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A low- and high-velocity based controller (LH controller) is developed to model the force-velocity relationship of a magnetorheological (MR) fluid damper that enables the controlling current to be calculated as a function of required control force. The proposed bilinear force-velocity model predicts the high-velocity region as well as the often neglected low-velocity region that corresponds to the damper responses in the postyield and preyield regions, respectively. The calculated current may then be supplied to an experimentally parameterized prototype small-capacity MR damper (50 kN) to control seismic responses at a lower cost. Numerical examples are used to demonstrate the ability of the LH controller to reduce structural displacements and accelerations in comparison with three other state-of-the-art controllers, namely, the clipped optimal controller, modified clipped optimal controller, and inverse model, which neglect the low-velocity region of the damper. After including this region, the LH controller significantly lowers peak accelerations by 57.7, 33.4, and 13.0%, respectively, over the three other common controllers and also lowers mean displacements by 85.9, 81.7, and 85.4%, respectively. Lastly, the LH controller is used to reduce the peak drifts and accelerations in comparison with those of a 20-story benchmark building. [ABSTRACT FROM AUTHOR]

The target displacement ductility requirements for circular RC single-column bridge bents are considered using a proposed multifailure mode algorithm to determine the required thickness of fiber-reinforced polymer wraps (FRPs). The procedure is developed using two in-house computer algorithms, PACCC (plastic analysis of circular concrete columns) and PACCC-FRP, to generate a moment-curvature analysis using circular segment slices and subsequent failure mode predictions in single-column bents for both FRP-wrapped and unwrapped circular RC sections. The results of the study showed good comparison to published experimental tests at the ultimate force-deflection states of RC sections and against three commercial 'software test beds.' The study uses PACCC-FRP to show that single columns experiencing a brittle failure may be retrofitted with FRP wraps in order to increase the displacement ductility and satisfy target ductility values within the ductility wrap envelope, or wrap-saturation level, as established herein. [ABSTRACT FROM AUTHOR]

The random vibration analyses of gradually yielding shear-frame buildings are considered using a recently proposed constitutive model that is used to calculate the detailed degradation of the stiffness of structures which permits the prediction of their global responses, as well as the states of stress in their members. It is shown that the detailed stress degradation model can also be used in connection with a global force-displacement model, such as the Bouc and Wen model, to predict the time evolution of the various stress-related variables and time passages to failure. The two models are applied in separate analyses and are exemplified using both a single-story building and a four-story building subjected to artificial ground motions. The corresponding probability density functions of the various stress-related responses, including the strains and plastic hinge lengths, and the first time passages to failure are presented and discussed. [ABSTRACT FROM AUTHOR]

A gradient-based optimization algorithm is used to simultaneously control all interstory displacements in nonlinearly degrading steel buildings using optimal viscous dampers. Optimal damping ratios are computed in each mode of vibration such that the sum of the errors between the interstory displacements and the “just-yielded” performance objectives is minimized. A representative damping formulation is used to determine the sizes and locations of the damper devices. The members of the buildings are assumed to degrade smoothly according to a constitutive rule that was developed to model the behavior of kinematically strain-hardened materials. Numerical examples are used to demonstrate the ability of the algorithm to control potential damages in a 10-story building and also in an 8-story building responding at significant higher modes of vibration. It is found that the interstory displacements in the 10-story building are very adequately controlled. Although demands in the 8-story building are significantly reduced, some modes remain overdamped and not all performance levels are exactly met as some stories remain marginally damaged. Finally, the algorithm is applied in a 20-story benchmark building, and it is shown that the interstory displacements, postyield curvatures, and plastic damages are very adequately controlled. [ABSTRACT FROM AUTHOR]