124 research outputs found
STRUCTURAL VIBRATION CONTROL BY TMD'S USE
The paper refers the use of Tuned Mass Dumper (TMD) in different constructions recently built in Italy to improve their serviceability structural performances. In two footbridges and a new tall building the dynamic behaviors are analyzed in the two conditions: without and with TMD. The structural analysis show the improvements in the Serviceability Limit State (SLS).
In the footbridge cases the use of the TMD allows the control of the deck vibrancy, either in the daily use and in extreme overcrowding case; in the tall building case the improvements are appreciated in relation to a greater comfort for the occupants due a better wind structural response
Understanding CME and associated shock in the solar corona by merging multi wavelengths observation
Using multi-wavelength imaging observations, in EUV, white light and radio,
and radio spectral data over a large frequency range, we analyzed the
triggering and development of a complex eruptive event. This one includes two
components, an eruptive jet and a CME which interact during more than 30 min,
and can be considered as physically linked. This was an unusual event. The jet
is generated above a typical complex magnetic configuration which has been
investigated in many former studies related to the build-up of eruptive jets;
this configuration includes fan-field lines originating from a corona null
point above a parasitic polarity, which is embedded in one polarity region of
large Active Region (AR). The initiation and development of the CME, observed
first in EUV, does not show usual signatures. In this case, the eruptive jet is
the main actor of this event. The CME appears first as a simple loop system
which becomes destabilized by magnetic reconnection between the outer part of
the jet and the ambient medium. The progression of the CME is closely
associated with the occurrence of two successive types II bursts from distinct
origin. An important part of this study is the first radio type II burst for
which the joint spectral and imaging observations allowed: i) to follow, step
by step, the evolution of the spectrum and of the trajectory of the radio
burst, in relationship with the CME evolution; ii) to obtain, without
introducing an electronic density model, the B-field and the Alfven speed.Comment: 17 pages, 13 figure
Seismic vulnerability assessment of an Italian historical masonry dry dock
Abstract The paper presents the seismic vulnerability analysis of the military dry dock built in 1861 inside the Messina's harbor. The study appears very important not only for the relevance of the dry dock itself, but also for its social, military and symbolic role. As a first step, the historical documentation about the dry dock delivered by the Military Technical Office, in charge of its maintenance, was thoroughly examined. This activity was fundamental to understand the construction methods, the rehabilitation works executed after the severe earthquake of 1908 and, finally, the works carried out to increase the size of the dry dock in 1950. After this first step, numerical seismic analyses were done with some implemented finite element models (FEM) of the structure. In each FEM, the vertical loads were applied according to the "construction stages" analysis technique, in order to achieve an appropriate representation of the soil stresses around the structure. The analysis results were evaluated according to the Italian design code (NTC 2008) in order to determine the seismic vulnerability of the dry dock
SEISMIC VULNERABILITY ASSESSMENT OF A MILITARY DRY DOCK IN MESSINA
The paper summarizes the studies conducted on the military dry dock in the Port of Messina (built in 1861), to assess the seismic vulnerability. For this work was conducted an accurate research on the historical sources of Technical Office of the Italian Civil Engineers, to know the construction methods, the operations made after the earthquake of 1908 and to increase the size on 1950. Studies have included the implementation of a finite element model for seismic analysis and with a simulation of construction stages.
The analysis results are evaluated against mandatory italian design code to assess the seismic vulnerability of the structure
Seismic Vulnerability of R.C. Bridges Exposed to Corrosion
Recently, the engineering interest about the durability of existing reinforced concrete structures has significantly in- creased as confirmed by the conspicuous scientific literature. The results of these studies are influencing the development of new structural codes. Among the wide range of existing reinforced concrete structures, motorway viaducts stand out for their strategic relevance. Most of these structures were built between ’60 and ’70 years and, nowadays, the materials degradation phenomena are leading to strength capacity reduction, either in serviceability condition or in presence of exceptional loads such as the seismic ac- tion. In order to evaluate the degradation phenomena effects on the seismic vulnerability of motorway viaducts, this paper shows a new procedure to evaluate the seismic performance of reinforced concrete bridges starting from the modelling of the materials deg- radation - according to several scenarios - and by carrying out multimodal pushover analyses.
The degradation is considered in terms of reduction of the concrete cross-section and steel rebar area. The results give an accurate estimation of seismic performance in terms of seismic vulnerability index variation and consequent management activities (e.g. planning and execution of rehab works)
Conditions for electron-cyclotron maser emission in the solar corona
Context: The Sun is an active source of radio emission ranging from long duration radio bursts associated with solar flares and coronal mass ejections to more complex, short duration radio bursts such as solar S bursts, radio spikes and fibre bursts. While plasma emission is thought to be the dominant emission mechanism for most radio bursts, the electron-cyclotron maser (ECM) mechanism may be responsible for more complex, short-duration bursts as well as fine structures associated with long-duration bursts.
Aims: We investigate the conditions for ECM in the solar corona by considering the ratio of the electron plasma frequency ωp to the electron-cyclotron frequency Ωe. The ECM is theoretically possible when ωp/ Ωe< 1.
Methods: Two-dimensional electron density, magnetic field, plasma frequency, and electron cyclotron frequency maps of the off-limb corona were created using observations from SDO/AIA and SOHO/LASCO, together with potential field extrapolations of the magnetic field. These maps were then used to calculate ωp/Ωe and Alfvén velocity maps of the off-limb corona.
Results: We found that the condition for ECM emission (ωp/ Ωe40 G and electron densities are >3 × 108 cm-3. In addition, we found comparatively high Alfvén velocities (>0.02c or >6000 km s-1) at heights <1.07 R⊙ within the active region.
Conclusions: This demonstrates that the condition for ECM emission is satisfied within areas of the corona containing large magnetic fields, such as the core of a large active region. Therefore, ECM could be a possible emission mechanism for high-frequency radio and microwave bursts
Sound Regular Corecursion in coFJ
The aim of the paper is to provide solid foundations for a programming paradigm natively supporting the creation and manipulation of cyclic data structures. To this end, we describe coFJ, a Java-like calculus where objects can be infinite and methods are equipped with a codefinition (an alternative body). We provide an abstract semantics of the calculus based on the framework of inference systems with corules. In coFJ with this semantics, FJ recursive methods on finite objects can be extended to infinite objects as well, and behave as desired by the programmer, by specifying a codefinition. We also describe an operational semantics which can be directly implemented in a programming language, and prove the soundness of such semantics with respect to the abstract one
STRUCTURAL ANALYSIS FOR AN HISTORICAL R.C. TALL BUILDING RESTORATION
n this paper a detailed structural analysis (under the seismic and wind loads) of an historical tall building in Milan is carried out. It’s one of the first tall building (109 m height) realized in Italy in the 56- 59 years, and an important restoration is affecting it with intended use change (from office to luxury hotel and residences).
To investigate the characteristics of concrete several destructive, non-destructive and combined tests are conducted. Moreover, additional destructive and chemical tests on the reinforced bars steel are performed too. Some finite elements models (FEMs) are implemented by using beam and plate elements considering two different boundary conditions (base fixed and elastic soil by Winkler model) and the interaction of the close existing lower constructions presence.
In all of the FEMs, the materials characteristics are assigned basing on the tests results and a their subsequent statistical interpretation. The seismic load, implemented by a response spectrum analysis, and the wind load are applied in according to the Italian Construction Code (NTC).
The structural resistance verifies are carried out in terms of shear and combined compressive-bending stress, whereas further ductility verifies are conducted considering appropriate nonlinear behaviours of the concrete and the steel bars.
Finally some hypothesis to improve the structural behaviour under the lateral loads are proposed by considering cost-benefit analysis
On the structural behaviour of existing RC bridges subjected to corrosion effects: Numerical insight
The evaluation of the structural behaviour of existing reinforced concrete (RC) bridges represents one of the most current structural engineering research topics due to their strategic importance, especially if they are subjected to corrosion effects which can lead to a significant reduction of load-bearing capacity of the main structural elements (e.g., the piers). In the last decades, different types of numerical approaches have been proposed for the evaluation of the structural behaviour of these strategic infrastructures, especially after the recent collapses that have affected this type of structures during last years. In this paper, the structural behaviour of an existing RC bridge subjected to corrosion effects due to carbonation is analysed by means of an efficient procedure based on the implementation of a Finite Element Model (FEM) where the main structural elements are implemented using only Timoshenko beam elements. The safety level of the bridge has been evaluated considering different load conditions (e.g. traffic load, seismic action, etc.) calculated according to the Italian Design Code (NTC2018). Finally, a retrofitting intervention is proposed in order to guarantee and adequate safety level of the bridge under the considered different load combinations
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