Dynamic Loading Does Not Interfere With the Initial Repopulation of Decellularized Tendons: An ExVivo Study.

Microseismic events commonly occur during the excavation of long wall panels and often cause rock-burst accidents when the roadway is influenced by dynamic loads. In this paper, the Fast Lagrangian Analysis of Continua in 3-Dimensions (FLAC3D) software is used to study the deformation and rock-burst potential of roadways under different dynamic and static loads. The results show that the larger the dynamic load is, the greater the increase in the deformation of the roadway under the same static loading conditions. A roadway under a high static load is more susceptible to deformation and instability when affected by dynamic loads. Under different static loading conditions, the dynamic responses of the roadway abutment stress distribution are different. When the roadway is shallow buried and the dynamic load is small, the stress and elastic energy density of the coal body in the area of the peak abutment stress after the dynamic load are greater than the static calculations. The dynamic load provides energy storage for the coal body in the area of the peak abutment stress. When the roadway is deep, a small dynamic load can still cause the stress in the coal body and the elastic energy density to decrease in the area of the peak abutment stress, and a rock-burst is more likely to occur in a deep mine roadway with a combination of a high static load and a weak dynamic load. When the dynamic load is large, the peak abutment stress decreases greatly after the dynamic loading, and under the same dynamic loading conditions, the greater the depth the roadway is, the greater the elastic energy released by the dynamic load. Control measures are discussed for different dynamic and static load sources of rock-burst accidents. The results provide a reference for the control of rock-burst disasters under dynamic loads.

Axle load spectra constitute a crucial part of the data for pavement design and pavement distress analysis. Typically, axle load spectra represent static load from vehicles and do not include dynamic loads generated by vehicles in motion. While dynamic loads can significantly contribute to faster pavement distress, this fact is mostly omitted in pavement design methods. The paper presents a methodology for consideration of dynamic loads in axle load spectra for mechanistic-empirical pavement design. Calculations of dynamic axle load spectra for pavements of various evenness (expressed by IRI) and various vehicle speeds were performed and discussed. The effect of dynamic axle load spectra on pavement performance was analysed. M-EPDG calculations performed for three selected flexible pavements show that dynamic loads have a minor effect on pavement performance if the pavement is smooth and IRI is close to 1.0 mm/m. The detrimental effects of dynamic axle loads increase rapidly with the pavement evenness deterioration, resulting in faster (up to 25%) development of pavement distresses for IRI = 4.0 mm/m and a vehicle speed of 60 km/h. The analysis proved that thinner pavement structures are more sensitive to dynamic loads than thicker pavement structures. The investigation of vehicle speed impact on vehicle dynamic loads and pavement performance showed that at low vehicle speed (30 km/h) dynamic loads have a minor effect and pavement distress results mostly from a decrease in stiffness modulus of asphalt mixture and increase in permanent deformations, while for vehicle speeds higher than 90 km/h dynamic loads significantly contribute to pavement distress and adverse dynamic effects are not compensated by an increase in stiffness modulus of asphalt mixtures. The results also emphasise the significance of proper pavement evenness maintenance, especially on high speed motorways.

Pavement surfaces are not ideally even, which causes dynamic loads of vehicle axles. Distribution of dynamic loads of a given axle is similar to normal distribution and can be described by static load and dynamic load coefficient. The dynamic load coefficient depends on road profile, vehicle speed, properties of suspensions and static load of axle. While for a given road section road profile remains constant, vehicle speed and suspension properties are subject to limited variations, the static loads of particular axle vary significantly. The weigh-in-motion systems are the source of data on static loads, which are characterized by axle load spectra. The axle load spectra are the key data input for pavement design. The article presents a new approach to inclusion of the dynamic loads in axle load spectra. The theoretical explanation is supported by sample calculations. A one-kilometer road section was selected for calculations and its profile was measured using laser road surface profilograph. The dynamic loads were then calculated using the quarter car model and parameters appropriate for heavy vehicle suspensions. This part of calculations proved that dynamic loads significantly increase for less loaded axles. Dynamic axle load spectra were calculated based on static axle load spectra and function of dynamic load coefficient. The load equivalency factors and truck factors were calculated using the fourth power equation and considering both static and dynamic axle load spectra. Contribution of dynamic loads to pavement failure equals up to 19% for the considered example of road profile, which is characterized by IRI = 1.54 m/km.

Pavement distresses are induced by mechanistic responses in pavement structure subjected to dynamic loads of moving vehicles. Pavement surface evenness deteriorates as pavement distresses propagate, which results in dynamic axle loads and faster pavement deterioration. It is vital to consider the dynamic axle load spectra to predict pavement deterioration using traffic-monitoring data. This study aimed to evaluate the effect of dynamic loads and overweight traffic on asphalt pavement overlay performance using mechanistic–empirical (M–E) pavement analysis. The relationship between dynamic load coefficients (DLCs), axle loads, and international roughness index (IRI) was obtained for accurate quantification of dynamic axle loads. Then the dynamic axle load spectra were derived by shifting the static axle load spectra in weigh-in-motion (WIM) data, given the DLC value. AASHTOWare Pavement ME software was used to analyze pavement performance with static and dynamic axle load spectra, and the impact of overweight traffic on asphalt pavement overlay performance. The impact of dynamic loads on reflective fatigue cracking was distinguished at an early stage of the service period and eliminated after the 10-year analysis period, when the propagation of reflective cracking reached a specific level. On the other hand, the consideration of dynamic axle loads increased the impact of overweight truck traffic on pavement distresses, and pavement structures of major highways tend to be more sensitive to overweight traffic because of greater DLC excitement at higher operational speeds.

This paper investigates the stiffness of a magnetic bearing that is subjected to the combined action of static and dynamic loads. Since their sum cannot exceed the saturation load, a large static load will imply that the bearing can carry only a small dynamic load. This smaller dynamic load together with the practical vibration amplitude define a practical upper bound to the dynamic stiffness. This paper also presents approximate design formulas and curves for this stiffness capacity as a function of the ratio of dynamic and static loads. In addition, it indicates that vibrations larger than a certain gap fraction can destabilize the magnetic bearing. This gap fraction, called the critical gap fraction, depends on the dynamic and static load ratio. For example, if the dynamic load is half of the static load, the use of more than 25 percent of gap can destabilize the bearing.

To address the frequent occurrence of rock burst disasters in areas with wide coal pillars during mining in the western mining area of China, the wide coal pillar area of the Tingnan coal mine in Shanxi Province was used as the research background. Theoretical analysis, numerical simulation, and field tests were used to establish the mechanical criterion and the energy criterion for the dynamic instability of wide coal pillars. The process and mechanism of wide coal pillar dynamic instability under dynamic and static load disturbances were revealed, and a wide coal pillar rock burst prevention and control scheme was proposed. The results indicated that when the load above a coal pillar reached the stress failure index and the energy failure index was met, the coal pillar reached the critical conditions for rock burst. With increasing static load, the stress, energy, and range of the plastic zone all showed increasing trends on both sides of the coal pillar. Under a given dynamic load, the stress and plastic zone range of the coal pillar significantly increased compared to those without a dynamic load. Under a given static load, the greater the dynamic load, the more likely the coal pillar was to undergo dynamic instability. The evolution of coal pillar dynamic instability was divided into three stages: energy accumulation, local instability, and dynamic instability. When the critical stress and energy conditions for coal pillar dynamic instability are exceeded, rock burst will occur. To reduce the static and dynamic loads of coal pillars, a rock burst prevention and control scheme of energy release and load reduction was proposed and applied onsite. The monitoring results showed that this control plan effectively reduced the stress of the coal pillar and the dynamic load generated by the fracture of the overlying rock layer, indicating safe mining in this area of wide coal pillars.

Background:Recent studies on lateral knee anatomy have reported the presence of a true ligament structure, the anterolateral ligament (ALL), in the anterolateral region of the knee joint. However, its biomechanical effects have not been fully elucidated.Purpose:To investigate, by using computer simulation, the association between the ALL and anterior cruciate ligament (ACL) under dynamic loading conditions.Study Design:Descriptive laboratory study; Level of evidence, 5.Methods:The authors combined medical imaging from 5 healthy participants with motion capture to create participant-specific knee models that simulated the entire 12 degrees of freedom of tibiofemoral (TF) and patellofemoral (PF) joint behaviors. These dynamic computational models were validated using electromyographic data, muscle activation data, and data from previous experimental studies. Forces exerted on the ALL with ACL deficiency and on the ACL with ALL deficiency, as well as TF and PF contact forces with deficiencies of the ACL, ALL, and the entire ligament structure, were evaluated under gait and squat loading. A single gait cycle and squat cycle were divided into 11 time points (periods 0.0-1.0). Simulated ligament forces and contact forces were compared using nonparametric repeated-measures Friedman tests.Results:Force exerted on the ALL significantly increased with ACL deficiency under both gait- and squat-loading conditions. With ACL deficiency, the mean force on the ALL increased by 129.7% under gait loading in the 0.4 period (P < .05) and increased by 189% under high flexion during the entire cycle of squat loading (P < .05). A similar trend of significantly increased force on the ACL was observed with ALL deficiency. Contact forces on the TF and PF joints with deficiencies of the ACL, ALL, and entire ligament structure showed a complicated pattern. However, contact force exerted on TF and PF joints with respect to deficiencies of ACL and ALL significantly increased under both gait- and squat-loading conditions.Conclusion:The results of this computer simulation study indicate that the ACL and the ALL of the lateral knee joint act as secondary stabilizers to each other under dynamic load conditions.

Objective To investigate the potential differences in efficacy of anterior and posterior cruciate ligaments(ACL & PCL) reconstruction by using arthroscopy between autologous tendon and tendon allograft. Methods A total of 144 patients with ACL or PCL fracture were assigned into two groups, namely anterior tibial muscle tendons allograft(n=82) and tendons autograft(n=63). The graft was fixed by using the Endobutton and Intrafix systems.The general information, drawer test, Lachman test, IKDC score, Lysholm score and Tegner score were compared between groups before and after surgery.The mean follow-up period was 16 months, ranged from 6 to 24 months. Results Both two groups received significant improvement after surgery and met the requirements of ligament reconstruction.However, those patients received autologous tendon had less complications, better knee stability.There were significant differences in Lachman score, ADT/PDT score, IKDC score[(83.43±4.37)points vs.(81.05±4.41)points], Lysholm score[(90.59±3.43)points vs.(89.03±3.25)points], and Tegner score[(7.79±0.94)points vs.(7.37±0.90)points]between the two groups in 12-month(χ2=9.509, 9.080, t=3.237, 2.770, 2.729, all P<0.05). Conclusion The efficacy of autologous tendon is better than tendon allograft in anterior and posterior cruciate ligaments reconstruction, which should be considered has highest priority in treating patients with anterior or posterior cruciate ligaments fracture. Key words: Arthroscopy; Anterior cruciate ligament; Posterior cruciate ligament; Bone-patellar tendon-bone graft

Introduction The etiology of spinal deformity in idiopathic scoliosis is unclear to date. One of the suspected influences is the asymmetric loading condition involved in the disorder. The aim of this project is to test the hypothesis that asymmetric dynamic loading influences the morphological and biological characteristics of the intervertebral discs in scoliosis. The study is performed with organ cultured discs by using a custom-designed asymmetrical loading device. Material and Methods Bovine caudal discs (6–10 months) were used in current study. For symmetric dynamic loading (Parallel), discs were placed in custom-designed chambers, and compressed by parallel metal plates in a Bose mechanical testing device. For asymmetric dynamic loading (Wedge), a 10° wedge was placed underneath the discs to mimic the load bearing condition of discs in scoliotic patients. The discs were submitted to 2 different load regimes: (1) 1 hour dynamic loading (0.02–0.4 MPa, 1Hz) and 23 hours free swelling culture for 7 days; (2) 1 hour dynamic loading (0.02–0.4 MPa, 1Hz) and 23 hours static loading (0.2 MPa) for 7 days. Disc heights were measured with caliper before and after each loading. After 7 days of culture, gene expression levels of aggrecan (ACAN), type I and II collagen (COL1 and COL2), IL1, IL6, and MMP1 in the annulus fibrosus was analyzed by real-time PCR. Genes that have been found dysregulated in human scoliotic discs compared with healthy controls were also measured in the organ cultured discs, including MMP13, type X collagen (COL10), CXCR4, BMP3, S100A12, and S100A8 ( n = 8). Results Disc height showed a constant drop in load regime 2, while a temporary decrease after 1h dynamic loading followed by free swelling recovery was noted in load regime 1. After 7th dynamic loading, the change in shape was greater in load regime 2 (disc height ratio wedged to non-wedged side of 0.81), than that in load regime 1 (height ratio of 0.87, p &lt; 0.05). Under load regime 2, MMP13 gene expression level increased 6.1-fold in Wedge disc compared with Parallel disc, while gene expression levels of COL10, CXCR4, BMP3, S100A12, and S100A8 were not affected. Gene expression levels of ACAN, COL1 and COL2 under load regime 1 were significantly higher compared with load regime 2. Moreover, discs under load regime 2 showed a trend in higher IL1, IL6, and MMP1 gene expression compared with regime 1. Conclusion Diurnal dynamic loading and free swelling recovery could maintain the gene expression of organ cultured discs at their physiological level. Diurnal dynamic loading followed by static loading mimicked a degenerative condition, as indicated by lower anabolic and higher catabolic gene expression. These results suggest that recovery of disc height and morphology after dynamic load may help to prevent degeneration of discs under constant loading. Asymmetric dynamic and static loading regime induces an increase in MMP13 gene expression compared with symmetric loading, which was also observed in a human scoliosis sample dataset. These results indicate that short-term asymmetric loading may be used to mimic early changes associated with the onset of scoliosis. Acknowledgment This study is supported by AOSpine International.

Instability of cylindrical panels under combined static and dynamic loads

Editorial Commentary: Increased Risk of Second Ruptures and Poorer Outcomes After Anterior Cruciate Ligament Injury and Reconstruction in Hypermobile Athletes: A Potential Synergism of Passive Ligamentous and Active Muscular Control of Dynamic Knee Stability Related to Age and Sex?

Pavement-related rolling resistances, caused by pavement–vehicle interaction, are important components of pavement life-cycle assessment (LCA). Structure-induced rolling resistance (SRR) is caused by dissipated vehicle kinetic energy in the pavement structure. This paper presents an integrated vehicle–tire–pavement approach to evaluate asphalt pavement SRR under dynamic loading. A three-dimensional (3D) semitrailer-truck model was used to calculate dynamic wheel loads on various pavement surface-roughness profiles. The dynamic wheel loads were then transformed into 3D tire–pavement contact stresses using a deep-learning tire model. Next, an advanced 3D finite element pavement model, validated in previous studies, was used to simulate pavement structure under moving tire–pavement contact stresses. The dynamic load coefficient of axle forces was found to increase linearly with truck speed. The increasing trend became more significant as pavement roughness increased. Ignoring the dynamic loading effect resulted in 12% error in predicting SRR. A case study was performed to illustrate the computation procedures of asphalt pavement SRR under static and dynamic loading. Dynamic loading accounted for 4.74%, 7.37%, 10.73%, and 14.02% of SRR for four pavement surface-roughness levels at a truck speed of 40 mph. In addition, SRR was found to be highly nonlinear and increased as speed decreased and axle load increased. A modified Illinois Center for Transportation SRR model was developed to quickly assess the SRR component of the pavement LCA’s use stage. This study demonstrates the importance of vehicle–tire–pavement interaction in SRR prediction, which may not be overlooked.

Analysis of dynamic vehicle loads using vehicle pavement interaction model

PurposeThe safety assessment of engineering structures under repeated variable dynamic loads such as seismic and wind loads can be considered as a dynamic shakedown problem. This paper aims to extend the stress compensation method (SCM) to perform lower bound dynamic shakedown analysis of engineering structures and a double-closed-loop iterative algorithm is proposed to solve the shakedown load.Design/methodology/approachThe construction of the dynamic load vertexes is carried out to represent the loading domain of a structure under both dynamic and quasi-static load. The SCM is extended to perform lower bound dynamic shakedown analysis of engineering structures, which constructs the self-equilibrium stress field by a series of direct iteration computations. The self-equilibrium stress field is not only related to the amplitude of the repeated variable load but also related to its frequency. A novel double-closed-loop iterative algorithm is presented to calculate the dynamic shakedown load multiplier. The inner-loop iteration is to construct the self-equilibrated residual stress field based on the certain shakedown load multiplier. The outer-loop iteration is to update the dynamic shakedown load multiplier. With different combinations of dynamic load vertexes, a dynamic shakedown load domain could be obtained.FindingsThree-dimensional examples are presented to verify the applicability and accuracy of the SCM in dynamic shakedown analysis. The example of cantilever beam under harmonic dynamic load with different frequency shows the validity of the dynamic load vertex construction method. The shakedown domain of the elbow structure varies with the frequency under the dynamic approach. When the frequency is around the resonance frequency of the structure, the area of shakedown domain would be significantly reduced.Research limitations/implicationsIn this study, the dynamical response of structure is treated as perfect elastoplastic. The current analysis does not account for effects such as large deformation, stochastic external load and nonlinear vibration conditions which will inevitably be encountered and affect the load capacity.Originality/valueThis study provides a direct method for the dynamical shakedown analysis of engineering structures under repeated variable dynamic load.

Modern design standards of developed countries have significant differences in the design provisions for determining the bearing capacity of monolithic reinforced concrete slabs for punching and do not fully take into account the features of design solutions and operating conditions. The available design positions are designed for the static loading mode of structures. The stress-strain state of plates for punching under dynamic load is currently little studied, and as a result, there are no methods for determining the bearing capacity of plates for punching under dynamic loading. The article presents the results of experimental and theoretical studies of the bearing capacity of plates under static and dynamic loads. The methodology of experimental studies and the design of prototypes, equipment for conducting power tests are described, the results of studies on the penetration of fragments of the interface of flat reinforced concrete monolithic slabs with a column under dynamic and static loading are presented. A comparison of the destructive load for samples tested under dynamic loading with the destructive load for samples tested under static load is presented. The factors affecting the strength of the plates during punching under dynamic loading are determined. Proposals have been developed to improve the methodology for calculating the strength of flat reinforced concrete slabs when pushing through static and dynamic loads.