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SIMPLIFIED MODELS FOR ESTIMATING STRESSES AND STRAINS IN PAVEMENTS ON CONCRETE AND STEEL BRIDGES
No full textSimplified models for estimating stresses and strains in pavements both on concrete and steel bridges are presented in this paper. These models represent a very
useful tool for a faster prediction of structural behavior of pavements at a preliminary design level.The simplified model proposed for asphalt pavements on concrete bridges can be identified in the elastic multilayer system, which is represented by the layers of the pavement and waterproofing supported by a rigid half-space (concrete deck). The results obtained show that the validity field of this model is influenced by the thickness and dynamic modulus of the pavement, as well as the stiffness of the waterproofing.
The model developed for the asphalt pavements on steel bridges, instead, can be identified in a small-scale model, compared to the full-scale bridge, which is represented with a supported continuous plate composed by the pavement, waterproofing, and steel deck. In keeping with the international literature, similar models for steel bridges have been validated in laboratory by reduced-scale tests, as a result the author is confident that the model proposed also permits to estimate accurately enough the stresses and strains
Stresses and Strains Prediction Model of Asphalt Pavements on Concrete Bridges
No full textTraditional methods for the design of pavements cannot generally be applied for evaluating stresses and strains in asphalt pavements on concrete bridges. This paper presents a specific three-dimensional finite-element model (FE) that overcomes the limitation of the classical design approach that is implicitly in assuming pavements as being supported by foundation soils. Concrete bridges are generally formed by the deck, longitudinal beams and cross beams that behave globally in a way that is different from foundation soils. Based on the model developed, a finite-element software is used for estimating stresses and strains in pavements on bridges as a function of loads, temperatures, and dynamic modulus of an asphalt mixture. A simplified method for designing pavements on bridges is also derived from the results of the finite-element model. This method may be identified with a calculation based on the elastic multilayer system, which is represented by the layers of pavement and waterproofing, supported by a rigid half-space (concrete bridge deck). The simplified method represents a useful tool for a faster estimation of stresses and strains in asphalt pavements on concrete bridges at a preliminary design level. A preliminary design is used, for example, when the designer does not yet know the exact values of the input parameters concerning pavement and waterproofing, which will subsequently be measured for that specific bridge project, but uses the average values available or estimated from existing analytical correlations. The simplified method, although slightly less accurate, is not so time-consuming as the FE method. This latter method, in contrast, should be used when better information on the exact values of input parameters has been obtained from direct measurements (e.g. from laboratory tests)
Stress and Strain Reductions due to Asphalt Pavements on Orthotropic Steel Bridge Decks
No full textThe paper focuses on the structural behaviour of asphalt pavements on steel bridges and on the influence of the pavement on the reduction of stresses and strains in orthotropic decks. For this aim a simplified model has been proposed for evaluating the effects attributable to local bending of the steel deck. This model can be represented by a simply supported continuous plate that is made by the pavement, waterproofing, and deck. The pavement and waterproofing are considered to be an integral part of the structural deck system. Based on this model, a finite-element software was used for estimating stresses and strains both in the pavement and deck as a function of loads, temperatures, and dynamic modulus of asphalt mixture. The results showed that tensile stresses and strains at the bottom of the pavement due to the positive bending moment are higher than those at the top of the pavement produced by negative bending moment. The pavement contributed significantly towards reducing stresses and strains in the orthotropic deck by increasing the dynamic modulus of asphalt mixture. This means that a higher fatigue life of steel orthotropic decks might be expected. Thus, it is proposed that bridge designers should take these results into account
Crash Prediction Models for Roads Including Rainfall and Hazardous Points
No full textPredictive models for multilane roads including also the effects of rainfall and hazardous points on the crash frequency are presented in this paper. Accident data observed on a specific motorway during a period of eight years were used in statistical analysis. Negative Binomial Distribution, was applied for modelling the random variation of the crash data. Model parameters were estimated by Maximum Likelihood Method, and the Generalised Likelihood Ratio Test was used to detect the significant variables to be included in the final model. Separate prediction models for curves and tangents are proposed. For curves, it is found that the crash frequency is positively associated with the following variables: length (L), curvature (1/R), and the presence of hazardous points such as junctions (J) or tunnels (T); whereas for tangents with L and T. The effect of rain precipitation shows that with a wet pavement significant increases in crash frequency are expected, more especially on curves compared to tangents. This might be due to the combined effect of rain and centrifugal force in curve
Evaluation of Stress and Strain Reductions in Orthotropic Steel Bridge Decks attributable to Asphalt Surfacing
No full textThe paper focuses on the structural behaviour of asphalt pavements on steel bridges and on the influence of the pavement on the reduction of stresses and strains in orthotropic decks. For this aim a simplified model has been proposed for evaluating the effects attributable to local bending of the steel deck. This model can be represented by a simply supported continuous plate that is made by the pavement, waterproofing, and deck. The pavement and waterproofing are considered to be an integral part of the structural deck system. Based on this model, a finite-element software was used for estimating stresses and strains both in the pavement and deck as a function of loads, temperatures, and dynamic modulus of asphalt mixture. The results showed that tensile stresses and strains at the bottom of the pavement due to the positive bending moment are higher than those at the top of the pavement produced by negative bending moment. The pavement contributed significantly towards reducing stresses and strains in the orthotropic deck by increasing the dynamic modulus of asphalt mixture. This means that a higher fatigue life of steel orthotropic decks might be expected. Thus, it is proposed that bridge designers should take these results into account
CRITERIO DI DIMENSIONAMENTO DELLE SOVRASTRUTTURE FLESSIBILI BASATO SULLA DEFORMAZIONE ELASTICA DEI TERRENI DI SOTTOFONDO
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