ABSTRACT
The use of statistical tools to assess the seismic vulnerability of civil structures has increased in the last two decades. During the analysis, different sources of uncertainty which are believed to affect the structural capacity and demand can be included, increasing the complexity of the analytical models evaluated. Considering this, it is important to understand which parameters affect significantly the structural vulnerability. Based on this scenario, this paper assesses the influence of mechanical properties variation for natural rubber seismic isolators on the development of fragility curves for a portfolio of retrofitted concrete bridges.
In this study, four sets of bridge fragility curves are developed, considering different configurations for shear stiffness and damping of the elastomeric devices, to assess the influence of these mechanical properties on the fragility of critical bridge components and bridge system. The results demonstrate that variations in the mechanical properties of natural rubber seismic isolators have higher impact on the fragility of critical bridge components, such as columns and abutment walls, when compared to bridge system fragility. Differences higher than 10% on median PGA and 15% on dispersion values of critical bridge components fragility are found considering different configurations of shear stiffness and damping ratio for the seismic isolators. In the case of bridge system fragility, the differences on median and dispersion values are lower than 7.5%. Depending on the level of evaluation, bridge components or bridge system fragility, the results demonstrate the importance of properly consider the variations on both mechanical properties of seismic isolation devices during the seismic vulnerability assessment for a portfolio of retrofitted bridges.
Figure 1 presents a comparison between fragility curves for slight damage of columns and moderate damage for abutment wing-walls. Fragility curves for slight damage of columns and moderate damage of abutment wing-walls. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig193_1.tif"/>
Considering the fragility placed on critical bridge components, the impact of explicitly consider the mechanical properties variations are more pronounced depending on the component evaluated, where sometimes the results can be conservative or nonconservative, depending on the damage level and the range of PGA values considered. In the case of system fragility, these impacts are less pronounced for slight and moderate damages.
