Narrow Results

Earthquakes have always been a menace to the lives and properties of human beings since the beginning of modern times. Several methods have been proposed since to mitigate the various types of seismic hazards, base isolation being one of them. The base-isolated structures being very effective for general far-fault earthquakes, are, however susceptible to high responses under near-fault ground motions; thus, several inerter-based supplementary damping devices have been proposed in this study to be applied alongside a highly nonlinear and effective unbonded fiber-reinforced elastomeric isolators (UFEI) system. The dampers are optimally designed and comparatively investigated with the isolation system for mitigation of a wide range of ground motions to the benchmark structure. Furthermore, two parametric studies were also carried out, which investigated the effect of the inertance-mass ratio and floor connectivity of the grounded damper on various responses of the isolator-damper-structure system. The parametric results are further used to suggest the best configuration and inertance-mass ratios for various dampers for effective seismic mitigation of the aforementioned base-isolated structure. The results show an effective reduction in seismic responses with the use of optimal inerter-based dampers in UFEI-isolated structures.

A self-anchored suspension bridge balances forces internally without external anchorage requirements, making it suitable for sites where anchorages would be difficult to construct. It often adopts either a full-floating or a semi-floating tower-girder connection system, which may result in large displacement responses along bridge longitudinal direction during earthquakes. This study investigated the efficacy of using the fluid viscous damper (FVD) for seismic control of a single-tower self-anchored suspension bridge. First, the energy dissipation behaviors of the FVD under sinusoidal excitations were studied. It revealed that besides the damper parameters (i.e. damping coefficient and velocity exponent) of an FVD itself, the energy dissipation capacity also relies on the characteristics of external excitations. Therefore, optimum damper parameters added to a structure should be determined on a case-by-case basis. Parametric study was then carried out on the prototype bridge, which indicated a tendency of decreasing the longitudinal deck/tower displacements and tower forces with increasing damping coefficient $C$ and decreasing velocity exponent $\alpha$. Compared with the linear FVD, the nonlinear FVD with a smaller velocity exponent can develop more rectangular force-displacement loops and thus achieve better energy dissipation performance. With selected optimum damper parameters (i.e. $C=3000$kN$\cdot$m${}^{-0.3}$s${}^{0.3}$ and $\alpha =0.3$) for the two FVDs added between the deck and the tower, the longitudinal deck and tower displacements could be reduced by 54%, while the peak bending moment and shear force at the tower base could be reduced by 30% and 19%, respectively. It is concluded that the nonlinear FVD can provide a simple and efficient solution to reduce displacement responses of self-anchored suspension bridges while simultaneously reducing the bending moment and shear force in the tower.

This paper developed multi-objective optimization design of proportional–derivative (PD) and proportional–integral–derivative (PID) controllers for seismic control of high-rise buildings. The case study is an 11-story realistic building equipped with active tuned mass damper (ATMD). Four earthquakes and nine performance indices are taken into account to assess the performance of the controllers. To create a good trade-off between the performance and robustness of the closed-loop structural system, a non-dominated sorting genetic algorithm, NSGA-II, is employed. To evaluate the degree of robustness of the controllers, four structural models with uncertainties in the nominal model of the structure is considered. For comparison purposes, a linear quadratic regulator (LQR) controller is also designed in the numerical simulations. Simulation results show that the proposed PD and PID controllers significantly perform better than the LQR in reduction of structural responses. Also, it is shown that the LQR does not provide a good performance in strong earthquakes. However, PD and PID controllers are able to significantly reduce structural responses. Moreover, it is shown that the PID has a better performance than the PD. The results also show that the proposed controllers are capable of maintaining a desired performance in the presence of modeling errors. They also have several advantages over modern controllers in terms of simplicity and reduction of required sensors and computational resources in tall buildings.

The seismic behavior of the structures equipped with ATMD is often investigated based on the rigid base assumption without considering soil-structure interaction (SSI) effects. The SSI effects significantly modify the dynamic characteristics of the structures, while these changes may be ignored in the design process of the controllers. The present paper aims to address the issue of the SSI effects on the seismic behavior of the structures and performance of the adopted controllers. For this purpose, a mathematical model is developed for the time domain analysis of tall building equipped with ATMD including SSI effects. Considering the fixed base case and three types of ground states, namely soft, medium and dense soil, the numerical studies are carried out on a 40-story structure subjected to different earthquake excitations. Two well-known controllers, proportional-integral-derivative (PID) and linear-quadratic regulator (LQR) controllers, are employed for tuning control force of ATMD in different conditions of ground state. A particle swarm optimization (PSO) algorithm is used for the optimum design of Tuned mass damper (TMD) parameter and the gain matrices of the controllers in both cases without and with SSI effects. It is found that TMDs are more effective for the higher soil stiffness and their efficiencies are degraded in soft soils. Furthermore, the SSI significantly affects on the optimum design of the PID and LQR controllers. The adopted controllers are significantly able to mitigate the peak top floor displacement of the tall building. In addition that the PID controller is a simple strategy with design variables much less than LQR controller, it performs better than the LQR controller in most earthquakes for different conditions of ground state. The performance of the controllers decreases with increasing soil softness, so that ignoring the SSI effects may result in incorrect and unrealistic results of the seismic behavior of the structures.