Development of a Practical Approach for Probabilistic Seismic Analysis of Cable Stayed Bridges Considering Accuracy and Computational Effort Simultaneously

Document Type : Original Research

Authors
V. Akhoondzade-Noghabi
K. Bargi
School of Civil Engineering, College of Engineering, University of Tehran
10.22034/23.3.189
Abstract
Different methods of seismic analysis of structures generally include Incremental Dynamic Analysis (IDA), Time History Analysis (THA), and Static Pushover Analysis (SPA), which in the same order have a decreasing trend in the computational effort and the estimation accuracy of seismic demands. In the structural engineering problems involving probabilistic seismic analyses such as seismic fragility assessment, and seismic risk based design optimization due to the consideration of a wide range, respectively, for uncertain parameters and the decision-making variables, many repetitions of the time-consumed seismic analyses on the finite element models has been required. This issue is considered as a burden for computational efficiency due to the significant increase in the computational cost, especially in the case of large-scale structural systems such as Cable Stayed Bridges (CSBs). Therefore, in this paper, an attempt will be made to develop and adapt the approach of the static pushover method to the seismic behavior of the CSB in both longitudinal and transverse direction. This approach includes producing the structure's capacity curve through the proposed static pushover approach and intersecting it with the corresponding record demand spectrum, while considering all the important linear and nonlinear behavior modes of the structure in order to calculate the performance point of the CSB. Then the desired seismic responses of the CSB has been recorded at the performance point of structure. The intended seismic demands of the CSB include pylon head displacement, critical pylon section curvature, cable tension, and bearing device displacement. It is worth mentioning that according to the purpose of this research, which includes the probabilistic form of seismic analysis, the seismic analyses consist of the applying the various seismic records on the samples produced by the uniform design sampling method in such a way that the uncertainty in the structural and seismic parameters is taken into account at the same time. In this way, the mentioned approach as well as other more accurate methods including IDA and THA are used in order to estimate the probability distribution of aforementioned seismic demands in three case studies of existing CSBs in Iran. Then, in relation to the above-mentioned proposed approach entitled Developed Nonlinear Static Pushover (DNSP) method, the complete justification of the relatively small errors in the outputs estimation of this method will be performed by explaining the sufficient reasons and details to clarify its effective computational efficiency in the seismic assessment of the CSBs. In the next step, the seismic fragility curves related to the various components of the case studies are generated as the final result of probabilistic seismic analysis of structures. For the comprehensiveness of validation and in line with the recommendation of the DNSP method for the CSBs, the relationship between the accuracy of methods in estimating seismic responses and seismic fragility is also will be discussed. In the end, after comparing the seismic outputs and the computational cost of different methods, this study concluded that the proposed DNSP approach in estimating the demand and seismic fragility of the CSBs has an appropriate accuracy and at the same time leads to that the computational workload has been significantly reduced compared to existing methods.

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Modares Civil Engineering journal
Volume 23, Issue 3
July and August 2023
Pages 189-205