1,720,979 research outputs found
Observed behavior of buildings seismically isolated with CSSs under a low energy earthquake
No full textThe observed behavior of four buildings, seismically isolated by means of curved surface sliders (CSS), under a moderate seismic event is analyzed in the framework of their structural health monitoring. The results showed that the CSS isolation systems were not activated for most of the buildings, even though the acceleration peaks in the superstructures were significant. The reason for this behavior is related to an inaccurate evaluation of the friction coefficients under the vertical loads acting on the devices in seismic conditions. Actually, vertical loads influence the friction and so the onset of motion. The importance of a continuous monitoring of the actual seismic behavior is also evident to analyze the structural health status of the devices and to plan maintenance interventions when needed
Onset of Motion of Curved Surface Sliders Used in Seismic-Isolation Systems
No full textCurved surface sliders are generally preferred for the seismic isolation of buildings because of their technical features, such as the fact that the value of the vibration period is theoretically independent of the mass. Given the experimental evidence that indicates that the isolated system did not work under low seismic actions, in this paper, the influence of the static friction on the global behavior of some structures is studied in detail. By adopting a suitable model of friction, the onset of motion is analyzed with reference to simple isolation systems in which the influence of the friction values and its variability among the isolation devices are analyzed. The results pointed out that the behavior of curved surface sliders is not independent of the vertical load and highlights the importance of a suitable choice of the design friction, which must be different for devices with different vertical loads
Structural assessment of the pedestrian bridge accessing Civita di Bagnoregio, Italy
Full text linkThe paper presents the results of the vibration tests carried out on the pedestrian bridge accessing Civita di Bagnoregio, Italy. The structure was in bad health condition. The external beams were damaged due to deterioration exacerbated by the combined actions of rain and wind. The circular piers were also damaged with several cracks where the concrete cover was spliced and the reinforcement bars were exposed. The analysis presented in the paper focuses on the highest five piers, which seemed to show an irregular behavior during a preliminary experimental campaign. The results of the experimental campaign presented in this paper showed that the structural behavior of the bridge was qualitatively similar to the expected one. The reduced stiffness, due to the observed widespread damage state, amplified the vibrations uniformly along the structure. The Italian Guidelines for the risk and safety assessment of bridges and viaducts, issued in 2020, have been applied and tested in this study and the results are presented in the paper
The SHM as Higher Level Inspection in the Evaluation of Structures
No full textThe SHM is a useful tool to improve the knowledge of an existing structure. Through the analysis of recorded data of selected physical phenomena, the SHM allows to understand the behaviour of a monitored structure. Data can be obtained through measurements during static or dynamic tests set up on purpose, or acquired on environmental vibrations or recorded during exceptional events such as earthquakes. On the other hand, the level of knowledge is a fundamental parameter in the safety check of an existing structure. To introduce and encourage the use of SHM to improve the knowledge of a structure, a clear regulatory framework is needed, with standards harmonized among the various countries, that account for the most recent scientific research in this field. In this work, a critical analysis of the main regulations in the world is carried out in the context of monitoring and preliminary suggestions are provided on how SHM may affect the level of knowledge
Observed Seismic Behaviour of Base Isolation Systems in Italy
No full textThe observed behaviour of seismically isolated structures in different countries allowed testifying the suitability of this technique to protect structures against strong earthquakes. In Italy, up to now, base isolated buildings have been subjected only to low energy earthquakes. This paper describes and compares the observed behaviours under a low energy earthquake of three buildings with different isolation systems. In the first one, seismically isolated by means of HDRBs, the structure showed resonance frequencies higher than the design ones but the decoupling was always guaranteed also thanks to the high stiffness of the superstructure. In the second one, seismically isolated with CSSs, the onset of motion was governed by the friction, which was much higher than the design one. Finally, in a building seismically isolated with HDRBs and SDs, the onset of motion was governed by the SDs and the successive motion by the HDRBs
Seismic response of a R.C. viaduct during different earthquakes
No full textThe experimental seismic behavior of a typical viaduct in Italy subjected to subsequent events is analyzed. The structure is located along a freeway in Umbria region. Two spans and two piers were monitored in the framework of the Osservatorio Sismico delle Strutture monitoring network, managed by the Italian Civil Protection Department. The changes of the dynamic characteristics of the structures were analyzed through the analysis of the data recorded during five recent seismic events. These five earthquakes were characterized by different magnitude and different Arias Intensity at the site. The analysis allowed determining the first natural vibration frequencies of the structure in three perpendicular directions and the associated modal shapes. The results pointed that the horizontal vibration frequencies of the structure changed significantly during the different earthquakes, which had different effects at the site. Anyway, the bridge recovered its dynamic characteristics also after the strongest events, shoving a linear behavior. This work is part of research project on the use of SHM to support the road and highway operators in the knowledge of the health status of the existing bridge and viaduct network and for an effective and prompt response to any emergencies
Masonry Arch Bridges with Finite Compression Strength Subject to Horizontal Longitudinal Seismic Actions
Full text linkThe great diffusion of masonry arch bridges, sometimes of historical interest, requires the development of simple but effective methodologies for a preliminary but reliable evaluation of their static and seismic capacity. In this paper, the behaviour under longitudinal seismic actions is analysed by using the mechanism method. The masonry is supposed to have no tension strength but a rigid–perfect plastic behaviour with finite strength in compression. The arch is subject to permanent loads and to a horizontal acceleration acting in the longitudinal direction, which causes a horizontal inertial loading acting on the arch. Three hypotheses about the effects of the inertial actions of the backfill are considered, which correspond to three different real behaviours. A comprehensive numerical investigation is performed, which allows us to point out the influence of the geometrical and mechanical parameters on the seismic capacity of a masonry arch bridge. The results are given by means of diagrams that can be easily used for a preliminary seismic check of a masonry arch bridge
Seismic response of a r.c. viaduct during different earthquakes
No full textThe experimental seismic behavior of a typical viaduct in Italy subjected to subsequent events is analyzed. The structure is located along a freeway in Umbria region. Two spans and two piers were monitored in the framework of the Osservatorio Sismico delle Strutture monitoring network, managed by the Italian Civil Protection Department. The changes of the dynamic characteristics of the structures were analyzed through the analysis of the data recorded during five recent seismic events. These five earthquakes were characterized by different magnitude and different Arias Intensity at the site. The analysis allowed determining the first natural vibration frequencies of the structure in three perpendicular directions and the associated modal shapes. The results pointed that the horizontal vibration frequencies of the structure changed significantly during the different earthquakes, which had different effects at the site. Anyway, the bridge recovered its dynamic characteristics also after the strongest events, shoving a linear behavior. This work is part of research project on the use of SHM to support the road and highway operators in the knowledge of the health status of the existing bridge and viaduct network and for an effective and prompt response to any emergencies
Influence of Friction in the Seismic Behaviour of HDRB+SD Isolation Systems
No full textThe response of an isolation system made of HDRBs and SDs under low energy earthquakes, classified on the basis of the energy at the basement, is analyzed. The study pointed out that for very low values of the energy, measured by means of the Arias intensity, the isolation system was not put in action, and the superstucture behaved like a fixed base one. The behaviour has been correlated to the ratio between the inertial force resultant and the maximum friction forces of the slider devices. For higher values of the energy, instead, the isolation system was activated and a value of the Arias intensity was individualized, which separates the two behaviours. The variability of the first resonance frequencies with the input energy has been particularly analyzed, as well as the structural response in terms of maximum accelerations, maximum displacements and relative horizontal displacements in the building
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