1,720,963 research outputs found
Eigenfrequencies of continuous prestressed concrete bridges subjected to prestress losses
No full textThe paper presents a numerical procedure to evaluate the consequences of prestress loss on the frequencies of vibration of continuous prestressed concrete (PSC) bridges. The importance of being able to identify an excessive loss of prestressing, caused for instance by the breaking of some strands, is evident considering that currently the majority of collapses occurred in prestressed bridges is due to the stress-corrosion cracking of the prestressing steel.The method allows to solve the structural problem taking into account the following mutually interconnected features: non-linearity of the materials mechanical properties, redistribution of stresses based on the actual flexural stiffness of the beam segments in statically indeterminate structures and loss of prestressing. The application of the proposed procedure to two case studies found in the literature indicates that the variation of the first three eigenfrequencies for a prestress loss of 30% turned out to be in the range 1.5%–2.5%. The procedure could, thus, be included in continuous monitoring systems of PSC bridges that already take into account the frequency variations produced by other causes (temperature, humidity, ...) for a timely detection of relevant prestress losses
Identification of nonlinear systems through statistical analysis of the dynamic response
No full textIn this paper an extension to the method for the identification of mechanical parameters of nonlinear systems proposed in Breccolotti and Materazzi (2007) for MDoF systems is presented. It can be used for damage identification purposes when damage modifies the linear characteristics of the investigated structure. It is based on the following two main features: the solution of the Fokker-Planck equation that describes the response probabilistic properties of the system when it is excited by external Gaussian loads; and a model updating technique that minimizes the differences between the response of the actual system and that of a parametric system used to identify the unknown parameters. Numerical analysis, that simulate virtual experimental tests, are used in the paper to show the capabilities of the method and to analyse the conditions required for its application
Fatigue behaviour and damage accumulation in RAC subjected to cyclic compressive loadings
No full textIn this paper a constitutive modelling developed by the authors for Natural Aggregate Concrete (NAC) is used to investigate the fatigue behaviour of Recycled Aggregate Concrete (RAC) subjected to compressive constant and variable amplitude stress cycles. The constitutive modelling takes into account the non-linear damage accumulation occurring in the material by using the stress-strain envelope concept. The identification of the parameters that define the constitutive modelling for RAC has been carried out through calibration with the available experimental data found in the literature. The present investigation allows to set up a predictive model that can be used to estimate the fatigue performance of RAC elements taking into account the compressive strength fc′, the replacement percentage of coarse natural aggregates with recycled ones ρ and the concrete mix type. Finally, a comparison between the fatigue experimental data and the provisions of the fib Model Code is carried out
Ductility evaluation of precast RC shear walls in Italian existing buildings
No full textThis paper investigates the seismic behaviour of structural RC shear walls made with precast panels according to several proprietary technologies to build existing structures. The study focuses on determining the maximum ductility of these construction systems through in-plane lateral thrust numerical simulations by means of FE analysis. The investigations are carried out on three types of precast constructions systems, each one characterized by its own details and reinforcements, used to construct many buildings in central Italy between the early 70′s and the late 80′s. For reference and comparison purposes a coeval cast-in-place shear wall has been also analysed. The ductility values obtained from the analyses show that the shear walls made with these techniques have a similar or, in some cases, grater ductility than the cast-in-place shear walls built in the same period. In detail the lowest value of ductility, equal to 3.42, has been obtained by the cast-in-place shear wall while ductility values in the range 4.15–6.29, have been obtained by the three precast RC assemblies. The results of this research may provide a support for the seismic vulnerability analysis of existing buildings constructed with precast RC shear walls and may supply information for the behaviour factors estimation of this type of structures
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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