Evaluation of the Lateral Vibration Response of Footbridges under Uncertainty Conditions

<p>The evaluation of the vibration performance of footbridges due to walking pedestrians is an issue of increasing importance in current footbridge design practice. The growing trend of slender footbridges with long spans and light materials has led to serviceability problems in lateral vibrations, which occur when the number of pedestrians reaches a “critical number”. Considering the mode of vibration in which the lateral instability is more likely to develop, the structural response depends on the modal characteristics of the footbridge; in particular, the natural frequency and the damping ratio. These modal parameters are stochastic variables, as it is not possible to determine them without a level of uncertainty. Thus, the purpose of this paper is to obtain the value of the lateral dynamic response of slender footbridges with a certain confidence level under uncertainty conditions. The uncertainties of those modal parameters are considered using a probabilistic approach. Both the natural frequency and the damping ratio are modelled as uncorrelated random variables that follow a predetermined probabilistic distribution function. Consequently, the structural response will also be described by a probabilistic distribution function, which can be estimated through Monte Carlo numerical simulations. As a result, the study allows the footbridge lateral response and the critical number of pedestrians to be calculated for different confidence levels and load scenarios, especially for crowd densities above the “critical number”.</p>

Permitted speed decision of single-unit trucks with emergency braking maneuver on horizontal curves under rainy weather

Under adverse weather conditions, visibility and the available pavement friction are reduced. The improper selection of speed on curved road sections leads to an unreasonable distribution of longitudinal and lateral friction, which is likely to cause rear-end collisions and lateral instability accidents. This study considers the combined braking and turning maneuvers to obtain the permitted vehicle speed under rainy conditions. First, a braking distance computation model was established by simplifying the relationship curve between brake pedal force, vehicle braking deceleration, and braking time. Different from the visibility commonly used in the meteorological field, this paper defines "driver’s sight distance based on real road scenarios" as a threshold to measure the longitudinal safety of the vehicle. Furthermore, the lateral friction and rollover margin is defined to characterize the vehicle’s lateral stability. The corresponding relationship between rainfall intensity-water film thickness-road friction is established to better predict the safe speed based on the information issued by the weather station. It should be noted that since the road friction factor of the wet pavement not only determined the safe vehicle speed but also be determined by the vehicle speed, so we adopt Ferrari’s method to solve the quartic equation about permitted vehicle speed. Finally, the braking and turning maneuvers are considered comprehensively based on the principle of friction ellipse. The results of the TruckSim simulation show that for a single-unit truck, running at the computed permitted speed, both lateral and longitudinal stability meet the requirements. The proposed permitted vehicle speed model on horizontal curves can provide driving guidance for drivers on curves under rainy weather or as a decision-making basis for road managers.

Lateral Instability in Total Ankle Arthroplasty: A Comparison Between the Brostrom-Gould and Anatomic Lateral Ankle Stabilization (ATLAS)

Background Lateral ankle instability is not uncommon after osseous cuts and soft tissue releases are performed during Total Ankle Arthroplasty (TAA), particularly with varus malalignment. The purpose of the present study was to compare the outcomes of ankles that underwent TAA with concurrent Brostrom-Gould (BG) or Anatomic Lateral Ankle Stabilization (ATLAS) at a minimum of 1-year follow-up. Methods Thirty-eight TAAs underwent BG (21 INFINITY, 4 CADENCE) or ATLAS (13 INBONE-2) between August 2015 and February 2019 at a single institution and were at least 1 year postoperative (mean 18.3 months, range: 12-40). Baseline patient demographics, characteristics, and operative factors were assessed via medical record and chart reviews. Radiographs parameters were measured preoperatively, at 6 weeks postoperative, and during the latest follow-up. Revisions, reoperations, and complications were classified according to the criteria established by Vander Griend et al and Glazebrook et al, respectively. Univariate and multivariate analyses were performed. Results Survivorship for TAA with concurrent BG/ATLAS was 97%. Overall, TAA with concurrent BG had higher incidences of early TAA revision (4%), recurrent instability (4%), reoperation (16%), and complications (29%) compared to ATLAS. Postoperative coronal and sagittal tibiotalar alignment changes were significant for both groups (P < .001, P = .014); however, the differences were greater for ATLAS (P = .045, P < .001). Conclusion The present study is the first to compare outcomes between techniques for addressing ankle instability in the TAA population. At short-term follow-up, anatomic reconstruction produced better outcomes than the traditional BG procedure. Additional comparative studies between techniques to address instability in the TAA population are warranted. Level of Evidence: Level III: Retrospective cohort study

Rethinking Margin of Stability: Incorporating Step-To-Step Regulation to Resolve the Paradox

ABSTRACTMaintaining frontal-plane stability is a major objective of human walking. Derived from inverted pendulum dynamics, the mediolateral Margin of Stability (MoSML) is frequently used to measure people’s frontal-plane stability on average. However, typical MoSML-based analyses deliver paradoxical interpretations of stability status. To address mediolateral stability using MoSML, we must first resolve this paradox. Here, we developed a novel framework that unifies the well-established inverted pendulum model with Goal-Equivalent Manifold (GEM)-based analyses to assess how humans regulate step-to-step balance dynamics to maintain mediolateral stability. We quantified the extent to which people corrected fluctuations in mediolateral center-of-mass state relative to a MoSML-defined candidate stability GEM in the inverted pendulum phase plane. Participants’ variability and step-to-step correction of tangent and perpendicular deviations from the candidate stability GEM demonstrate that regulation of balance dynamics involves more than simply trying to execute a constant-MoSML balance control strategy. Participants adapted these step-to-step corrections to mediolateral sensory and mechanical perturbations. How participants regulated mediolateral foot placement strongly predicted how they regulated center-of-mass state fluctuations, suggesting that regulation of center-of-mass state occurs as a biomechanical consequence of foot placement regulation. We introduce the Probability of Instability (PoI), a convenient statistic that accounts for step-to-step variance to properly predict instability likelihood on any given future step. Participants increased lateral PoI when destabilized, as expected. These lateral PoI indicated an increased risk of lateral instability, despite larger (i.e., more stable) average MoSML. PoI thereby explicitly predicts instability risk to decisively resolve the existing paradox that arises from conventional MoSML implementations.

Coupled Flow-Seepage–Elastoplastic Modeling for Competition Mechanism between Lateral Instability and Tunnel Erosion of a Submarine Pipeline

The instability of a partially embedded pipeline under ocean currents involves complex fluid–pipe–soil interactions, which may induce two typical instability modes; i.e., the lateral instability of the pipe and the tunnel erosion of the underlying soil. In previous studies, such two instability modes were widely investigated, but separately. To reveal the competition mechanism between the lateral instability and the tunnel erosion, a coupled flow-seepage–elastoplastic modeling approach was proposed that could realize the synchronous simulation of the pipe hydrodynamics, the seepage flow, and elastoplastic behavior of the seabed soil beneath the pipe. The coupling algorithm was provided for flow-seepage–elastoplastic simulations. The proposed model was verified through experimental and numerical results. Based on the instability criteria for the lateral instability and tunnel erosion, the two instability modes and their corresponding critical flow velocities could be determined. The instability envelope for the flow–pipe–soil interaction was established eventually, and could be described by three parameters; i.e., the critical flow velocity (Ucr), the embedment-to-diameter ratio (e/D), and the non-dimensional submerged weight of the pipe (G). There existed a transition line on the envelope when switching from one instability mode to the other. If the flow velocity of ocean currents gets beyond the instability envelope, either tunnel erosion or lateral instability could be triggered. With increasing e/D or concurrently decreasing G, the lateral instability was more prone to being triggered than the tunnel erosion. The present analyses may provide a physical insight into the dual-mode competition mechanism for the current-induced instability of submarine pipelines.

Decreasing the Abnormal Internally Rotated Talus After Lateral Ankle Stabilization Surgery

Background: Increased internal rotation of the talus has been found in patients with mechanical ankle instability (MAI). Purpose/Hypothesis: To evaluate and compare the talar rotation position before and after lateral ankle lateral stabilization surgery in patients with MAI. We hypothesized that the abnormal internal talus rotation in patients with MAI will decrease after surgery for ankle lateral instability and that there will be no significant difference in internal talus rotation between the ligament repair and reconstruction groups. Study Design: Case-control study; Level of evidence, 3. Methods: We retrospectively studied 56 patients with MAI who underwent ankle lateral stabilization surgery after arthroscopic evaluation (repair, 36 cases; reconstruction, 20 cases). Before and after the operation, magnetic resonance images of all the participants were reviewed. The rotated position of the talus was measured and calculated by the Malleolar Talus Index at the magnetic resonance axial plane. Results: The internal rotation of the talus decreased significantly after ankle lateral stabilization surgery in patients with MAI as compared with before surgery (mean ± SD, 83.3° ± 3.3° vs 86.7° ± 3.9°; P < .01). However, there was no statistically significant difference between the ligament repair and reconstruction groups before or after the operation. Conclusion: Abnormal internal rotation of the talus in patients with MAI was decreased after ankle lateral stabilization surgery.

Improvement of surgical treatment of patients with posttraumatic posterior-lateral instability of the knee joint

One of the most pressing and complex problems of modern orthopedics is the treatment of patients with multiligamentary knee injury. The most difficult category of patients is considered, in whom, along with rupture of one or both cruciate ligaments, damage to the ligamentous-tendon complex, which provides posterolateral stability of the knee joint, occurs. These structures, which have received the name posterolateral angle of the knee joint in the specialized scientific literature, usually include the peroneal collateral ligament, the hamstring of the popliteal muscle and the peroneal-popliteal ligament. Objective difficulties in the reconstruction of these elements are explained by the complexity of the anatomy and biomechanics of these anatomical structures, the polymorphism of their injuries, the proximity of the common peroneal nerve, as well as the shortcomings of the available plastic methods and the lack of generally accepted surgical tactics. Lack of applied precision data on the structure of the peroneal collateral ligament and the ligamentous-tendinous complex, called the postero-lateral angle of the knee joint in the specialized literature, analyzed from the standpoint of substantiating rational surgical tactics for treating patients with varus instability in combination with a large number of unsatisfactory results of their surgical treatment, determined the relevance of the topic of the chosen work (2 figures, bibliography: 17 refs).

New classification of osteochondral lesions of the talus in adults

Osteochondral lesions (OCL) of the ankle in adults are frequent lesions that mainly affect the cartilage and the subchondral bone, are relatively common, and have varied etiologies. However, in 50% of patients, these lesions may occur concomitantly with chronic instability of the ankle associated with lower limb deformities, acute sprains of the ankle, or fractures. We propose a classification into four types of lesions (traumatic, non-traumatic, with lateral instability of the ankle, and with mechanical axis defects), focusing not only on the diagnosis and treatment of OCL but also on associated injuries, such as instability and/or supramalleolar and hindfoot deformities. Level of Evidence V; Therapeutic Studies; Expert Opinion.

Correlation between Balance and BMI in Collegiate students: A cross sectional study

Background: Balance deficits are usually related to medial-lateral instability. BMI could be an important factor to consider as; excess body mass or increased accumulation of adipose tissue can directly impact the postural stability which in return impacts balance. Purpose of the study: To find the correlation between BMI and Balance. Method: Sample consisted of 149 students, out of which 100 (67%) were males and 49 (33%) were females. BMI was calculated and was categorized into groups. Bilateral limb length was measured for normalising the data. Static balance was measured by performing blinded stork test and dynamic balance by performing Y- balance test. Data was analysed using Pearson’s correlation test. Result: There was significant correlation between BMI and static balance of left leg (r=0.713, 95% CI 0.623, 0.784, p=0.01) but on comparison, there was no significant correlation between BMI and static balance of right leg (r=0.0458, 95% CI -0.11, -0.205, p=0.58). It was found that there was no significant correlation between BMI and Left Anterior (r= -0.134, 95% CI -0.289, -0.0274, p= 0.103), Left Posterolateral (r=-0.0775, 95% CI -0.235, 0.0843, p=0.347), Left Posteromedial (r=-0.0903, 95% CI -0.248, -0.0715, p=0.273) respectively. Also, it was found that there was no significant correlation between BMI and Right Anterior (r=-0.236, 95% CI -0.382, -0.0778, p=0.00381), Right Posterolateral (r=-0.193, 95% CI -0.343,-0.0334, p=0.0183), Right Posteromedial (r=-0.126, 95% CI -0.281, -0.0354, p=0.125) respectively. Conclusion: There was significant correlation between BMI and static balance of left leg and no correlation was established between BMI and static balance on right leg and also no correlation was established between BMI and static and dynamic balance for right and left leg. KEY WORDS: Static balance, Dynamic balance, Body Mass Index, Obesity, Limb length.