1,017 research outputs found
Valutazione dei criteri di selezione per accelerogrammi basati sulla spettrocompatibilità per l’analisi non lineare
No full textAmong the currently employed methods for the analysis and the design of structures potentially subjected to seismic actions, nonlinear dynamics analysis is one of the most accurate in describing the structural behavior. These time-domain analyses allow to predict the response of every element of the structure, studying how they interact during the formation and propagation of damage.
Numerous approaches have been proposed for selecting recorded accelerograms in order to obtain robust estimates of the structural response. The PSHA has got a fundamental role in the selection procedure, in fact the accepted process is to perform hazard analysis on selected ground-motion parameters, and use the hazard information for record selection and uncertainties propagation, aware that there is no single parameter capable of capturing all intensity, frequency content, and duration information that affect the elastic and inelastic response of soil-structure systems.
All the most important seismic codes, allowing to adopt nonlinear dynamic analyses, prescribe the use of suites of accelerograms representative of the seismicity at the considered site and whose average pseudo-acceleration response spectrum is compatible with a given UHS in an appropriate period range. This calculation of the structural response may lead to wrong estimates when dealing with non-linear systems.
In this paper we focused on the definition of a procedure for estimating the reference mean structural response associated to a desired return period for non-linear structures. We first defined attenuation relationships for the inelastic demand on various SDOF and MDOF structures and then performed PSHA using the obtained models. We obtained the interstorey drift levels with a 475 year return period: these were used as reference response and compared to the estimates of the average response obtained using spectrum-compatible suites of accelerograms with the same return period, selected according to different criteria. Following this approach we were then able to evaluate how the application of each of these criteria to the data-set affected the composition of the spectrum compatible suites of ground motions
Seismic performance of alternative risk-reduction retrofit strategies to support decision making
No full textHow can we evaluate the cost-effectiveness of retrofit interventions aiming at reducing the seismic vulnerability of an existing building? What level of shaking intensity should the retrofitted building sustain? These are open questions affecting either the pre-earthquake prevention, the post-earthquake emergency and the reconstruction phases. The (mis)conception that the cost of retrofit interventions would increase linearly with the level of safety required in designing the intervention often discourages stakeholders to consider alternative retrofit options. As a result, a minimum (in some cases prescribed by-law) level of safety is often targeted, leading in some cases to no-action. Furthermore, the performance measure enforcing owners to take action is generally evaluated following a deterministic approach. When the assessment does not directly reflect, even in simplified terms, epistemic uncertainties and aleatory randomness, it can result in misleading confidence on the expected performance. The present study aims at contributing to the delicate decision-making process of retrofitting existing structures, by developing a framework to assist stakeholders with the evaluation of the actual improvement of the performance, expressed in terms of reduction of collapse probability, of alternative strategies of intervention as well as targeted retrofit levels. With reference to a pre-1970 case study building located in New Zealand, alternative retrofit solutions are considered, targeting different levels of performance, and the probability of reaching collapse when considering a set of ground-motions is evaluated, providing a correlation between the deterministic safety index adopted in the design phase (named "Percentage of New Building Standard" adopting New Zealand regulations) and the expected annual probability of collapse
UN PRIMO INVENTARIO DEI DANNI IN EDIFICI PREFABBRICATI A SEGUITO DEL SISMA DELL’EMILIA DEL 2012
No full textThe 2012 Emilia (Italy) earthquakes hit a
highly industrialized area including several
thousands of precast RC buildings. Due to the
lack of specific design and detailing for
earthquake resistance, these buildings suffered
from severe damages and even partial or total
collapses in many cases. The present study
reports a preliminary data inventory of damages
from field surveys concerning 1133 prefabricated
industrial buildings. The damage distributions
were related first with the epicentral distance.
Then, making use of available shakemaps of the
mainshocks, empirical vulnerability curves of
buildings with different damage grades were
developed. It was found that about 90% of
severely damaged to collapsed buildings are
located at epicentral distances smaller than 14 km
and experienced a Pseudo-Spectral Acceleration
for a period of 1 second (PSA at 1 s) larger than
0.13g. For 90% of the buildings with slight to
moderate damages, the minimum epicentral
distance is smaller than 23 km and the maximum
PSA at 1 s did not exceed 0.07g. Finally, it has
been underlined that 10% of the undamaged
buildings are located within 9 km from the closest
epicentre and suffered from a maximum PSA at 1
s greater than 0.21g
Observational failure analysis of precast buildings after the 2012 Emilia earthquakes
No full textThe 2012 Emilia (Italy) earthquakes struck a highly industrialized area including several thousands of industrial prefabricated buildings. Due to the lack of specific design and detailing for earthquake resistance, precast reinforced concrete (RC) buildings suffered from severe damages and even partial or total collapses in many cases. The present study reports a data inventory of damages from field survey on prefabricated buildings. The damage database concerns more than 1400 buildings (about 30% of the total precast building stock in the struck region). Making use of the available shakemaps of the two mainshocks, damage distributions were related with distance from the nearest epicentre and corresponding Pseudo-Spectral Acceleration for a period of 1 second (PSA at 1 s) or Peak Ground Acceleration (PGA). It was found that about 90% of the severely damaged to collapsed buildings included into the database stay within 16 km from the epicentre and experienced a PSA larger than 0.12 g. Moreover, 90% of slightly to moderately damaged buildings are located at less than 25 km from the epicentre and were affected by a PSA larger than 0.06 g. Nevertheless, the undamaged buildings examined are almost uniformly distributed over the struck region and 10% of them suffered a PSA not lower than 0.19g. The damage distributions in terms of the maximum experienced PGA show a sudden increase for PGA≥0.28 g. In this PGA interval, 442 buildings were collected in the database; 55% of them suffered severe damages up to collapse, 32% reported slight to moderate damages, whereas the remaining 13% resulted undamaged
Analysis of code-based ground-motion selection procedures in terms of inelastic interstorey drift demands
No full textVeronica mas, Spirea, Barbarea
No full text1. Nome scientifico: Veronica chamaedrys L.
(Scrophulariaceae)
Nome attuale: Veronica comune
2. Nome scientifico: Spiraea hypericifolia L.
(Rosaceae)
Nome attuale: Spirea spagnola
3. Nome scientifico: Barbarea vulgaris r. Br.
(Brassicaceae, Cruciferae)
Nome attuale: Erba di Santa Barbar
Veronica alpina (Alpine Brooklime) : Alpine Brooklime
No full textClass: Dicotyledoneae
Family: Scrophulariaceae
Genus: Veronica
Species: alpin
Veronica peregrina (Hairy Speedwell) : Hairy Speedwell
No full textClass: Dicotyledoneae
Family: Scrophulariaceae
Genus: Veronica
Species: peregrin
Ep. #024 - Veronica Strang
No full textThis recording and transcript form part of a collection of podcasts conducted by the Cultures of Energy at Rice University. Cultures of Energy brings writers, artists and scholars together to talk, think and feel their way into the Anthropocene. We cover serious issues like climate change, species extinction and energy transition. But we also try to confront seemingly huge and insurmountable problems with insight, creativity and laughter.Water, water everywhere. The human sciences have become animated by the politics, ethics and materiality of water of late and for good reason. Our guest (11:13) on this week’s Cultures of Energy podcast was one of the first to get this conversation started. Anthropologist Veronica Strang, currently Executive Director of the Institute for Advanced Study at Durham University, is the author of The Meaning of Water (Oxford, 2004) and Water: Culture and Nature (Reaktion, 2015) and a recipient of UNESCO’s International Water Prize. We talk about how the transgressive and transformative properties of water cut across cultures and how its material liquidity complicates our cultural and legal understandings of ownership and property. Veronica explains why we have to think water across scales, from its mediation of individual bodies to how its flows form communities. We talk about the infamous case of Bolivia’s water privatization, efforts to enclose water resources across the world and how contemporary politics of water are undermining democracy. Veronica also reminds us though that efforts to centralize control over water are ancient and that the movements that are now seeking to decentralize water resources also have hope. In closing we discuss cosmological and mythological water beings ranging from rainbow serpents to Chinese water dragons to the Lambton Worm, reputed to live in Durham’s own River Wear. Is our concern with hydration and floods these days informed by the moral economy and sacred vitality of water? Has urbanization caused us to lose touch with the hydrological cycle that so powerfully informed the cultural imaginations of our ancestors? Pour yourself a glass of water and listen on
The "Emilia" earthquake: an overview of damages and collapses in industrial precast buildings
No full textA series of earthquakes struck the Emilia region, in Northern Italy, in May 2012. Two main mainshocks, characterized by moment magnitudes of 6.1 and 6.0 were identified. The area struck by the earthquakes was not considered as seismic until a few years ago: only in 2001 an update in the Italian seismic hazard map assigned to that region a low to moderate seismicity, becoming mandatory for designers only in 2005. For this reason, most of the buildings that experienced the earthquake were designed without seismic criterion. As the region is one of the most productive in Italy, a high concentration of industrial precast buildings can be found and the ground-shaking resulted particularly severe for these structures.
In the paper, an overview of the damages and collapses caused by the earthquake on precast industrial buildings is given. Extensive field surveys took place immediately after the shocks, enabling the authors to observe and collect a vast amount of data on damages of these buildings. They were very vulnerable for several reasons. The absence of connections between the various precast monolithic elements was the main cause of most collapses. The inadequacy of connection of external precast walls to the bearing elements and the interaction between non-structural walls and structural elements were also critical aspects in many cases. For recently designed industrial buildings, the inadequacy of columns and foundations was responsible of very serious failures. Finally, some collapses were related to the overturning of metallic shelves not designed to sustain horizontal actions
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