A. F. Nateghi, A. Vasseghi, and V. L. Shahsavar,
Volume 25, Issue 1 (7-2006)
Abstract
Bridges are potentially one of the most seismically vulnerable structures in the highway system during earthquake
events. It is known that the seismic performance of transportation systems plays a key role in the post-earthquake emergency management. Hence, it is necessary to evaluate both physical and functional aspects of bridge structures. The physical aspects of the seismic performance of bridges are evaluated by seismic fragility functions or damage probability matrices of transportation facilities. The fragility curves represent the probability of structural damage due to various levels of ground shaking. The fragility curve describes a relationship between a ground motion and a level of damage.
In this paper, the fragility curves (F.C) are developed. The vulnerability of a railway prestreed concrete bridge is assessed using fragility curves derived from dynamic nonlinear finite element analysis. A software package is developed in MATLAB to study the results obtained. Modeling of the bridge using 3D nonlinear models and modeling of abutments, bearings, effect of falling of girder on its bearings, and nonlinear interaction of soil-structure are some of the advantages of this research compared to previous ones. Reliability curves developed in this study are unique in their own kind. The proposed method as well as the results are presented in the form of vulnerability and structural reliability relations based on two damage functions.
M. R. Tabeshpour, A. A. Golafshani, A. Bakhshi, and A. Moayed Alaei,
Volume 25, Issue 2 (1-2007)
Abstract
The assessment of seismic performance of existing structures is becoming an important problem in earthquake engineering. Some important ructures are considerably old and, therefore, their strengths and ductilities are less than strength and ductility demands because of changes in codes and design methodologies. Such structures must be strengthened to resist future earthquakes. First, a structural model must be developed and then, based on seismic hazard and seismic risk analysis or code quantities, the design (or control) parameters can be determined. The next step is defining the damage indices in order to quantify the structural damage. Then the nonlinear dynamic analysis is carried out and damage indices are calculated. In the present paper, a power plant stack (located in Mashhad) is investigated for some levels of peak ground acceleration (PGA) considering return periods of 75, 500, 1000, and 2500 year. The height of stack is 100 m and the external diameter of the structure is 10 m. Several records are used for nonlinear dynamic analysis. It has been used from Park-Ang damage index that is a suitable model for concrete structures and has been considered in IDARC. It is clear that nonlinear dynamic analysis is necessary for the seismic vulnerability of existing structures. Special structures such stacks can be modeled with some 2-D or 3-D elements. However, the beam-column element is a proper model for special structures such as chimneys, considering calculation cost.
