1,720,975 research outputs found
An Application of Topological Optimization to Bridge Design
No full textRecently, structural optimization has become an important tool for structural designers, because it allows a better exploitation of material, thus decreasing a structure's self-weight and saving material costs. Moreover, structural optimization helps the designer to find innovative design solutions and structural forms that not only better exploit material but also give the structure greater aesthetic value from an architectural point of view. In this article, the seismic retrofitting of a bridge originally designed in reinforced concrete is illustrated, showing how lightening the bridge superstructure, rather than reinforcing the already completed foundations and abutments, allowed these latter features to resist greater seismic actions as required in the recent update of the Italian seismic code. Therefore, besides using the steel-concrete composite typology, the bridge superstructure was lightened through structural optimization. After having optimized the thickness of webs and flanges, it was necessary to further lighten the bridge superstructure by removing unexploited material from the bottom flange through the insertion of large cavities. For this purpose, topology optimization is shown to be a powerful tool that allowed the designer to find that the hole shape was basically elliptic, thus suggesting their regularization as ellipses. Comparisons were made between several design solutions, each characterized by a specific volume reduction of the bottom flange. Identification of the highest-performing solutions through computer-aided procedures led to a weight reduction of 40% with respect to the design solution in reinforced concrete. Retrofitting the already existing foundations and abutments to satisfy the updated provisions of the new seismic code was thus avoided by defining an innovative layout of arch bridges with holes in the bottom flange, which has never been used before
TOPOLOGY OPTIMIZATION OF BRIDGES SUPPORTED BY A CONCRETE SHELL
No full textA shell-supported footbridge was designed by shaping an anticlastic membrane in compression between deck and foundations. Since it would be subject to biaxial compression, it was appropriate to be made of concrete because concrete strength could be exploited and crack propagation prevented. With reference to Musmeci's work, a form-finding algorithm shaped the shell as a tension structure with same loads, restraint reactions and internal normal forces, but with the opposite sign. Using a finite element (FE) model of the shell, unwished bending moments (and therefore tensile stresses) were, however, found, because of second order displacements and (contrary to a tension structure) because of the bending stiffness of the reinforced concrete (RC) shell. Tensile stresses were progressively eliminated by removing material from the shell regions where unwished bending moments occurred. For this purpose, topology optimization with the Solid Isotropic Material with Penalization (SIMP) method was used, and different shell structures with cavities for different values of given volume reduction were obtained. Appropriate indexes for structural response were defined, and an optimization index was finally used to identify the most suitable pattern of cavities along the shell
Experimental and numerical investigation of the cyclic behaviour of an innovative prefabricated beam-to-column joint
No full textEquivalent linearization of bridges with bilinear isolation systems
No full textAlthough maximum displacement demands of bridges can be obtained through non-linear time history analysis, many approximate methods have been proposed in recent codes to reduce the required computational time distinctive of non-linear approaches. Among these methods, equivalent linearization method is best known. This paper evaluates the accuracy of equivalent linearization method adopted in AASHTO through comparison of non-linear and linear time history analysis. The isolation system is characterized by bilinear hysteretic behavior and the bridge is simplified to be a single-degree-of-freedom (SDOF) system. A comprehensive parametric study is performed using a program developed by MATLAB in combination with OpenSees. Results show that the predicted maximum displacement is significantly underestimated by AASHTO method when the strain hardening ratio and ductility ratio are relatively small. To improve the estimation accuracy of equivalent linearization technique, a new equation of equivalent damping ratio is proposed by modifying AASHTO method. © 2014 Taylor & Francis Group
Friction pendulum system as a retrofit technique for existing reinforced concrete building
No full textFriction pendulum system (FPS) is one of the most effective base isolation systems, which is widely used for seismic upgrading of existing buildings. FPS is almost always non-linear and often strongly non-linear, so a mechanical model of FPS bearing is of great importance in seismic analysis. In this paper, three different models of FPS bearing are described and a building severely damaged by the L'Aquila earthquake in 2009 is examined according to the latest Italian code. Then, a case study presenting briefly an innovative technique that is able to introduce base isolation on existing buildings is provided with reference to the use of FPS. Different kinds of analyses, including response spectrum analysis and linear and non-linear dynamic analyses, are performed under the life-safety limit state. Storey shear, inter-storey drift, effective stiffness and energy dissipation are the considered parameters to investigate the effectiveness of the retrofitting procedure and analysis techniques
Bond slip model for generalized excitations
No full textCorrect evaluation for bond-slip effects is a crucial point when investigating progressive damage of reinforced concrete structures under random or earthquake excitations. For bridges, this aspect affects in particular the seismic response of piles' base and pier-deck joint in Integral Abutment Bridges as well. The need for a bond model, more accurate than those currently available in literature, without renouncing to ease of implementation, suggested to develop a new one. This model is defined by summing the effects of different bond resistance contributes (namely mechanical bond, friction bond and virgin bond) defined by means of continuous functions. This allows to fit, with reasonable precision, experimental monotonic and cyclic bond-slip paths, even along reloading branches. New relationships have been provided for updating the main law parameters at each load reversal. Moreover a specific progressive damage rule is introduced, able to account for generalized excitation. The proposed law has been validated by comparison with several existing pull-out cyclic data obtained from short-anchorage tests in good confinement conditions. © 2012 Taylor & Francis Group
Bridge Structural Optimization Through Step-by-Step Evolutionary Process
No full textIn this paper, the structural optimization process aiming to reduce the weight of the superstructure of a five span arch bridge, built in the Province of Venice, Italy, and spanning the Piave River in the town of San Donà, is presented. The original project, with a pre-stressed concrete superstructure, was re-considered during construction because of the following two unexpected events. First, the approved new seismic national regulation became effective when the bridge was already partially built. As a result, existing foundations became unable to withstand the prescribed new seismic action. Furthermore, the Venice Water Authority, responsible for the management of the river spanned by the bridge, declared that erection phases without any provisional supports and scaffolding , resting on the riverbed, as foreseen by the original project, should be preferred. Between the two possible identified design strategies able to deal with the mentioned problems, namely, the strengthening of the foundations or the lightening of the superstructure, the second option was chosen, on the basis of engineering judgement concerning the simplification of construction procedures, timing and budget. The search for the lightest possible solution, with the restraint given by the approved aesthetics of the original design and the need of keeping within the former budget, brought to the conclusion that an evolutionary structural optimization (ESO) process could be suitably applied to a composite steel and concrete superstructure
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
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