The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
Xiao Dong Chen - One of the best experts on this subject based on the ideXlab platform.
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microwave heating of an infinite Solid Slab and its thermal stability analysis using steady state bifurcation theory
Journal of Food Engineering, 1998Co-Authors: Xiao Dong ChenAbstract:This paper presents an analytical solution of the steady state temperature profiles in a microwave heated Slab. The analytical solution has been obtained by taking advantages of the well known Frank-Kamenetskii thermal ignition theory. Both the finite Biot number and infinite Biot number boundary conditions have been considered and their effects upon the critical parameters for the onset of thermal instability evaluated.
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some characteristics of transient self heating inside an exothermically reactive porous Solid Slab
Process Safety and Environmental Protection, 1995Co-Authors: Xiao Dong Chen, L V ChongAbstract:We report the results of numerical simulations and laboratory investigations carried out to explore the characteristics of the transient self-heating process. Various initial and boundary conditions were considered. It was demonstrated that a characteristic temperature, defined as the crossing-point temperature, does not change (to within ±0.01°C) for the same exothermicity, activation energy, thermal properties, half-thickness and boundary temperature when only the initial uniform temperature is varied. This initial temperature must be lower than the critical ignition boundary temperature and the boundary temperature must not be supercritical to lead to a periphery ignition. This crossing-point temperature may be used as a physicochemical property to indicate the propensity of a Solid material to self-heat. The calculations also suggest a linear temperature dependence of the heat conduction term in the energy balance applied at the symmetry of a Slab for a certain temperature range, from a value smaller than the crossing-point temperature to a value just before ignition. This concept of a crossing-point temperature was confirmed by experiments carried out on a wood sawdust
E. Vishnuvardhanarao - One of the best experts on this subject based on the ideXlab platform.
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Conjugate heat transfer study of incompressible turbulent offset jet flows
Heat and Mass Transfer, 2009Co-Authors: E. Vishnuvardhanarao, Manab Kumar DasAbstract:In the present case, the conjugate heat transfer involving a turbulent plane offset jet is considered. The bottom wall of the Solid block is maintained at an isothermal temperature higher than the jet inlet temperature. The parameters considered are the offset ratio (OR), the conductivity ratio ( K ), the Solid Slab thickness ( S ) and the Prandtl number ( Pr ). The Reynolds number considered is 15,000 because the flow becomes fully turbulent and then it becomes independent of the Reynolds number. The ranges of parameters considered are: OR = 3, 7 and 11, K = 1–1,000, S = 1–10 and Pr = 0.01–100. High Reynolds number two-equation model ( k –ε) has been used for turbulence modeling. Results for the Solid–fluid interface temperature, local Nusselt number, local heat flux, average Nusselt number and average heat transfer have been presented and discussed.
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Computational study of heat transfer in a conjugate turbulent wall jet flow with constant heat flux
International Journal of Numerical Methods for Heat & Fluid Flow, 2009Co-Authors: E. VishnuvardhanaraoAbstract:Purpose – The purpose of this paper is to consider the conjugate heat transfer from a flat plate involving a turbulent plane wall jet. The bottom wall of the Solid block is heated by a constant heat flux.Design/methodology/approach – High Reynolds number two‐equation model (κ‐ϵ) has been used for turbulence modeling. The parameters considered are the conductivity ratio of Solid and fluid, the Solid Slab thickness and the Prandtl number. The Reynolds number considered is 15,000 because the flow becomes fully turbulent and then is independent of the Reynolds number. The range of parameters considered are: conductivity ratio = 1‐1,000, Solid Slab thickness = 1‐10 and Prandtl number = 0.01‐100.Findings – The non‐dimensional bottom surface temperature is high for high‐Prandtl number fluid and vice versa. As conductivity ratio increases, it decreases whereas it increases with the increase in Slab thickness. Similar trend is observed for the distribution of the interface temperature. The Nusselt number computed ...
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Computational Study of Heat Transfer in a Conjugate Turbulent Wall Jet Flow at High Reynolds Number
Journal of Heat Transfer-transactions of The Asme, 2008Co-Authors: E. VishnuvardhanaraoAbstract:In the present case, the conjugate heat transfer involving the cooling of a heated Slab by a turbulent plane wall jet has been numerically solved. The bottom of the Solid Slab is maintained at a hot uniform temperature, whereas the wall jet temperature, is equal to the ambient temperature. The Reynolds number considered is 15,000 because it has already been experimentally found and reported that the flow becomes fully turbulent and is independent of the Reynolds number. The high Reynolds number two-equation model (K-e) has been used for the turbulence modeling. The parameters chosen for the study are the conductivity ratio of the Solid-fluid (K), the Solid Slab thickness (S), and the Prandtl number (Pr). The ranges of parameters are K= 1-1000, S=1-10, and Pr=0.01-100. Results for the Solid-fluid interface temperature, local Nusselt number, local heat flux, average Nusselt number, and average heat transfer are presented and discussed.
Joost C. Walraven - One of the best experts on this subject based on the ideXlab platform.
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Using Eurocodes and Aashto for assessing shear in Slab bridges
Proceedings of the Institution of Civil Engineers - Bridge Engineering, 2016Co-Authors: Eva O. L. Lantsoght, C. Van Der Veen, A. De Boer, Joost C. WalravenAbstract:Reinforced concrete short-span Solid-Slab bridges are used to compare Dutch and North American practices. As an assessment of existing Solid-Slab bridges in the Netherlands showed that the shear capacity is often governing, this paper provides a comparison between Aashto (American Association of State Highway and Transportation Officials) practice and a method based on the Eurocodes, and recommendations from experimental research for the shear capacity of Slab bridges under live loads. The results from recent Slab shear experiments conducted at Delft University of Technology indicate that Slabs benefit from transverse force redistribution. For ten selected cases of straight Solid-Slab bridges, unity checks (the ratio between the design value of the applied shear force and the design beam shear resistance) are calculated according to the Eurocode-based method and the Aashto method. The results show similar design shear forces but higher shear resistances in the North American practice, which is not surprising as the associated reliability index for Aashto is lower.
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effective width in shear of reinforced concrete Solid Slab bridges under wheel loads
93rd Annual Meeting Transportation Research Board Washington USA 12-16 January 2014; Authors version, 2014Co-Authors: Eva O. L. Lantsoght, C. Van Der Veen, A. De Boer, Joost C. WalravenAbstract:ABSTRACT 4 5 For the assessment of reinforced concrete Slab bridges in the Netherlands, the shear stress 6 resulting from the dead loads and live loads is determined in a spreadsheet or from a finite 7 element model. In a spreadsheet-based approach, an assumption for the distribution of the loads 8 from the wheel prints is necessary. When finite element methods are used, it is necessary to 9 determine over which length (a multiple of the effective depth) the peak shear stress can be 10 distributed for comparison to the design shear capacity. 11 To recommend a load-spreading method, experiments were executed on Slab strips of 12 increasing widths. The shear capacity did not increase with the increasing width upon passing a 13 threshold. This threshold is compared to different load spreading methods, indicating that a 14 distribution from the far side of the wheel print is to be preferred. This recommendation is also 15 supported by the results of a statistical analysis and the stress distribution in nonlinear finite 16 element models. 17 To find the distribution width in a finite element method, a numerical model is compared 18 to an experiment on a Slab subjected to a concentrated load in which the support consists of a line 19 of 7 bearings equipped with load cells measuring the reaction forces. These measurements were 20 compared to the stress profile at the support from the model, showing that the peak can be 21 distributed over 4 times the effective depth. 22 These recommendations for the effective width and distribution width are research-based 23 tools that replace the previously used rules of thumb resulting from engineering judgement. 24
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Applying Experimental Results to the Shear Assessment Method for Solid Slab Bridges
2013Co-Authors: Eva O. L. Lantsoght, C. Van Der Veen, Joost C. Walraven, A. De BoerAbstract:The combination of increased live loads and a more conservative shear capacity in the recently implemented Eurocodes, resulted in a large number of existing Solid Slab bridges in the Netherlands being shear-critical upon assessment. However, an enhancement of the shear capacity can occur in Slabs under concentrated wheel loads due to transverse load redistribution. To quantify this effect, a comprehensive series of experiments on Slabs and Slabs strips under a concentrated load near to the support and under a combination of a concentrated and a line load was carried out. The experiments show the difference in behaviour for Slabs, carrying the load in a two-dimensional way, as compared to beams in shear. The results from the laboratory research are used to develop recommendations, that are easily used in combination with the codes. These recommendations are implemented in a spreadsheet-based first-level assessment tool, the Quick Scan method. The assessment with this tool of selected cases of existing Solid Slab bridges shows that applying the experimental results into the assessment practice leads to an improved selection ability of the Quick Scan method.
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Shear assessment of reinforced concrete Slab bridges
IABSE Symposium Report, 2013Co-Authors: Eva O. L. Lantsoght, C. Van Der Veen, Joost C. Walraven, A. De BoerAbstract:The capacity of reinforced concrete Solid Slab bridges in shear is assessed by comparing the design beam shear resistance to the design value of the applied shear force due to the permanent actions and live loads. Results from experiments on half-scale continuous Slab bridges are used to develop a set of recommendations for the assessment of Slab bridges in shear. A method is proposed allowing to take the transverse force redistribution in Slabs under concentrated loads into account, as well as a horizontal load spreading method for the concentrated loads. For selected cases of existing straight Solid Slab bridges, a comparison is made between the results based on the shear capacity according to the Dutch Code NEN 6720 and from the combination of the Eurocode (EN 1992-1- 1:2005) with the recommendations, showing an improved agreement.
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Shear capacity of Slabs under a combination of loads
2013Co-Authors: Eva O. L. Lantsoght, C. Van Der Veen, Joost C. WalravenAbstract:Existing Solid Slab bridges under a combination of wheel loads and distributed traffic loads sometimes do not fulfil the code requirements for shear. However, reinforced concrete Slabs loaded close to the support are subjected to shear stresses which might result in a failure mode of combined punching and shear. This behaviour is studied in a first series of experiments on Slabs under a concentrated load close to the support, and these experiments resulted in a set of recommendations. To verify if these recommendations can be used when assessing Solid Slab bridges under distributed and concentrated loads, Slabs under a combination of a line load, representing the dead weight, and a concentrated load, representing a wheel load, are tested up to failure. The experimental results are used to assess the ultimate shear which can be carried at the support and the influence of the varied parameters is discussed. The results demonstrate how different types of loading such as dead loads and live loads can be superposed and how a stress check at the support can be carried out.
L V Chong - One of the best experts on this subject based on the ideXlab platform.
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some characteristics of transient self heating inside an exothermically reactive porous Solid Slab
Process Safety and Environmental Protection, 1995Co-Authors: Xiao Dong Chen, L V ChongAbstract:We report the results of numerical simulations and laboratory investigations carried out to explore the characteristics of the transient self-heating process. Various initial and boundary conditions were considered. It was demonstrated that a characteristic temperature, defined as the crossing-point temperature, does not change (to within ±0.01°C) for the same exothermicity, activation energy, thermal properties, half-thickness and boundary temperature when only the initial uniform temperature is varied. This initial temperature must be lower than the critical ignition boundary temperature and the boundary temperature must not be supercritical to lead to a periphery ignition. This crossing-point temperature may be used as a physicochemical property to indicate the propensity of a Solid material to self-heat. The calculations also suggest a linear temperature dependence of the heat conduction term in the energy balance applied at the symmetry of a Slab for a certain temperature range, from a value smaller than the crossing-point temperature to a value just before ignition. This concept of a crossing-point temperature was confirmed by experiments carried out on a wood sawdust
Eva O. L. Lantsoght - One of the best experts on this subject based on the ideXlab platform.
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Shear capacity of the Ruytenschildt bridge
2020Co-Authors: Eva O. L. Lantsoght, C. Van Der Veen, A. De BoerAbstract:In August 2014, the Ruytenschildt Bridge, a reinforced concrete Solid Slab bridge (reinforced with plain bars) in the Friesland province in the Netherlands was tested until failure. One of the goals of proof loading and testing this bridge to failure, was to study the failure mode of existing Slab bridges. The combination of smaller shear capacities as prescribed by the Eurocode in combination with the heavier live load models, has raised concerns with regard to a number of existing Slab bridges in the Netherlands. As the shear capacity of existing bridges is under study, the results of testing an actual Slab bridge until failure are used to compare to the results of testing half-scale Slab specimens in the laboratory, and the conclusions resulting from those experiments. In this paper, the results of the predictions based on the first order of approximation rating procedure from the Netherlands for shear, the Quick Scan method, as well as based on predictions of the failure mode and the average predicted capacity are compared to the experimental results. The predictions show a possibility of shear failure in the second span of the bridge. The experiment showed that both spans of the bridge failed in flexure. The observed failure mode is important, as some of the results indicate that the Solid Slab bridges, currently under discussion with regard to their shear capacity, fail in flexure in reality. Flexural failure is considered a ductile failure compared to the brittle failure mode in case of a shear failure.
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Shear and Moment Capacity of the Ruytenschildt Bridge
2020Co-Authors: Eva O. L. Lantsoght, C. Van Der Veen, A. De BoerAbstract:In August 2014, the Ruytenschildt Bridge, a reinforced concrete Solid Slab bridge, in Friesland, the Netherlands was tested until failure. One of the goals of the experiment is to analyze the failure mode of the Slab bridge under a tandem of 4 wheel loads and to compare the capacity of the full bridge structure to the predicted results, to have an idea of the residual strength of existing bridges. The methods used are experi-mental (testing of the bridge to failure in two of its five spans) and analytical. The analytical work involved predicting the bending moment capacity, the shear capacity and the punching capacity of the bridge. In both spans, the bridge failed in flexure. The total capacity during the experiment was significantly higher than pre-dicted. The results indicate that the traditional rating procedures for shear are very conservative when applied to Slab bridges that benefit from transverse load redistribution.
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Determination of Loading Protocol and Stop Criteria for Proof Loading with Beam Tests
High Tech Concrete: Where Technology and Engineering Meet, 2018Co-Authors: Eva O. L. Lantsoght, Cor Van Der Veen, Yu-guang Yang, Ane De Boer, Dick A. HordijkAbstract:Proof loading of existing bridges is an interesting option when insufficient information about a bridge is available. To safely carry out a proof loading test, high loads are placed on the bridge. To avoid permanent damage to the structure, a controlled loading protocol needs to be described, and the measurements need to be closely monitored to identify the onset of distress. The criteria from existing codes and guidelines to evaluate the measurements, called stop criteria, are not universally applicable. To develop recommendations for proof loading of reinforced concrete Solid Slab bridges, beam experiments were analysed. The beams were heavily instrumented to evaluate the existing stop criteria, and possibly develop new stop criteria. The result of these experiments is the development of a standard loading protocol for the proof loading of reinforced concrete Slab bridges. Recommendations for the use of the stop criteria are also formulated. These insights are used to develop a new guideline for the proof loading of reinforced concrete Slab bridges in the Netherlands.
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Probabilistic prediction of the failure mode of the Ruytenschildt Bridge
Engineering Structures, 2016Co-Authors: Eva O. L. Lantsoght, Cor Van Der Veen, Ane De Boer, Da Dick HordijkAbstract:In the Netherlands, the shear capacity of a large number of existing reinforced concrete Solid Slab bridges is subject to discussion, as initial assessments indicated that their capacity was insufficient. In certain cases, the deterministic value of the moment capacity is larger than the deterministic value of the shear capacity. However, when the variability of the material properties, and of the capacity models themselves are factored in, a probability of a certain failure mode can be calculated. Here, a method is introduced to calculate the chance that a cross-section fails in shear before it fails in bending. The method that is derived here is applied to the Ruytenschildt Bridge. This case study is a reinforced concrete Solid Slab bridges that was tested to failure in two spans during the summer of 2014. The relative probability of failure in shear of the bridge was determined. The predictions indicated a smaller probability of a shear failure than of a bending moment failure. In the first tested span, failure was not reached, but indications of flexural distress were observed. In the second span, a flexural failure was achieved, in line with the probabilistic predictions. The presented method can be used in the assessment of existing bridges to determine which failure mode is most probable, taking into account the variability of materials and capacity models.
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Using Eurocodes and Aashto for assessing shear in Slab bridges
Proceedings of the Institution of Civil Engineers - Bridge Engineering, 2016Co-Authors: Eva O. L. Lantsoght, C. Van Der Veen, A. De Boer, Joost C. WalravenAbstract:Reinforced concrete short-span Solid-Slab bridges are used to compare Dutch and North American practices. As an assessment of existing Solid-Slab bridges in the Netherlands showed that the shear capacity is often governing, this paper provides a comparison between Aashto (American Association of State Highway and Transportation Officials) practice and a method based on the Eurocodes, and recommendations from experimental research for the shear capacity of Slab bridges under live loads. The results from recent Slab shear experiments conducted at Delft University of Technology indicate that Slabs benefit from transverse force redistribution. For ten selected cases of straight Solid-Slab bridges, unity checks (the ratio between the design value of the applied shear force and the design beam shear resistance) are calculated according to the Eurocode-based method and the Aashto method. The results show similar design shear forces but higher shear resistances in the North American practice, which is not surprising as the associated reliability index for Aashto is lower.