Joint Stress Research Articles

Reliability analysis for bond stress of precast panel joints

Reliability analysis for bond stress of precast panel joints

Reliability analysis for bond stress of precast panel joints

Reliability analysis for bond stress of precast panel joints

Experimental Methods for Studying the Contact Mechanics of Joints.

Biomechanics researchers often experimentally measure static or fluctuating dynamic contact forces, areas, and stresses at the interface of natural and artificial joints, including the shoulders, elbows, hips, and knees. This information helps explain joint contact mechanics, as well as mechanisms that may contribute to disease, damage, and degradation. Currently, the most common in vitro experimental technique involves a thin pressure-sensitive film inserted into the joint space; but, the film's finite thickness disturbs the joint's ordinary articulation. Similarly, the most common in vivo experimental technique uses video recording of 3D limb motion combined with dynamic analysis of a 3D link-segment model to calculate joint contact force, but this does not provide joint contact area or stress distribution. Moreover, many researchers may be unaware of older or newer alternative techniques that may be more suitable for their particular research application. Thus, this article surveys over 50 years of English-language scientific literature in order to (a) describe the basic working principles, advantages, and disadvantages of each technique, (b) examine the trends among the studies and methods, and (c) make recommendations for future directions. This article will hopefully inform biomechanics investigators about various in vitro and in vivo experimental methods for studying the contact mechanics of joints.

Correlation between Temporomandibular Joint Disorders, Sleep Quality and Stress among Dental Students: A Cross-sectional Study

Introduction: Dental students are subjected to high levels of stress during their academic performance. The quality of sleep could also be affected in those with increased stress levels. Stress and sleep quality could be considered as risk factors in Temporomandibular Joint Disorders (TMD). Identification of the risk factors in TMD at the initial stages can lead to minimising the long term effects. Aim: To investigate the relationship between TMD symptoms, sleep quality and stress among dental students. Materials and Methods: A cross-sectional questionnairebased survey was conducted in the Department of Oral Medicine and Radiology, Sinhgad Dental College and Hospital, Pune, Maharashtra, India, from November 2021 to December 2021 among 255 dental students. Fonseca Anamnestic Index (FAI) questionnaire was used for evaluation of TMD, while Perceived Stress Scale (PSS) and Pittsburgh Sleep Quality Index (PSQI) were used to assess stress scores and sleep quality, respectively. The students were surveyed to categorise them, if they were showing any symptoms of mild, moderate or severe TMD. Similarly the sleep quality and stress scores were assessed. The relationship between TMD with stress and sleep quality was also evaluated. Data analysis was done using International Business Machines (IBM) Statistical Package for Social Sciences (SPSS) version 26.0. Comparison of frequencies of scores of PSS, PSQI and FAI within groups was done using Chi-square test. Bivariate correlation between PSS/PSQI, PSS/ FAI ad FAI/PSQI was assessed using correlation coefficient. Results: Out of 255 participants, 182 were females and 73 were males. It was observed that 221 (86.7%) students reported moderate stress levels, 21 (8.2%) students showed mild and 13 (5.1%) subjects showed high stress levels. Temporomandibular symptoms were reported as mild, moderate and severe in 130 (51%), 21 (8.2%) and 9 (3.5%) students, respectively. A total of 229 (89.8%) students showed poor sleep quality and 26 (10.2%) students showed good sleep quality. Moderate stress was correlated with poor sleep quality and mild TMD. Conclusion: The stress levels were significantly correlated with sleep quality and TMD symptoms. Thus, increased stress and poor sleep may be considered as risk factors of TMD. However, longitudinal studies in large samples are required to determine the cause and effect relationships between sleep quality, stress levels and TMD.

Board-Level Drop Impact Reliability Analysis of Dual-Side Molding System-in- Package (SiP) Modules

System-in-package (SiP) modules are widely used in portable electronics such as Internet of Things (IoT) devices and mobile consumer equipment since they integrate multiple components in a single package and thus facilitate device miniaturization. An advanced packaging technology referred to as dual-side molding (DSM) has recently been proposed as a means of achieving even smaller form factors and lower cost solutions. However, shrinking the package size reduces the solder joint connection area between the SiP module and the printed circuit board (PCB). Consequently, the board-level drop reliability may be severely impaired. Accordingly, the present study utilizes a numerical model to investigate the board-level solder joint reliability of a DSM SiP package in drop impact tests performed in accordance with the Joint Electron Device Engineering Council (JEDEC) standard. The validity of the numerical model combined with a full-factorial design method is then employed to examine the effects of the main design parameters of the DSM SiP package on the reliability of the solder joints in the drop impact test. Overall, the present results show that a higher EMC coverage of the solder ball joints yields a significant improvement in the solder joint reliability. In addition, a larger solder joint volume is beneficial in reducing the solder joint stress by absorbing a greater proportion of the impact load and energy produced in the drop impact event.

Finite element analysis to predict the cyclic performance of GFRP-RC exterior joints with diagonal bars

This paper presents a finite element modeling (FEM) approach to predict the cyclic response of glass fiber-reinforced polymer (GFRP) reinforced concrete (RC) exterior beam-column joints with different joint details. Four GFRP-RC exterior beam-column joints detailed with U or L-shaped anchorages at the end of the longitudinal bars of the beam, horizontal stirrups and additional diagonal bars (Z or U-shaped) at the joint region were modeled and analyzed under reversed cyclic loading. The FEM cyclic behavior in terms of load-drift ratio, cracking patterns, joint shear stress and strain evolutions were compared with the experimental behaviors. The FEM predicted load-drift ratio response, cracking patterns and dissipated energy showed good correlations with the experimental results. A parametric study was conducted to evaluate the influence of compressive strength of concrete, column axial load ratio and size of the additional diagonal bar on the performance of the GFRP-RC joints. It was found that an increase in the column axial load significantly degraded the performance in terms of strength, maximum joint shear stress and ductility of the GFRP-RC joints. Also, GFRP-RC joints with additional U-bars were able to resist higher joint shear stress and drift ratio than GFRP-RC joints with additional Z-bars, respectively.

Biomechanical application of finite elements in the orthopedics of stiff clubfoot

BackgroundThe purpose of this study was to evaluate the effect of varying the different correction angles of hindfoot osteotomy orthosis on the biomechanical changes of the adjacent joints after triple arthrodesis in adult patients with stiff clubfoot to determine the optimal hindfoot correction angle and provide a biomechanical basis for the correction of hindfoot deformity in patients with stiff clubfoot.MethodsA 26-year-old male patient with a stiff left clubfoot was selected for the study, and his ankle and foot were scanned using dual-source computed tomography. A three-dimensional finite element model of the ankle was established, and after the validity of the model was verified by plantar pressure experiments, triple arthrodesis was simulated to analyze the biomechanical changes of the adjacent joints under the same load with “3°” of posterior varus, “0°” of a neutral position and “3°, 6°, 9°” of valgus as the correction angles.ResultsThe peak plantar pressure calculated by the finite element model of the clubfoot was in good agreement with the actual plantar pressure measurements, with an error of less than 1%. In triple arthrodesis, the peak von Mises stress in the adjacent articular cartilage was significantly different and less than the preoperative stress when the corrected angle of the hindfoot was valgus “6°”. In comparison, the peak von Mises stress in the adjacent articular cartilage was not significantly different in varus “3°”, neutral “0°”, valgus “3°” and valgus “9°” compared with the preoperative stress.ConclusionThe results of this study showed that different angles of hindfoot correction in triple arthrodesis did not increase the peak von Mises stress in the adjacent joints, which may not lead to the development of arthritis in the adjacent joint, and a hindfoot correction angle of “6°” of valgus significantly reduced the peak von Mises stress in the adjacent joints after triple arthrodesis.

NUMERICAL ANALYSIS OF STRESS AND STRAIN STATE IN MEMBRANE WALLS WELD JOINTS PERFORMED BY SUBMERGED ARC WELDING

The article presents investigation on stress and strain state in weld joints of boiler membrane wall by performing numerical analysis (finite element method). The main purpose was to create 3D model which will correspond to real membrane wall geometry under consideration, which will allow to perform strength simulation of numerical models considering variable parameters depending on the temperature. The model was fragment of boiler membrane wall made of X10CrMoVNb9-1 pipe and 10CrMo9-10 flat bar welded with submerged arc method. The research included the assumption of boundary conditions such as temperature cycles, welding method, type of mounting and base materials or heat treatment cycle. Three simulations have been performed depended on base material and temperature cycle adopted. As a result of the simulations, the distribution of temperature, displacement and stress in analyzed cases were obtained. The numerical simulation in dissimilar welded joints X10CrMoVNb9-1 pipe and 10CrMo9-10 flat bar heat treated afterwards, showed that the differences in linear expansion coefficients favour the development of cracks in the welds caused by increased level of stress. In parallel materials used for boiler membrane walls are the reason for difficulties in determine the proper technology of welding, preheating temperature and post-weld heat treatment parameters. Simulations indicated that the state of stress in weld joint is dependent on type of parameters adopted, and in closest scenario to real conditions, simulation showed that post-weld heat treatment had no positive effect on the stress state caused by discrepancy in linear expansion coefficients of both base materials.

Medial meniscus posterior root tears and partial meniscectomy significantly increase stress in the knee joint during dynamic gait.

As a simple and invasive treatment, arthroscopic medial meniscal posterior horn resections (MMPHRs) can relieve the obstructive symptoms of medial meniscus posterior root tears (MMPRTs) but with the risk of aggravating biomechanical changes of the joint. The aim of this study was to analyze dynamic simulation of the knee joint after medial meniscus posterior root tear and posterior horn resection. This study established static and dynamic models of MMPRTs and MMPHRs on the basis of the intact medial meniscus model (IMM). In the finite element analysis, the three models were subjected to 1000N axial static load and the human walking gait load defined by the ISO14243-1 standard to evaluate the influence of MMPRTs and MMPHRs on knee joint mechanics during static standing and dynamic walking. In the static state, the load ratio of the medial and lateral compartments remained nearly constant (2:1), while in the dynamic state, the load ratio varied with the gait cycle. After MMPHRs, at 30% of the gait cycle, compared with the MMPRTs condition, the maximum von Mises stress of the lateral meniscus (LM) and the lateral tibial cartilage (LTC) were increased by 166.0% and 50.0%, respectively, while they changed by less than 5% during static analysis. The maximum von Mises stress of the medial meniscus (MM) decreased by 55.7%, and that of the medial femoral cartilage (MFC) increased by 53.5%. After MMPHRs, compared with MMPRTs, there was no significant stress increase in articular cartilage in static analysis, but there was a stress increase and concentration in both medial and lateral compartments in dynamic analysis, which may aggravate joint degeneration. Therefore, in clinical treatments, restoring the natural structure of MMPRTs is first recommended, especially for physically active patients.

Variation in stress distribution modified by mandibular material property: a 3D finite element analysis

BackgroundTemporomandibular joint disorder (TMD) is a common oral and maxillary facial disease. Finite element method (FEM) has been widely used in TMD studies. Material assignment significantly affects FEM results. The differences in the methods of material assignment used in previous studies have not been comprehensively assessed for further calculations. MethodsThe mandible material modelling approaches were of four types, namely: uniform modelling with (A) cortical bone; and (B) cancellous bone; (C) semi-uniform modelling with division of cortical and cancellous bone; and (D) non-uniform modelling with Computed tomography (CT) gray value related modulus. Meanwhile, the Young's modulus of values ranging from 20 to 300 GPa were considered for the teeth. Ten modellings were used to analyze and discuss the differences in contact pressure and contact force. Results(1) The increase in teeth elastic modulus increased the maximum contact pressure on the alveolar bone and contact force on teeth, but induced insignificant stress variation on the temporomandibular joint; (2) The location of the maximum contact pressure was steady for all four modelling approaches of the mandibular material. However, the maximum contact pressure and contact force exhibited an insignificant difference. ConclusionsTeeth with a higher elastic modulus significantly enhanced the stress concentration in the alveolar bone; in contrast, it induced minor variations in the temporomandibular joint stress states. The extreme stress regions predicted by the four mandibular models were consistent with the actual damaged regions. However, non-uniform modellings based on CT values could better describe the mechanical properties of the human bone, which should be primarily considered.

Biomechanical assessment of disease outcome in surgical interventions for medial meniscal posterior root tears: a finite element analysis

BackgroundThe adverse consequences of medial meniscus posterior root tears have become increasingly familiar to surgeons, and treatment strategies have become increasingly abundant. In this paper, the finite element gait analysis method was used to explore the differences in the biomechanical characteristics of the knee joint under different conditions.MethodsBased on CT computed tomography and MR images, (I) an intact knee (IK) model with bone, cartilage, meniscus and main ligaments was established. Based on this model, the posterior root of the medial meniscus was resected, and (ii) the partial tear (PT) model, (iii) the entire radial tear (ERT) model, and (iv) the entire oblique tear (EOT) model were established according to the scope and degree of resection. Then, the (v) meniscus repair (MR) model and (vi) partial meniscectomy (PM) model were developed according to the operation method. The differences in stress, displacement and contact area among different models were evaluated under ISO gait loading conditions.ResultsUnder gait loading, there was no significant difference in the maximum stress of the medial and lateral tibiofemoral joints among the six models. Compared with the medial tibiofemoral joint stress of the IK model, the stress of the PM model increased by 8.3%, while that of the MR model decreased by 18.9%; at the same time, the contact stress of the medial tibiofemoral joint of the ERT and EOT models increased by 17.9 and 25.3%, respectively. The displacement of the medial meniscus in the ERT and EOT models was significantly larger than that in the IK model (P < 0.05), and the tibial and femoral contact areas of these two models were lower than those of the IK model (P < 0.05).ConclusionsThe integrity of the posterior root of the medial meniscus plays an important role in maintaining normal tibial-femoral joint contact mechanics. Partial meniscectomy is not beneficial for improving the tibial-thigh contact situation. Meniscal repair has a positive effect on restoring the normal biomechanical properties of the medial meniscus.

Effect of moisture-heat coupling on mechanical behavior of nano-SiO2 adhesives and CFRP-steel lap joints

The accelerated aging tests are carried out to examine the effects of moisture-heat coupling on the mechanical properties of nano-SiO2 adhesive specimens and the bonding behavior of CFRP-steel lap joints. The microstructure of the cross-section on the failed tensile specimen is observed by scanning electron microscopy (SEM). The results indicate that the glass transition temperatures (Tg,s, Tg,t) of the adhesive decrease when the aging time of water bath increases at 25 °C, while the glass transition temperatures increase at 55 °C and 70 °C due to the re-curing effect of elevated temperature. Then, the shape of the stress–strain curve remains constant when the adhesive specimens take the water bath at 25 °C and 55 °C, respectively. This shape varies obviously at 70 °C, characterized by an obvious decreasing strength and increasing ductility, respectively. Therefore, the moisture-heat temperature is recommended to be less than Tg,s for the adhesive in practical applications. Moreover, the water bath resulting in an apparent plasticization phenomenon around the pores that is the nano-SiO2 pulled out from resin matrix. In addition, the shear strength of CFRP-steel lap joint decreases because moisture-heat aging results in a decreasing bonding effect at the interfaces of CFRP-adhesive layer and steel-adhesive layer, respectively. After a water bath, the shear stress of the lap joint concentrates, and the toughness of interface decrease, resulting in a reduction of transfer length of shear stress.

Biomechanical Effect of Osteoporosis on Adjacent Segments After Anterior Cervical Corpectomy and Fusion

Adjacent segmental degeneration (ASD) is one common long-term complication of anterior cervical corpectomy and fusion (ACCF), and osteoporosis is one basic disease in the elderly. After ACCF, patients may experience osteoporosis with age. However, the influence of osteoporosis on ASD remains unclear. The purpose of this study was to determine whether osteoporosis could affect the development of ASD following ACCF. Three finite element models of the cervical spine, including 1 normal model, 1 ACCF model, and 1 ACCF with osteoporosis model, were constructed. ACCF was simulated at the C4-C6 level. A 73.6N follower load and a 1 Nm moment were imposed on the normal model, and the same follower load together with an adjusted moment was applied to the ACCF model and the ACCF with osteoporosis model, to simulate movement in each direction. The range of motion, intradiscal pressure, shear stress on anulus fibrosus, and facet joint stress at C3-C4 and C6-C7 levels of the models were calculated. In this study, the normal model was well validated. In flexion, extension, right lateral bending, and right axial rotation, the overall range of motion was 8.92°, 19.7°, 15.37°, and 45.27° in the normal model, and the adjusted moment was 1.4 Nm, 2.7 Nm, 1.1 Nm, and 2.6 Nm in the ACCF model, and 1.3 Nm, 2.5 Nm, 1.1 Nm, and 2.4 Nm in the ACCF with osteoporosis model. Despite of a few exceptions, the maximum values of the outcome measurements were mostly found in the ACCF model, and the minimum values in the normal model. Compared with the ACCF model, most of the outcome measurements were decreased in the ACCF with osteoporosis model. Osteoporosis can retard the adverse influence of ACCF on adjacent segments.

FEA and Experimental Investigation of Prosthetic Knee Joint

The aim of this study is to look at how stresses are distributed in a polyethylene-based prosthetic knee joint. Ansys 18.1 software is used for finite element analysis. In experimental studies, the effects of sagittal radius, flexion angle, and external load on knee joint stresses were investigated. The prosthetic knee joint is created as a 2D model using parameters like sagittal radius and flexion angles in design modeling software. The experimental work has been carried out in a polariscope machine setup, The photo elastic model is tested in different loading conditions and finds stress in that model. Finally, results are validated experimental results with FEA results.

Predicting residual stress in a 316L electron beam weld joint incorporating plastic properties derived from a crystal plasticity finite element model

Electron beam welding is an advanced joining technique which induces narrow weld region with minimal heat affected zone and weld-induced distortion. This reduces residual stresses in the joints which can be detrimental to structural performance of components in safety critical industries. Being an autogenous process, electron- beam welding generates a highly textured, columnar microstructure in the weld zone which have distinct properties when compared to the parent material region. Determining mechanical properties of the weld material assists in accurate assessment of the joint. However, extracting weld material specimens to determine plastic properties becomes increasingly cumbersome in thinner weld joints. An alternate approach has been demonstrated in this work wherein mechanical properties were derived using the weld microstructure in a crystal plasticity finite element (CPFE) framework. The initial calibration of the CPFE parameters was done using experimental data from thick weldment. These calibrated values were used to obtain the elastic and elastic-plastic properties of thinner weld materials by deforming corresponding synthetic microstructures whose attributes were determined by Electron Backscatter Diffraction analysis. The resultant properties were incorporated in a finite element (FE) based weld simulation to determine the residual strain. These results were compared with the residual strain data obtained using X-ray diffraction and good agreement was observed.

Elastoplastic analysis of shear resistance of special-shaped concrete-filled steel tubular connection

The experimental and analytical methods were used in this research to comprehend the elastoplastic shear behavior of special-shaped Concrete-Filled Steel Tubular (CFST) joint and develop damage models for its joint under low-reversed cyclic and axial loading. It is identified that the shear failure occurs in the panel zone and the joint's shear force-lateral displacement hysteretic curves and stress distribution are obtained. The joint is divided into individual components, including webs, steel frame, and core concrete, so as to investigate the elastoplastic shear behavior of the joint at the material level. In order to accurately calculate the elastoplastic shear resistances of joint components while considering the loading and boundary conditions and interactions between web and flange limbs, the shear resistances models of the webs, steel frame, and core concrete are presented based on the analytic function of shear stress, plastic hinge damage mechanism, and concrete compression strut mechanism. Furthermore, the above models are used to develop a design calculation formula for the shear resistances, in which the plastic development of the webs, the stress state of the plastic hinges, and the shear resistance increasing factor of the concrete compression strut can be considered. Finally, a design formulation to calculate the shear capacity of the special-shaped CFST joint is put forward，and the calculated results are compared with experimental data.

The Effect of 13 Weeks Long-Distance Bicycle Riding on Inflammatory Response Indicators Related to Joint Cartilage and Muscle Damage.

This study was to investigate the effects of 13 weeks of long-distance cycling on biomarkers of joint cartilage, muscle damage and inflammation. All subjects in this study were seven participants of the “One Korea New-Eurasia Peace Cycle Expedition”, in which they rode cycles from Berlin, Germany to Seoul, Korea for thirteen weeks. The total course of the expedition was divided into three sub-courses: course 1 (from Berlin to Moscow), course 2 (from Moscow to Ulaanbaatar) and course 3 (from Ulaanbaatar to Seoul). All the selected participants rode 87.4 km/day (course 1), 70.4 km/day (course 2) and 57.6 km/day (course 3) on average, respectively. We collected their blood samples before the expedition in Seoul (S1), after course 1 in Moscow (M), after course 2 in Ulaanbaatar (U) and after the expedition in Seoul (S2), to analyze biomarkers of joint cartilage damage (Cartilage Oligomeric Matrix Protein; COMP), muscle damage (Creatine Phosphokinase; CPK, Lactate Dehydrogenase; LDH, Myoglobin), inflammation (Interleukin-6; IL-6, Interleukin-1β; IL-1β, Tumor Necrosis Factor-α; TNF-α, C-Reactive Protein; CRP) and stress hormone (Cortisol). According to this result, COMP (S1; 188.37 ± 46.68 ng/mL) showed a significant increase after the expedition course 1 (M; 246.69 ± 51.69 ng/mL, p = 0.012) and course 2 (U; 237.09 ± 62.57 ng/mL, p = 0.047), and recovered to the stable state after expedition course 3 (S2; 218.46 ± 34.78. p = 0.047). Biomarkers of muscle damage (CPK, LDH and Myoglobin) and inflammation (IL-6, IL-1β, TNF-α and CRP) were not significantly changed in all courses, but CRP (S1; 1.07 ± 0.76 ng/mL) showed a tendency to decrease after the expedition course 1 (M; 0.3 ± 0.1 mg/mL, p = 0.044). Lastly, the Cortisol level significantly increased in all courses (per p < 0.05), but the Cortisol level after expedition course 3 (S2; 21.00 ± 3.65 mg/mL) was lower than that of after the expedition course 1 (M; 24.23 ± 2.47 mg/mL, p = 0.028). In summary, it seems that repetitive and continuous 50−90 km/day of cycling can increase joint cartilage damage risk and stress hormone temporarily. However, this result suggests that the appropriate intensity of cycling for thirteen weeks does not increase physical damage, and rather enhances the human body to adapt to exercise training.

Surveillance of Side Effects after Two Doses of COVID-19 Vaccines among Patients with Comorbid Conditions: A Sub-Cohort Analysis from Saudi Arabia.

Background: Individuals with underlying chronic illnesses have demonstrated considerable hesitancy towards COVID-19 vaccines. These concerns are primarily attributed to their concerns over the safety profile. Real-world data on the safety profile among COVID-19 vaccinees with comorbid conditions are scarce. This study aimed to ascertain the side-effects profile after two doses of COVID-19 vaccines among chronic-disease patients. Methodology: A cross-sectional questionnaire-based study was conducted among faculty members with comorbid conditions at a public educational institute in Saudi Arabia. A 20-item questionnaire recorded the demographics and side effects after the two doses of COVID-19 vaccines. The frequency of side effects was recorded following each dose of vaccine, and the association of the side-effects score with the demographics was ascertained through appropriate statistics. Results: A total of 204 patients with at least one comorbid condition were included in this study. A total of 24 side effects were reported after the first dose and 22 after second dose of the COVID-19 vaccine. The incidence of at least one side effect was 88.7% and 95.1% after the first and second doses of the vaccine, respectively. The frequent side effects after the first dose were pain at the injection site (63.2%), fatigue (58.8%), fever (47.5%), muscle and joint pain (38.7%), and headache (36.3%). However, pain at the injection site (71.1%), muscle and joint pain (62.7%), headache (49.5%), fever (45.6%), and stress (33.3%) were frequent after the second dose. The average side-effects score was 4.41 ± 4.18 (median: 3, IQR: 1, 6) and 4.79 ± 3.54 (median 4, IQR: 2, 6) after the first and second dose, respectively. Female gender, diabetes mellitus, hypertension, hyperlipidemia, comorbidity > 2, family history of COVID-19, and the AstraZeneca vaccine were significantly associated with higher side-effect scores. Only 35.8% of study participants were satisfied with the safety of COVID-19 vaccines. Conclusions: Our analysis showed a high proportion of transient and short-lived side effects of Pfizer and AstraZeneca vaccines among individuals with chronic illnesses. However, the side-effects profile was comparable with the safety reports of phase 3 clinical trials of these vaccines. The frequency of side effects was found to be associated with certain demographics, necessitating the need for further investigations to establish a causal relationship. The current study’s findings will help instill confidence in the COVID-19 vaccines among people living with chronic conditions, overcome vaccine hesitancy, and increase vaccine coverage in this population.

An Updated Model Does Not Reveal Sex Differences in Patellofemoral Joint Stress during Running.

Structure-specific loading may have implications in understanding the mechanisms of running related injury. As females demonstrate a prevalence of patellofemoral pain twice that of males, this may indicate differences in patellofemoral loads between males and females. Previous works investigating differences in patellofemoral joint stress have shown conflicting results, but the models employed have not used estimates of muscle forces or sex specific contact areas. The aim of this study was to examine sex differences in patellofemoral joint stress using an updated model to include estimates of quadriceps muscle force and sex-specific patellofemoral contact area. Descriptive Laboratory Study. Forty-five healthy recreational runners ran at a controlled speed down a 20-meter runway. Kinetic and kinematic data were utilized to estimate muscle forces using static optimization. Quadriceps muscle force was utilized with sex-specific patellofemoral joint contact area in a two-dimensional patellofemoral joint model to estimate patellofemoral joint stress. Multivariate tests were utilized to detect sex differences in patellofemoral loading and hip and knee kinematics. No differences were found between sexes in measures of patellofemoral loading or quadriceps force. Females displayed a reduced knee extension moment and greater hip adduction and internal rotation than males. The inclusion of static optimization to estimate quadriceps muscle force and sex-specific contact area of the patellofemoral joint did not reveal sex differences in patellofemoral joint stress, but differences in non-sagittal plane hip motion were detected. Therefore, two-dimensional patellofemoral models may not fully characterize differences in patellofemoral joint stress between males and females. Three-dimensional patellofemoral models may be necessary to determine if sex differences in patellofemoral joint stress exist. 3b.

Experimental Study on Seismic Behavior of a new fully precast rocking beam-column joint

A new fully precast replaceable energy dissipation rocking beam-column joint (RBCJ), formed by adopting the splice joint and connecting through energy-dissipating steel plates, was proposed via referring to the mortise-tenon work in Chinese ancient architectures, aiming to improve the repairable performance of reinforced concrete (RC) joints after strong earthquakes, reduce the residual deformation of the structure and realize the rapid recovery of building functions after earthquakes. Two one-half scale beam-column joints with different lap lengths were designed and fabricated. Unidirectional low-cycle reciprocating loading of the specimen by quasi-static test, the failure process, and the influence of lap length of the splice joint on the seismic performance of the specimen were studied, and the hysteresis tests was carried out on the repaired specimen again to study the repairable performance of the RBCJ. The research showed that the residual displacement of the specimen was small, and the plastic deformation was concentrated on the replaceable energy-dissipating parts. The concrete at the edge of the dapped-end part in the long-lap-RBCJ-connecting specimen was slightly cracked, and there was no serious damage in other areas of the prefabricated member. The short-lap specimen had better seismic performance than the long-lap one. After the loading drift of the short-lap specimen reached 1 /50, the repair work was completed by replacing energy-dissipating connecting steel plates, and the seismic performance of the repaired joint had not decreased significantly. To facilitate engineering application, the equations of yield load and ultimate load that joint can undergo were deduced according to thin plate theory, the relationship between ultimate bearing capacity and thickness of energy-dissipating steel plates was given, and local stress and failure mechanism of the splice joint were analyzed, and shear and pull-out checking calculations of bolts were carried out.