Seismic assessment of suspended ceilings through cyclic quasi-static tests

The purpose of this work is the evaluation of the seismic behaviour of suspended ceilings by means of a combined experimental and numerical approach. As concerning the experimental aspects, nowadays the most common experimental produre applied to suspended ceilings worldwide regards shake-table tests, with a protocol defined to certify the ceilings for a determined seismic level. This methodology has some shortcomings, including the high cost and the influence of the input chosen on the experimental results. In fact, these tests have the aim to certify the product rather than providing mechanical characteristics of the specimen tested. Moreover, the results obtained with the certification process cannot be extended to similar products or geographic zones with different seismic risk. To overcome these limitations, an innovative experimental setup for monotonic and cyclic testing of suspended ceiling systems was designed, realized and applied. In order to have a complete characterization of suspended ceilings, an initial experimental campaign on inner joints was realized. These components, in fact, performed poorly in past earthquakes. In detail, 'standard' joints were compared to 'seismic' joints, specifically designed to resist to earthquake motion. Real-scale tests were then performed on the most common T-Grid suspended ceilings and other two typologies of metal ceilings with different structure. Moreover, dry-wall suspended ceilings with single and double plasterboard were tested. For each typology one monotonic and one cyclic quasi-static test were performed. Monotonic tests have the aim to identify the yielding parameters and the damage mechanisms and cyclic tests are performed according to the protocol described in FEMA 461 for cyclic quasi-static tests of non-structural components. The results allow to define the performance of suspended ceilings and to elaborate their capacity curves. As concerning the numerical part of the work, a numerical cascading approach was applied to study the uncoupled behaviour of suspended ceilings installed at different levels of buildings. Results from experimental campaign were used as input data for the numerical anlyses. Elastic linear time history analyses were performed on multi-story buildings with different vibration periods and the elastic floor response spectra were defined. Capacity curves defined experimentally and floor spectra were plotted in an ADRS (Acceleration Displacement Response Spectrum) domain in order to assess the seismic demand in terms of acceleration and displacement of suspended ceilings compared to their capacities. Dynamic analyses of suspended ceilings were conduced both in linear and non linear hypothesis and the results compared in order to assess the effectiveness of standard linear, or equivalent linear, static calculations