Modification of soil modeling and using it in the fish-bone model

Document Type : Article

Authors

1 Department of Civil Engineering, Faculty of Engineering and Technology, University of Mazandaran, Babolsar, Iran.

2 Department of Civil Engineering, Babol Noshirvani University of Technology, Babol, Iran.

Abstract

The basic design of any structure requires sufficient and detailed modeling of each structural element. It must be taken into consideration that the modeling of each member of the structure and performing nonlinear dynamic analysis due to the presence of multiple degrees of freedom, is time consuming. Therefore, a wide range of structures cannot be evaluated. To resolve this issue, researchers have recommended using simplified equivalent models to study a wide range of structures, provided that the equivalent ones significantly reflect the behavior of the original structure. One of these models is the fishbone model, which is used for modeling moment resisting steel structures and it also has a suitable accuracy. Additionally, the presence of soil can significantly change the response of the structure. This is despite the fact that accurately modeling of the soil will lead to an increase in degrees of freedom. In this study, the aim is to examine the seismic performance of soil-structure systems and to evaluate the accuracy of the models presented in seismic codes, and after modification, provide a simplified model for placement under the fishbone frame. In this regard, first by modeling a number of foundations on distributed Winkler springs considering nonlinear behavior for the soil, the moment-rotation capacity curve of the foundations were drawn, and then the aforementioned graphs were simplified into bilinear curve through an algorithm. The bilinear models which are presented, has a greater stiffness and strength compared to the model presented by the seismic code. Two equation were suggested for determining the coefficients of the bilinear model by regression. In the next step, instead of modeling vertical distributed springs beneath foundation, a rotational spring with modified bilinear behavior was placed under the fishbone model. The analysis of the seismic response of soil-structure systems under earthquake records shows that using the modified model instead of the model presented in the seismic code leads to responses with appropriate accuracy. In addition, by using the modified model, the time required for the time history analysis is noticeably reduced, which is important in research studies.

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Sharif Journal of Civil Engineering

Articles in Press, Accepted Manuscript
Available Online from 21 September 2024

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