1,720,980 research outputs found
Optimal design of new steel connections
No full textThe Limited Resistance Rigid Perfectly Plastic Hinge (LRPH) are special steel connections mainly usable to join beam elements of plane or spa-tial steel frames. The fundamental characteristics of these devices are the mutu-al independence of their own resistance and stiffness features as well as the re-spect of assigned constraints related to the elastic and limit behaviour of the joined elements. Within the frame structural scheme, the device plays the role of a rigid perfectly plastic hinge, constituted by a suitably sized sandwich sec-tion. The efficient use of the LRPH in the relevant frame depends on the appro-priate design of the device geometry. In the present paper, a new approach de-voted to the optimal flexural design of the LRPH is presented, according with the imposed mechanical constraints as well as with further suggested technolog-ical ones. The optimization procedure is based on a genetic algorithm approach and different applications are reported confirming the good applicability of the computational method as well as the reliability of the relevant device
Comparison among different dynamic shakedown approaches
No full textThe paper concerns the search for the limit load multiplier of structures subjected to seismic actions under shakedown conditions. The search problem is treated referring to two fundamental different approaches: The unrestricted dynamic shakedown approach and a new stochastic one recently proposed. The comparison between the above cited approaches is effected with the aim of evaluate the goodness of the obtainable results and the related computational effort. The structure sensitivity with respect to shakedown is evaluated through the analysis of the shakedown limit load multiplier cumulative distribution function. This function is determined by means of the stochastic approach, adopting the Monte Carlo method and on the grounds of a suitably defined generalized Ceradini theorem. For the sake of simplicity and without loss of generality, the search problems are formulated referring to elastic perfectly plastic steel frames. The effected numerical applications allow obtaining very interesting information on the structure shakedown behaviour, they confirm the great reliability of the stochastic approach and they provide useful suggestions for the improvement of the method
Numerical validation of LRPH behaviour by FEM analysis
No full textLRPH connection is a special steel device mainly usable to join beam elements of plane or spatial steel frames. It is identified as Limited Resistance Rigid Perfectly Plastic Hinge and it is covered by patent n. 102017000088597 at the Italian Ministry of Economic Development and identified in the International Patent System with the number PCT/IB2018/055766. The fundamental innovations of this device are the mutual independence of their own resistance and stiffness features and the respect of assigned constraints related to the elastic and limit behavior of the joined elements. Within the frame structural scheme, the device plays the role of a rigid perfectly plastic hinge, and it is constituted by a sequence of three steel elements of limited length bounded by two parallel steel plates joined up with the connected structure elements. The cross-sections of the steel elements are I-shaped with specific thickness and length obtained by a suitable optimal design. The efficient use of the LRPH in the relevant frame substantially depends on the appropriate design of the device geometry carried out taking into account only bending moment. Starting from an assigned geometry of the LRPH fulfilling some suitably fixed behavioral data, the present paper is devoted to numerically investigate on the reliability of the device by utilizing appropriate FEM analysis. In particular, the yield conditions and the kinematical performance of the device are investigated. The obtained results, related to some common standard steel profiles, confirm the wide applicability of the LRPH in the field of steel structures
Fixed strength and stiffness hinges for steel frames
No full textA new type of device able to connect steel beam elements is proposed. Specifically, the device is designed in such a way that the required bending stiffness and limit resistance can be independently imposed. To this goal, the device is realized as a "sandwich" section whose wings possess a particular geometry able to guarantee the required characteristics. Further technological requirement is that the device has to engage plan dimensions equal to those of the elements to which it is connected. The procedure to design the device is presented in the paper with reference to a simple plane steel portal constituted by appropriate profiles in such a way it behaves following an assigned force/displacement diagram. The device is proposed as constraint at the base of the pillars as well as connection node between the beam and the pillars. For each device utilized, even in the same frame, a different limit resistance in terms of bending moment can be fixed. Therefore, the elastic plastic response of the frame to a monotonically increasing load shows a complete independence between elastic and resistance characteristics. The effected application shows the great effectiveness and wide applicability of the proposed device
On the post-elastic behavior of LRPH connections
No full textThe paper concerns the study of the post-elastic behavior of a recently proposed innovative device, named Limited Resistance Rigid Perfectly Plastic Hinge (LRPH). In particular, LRPH is a steel device of finite length realizing a moment connection between beam elements of a steel frame; it is designed in order to possess two main and independent requirements: its bending moment resistance must be suitably lower than the one of the connected beam element and its overall bending stiffness must be equal to that of the connected beam element characterized by the same length. In order to make the proposed device reliable, LRPH must be capable of realizing a full plastic hinge for the assigned bending moment limit value. This feature can be ensured by imposing some appropriate lower bound constraints on the geometry of the relevant device. The correct definition of these bounds is achieved by means of a preliminary FEM analysis of the device. The present paper is devoted to the definition of these bounds and to the consequent formulation of a wider optimization problem of the LRPH device
LRPH device optimization for axial and shear stresses
No full textThe paper concerns an in-depth study of a special connection for steel structures and the formulation of the related optimal design problem. The connection is called Limited Resistance Rigid Perfectly Plastic Hinge (LRPH) and it represents an innovative device devoted to join steel beam elements of frame structures. The device consists in a sequence of steel cross sections constituted by two parallel flanges with suitably different thickness connected by as many webs with constant and equal thickness. The fundamental innovation of the device is the possibility of designing special connections with elastic stiffness and limit strength independent of each other. Such a special characteristic makes the proposed device definitely unique within the steel structure constructions. The LRPH limit strength is evaluated with respect to axial force, bending moment and shear force, coherently to the international standards. The optimal design problem is formulated minimizing the ratio between outer and inner flange thickness, taking into account constraints related to the imposed reduced resistance, to the required elastic stiffness and to further suitably defined technological requirements. In the application stage, the optimal design is reached by means of a standard non-linear solver for continuous variable problems
Reliable measures of plastic deformations for elastic plastic structures in shakedown conditions
No full textA new formulation for evaluating reliable measures of the plastic deformations occurring in the transient phase of a structure in shakedown conditions is proposed. The structure is thought as constituted by elastic perfectly plastic material and subjected to a combination of fixed and cyclic loads. The proposed formulation consists in the search for the optimal plastic strain field that minimize a suitable objective function defining a strain energy measure related to the plastic strains at the shakedown limit. The typical self-stress field can be obtained as the elastic structural response to an assigned plastic strain field respecting appropriate ductility limits for the material. Without loss of generality, reference is made to plane steel frames and the limit behaviour of the typical cross section is evaluated just in terms of bending moment. Once the optimization problem, formulated under appropriate constraints related to the structure plastic admissibility and to the ductility limit behaviour of the material, is solved, the chosen measure of the plastic strains occurring during the transient phase is evaluated solving a simple linear elastic analysis problem. The design variables reduce just to the plastic strains evaluated in correspondence of suitably chosen cross sections of the structure (Gauss points)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
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