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Steel and Composite Structures
  Volume 27, Number 5, June10 2018 , pages 623-632

A lateral load pattern based on energy evaluation for eccentrically braced frames
Ali Fakhraddini, Mohammad Javad Fadaee and Hamed Saffari

    Performance-Based Plastic Design (PBPD) method has been recently developed to evaluate the behavior of structures in different performance levels. The PBPD method utilizes a base shear force and a lateral load pattern that are estimated based on energy and yielding mechanism concepts. Using of current lateral force pattern results in weak structural members in upper stories of a structure so that the values of the story drift in these stories are larger than the target drift, particularly in high-rise buildings. Therefore, such distribution requires modifications to overcome this drawback. This paper proposes a modified lateral load pattern for steel Eccentrically Braced Frames (EBFs) based on parametric study. In order toachieve the modified load pattern, a group of 26 EBFs has been analyzed under a set of 20 earthquake ground motions. Additionally, results of nonlinear dynamic analyses of EBFs have been post-processed by nonlinear regression analysis in order to derive the new load pattern. To prove the efficiency of present study, three EBFs as examples were designed by modified pattern and current PBPD distribution. Inelastic dynamic analyses results showed that the story drifts using modified lateral load pattern were well within the target values in comparison with current pattern in PBPD, particularly where the effect of the height is significant. The modified load pattern reduces the possibility of underdesigning in upper levels and overdesigning in lower levels of the frames.
Key Words
    performance-based plastic design; lateral load pattern; eccentrically braced frames; energy balance; steel building
Department of Civil Engineering, Shahid Bahonar University of Kerman, P.O. Box 76175-133, Kerman, Iran.

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