Track stiffness is the one of the most critical parameters of the track structure. Its evaluation is important to assess track quality, component performance, localised faults and optimise maintenance periods and activities. Keeping the track stiffness within acceptable range of values is connected with keeping the railway network in a satisfactorily performing condition, allowing thereby upgrade of its capacity (speed, load, intensity). Current railway standards are changing to define loading and stiffness requirements for improved ballasted and ballastless performance under high speed train traffic. In recent years various techniques have been used to measure track deflection which have been also used to validate numerical models to assess various problems within the railway network. Based on recent introduction of the Video Gauge for its application in the civil engineering industry this project provides the proof of effective applicability of this DIC (Digital image correlation) tool for the accurate assessment of track deflection and the calculation of track stiffness through its effective applicability in various track conditions for assessing the stiffness of various track forms including track irregularities where abrupt change in track stiffness occur such as transition zones and rail joints. Attention is given in validation of numerical modelling of the response of insulated rail joints under the passage of wheel load within the goal to improve track performance adjacent to rail joints and contribute to the sponsoring company s product offering. This project shows a means of improving the rail joint behaviour by using external structural reinforcement, and this is presented through numerical modelling validated by laboratory and field measurements. The structural response of insulated rail joints (IRJs) under the wheel vertical load passage is presented to enhance industry understanding of the effect of critical factors of IRJ response for various IRJ types that was served as a parametric FE model template for commercial studies for product optimisation.

abstract: This paper describes an effort to bring wing structural stiffness and aeroelastic considerations early in the conceptual design process with an automated tool. Stiffness and aeroelasticity can be well represented with a stochastic model during conceptual design because of the high level of uncertainty and variability in wing non-structural mass such as fuel loading and control surfaces. To accomplish this, an improvement is made to existing design tools utilizing rule based automated design to generate wing torque box geometry from a specific wing outer mold-line. Simple analysis on deflection and inferred stiffness shows how early conceptual design choices can strongly impact the stiffness of the structure. The impacts of design choices and how the buckling constraints drive structural weight in particular examples are discussed. The model is then carried further to include a finite element model (FEM) to analyze resulting mode shapes and frequencies for use in aeroelastic analysis. The natural frequencies of several selected wing torque boxes across a range of loading cases are compared. / Dissertation/Thesis / Masters Thesis Aerospace Engineering 2018

L'homéostasie épidermique repose sur différents paramètres dont les propriétés mécaniques du tissu de soutien, le derme, et les tensions intrinsèques dans le tissu épithélial. Lors de la cicatrisation, l'augmentation de la rigidité cutanée résultante peut perturber les conditions initiales de l'homéostasie. Afin de mieux comprendre les mécanismes cellulaires dans ce contexte physiopathologique, et l'incidence des propriétés mécaniques du derme sur le comportement du kératinocyte humain, des cellules primaires ont été cultivés à la surface d'hydrogels de polyacrylamide de différentes rigidités, et sur le plastique (> GPa), condition in vitro classiquement utilisée. Nos résultats ont mis en évidence que les substrats les plus mous favorisent un arrêt de prolifération et un profil phénotypique similaire à un kératinocyte différencié, alors que les substrats les plus rigides facilitent l'adhérence et la prolifération au détriment de la capacité de différenciation, et ce de façon graduelle. L'analyse transcriptomique par séquençage haut débit a permis d'identifier un récepteur membranaire orphelin couplé à la protéine G, GPRC5A (G Protein-Coupled Receptor Class C Group 5 Member A) et une protéine du cytosquelette, la spectrine beta III, dont les augmentations d'expression sont corrélées à l'augmentation de la rigidité. In vivo, GPRC5A est exclusivement localisé dans les berges de la plaie, lieu des kératinocytes en migration. Ces observations ont été confirmées par l'utilisation d'outils d'ARN interférence (siRNA et shRNA) dirigés contre GPRC5A dans les kératinocytes humains, montrant l'implication de ce récepteur dans l'adhérence et la migration cellulaire. De plus, les résultats montrent que la diminution de GPRC5A entraine un défaut de différenciation et d'organisation du feuillet épidermique, conduisant notamment à une mort cellulaire accrue, dans un modèle d'épiderme reconstruit. En parallèle, par des approches similaires d'ARN interférence dirigée contre le gène SPTBN2 (spectrin beta non-erythrocytic 2) codant pour la spectrine beta III, les résultats mettent en évidence un rôle fonctionnel de la spectrine beta III dans la prolifération cellulaire, l'étalement, la migration des kératinocytes et participe à la mécanotransduction en réponse à la rigidité en permettant la survie cellulaire. L'ensemble des résultats de la thèse montrent une adaptation phénotypique des kératinocytes dépendante de la rigidité du substrat sur lequel ils se trouvent et positionne GPRC5A et la spectrine beta III comme des acteurs clés dans la réponse du kératinocyte primaire humain aux changements mécaniques. Ces résultats permettent d'ouvrir de nouvelles voies stratégiques pour le traitement de la cicatrisation et plus largement dans les pathologies affectant la mécanique cutanée / Epidermal homeostasis is determined by several characteristics, including dermis mechanical properties. During skin wound healing, dermis mechanical properties are modified and can alter epidermal integrity. Accordingly, it is essential to understand how keratinocytes respond and adapt to mechanical changes; however, these mechanisms remain unclear. To investigate how mechanical properties of cell microenvironment affect the human keratinocyte, primary cells were seeded on polyacrylamide hydrogels of different compliances (soft: 4 kPa, medium: 14 kPa, rigid: 45 kPa) in comparison with glass coverslip (> GPa). The results showed that on the softer hydrogel, keratinocyte spreading and proliferation were strongly decreased, while a strong increase in the expression of late differentiation markers was observed. On the contrary, the stiffer substrates promote adhesion and proliferation. Moreover, a transcriptomic profiling analysis reveals G protein-coupled receptor, class C, group 5, member A (GPRC5A) and spectrin beta non-erythrocytic 2 (SPTBN2) as potential mechanosensors for substrate adaptation of the keratinocyte. Actually, GPRC5A and SPTBN2 gene expression levels are associated with stiffness increase. We have characterized a dynamic relocation of GPRC5A during keratinocyte adhesion. Furthermore, the knockdown of GPRC5A increased cell adhesion and reduced cell migration. These results were confirmed by GPRC5A immunostaining in healing wounds from mice skin, showing a transient and specific expression of GPRC5A at wound leading edges, a site of cell migration, thus strengthening a role of GPRC5A in the keratinocyte migration process. Concerning SPTBN2, the knockdown of SPTBN2 decreased cell proliferation, spreading and migration, indicating a functional role in keratinocyte processes. Moreover, SPTBN2 knockdown induced keratinocyte death on soft substrate. In conclusion, we demonstrated an adaptive response of keratinocytes depending on substrate stiffness. We also found a new function of GPRC5A in keratinocyte process during skin wound healing and a mechanosensor role of SPTBN2 in keratinocyte. All of these results place GPRC5A and SPTBN2 as key regulators in the response to mechanical changes. These results pave new strategic pathways in skin wound healing treatment, and more widely in the pathologies affecting cutaneous mechanics

Shallow embedded steel column connections are widely used in steel buildings; however, there is insufficient research about this connection type to understand the actual rotational stiffness that the connection provides. Shallow embedded steel columns are when a steel column is anchored to the foundation slab and then unreinforced concrete is poured around the base plate and the base of the column. This thesis seeks to further quantify the rotational stiffness available in this type of connection due to the added concrete and improve an existing model in order to represent the rotational stiffness. Existing data from two series of experiments on shallow embedded columns were used to validate and improve an existing rotational stiffness model. These two data sets were reduced in the same manner so that they could be compared to one another. In addition, the rotational stiffness for each test column was determined so they could be evaluated against the outputs of the model. The existing model was improved by evaluating each parameter in the model: the modulus of subgrade reaction, exposed column length, modulus of concrete for the blockout and the foundation slab, flange effective width, embedment depth, and effective column depth. It was determined that the model was sensitive to the subgrade reaction, modulus of concrete, embedment depth and effective column depth. The exposed length was not a highly sensitive parameter to the model. Flange effective width was determined to not be needed, especially when the other parameters were altered.

This work develops and examines design strategies for reducing the stiffness of 3D-printed compliant mechanisms. The three aspects of a flexure that determine its stiffness are well known: material, boundary conditions, and geometry. In a highly constrained design space however, flexure stiffness may remain unacceptably high even while arriving at the limits of design constraints. In this work, changes to geometry and boundary conditions are examined that lead to drastically reduced stiffness behavior without changing flexure thickness, width, or length. Changes to geometry can result in very complex mechanisms. However, 3D printing enables almost arbitrarily complex geometries. This dissertation presents three design strategies for stiffness reduction: static balancing, lattice flexures, and compound joints. Static balancing refers to changes in the boundary conditions that result in a near-zero net change in potential energy storage over the useful deflection of a flexure. In this work, I present a method for static balancing that utilizes non-dimensional parameters to quickly synthesize a joint design with stiffness reduced by nearly 90%. This method is not only simple and straightforward, it is applicable to a wide range of flexure topologies. The only requirements on the joint to be balanced are that it must be approximated as a pin joint and torsion spring, and it must have a well-understood stiffness when subjected to a compressive load. Lattice flexures result from modifications to geometry that reduce cross-sectional area without changing width or thickness. However, the reduction in stiffness is greater than the reduction in cross sectional area. This can occur because the bending load is now carried by beams partially in torsion. Two lattice geometries are proposed and analyzed in detail using analytic and numeric techniques. It is shown that the off-axis stiffness behavior of lattice flexures can be better than that of conventional blade flexures while bending stiffness is reduced >60%. Compound joints are those that consist of arrays of flexures arranged co-axially. This arrangement provides increased range of motion, generally decreased stiffness, and improved stability. Additionally, a method is herein presented to reduce the parasitic center shift of a compound joint to nearly zero at a specified deflection. The penultimate chapter demonstrates how all three strategies can be used together, and includes new results to facilitate their combination.

This paper focuses on illustrating the effectiveness of the new material model, 𝜏𝐵𝑇𝑅 in comparison with the Specifications for Structural Steel Buildings (2016) material model, 𝜏𝐴𝐼𝑆𝐶 , against a detailed finite element model to determine the accuracy of modeling the inelastic behavior of steel W-Shapes. A total of seven steel columns were analyzed, using a W8x31 section, and eleven benchmark frames to compare the performance of the two material models. An ultimate strength study was conducted using the following slenderness ratios, L/r, of 40, 60, 80, 100, 120, 160, and 200 and oriented such that minor-axis bending occurs. The benchmark frames were modeled under a limit load analysis to illustrate the magnitude of stiffness reduction considering both major and minor-axis bending. Lateral displacements were recorded and compared for the eleven frames up to the collapse condition. Additional information is provided discussing the capabilities of the two material models and their performance when compared to a detailed finite element model. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

<p>There is consistent research evidence that shows improvement of the engineering properties of subgrade soils treated with lime or cement. However, limited information is available on the effect of climatic changes on the subgrade stiffness. The thesis studies the effects of changes in soil moisture content and temperature on the resilient modulus of treated and untreated subgrades in Indiana. Two types of soils were tested: A-6 and A-7-6, from two locations in Indiana: Hartford City and Bloomington, respectively. When existing standards ASTM D559/559-15 and ASTM D560/560-16 for wetting/drying (WD) and freezing/thawing (FT) processes, respectively, were followed, the treated and untreated samples failed through the process of preparation due to the stringent procedures in the standards. Appropriate test conditions were investigated, as part of the research, to develop new protocols more appropriate to the field conditions in Indiana. Two new test protocols were developed and successfully applied to the treated soils. A total of 26 resilient modulus, M_R, tests were conducted following the standard AASHTO T307-99. The M_R results showed that the repeated action of WD and FT cycles reduced the stiffness of the chemically-treated soils down to values similar to or lower than those of the untreated soils. However, when the amount of chemical was doubled, with respect to the optimum, the M_R of the treated soils improved over that of the untreated soils, even after the wetting-drying cycles.</p>

The goal of this thesis is to determine whether continuity ties in large wood diaphragms are stiff enough to engage and provide diaphragm flexural stiffness in a collective chord model. Four series of continuity tie assemblies using Simpson Strong-Tie steel connectors were tested to determine the stiffness of each assembly. The results found from testing were applied to an example building and then analyzed using both the traditional chord method and the collective chord method. The completed analysis on a typical size warehouse building showed that the collective chord model will act inadvertently on an existing building designed with a traditional chord, or alternatively will potentially act intentionally in the design of a new building. The relative stiffness of the continuity ties will determine if they engage and allow them to act collectively. The testing and analysis completed creates a basis for further research into the actual static and dynamic behavior of these diaphragms. The collective chord model does seem to be a reasonable approximation for how diaphragms actually behave. If more research is conducted into different shaped and sized buildings to confirm that the collective chord model will work on most buildings then it will be a more accurate way to design new diaphragms and analyze existing diaphragms than the current traditional model.

One of the major challenges of engineering is finding the proper balance between economical and safe. Currently engineers at Nucor Corporation have ignored the additional lateral bracing provided by standing seam roofing systems to joists because of the lack of methods available to quantify the amount of bracing provided. Based on the results of testing performed herein, this bracing is significant, potentially resulting in excessively conservative designs and unnecessary costs. This project performed 26 tests with Vulcraft joists in a pressure box to investigate the effects of how many variables influence the lateral bracing provided to joists from standing seam roofing systems, including the variables joist length, panel gauge, clip height, thermal block presence, insulation thickness, and top chord size. Two methods were developed to account for this additional bracing: finite element computer modeling and an application of the Rayleigh-Ritz method called the Column-on-Elastic-Foundation Method. Variables influencing the pressure at failure, namely chord size and deck gauge, were those with the greatest effect on additional lateral bracing provided from standing seam roof systems. It was determined that higher roof stiffness values and higher failure pressures yield shorter effective lengths.

Introduction: Chronic hepatitis B (CHB) is a viral infection that can lead to development of fibrosis and hepatocellular carcinoma (HCC). Several factors affecting disease progression have been reported, such as sex and region of origin. Liver stiffness and fibrosis can be evaluated using transient elastography. The degree of fibrosis is an important parameter when deciding if treatment and HCC surveillance is indicated. Aim1) To compare patients with CHB according to sex and region of origin regarding the parameters liver stiffness, presence of significant fibrosis, hepatitis B e antigen (HBeAg) positivity, frequency of elevated alanine aminotransferase (ALT) levels and HCC surveillance.2) To identify factors associated with significant liver fibrosis. Methods: 410 patients with a registered doctor’s visit 2015–2018 at the Department of Infectious Diseases at Örebro University Hospital were included. A systematic review of medical records was performed and groups (women-men, regions of origin) were compared. Multivariate logistic regression was used to identify factors associated with significant fibrosis. Results: Men had significantly higher liver stiffness values, higher presence of significant fibrosis, and were more frequently under HCC surveillance compared to women. No other significant differences were found regarding the studied parameters, neither related to sex, nor to region of origin. Factors associated with significant fibrosis were: male sex, elevated ALT levels and hepatitis D virus (HDV) co-infection. Conclusions: Men had a higher frequency of significant fibrosis compared to women. Factors associated with significant fibrosis were male sex, elevated ALT values and HDV co-infection.