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Month: July 2013
ANALYSIS OF FIBER-REINFORCED ELASTOMERIC ISOLATORS INCLUDING STRETCHING OF REINFORCEMENT AND COMPRESSIBILITY OF ELASTOMER
The mechanics of fiber reinforced multi-layered elastomeric isolation bearings is studied in this paper. Such bearings offer the possibility of light-weight low-cost seismic isolators that can be mass-produced and used for public buildings and housing of highly seismic areas in developing countries.
The fiber reinforcement, in contrast to the steel reinforcement in conventional isolators, assumed to be rigid both in extension and flexure, is flexible in extension, but completely without flexural rigidity. In addition the rubber layers in these bearings tend to be very thin leading to large shape factors and the need to include bulk compressibility in the elastomer. These aspects of the bearings lead to interesting mechanics problems and in this paper the influence of the stretching of the reinforcement and the compressibility of the elastomer on the mechanical response is developed and confirmed by finite element analyses. A surprising result of the analysis of the combined response of the apparently unrelated effects of stretching of the reinforcement and compressibility in the elastomer is that the mathematical structure of the theory is the same for both effects and that they can be combined in the result- ing solution in a simple way. It is shown that it is possible to produce a fiber-reinforced isolator that matches the behavior of a steel-reinforced isolator. The fiber-reinforced isolator will be significantly lighter and could lead to a much less labor intensive manufacturing process.
CONCAVE SLIDING ISOLATOR’S PERFORMANCE UNDER MULTI-DIRECTIONAL EXCITATION
Due to their large displacement capability and stable energy dissipation associated with a compact shape and new highly performing materials, the use of concave sliding isolators have been continuously increasing for application in buildings and bridges. In this paper the results of dynamic tests on full scale devices are presented. Their response was studied in a wide velocity range, for bi-directional patterns under different compressive loads. In this range of loading characteristics, which is typical of design for earthquake excitation, the behavior of these isolators appears significantly affected by the multi-directionality of the motion, and more specifically by the degradation of the coefficient of friction due to heating phenomena at the sliding surface. An analytical model, applicable to the prediction of bi-directional sliding behavior of friction-based isolators has been experimentally validated. Results of this study suggest that these phenomena should be considered in the design of structures equipped with these popular anti-seismic devices.
SEISMIC ANALYSIS OF MASONRY VOUSSOIR ARCHES ACCORDING TO THE ITALIAN BUILDING CODE
This paper is addressed to construction professionals, engineers and architects entrusted to assess the seismic vulnerability level of historical and architectural heritage buildings and to ensure their safety. Masonry building collapses caused by seismic events highlight frequent cases of loss of equilibrium, that is, the rigid overturning of structural portions. The study of collapse mechanisms can be effectively performed using the kinematic analysis methods, recently adopted by the Italian Building Code. Referring to a particular structural element (the masonry arch), a typical component of historic buildings, this paper proposes an original approach to perform seismic verification based on an algorithm devoted to this topic. Thanks to this algorithm, the a-priori choice of failure interfaces is avoided, as it is possible to individualize the kinematism and its related collapse load factor. The seismic verification which follows is performed according to the Italian Building Code.
MULTI-SITE DAMAGE LOCALIZATION IN A SUSPENSION BRIDGE VIA AFTERSHOCK MONITORING
In earthquake affected areas the speed and reliability in assessing the damage suffered by strategic structures, such as long-span bridges, is of paramount importance both for civil protection operations and for organization and coordination of immediate remedial measures for the structure safety. In this paper we present the results obtained by applying a damage identification method termed Interpolation Damage Detection Method to a numerical model of the Shimotsui-Seto bridge, a suspension bridge with a long span steel truss deck (940 m). The method allows to detect localized reductions of stiffness along the bridge deck on the base of accelerometric responses recorded on the main girder during a damaging seismic event, or during an aftershock following the onset of damage. This is possible as long as responses recorded at the same locations on the undamaged structure are available. The response of the suspension bridge, subject to seismic excitation, has been calculated in the ANSYS framework using a finite element model derived from the original design data. In order to reproduce real life conditions, the numerical results in terms of temporal responses are artificially modified by including a background noise characteristic of classes of Micro Electro-Mechanical Systems type sensors. The reliability of the Interpolation Damage Detection Method has been numerically verified by simulating the damage through a reduction of stiffness in one or more elements of the deck. Several different locations of damage have been considered in order to study the influence on damage location the results provided by this Structural Health Monitoring methodology.
“THE WORD OF SCIENCE. THE L’AQUILA EARTHQUAKE AND THE ITALIAN COMMITTEE FOR DISASTER PREVISION AND PREVENTION. AN ANTHROPOLOGICAL ANALYSIS”
Review of the book by Antonello Ciccozzi