322,979 research outputs found
Sensitivity and Preliminary Analyses for the Seismic Assessment of Ardinghelli Palace
No full textWhen dealing with the seismic assessment of historical buildings, a higher diversity in uncertainties related to construction details, geometry, and material properties is expected. Moreover, for the conservation of the monument a very low invasiveness degree is required during the investigation process. The procedures available in standards, based on the definition of a Knowledge Level for the whole structure, by following investigation plans that do not take into consideration the specific features of the building, may not serve efficiently in this context. These facts rise the need for a new procedure, rationally implemented to best fit the characteristics of the structure under investigation time by time. Within this context, the procedure based on a Sensitivity and a Preliminary Analyses proposed in Cattari et al. 2014 and Haddad et al. 2016/2017 is executed on Ardinghelli Palace in L’Aquila Italy. The sensitivity analysis is addressed to detect the uncertain parameters mostly affecting the structural response and defines what to investigate. While the preliminary analysis carries out a complementary role in identifying where in the structure shall we investigate, in order to set an effective investigation plan and increase the knowledge about it
Seismic assessment of single-block rocking elements in masonry structures
No full textThis paper summarizes the main results achieved as a result of a PhD research project into the seismic assessment of single-block rocking elements in masonry structures (such as parapet walls, pinnacles, spires, etc...). In particular, this work refers to those elements located in the upper levels of structures. As demonstrated by past earthquakes, these elements are all significantly vulnerable to seismic events, due to their high slenderness and narrowness. Furthermore, due to their elevated position the seismic effect at their base is usually amplified by the dynamic response of the main building. Seismic assessment compares the structural capacity of an element with the seismic demand (loading) in order to check if the element is able to fulfil its design function, with an appropriate safety level. To this aim, two methods of analysis can be adopted: nonlinear dynamic analysis, which is complex and demanding, or the Displacement-Based Approach (DBA), which is based on an incremental static analysis. DBA requires three fundamental steps: i) the definition of the capacity model, which is an equivalent single-degree-of-freedom system; ii) the definition of the seismic input in terms of a floor acceleration-displacement spectrum; iii) a computational procedure which enables the displacement demand, to be compared with the capacity. The final goal of this research was to prove the applicability of the DBA approach to the seismic assessment of elevated single-block rocking elements in masonry structures, in order to provide practise-oriented tools. Original contributions have been achieved in all the three fundamental steps of the procedure
Linear static procedures for the seismic assessment of masonry buildings: Open issues in the new generation of European codes
No full textLinear procedures (lateral static force method or modal response spectrum analysis) are the standard approach for the seismic design of new structures. On the contrary, nonlinear procedures, in particular incremental pushover analysis, should be used for the seismic assessment of existing buildings, because it is difficult to estimate the behavior factor of a building in the absence of a standardized capacity design. Moreover, in the case of existing buildings, the use of linear procedures provides results that are excessively conservative, therefore unreliable. Despite this, seismic codes consider linear procedures because of their theoretical simplicity and robustness with respect to model uncertainties and non-linear issues, a priori avoiding convergence problems. The paper deals with the critical issues related to the application of linear static procedures for the seismic assessment of masonry buildings. Methods proposed by the present draft of the Eurocode 8 (Part 3) and the new Italian Seismic code (NTC 2018) have been applied to a case study building, under two configurations (regular, irregular); in particular, the modelling options usually adopted by professionals have been considered. Results are compared with the assessment carried out through the nonlinear pushover analysis, which may be assumed as able to better estimate the actual seismic behavior. Anyhow, the aim of the paper is not a validation of the code procedures but a comparison between alternative allowed methods. Conclusions show that even by considering the recent improvements in the codes, in the regions characterized from medium to high seismic hazard, linear methods result almost inapplicable leading to almost all buildings not verified in contrast with the evidences of most recent earthquakes
The heuristic vulnerability model: fragility curves for masonry buildings
No full textIn the framework of seismic risk analyses at large scale, among the available methods for the vulnerability assessment the empirical and expert elicitation based ones still represent one of most widely used options. In fact, despite some drawbacks, they benefit of a direct correlation to the actual seismic behaviour of buildings and they are easy to handle also on huge stocks of buildings. Within this context, the paper illustrates a macroseismic vulnerability model for unreinforced masonry existing buildings that starts from the original proposal of Lagomarsino and Giovinazzi (Bull Earthquake Eng 4(4):445–463, 2006) and has further developed in recent years. The method may be classified as heuristic, in the sense that: (a) it is based on the expertise that is implicit in the European Macroseismic Scale (EMS98), with fuzzy assumptions on the binomial damage distribution; (b) it is calibrated on the observed damage in Italy, available in the database Da.D.O. developed by the Italian Department of Civil Protection (DPC). This approach guarantees a fairly well fitting with actual damage but, at the same time, ensures physically consistent results for both low and high values of the seismic intensity (for which observed data are incomplete or lacking). Moreover, the method provides a coherent distribution between the different damage levels. The valuable data in Da.D.O. allowed significant improvements of the method than its original version. The model has been recently applied in the context of ReLUIS project, funded by the DPC to support the development of Italian Risk Maps. To this aim, the vulnerability model has been applied for deriving fragility curves. This step requires to introduce a correlation law between the Macroseismic Intensity (adopted for the calibration of the model from a wide set of real damage data) and the Peak Ground Acceleration (at present, one of most used instrumental intensity measures); this conversion further increases the potential of the macroseismic method. As presented in the paper, the first applications of the model have produced plausible and consistent results at national scale, both in terms of damage scenarios and total risk (economic loss, consequences to people)
A Practice-Oriented Proposal to Consider the Flange Effect in Equivalent Frame Modeling of Masonry Buildings
No full textThis paper focuses on the so-called “flange effect” in unreinforced masonry buildings when the connection among walls is good, thus forming a 3D assembly of intersecting piers (with L-, C-, T-, or I-shaped cross-sections). Given the direction of the horizontal seismic action, the presence of such flanges (the piers loaded out-of-plane) can influence the response of the in-plane loaded pier (the web) in terms of failure modes, maximum strength, and displacement capacity. Specific rules are proposed in codes to evaluate the effective width of the flange, for the in-plane verification of a single masonry wall. However, in the case of 3D equivalent frame (EF) modeling of the whole building, all the intersecting piers should be considered entirely, to model the response in both the orthogonal directions as well as the torsional behavior, but this may lead to overestimating the flange effect if a perfect connection is assumed. This paper investigates the capability of simulating the actual behavior in EF models by introducing an elastic shear connection at the intersection between two piers using an “equivalent beam”, coupling the nodes at the top of piers. A practice-oriented analytical formulation is proposed to calibrate such a flange effect on the basis of the geometric features and material properties of the web and the flange. Its reliability is tested at the scale of simple 3D assemblies and entire buildings as well. Finite element parametric analyses on masonry panels with symmetrical I- and T-shaped cross-sections have been performed to investigate the axial load redistribution between the flanges and the web and the consequent repercussion on the overall performance of the web. The results have proven that, after a calibration of the shear connection, the variation of axial force between the web and the flanges is correctly reproduced and the strength criteria for 2D panels provide reliable results. Finally, in the conclusions, some practical hints for simulating an imperfect wall-to-wall connection are also provided, since this case is relevant in historic masonry buildings, which are characterized by different masonry types, transformations over time, and already-cracked conditions
Unreinforced masonry buildings in aggregate of urban settlements: Current approaches and critical issues for the seismic vulnerability assessment
No full textThe paper explores the architectural complexity of unreinforced masonry buildings in aggregate typical of urban historic centers, focusing on their seismic vulnerability. These buildings often stem from the gradual transformation of urban areas over centuries, also leading to significant variability in materials, geometries, construction techniques, maintenance status, and connections between adjacent Structural Units (SUs). The study outlines the key features and vulnerability factors of this structural typology, with a particular focus on the methodologies proposed in the literature for the seismic safety verification of a single SU, as well as for assessing the seismic vulnerability of buildings in aggregate at the urban scale. The paper highlights the peculiarities and shortcomings of each currently available methodology, emphasizing the unresolved issues and drawing possible solutions, with particular reference to the “aggregate” effect, i.e. the interaction between the SUs. This study underscores the complexity of assessing the seismic vulnerability of buildings in aggregate, emphasizing the importance of considering both in-plane (IP) and out-of-plane (OOP) mechanisms, as well as the pounding effect
Validation of displacement-based procedures for rocking assessment of cantilever masonry elements
No full textAre the nonlinear static procedures feasible for the seismic assessment of irregular existing masonry buildings?
No full textThe nonlinear static procedure (NSP) is commonly adopted by practitioners for the seismic assessment of unreinforced masonry (URM) buildings, although a systematic validation of the procedure when applied to this type of buildings still lacks in the literature. The aim of this paper is to contribute to the validation and the improvement of the NSP when used for the seismic assessment of irregular URM buildings. The effectiveness of the NSP is tested on numerical models representative of URM buildings that present both in plan and in elevation irregularities. The concept of irregularity is also extended to that consequent to the presence of flexible/stiff diaphragms, so frequent in existing URM buildings. To this aim a total of 13 numerical models representative of 3 and 4 stories URM buildings were developed. The results derived by the application of the NSP are compared with the nonlinear dynamic procedure, considered as the reference solution. Based on the findings of the present research, original contributions are provided to: (1) the load patterns to apply for the pushover analysis; (2) the identification of damage levels; (3) the evaluation of the target displacement and the corresponding intensity measure that causes its attainment
Seismic assessment of existing URM buildings in codes: Comparison between different linear and nonlinear static procedures
No full textNonlinear static procedures are considered, at research level, the reference method for the seismic assessment of existing masonry buildings. However, at engineering practice level, the use of linear static procedures would be desirable, due to repeatability of results. The updated version of the Italian building code was released in 2018 and the review of Eurocode 8 Part 3 is going to be concluded. The aim of the paper is to analyze the outcome from the new linear static procedures and to compare it with the new nonlinear static procedures, when applied for the seismic assessment of existing unreinforced masonry buildings. This comparison is undertaken for both the new versions of the Italian and the European codes. Modelling issues such as the explicit consideration of the role of spandrels and of the flange effect will be also discussed
Displacement-Based Simplified Seismic Loss Assessment of Masonry Buildings
No full textIn the framework of the evaluation of the consequences of an earthquake, the paper provides a procedure for the economic loss assessment in unreinforced masonry (URM) buildings, proposing an analytical approach based on a cost function directly dependent on the damage level associated to different structural elements and identified by specific engineering demand parameters. The procedure follows a component-based approach, to be implemented within modern probabilistic seismic risk analyses, and it includes both the in-plane and out-of-plane damage modes that can be activated in a URM structure. It is applied to a three-storey building, examined varying some configurations of structural details, aimed to simulate two different in-plane collapse mechanisms (with damage concentrated mostly on piers or also in spandrels), or to allow, in one case, also the activation of local out-of-plane mechanisms
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