Seismic isolators

For friction FEs 263/264, the "Unloading with initial stiffness" option is implemented. With this option, you can apply the hysteresis behaviour of FE in the cyclic loading: the friction load T=N*mf, where mf is the friction coefficient defined in the stiffness parameters, activates when the direction of motion changes (i.e., when the velocity equals 0). In "unloading with initial stiffness", the FE of friction enables you to describe, for example, the behaviour of a friction seismic isolator and, in combined behaviour with the FE of an elastic spring, a friction pendulum seismic isolator.