1,721,091 research outputs found
Probabilistic seismic response and fragility assessment of steel-concrete composite bridges with dual load path
No full textInfluence of FPS bearing properties on the seismic performance of base-isolated structures
No full textThe paper analyzes the influence of friction pendulum system (FPS) isolator properties on the seismic
performance of base-isolated building frames. The behavior of these systems is analyzed by employing a
two-degree-of-freedom model accounting for the superstructure flexibility, whereas the FPS isolator behavior
is described by adopting a widespread model that considers the variation of the friction coefficient with
the velocity. The uncertainty in the seismic input is taken into account by considering a set of natural records
with different characteristics scaled to increasing intensity levels. The variation of the statistics of the
response parameters relevant to the seismic performance is investigated through the nondimensionalization
of the motion equation and an extensive parametric study carried out for different isolator and system properties.
The proposed approach allows to explore a wide range of situations while limiting the required
nonlinear response history analyses.
Two case studies consisting of base-isolated building frames described as shear-type systems are finally
investigated in order to demonstrate the capabilities of the proposed simplified model in unveiling the essential
characteristics of the performance of buildings isolated with FPS bearings
Influence of FPS bearing properties on the seismic performance of base-isolated structures
No full textThe paper analyzes the influence of friction pendulum system (FPS) isolator properties on the seismic
performance of base-isolated building frames. The behavior of these systems is analyzed by employing a
two-degree-of-freedom model accounting for the superstructure flexibility, whereas the FPS isolator behavior
is described by adopting a widespread model that considers the variation of the friction coefficient with
the velocity. The uncertainty in the seismic input is taken into account by considering a set of natural records
with different characteristics scaled to increasing intensity levels. The variation of the statistics of the
response parameters relevant to the seismic performance is investigated through the nondimensionalization
of the motion equation and an extensive parametric study carried out for different isolator and system properties.
The proposed approach allows to explore a wide range of situations while limiting the required
nonlinear response history analyses.
Two case studies consisting of base-isolated building frames described as shear-type systems are finally
investigated in order to demonstrate the capabilities of the proposed simplified model in unveiling the essential
characteristics of the performance of buildings isolated with FPS bearings
Performance-based seismic risk assessment for buildings equipped with linear and nonlinear viscous dampers
No full textThis paper introduces an efficient methodology for assessing the seismic risk of structural systems equipped with linear and nonlinear viscous damping devices while accounting for the uncertainties affecting both seismic input and model parameters. The proposed methodology employs a combination of efficient and accurate analytical and simulation techniques to estimate the probabilistic properties of the structural response under a seismic input modeled as a non-stationary stochastic process.
The effectiveness of the proposed methodology is illustrated through a parametric study, with respect to the dampers’ properties, of the performance of two adjacent steel buildings connected by linear and nonlinear viscous dampers. The results of the study provide useful information regarding the accuracy of the approximations introduced by the proposed reliability assessment approach, and the effectiveness of the added dampers in reducing the system seismic risk
Probabilistic seismic response assessment of linear systems equipped with nonlinear viscous dampers
Full text linkThe paper aims at evaluating the influence of damper properties on the probabilistic seismic response of structural systems equipped with nonlinear viscous dampers.
For this purpose, a linear single-degree-of-freedom system with an added linear or nonlinear viscous damper is considered, and the response statistics are evaluated for a set of natural records describing the ground motion uncertainty. A dimensional analysis of the seismic problem is carried out first to identify the minimum set of characteristic parameter s describing the system and controlling the seismic response. An extensive parametric study is then performed to estimate the influence of the damper properties on the statistics of the main response quantities of interest (i.e. maximum displacements, accelerations and damper forces), for a wide range of values of the characteristic parameters. Finally, a set of case studies is investigated to show some interesting issues concerning the influence of the damper nonlinear behaviour on the evaluation of the system reliability and to highlight some limitations of current deterministic approaches neglecting the probabilistic properties of the response
Influence of nonlinear viscous dampers on the probabilistic seismic response of linear structure
No full textThe paper aims at evaluating the influence of damper properties on the probabilistic seismic response of structural systems equipped with nonlinear viscous dampers. For this purpose, a linear single-degree-of-freedom system with an added linear or nonlinear viscous damper is considered, and the response statistics due to a set of natural records describing the ground motion uncertainty is analyzed in detail. A dimensional analysis of the seismic problem is applied first to identify the minimum set of characteristic parameters describing the system and controlling the seismic response. An extensive parametric study is then carried out to estimate the influence of the damper properties on the statistics of the main response quantities of interest (i.e., maximum displacements, accelerations and forces), for a wide range of values of the characteristic parameters. Finally, a set of case studies is investigated in order to show some interesting issues concerning the influence of the damper nonlinear behaviour on the evaluation of the system reliability and to highlight some limitations of current approaches neglecting the probabilistic properties of the respons
Uncertainties propagation in the seismic response of structures with nonlinear viscous dampers
No full textSeismic risk sensitivity of structures equipped with anti-seismic devices with uncertain properties
Full text linkDamping and isolation devices are often employed to control and enhance the seismic performance of structural systems. However, the effectiveness of these devices in mitigating the seismic risk may be significantly affected by manufacturing tolerances, and systems equipped with devices whose properties deviate from the nominal ones may exhibit a performance very different than expected.
The paper analyzes this problem by proposing a general framework for investigating the sensitivity of the seismic risk of structural systems with respect to system properties varying in a prescribed range. The proposed framework is based on the solution of a reliability-based optimization (RBO) problem, aimed to search for the worst combination of the uncertain anti-seismic device parameters, within the allowed range of variation, that maximizes the seismic demand hazard. A hybrid probabilistic approach is employed to speed up the reliability analyses required for evaluating the objective function at each iteration of the RBO process. This approach combines a conditional method for estimating the seismic demand at a given intensity level, with a simulation approach for representing the seismic hazard.
The proposed method is applied to evaluate the influence of the variability of the properties of linear and nonlinear fluid viscous dampers on the seismic risk of a low-rise steel building. The study results show that the various response parameters considered are differently affected by the damper properties and unveil the capability of the proposed approach to evaluate the potentially worst conditions that jeopardize the system reliability
An evaluation of stress-softening behaviour of HDNR bearings on the seismic response of base-isolated structures
No full textIn the last few decades, high damping natural rubber (HDNR) bearings have been extensively employed for seismic isolation of bridges and buildings because of their low horizontal stiffness and high damping capacity, which allows shifting the vibration period of the isolated structure away from where the earthquake input has the highest energy content and at the same time controlling the motion of the system. In HDNR material, filler is added to the natural rubber in order to improve its properties such as stiffness and dissipative capacity. The addition of the filler induces also a stress-softening behavior, known as “Mullins effect”. This effect makes the response of HDNR bearings path-history dependent and thus may influence the seismic performance of isolated systems. Published literature has suggested that the initial “virgin” properties of the material are eventually recovered. Accordingly, current seismic codes make the assumption that “Mullins effect” is a reversible phenomenon. The present work aims at studying the consequences of such strain-history dependent behavior on the seismic response of structural systems isolated with HDNR bearings. In particular, the first part of the paper reports a wide experimental campaign carried out on a large number of virgin rubber samples in order to better investigate some aspects of the stress-softening behavior of filled rubber, such as the direction-dependence and the recovery prosperities, and to characterize the stable and transient response under different strain histories. Test results are used to define a model for simulating the behavior of HDNR bearings in shear, which is an advancement in the description of both the stable and the transient behaviors. The proposed model has been used to analyze the seismic response of a simplified isolated structure modeled as a S-DOF (single degree of freedom) system under ground motions with different characteristics and by considering two different conditions for the bearings: one assuming the virgin (or fully recovered) rubber properties and the other assuming the stable (or fully scragged) rubber properties. The obtained results show that, except for the special case of near-fault (NF) ground motions, the differences between the responses are limited although not negligible, whereas for NF records, the assumption of the virgin (or fully recovered) condition significantly reduces the effect of this type of motion on isolated structures
Modal properties of existing building retrofitted by external bracings with viscous dampers
No full textThe paper deals with the seismic protection of existing buildings using external viscous damper systems to increase energy dissipation capacity. Dampers and bracings can be arranged in very different configurations and the possible solutions can be grouped into different categories, depending on the specific kinematic behavior. In this work, the formulation of the problem involving the coupling of the existing frame with an external damping system is presented in general terms and some issues concerning the influence of the bracing properties on the dynamic response of the coupled system are investigated. Presented results concern the so called "dissipative tower", a recent solution which exploits the rocking motion of a stiff steel truss hinged at the foundation level for the dampers activation; the influence of the external dissipative bracings on the most important modal properties of the system, such as the mode displacement profile, relevant internal action distribution and relations between damper dimensions and effective modal damping are shown. Finally the global effect on the seismic response, in terms of displacements and base shear, is presented by solving the dynamic problem with the modal decomposition method in order to investigate the contribution of the higher modes on the dynamic response
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