1,720,994 research outputs found
Optimization of Intervention Strategies for Masonry Buildings Based on CLT Components
Full text linkUnreinforced masonry has been for centuries one of the most widespread constructive techniques for both massive structures and civil buildings (e.g., palaces, hospitals, houses), for the most still standing nowadays. Their future conservation relies on (i) their protection from main natural threats (e.g., earthquakes) and (ii) updating to current functionality and hygrothermal standards. In the former framework, existing masonry buildings proved to have some intrinsic vulnerabilities, depending on composition (units and binder) and structural typologies. Based on experience gathered from seismic events, various retrofitting techniques have been proposed. In such a context, the use of cross-laminated timber (CLT) components is a very promising solution, in terms of compatibility with built heritage and integration of seismic and hygrothermal performances. This paper aims at improving the knowledge of the structural performances of compound timber-masonry interventions by numerical simulations carried out at (i) pier scale and (ii) building full scale via finite element modeling and nonlinear static analyses (pushover). First, a coupled timber-masonry wall was simulated and underwent sensitivity analyses with the properties of both components varying; then, the optimized solution was applied to a case study to assess the intervention benefits, and the results were also cross-checked with those of more traditional interventions (e.g., grout injections)
Italiano come L2 per studenti adulti
No full textnello specifico "Autovalutazione, certificazioni e portfolio" per il Progetto Alias, Università Ca' Foscari di Venezi
Seismic vulnerability assessment of free-standing massive masonry columns by the 3D Discrete Element Method
No full textFree-standing masonry column is a recurrent typology of built cultural heritage. Usually raised without seismic design, columns are subject to intense rocking and overturning under strong ground motions. In this paper, a strategy to assess their seismic vulnerability using the 3-D Discrete Element Method is proposed. It includes calibrating the elastic parameters (joint stiffness parameters) using ambient vibration test data and developing fragility curves from a large set of time history analysis results. This procedure was verified for four selected water towers, a representative archaeological monument in Pompeii, Italy. Based on preliminary structural analyses, the water towers were modeled as rigid monolithic blocks. The outcomes of modal analysis were used to calibrate the input elastic parameters, starting from a range of values given by analytical calculations derived by literature. Artificial earthquakes with peak ground acceleration levels ranging from 0.167 g to 0.803 g were implemented as ground motions. Collapses and non-collapses configurations were subdivided through a threshold concerning the maximum allowable rotation of the blocks. Fragility curves were statistically developed; these revealed the overturning probabilities of the investigated structures and also enabled to conduct a parametric study of the Rayleigh damping constants
Equivalent frame modelling of an unreinforced masonry building in finite element environment
No full textEquivalent frame method (EFM) is a viable modelling option for global seismic analysis of masonry buildings in comparison to more refined techniques, such as finite elements (FE), especially in professional practice [1–3]. EFM takes advantage of a building’s geometric regularity, both in plan and elevation, as well as of the good quality of masonry and floors stiffness, as required for the activation of box-like behaviour under seismic loads. However, typical vulnerabilities in existing unreinforced masonry (URM) buildings, e.g. highly flexible floors, openings too close one another, poor quality masonry, isolated pillars or non-vertically aligned walls, limit the effectiveness of EFM application. Recently, many studies have been devoted to expanding the possibilities of applying EFM to buildings which do not meet box-behaviour hypotheses [4–6]. The paper describes the procedure for implementing an EF model of an existing URM building in Midas GEN, a FE software commonly used for design of steel and r.c. structures. The equivalent frame (piers and spandrels) consists of a system of mono-dimensional, lumped plasticity beam elements [7]. In MIDAS, the frame is defined by the user, who also have to control the modelling process, by using the theoretical criteria available [8–10] and adapting their results to a building’s characteristics. Therefore, some peculiar vulnerabilities of the original building may be specifically implemented, thus obtaining a more refined model. The case study is Palazzo Carraro, a cultural heritage building, located close to the old town of Noale (Venezia). The palace complies with the main requirements of EFM except for floors stiffness, although horizontal connections may be considered sufficient at this level of analysis. Pro and cons of the specific procedure are here discussed, also referring to other state-of-the-art techniques, such as continuum models [11] implemented through the DIANA FEA code. Finally, the work explores the response of the EF model to different modelling choices, but also its reliability in overall analyses
Numerical investigation of the structural role of vertical connectors between drums in ancient columns
No full textThe present paper is part of a research program, aiming to investigate the effect of vertical
connectors (gomfoi) on the seismic behaviour of columns and colonnades, in ancient Monuments.
The columns in ancient Monuments are constructed following the dry construction system, i.e., large
dimensions structural members (marble or porous stones, depending on the importance of the monument and
the availability of materials at the vicinity of the construction site) are positioned without mortar. Since the
Classical Era, connectors are used for the better connection of the consecutive drums. The system of “poloiempolia”, which are of cylindrical shape, positioned in the centre of the drum, is in many cases replaced, or
co-esixts in the Hellenistic and Roman Era, by vertical connectors of orthogonal parallelepiped shape (gomfoi),
positioned near the edges of the drums.
The dimensions and the positions of the vertical connectors (gomfoi) in ancient columns have been
documented, based on published work and in situ observation, in monuments in Greece. Among the
investigated monuments, the Gymnasium in Ancient Messene has been chosen for further analytical and
experimental investigation. Preliminary numerical modelling and analysis (under seismic actions) of single
columns has been performed, using two different types of numerical modelling, namely a finite element and a
discrete element program. The results of the different procedures are presented here and are commented
upon. The columns are modelled without connectors, in order to study the effect of the number and the height
of the drums in the behaviour of the columns. The original column, consisting of three drums and a capital, is
modelled also with vertical connectors, and the structural role of the connectors is commented upon. The
modelling of the columns leads to the selection of the exact geometry of the columns to be tested, the expected
actions on the interfaces, the required characteristics of the seismic excitations to be imposed to them, etc. as
well as to the adequate design of the specimens and the setup for the shaking table tests
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
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Evaluation of the effect of compatible interventions applied to horizontal components of URM buildings with EFM and FEM models. The case of palazzo carraro in Noale (Italy)
No full textURM buildings suffer generally of their weak vertical structure and absence of horizontal connections between the walls. Nevertheless, traditional building practice in Veneto plains, where poor soil conditions are extremely common, required to build very deformable and lightweight houses to adapt to differential foundation settlement. Such peculiar features must be considered in the restoration and adaption to present safety criteria of those buildings. Therefore, 'improvement' interventions as defined by Italian technical standards, rather than structural retrofitting, seems to be more appropriated for reducing both, the alteration of the seismic behavior and the structural weight on foundations. Thanks to the regularity, both in plan and in elevation, of this set of buildings, equivalent frame modeling (EFM) is a viable way to perform global analysis if compared to the complexities of a continuum finite element model (FEM). In the paper, two software will be used for the implementation of the EF model, i.e., TRE Muri and Midas GEN, and their results will be compared with a continuum FE model built with DIANA FEA. In the three models, global seismic behavior through pushover analyses, as the building is and after interventions, is explored. Structural interventions are intentionally limited to horizontal structures stiffening. The case study is represented by a medium sized building placed just outside the old town of Noale, in the metropolitan district of Venice (Italy), dating back to the XVII cent
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