Rigid Joints Research Articles

Simplified methods to predict the robustness of steel parking-structure joints

An innovative simplified method for incorporating the behaviour of structural joints in structural analyses of steel parking-structure is proposed in this study. The method is based on the conventional mechanical modelling of joints through special springs that accommodate the arching effect and moment-axial force (M-N) interaction. The characterization of these springs in terms of stiffness and resistance is performed using analytical formulae. The accuracy of the proposed method is validated through comparisons to results from advanced numerical methods conducted on a multi-scale approach. Its implementation in sub-structure models is then demonstrated, with the main advantage of extremely reducing the modelling and computational time. Validated sub-structure models are finally employed to investigate the influence of the joint properties on the response of parking structures under vehicle collision scenarios. The results show that considering the rigid and semi-rigid joints in the research are characterised by the welded and bolted connections in the research, for a structure built in a courtyard, bolted connections (semi-rigid joints) are recommended, while for the same structure built near an urban road, welded connections (rigid joints) should be considered to enhance the overall robustness.

A Reinforcement Learning Approach for Continuum Robot Control

Rigid joint manipulators are limited in their movement and degrees of freedom (DOF), while continuum robots possess a continuous backbone that allows for free movement and multiple DOF. Continuum robots move by bending over a section, taking inspiration from biological manipulators such as tentacles and trunks. This paper presents an implementation of a forward kinematics and velocity kinematics model to describe the planar continuum robot, along with the application of reinforcement learning (RL) as a control algorithm. In this paper, we have adopted the planar constant curvature representation for the forward kinematic modeling. This choice was made due to its straightforward implementation and its potential to fill the literature gap in the field RL-based control for planar continuum robots. The intended control mechanism is achieved through the use of Deep Deterministic Policy Gradient (DDPG), a RL algorithm that is suited for learning controls in continuous action spaces. After simulating the algorithm, it was observed that the planar continuum robot can autonomously move from any initial point to any desired goal point within the task space of the robot. By analyzing the results, we wanted to recommend a future direction for research in the field of continuum robot control, specifically in the application of RL algorithms. One potential area of focus could be the integration of sensory feedback, such as vision or force sensing, to improve the robot’s ability to navigate complex environments. Additionally, exploring the use of different RL algorithms, such as Proximal Policy Optimization (PPO) or Trust Region Policy Optimization (TRPO), could lead to further advancements in the field. Overall, this paper demonstrates the potential for RL-based control of continuum robots and highlights the importance of continued research in this area.

Improvement on the axial force accuracy of the ANCF Euler-Bernoulli beam element with the second-order approximate function of the centerline and precise constraint equations

The conventional Euler-Bernoulli beam element of the absolute nodal coordinate formulation (ANCF) yields incorrect axial force due to the existence of the first-order approximate function of the centerline and over-constraint equations. This work aims to improve the axial force accuracy of the element by using the second-order centerline approximate function and precise constraint equations. The second-order function includes the quintic Hermite shape function and the vector of nodal coordinates containing zeroth to second-order derivatives of position. The elastic force vector of the element and its tangent stiffness were then formulated based on the decoupled elastic line method. The exact kinematic requirements of three types of constraint points were fully clarified. On this basis, the corresponding concise constraint equations, constraint Jacobian and Hessian matrices were rigorously derived in the context of ANCF, where G2 continuity was demonstrated to be satisfied at the node acted by an inclined concentrated force, the relative rotation constraint of the rigid joint was described using the dot product of the gradients on both sides of the joint, and the fixing gradient direction at the partially-clamped end was expressed by using the zero cross product of the end gradients in the initial and deformed configurations. Large deformation problems of typical beams under fixed and follower loads were solved using five types of elements, where the results of the ABAQUS B22 elements were taken as a reference for validation. It is found that when using the first- and second-order beam elements having over-constraint equations of the three types of constraint points, obvious axial force error occurs near the corresponding constraint points. In comparison, a few second-order elements containing the derived constraint equations output correct axial force consistent with ABAQUS. However, a large number of the first-order elements containing the correct constraint equations still yield inaccurate axial force in certain beam regions.

Imbalance and gait impairment in Parkinson's disease: discussing postural instability and ataxia.

Gait and balance difficulties pose significant clinical challenges in Parkinson's disease (PD). The impairment of physiological mechanisms responsible for maintaining natural orthostatism plays a central role in the pathophysiology of postural instability observed in PD. In addition to the well-known rigidity and abnormalities in muscles and joints, various brain regions involved in the regulation of posture, balance, and gait, such as the basal ganglia, cerebellum, and brainstem regions like the pontine peduncle nucleus, are affected in individuals with PD. The recognition of the cerebellum's role in PD has been increasingly acknowledged. Cortical areas and their connections are associated with freezing of gait, a type of frontal lobe ataxia commonly observed in PD. Furthermore, impairments in the peripheral nervous system, including those caused by levodopatherapy, can contribute to gait impairment and imbalance in PD patients. Consequently, individuals with PD may exhibit frontal ataxia, sensory ataxia, and even cerebellar ataxia as underlying causes of gait disturbances and imbalance, starting from the early stages of the disease. The complex interplay between dysfunctional brain regions, impaired cortical connections, and peripheral nervous system abnormalities contributes to the multifaceted nature of gait and balance difficulties in PD. Understanding the intricate mechanisms is crucial for the development of effective therapeutic approaches targeting these specific deficits in PD.

Translucent monolithic zirconia titanium-supported FP1 full-arch prosthesis: A novel proof of concept to address esthetic, functional, and biologic challenges.

Despite the wide clinical use of translucent zirconia for full-arch implant prostheses, reduced flexural strength and fracture toughness compared with high-strength opaque zirconia needs to be addressed. A novel proof of concept for FP1 full-arch prosthesis featured by translucent monolithic zirconia and titanium framework was presented. Computer-guided implant planning and surgery were executed and digitally designed FP1 temporary prosthesis prefabricated. Implant and prosthetic placement were achieved with a set of three-dimensional (3D)-printed templates. Implants were immediately loaded. After 4 months intraoral optical scan was taken to record implant coordinates, soft tissue anatomy, and temporary FP1 prosthesis. A novel digital workflow was used to design and mill overlaying translucent zirconia and anatomically shaped titanium framework with a scalloped soft-tissue interface. Final FP1 prosthesis was assembled cementing zirconia jacket on titanium counterpart. Translucent zirconia supported by titanium framework can address esthetic and mechanical requirements of FP1 full-arch prosthesis, minimizing risk of fracture and providing a rigid and passive joint with supporting implants. The smooth and highly polished titanium surface with an anatomic design, tightly matching scalloped soft tissue interface, can limit food impaction, air and saliva leakage and contribute to overall biologic integration of FP1 full-arch prosthesis. Translucent monolithic zirconia featured with anatomically shaped titanium framework with scalloped transmucosal part, combining a pleasant esthetic outcome with increased flexural strength and fracture toughness, may be indicated to increase the clinical performance of FP1 full-arch prosthesis.

A JOINT WEARABLE STRUCTURAL REINFORCING DEVICE FOR VIBRATION SUPPRESSION IN ROBOTIC MILLING

The structural vibration caused by poor rigidity is one of the main obstacles limiting the machining efficiency of robot milling. The existing vibration suppression strategies mainly focus on process parameter optimization, passive vibration absorption at the end and feedback control of joint motor. Although these strategies have certain vibration suppression effects, they cannot directly improve the structural rigidity of the robot. In this paper, a joint wearable structural reinforcing device (JWSRD) is proposed, which can achieve vibration suppression effect by improving the rigidity of the robot joints, fundamentally improve the processing ability of the robot, and ensure the processing stability. Firstly, the structure of the device is designed without affecting the processing flexibility. Secondly, the braking torque of the JWSRD is tested. Considering the feedback of joint braking torque, the vibration simulation model under harmonic excitation is derived. Finally, the offset mass experiments are carried out to verify the vibration suppression effect of the JWSRD. The results show that the JWSRD installed on the robot joint has the notable potential to enhance the structural rigidity, reduce the machining vibration and improve the machining efficiency.

Finite Element Analysis and Parametric Study of Panel Zones in H-Shaped Steel Beam–Column Joints

This paper investigates the mechanical properties of a traditional welded rigid joint with a weakened panel zone under seismic load. The created finite element model is calibrated by the high-strength steel joint test, carried out by the team in the early stage, and the effectiveness of the finite element method was verified. The finite element software ABAQUS is used to investigate the influence of different joint web thicknesses on the mechanical properties of middle column joints under a low-cyclic-loading test. Supported by a validated numerical model, the ductility, energy dissipation, and other properties of different thicknesses of panel zone column webs are carefully analyzed. The results indicate that the thickness of the web plate in the panel zone significantly affects the location of the joint plastic hinge. The ultimate loading capacity of the joints increased significantly with an increase in the thickness of the webs in the panel zones. Compared with the joint with a weakened panel zone, the hysteresis curve of the strengthened joint is fuller; meanwhile, it cannot alleviate the stress concentration at the weld holes of the web. When the thickness of the joint domain web is too weak, excessive deformation in the joint domain will lead to a decrease in the bearing capacity of the joint, causing damage. The stiffness degradation coefficient of the web-thickened specimen was found to be dominated and controlled by the stiffness of the beam; however, with an increase in the thickness of the web, the stiffness degradation coefficient remained basically unchanged. Finally, a recommendation for weakened beam–column interior joints based on the steel frame panel zone is made, which will lay a foundation for the simulation and analysis of the seismic performance of this structure.

Osteotomies around the knee alter alignment of the ankle and hindfoot: a systematic review of biomechanical and clinical studies

Purpose Emerging reports suggest an important involvement of the ankle/hindfoot alignment in the outcome of knee osteotomy; however, a comprehensive overview is currently not available. Therefore, we systematically reviewed all studies investigating biomechanical and clinical outcomes related to the ankle/hindfoot following knee osteotomies. Methods A systematic literature search was conducted on PubMed, Web of Science, EMBASE and Cochrane Library according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and registered on international prospective register of systematic reviews (PROSPERO) (CRD42021277189). Combining knee osteotomy and ankle/hindfoot alignment, all biomechanical and clinical studies were included. Studies investigating knee osteotomy in conjunction with total knee arthroplasty and case reports were excluded. The QUality Appraisal for Cadaveric Studies (QUACS) scale and Methodological Index for Non-Randomized Studies (MINORS) scores were used for quality assessment. Results Out of 3554 hits, 18 studies were confirmed eligible, including 770 subjects. The minority of studies (n = 3) assessed both high tibial- and distal femoral osteotomy. Following knee osteotomy, the mean tibiotalar contact pressure decreased (n = 4) except in the presence of a rigid subtalar joint (n = 1) or a talar tilt deformity (n = 1). Patient symptoms and/or radiographic alignment at the level of the ankle/hindfoot improved after knee osteotomy (n = 13). However, factors interfering with an optimal outcome were a small preoperative lateral distal tibia angle, a small hip–knee–ankle axis (HKA) angle, a large HKA correction (>14.5°) and a preexistent hindfoot deformity (>15.9°). Conclusions Osteotomies to correct knee deformity alter biomechanical and clinical outcomes at the level of the ankle/hindfoot. In general, these changes were beneficial, but several parameters were identified in association with deterioration of ankle/hindfoot symptoms following knee osteotomy.

Structural performance of a novel combined nested bolted joint for aluminum alloy mega-latticed structures

A novel steel-aluminum joint system is first presented for aluminum alloy mega-latticed structures. This joint can be effectively applied to the connection of large-diameter tube members with complex spatial locations in space structures. The joint's finite element model is examined and validated, followed by a case study of one joint, including static analysis and an analysis of the bending moment-rotation curve. According to the moment-rotation curve, the joint is classified as a type of semi-rigid joint. Furthermore, the analysis considers key parameters that impact the joint's bending, axial, and torsional performance, such as the number of bolts per ring, the rings of bolts, and the thickness of the joint zone. Two simplified formulas for joint stiffness are proposed to evaluate the overall structural stability. Finally, a stability analysis of an aluminum alloy mega-latticed structure is conducted, incorporating this joint and the proposed simplified formulas. The ultimate load of the mega-latticed structure with the joints is found to be about 0.7 of that with ideal rigid joints with the same parameters. This paper presents a potential solution for appropriate connections in large-span aluminum alloy mega-lattice structures, thereby serving as a reference for the design of the joints in related space structures.

Исследование рассеяния энергии и жесткости сварных соединений стыковой сварки давлением

Introduction. When studying the energy dissipation associated with internal friction in a weld, it is extremely important to choose a measurement technique, since the reliability and integrity of the data obtained depends on it. At the same time, it is necessary to investigate the change in internal friction depending on the presence of defects in the weld. Of the variety of methods for non-destructive testing of joints obtained by pressure welding, only ultrasonic is currently used. However, lightly oxidized lacks of welding penetration are not detected, which can be detected only in the presence of other defects accompanying it. Compounds of dissimilar materials are not controlled by ultrasound at all. Therefore, the development of non-destructive testing methods for such compounds is very relevant. The purpose of the work: to find a procedure for testing the quality of a welded joint in metals and alloys that will be a quick and simple alternative to the known methods of non-destructive testing, by measuring the energy dissipation in the weld of the sample by the static hysteresis loop method. The method of investigation is non-destructive quality control of the welded joint in metals and alloys by measuring the energy dissipation in the weld of the sample by the static hysteresis loop method. Results and discussion. It is established that with an increase in the lacks of welding penetration, the energy dissipation increases at the same values of the torque amplitude under static loading conditions. The rigidity of the qualitative welded joints remains constant, and the joints with lacks of welding penetration decrease with increasing torque amplitude. The relationship of strength with stiffness and damping ability obtained by the static hysteresis loop method is preserved for various structural states of the sample material.

I‐beam to RHS‐column joints with welded studs under cyclic loading

AbstractThe design of removable beam‐column joints between open structural steel beams and rectangular hollow section (RHS) columns is not easy because of the inaccessibility to the tube interior from outside. I‐beam to RHS‐column joints with threaded welded studs are of great interest due to their low‐cost assembling technique and easy on‐site execution. This study examines the cyclic performance of these joints with welded studs. A quasi‐static experimental study on the cyclic response of eight joint specimens is described. The strength of the joint and the failure modes were revealed. The ductility of the joints was also evaluated according to the rotation capacity after yielding, classifying all of them as having intermediate ductility and, therefore, implying some capacity to withstand limited plastic deformations when subjected to seismic forces. Some equations were also used to classify the joints according to the components that mainly govern the deformation of the full joint. In addition, the energy dissipation rate was assessed for all the specimens, finding the highest energy dissipation rates in the most rigid joints.

Full-scale experimental study and mechanical model for beam-wall joints of prefabricated enclosure structure

Owing to long exposure to the urban environment, the construction technology of the enclosure structure is closely related to the urban low-carbon development. Shenzhen Metro has recently proposed a novel prefabricated enclosure structure and demonstrated its application. Among them, the mechanical properties of the beam-wall joint between precast diagram wall and precast beam are the core for the performance of the prefabricated enclosure structure. This study demonstrated foremost the application of prefabricated enclosure structure and its key joint mechanical model in Shenzhen Metro Phase V stations. First, this study conducted a full-scale bending experimental study on beam-wall joints and continuous joints. Second, the Joint Coordinating Contact Model (JCCM) of the beam-wall joint was proposed. Third, the model was validated and assessed by using the experiment data. The main conclusions include: (1) The beam-wall joint showed semi-rigid properties despite using reliable assembly. (2) The performance degradation of the beam-wall joint originated from the interface. The interface weak link changed the solid continuity of the joint. (3) With reasonable rebar splices (≥66%), the joint stiffness does not change substantially. However, the joint performance with too few rebar splice showed significant degradation (≤33%). (4) JCCM assessment suggested a rigid beam-wall joint by enlarging the joint height by 31.3% and using 44% rebar splice ratio. The research achievement provides a theoretical basis and application value for the assessment of beam-wall joints and the promotion of prefabricated enclosure structures.

Parkinson Disease

Parkinson's disease is a disorder of brain function caused by the process of degeneration of the basal ganglia in the substantia nigra pars compacta (SNc) cells and is characterized by characteristics such as tremor at rest, rigidity of muscles and joints (rigidity), slowness of movement and speech (bradykinesia) and instability upright position (postural instability). Parkinson's Disease occurs in the range between the ages of 55 to 65 years and occurs in 1% -2% of people over the age of 60 years, increasing to 3.5% at the age of 85-89 years. Approximately 0.3% of the general population, the prevalence is higher in males than females with a ratio of 1.5:1.0. Manifestations that can be found in patients with Parkinson's Disease can be assessed through the Hoehn and Yahr Scale (HY). Current treatment for Parkinson's disease aims to reduce motor symptoms and slow the progression of the disease.

Nonlinear dynamics of bolted joined conical-cylindrical shells considering displacement-dependent characteristics

This paper investigates the nonlinear dynamic characteristics of joined conical-cylindrical shells (JCCSs) with bolt connection for the first time. In the process of developing mechanical model of the bolt connection, the displacement-dependent stiffness and damping are taken into account, which could simulate the change of the contact state at the connection interface under different excitations. Both theoretical and experimental studies are performed to illustrate the nonlinear vibration behaviors of the bolted JCCSs. Successive uniform distributed artificial springs between the conical and cylindrical shells are adopted to simulate the rigid joint of the two shells. Donnell's shell theory is employed in theoretical modeling, and the governing equation is obtained by the Lagrange equation. The displacement admissible function applied in the research is Chebyshev polynomial. By comparison with existing literature and experimental data, the accuracy of present theoretical model is validated. It is found that both theory and experiment show a dynamic softening phenomenon with the increase of excitation level. Taking the displacement-dependent characteristics in bolt connection zone into consideration can effectively illustrate this soft phenomenon. The established model is capable of predicting the nonlinear vibration characteristics of JCCSs with bolt connection.

SUGGESTIONS FOR IMPROVEMENTS IN TIMBER PORTAL FRAME DESIGN WITH SEMI-RIGID KNEE JOINTS

Timber portal frames assembled on the construction site are the most suitable solution from the point of view of limitations of transportation options. However, the connections of the rafters and columns assembled at the construction site in the knee joints, using bolts, show a certain tendency to show plastic deformations under load. In addition, the transmitted shear forces at the knee joint form different angles with the fiber direction in the rafter and column elements. Service experience of timber portal frames shows that the vertical displacement of the apex point increases, also cracks appear in the rafter elements near the knee joints over time. Unfortunately, code design formats do not present specifications for timber structures incorporating L-shape joints with mechanical fasteners. This article presents the results of studies that confirm the need to supplement the design rules for wooden portal frames. It is recommended to implement the rotational spring constant when define rigidity of L-shape joints for RFEM model of structure. The Hoffman failure criterion has been chosen as the most appropriate of the known ones for evaluating the crack resistance of structural wooden elements, because this criterion includes more important specific properties affecting the development of plastic deformations and the formation of cracks in wood.

Comparative Analysis of Steel Structure with Rigid and Semi Rigid Joint using Analysis Tool ETABS

Generally, in steel structure the connection between beam and column are designed as moment connection and pinned connection, but in actual condition the structure behaves between these two conditions, resulted into semi-rigid condition which is intermediate stage between rigid and pinned joints. Effect of semi-rigid connection on multi-story multi-bay frame is accomplished in this Study. The present study introduces the effect of static and dynamic loading on high rise steel structure of G+12 story with 4m, 6m and 8m three bay span length. Structure is analyzed under two different condition of partial release of semi-rigid connections which is derived by fixity factor of values 0.5 and 0.75 in this study. The analysis is done commercially available software ETABS. From the non-linear analysis, the story displacement and story drift are obtained. The overall performance of the structure from the analysis, semirigid joints display more story displacement and story drift compared to rigid joints. To overcome the results, bracing system is introduced at different location of periphery of structure. These brace frame structure consist of X- bracing and diagonal bracing. Again, comparative analysis is to be performed in ETABS on these three-bay span lengths. It is found that braced semi-rigid frame structure perform quite well as compared to unbraced frame structure.

Tibial Bone Transport with a Single Implant All-Internal Bone Transport Nail.

A single implant all-internal magnet-driven bone transport (BT) intramedullary nail (BTN - NuVasive Specialized Orthopaedics, Inc.) has recently been introduced as a treatment method for segmental tibial bone defects. This innovation provides promise in the management of segmental bone defects as it negates numerous complications associated with circular external fixation and the need for multiple implants when considering hybrid plate assisted bone segment transport (PABST) constructs. Given the novelty of the BTN, description of the surgical application and patient outcome measures are scarce in the current literature. To date, we have treated four patients with an average age of 27 years (range: 19-44 years) using the BTN for segmental tibial defects ranging from 50-128 mm. We have accumulated data over an average follow up of 18.07 months (range: 12.96-25.13 months) demonstrating good patient tolerance of the device. Three patients successfully completed their treatment course with a calculated average bone healing index of 41.4 days/cm (range: 31.41-54.82 days/cm). One patient was noted to experience an asymptomatic docking site nonunion requiring subsequent surgery for nonunion repair. Implant-associated complications included symptomatic implant, axial malalignment, docking site nonunion, and External Remote Control technical malfunction. Injury-related complications were encountered and noted to include: superficial infection, wound dehiscence, peroneal tendonitis, and joint rigidity. In this study, the authors present a case series utilizing this implant to date and discuss our experiences with the BTN with reference to clinical indications, tibial bone preparation, BTN implantation, transport protocol, docking site procedure, and clinical/radiographic outcomes.

Concrete Structure by Using Carbon Nanotube and Its Use to Monitor Its Structural Health

Abstract: Cementitious materials doped with carbon nanoparticles are robust materials that can convert stress into changes in electrical resistance. These properties encourage the development of spatially distributed sensors for structural health monitoring of concrete structures. However, very few applications of cement-based nanocomposite transducers to structural elements have been documented. Most applications are limited to measuring static reactions. CNTs could effectively arrest crack propagation, increase joint rigidity, and reduce deformation of concrete corbels between steel ribs. Higher aspect ratio CNTs could make a better contribution with their micro crack bridging effect. Microscopic analysis confirmed the adequate distribution and bridging of micro cracks by CNTs and delayed the propagation of macro cracks within the transition zones between aggregate and reinforced concrete

Static analysis of structural grillages made of steel reciprocal beams

The article concerns structural grillages made of short reciprocally supported beams. The history of reciprocal structures, as well as origin of the renewed interest in them have been characterised in the introductory part of the article. The main part presents the methodology of forming the grillages from short beams and the results of a static analysis. It has aimed at comparing the values of maximum bending moments and deflections of the grillages, due to the load acting perpendicular to the plane of the grillage. The first series of tests has included the grillages differing in the beams configuration, which supported the identical square slab. The second series has included the grillages of analogous configuration, but supporting the square slabs of different sizes. The results prove that the configuration of the beams does not have a significant impact on the values of bending moments and deflections, which are mainly determined by the overall dimensions of the grillage. The conclusion is that configuration of grillage based on reciprocity of beams let to replace rigid joints with articulated ones, which does not affect the load-bearing capacity and facilitates construction of the grillage.

A study on the flexible Bricard mechanisms with plane-symmetric structure

The six-bar single-loop overconstrained Bricard linkages have been attracting continuous attention due to their special geometry and remarkable mobility. During the past century, a great number of papers have been published in various aspects, however, almost all of them focus on those only consisting of rigid links and joints. In this paper, the concept of ‘Flexible Bricard Mechanisms’ is introduced to extend these classical overconstrained linkages from the category of rigid-body systems to the scope of flexible ones. In these novel designs, slender elastic beams are used to replace the rigid links and joints, such that the mobility of flexible Bricard mechanisms is achieved not only via the relative motion from rigid joints, but also the large-scale deformations of elastic links. The plane-symmetric case is studied to demonstrate the realization, analysis methodology, and potential applications of this new type of Bricard mechanism. A candidate with a specialized structure is elaborated as a case study, about which a proof-of-concept prototype is developed. Preliminary experiments are conducted to verify the feasibility of the proposed idea.