132,057 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
New precast constructions for integrated complex urban interventions / Neue fertigteilkonstruktionen für integrierte komplexe städtische interventionen
No full textThe world of construction today requires a series of sophisticated technological solutions needed to fulfil technical specifications that are becoming more and more stricter and wider. The traditional cast-in-situ concrete constructions, relying on a semi-artisanal work, struggle to reach these objectives. A partial prefabrication in concrete made with precast systems with wet joints only partially addresses this issue. It is our opinion that the near future of concrete technology is going to be based on a process that avoids as much as possible the uncertainty coming from handicraft, granting the needed quality of construction and providing it in short times. The natural way to commit to this view is to improve the industrialisation of the construction process, taking advantage of the multiple innovations allowed by dry assemblage procedures. The paper describes a complete solution for rapid complex urban interventions characterised by a high level of industrialisation. This solution includes precast systems for residential, commercial and industrial buildings, produced in a unique plant. The structural optimisation of components, automatisation of design process, and innovative production techniques imprint robustness, speed of construction and high competitiveness to the precast products.Das bauwesen erfordert heute eine Reihe von hochentwickelten technologischen Losungen, um technische Anforderungen zu erfullen, die immer strenger und umfassender werden. Viele traditionelle Ortbetonkonstruktionen, die sich zum Teil auf handwerkliches Geschick stutzen, konnen diese Ziele kaum noch erreichen. Bausysteme, die nur zum Teil auf Betonfertigteilkonstruktionen beruhen, losen dieses problem nue teilweise. Die Autoren sind der Meinung, dass die nahe Zunkuft der Betontechnologie auf einem Prozess basieren wird, der die handwerklichen Unsicherheitsfaktoren so weit wie moglich reduziert, um die erforderliche Qualitat der Konstruktion zu gewahrleiskonsequenteste Weg, sich dieser Sichtweise anzushliessen, besteht darin, die Industrialisierung des Bauprozesses zu verbessern, indem die zahlreichen Innovationen genutztwerden, die durch Montageverfahrenmoglich sind. In diesem Beitrag wird eine umfassende Losung fur schnelle komplexe stadtische Interventionen, die durch ein hohes Mass an Industrialisierung gekennzeichnet ist, beschrieben. Diese Losung umfasst Fertigteilsysteme fur Wohn-, Gewerbe-, und Industriegebaude, die in einem einzigen Werk hergestellt werden. Die bautechnische Optimierung von Komponenten, die Automatisierung von Konstruktionprozessen und innovative Produktionstechniken garantieren Robustheit, hohe Montagegeschwindigkeiten und damit eine hohe Wettbewerbsfahigkeit von Betonfertigteilen
Recent advances and experimental findings on the structural behaviour of an innovative dry-assembled precast concrete wall system
No full textThe paper presents the evolution of the research related to the structural behaviour of an innovative dry-assembled precast concrete wall system named Domus® performed over the last 10 years. This system is made with hollow bearing walls which can be fully prefabricated and assembled in-situ through dry joints. The wall element, named Master®, has been experimentally tested under simulated earthquake loadings as a bracing wall into a full-scale 3-storey precast building prototype with regard to its flexural performance within the framework of the Safecast (FP7-SME-2007-2 with GA 218417/2009) European research project. The preliminary results of a recent test programme concerning the mechanical characterisation of (a) the shear behaviour of a single wall modulus, which is peculiar due to the presence of the hollow cavities and of the discrete mechanical wall-to-wall (or foundation) vertical connections, and (b) the shear behaviour of mechanical wall-to-wall horizontal connections are also presented. This experimental programme has been carried out within the framework of a joint research between Politecnico di Milano and DLC Consulting-Milan aimed at the exploitation of a registered invention patent and has been partially funded by the programme “Brevetti+” (g.u. 179 of 02/08/2011)
Progetto safecast problematiche riscontrate confrontando progetto e prove sismiche
No full textWithin the SAFECAST Research project, a large experimental campaign on the real time behaviour of a full scale multi-storey precast frame mounted in the Elsa/JRC laboratory can give straightforward suggestions for a relaunch of the precast concrete industry in the realization of multi-storey prefabricated structures.
The 3-storey dry assembled structure, without cast-in-situ slab, with dowel and mutual weld connections to realize a rigid diaphragm, the flat slab at the intrados, the stable straight floor members without camber, the adaptation of hinged nodes to clamped, the reduction of the nodal moments with respect to the cast-in-situ technology, the freedom to choose wherever and whenever to adapt the nodes to clamped, displays important subjects that confirm the great advantages of prefabrication especially in seismic area with respect to the traditional cast-in-situ structures
Precast Structures with Adaptable Restraints
No full textIn Southern Europe the heritage and the everyday practice of precast structures consists mostly in dry or semidry
assembled frames with hinged beams and cantilever columns restrained at their base. Such structures can
provide a large energy dissipation, but they are intrinsically very flexible, especially if moving from industrial
mono-storey buildings to commercial or residential multi-storey buildings. Their design becomes influenced by
the need of reducing such flexibility, thus largely over-dimensioning the members and obtaining a complex
seismic behaviour due to the influence of higher modes.
Two solutions are envisaged to solve this problem by keeping the key feature of precast structures, that is the
speed of erection: the introduction of dry or semi-dry assembled precast walls (particularly favourable in case of
residential buildings) or the stiffening of the classical statically determined frame by means of introduction of
moment resisting beam-column connections made with mechanical devices (mostly envisaged in the case of
commercial buildings).
In such enhanced frames, the realization of clamped joints can be performed in a second stage of the erection
process, adapting the existing hinged connection realized at the first stage to clamped by activating the
mechanical devices.
Precast structures with adaptable restraints (PRESAR) are therefore presented in their essential features, among
them the possibility of mix of a high quality dry precast construction technology with high speed of erection and
the stiffness and redundancy provided by a traditional cast-in-situ frame. If properly designed, the horizontal
members can fully be exploited by transferring the dead loads in a simply supported scheme before being
adapted to clamped, with improvements in the behaviour and design of the whole building.
A design comparison among 3 precast frames with similar geometries but different static schemes shows how
this structural flexibility can be exploited to optimize the structure. A further comparison made on the real nonlinear
dynamic behaviour of 4 different structures, ranging from flexible hinged frame to stiff coupled wallframe
Telai prefabbricati ad assetto variabile
No full textThe possibility of realizing dry precast emulative moment-resisting frames is a relevant innovation,
while the heritage of precast structures consists mostly in frames with hinged beams and cantilever columns
restrained at their base.
The transformation of hinges in restraints becomes necessary while facing the need to reduce
deformations under severe horizontal loads, especially seismic. Reduced stresses and increased ductility can
be achieved, avoiding the ???soft floor??? mechanism through the energy dissipation provided by the steel
placed in horizontal members.
Precast structures with adaptable restraints (PRESAR) are therefore presented in their essential features,
among them the possibility of mix of a dry precast construction technology and the stiffness and
redundancy provided by a traditional cast-in-situ frame.
A design comparison between 3 precast frames with the same geometries but different static schemes
shows how this structural flexibility can be exploited to optimize the structure
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Causes of local collapse of a precast industrial roof after a fire
No full textPrecast roofing systems employing prestressed elements often serve as smart structural solutions for the construction of industrial buildings. The precast concrete elements usually employed are highly engineered, and often consist in thin walled members, characterised by a complex behaviour in fire. The present study was carried out after a fire event damaged a precast industrial building made with prestressed beam and roof elements, and non prestressed curved barrel vault elements interposed in between the spaced roof elements. As a consequence of the exposure to the fire, the main elements were found standing, although some locally damaged and distorted, and the local collapse of few curved barrel vault elements was observed in one edge row only. In order to understand and interpret the observed structural performance of the roof system under fire, a full fire safety engineering process was carried out according to the following steps: (a) realistic temperature time curves acting on the structural elements were simulated through computational fluid dynamics, (b) temperature distribution within the concrete elements was obtained with non linear thermal analysis in variable regime, (c) strength and deformation of the concrete elements were checked with non linear thermal mechanical analysis. The analysis of the results allowed to identify the causes of the local collapses occurred, attributable to the distortion caused by temperature to the elements causing loss of support in early fire stage rather than to the material strength reduction due to the progressive exposure of the elements to fire. Finally, practical hints are provided to avoid such a phenomenon to occur when designing similar structures
Numerical and experimental investigation on angle multiple slit bolted connections for precast wall panels
No full textFlat Multiple Slit Devices (MSDs) have been introduced in steel constructions located in earthquake-prone areas as compact hysteretic dampers connected to braces, and were further proposed to be employed also in other structural typologies, including aligned precast concrete walls. Nevertheless, similar angle connections needed for horizontal joints of orthogonal walls are not tackled in literature. The shape of MSDs, obtained by selective weakening by removing part of the steel area of flat plates, may allow to attain a highly ductile and stable dissipative behaviour, given local plate buckling is avoided, protecting the bolted joints through capacity design. Laser cutting as an alternative to mechanical milling introduces the possibility to easily optimise the shape of the slits in order to attain better performance under laterally imposed cyclic load. This paper analyses the application of right-angle-bent MSDs for the horizontal connection between orthogonal precast walls typical of panel structures with rigid diaphragms. In particular, bolted angle plates with hourglass-shaped multiple slits obtained after laser cutting are investigated numerically via non-linear finite shell elements and experimentally with original cyclic tests. The effect of the aspect ratio of the plate and of the restraint condition, possibly affecting the performance under imposed shear deformation due to the presence of the bent corner, is investigated by parametric analysis. Finally, general design rules and recommendations are presented
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