Floor acceleration control of self-centering braced frames using viscous dampers

The self-centering braced frames (SCBFs) have been widely investigated for enhancing the building structures' post-earthquake repairability by reducing or even eliminating the residual inter-story drifts. Nevertheless, it has been highlighted in recent research that the flag-shaped hysteretic behavior of SCBFs amplifies structural floor acceleration (FA) responses, which may lead to severe nonstructural damage. This paper intends to overcome this critical shortcoming of SCBFs by controlling FA responses using viscous dampers. This paper focuses on proposing a practical performance-based design strategy for designing viscous dampers to control the FA responses of the SCBF to the targeted level. To this end, the parametric dynamic analyses of a single-degree-of-freedom (SDOF) system were conducted to investigate the influence of the hysteretic parameters of self-centering braces (SCBs) and the contribution of viscous dampers (VDs) on the peak acceleration control in the SCBFs. Based on the results from the parametric dynamic analysis, the prediction models of inelastic displacement and acceleration ratios of the SCBF with VDs (denoted as the hybrid self-centering braced frame, HSCBF) were developed using the artificial neural network (ANN). The design steps included in the proposed method were presented, where a formula was proposed for predicting the absolute FAs of the HSCBF. Four demonstration buildings with 3, 6, 9, and 12 stories were designed and simulated to verify the developed performance-based design method. The analysis results show that the VDs can effec-tively control the FA responses of the SCBFs and the mean FAs of the designed systems can reach the desired performance level. Moreover, the reasons why VDs can reduce the accelerations of self-centering building structures are preliminarily discussed from the perspectives of frequency domain and higher mode effects. The analysis results indicate that compared to the original SCBFs, the HSCBF tends to vibrate with a lower frequency and show smaller high-mode responses.