EFFECT OF AN INNOVATIVE ISOLATION SYSTEM ON THE SEISMIC RESPONSE OF CULTURAL HERITAGE BUILDING CONTENTS

An experimental study was conducted at the University of Pavia and at the EUCENTRE Foundation (Pavia, Italy) to assess the effectiveness of an innovative seismic isolation device at protecting cultural heritage building contents. The recently patented isolator, named “Kinematic Steel Joint (KSJ)”, is based on a multiple articulated quadrilateral mechanism and is entirely made of steel components obtained by simply cutting, folding, and pinning metal sheets, eventually employing stainless steel to limit corrosion issues. The trajectory imposed by the KSJ isolator to the supported mass combines horizontal with increasing vertical displacements, resulting in a pendulum-type motion with self-centering behavior. The friction developing within the pinned joints can be exploited to grant energy dissipation capacity to the device. The KSJ isolator can be manufactured with different sizes, payloads, and displacement ranges. In fact, seismic isolation can be applied at a global building level as an integrated system or as a retrofit solution in new or existing construction, respectively, or at a local scale as a passive protection technique for non-structural components. Despite their undeniable effectiveness in reducing the seismic accelerations transmitted to the isolated structure and to its content, currently available isolation devices may add significantly to the construction cost of buildings, and may require particular maintenance to preserve a stable performance over time. The proposed KSJ solution will allow for a reduction in manufacturing and maintenance burdens compared to established technologies. This paper discusses the main results of a shake-table test conducted at the EUCENTRE Foundation laboratories on an assembly with four prototypes of the KSJ device. The experimental setup included a 19-t rigid mass supported by the isolators, simulating the building superstructure, and four marble blocks installed above the rigid mass, representing non-structural rocking components such as parapets, pinnacles, statues, or other architectural ornaments. Moreover, a museum showcase with a small-scale replica of Michelangelo’s David was mounted above the rigid block, while two clay vases completed the setup, to encompass additional cultural heritage features. Accelerometers and potentiometers were deployed at several locations to monitor the kinematic response of the individual isolators, as well as their effect on the dynamic response of the rigid mass and of the different non-structural elements. The experiment was conducted first with the KSJ devices allowed to displace freely, then after fastening the rigid mass to the shake-table through post-tensioning rods, following the same incremental dynamic test sequence. This allowed comparing the response of the non-structural components with and without seismic isolation, to better understand the effect of the proposed isolation devices on the overall test assembly and on each sub-component.