Adequate selection of sensors placement plays a key role in structural health monitoring (SHM) in base isolated (BI) structures. This critical issue is usually done by past experience and knowledge on the force and vibration situations of a structure. During recent decades, techniques have received increasing attention as a tool for determining an arrangement of sensors suitable for SHM. In this paper, a multi- objective numerical method for optimal sensor placement (OSP) in BI structures based on the combination of traditional OSP algorithms and nonlinear time-history analysis (NTH) has been proposed. Next, genetic algorithm (GA) was employed to determine the location of sensors on the structure based on the structural dynamic response of the BI system. To show the efficiency of the proposed method, a BI building was modeled using finite element method (FEM) in which NTH were undertaken using the seismic scaled records of near-fault earthquakes (NF). The novel numerical approach called transformed time history to frequency domain (TTFD) was evaluated to transform NTH results to frequency domain and then the effective frequencies according the maximum range of Fourier amplitude were selected. The modified type of modal assurance criteria (MAC) values can be achieved from MAC with the exact seismic displacement. Results show that the proposed method can provide the optimal sensor locations and remarkably reduce the number of required sensors and also improve their optimum location. پرونده مقاله

Bridges are vital to modern transportation infrastructure, providing convenient and efficient access to different locations. Because of their structural simplicity and low degree of indeterminacy, bridges tend to be particularly vulnerable to damage and even collapse when subjected to earthquakes. The costs of their construction and retrofitting are high, so the maintenance of these capitals is one of the necessities of urban management. This paper investigates the influence of increasing the height of bridge piers on seismic behavior of isolation systems in urban reinforce concrete (RC) bridge. For this purpose, the seismic performance of the Hesarak Bridge constructed in Karaj city, Iran with two isolation systems; i.e. the existing elastomeric rubber bearing (ERB) and a proposed lead rubber bearing (LRB) are discussed by changing three times the height the bridge piers as compared with the existing situation. The numerical model was implemented in the well-known FEM software CSiBridge. The isolated bridge has been analyzed using nonlinear time history analysis (NTHA) method with seven pairs of earthquake records and the results are compared for the two isolation systems in both height modes. The results showed that with the increase in the height of the bridge piers, the natural period of the LRB isolated system changes from 2.7 to 2.77 seconds and on the other hand, this value increases from 1.37 to 1.62 in the ERB isolated system. The ratio of maximum base shear force for the bridge with the LRB to the ERB isolators under given ground motions in longitudinal and transverse directions showed higher values with increasing the height of bridge piers in comparison with the current situation, which indicates the weaker seismic performance of LRB isolators. Also, the results of the numerical Analysis illustrate the pier head relative displacement of columns increases in the longitudinal direction of the bridge with increasing height of bridge piers. پرونده مقاله