Análise estrutural dinâmica e verificação de projeto à fadiga de pontes rodoviárias em aço e mistas (aço-concreto)

Abstract

Road bridges are subject to relevant dynamic loading actions, resulting from random traffic conditions, throughout their service life. The roughness of asphalt pavements represents a key factor for the significant increase in the values of displacements and tensions on the bridge decks. The actions of dynamic loads, mainly cyclical ones, can cause fractures to nucleate or even propagate them over the structure. These effects can compromise the structural system and its reliability, in addition to reducing the useful life of bridges. Therefore, this research work aims to develop a methodology for dynamic structural analysis and fatigue verification of steel and mixed (steel-concrete) road bridges, when subjected to loads caused by the crossing of vehicles, considering- the dynamic interaction of the vehicle-structure system with the irregularities of the road, as well as the inclusion of the effect of the progressive deterioration of the pavement over time, was used for this purpose. Thus, a computational application was developed based on the methodology associated with the calculation of structural stresses for fatigue analysis, aiming at the interconnection between the finite element program ANSYS and the program MATLAB. Local approaches to fatigue verification are investigated on certain structural details of welded bridge connections, as these hold the most critical problems and require efficient tools to allow viable solutions. Aiming to contextualize and contribute to the main research developments, the relevant fatigue analysis methods available in the design codes are studied, such as: the global rated stress method and the hot-spot stress method in detail with welded connections. In this context, two road bridges were initially adopted as case studies, aiming to compare the respective responses in terms of dynamic behavior, in order to finally select one of these structures for the investigation. The selected case study corresponds to a typical mixed road bridge, with a straight axis and span of 40 meters. The structural system consists of four metal stringers and a 0.225 m thick concrete slab. The numerical model of the bridge and the model of the vehicle were developed based on the use of the ANSYS program, through the use of usual discretization techniques, using the Finite Element Method (FEM). Considering the hot-spot stress approach, the investigation results showed that this method is more efficient and capable of providing more realistic structural responses when compared to conventional analysis methods. In order to illustrate the application of the hot-spot stress method to verify the fatigue of the investigated road bridge, the results obtained for the service life of the structure are presented and discussed, considering several damage scenarios based on simulated road traffic. throughout the study. Finally, the results achieved demonstrate the relevance of the renovation of the pavement of the track from the fourteenth year onwards, with reference to the beginning of vehicle traffic on the deck, since this measure effectively contributes to the reduction of stress values and structural damage, producing a significant increase in fatigue life of the most critical road bridge details.