The Federal Rail Association (FRA) mandated an increase in freight railcar weight limits from 1170 kN (263,000 lb) to 1272 kN (286,000 lb). However, most of the railway bridges were built prior to World War II and are not designed to handle this increased railcar weight. Thus, there is a need for accurate and efficient methods to evaluate and load rate existing bridges that will reveal their actual capacities.
In this study, the research approach adopted is aimed at providing an efficient method to load rate railway bridges. Three load rating methods were utilized and compared: (1) traditional method based on American Railway Engineering and Maintenance-of-Way Association (AREMA) specifications, (2) refined traditional method using data from field tests, and (3) load rating using testing data and finite element (FE) modeling. Various types of bridges were field tested and evaluated. Results from a typical railway bridge will be used to demonstrate and compare each one of the three load rating methods. For this bridge, non-destructive testing was performed. The collected responses were used to improve the traditional method and calibrate a 3-D FE model. The rating results indicated that method (1) can be relatively conservative and does not reflect the actual behavior of the structure while method (3) provided accurate results it was more tedious. It is suggested that the refined traditional method (2) be used since it provided similar accurate rating results without developing a detailed FE model.
Introduction: Stair gait is an activity performed daily. Inherently falls during stair gait continue to be a concern especially for older adults 65 years +. Recently falls have become the most common cause of injury-related deaths in individuals over the age of 75 y.o. Stair descent falls account for 75% of stair falls and also present a greater injury severity. Poor shoes or insoles and lighting condition can contribute to an increased risk of falls during stair locomotion. Stability can be measured using the COM-BOS ‘stability margin’ relationship. Center of pressure (COP), another stability measure,can be calculated from a multi-axis force-plate system. As well, plantar pressure is an important indicator of gait pattern efficiency. Aim: To identify aspects of stair gait that increase the risk of falls. By measuring the COM-BOS ‘stability margin’, the COP and plantar pressure patterns of individuals during stair gait, while modifying insoles and lighting. Methods: Young and older adults will ascend and descend a 4 level staircase, with two imbedded AMTI-force platforms in varying lighting condition (low, normal). Participants will be fitted with standardized footwear with Medi-logic insoles placed under varying hardnesses of insoles. An Optotrak motion capture system will record 12 IRED markers placed on the individual to determine the COM trajectory and BOS of location. Hypothesis: Partipants should demonstrate a greater lateral displacement in the single support phase during dim lighting as opposed to normal lighting. The stability of older adults will be compromised with alteration to the insoles (soft and hard).
This poster presents a polymer-based microfluidic resistive sensor for detecting distributed loads. The sensor is comprised of a polymer rectangular microstructure with an embedded electrolyte-filled microchannel and an array of electrodes aligned along the microchannel length. Electrolyte solution in the microchannel serves as impedance transduction. Distributed loads acting on the polymer microstructure give rise to different deflection along the microstructure length, which is recorded as the resistance change in electrolyte solution. This sensor can detect distributed loads by monitoring the resistance change at each pair of electrodes. Owing to great simplicity of the device configuration, a standard polymer-based fabrication process is employed to fabricate this device. With custom-built electronic circuits and custom LabVIEW programs, fabricated devices filled with two different electrolytes, 0.1M NaCl electrolyte and 1-Ethyl-3-methylimidazolium dicyanamide electrolyte, are characterized, demonstrating the capability of detecting distributed static and dynamic loads with a single device.
This study investigated the association of serum C-propeptide (sCPII), urinary CTX-II (uCTX-II), and uCTX-II:sCPII with peak vertical ground reaction force (PVGRF) and quadriceps strength during jump-landing in patients with ACL reconstruction (ACLR). METHODS: twenty two patients with ACLR (Male=14, age=19.6 ± 4 yr) were tested 20 weeks after the surgery. Blood and urine samples were collected. sCPII and uCTX-II, biomarkers of articular degradation and synthesis respectively, were analyze using commercial ELISAs. Subjects performed 3 trials of a forward drop land and a drop vertical jump. Subjects started on a 20 cm step and landed on a force platform (AMTI). PVGRF was analyzed on the surgical side. Quadriceps strength (PKET) was assessed with an isokinetic dynamometer (60°/s). PVGRF and PKET were normalized to body weight (BW). Pearson’s correlation, with and without adjustment for age, was used to analyze associations among variables. RESULTS: Mean (± SD) log concentrations were 2.88 ± 0.19 and 3.32 ± 0.49 ng/mmol for sCPII and uCTX-II respectively; and for uCTXII:CPII was 1.16 ± 0.18. PVGRF was 3.2 BW ± 0.3 and 1.4 BW ± 0.3 for the forward drop land and drop vertical jump tasks, respectively; PKET was 0.92 BW ± 0.2. There were no significant correlations among variables (p≥0.2), except for a trend towards a positive correlation between PKET and uCTXII:sCPII (r = 406, p = .076). CONCLUSSIONS: Biomarkers of type II collagen metabolism were not associated with jump-landing forces. However, higher quadriceps strength may be associated with a shift in articular cartilage metabolism towards degradation.
Background: Numerous studies have described 3D kinematics, 3D kinetics and electromyography (EMG) of the lower limb during quasi-static or dynamic squatting activities. However there is only little information on the comparison of these two squatting conditions. Only one study compared these activities in terms of 3D kinematics, but no information was available on 3D kinetics and EMG. The purpose of this study was to compare simultaneous recordings of 3D kinematics, 3D kinetics and EMG of the lower limb during quasi-static and fast dynamic squats. Methods: Ten subjects were recruited. 3D knee kinematics was recorded with a motion capture system, 3D kinetics was recorded with a force plate, and EMG of 8 muscles was recorded with surface electrodes. Each subject performed a quasi-static squat and several fast dynamic squats from 0° to 70° of knee flexion. Findings: Mean differences between quasi-static and dynamic squats were 1.6° for rotations, 1.8 mm for translations, 38 N ground reaction forces (2.1 % of subjects’ body weight), 6 Nm for torques, 13.0 mm for center of pressure, and 7 µV for EMG (6.3% of the maximum dynamic electromyographic activities ). Some significant differences (P < 0.05) were found in anterior-posterior translation, vertical forces and EMG. Interpretation: All differences found between quasi-static and fast dynamic squats can be considered small. 69.5% of the compared data were equivalent. In conclusion, this study show for the first time that quasi-static and dynamic squatting activities are comparable in terms of 3D kinematics, 3D kinetics and EMG.
Development of neuronal prosthetics, where neuronal activity is used to control artificial limbs, has so far relied on decoding kinematic parameters of movements, such as movement position or velocity. In addition to kinematic control, proper control of forces exerted by the prosthetic device is necessary for successful interaction with the environment. In our study, we analysed the possibility of classifying and decoding different grasp related forces during active grasping. Two macaque monkeys were trained to reach, grasp and pull an object in response to visual cues. Cues instructed the monkeys to grasp the object with one out of two grip types (precision or side grip) and pull the object with one of two different forces (0.5N or 2N). Monkeys obtained a food reward after successfully performing the instructed grip and pull. During the task execution, we recorded electrophysiological signals from the multielectrode arrays implanted intracortically in the hand and arm area of the monkey’s motor cortex. Six different parameters of the grip: four pressure forces on each side of the object, pull force on the object and the object displacement, were recorded simultaneously with the neuronal activity. Recorded neuronal activity was used to classify different grip types or loading forces, and to decode the continuous traces of different forces during the grip. Our results show that kinetic grip parameters can be decoded with high accuracy, thereby improving the feasibility of constructing fully functional anthropomorphic neuronal prosthesis that relies on kinetic (force) control.
A large number of experiments have isolated a coalition of constraints, including cortical and subcortical neural crosstalk, that influence the coordination of the two hands functioning together. Recent findings, however, have demonstrated that these constraints are minimized when integrated feedback (Lissajous feedback) is used. Two experiments were designed to determine participants’ ability to coordinate 1:2 and 2:3 rhythmical bimanual force production tasks. We hypothesized that neural crosstalk should be more easily detected and characterized in tasks where the forces required to produce the goal pattern of coordination are increased. The task was to rhythmically produce and coordinate a pattern of isometric forces. A Lissajous display illustrated the specific pattern of force requirements needed to produce the goal pattern. The results indicated very effective temporal performance of the bimanual coordination patterns. This result is similar to that observed in our earlier work with reciprocal and circling motion, but is especially informative given that the increased forces required to produce the desired bimanual coordination pattern resulted in a consistent and identifiable distortion of the left limb forces that could be attributable to the production of right hand forces. We were not able to detect distortions of the forces produced by the right limb that could be attributable to the left limb. This type of right to left limb influence, which may be attributable to asymmetrical cortical and subcortical crosstalk, was not evident in our earlier work when the bimanual coordination tasks involved movements of the limbs in a relatively frictionless environment.
The concept of a leaf spring structured midsole shoe (LEAF) is based on shifting the foot anteriorly during the first part of stance phase in heel-toe running. The aim of the current study is to analyze the effects of a LEAF compared to a standard foam midsole shoe (FOAM) on the foot kinematics in overground and treadmill running at two running speeds.
Nine male heel strikers ran on a treadmill with the LEAF and the FOAM at 3 and 4 m/s, each for 5 min. Furthermore, the participants performed with both shoes six runs each on a 40 m indoor track at running speeds of 3 and 4 m/s. For one stance phase the ground reaction forces were measured using a force plate imbedded in the track. Running speed and shoe order were randomized. Kinematics (VICON, 200Hz) and kinetics (AMTI, 1000Hz; only overground) were used to calculate the anterior shift of the foot, the foot ground angle at heel strike (FGA at HS) and the horizontal path of the center of pressure (COP).
The LEAF increases the anterior foot shift in treadmill and overground running at both running speeds compared to the FOAM, without changing the individuals’ strike pattern. Furthermore, the anterior foot shift affects the COP leading to an overall enlarged COP path. These findings indicate a benefit of the structured midsole on performance at least at moderate running speeds
Dexterous manipulation relies on modulation of digit forces as a function of digit placement. However, little is known about the sense of position of the finger pads relative to each other. We quantified subjects' ability to match perceived vertical distance between the thumb and index finger pads (dy) of the right hand (“reference” hand, Rhand) using the ipsilateral or contralateral hand (“test” hand, Thand) without vision of the hands. The Rhand digits were passively placed non-collinearly (dy = ±30 mm) or collinearly (dy = 0 mm). Subjects reproduced Rhand dy by using a congruent or inverse Thand posture. We hypothesized that matching error would be greater (a) for collinear than non-collinear digits positions, (b) when Rhand and Thand postures were not congruent, and (c) when subjects reproduced dy using the contralateral hand. Subjects made greater errors when matching collinear than non-collinear dys, when the posture of Thand and Rhand were not congruent, and when Thand was the contralateral hand. Under-estimation errors were produced only for non-collinear digits positions, when the postures of Thand and Rhand were not congruent, and when Thand was the contralateral hand. These findings indicate that perceived finger pad distance is transferred across hands less accurately than when it is reproduced within the hand and reproduced less accurately when a higher-level processing of the somatosensory feedback is required for non-congruent hand postures. We propose that erroneous representation of finger pad distance, if not compensated for between contact and onset of manipulation, might lead to manipulation performance errors.
The inherent reduction in mechanical loading associated with microgravity has been shown to result in dramatic decreases in the bone mineral density (BMD) and mechanical strength of skeletal tissue. Importantly, there is a concomitant increase in fracture risk during long-duration spaceflight missions. Thus, the objective of this study was to investigate the effects of microgravity loading on long-bone fracture healing in a previously-developed Haversian bone model of simulated microgravity over a 4-week period. For in vivo mechanical evaluation, strains of an implanted orthopaedic fixation plate were quantified for known hindlimb ground reaction forces with a six degree-of-freedom load cell (AMTI, Watertown, MA). In vivo strain measurements demonstrated significantly higher orthopaedic plate strains in the Microgravity Group as compared to the Control Group following the 28-day healing period due to inhibited healing in the microgravity environment. DEXA BMD in the treated metatarsus of the Microgravity Group decreased 17.6% at the time of the ostectomy surgery and decreased an additional 5.4% during the 28-day healing period. Four-point bending stiffness of the Microgravity Group was 4.4 times lower than that of the Control Group (p<0.01), while µCT and histomorphometry demonstrated reduced periosteal callus area, mineralizing surface, mineral apposition rate (p<0.001), bone formation rate, and periosteal/endosteal osteoblast numbers as well as increased periosteal osteoclast number. These data provide strong evidence that the mechanical loading environment dramatically affects the fracture healing cascade and resultant mineralized tissue strength, and that the microgravity loading environment has negative effects on fracture healing in Haversian systems.