Search

The scope of this study is the comparison between experimental results of tests performed on a base isolated building using helical wire rope isolators (WRs), and results of Nonlinear Response History Analyses (NRHAs) performed using SAP 2000, a commercial software for structural analysis. In the first stage of this research, WRs have been tested under shear deformation beyond their linear range of deformation, and analytical models have been derived to describe the nonlinear response of the bearings under different directions of loading. On the following stage, shaking table tests have been carried out on a 1/3 scale steel model isolated at the base by means of curved surface sliders (CSS) and WRs. The response of the structure under ground motion excitation has been compared to that obtained using numerical analyses in SAP 2000. The feasibility of modelling the nonlinear behavior of the tested isolation layer using multilinear link elements embedded in SAP 2000 is discussed in this paper, together with the advantages of using WRs as supplemental devices for CSSs base isolated structures.

International audience; Model selection is a challenging problem that is of importance in many branches of the sciences and engineering, particularly in structural dynamics. By definition, it is intended to select the most plausible model among a set of competing models, that best matches the dynamic behaviour of a real structure and better predicts the measured data. The Bayesian approach is based essentially on the evaluation of a likelihood functionandisarguablythemostpopularapproach. However, in some circumstances, the likelihood function is intractable or not available even in a closed form. To overcome this issue, likelihood-free or approximate Bayesian computation (ABC) algorithms have been introduced in the literature, which relax the need of an explicit likelihood function to measure the degree of similarity between model prediction and measurements. One major issue with the ABC algorithms in general is the low acceptance rate which is actually a common problem withthetraditionalBayesianmethods. Toovercomethisshortcoming and alleviate the computational burden, a new variant of the ABC algorithm based on an ellipsoidal nested sampling technique is introduced in this paper. It has been called ABC-NS. This paper will demonstrate how the new algorithm promises drastic speedups and provides good estimates of theunknownparameters. Todemonstrateitspracticalapplicability, two illustrative examples are considered. Firstly, the efficiency of the novel algorithm to deal with parameter estimation is demonstrated using a moving average process based on synthetic measurements. Secondly, a real structure called the VTT benchmark, which consists of a wire rope isolators mounted between a load mass and a base mass, is used to further assess the performance of the algorithm in solving the model selection issue.

In this paper, the results of experimental tests performed on a Helical Wire Rope Isolator (HWRI) are presented in order to describe the dynamic and static behavior of the selected metal device in three different displacements ranges, namely small, relatively large, and large displacements ranges, without and under the effect of a vertical load. A testing machine, allowing to apply horizontal displacement or load histories to the tested bearing with a constant vertical load, has been adopted to perform the dynamic and static tests. According to the experimental results, the dynamic behavior of the tested device depends on the applied displacement amplitude. Indeed, the HWRI displays a softening and a hardening stiffness at small and relatively large displacements, respectively, and a stronger nonlinear stiffening behavior at large displacements. Furthermore, the experimental tests reveal that the application of a vertical load allows to have a more flexible device with higher damping properties and that the applied vertical load affects much less the dynamic response of the metal device at large displacements. Finally, a decrease in the static to dynamic effective stiffness ratio with increasing displacement amplitude has been observed., {"references":["M. L. Tinker and M. A. Cutchins, \"Damping phenomena in a wire rope\nvibration isolation system,\" Journal of Sound and Vibration, vol. 157,\nno. 1, pp. 7-18, 1992.","G. F. Demetriades, M. C. Constantinou and A. M. Reinhorn, \"Study of\nwire rope systems for seismic protection of equipment in buildings,\"\nEngineering Structures, vol. 15, no. 5, pp. 321-334, 1993.","G. Serino, F. Bettinali and G. Bonacina, \"Seismic base isolation of gas\ninsulated electrical substations: comparison among different solutions,\"\nProceedings of the 4th US Conference on Lifeline Earthquake\nEngineering, San Francisco, California, 1995.","G. Serino, G. Bonacina and F. Bettinali, \"Passive protection devices for\nhigh-voltage equipment: design procedures and performance\nevaluation,\" Proceedings of the 4th US Conference on Lifeline\nEarthquake Engineering, San Francisco, California, 1995.","M. Di Donna and G. Serino, \"Base isolation of high-voltage equipment:\ncomparison between two different solutions,\" Proceedings of the 7th\nInternational Conference on Probabilistic Methods Applied to Power\nSystems, Napoli, Italy, 2002.","S. Alessandri, R. Giannini, F. Paolacci and M. Malena, \"Seismic\nretrofitting of an HV circuit breaker using base isolation with wire ropes.\nPart 1: Preliminary tests and analyses,\" Engineering Structures, vol. 98,\npp. 251-262, 2015.","G. De Canio, \"Marble devices for the base isolation of the two bronzes\nof Riace: a proposal for the David of Michelangelo,\" Proceedings of the\n15th Word Conference on Earthquake Engineering, Lisbon, Portugal,\n2012.","S. Alessandri, R. Giannini, F. Paolacci, M. Amoretti and A. Freddo,\n\"Seismic retrofitting of an HV circuit breaker using base isolation with\nwire ropes. Part 2: Shaking-table test validation,\" Engineering\nStructures, vol. 98, pp. 263-274, 2015.","S. Pagano, M. Russo, S. Strano and M. Terzo, \"A mixed approach for\nthe control of a testing equipment employed for earthquake isolation\nsystems,\" Journal of Mechanical Engineering Science, vol. 228, no. 2,\npp. 246-261, 2014. [10] A. K. Chopra, Dynamics of Structures: Theory and Applications to\nEarthquake Engineering, 4th ed. Englewood Cliffs, NJ: Prentice Hall,\n2012."]}

The results of an extensive series of dynamic and static experimental tests conducted on four Wire Rope Isolators (WRIs) under different values of vertical load are presented. The main aim of this work is identifying the mechanical characteristics of WRIs in three displacements ranges, that is, small, relatively large and large displacements ranges, to allow the use of these metal devices in the base isolation system of seismically base-isolated lightweight structures. In order to simulate the dynamic behavior of WRIs in the two principal horizontal directions, namely, Roll and Shear directions, a one dimensional (1d) Nonlinear Exponential Model, able to simulate the increase of the tangent stiffness observed at larger displacements, is proposed. Compared to the widely used Bouc-Wen model, the proposed one does not require the numerical solution of a first order ordinary nonlinear differential equation, thus decreasing the computational effort of nonlinear time history analyses, and contains a smaller number of parameters to be identified. The mathematical model has been validated by comparing the experimental hysteresis loops obtained during cyclic tests with those predicted analytically.

The wire rope isolator (WRI) can effectively provide vibration isolation of equipment and structures. The main advantage of WRI is the effective isolation in all three planes and in all directions. The WRI provides the damping of the external disturbance through its friction between the wire strands. The present work is the study on the performance of WRI in the isolation of equipment supported on structures. This study is performed in four different cases namely, Fixed Structure and Fixed Equipment, Isolated Structure and Fixed Equipment, Fixed Structure and Isolated Equipment, Isolated Structure and Isolated Equipment. The present work compares the performance of WRI in all the four cases. The study also extended on the parametric study for the effects of frequency of external excitation, weight of the equipment and excitation direction. It is found that the WRI were effective in providing the isolation for the frequency studied and increased weight of the equipment enhances the performance of WRI. The present study can be used to identify the different ways to provide the isolation of the equipment supported on the structures through WRI. Published version