Hybrid protection of earthquake excited structures by using seismic base isolation and multiple tuned mass damper systems

Afghanistan is one of the countries located in the active seismic regions and has a large number of non-standard buildings that have never been structurally analyzed /designed before they are built nor they abide even with the basics of Earthquake. Every year the number of middle to high-rise buildings are increasing and this danger is at the forefront of ever-present serious concerns of civil engineers and experts. In this study, the most effective/modern earthquake resistant/vibration control systems are considered and the different behaviors of 5, 10 and 15-storey buildings isolated with seismic base isolation systems and equipped with single/multiple tuned mass dampers at the top and floor levels are investigated. Until now there is no any single 'base isolated building' in Afghanistan and I hope this to be a 'start' to construction of such resistant buildings to save people's lives and properties. In this study, seismic response of base-isolated (BI) building equipped with single tuned mass damper (STMD), multiple tuned mass dampers (MTMDs) and distributed multiple tuned mass dampers (d-MTMDs) under real earthquake ground motions is investigated. Numerical study is carried out using analytical model of a 5, 10 and 15-storey base-isolated buildings equipped with STMD, MTMDs and d-MTMDs. The buildings are modeled as shear type structure with a lateral degree of freedom at each floor level and the buildings are isolated with laminated rubber bearings (LRB), lead rubber bearing (N-Z), friction pendulum system (FPS) and Resilient-friction base isolator (R-FBI) isolation systems. Installing a TMD at each floor level of base-isolated building reduces the structural response in terms of top floor accelerations, and bearing displacements. Parametric study is conducted by changing the number of stories as 5, 10 and 15 storey and the isolator time period altered from 2 to 2.5 and 3sec. Furthermore, mass ratio considered as 2, 3, 5 and 10% for all the cases of STMD. In addition, MTMDs placed at topmost floor as well as base, and distributed along the height of the isolated building. Also, two sets of MTMDs (i.e., (i) MTMDs with equal stiffness and equal damping ratio (ii) MTMDs with equal mass and equal damping ratio) are considered for parametric study. It is found that the effectiveness of the TMD reduces with increase in flexibility (time period) of the isolators in a hybrid system having equal mass ratio. Further, the placement of the TMD at top or any other floor level slightly affects the effectiveness of the TMD for low-rise buildings. It is also found that the importance of the placement of the TMD will be higher as the number of stories increase. In addition, it is observed that installing MTMDs and d-MTMDs are significantly beneficial in reducing top floor acceleration comparing to STMD. Furthermore, almost equal reduction in bearing displacement could be obtained from installing STMD, MTMDs at top and d-MTMDs in base-isolated buildings. The d-MTMDs are more beneficial as compared to STMD and MTMDs as the huge mass is divided and distributed on different floor levels. Keywords: Seismic Base-Isolator, Damping, Tuned Mass Damper, Friction, Earthquake Resistant Buildings, Reinforced Concrete Buildings