117,501 research outputs found
A Comparison Between Empirical Procedures for the Definition of Vulnerability Classes of Masonry Buildings: Application to Five Historical Centres Struck by 2016 Central Italy Earthquake
No full textThe definition of seismic risk scenarios necessarily depends on the attribution of a
vulnerability class to each building of a stock. In the macroseismic scale (EMS-98) the
vulnerability class – from A to F – results from the combination between horizontal and vertical
structures. On the basis of post-event surveys carried out in Italy after the earthquakes occurred
in the last 50 years, many rules for converting the masonry quality and the stiffness of horizontal
diaphragms into a vulnerability class have been proposed. However, despite the now high
number of retrofitted or strengthened buildings in Italy, structural interventions are not
mentioned in these procedures, except for metal tie rods and r.c. tie beams.
The paper proposes a critical approach to the definition of vulnerability classes, by the means
of applying the conversion rules to the same sample of 525 masonry buildings located in five
historical centres struck by 2016 Central Italy earthquake: Acquasanta Terme, Campi Alto di
Norcia, Castelsantangelo sul Nera, Muccia and Vezzano. They have been chosen due to the
extensive strengthening campaigns that had been carried out after earlier seismic events. The
preliminary recognition of the structural features of each building happens at the terms of the
MUSE-DV Masonry, a rapid visual screening procedure recently proposed by the authors.
The damage probability matrices (DPMs), obtained from each conversion, are compared to
those from a theoretical model proposed for the EMS-98. Given the same poor masonry quality,
the existing rules classify buildings in class A or B depending only on floors’ stiffness and
horizontal connections. As a result, both low and high damage may appear in the same
vulnerability class causing a bimodal trend in the damage distributions. Conversely, the
MUSE-DV procedure allows to reduce these two frequency peaks by considering interventions.
In fact, overall interventions, even on very poor masonry structures, may lead to a very low
damage and, consequently, to low vulnerability classes (even C or D), while uncontrolled
interventions could obtain a high damage and a high vulnerability. The twofold consequence is
that a) structural interventions have a ‘relative’, i.e. positive or negative, contribution; b) the
usual limitation to A and B vulnerability classes for random masonry buildings needs to be
widened to better explain the damage observed in the 2016 Central Italy earthquake
Empirical fragility curves for masonry buildings struck by the 2016 Central Italy earthquake
No full textThe prevention of seismic risk at urban scale can be pursued through the estimate of the probability to reach or exceed a certain
damage grade given the seismic input. In this framework, seismic fragility curves are nowadays of large interest as they express
this probability in a synthetic way, also extended to large-scale applications. Real damage data are crucial in making more reliable
predictions of damage occurrence, although they can be influenced by a proper definition of the structural types and the
completeness of observations. The paper shows the empirical fragility curves obtained for a sample of 2263 masonry buildings
located within 19 historical centers struck by the 2016 Central Italy earthquake. The damage grade was evaluated according to the
European Macroseismic Scale (EMS-98), also considering undamaged buildings, at the end of the sequence that spanned between
August and October. The buildings largely underwent several repairs and strengthening actions with reinforced concrete elements
starting from the 1980s. The systematization of the structural features led to a taxonomy for strengthened and original buildings,
which, based on the observed damage patterns, was matched to the EMS-98 vulnerability classification. The sample ranges from
class A (worst behavior) to D (best behavior). Class A was typically assigned to original buildings (without interventions) or illadvisedly tampered ones, i.e., those in which interventions had an unfavorable contribution to their seismic behavior. Class D
described buildings with properly designed strengthening interventions, classes B and C intermediate situations. Fragility curves
were obtained per each vulnerability class, as a function of the highest peak ground acceleration (PGA) observed in the sequence
from ShakeMaps. The results were then compared to other empirical fragility model
Design Criteria and Procedures for Archaeological Shelters: Towards Flexibility Thanks to Algorithmic Modelling
No full textMany examples of archaeological shelters can be found over sites and a wide
range of literature illustrates their features. However, it seems that only a few have passed
through a proper assessment phase of their effectiveness and compatibility to the
archaeological remains. which is mainly due to proper detailing of the building solution in
respect of general conservation criteria. Furthermore, in some cases, shelters have proven to
worsen environmental conditions that they are supposed to protect. In this paper design criteria
for archaeological shelters are proposed, in respect of the three main themes recognized as
crucial: general architectural quality, conservation effectiveness, structural and functional
detailing. To deal with the wide range of cases where such criteria must be applied, an
innovative tool providing the desired flexibility in the design procedure is taken into
consideration. Algorithmic modelling in Grasshopper environment, a plugin for Rhinoceros 3D
software, offers the required features thanks to a linear workflow, where the general
characteristics of the structure as far as its structural details can be implemented. Every
element is represented by a set of parameters in the plugin rather than a single object in the
‘parent’ modelling tool, thus allowing easy change to the design. Other plugins provide
additional tools for specific tasks, such as finite element analysis, safety verifications and
structural optimization. The paper presents the methodology for the implementation of the
entire workflow and the preliminary assessment of its results, from the structural and
architectural point of view, showing good adaptability to several possible design choices
(position of pillars, truss number, roof pitch, etc.). Structural optimization is also executed. The
future implementation of environmental parameters (e.g. daylight, ventilation, temperature), as
an additional set of restraints, will complete the framework on which a final assessment will
take place
Validation of design tools for the prediction of mechanical behaviour of masonry arches strenghtened with inorganic matrix-based composite systems
No full textStrengthening of masonry arches and vaults with composite materials has become a quite common strategy of intervention, especially in seismic area. In the last decades, fibre reinforced polymers (FRP) have been conven-iently replaced with inorganic matrix-based composites (mostly known as FRCM, fibre reinforced cementi-tious matrix). Nowadays, several experimental works provide a significant dataset to characterize and interpret the mechanical behaviour under various strengthening configurations on different types of arches and vaults. From one hand, these studies contributed to the definition of design and assessment approaches, which have been only recently agreed in the scientific community for FRCM (e.g., ACI-Rilem recommendations, to be is-sued). From the other hand, design tools currently available for the design and assessment of curved structures in strengthened conditions need to be validated and/or upgraded according to the current scientific state-of-the-art. In this paper, based on the experimental results obtained in twenty-six literature cases, a comparative study among different conditions of masonry arches strengthened with FRCM systems is proposed. The main parameters affecting the structural behaviour of components in both plain and strengthened conditions are identified, and their influence in analytical procedures implemented in common software able to predict fail-ure modes and bearing capacity (either limit state or rigid block analyses-based) are discussed. The pro and cons, as well as the strategies for representing at best the experimental outcomes are also presented. This paper is intended to support the choices required to professionals approaching the design and assessment issues of arches and vaults strengthened with the new generation of composites, in absence of recommendations and standards, and by using the simplified methods implemented in the available engineering tools
Testing Calibration Issues in Resistance Drilling Applied to Timber Elements
No full textResistance drilling devices are commonly used for the onsite inspection of wood and timber
structural components in existing buildings. Although they provide a measure related to the
density variation along a section of an element, results are used mainly qualitatively, due to
several parameters that affect the computed values.
In this paper, several new and old timber elements, taken from the dismantling of original roofs
from a large existing historical building in northern Italy, are tested through a series of ND
(non-destructive), SD (semi-destructive) and destructive testing procedures. Various wood
species (spruce, fir, larch, oak, elm, pine) are taken into consideration.
Among the applied testing methods (visual inspection, resistance drill, ultrasonic, needle
penetration, radar, lab tests bending/compression), not all reported here, a focus on the
resistance drill tests results is addressed, to evaluate the influence of consumption of the needle
tip on the amplitude output. This was done by correlating the drillings to a reference sample
on each test position to obtain data with an enhanced quantitative content. From the visual old
timber elements grading, SD tests execution and successive element strength characterization
through laboratory tests, it finally emerged the need for proper calibration of assessment
methodologies through the application of a combined approach, in order to achieve more
reliable results
Mechanical behavior of historic masonry structures strengthened by bed joints structural repointing
No full textA study on mechanical behaviour of brick masonry structures subjected to overloading phenomena is here presented. Such structures suffer a very specific damage, represented by diffused thin cracks, which can lead to long terms effects up to a sudden collapse. A strengthening technique, based on the insertion of steel bars in the bed joints is proposed. Experimental tests and numerical analyses showed that the presence of the bars allows control of the cracking phenomena, keeping the structure in the desired safety conditions. Two case studies, recently carried out by the Polytechnic of Milan on masonry towers are also discussed. Finally, the application of the strengthening technique to two masonry churches is briefly describe
Local mechanism analysis in unreinforced masonry buildings according to a new procedure based on floor spectra evaluation
No full textLocal rather than global seismic behaviour is a well-known feature in both masonry aggregates
and monumental buildings with large internal spans, such as churches or palaces. In such cases safety assessment through local mechanisms kinematic analysis is generally considered a viable solution. However, the
definition of the seismic forces acting on secondary architectural elements (pinnacles, upper portions of facades, turrets, etc.) or masonry macroblocks, which may interact dynamically with the main structure, is not
banal.
Therefore, the recent update of Italian seismic code stresses the role of a building’s global dynamic response
and floors’ stiffness in the evaluation of seismic actions on the macroblocks in which it can be subdivided.
This result in a complete new definition of floor spectra which are strongly dependent on the dynamic parameters (damping, frequencies) of both, the building and the local mechanism, which also change at the different
limit states.
The paper aims at the implementation of the new procedures in an existing unreinforced masonry building
(Palazzo Carraro in Noale – Venice) with flexible horizontal diaphragms. Modal analysis is used to detect the
possible local mechanism and its results are compared to the evidence of the visual inspection of vulnerability
factors, showing some correspondence. Safety evaluations, in linear and non-linear field, according to the
previous and the current Italian seismic codes are carried out and compared. For the case study, the new procedure is much more pejorative, since acceleration and displacement demands are more than twice the ones
obtained in the old one
Assigning the macroseismic vulnerability classes to strengthened ordinary masonry buildings: An update from extensive data of the 2016 Central Italy earthquake
No full textDamage scenarios caused by the 2016 Central Italy earthquake confirmed the relevant role of interventions on masonry buildings’ seismic performance, also by increasing (rather than reducing) their vulnerability. Notwithstanding, current literature procedures aimed at assigning to buildings an European Macroseismic Scale 1998 (EMS-98) vulnerability class (A to F) do not consider such influence especially referring to the several intervention techniques applied to masonry buildings since the 1980s in Italy. This impaired a proper matching of vulnerability classes to the real performances, as strengthened buildings are conventionally assigned to average vulnerability conditions (class C). In the present work, vulnerability classes are appropriately assigned to buildings in strengthened conditions, basing on the analysis of 2264 dwellings placed in 19 settlements. Inspections were carried out with a purposely developed rapid visual screening procedure. A performance-based definition of structural types considered a building's masonry quality, diaphragms' stiffness, and kind of interventions graded between downgrading and upgrading. Types with the same behaviour were grouped into vulnerability classes, in the full range from A to D, through a literature model compatible with the EMS-98. Rubble stone buildings with downgrading or worsening interventions behaved like those in original conditions (class A), whereas improved buildings typically performed like class C. Upgrading interventions led to class D, similarly to modern clay block buildings. Masonry quality influenced the classification more than diaphragms' stiffness. The empirical membership of each type to vulnerability classes was obtained, that which allowed to include variously strengthened masonry buildings within the EMS-98 framework
Experimental and analytical studies for the choice of repair techniques applied to historic buildings
No full textA study concerning the application of different repair techniques on damaged historic masonry buildings is presented. In particular, three techniques are considered: injections, jacketing, and repointing of bed Joints reinforced by stainless steel wires.
The results of an experimental research carried out in the last years on some study cases are shown. Laboratory and in situ tests are included and the interpretation of the mechanisms of failure by mechanical and numerical models is also given
Intervention strategies for the seismic improvement of masonry buildings based on FME validation: The case of a terraced building struck by the 2016 central italy earthquake
No full textResidential masonry buildings represent a large stock among highly vulnerable structures in medium–high seismic hazard areas, often built without any anti-seismic provisions. Their rehabilitation and/or strengthening according to optimised intervention strategies is topical and may contribute to revaluating zones characterized by depopulation phenomena. In this paper, a terraced building struck by the 2016 Central Italy earthquake is analysed through a frame by macro element (FME) model. The building is composed of six two-storey units made of stone and clay block masonry walls and semi-rigid diaphragms. The numerical model was calibrated based on the damage pattern caused by the earthquake and then used to carry out parametric analyses on the strengthened conditions by simulating both one unit and the entire terrace. The effects of interventions applied to either vertical or horizontal components, both singularly and in combination, were analysed in terms of nonlinear static analyses, and quantified by a performance factor, according to the upgraded seismic code in Italy. Kinematic analyses also completed the assessment of the building. Results compared the capacity of interventions in attaining the targets defined for improvement at both local and overall levels
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