1,721,109 research outputs found
Energy-based method for identifying vulnerable macro-elements in historic masonry churches
Full text linkSeismic vulnerability of historic churches is a well known issue in earthquake engineering. The need of preserving these buildings encourages the development of reliable numerical methods to assess their seismic behavior. In this paper a new approach is presented, based on evaluating damage pattern obtained by non-linear dynamic analysis and the energy dissipated by each macro-element during earthquakes. A “hierarchy of dissipated energy” concept emerges to give a scale of vulnerability of the parts that compose the church. By modifying masonry mechanical parameters or geometric characteristics, the crack pattern and amount of energy dissipation density of each element is varied and calibrated to achieve the desired hierarchy. The structural designer can therefore state the effectiveness of strengthening devices by checking reduction and possibly migration of dissipated energy density from weaker structural elements to more resistant ones, together with a preferable damage pattern. The proposed strategy is applied to a single nave church, hit by the Emilia Romagna earthquake (Italy, 2012), first defining a scale of vulnerability of the macro-elements and then proposing a rehabilitation strategy, which improves the seismic response in terms of damages and dissipated energy. In the case study the strong vulnerability of the main dome vault was shown, due to the combination of its high dissipated energy density with its intrinsic weakness. Strengthening techniques have been aimed to reduce the amount of dissipated energy of vulnerable macro-elements and to attenuate out-of-plane mechanisms
Elementi di Tecnica e Tecnologia delle Strutture, Progetto di Strutture a Traliccio e Fondamenti di Ingegneria Sismica
No full textIl testo, a carattere didattico, tratta due macro-argomenti: progetto e verifica di strutture a traliccio e fondamenti di ingegneria sismica. Il primo illustra l’approccio progettuale semi-probabilistico agli stati limite applicato alle strutture a traliccio in acciaio e alle funi elastiche, con la trattazione di membrature composte e di collegamenti saldati e bullonati. La seconda parte presenta nozioni basilari di ingegneria sismica, partendo dalle basi teoriche di dinamica strutturale verso la modellazione dell’azione sismica e le analisi sismiche lineari. Vengono forniti, per ogni argomento trattato, esempi risolti con riferimento alle Nuove Norme Tecniche del 2018
Le valutazioni elementari sulle strutture: modellazione di aspetti critici di strutture in muratura e in c.a.
No full textL’Ingegnere Forense ha il compito di ricostruire le cause che hanno condotto ad un determinato evento dannoso, tramite tecniche scientifiche proprie dell’Ingegneria, che rivestono dunque carattere di oggettività. Tra tali tecniche, impiegabili nei procedimenti giudiziari civili, uno strumento di essenziale importanza è rappresentato dalla modellazione strutturale, che risulta in grado di confortare le assunzioni dell’Analista ed eventualmente prevedere altri fenomeni in presenza di condizioni al contorno variate. L’obiettivo di individuare le cause che hanno generato una situazione anomala in una struttura può essere quindi efficacemente supportato da una sua appropriata modellazione. Numerose criticità intervengono in tale processo, partendo dalla fase di input, in cui viene definito il modello geometrico e meccanico, per terminare in quella di output, in cui occorre fornire un’interpretazione ragionata dei risultati per mettere in luce le modalità che hanno innescato il fenomeno e definire le conseguenti responsabilità. Nel presente contributo si offrono degli spunti per una corretta modellazione di strutture in muratura e in calcestruzzo armato, riferendosi sia ad analisi locali che globali. La maggiore complessità e grado di incertezza che affliggono questi materiali consentono di trarre delle considerazioni di natura generale applicabili anche ad altri materiali costruttivi. Vengono illustrati diversi casi applicativi in cui la modellazione si avvale di tecniche di back analysis o di semplificazione di modelli complessi, discutendo per ciascuno la tipologia di modellazione più adatta e le modalità di interpretazione dei risultati
Design strategy for the rocking stability of horizontally restrained masonry walls
Full text linkThis paper investigates the pure rocking of a rigid block with horizontal restraints. The model simulates the behavior of a masonry wall connected to transverse walls and/or steel tie-rods, very frequently adopted as safety measures against seismic actions. From the system rotational stiffness, found for a Winkler-type model and for a single restraint, the resonance conditions of the horizontally restrained blocks are defined. The role of the horizontal restraint can be unilat-eral (acting only one direction of rotation) and/or bilateral (restraint with similar stiffness in both directions). Real earthquakes or Ricker’s wavelets, representing near-fault ground mo-tions, are assumed as input parameters. It is found that in the bilateral case the response is more predictable, as response spectra are monotonic curves whit a reduction of normalized rotation obtained for higher values of restraint stiffness. Moreover, the effect of horizontal re-straints is beneficial for the range of frequency parameters valid for typical masonry walls. These considerations allow to define a design strategy to ensure the rocking stability of re-strained masonry walls, through a self-centered rocking behavior
Rebound Effects And Oscillation Motion Of Restrained Rocking Façades
No full textStructural or non-structural masonry or r.c. elements, such as building façades or pre-cast panels subjected to out-of-plane modes, can be considered like rocking blocks restrained by horizontal springs. Restrained rocking blocks respond to earthquakes in different way from free-standing rigid elements. Horizontal restraints considered in this paper are transverse walls connected to rocking elements. Their effect could improve the dynamic response of blocks in terms of reduction of rotation amplitude, if the stiffness is properly high. Nevertheless, these restraints can affect the response in negative way, causing overturning when low values of stiffness or one-sided motion are assumed. Oscillatory motion or rebound effects are obtained depending on the linearity or non-linearity assumptions and on the value of spring horizontal stiffness. It is then preferable to have similar stiffness in clockwise and counterclockwise rotations to achieve a reduction of amplitude ratio by increasing this stiffness and make the response safer
Rocking analysis of masonry walls interacting with roofs
Full text linkThis paper investigates the out-of-plane behavior of masonry walls interacting with roofs. Often, collapses of masonry portions supporting roofs may occur due to the roof thrust, which generates a destabilizing effect over motion. Nevertheless, the roof weight can produce a positive stabilizing effect for rotation amplitudes smaller than the critical value. The dynamics of a rocking masonry block interacting with roofs is discussed, by properly modifying the Housner equation of motion of the free-standing single degree-of-freedom block. The dependence of the restoring moment on the rotation angle is investigated and the minimum horizontal stiffness is calculated so that the same ultimate displacement as the system without roof thrust is obtained. Two case studies are presented as applicative examples of the proposed method: an unreinforced masonry structure tested on shaking table and a spandrel beam subjected to roof thrust that survived the Emilia Romagna earthquake. Inertia moments and radius vectors of different failure mechanisms are also provided to solve the equation of motion for different block shapes. Finally, a parametric analysis of a trapezoidal rocking block has been carried out by changing its geometrical shape. This analysis shows that the influence of the shape is relevant for the calculation of the failure load, although is not possible to determine an a priori most critical shape
Tests results and simple structural analysis of the main lighthouse in the Harbor of Livorno (Italy)
No full textThe present work assesses the structural analysis of the main lighthouse of Livorno’s
harbor. It is made by a r.c. framework, built in the 50s as reconstruction of medieval tower similar to
it. The wind and seismic actions (with and without collaboration of the masonry infill and façade) are
investigated, showing the fundamental contribution of the masonry layers for a satisfactory structural
response
Rocking analysis of masonry walls interacting with roofs
No full textThis paper investigates the out-of-plane behavior of masonry walls interacting with roofs. Often, collapses of masonry portions supporting roofs may occur due to the roof thrust, which generates a destabilizing effect over motion. Nevertheless, the roof weight can produce a positive stabilizing effect for rotation amplitudes smaller than the critical value. The dynamics of a rocking masonry block interacting with roofs is discussed, by properly modifying the Housner equation of motion of the free-standing single degree-of-freedom block. The dependence of the restoring moment on the rotation angle is investigated and the minimum horizontal stiffness is calculated so that the same ultimate displacement as the system without roof thrust is obtained. Two case studies are presented as applicative examples of the proposed method: an unreinforced masonry structure tested on shaking table and a spandrel beam subjected to roof thrust that survived the Emilia Romagna earthquake. Inertia moments and radius vectors of different failure mechanisms are also provided to solve the equation of motion for different block shapes. Finally, a parametric analysis of a trapezoidal rocking block has been carried out by changing its geometrical shape. This analysis shows that the influence of the shape is relevant for the calculation of the failure load, although is not possible to determine an a priori most critical shape
Fragility curves and seismic demand hazard analysis of rocking walls restrained with elasto‐plastic ties
No full textThe dynamic stability of out-of-plane masonry walls can be assessed through non-linear dynamic analysis (rocking analysis), accounting for transverse walls, horizontal diaphragms and tie-rods. Steel tie-rods are widely spread in historical constructions to prevent dangerous overturning mechanisms and can be simulated by proper elasto-plastic models. Conventionally, design guidelines suggest intensity-based assessment methods, where the seismic demand distribution directly depends upon the selected intensity measure level. Fragility analysis could also be employed as a more advanced procedure able to assess the seismic vulnerability in a probabilistic manner. The boundedness of this approach is herein overcome by applying a robust stochastic seismic performance assessment to obtain seismic demand hazard curves. A sensitivity study is carried out to account for the influence of wall geometry, the minimum number of seismic inputs, and the mechanical parameters of tie-rods. Fragility analysis, prior to seismic demand hazard analysis is applied on over 6000 analyses, revealing that intensity measures are poorly correlated both for 1-D and 2-D correlation, hardly leading to the selection of the optimal intensity measure. The tie-rod ductility, followed by its axial strength and wall size, is the mechanical parameter mostly influencing the results, whereas the wall slenderness does not play a significant role in the probabilistic response
Risk Assessment of Road Blockage after Earthquakes
Full text linkThis paper presents a safety tool to assess the risk of road blockage during and after emergency situations, mainly due to earthquakes. This method can be used by public authorities to calculate the risk of road paths prone to blockage in case of seismic events. Typological classes of elements interfering with roads, such as unreinforced masonry and reinforced concrete buildings, unreinforced masonry and reinforced concrete bridges, retaining walls, and slopes, are considered. The mean annual frequency (MAF) of exceedance of a blockage limit state is calculated for a path with redundant road segments considering fragility curves from the literature. A practical example is presented for Amatrice, a town in Central Italy hit by the 2016 earthquake. After verifying that the MAF of exceedance demand is lower than the capacity for two roads, a strengthening solution is assumed for two buildings in the path, resulting in a reduction by more than 50% of the MAF demand. For a higher safety level, a bypass is proposed obtaining a demand/capacity ratios four orders of magnitude lower than that obtained with strengthening solutions, highlighting and quantifying the beneficial effect of removing vulnerable structures along the path
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