ABSTRACT
Bridges are elements used in developing routes and roads that allow vehicles to cross natural or artificial obstacles, such as rivers. These elements are built considering the efforts which will be submitted and how they will be spread in their structure. In this paper were analyzed some problems of vibration in the design and maintenance of bridges and viaducts, due to changes in rigidity and mass. In this project, a parametric search was made of the dynamic characteristics of such structures, such as the effect on the rigidity of the distribution of girders and crossbeams, or the mass due to the train type present in force, as well as the development of structural damage during its lifetime. Regarding the rigidity, the hypothesis was adopted that the way girders and crossbeams are distributed can lead to a better dynamic performance. It was adopted different design situations, considering the presence of small defects or damage to the structure. For that were made models with geometry variation (area and inertia). Analyses were carried out by the Finite Element Method, using the commercial program, SAP2000. According to AJEJE (2011), discrete models of Finite Element Method (FEM) allow to obtain approximate solutions to geometric conditions, contour and general cargo.
With the study, was expected to conclude the work with larger girders and undamaged present shorter period.
Compare the period and frequency of a bridge by varying the height of its crossbeams. They not achieved major differences.
Then, compare the period and frequency of a bridge by varying the alture of its girders. The differences were much more significant. This comparison was made for the first two methods
This bridge was then verified with “damage”. This analysis was made in 4 points. In the central and extreme girder in different vains. This analysis was done at first by removing part of the element model. The difference on period and frequency were exaggerated. Thus it was decided just to reduce the height of these elements for a closer analysis of reality. The results obtained were lower, though more real.
This is due to the idea that the mass and rigidity are directly related to vibration of the structure.
It is observed that, over time, the bridges have been required to bear ever more loads and, therefore, a greater expenditure of materials is necessary. Bridges with girders are heavily used and the intermediate crossbeams appear frequently, especially in older builidings. The work was done in order to determine that the use of crossbeams result in a considerable reduction in vibrations, stimulating its use in bridge projects, which did not occur.
Currently, most of the bridges are built without intermediate crossbeams, because in addition to their participation in the frequency of the bridge be negligible, their implementation is not always advantageous, given the constructive and esthetic disadvantages that these imply.
