engleski

Multimodal Pushover Target Acceleration Method Versus Dynamic Response of R/C Frames

A new multimodal pushover target acceleration method for the nonlinear analysis of reinforced concrete (R/C) frames subjected to seismic action is presented in chapter. The aim of research shown in this chapter was to find the influence of multimodal combinations in assessing the bearing capacity of R/C frames based on linear (L) combination of modes, and to compare the target ground acceleration agr, t (agr, u) of the multimodal pushover target acceleration method with the failure peak ground acceleration agr, d obtained by a dynamic transient response of R/C frames. The target acceleration presents the lowest seismic resistance and it is the minimum acceleration of the base that leads to the ultimate limit state of structure, and it is reached by an iterative procedure. In accordance with the Eurocode 8 rules, application of the pushover method favors access utilizing the first mode. Examples of presented 5-storey spatial R/C frame show the significant influence of higher modes. A formulation for determining the equivalent structural system damping by equalizing the dissipated energy during one cycle of vibration of the nonlinear system and the equivalent linear system is presented in this chapter. Results of the dynamic response of R/C frames are also presented in this chapter. As seismic excitation eight real earthquake accelerograms are taken. On the basis of the results obtained by nonlinear dynamic time-history analysis validation of the procedure of searching the target ground acceleration was made. Taking into account the elastic spectrum with calculated equivalent structural damping and usability of the capacity curve up to 3/3 of a displacement, the comparison of the target acceleration agr, u of the multimodal pushover method with the failure peak ground acceleration agr, d, obtained by a dynamic response of the structure, shows a very good agreement between the target acceleration and the failure peak ground acceleration.

Target acceleration, Multimodal pushover method, Dynamic response, Seismic load, R/C frame, Linear combination of modes, Structural damping

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