Full Scale Dynamic Tests on Concave Curved Surface Sliders: Comparison of Time History and Cyclic Sinusoidal Tests

Full scale dynamic testing of seismic isolation devices in combined compression and shear is nowadays required by all international standards on seismically isolated structures and/or on anti-seismic devices, for prototype tests, and sometimes for production control (or acceptance) tests. The Type tests aim at understanding the effects on the isolator's hysteretic behavior of different actions, such as vertical loads, amplitude and velocity of the horizontal displacements, and at introducing such effects in proper modelling of seismically isolated structures. The dynamic tests required by the standards are usually cyclic sinusoidal tests under different vertical loads, with different amplitude, frequency and number of cycles, thus resulting very demanding, in terms of global energy dissipation and cumulated displacement. Testing protocols for production control are usually simpler. As a contribution to future revision of the testing protocols in the standards, this paper presents a comparison between cyclic loading tests and Time History (TH) tests performed under the design vertical load on a pendulum isolator characterized by ±450mm maximum displacement capacity. The input of TH tests is the displacement TH resulting as output of non-linear dynamic analyses on the structure in which the isolator are installed. A total of 9 time-history tests were performed: 3 couples of records of Turkish earthquakes, scaled to the MCE spectrum, and 3 generated earthquakes compatible with the same spectrum. The results are compared with that of cyclic sinusoidal tests similar to those required by standards, in terms of energy dissipation and cumulated displacement.