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1. Experimental Characterization of Plastic Hinge Behavior from Flexure and Axial Effects

   https://doi.org/10.21838/uhpc.16690  

   Sthapit, Ronit; Bandelt, Matthew (June 2023, International Interactive Symposium on UHPC)

   Aaleti, Sriram; Okumus, Pinar (Ed.)

   The unique mechanical properties of ultra-high performance concrete (UHPC) causes changes in failure modes and ductility in reinforced components. Numerous experiments have shown these materials, and others with similar ductile characteristics in tension, can improve the damage tolerance, strength, and ductility of members subjected to large deformations from seismic loading and similar extreme conditions. The use of these materials, however, has not been systematically studied to understand their application at a system-level performance and design procedures have been complicated due to their unconventional failure mechanism. This project aims to fill this gap by testing a targeted set of components subjected to combined effects of axial loads and bending with variations in axial load ratio and longitudinal reinforcement ratio. Additional experiments are planned to compare performance across other ductile concrete materials with variations in mechanical properties. The experimental results including load-deformation, reinforcement strain, concrete surface strain will be used to understand the parameters that have the highest influence on plastic hinge length and moment-rotation response which can ultimately help to validate analytical models against experiments based on these key parameters. 

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2. Effects of Axial Load and Tensile Strength on Reinforced UHPC Plastic Hinge Length

   https://doi.org/10.21838/uhpc.16658  

   Almeida, Joseph; Bandelt, Matthew (June 2023, International Interactive Symposium on UHPC)

   Aaleti, Sriram; Okumus, Pinar (Ed.)

   Researchers have explored the high energy absorption capacity and strength of UHPC materials to improve the seismic performance of structural components. Experimental results in the literature of reinforced UHPC members have indicated superior damage tolerance, higher strength and deformation capacities, and lower potential for collapse across a range of structural components. Investigations into the underlying failure mechanisms have highlighted the significance of the synergy between material tensile strength and reinforcement properties on member flexure response. Although research into the seismic application of reinforced UHPC continues to expand, relatively little is known about the effects of varying axial load on the plastic hinge response of beam-column elements across a range of UHPC tensile properties and reinforcement levels. Therefore, in this study, the effects of varying tensile properties on beam-column elements through numerical simulations across a range of axial load ratios were investigated. Two dimensional numerical models accounting for material nonlinearities (e.g., bond-slip, UHPC tensile strength and strain capacity) were used to capture component responses. Trends in the moment-drift responses and plastic hinge lengths have highlighted the diminishing returns of using higher fiber volume percentages (2%) as higher axial loads tend to relieve tensile demands. Additionally, existing plastic hinge length expressions for RC components were found to over-predict hinge length consistently while those developed for HPFRCC components accurately predict plastic hinge lengths at low axial load levels. 

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3. Galactic mass-to-light ratios with superfluid dark matter

   https://doi.org/10.1051/0004-6361/202243216  

   Mistele, T.; McGaugh, S.; Hossenfelder, S. (August 2022, Astronomy & Astrophysics)

   Context. We make rotation curve fits to test the superfluid dark matter model. Aims. In addition to verifying that the resulting fits match the rotation curve data reasonably well, we aim to evaluate how satisfactory they are with respect to two criteria, namely, how reasonable the resulting stellar mass-to-light ratios are and whether the fits end up in the regime of superfluid dark matter where the model resembles modified Newtonian dynamics (MOND). Methods. We fitted the superfluid dark matter model to the rotation curves of 169 galaxies in the SPARC sample. Results. We found that the mass-to-light ratios obtained with superfluid dark matter are generally acceptable in terms of stellar populations. However, the best-fit mass-to-light ratios have an unnatural dependence on the size of the galaxy in that giant galaxies have systematically lower mass-to-light ratios than dwarf galaxies. A second finding is that the superfluid often fits the rotation curves best in the regime where the superfluid’s force cannot resemble that of MOND without adjusting a boundary condition separately for each galaxy. In that case, we can no longer expect superfluid dark matter to reproduce the phenomenologically observed scaling relations that make MOND appealing. If, on the other hand, we consider only solutions whose force approximates MOND well, then the total mass of the superfluid is in tension with gravitational lensing data. Conclusions. We conclude that even the best fits with superfluid dark matter are still unsatisfactory for two reasons. First, the resulting stellar mass-to-light ratios show an unnatural trend with galaxy size. Second, the fits do not end up in the regime that automatically resembles MOND, and if we force the fits to do so, the total dark matter mass is in tension with strong lensing data. 

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4. Ultra and Very Long Period Seismic Signatures of Unsteady Eruptions Predicted From Conduit Flow Models

   https://doi.org/10.1029/2022JB024313  

   Coppess, Katherine R.; Dunham, Eric M.; Almquist, Martin (June 2022, Journal of Geophysical Research: Solid Earth)

   Abstract Explosive volcanic eruptions radiate seismic waves as a consequence of pressure and shear traction changes within the conduit/chamber system. Kinematic source inversions utilize these waves to determine equivalent seismic force and moment tensor sources, but relation to eruptive processes is often ambiguous and nonunique. In this work, we provide an alternative, forward modeling approach to calculate moment tensor and force equivalents of a model of eruptive conduit flow and chamber depressurization. We explain the equivalence of two seismic force descriptions, the first in terms of traction changes on conduit/chamber walls, and the second in terms of changes in magma momentum, weight, and momentum transfer to the atmosphere. Eruption onset is marked by a downward seismic force, associated with loss of restraining shear tractions from fragmentation. This is followed by a much larger upward seismic force from upward drag of ascending magma and reduction of magma weight remaining in the conduit/chamber system. The static force is upward, arising from weight reduction. We calculate synthetic seismograms to examine the expression of eruptive processes at different receiver distances. Filtering these synthetics to the frequency band typically resolved by broadband seismometers produces waveforms similar to very long period seismic events observed in strombolian and vulcanian eruptions. However, filtering heavily distorts waveforms, accentuating processes in early, unsteady parts of eruptions and eliminating information about longer (ultra long period time scale depressurization and weight changes that dominate unfiltered seismograms. Our workflow can be utilized to directly and quantitatively connect eruption models with seismic observations. 

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5. Functional Evaluation of a Personalized Orthosis for Knee Osteoarthritis: A Motion Capture Analysis

   https://doi.org/10.1115/1.4051626  

   Huber, Martin; Eschbach, Matthew; Kazerounian, Kazem; Ilies, Horea (December 2021, Journal of Medical Devices)

   null (Ed.)

   Abstract Orthotic treatments for knee osteoarthritis (OA) typically rely on simple mechanisms such as three-point bending straps and single-pin hinges. These commonly prescribed braces cannot treat bicompartmental knee OA, do not consider the muscle weakness that typically accompanies the condition, and employ hinges that restrict the knee's natural biomechanics. Utilizing a novel, personalized joint mechanism in conjunction with magnetorheological dampers, we have developed and evaluated a brace which attempts to address these shortcomings. This process has respected three principal design goals: reducing the load experienced across the entire knee joint, generating a supportive moment to aid the thigh muscles in shock absorption, and interfering minimally with gait kinematics. Two healthy volunteers were chosen to test the system's basic functionality through gait analysis in a motion capture laboratory. Combining the collected kinematic and force-plate data with data taken from sensors onboard the brace, we integrated the brace and leg system into a single inverse dynamics analysis, from which we were able to evaluate the effect of the brace design on the subjects' knee loads and moments. Of the three design goals: a reduction in knee contact forces was demonstrated; increased shock absorption was observed, but not to statistical significance; and natural gait was largely preserved. Taken in total, the outcome of this study supports additional investigation into the system's clinical effectiveness, and suggests that further refinement of the techniques presented in this paper could open the doors to more effective OA treatment through patient specific braces. 

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