1,720,983 research outputs found
Modeling strategies for the lateral response of curved surface slider devices under extreme displacement demands
No full textBase isolation represents one of the most efficient strategy for the reduction of the structural vulnerability of buildings and bridges. Design procedures generally aim to provide the proper period shift, in order to reduce spectral acceleration values and, consequently, the base shear and internal forces. On the other hand, high displacement demands can be achieved, which can be partially limited by providing dissipative capacity through hysteretic behaviors. Although design procedures allow to fairly estimate the design displacement of the adopted devices, extreme seismic event can occur, and displacement higher than the design value can be experienced. Especially for Curved Surface Slider devices, if the displacement demand exceeds a certain geometrical limit, non-negligible damage can occur at the sliding pad, and variations in the force response are consequently noticed. In this work modeling strategies for the computation of the seismic response of base-isolated buildings are presented, by considering extreme earthquake loading conditions. Analytical models are reported for Curved Surface Slider devices, calibrated through the experimental outcomes of tests performed at the Laboratory of EUCENTRE Foundation in Pavia (Italy). In addition, simplified dynamic systems are defined, which allow fast assessments of the global response of a base-isolated structure, even though extreme seismic events are applied. Results have been compared to the response returned by an experimental hybrid simulation, in order to evaluate the accuracy of the presented dynamic systems
Definition of a Simplified Design Procedure of Seismic Isolation Systems for Bridges
No full textIn the recent past, numerical and experimental investigations on full-scale isolators have led to extensive improvements in seismic isolation techniques for bridge structures. Significant advances in dynamic testing techniques have been made at both software and hardware levels, and the response of an isolated bridge can be realistically simulated. In general, the response of an isolated bridge structure is strongly affected by the valley topography; therefore, high piers may not need isolation devices, since they are flexible enough to accommodate the design displacement in the elastic range. On the other hand, at those locations no hysteretic damping is provided and higher displacements can be achieved, compared to the maximum displacement allowance. In this work, a simplified procedure is proposed for the optimization of isolation systems for bridge structures. The seismic response of a designed case study structure is investigated through nonlinear time history analyses, and the effective contributions of both the nonlinear hysteretic behaviour of isolators and the elastic response of piers are considered. Regarding displacement and force responses in particular, the results show a very good agreement between mean and single-event peak responses, and the corresponding values returned by the proposed design procedure
Assessment of the Seismic Response of Isolated Bridges under extra-stroke displacement demands
No full textSeismic isolation techniques for bridge structures have been more and more improved in last years, thanks to results of both numerical and experimental investigations on full-scale devices. In addition, significant advances on testing techniques have led to extremely realistic responses of an isolated bridge. Particularly, hybrid tests allow to consider a numerical model of the overall structure, together with an experimental contribution, represented by the real force of a full-scale isolation device. Generally, the response of an isolated bridge structure is strongly affected by the valley topography: consequently high piers may not need isolation devices, since they are enough flexible to accommodate the design displacement in the elastic range. On the other hand, at those locations no hysteretic damping is provided and higher displacements can be achieved, in comparison to the design value. In this work the seismic response of an isolated bridge case study structure has been investigated, through non linear time history analyses, by accounting for the effective contribution of both isolators and elastic response of piers. Moreover, the actual hysteretic behaviour of all devices has been properly modelled, also for displacements higher than the design value, so in the extra-stroke range. Results have been compared to the ordinary response, which accounts for no difference between forces under displacements lower rather than higher than the target value, in order to highlight main consequences of such a behaviour on the overall response parameters
Experimental comparison between flat and curved sliding conditions for the response evaluation of curved surface slider devices
No full textCurved Surface Slider devices have been widely used in last years for the protection of both building and structural systems. The spherical shape of the implemented sliding surfaces provide a certain recentering capability, which is generally combined to significant amount of energy dissipation, due to the frictional characteristics of the adopted sliding material. Since both behaviors act simultaneously during motion, experimental tests could return significantly high force values, especially if large bearings are considered. In some of those cases, the maximum force capacity of the testing equipment can be even overcome, and consequently experimental tests can not be performed. The scope of the present work is to provide experimental evidence of the comparison between flat and curved sliding motions. Precisely, the outcomes of bi-directional tests performed on on full-scale Double Curved Surface Slider and Flat Slider devices have been analyzed. On the former typology the frictional and the recentering behaviors have been numerically decoupled, in order to compare the obtained results to the frictional response of the latter device. Results have shown a good agreement between the considered sliding motions, which seems to suggest that the experimental evaluation of flat sliding characteristics could be representative of curved sliding motions
Influence of cyclic effect and extra-design displacement demands on Curved Surface Slider devices
No full textCurved Surface Slider devices are widely used for seismic isolation applications in structural engineering. The response of the superstructure is significantly mitigated, thanks to the high dissipative capacity of the resulting isolation layer, and consequently low force and displacement demands can be achieved during earthquake excitations. Nonetheless, extreme seismic events can occur during the life-cycle of the structure, and consequently devices can be subjected to severe motions along both planar directions. In some cases, especially for earthquake with high return period, the induced displacement demand could exceed the design value. Recent experimental campaign carried out at the Laboratory of EUCENTRE Foundation in Pavia (Italy) have revealed a certain extra-design displacement capacity for Curved Surface Slider devices, with a stable force response. The present endeavor analyses such effects, in addition to the commonly known dependencies of frictional properties on some response parameters
Consequences of mechanical properties variability of seismic isolation systems on the structural response of buildings
No full textStructural vulnerability of buildings can be significantly reduced if seismic isolation systems are implemented at the base of the overall system. Thanks to the low stiffness characteristics, reduced forces are experienced during a seismic event, whereas displacements are limited by the provided energy dissipation of the installed devices. In the design phase, for the assessment of the response of a considered structure, deterministic mechanical parameters are generally assumed, which correspond to the mean values of the real experimental response. On the other hand, outcomes of several testing campaigns have revealed non negligible variability of the main response characteristics of isolators, which may lead to unexpected behaviors of the isolated structure. In the present endeavor a parametric study has been performed, in order to evaluate the consequences of the variability of the main mechanical characteristics of the implemented devices on the response of a base-isolated structure. Concave Surface Slider devices have been considered: results have led to preliminary guidelines for the correct assumptions in the design phase of isolation devices in real applications
Experimental Validation of Fast Design Rules for Curved Surface Slider Devices through the Hybrid Simulation Technique
No full textIn this work fast design procedures for a get-started definition of the seismic isolation system for buildings have been validated through the analysis of the outcomes of experimental hybrid tests. More specifically, earthquake simulations have been performed, by adopting both numerical and physical substructures, represented by an equivalent Multi Degree of Freedom for the building and a full-scale Double Curved Surface Slider isolator for the whole isolation system. A suite of seven natural seismic events has been selected, by ensuring the proper spectrum compatibility with respect to the hazard of the considered case study structure, in terms of acceleration response spectrum. Special attention has been focused on global results of the isolation layer, in terms of displacement and total force responses, together with the evaluation of the effective protection of the superstructure against eventual plastic deformation demands. The response parameters returned by both the single-events and as average values among the suite of selected events have been compared to the performance initially estimated through fast design rules. Furthermore, Non-Linear Time History Analyses have been performed, by adopting the same analytical model of the building used within the hybrid tests algorithm, for sake of comparison between numerical and experimental simulations
Investigation of the response variability of base-a isolated building equipped with lead rubber bearings
No full textNowadays analytical models of seismic isolators can fairly reproduce the force response of such devices, when implemented in a large variety of structural systems, such as buildings and bridges. Consequently, realistic hysteretic rules are available for the definition of the dynamic system for Non-Linear Time History Analyses, and earthquake simulations of the considered isolated structural systems can be computed. Such models are generally defined, according to mean values of mechanical properties of isolation devices, even though a certain variability has been experimentally assessed: precisely, statistical analyses of the outcomes of test database have outlined that the main response parameters of isolators should be considered as random variables, rather than as deterministic values. On the other hand, in the common practice both design and assessment procedures are mainly based on deterministic approaches, and bound analyses are ruled in just few standard codes. The present endeavor presents a wide parametric study on a case study structure, in order to assess the variability of the main response parameters, by accounting for random mechanical properties of isolation devices. Precisely, a combination of Lead Rubber Bearings and Flat Slider devices have been considered, and the spatial layout of isolators has been defined, according to a given performance point. The structural response of the case study building has been computed through Non-Linear Time History Analyses, by extracting 10’000 individual values of mechanical properties of devices. Presented results are related to the mean response of a spectrum-compatible set of natural records, in terms of displacement and force of both superstructure and isolation system
Application of the new Italian assessment guidelines to a 1960s prestressed concrete road bridge
No full textExperimental Assessment of the Seismic Response of a Base-Isolated Building Through a Hybrid Simulation Technique
No full textBase-isolated structural systems have been more and more investigated through both numerical and experimental campaigns, in order to evaluate their effective advantages, in terms of vulnerability reduction. Thanks to the lateral response of proper isolation devices, large displacement demands can be accommodated, and the overall energy of the seismic event can be dissipated, by means of hysteretic behaviors. Among the common typologies of isolators, curved surface slider devices represent a special technologic solution, with potentially high dissipative capacities, provided by innovative sliding materials. On the other hand, the overall behavior is highly non-linear, and a number of research works have been developed, aiming at the definition of the most comprehensive analytical model of such devices. The most realistic response of a base-isolated structure could be returned by a shake table test of a full-scale building. However, dimensions of the available shake tables do not allow consideration of the common load conditions, to which the isolation devices are subjected, and consequently, scaled specimens are needed, and unrealistic responses could be found. Hybrid simulations seem to solve such an issue, by accounting for an experimental substructuring, represented by a physical device tested in a testing equipment, and a numerical substructuring, consisting of a numerical model of the superstructure. Thus, a much more realistic response of the full-scale structure can be computed. In this work, the outcomes of a number of hybrid simulations have been deeply analyzed and compared to a similar numerical model. Proper non-linear constitutive laws for isolation devices have been adopted, in order to evaluate the effectiveness of design and assessment procedures, commonly adopted in real-practice applications
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