670 research outputs found
Strutture di Acciaio Circolare 21 gennaio 2019, n. 7 C.S.LL.PP. alcune considerazioni
No full textLe nuove Norme Tecniche per le Costruzioni (NTC2018) sono ormai in vigore dal
marzo 2018 e di recente è stata emanata anche la relativa Circolare Esplicativa. Pur
mancando ancora il Documento Applicativo Nazionale degli Eurocodici, il corpus
normativo italiano è di fatto applicabile nella quotidiana attività lavorativa.
Nonostante il lungo processo di revisione a cui sono state sottoposte le norme
prima della loro emanazione, la presente nota mette in luce alcune criticità irrisolte
che potrebbero dare adito a una riduzione dell’effettivo coefficiente di sicurezza
nella progettazione delle costruzioni di acciaio. In particolare, si presentano
osservazioni relativamente alle verifiche di stabilità di elementi inflessi e elementi
presso-inflessi sottolineando anche l’importanza di adeguati strumenti di analisi agli
elementi finiti. Si paragonano infine i diversi approcci ammessi per le verifiche delle
unioni saldate con riferimento a un caso di interesse pratico
Advanced Seismic Design for Storage Pallet Rack Steel Frames
No full textIn the paper, a study on the design of braced and unbraced steel storage pallet racks in seismic zone is summarized. On the basis of a geometric layout of interest for routine design, rack performance has been evaluated via two alternative approaches: the well-established modal response spectrum analysis (MRSA) and an advanced strategy combining non-linear time-history analyses with the measurement of the damage in joints. Reference is made to two recent Italian earthquakes scaled by different values of the peak ground acceleration. Furthermore, cyclic joint behavior has been reproduced by means of a suitable model accounting for joint strength/stiffness degradation, whose excursions in plastic range has been considered to monitor the damage
DESIGN STRATEGIES FOR STEEL STORAGE RACKS IN SEISMIC ZONES
No full textThe use of storage racks is remarkably increased in the last years mainly because of i) the growing importance of the logistic in the context of the global economy and ii) the high levels of standardization of key rack components. A parametric analysis on braced and unbraced racks in seismic zone is presented in the paper. On the basis of a geometric layout of interest for routine design, rack performance has been evaluated via two alternative design approaches: the well-established modal response spectrum analysis and an advanced strategy combining non-linear time-history analyses with the assessment of the damage in joints. Reference is made to two recent Italian earthquakes scaled by different values of the peak ground acceleration. Furthermore, cyclic joint behavior has been reproduced by means of a suitable model accounting for joint strength/stiffness degradation
The One-Armed Spiral Instability in Neutron Star Mergers and its Detectability in Gravitational Waves
No full text<p>We distribute complete gravitational-wave signals in the Advanced LIGO band (10 Hz - 8192 Hz) of the inspiral and merger of two neutron stars. These waveforms been constructed by hybridizing numerical-relativity data obtained with the WhiskyTHC code [1] with tidal effective-one-body waveforms [2,3]. More details on the procedure used to generate these waveforms are given in [4]. </p>
<p>The waveforms are distributed as HDF5 files containing the amplitude and phase of the -2 spin-weighted spherical harmonics multipoles of the strain:</p>
<p><span class="math-tex"></span></p>
<p>where <span class="math-tex"></span> is the distance in cm from the source.</p>
<p>The data files include a machine readable "/metadata" group with:</p>
<ul>
<li>/metadata/EOS: name of the equation of state</li>
<li>/metadata/M_{A|B}: mass in isolation of star A (or B) in grams</li>
<li>/metadata/R_{A|B}: radius of star A (or B) in cm</li>
<li>/metadata/k2T: tidal coupling constant of the binary (see [3])</li>
<li>/metadata/kl_{A|B}: l=2,3,4 dimensionless Love numbers of star A (or B)</li>
</ul>
<p>We store amplitude and phase for multipoles modes up to l=4 as time series sampled at 16384 Hz.</p>
<p>We make these waveforms freely available in the hope that they will be useful. We kindly ask you to cite [3] and [4] in any publication resulting from the use of these waveforms.</p>
<p>---<br />
[1] http://www.tapir.caltech.edu/~david_e/whiskythc.html<br />
[2] https://eob.ihes.fr/<br />
[3] S. Bernuzzi, A. Nagar, T. Dietrich, T. Damour; Modeling the Dynamics of Tidally Interacting Binary Neutron Stars up to the Merger; Phys.Rev.Lett. 114 (2015) 16, 161103.<br />
[4] D. Radice, S. Bernuzzi, C. D. Ott; The One-Armed Spiral Instability in Neutron Star Mergers and its Detectability in Gravitational Waves; arXiv:1603.05726.</p>
SULLA VARIABILITÀ DEL MODULO ELASTICO NELL’ACCIAIO STRUTTURALE
No full textDesign of steel structures is frequently carried out in elastic range, considering
eventually the influence of the deformations (i.e. transversal displacements or,
equivalently, second order effects) for members and/or components that are flexible.
The value of the elastic modulus, E, is of paramount importance of the whole design
path but it is always assumed as a deterministic data, independently by the
considered design approach. Standard provisions for the characterization of the
structural steel grades require ladle and product chemical analyses and mechanical
tests to evaluate the main mechanical properties but do not impose the evaluation
of E. In the past, in Italy as well as in other countries, E for the structural steel was
considered equal to 206GPa. Now, standard provisions recommend E=210GPa, as in
all the Europe.
The present paper summarizes an analysis carried out on the variability of the elastic
modulus for steel grades currently used for structural applications. The considered
data derives from both the results published in several peer-review papers and from
technical report on material tests. Research outcomes stress out a relevant and
unexpected dispersion in the E distribution, suggesting the need of standard
requirements imposing the E evaluation, at least for the in-situ material checks,
especially if load tests are planned for the final testing phase
VERIFICA DI STRUTTURE IN ACCIAIO ALCUNE CONSIDERAZIONI IN ACCORDO ALLE NTC 2018
No full textLe nuove Norme Tecniche per le Costruzioni (NTC2018) sono ormai in vigore dal 22 marzo 2018. Con riferimento alla sola parte dedicata alla progettazione delle costruzioni in acciaio, si rileva la correzione di alcuni errori presenti nella precedente versione (NTC2008) e si osserva la leggera modifica di pochi contenuti proponendo comunque ancora e solamente una piccola parte di quanto riportato nella normativa europea di riferimento (EC3).
In questa breve nota, pur non essendo ancora completo iI quadro normativo nazionale per la progettazione strutturale (mancano la Circolare ed il documento applicativo degli Eurocodici), si propongono alcune considerazioni generali relative alla progettazione delle costruzioni in acciaio secondo le NTC2018, cogliendo al contempo l’occasione per commentare alcuni contenuti dell’EC3, con riferimento anche al suo prossimo imminente aggiornamento
Modal identification of storage racks for cheese wheels
No full textDuring the Emilia-Romagna earthquake (2012), a great number of steel racks used to store cheese wheels collapsed, causing a non-negligible damage to the Italian economy. Therefore, for similar structures that survived and are in service, a deep investigation towards the assessment of their effective safety is required. In the seismic analysis of these frames, the mechanical constraint acting onto the racks due to the reinforced concrete sidewalls, possible nonlinearities exhibited by the base-plate joints and the in-plane restraint provided by wooden boards that connects adjacent columns should be carefully modelled to ensure realistic design results. In the paper, an experimental activity, based on suitable modal identification techniques, is presented to capture the dynamic behaviour of these peculiar structures. The scope is to collect data useful to calibrate numerical finite element models in order to accurately define the aforementioned unknown parameters. Furthermore, a few numerical models based on ideal restraints are herein discussed stressing out non-negligible differences in terms of expected seismic and static response
Seismic Design of Grana Cheese Cold-Formed Steel Racks
No full textSince few years ago only one typology of racks was used to store Grana cheese wheels for aging, which was designed focusing on the sole static behavior. Battened steel columns made by vertical tubes welded to horizontal angles were connected by means of wood boards supporting the wheels. In 2012, a strong earthquake occurred in Emilia Romagna (Italy) and a great number of these structures collapsed owing to the absence of checks for resistance against earthquakes. This catastrophic event plus the need to maximize the structural efficiency led to the development of a new typology of rack systems based on the use of cold-formed steel members. Owing to an extremely limited state-of-the-art on these modern cheese rack, design is carried out in agreement with the standard provisions calibrated and proposed for adjustable pallet racks, despite the non-negligible differences between these structural systems. The paper is focused on the comparison between the available seismic design approaches for cheese rack in order to highlight their main advantages and limits. In particular, among the four design approaches admitted in the European standards, the modal response spectrum analysis (MRSA) and the nonlinear time-history (NLTH) have been considered and the associated results compared in terms of maximum safety index of the members, global displacements and interstorey drifts. Research outcomes stress the differences associated with the considered approaches in terms of expected performance underlining the importance of an accurate definition of the behavior (q-) factor
The Crucial Role of Green Soft Skills and Leadership for Sustainability: A Case Study of an Italian Small and Medium Enterprise Operating in the Food Sector
No full textIncreasing concerns about the human impact on the environment are leading to new
challenges for companies and their employees. Specifically, the food industry is facing the need to
provide sustainable services, requiring a specialized and skilled workforce. This article presents
a case study of an Italian sustainable Small and Medium Enterprise (SME) operating in the food
sector in order to determine the drivers of working for this company, the key skills needed, and the
Green Human Resource Management practices adopted. A total of 13 semi-structured interviews
were conducted with employees and thematically analyzed. The findings showed that soft skills
were perceived as more relevant than hard skills, although the food sector is characterized by high
technical complexity and subjected to several national and international regulations. Moreover, the
crucial role of organizational culture in determining the relevance of soft skills within the company
and in fostering the implementation of the holacracy organizational management method emerged.
Finally, by detecting the relevance recognized to values and soft skills during the recruitment and
selection process, our findings provided some evidence of Green Human Resource Management in
sustainable SMEs
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