Shaking table tests of a base isolated structure with a double concave friction pendulums

An extensive experimental seismic testing programme named JETBIS project (Joint Experimental Testing of Base Isolation Systems) has been developed within the RELUIS II project (Task 2.3.2) involving partners from different Italian universities. This paper describes the shaking table test performed by research unit of University of Basilicata (UNIBAS) on the experimental model with seismic isolators based on Double Concave Friction Pendulum (DCFP). The DCFP isolator contains two separate concave sliding surfaces and exhibits different hysteretic properties at different stages of displacement response. The experimental model was a 1/3 scaled steel framed structure with one storey and one bay in both directions. Four DCFP bearings with equal properties of the concave sliding surfaces were mounted under each column. The base isolated experimental model was subjected to a set of 7+1 natural earthquakes increasing seismic intensity in order to achieve the safe displacement of seismic bearings. The main objective of this work is to evaluate the DCFP effectiveness considering different experimental configurations (with both symmetrical and eccentric masses) and different sliding surfaces conditions (with and without lubrication). A further goal is to verify the reliability of the DCFP isolation system when relevant residual displacements occur due to previous earthquakes. Finally, this paper also shows the experimental testing outcomes compared with the results of non linear time history numerical analyses using SAP2000.