MODULATED HOMOGENEOUS FRICTION - A SEMIACTIVE DAMPING STRATEGY

A control strategy for semi-active friction devices leading to efficie nt hysteretic dissipaters is proposed. The control algorithm makes the contact force between the sliding surfaces of the damper proportional to the absolute value of the prior local peak of the damper deformati on. This control logic leads to a non-linear force-deformation relatio n that satisfies homogeneity of degree one; this means that, like in a linear viscoelastic damping model, when the deformation is scaled by a constant, the force results are scaled by the same constant. The clo sed-loop system shows rectangular hysteresis loops which enclose an ar ea proportional to the square of the deformation of the damper. Some c haracteristics of the dynamic response of structures incorporating thi s type of semi-active damper are investigated. It is demonstrated that in the case of single-degree-of-freedom models, the period of vibrati on and decay ratio are independent of the amplitude of vibration. In t he case of multi-degree-of-freedom models with this type of nonlineari ty, the free-vibration response can exhibit natural modes of vibration . A linearization method is proposed and modelling tools for the delay associated with actuator dynamics and for the flexibility of the brac e connecting the damper to the structure are presented.