1,721,089 research outputs found
Comparison of different distributions of viscous damper properties in asymmetric-plan frames
No full textIn this article, one of the procedures to design viscous dampers proposed in literature is applied to 3D asymmetricplan buildings, considering different distributions for the damping coefficients, which are assumed to be proportional to specific structural or response parameters. The main purpose was to investigate the effectiveness of different vertical and in-plan distributions of the damping coefficients of nonlinear viscous dampers for the seismic retrofit of existing buildings. For comparison purposes, all the distributions were applied utilizing both a simplified and an extended method for the 3D structures, where the simplified method takes into account only the translation in the seismic direction, and the extended method considers the translations along the two orthogonal directions together with the floor rotations. The proposed distributions were then applied to a typical case study involving an asymmetric-plan six-storey RC building. The effectiveness of the different distributions was examined through time-history analyses, assuming nonlinear behaviour for both the viscous dampers and the structural elements. The results of the nonlinear dynamic analyses were examined in terms of maximum and residual inter-storey drifts, peak floor accelerations and maximum damper forces
Instantaneous modal identification under varying structural characteristics: A decentralized algorithm
Full text linkOne of the latest trends in structural health monitoring involves the use of wireless decentralized sensing systems, developed to reduce costs and speed up the whole monitoring process. The main purpose of this paper is to present a novel decentralized procedure for the instantaneous modal identification of time-varying structures, also suitable in the presence of environmental variations and non-stationary ambient excitation. In particular, a modal assurance criterion (MAC)-based clustered filter bank (CFB) is obtained, capable of decomposing structural responses into modal components for the evaluation of time-varying natural frequencies and modal shapes through a nonlinear energy operator. The proposed algorithm is relatively simple and usable with low-cost smart sensing systems, as it requires low computational effort and works with few data at a time. To prove the effectiveness of the presented method, a simulated near-real-time modal identification procedure has been performed on a full-scale bridge under progressive damage scenarios. The estimated modal parameters have then been used for damage diagnosis. The results reveal a good correspondence between identified modal parameters and reference values, showing also promising outcomes for both damage detection and localization
Application of displacement-based procedures for the assessment of infilled RC frames
No full textThe purpose of this research was to propose an extension of the displacement-based approach for the assessment of the seismic response of infilled RC frames. In order to evaluate the behaviour of these structures, it was fundamental to define an appropriate analytical model. In this study the equivalent strut model for monotonic loading proposed by Al-Chaar was considered. This model was extended to the case of cyclic loading by calibrating the degradation of strength and stiffness, the residual strength and the loading and unloading branches through comparisons with available experimental results. The model was then applied for investigating the seismic response of infilled RC frames: pushover and nonlinear dynamic analyses were carried out for obtaining the response in terms of base shear-top displacement and for estimating the configuration of collapse. On the basis of the results of these analyses, a displacement-based method for the assessment of infilled frames was proposed. The method is based in particular on simplified criteria for the estimate of the equivalent damping and of the collapse displacement profile of infilled RC frames. The effectiveness of the method was verified through comparison between the displacement demand estimated with the proposed procedure and the one obtained from nonlinear dynamic analyses
Modelling of friction pendulum isolators in structures subjected to horizontal and vertical ground motions
No full textThis research focuses on the different modelling approaches for the simulation of the seismic response of structures with friction pendulum isolation systems. The behaviour of such systems is strongly affected by several parameters, as for example the friction coefficient and the axial load. The latter has a particular importance in presence of seismic actions characterized by the simultaneous presence of high horizontal and vertical accelerations. In many recent seismic events, as for example L’Aquila (2009) and Emilia (2012) in Italy, the vertical seismic component has been characterized by very high values of acceleration and has played a crucial role in damaging the buildings. To study these aspects, several nonlinear dynamic analyses have been performed considering a two degree of freedom model isolated at the base and subjected to recorded horizontal and vertical ground motions. The response of the isolation systems has been studied through different models, starting by the more simple ones based on constant friction coefficient to the more complex ones based on a friction coefficient varying as a function of sliding velocity and axial force. The analyses have been performed considering a set of ground motions with near field records that present different values of the ratio between the peak vertical and horizontal accelerations. The records have been also applied considering increasing values of intensity, in order to determine the collapse acceleration. The results have allowed to compare the different models and to study the effect of the vertical seismic component on the response of the isolators
On the probabilistic seismic assessment of structures with added viscous dampers
No full textThe purpose of this paper is to propose a simplified probabilistic procedure for the seismic assessment of nonlinear structures equipped with nonlinear fluid viscous dampers. The considered reference probabilistic approach is the 2000 SAC-FEMA method, which allows to obtain the probability of exceeding a specified performance level. Within this method, in general, the probabilistic seismic demand analysis is performed in terms of incremental dynamic analysis (IDA) by considering several earthquake records. This approach has been followed with reference to a set of case studies, characterized by RC frames with and without added dampers. The main characteristics of the proposed simplified approach are: the application of a direct procedure previously proposed by the authors for the response assessment of structures with dampers as an alternative to nonlinear incremental dynamic analyses; the study of the relation between the dispersion of seismic demand of structures with dampers with that of structures without dampers. The latter, in fact, can be estimated also on the basis of several available literature data. In this paper the direct procedure previously proposed by the authors has been applied to the case studies for increasing values of seismic intensity. The results of such applications have been then compared with those of the IDA analyses in terms of the relation between the roof displacement demand and the seismic intensity. The results of the IDA analyses have been also examined in order to determine the correlation between the dispersion of demand of structures with dampers with that of structures without dampers. Finally the values of probability obtained with the proposed simplified approach has been compared with those of the 2000 SAC-FEMA method based on IDA analyses
Effectiveness of different distributions of viscous damping coefficients for the seismic retrofit of regular and irregular RC frames
No full textThe main purpose of this research has been to investigate the effectiveness of different vertical distributions of the damping coefficients of nonlinear viscous dampers for the seismic retrofit of existing multi-storey reinforced concrete frames. In particular, different simple distributions were compared with other procedures proposed in literature, including two energy methods and a repetitive simplified sequential search algorithm. The effectiveness of the different distributions was then examined by performing time-history analyses and considering a nonlinear behaviour for both the viscous dampers and the structural members. The structures being considered are five RC frames with a different number of storeys and both regular and irregular configurations in elevation. The results of the nonlinear dynamic analyses were examined in terms of maximum and residual interstorey drifts, peak floor accelerations and maximum damper forces. The energy methods, in particular, provided good results in terms of reduction in cost, efficiency of the distribution and simplicity of application, compared to other effective, but more complex methods
Influence of vertical distribution of damper properties for seismic upgrading of regular and irregular RC frames
No full textThe main purpose of this research is to investigate the effects of different vertical distributions of the properties of nonlinear fluid-viscous dampers for the retrofit of existing multi-storey reinforced concrete frames. In particular, the different distributions are defined on the basis of the same value of the supplemental damping ratio. Since the viscous dampers are used for the retrofit of existing buildings, they are dimensioned assuming that the structure can exceed the elastic limit, with the only condition to satisfy the prefixed performance limit. In the design phase the different vertical distributions of damper properties are compared in terms of the total sum of the damping coefficients. The effectiveness of the different distributions is then examined by performing time-history analysis of several case studies considering a nonlinear behaviour both for the viscous dampers and for the structural members. The results of the nonlinear dynamic analyses are examined in terms of interstorey drifts and dampers forces. The considered case studies are five RC frames characterized by different number of storeys (3, 6 and 9 storeys) and also by different properties in terms of regularity in elevation. In this way it is also possible to investigate the effect of the vertical distribution of the damper properties for regular and irregular frames
Influence of the in-plan distribution of the properties of dampers for the seismic retrofit of RC plan-asymmetric frames
No full textIn this research, one of the procedures proposed in literature for the design of viscous dampers is extended to 3D plan-asymmetric buildings considering different distributions of the damping coefficients. In particular, simple distribution criteria, based on specific structural or response parameters, were considered with the purpose to improve the design of the damping system in terms of cost without significant change of response. All the distributions were applied considering, for comparison, both a simplified and an extended method, by neglecting or considering, respectively, the plan-asymmetry in the design. The effectiveness of the different distributions was examined by performing time-history analyses of a case study with different configurations of dampers adopting a nonlinear behaviour both for the viscous dampers and the frame members. The dampers were dimensioned considering that the structure can exceed the elastic limit, with the only condition to satisfy the prefixed performance limit. The considered case study is a RC frames characterized by six storeys and an irregular plan configuration. The examined response parameters were maximum interstorey drifts, residual interstorey drifts and peak floor accelerations as well as maximum damper forces
A procedure for the direct determination of the required supplemental damping for the seismic retrofit with viscous dampers
No full textThis paper describes a simplified procedure to calculate the supplemental damping ratio that must be provided in order to rehabilitate existing buildings with viscous dampers. The proposed method has been developed according to both analytical and graphical approaches. The graphical formulation is based on the construction of constant design acceleration or constant design displacement curves. These curves allow to estimate the required effective damping as a function of the effective period, associated to the secant stiffness at maximum displacement. Combining these curves with constant ductility curves, which provide a correlation between the effective damping and the supplemental damping for given available ductility and damper typology, it is possible to determine the required supplemental damping and to design the damping system. The proposed method has then been verified through nonlinear dynamic analyses considering a set of RC plane frames. Finally it has been applied to a case study regarding an existing building located in Italy and designed without considering the earthquake action
A model for the out-of-plane dynamic analysis of unreinforced masonry walls in buildings with flexible diaphragms
No full textThis paper proposes a model for simulating the dynamic behaviour of slender external walls of unreinforced masonry buildings with flexible diaphragms subjected to out-of-plane bending. The proposed model is characterized by two degrees of freedom (2DOF) and allows to perform time-history analyses in order to study the influence of diaphragm flexibility on the displacement capacity and demand of walls in out-of-plane bending. The wall has been modelled as an assemblage of two rigid bodies connected by an intermediate hinge and restrained at the top by a spring: the damping has been modelled through the introduction of the coefficient of restitution. The equations of motion of the 2DOF system have been derived and integrated in the time domain. Dynamic analyses of a set of walls subjected to Gaussian impulses and recorded ground motions have been performed in order to compare the response of the simply supported wall with that of the wall with an elastic spring at the top
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