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The design of structures to withstand seismic loading is primarily governed by horizontal ground motion, and the effects of vertical ground motion have long been deemed unimportant or secondary. However, an emerging body of evidence suggests that vertical ground motions have great destructive potential, especially for certain site conditions.Using nonlinear dynamic analyses, the seismic performance of frames is evaluated by simultaneously applying the horizontal and vertical components of earthquake motion. Three special moment frames are subjected to 15 recorded near-field earthquake motions and the results of the analyses are used for performance evaluations, based on FEMA 350 guideline. It is found that, within the elastic range of response, considering the vertical component of ground motion, does not alter the dynamic structural response significantly, however, some tangible differences emerge in nonlinear range of response once the horizontal component of ground motion is accompanied by the vertical component. [ABSTRACT FROM AUTHOR]

Semi-active control is one of the most effective methods for damage reduction in offshore platforms subjected to intense environmental forces. Despite its advantages, probable device time delays may drastically decrease the real performance of the control algorithm. Thus, the uncertainty could make the control process non-optimal. In this paper, a Kalman Filter is used to ponder previous responses and the history of the measured errors in order to estimate the real state variables of an offshore structure equipped with Magneto-Rheological (MR) dampers. In the current article, the amount of applied voltage to the MR damper is optimized via the Adaptive Particle Swarm Optimization (APSO) method. Furthermore, the structure is controlled by the Linear–Quadratic Regulator (LQR) algorithm. A newly installed offshore platform, located in the Persian Gulf at a depth of 64 m is considered as an example to demonstrate the performance of the controller. The offshore structure is assumed to be excited by near- and far-field earthquakes. The results of the parametric studies indicate that all the earthquake-induced vibrations of the platform can be effectively suppressed by the designed control system. Moreover, the life spans of the dampers may increase with the predicting-optimizing algorithm. A predictor-optimizing semi-active control system is designed to reduce structural responses of a fixed metal offshore platform equipped by horizontal MR dampers under earthquake excitations. The controller estimates the responses of the structure considering probable noises to reduce the time delays and inefficient actuator forces. In addition, the inlet voltages of the dampers are optimized to develop the dampers' duration and reduce the structural responses. Image 1 • Optimizing voltages of MR dampers placed on offshore platforms. • Structural state estimation for improving the efficiency of a control system. • Considering instrument noises and time delays to reach the real-time control. • Optimum-state estimating controller on a structure under far/near-field earthquakes. • Life span increase of semi-active Magneto-Rheological dampers. [ABSTRACT FROM AUTHOR]