerical finite-element simulation is carried out to validate the accuracy of the formulas, and parametric studies of delamination length ratio, the transverse shear effect, and the influence of interface compliance are conducted to demonstrate the improvement of the flexible joint model compared to the rigid and semirigid joint models. The explicit local delamination buckling solutions developed in this study facilitate the design analysis and optimization of laminated composite structures and provide simplified and improved practical design equations and guidelines for buckling analyses.