Torsional Capacity of R/C beams

The torsional capacity of R/C beams is considered in this paper. On the basis of Batti and Almughrabi theory, a new general formula is proposed. Accordingly to their theory, this formula takes into account that stirrups influence the concrete torsional capacity because of their involvement in the aggregate interlock. A large number of previous test results, available in the literature (87 beams), has been considered to determine a few coefficients, by minimizing the coefficient of variation of the experimental-to-theoretical torsional capacity ratio. The obtained contributions of concrete and reinforcement on torsional capacity have both a sound physical meaning, which was not the case of the original Batti and Almughrabi\u2019s expressions. The theoretical results obtained with the proposed formula have been compared with the torsional capacities provided by other already available formulae and by some design codes. It is shown that the proposed formula is very efficient, since the computed capacities are very close to the test results and - on the whole - much closer than other well known formulae

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Shear Strength and Ductility of Reinforced High Performance Concrete Beam

Durability requirements in the design of a new structure have never been a primary concern before today. The use of high performance concrete seems to be the best solution to solve this problem. However, the correct use of this material requires the application of suitable code recommendations. In this context, it is well known that an important problem of reinforced concrete structures consists in evaluating shear strength. Several experimental researches have shown that RC beams shear failure can occur prior to flexural failure, often in a brittle way. Experimental researches conducted on normal strength concrete beams are the basis of the empirical equations, proposed by different codes, to evaluate the shear strength even in high performance concrete beams. In this paper shear strength of high strength reinforced concrete beams with or without shear reinforcement and /or steel fibers is experimentally investigated. Compressive strength, shear span-depth ratio and incorporation of steel fibers were adopted as major factors. In the range of variables tested, results indicate that beams with fibers and no stirrups, show a moment response and strength comparable to the response of beams with fibers and stirrups. Fibers (with or without stirrups) increase significantly bending stiffness after first cracking; shear strength is increased too and this fact altered failure modes which turns into flexural and are characterized by an enhanced ductility. Experimental evidence shows that, stirrups may be replaced by an adequate amount of fibers without compromising the overall structural behavior

Development of a micro-scale method to assess the effect of corrosion on the mechanical properties of a biodegradable Fe-316L stent material

The application of biodegradable materials to stent design has the potential to transform coronary artery disease treatment. It is critical that biodegradable stents have sustained strength during degradation and vessel healing to prevent re-occlusion. Proper assessment of the impact of corrosion on the mechanical behaviour of potential biomaterials is important. Investigations within literature frequently implement simplified testing conditions to understand this behaviour and fail to consider size effects associated with strut thickness, or the increase in corrosion due to blood flow, both of which can impact material properties. A protocol was developed that utilizes micro-scale specimens, in conjunction with dynamic degradation, to assess the effect of corrosion on the mechanical properties of a novel Fe-316L material. Dynamic degradation led to increased specimen corrosion, resulting in a greater reduction in strength after 48 h of degradation in comparison to samples statically corroded. It was found that thicker micro-tensile samples (h > 200 μm) had a greater loss of strength in comparison to its thinner counterpart (h < 200 μm), due to increased corrosion of the thicker samples (203 MPa versus 260 MPa after 48 h, p = 0.0017). This investigation emphasizes the necessity of implementing physiologically relevant testing conditions, including dynamic corrosion and stent strut thickness, when evaluating potential biomaterials for biodegradable stent application

An Integrated Pipeline for Combining in vitro Data and Mathematical Models Using a Bayesian Parameter Inference Approach to Characterize Spatio-temporal Chemokine Gradient Formation

All protective and pathogenic immune and inflammatory responses rely heavily on leukocyte migration and localization. Chemokines are secreted chemoattractants that orchestrate the positioning and migration of leukocytes through concentration gradients. The mechanisms underlying chemokine gradient establishment and control include physical as well as biological phenomena. Mathematical models offer the potential to both understand this complexity and suggest interventions to modulate immune function. Constructing models that have powerful predictive capability relies on experimental data to estimate model parameters accurately, but even with a reductionist approach, most experiments include multiple cell types, competing interdependent processes and considerable uncertainty. Therefore, we propose the use of reduced modelling and experimental frameworks in complement, to minimize the number of parameters to be estimated. We present a Bayesian optimization framework that accounts for advection and diffusion of a chemokine surrogate and the chemokine CCL19, transport processes that are known to contribute to the establishment of spatio-temporal chemokine gradients. Three examples are provided that demonstrate the estimation of the governing parameters as well as the underlying uncertainty.This study demonstrates how a synergistic approach between experimental and computational modelling benefits from the Bayesian approach to provide a robust analysis of chemokine transport. It provides a building block for a larger research effort to gain holistic insight and generate novel and testable hypotheses in chemokine biology and leukocyte trafficking

The critical importance of spatial and temporal scales in designing and interpreting immune cell migration assays

Intravital microscopy and other direct-imaging techniques have allowed for a characterisation of leukocyte migration that has revolutionised the field of immunology, resulting in an unprecedented understanding of the mechanisms of immune response and adaptive immunity. However, there is an assumption within the field that modern imaging techniques permit imaging parameters where the resulting cell track accurately captures a cell’s motion. This notion is almost entirely untested, and the relationship between what could be observed at a given scale and the underlying cell behaviour is undefined. Insufficient spatial and temporal resolutions within migration assays can result in misrepresentation of important physiologic processes or cause subtle changes in critical cell behaviour to be missed. In this review, we contextualise how scale can affect the perceived migratory behaviour of cells, summarise the limited approaches to mitigate this effect, and establish the need for a widely implemented framework to account for scale and correct observations of cell motion. We then extend the concept of scale to new approaches that seek to bridge the current “black box” between single-cell behaviour and systemic response