26 research outputs found
On the Limit Behaviour of Moment Resisting Connections Under Uncertainties
No full textMoment resisting connections are mainly designed to transfer bending moments and
shear forces. Generally speaking, the design strength of a moment resisting connection can be
classified as full-strength (moment capacity of the connection equal to or greater than that of
the connected member) or partial-strength (the moment capacity of the connection less than
that of the connected member). Similar remarks can be made regarding the stiffness defining
connection rigid or semi-rigid if compared to the stiffness of the connected member. In the
past, full-strength connections have been widely adopted especially in moment resisting frames
and their structural performance relied on the proper behaviour of welding. However, the
research following the 1994 Northridge and 1995 Kobe earthquakes demonstrated the lower
than expected performance of welded connections, stimulating the onset and development of
pre-qualified connections to be adopted especially in seismic areas. Among these connections
the most studied ones are those belonging to the Reduced Beam Section (RBS) typology, being
the so-called “dogbone” connection the most adopted. The dogbone presents a bending
strength and a flexural stiffness lesser than the ones of the original structural member.
Recently, the authors proposed a special device suitably designed to realize an innovative
moment resisting connection for steel beam elements belonging to the RBS typology. Such a
device, called Limited Resistance Plastic Device (LRPD), is constituted by three different
portions: the central one is devoted to the onset and development of plastic deformations and
presents geometrical dimensions reduced with respect to those of the original structural
member; the external ones are devoted to recover the stiffness of beam-device system to that of
the original structural member and present greater geometrical dimensions. This latter remark
allows to affirm that, from a connectivity point of view, the stiffness of LRPD at the columnbeam
interface, is greater than the one of the original structural member. Another fundamental
remark is that the structural connections are intrinsically characterized by uncertainties related
either to geometrical or to material ones. Usually, the effect of uncertainties is covered by the
use of safety coefficients and the analyses are performed referring only to the nominal values
of the geometrical and mechanical characteristics. However, in order to perform a more
complete interpretation of the mechanical behaviour of the studied connections, a nondeterministic
analysis approach can be used. Aim of the paper is the characterization of the
structural behaviour of the referenced connections (“dogbone” and LRPD) taking into account
the main geometrical uncertainties and that related to the material strength by performing
suitably Monte Carlo simulations and by determining the relevant M-N domains. Starting from
the described characterization, different commercial steel profiles will be considered in order to
build a series of M-N domains useful to quantify the safety level and the range of usability of
the two different RBS approaches. Finally, the implemented applications will lead to
demonstrate the greater reliability of LRPD compared to the classical dogbone
Welded section defence by LRPD devices
No full textThe present paper concerns a special application of some recently proposed structural devices, called LRPD, able to protect the welded sections of frame steel structures from undesired brittle collapse ensuring the good expected ductile behaviour. Standard I-shaped cross-sections are treated, and the proposed devices are suitably considered as moment resisting connections between beams and columns. At first the domain representing the brittle safe conditions is defined in the N,V,M space; then a sample plane frame subjected to seismic load conditions is studied and it is proved that, equipping the structure with the proposed devices suitably designed, the generalized stresses at the welded sections remain within the relevant brittle safe domain and the structure is able to dissipate a significant amount of plastic dissipation energy
Tra amor dei e amor sui. Percorsi culturali del Seicento francese e inglese: Madeleine de Souvré, marchesa di Sablé e Damaris Cudworth, lady Masham
No full textDottorato di ricerca in Teoria e storia della storiografia filosofica, XX ciclo, A.a. 2006-2007Università della Calabri
Educare alla pace in famiglia, educare alla conciliazione famiglia-lavoro
No full textContributo a partire da un'intervista sul tema della conciliazione e della pace in famiglia e nel lavor
An innovative moment resisting steel connection: optimal design formulations, practical applications and experimental tests
No full textThis thesis concerns the study of an innovative moment resisting connection device to be adopted in the so-called moment resisting steel frames. Following previous seismic events, such as Northridge in 1994, many steel structures characterized by welded connections between beams and columns experienced extended damages and diffused brittle failures, making the facilities unserviceable and economically disadvantageous to repair. The answers to this problem is represented by a large number of studies, where several proposals for different devices, as well as special technical solutions, are available. However, the main idea developed among all the proposals is represented by the identification of a portion of the beam to be devoted to the onset of plastic strains, known in literature as Reduced Beam Section (RBS). In this way, this selected part is the only one of the beam to host the plastic strains, while the other portions behave elastically. The most representative example of this approach is the so-called dogbone proposed by Plumier. It reduces the strength of a specific cross-section by simply trimming off part of the flanges. This cut can follow different shapes, but the most common is the parabolic one. The dogbone certainly is effective, but on the other hand, it shows the side effect of increasing the flexural and torsional deformability of the element where it is realized, involving an additional percentage of interstorey drifts from 4% to 7%, as confirmed in international standard.
The device studied in this work presents the possibility to independently fix the flexural stiffness and the strength, and it is called Limited Resistance Plastic Device (LRPD). The LRPD is made up of three different I-shaped parts: two outer portions and an inner one. The two outer portions are equal to each other and show a flange thickness greater than the inner one. Moreover, the device is characterized by symmetry with respect to three orthogonal barycentric planes, and the flanges of all portions possess a unique common medium plane. The web thickness is the same in all the portions, and it is assumed to be equal to the web thickness of the connected beam element. The described geometry is useful to guarantee the desired strength reduction, permitting the full development of the plastic strains within the inner portion, and at the same time it allows the device to exhibit independently the preassigned bending stiffness.
The described features are obtained through the solution of an optimal design problem based on the minimization of a suitably chosen objective function while respecting appropriately assigned linear and nonlinear constraints. The chosen objective function is the volume of the device, while the constraints are related to the special device geometry, to the imposed resistance and stiffness, and, furthermore, to ensure that the device fully plasticizes avoiding undesired local buckling effects. The cited optimal design problem has been solved by means of a nonlinear programming tool such as the Matlab Optimization Toolbox. In addition, in this thesis, an approximate iterative procedure has been developed to obtain the geometric characteristics of LRPD without a specific numerical tool.
The device was validated using various FEM simulations, with the goal of verifying the behaviour in relation to the length of the inner part to ensure the expected onset of the plastic deformations. The results confirmed that the LRPD behaves as expected and allowed to define a minimum length of the inner part in dependence of commercial profile (HE of IPE one).
To check the affordability of the LRPD in real structures compared to its competitors, many examples of frames equipped with LRPD or dogbone subjected to static and dynamic loads prescribed by international standards were analyzed. The same frames without any device were analyzed under the same loading conditions, and the results were compared to those of the same frames equipped with dogbones and LRPD. It was observed that the presence of LRPD overcomes the greater deformability of the frames equipped with dogbones, allowing the interstorey drifts to be almost unaltered.
Some efforts were devoted also to the study of the strength domains of the common I-shape cross sections, not only in terms of N-M interaction but also considering the shear contribution. Furthermore, the N-M domains were investigated taking into account the uncertainties that commonly characterize the device’s constitutive parameters, allowing to approximately quantify the effective limit domains.
Another important topic focused on in the thesis was the realization of a breach in a masonry wall, and the consequent reinforcement of the panel by means of a steel frame. In this case, the goal is typically to recreate the element’s original stiffness while ignoring the variation in strength. It was demonstrated that by installing the LRPD in the reinforcement frame it is possible to adequately recreate the characteristics of the original panel.
Finally, an experimental campaign was carried out. The obtained results showed the full validity of the LRPD, serving as a real benchmark of the reliability of the proposed model
A ringed pole-on outflow from DO Tauri revealed by ALMA
No full textWe present new ALMA Band 6 observations including the CO (2-1) line and 1.3 mmcontinuum emission from the surroundings of the young stellar object DO Tauri. TheALMA CO molecular data show three different series of rings at different radial ve-locities. These rings have radii around 220 au and 800 au. We make individual fits tothe rings and note that their centers are aligned with DO Tauri and its optical high-velocity jet. In addition, we notice that the velocity of these structures increases withthe separation from the young star. We discuss the data under the hypothesis that therings represent velocity cuts through three outflowing shells that are possibly drivenby a wide-angle wind, dragging the environment material along a direction close to theline of sight (i= 19◦). We estimate the dynamical ages, the mass, the momentum andthe energy of each individual outflow shell and those of the whole outflow. The resultsare in agreement with those found in outflows from Class II sources. We make a roughestimate for the size of the jet/wind launching region, which needs to be of.15 au.We report the physical characteristics of DO Tauri?s disk continuum emission (almostface-on and with a projected major axis in the north-south direction) and its velocitygradient orientation (north-south), indicative of disk rotation for a 1-2 Mcentral star.Finally we show an HST [SII] image of the optical jet and report a measurement of itsorientation in the plane of the sky.Fil: Fernandez Lopez, Manuel. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Zapata Gonzalez, Luis Alberto. Universidad Nacional Autonoma de Mexico. Instituto de Astronomia; MéxicoFil: Rodríguez, Luis F.. Universidad Nacional Autonoma de Mexico. Instituto de Astronomia; MéxicoFil: Vazzano, María Mercedes. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Guzman, Andrés E.. National Astronomical Observatory Of Japan; JapónFil: López, Rosario. Universidad Autónoma de Barcelona. Facultad de Física. Departamento Astronomía y Meteorología; Españ
Molecular gas and star formation towards the IR dust bubble S 24 and its environs
No full textAims. We present a multi-wavelength analysis of the infrared dust bubble S 24, and the extended IR sources G341.220-0.213 and
G341.217-0.237 located in its environs, with the aim of investigating the characteristics of the molecular gas and the interstellar dust
linked to them, and analyzing the evolutionary state of the young stellar objects identified there and its relation to S 24 and the IR
sources.
Methods. Using the APEX telescope, we mapped the molecular emission in the CO(2-1), 13CO(2-1), C18O(2-1), and 13CO(3-2) lines
in a region of about 5′ × 5′ in size around the bubble. The cold dust distribution was analyzed using submillimeter continuum images
from ATLASGAL and Herschel. Complementary IR and radio data at different wavelengths were used to complete the study of the
interstellar medium in the region.
Results. The molecular gas distribution shows that gas linked to the S 24 bubble, G341.220-0.213, and G341.217-0.237 has velocities
between –48.0 km s−1 and –40.0 km s−1, compatible with a kinematical distance of 3.7 kpc generally adopted for the region. The gas
distribution reveals a shell-like molecular structure of ∼0.8 pc in radius bordering the S 24 bubble. A cold dust counterpart of the shell
is detected in the LABOCA and Herschel-SPIRE images. The presence of weak extended emission at 24 μm from warm dust and
radio continuum emission projected inside the bubble indicates the existence of exciting sources and that the bubble is a compact Hii
region. Part of the molecular gas bordering the S 24 Hii region coincides with the extended infrared dust cloud SDC341.194-0.221.
A molecular and cold dust clump is present at the interface between the S 24 Hii region and G341.217-0.237, shaping the eastern
border of the IR bubble. As regards G341.220-0.213, the presence of an arc-like molecular structure encircling the northern and
eastern sections of this IR source indicates that G341.220-0.213 is interacting with the molecular gas. The analysis of the available
IR point source catalogs reveals the existence of young stellar object (YSO) candidates linked to the IR extended sources, thus
confirming their nature as active star-forming regions. Gas and dust masses were estimated for the different features. The
total gas mass in the region and the H2 ambient density amount to 10300 M⊙ and 5900 cm−3, indicating that G341.220-0.213,
G341.217-0.237, and the S 24 Hii region are evolving in a high density medium. A triggering star formation scenario for the
Hii region is investigated.CONICET of Argentina under project PIP 0356,
UNLP under project 11/G120; CONICyT of Chile through FONDECYT
grant No. 1140839
Molecular gas and star formation towards the IR dust bubble S24 and its environs
No full textAims. We present a multiwavelength analysis of the infrared dust bubble S 24 and the extended IR sources G341.220-0.213 and G341.217-0.237 located in its environs. We aim to investigate the characteristics of the molecular gas and the interstellar dust linked to them and analyze the evolutionary state of the young stellar objects identified there and the relation of the bubble to S 24 and the IR sources. Methods. Using the APEX telescope, we mapped the molecular emission in the CO(2-1), 13CO(2-1), C18O(2-1), and 13CO(3-2) lines in a region of about 5′ × 5′ in size around the bubble. The cold dust distribution was analyzed using submillimeter continuum images from ATLASGAL and Herschel. Complementary IR and radio data at different wavelengths were used to complete the study of the interstellar medium in the region. Results. The molecular gas distribution shows that gas linked to the S 24 bubble and to G341.220-0.213 and G341.217-0.237 has velocities of between -48.0 km s-1 and -40.0 km s-1, compatible with the kinematical distance of 3.7 kpc that is generally adopted for the region. The gas distribution reveals a shell-like molecular structure of ∼0.8 pc in radius bordering the S 24 bubble. A cold dust counterpart of the shell is detected in the LABOCA and Herschel-SPIRE images. The weak extended emission at 24 μm from warm dust and radio continuum emission projected inside the bubble indicates exciting sources and that the bubble is a compact Hii region. Part of the molecular gas bordering the S 24 Hii region coincides with the extended infrared dust cloud SDC341.194-0.221. A molecular and cold dust clump is present at the interface between the S 24 Hii region and G341.217-0.237, shaping the eastern border of the IR bubble. The arc-like molecular structure encircling the northern and eastern sections of the IR source G341.220-0.213 indicates that the source is interacting with the molecular gas. The analysis of the available IR point source catalogs reveals some young stellar object candidates linked to the IR-extended sources, thus confirming their nature as active star-forming regions. Gas and dust masses were estimated for the different features. The total gas mass in the region and the H2 ambient density amount to 10 300 M⊙ and 5900 cm-3, indicating that G341.220-0.213, G341.217-0.237, and the S 24 Hii region are evolving in a high-density medium. A triggering star formation scenario for the Hii region is investigated.Fil: Cappa, Cristina Elisabeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto Argentino de Radioastronomia (i); Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Duronea, Nicolas Urbano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto Argentino de Radioastronomia (i); ArgentinaFil: Firpo, Verónica. Universidad de la Serena; ChileFil: Vasquez, Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto Argentino de Radioastronomia (i); Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Lopez Carballo, C. H.. Universidad de Chile. Departamento de astronomía; ChileFil: Rubio, Mónica. Universidad de Chile. Departamento de astronomía; ChileFil: Vazzano, María Mercedes. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto Argentino de Radioastronomia (i); Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentin
