For new railway bridges with short spans (L ≤ 35.00 m) superstructures with steel beams embedded in concrete are recommended or used, which can ensure the requirements of strength and stiffness in particular, regardless of velocity. They are built relatively easily compared to reinforced concrete structures or steel structures, they have high durability if designed, built and maintained correctly and don’t have high sensitivity to fatigue degradation in service. They are also used for road bridges when it is desired to achieve a reduced construction height.
In all the design prescriptions used so far for structures with steel beams embedded in concrete, the calculation is a simplified one, made on a single insulated longitudinal beam of the deck, if certain conditions related to the geometry of the structure are met (obliquity, curvature). Simplifications are also made regarding the state of deformation of the decks made in this constructive solution by introducing an effective moment of inertia in the displacement calculation, as an average of the inertia moments of the cross section considered to be cracked and respectively un-cracked.
The article aims to validate steel and concrete elasto-plastic models, based on an experiment from the technical literature, necessary for complex analyses of the percentage of concrete involved in the stiffness of the cross-sections, in case of bridges with steel beams embedded in concrete.
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Geotechnical and structural engineers are faced with a difficult task when their designs interact with each other. For complex projects, this is more the norm than the exception. In order to help bridge that gap, a method for modeling the behavior of a foundation using a simple elasto-plastic subgrade reaction was developed. The method uses an optimization technique to position 4-6 springs along a pile foundation to produce similar load deflection characteristics that were modeled by more sophisticated geotechnical finite element software. The methodology uses an Excel spreadsheet for accepting user input and delivering an optimized subgrade spring stiffness, yield, and position along the pile. In this way, the behavior developed from the geotechnical software can be transferred to the structural analysis software. The optimization is achieved through the solver add-in within Excel. Additionally, a beam on a nonlinear elastic foundation model is used to compute deflections of the optimized subgrade reaction configuration.
In this paper an alternative material model using a generalized J2 finite-strain flow plasticity theory with isotropic hardening is presented. The model is based on a new nonlinear continuum mechanical theory of finite deformations of elasto-plastic media which allows for the development of objective and thermodynamically consistent material models. As a result, the constitutive equation, the evolution equation and even the ‘normality rule’, characterising the plastic flow in the material during return mapping, can be expressed in various forms, using several instances of the yield surface and corresponding pairs of stress measures and strain rates, respectively, which are conjugate with respect to the internal mechanical power and its arbitrary higher order time derivative. Therefore the results of the material model when used in numerical analyses are not affected by the description and particularities of the material model formulation. Here, we briefly outline the nonlinear continuum theory along with a detailed description of the material model and finally present the model in a numerical example using a cross-shaped specimen in biaxial tension.
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The form of incremental constitutive equations for granular soils is discussed for the triaxial configuration. The classical elasto-plastic approach and the semi-empirical model are discussed on the basis of constitutive relations determined directly from experimental data. First, the general structure of elasto-plastic constitutive equations is presented. Then, the structure of semiempirical constitutive equations is described, and a method of calibrating the model is presented. This calibration method is based on a single experiment, performed in the triaxial apparatus, which also involves a partial verification of the model, on an atypical stress path. The model is shown to give reasonable predictions. An important feature of the semi-empirical incremental model is the definition of loading and unloading, which is different from that assumed in elasto-plasticity. This definition distinguishes between spherical and deviatoric loading/unloading. The definition of deviatoric loading/unloading has been subject to some criticism. It was therefore discussed and clarified in this paper on the basis of the experiment presented.
In this paper, the authors propose a studying method for the deformation that appears before crack of ductile materials using the Lode parameter determined by the numerical calculation applied on simple models, verified in previous studies. In order to highlight the influence of the Lode parameter, the tests were performed at simple but also at compound tests. The necessity of these studies lies in the fact that the acknowledged models (the use of the integral J, the critical stress intensity factor Kc or the CPCD method) do not fully explain the phenomenon of deformation before breaking the elasto-plastic materials. The tests were imagined under the form of sets. Each set of tests was performed on smooth specimens and on specimens with a notch radius of 0.5, 2, 4 and 10 mm. Also, each set of tests was performed for pure tensile and combined tensile-torque test.
This research investigates the physical-chemical, sensorial and mechanical characteristics of starch-based edible films incorporating three types of bee hive products: honey, propolis and bee bread, in concentrations varying from 1% to 3%, reported to starch. The results indicates an increasing of films moisture, water activity, ash content and acidity, in the order: honey<propolis<bee bread, all values increasing with the increasing of hive products percentage into the control film; aw is remaining at very low values, under 0.4. Sensorial analysis indicated honey as the better suited for improving taste and flavour and bee bread for increasing colour intensity of the films; the sensorial characteristics are maintained during 30 days of films storage, in all cases. Compared with the control starch-based film (which is elastic, brittle and hard), the films containing 2% bee hive products are elasto-plastic and more resistant to penetration, the resistance increasing in the order: bee bread<propolis<honey.