PHILIP JOUBERT  STEWART SCOTT

PHILIP JOUBERT STEWART SCOTT PowerPoint PPT Presentation


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Based on SAT Seminar (Pretoria)Presentations by: Products:Cobus Venter

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PHILIP JOUBERT STEWART SCOTT

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17. Percent Crack Reflection by length

43. Point out: Extreme peak in un-reinforced case, which greatly exceeds any of the normal strains (tension and compression); Percentage reduction in shear strain for reinforced case; In this case, we isolated the shear strain component. If we look at the horizontal tensile strains, then some of the benefits of the reinforcement appear to vanish, again, because of the lack of taking account of anisotropy. Point out: Extreme peak in un-reinforced case, which greatly exceeds any of the normal strains (tension and compression); Percentage reduction in shear strain for reinforced case; In this case, we isolated the shear strain component. If we look at the horizontal tensile strains, then some of the benefits of the reinforcement appear to vanish, again, because of the lack of taking account of anisotropy.

44. Observations: Some modelling of cracked affects and reinforcement benefits is possible using a simple axi-symmetric finite element program. However, an anisotropic model would be needed to accurately evaluate the benefits of reinforcement on the cracked case. Layered elastic modelling is not feasible here. Short answer. You cannot model cracked effects accurately by reducing the stiffness of the support. The benefits of reinforcement are more obvious when we investigate cracked effects, and we can perhaps start to make comparisons between the benefits of reinforcement for different design scenarios (e.g. we can model the reduction in shear strain with/without reinforcement for different overlay thicknesses, support stiffnesses etc.) Again: problem is anisotropy. Observations: Some modelling of cracked affects and reinforcement benefits is possible using a simple axi-symmetric finite element program. However, an anisotropic model would be needed to accurately evaluate the benefits of reinforcement on the cracked case. Layered elastic modelling is not feasible here. Short answer. You cannot model cracked effects accurately by reducing the stiffness of the support. The benefits of reinforcement are more obvious when we investigate cracked effects, and we can perhaps start to make comparisons between the benefits of reinforcement for different design scenarios (e.g. we can model the reduction in shear strain with/without reinforcement for different overlay thicknesses, support stiffnesses etc.) Again: problem is anisotropy.

45. Modelling of reinforcement using routine design tools that are presently widely available, is likely to give distorted results for reinforced pavements. In general, I believe we will underestimate the effect of reinforcement if we try and model using the tools we have, as they stand at the moment. Routinely trying to predict stresses and strains in reinforced structures are likely to raise more questions than answers (crack friction, anisotropic parameters, layer thickness, asphalt damage behaviour, etc.) The answers we can get from routine models are very general (even if they can become more accurate). A key problem with the models we have is that they only evaluate the effect of elastic behaviour. The damage inhibiting potential of the reinforcement is not taken into account at all. Thus if we try and evaluate the benefits of reinforcement from the point of view of the pavement, and the elastic behaviour, then we have to say that the effect appears to be fairly minimal, except perhaps in the cracked case. However, what if the real advantages lie in the crack retardation, and damage limiting performance of the reinforcement. Let me give a simple example: Modelling of reinforcement using routine design tools that are presently widely available, is likely to give distorted results for reinforced pavements. In general, I believe we will underestimate the effect of reinforcement if we try and model using the tools we have, as they stand at the moment. Routinely trying to predict stresses and strains in reinforced structures are likely to raise more questions than answers (crack friction, anisotropic parameters, layer thickness, asphalt damage behaviour, etc.) The answers we can get from routine models are very general (even if they can become more accurate). A key problem with the models we have is that they only evaluate the effect of elastic behaviour. The damage inhibiting potential of the reinforcement is not taken into account at all. Thus if we try and evaluate the benefits of reinforcement from the point of view of the pavement, and the elastic behaviour, then we have to say that the effect appears to be fairly minimal, except perhaps in the cracked case. However, what if the real advantages lie in the crack retardation, and damage limiting performance of the reinforcement. Let me give a simple example:

48. I believe we should work at compiling such a experience base, where we illustrate the performance of the products for specific design situations. Where, for example, we characterize a design situation in terms of the overall structural stiffness, and the relative stiffness of the immediate support.I believe we should work at compiling such a experience base, where we illustrate the performance of the products for specific design situations. Where, for example, we characterize a design situation in terms of the overall structural stiffness, and the relative stiffness of the immediate support.

49. This is the type of information we should have available for each case study.This is the type of information we should have available for each case study.

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