Seismic risk assessment of residential buildings by the Heuristic vulnerability model: influence of fragility curve models and inventory scale

Typological-observational methods still constitute one of the most commonly applied tools for evaluation of the seismic risk and vulnerability of the existing building stock. Their efficiency is mainly related to the effectiveness of the procedure for deriving fragility curves, and the reliability and completeness of the database that describes the building stock. This paper presents a comparison between the vulnerability and damage distribution assessment provided by fragility curves used in the Macroseismic and Heuristic methods, and a comparison of exposure evaluation methodologies according to two different approaches, namely a compartment- and a building-scale survey. An application to the case study of the residential building stock in the historic center of Alcamo, a town of 45,000 inhabitants in Western Sicily (Italy), shows the major reduction in fragility provided by recalibration of the masonry buildings’ ductility values that characterize the Heuristic method. Moreover, the efficiency of the compartment scale survey approach, based on the CARTIS typological-structural characterization method of ordinary buildings in urban areas, is underlined

Experimental investigation on the effectiveness of basalt-fibre strengthening systems for confining masonry elements

L\u2019impiego di materiali compositi per il rinforzo di colonne in muratura \ue8 diventato una pratica ampiamente diffusa nel corso degli ultimi decenni. Questa tecnica, che consiste generalmente nell\u2019applicazione di materiali polimerici fibrorinforzati (Fibre Reinforced Polymer-FRP), ha mostrato buone potenzialit\ue0, essendo in grado di garantire notevoli incrementi di resistenza e duttilit\ue0 dell\u2019elemento rinforzato, grazie ad un\u2019azione di confinamento passivo. Tuttavia, l\u2019impiego di compositi a matrice polimerica presenta alcuni limiti legati soprattutto alle prestazioni delle resine epossidiche, che a causa della loro natura sintetica danno luogo a problemi di compatibilit\ue0 con il supporto murario. Per questo motivo, recenti lavori di ricerca hanno avuto l\u2019obiettivo di sviluppare dei materiali di rinforzo non affetti dai problemi connessi all\u2019adozione delle resine epossidiche, portando allo sviluppo dei compositi FRCM (Fibre Reinforced Cementitious Matrix), in cui la matrice polimerica viene sostituita da una matrice di natura inorganica, come una malta cementizia. Inoltre, la crescente domanda di nuovi materiali prodotti con un dispendio minimo di energia in grado di garantire adeguati livelli di sostenibilit\ue0, senza per\uf2 rinunciare a buone prestazioni meccaniche, ha posto l\u2019attenzione sui materiali compositi facenti uso di fibre di basalto per il rinforzo di strutture in muratura. L\u2019obiettivo della presente tesi \ue8 quello di valutare l\u2019efficacia, in termini incrementi di resistenza e duttilit\ue0, dell\u2019azione di confinamento fornita da avvolgimenti in FRP o FRCM con fibre di basalto, quando questi sono applicati per il rinforzo di elementi in muratura. Lo studio viene condotto prevalentemente da un punto di vista sperimentale, attraverso la progettazione e realizzazione di una campagna di prove di compressione su cilindri in muratura di mattoni fasciati con FRP o FRCM. Preliminarmente si presentano i dettagli ed i risultati di un\u2019ampia fase di caratterizzazione dei materiali, finalizzata ad indagare le propriet\ue0 meccaniche della malta e dei mattoni che costituiscono la muratura, a caratterizzare la malta impiegata nel rinforzo FRCM e a definire il comportamento in trazione della fibra di basalto impiegata nei sistemi di rinforzo studiati. In una fase successiva si analizza il comportamento meccanico del rinforzo in FRCM attraverso prove di trazione su strisce di composito, discutendo i risultati in termini di curve tensione-deformazione ed analizzando l\u2019evoluzione del quadro fessurativo e le modalit\ue0 di rottura. Viene quindi studiato sperimentalmente il comportamento in compressione dei cilindri in muratura confinati con FRP o FRCM, mostrando l\u2019influenza delle principali variabili coinvolte nel problema, come il numero di giunti verticali di malta nella muratura o la percentuale di tessuto presente nel composito. I risultati ottenuti in termini di incrementi di resistenza a compressione e deformazione ultima permettono di formulare alcune considerazioni sull\u2019efficacia dei sistemi di rinforzo studiati. Tutte le prove condotte sono supportate dalla tecnica della Digital Image Correlation (DIC), che viene impiegata come sistema di misura, integrato talvolta a dispositivi tradizionali, in grado di fornire informazioni sui campi di spostamento e sulla formazione e propagazione delle fessure durante le prove condotte. Infine, sono proposte alcune formulazioni analitiche per la previsione del comportamento in compressione dei cilindri in muratura rinforzarti con FRP o FRCM. Le espressioni adottate si basano su alcune proposte esistenti in letteratura e vengono confrontate con i risultati sperimentali ottenuti, al fine di trarre alcune conclusioni sulla loro applicabilit\ue0 nelle pratiche applicazioni.The use of composite materials for the confinement of masonry columns having weak mechanical characteristics has become a widespread practice during the last decades. This technique, usually realized through the application of Fibre Reinforced Polymer (FRP) externally bonded jackets, has shown good capabilities, being able to significantly improve the load carrying capacity and the ductility of masonry members, thanks to a passive confinement action. However, FRP composites, when applied on masonry substrates, have shown some shortcomings due to the organic nature of the matrix. For this reason, during the last years growing attention has been paid to Fibre Reinforced Cementitious Matrix (FRCM) composites, in which the polymeric matrix is replaced by an inorganic matrix. Moreover, due to the increasing demand for new materials produced with low energy consumption that offer sustainability and good mechanical properties, composites reinforced with basalt fibres have lately attracted interest as material for strengthening masonry structures. The target of the present thesis is the evaluation of the effectiveness, in terms of strength and deformation capacity, of the confinement action provided by both basalt FRP and FRCM jackets, when the latter are applied on masonry members. In this framework, a detailed experimental investigation is performed by testing FRP and FRCM-confined clay brick masonry cylinders in compression. A preliminary investigation is carried out on the mechanical properties of constituent materials of masonry, namely bricks and mortar. Moreover, the strengthening systems are deeply analyzed through tests on the mortar matrix of the FRCM and an extensive study on the tensile behaviour of the basalt textile grid used as reinforcement. The mechanical behaviour of the FRCM composite is characterized under tension and the results are discussed in terms of stress-strain curves, evolution of cracks and failure modes. Then, the cylinders reinforced with FRP/FRCM jackets are subjected to uniaxial compressive loads, showing the influence of the key parameters involved in the problem, such as the number of vertical mortar joints in the masonry and the number of wrapping layers. The results in terms of compressive strength increases and corresponding strains allow drawing some conclusions on the effectiveness of the investigated strengthening systems. The whole experimental study is carried out employing the Digital Image Correlation (DIC), which is the only monitoring system in some cases and serves as support to traditional systems in other tests, giving information about the displacement fields and the development of cracks during the performed tests. Finally, analytical formulations useful for the prediction of the compressive behaviour of FRP/FRCM-confined masonry are proposed and compared to the experimental results, allowing some conclusions to be drawn on their reliability for practical design/verification purposes

Performance Assessment of Basalt FRCM for the Confinement of Clay Brick Masonry Cylinders

Fibre Reinforced Cementitious Matrix (FRCM) composites have been proved to be a suitable strengthening material for masonry structures in the last years. Moreover, basalt fibres are increasingly used as reinforcement of composites as a more sustainable alternative to glass fibres. The goal of this work is to investigate the effectiveness of basalt FRCM to confine masonry circular columns. A total of eighteen clay brick masonry cylinders were tested in compression. The specimens were cored from two different masonry assemblies and wrapped with one or two layers of BFRCM composite. The stress-strain curves and the gains of strength and strain capacity of confined cylinders compared to the control specimens are reported together with a description of the failure modes

Hall Anomaly and Vortex-Lattice Melting in Superconducting Single Crystal YBa2Cu3O7-d

Sub-nanovolt resolution longitudinal and Hall voltages are measured in an ultra pure YBa2Cu3O7-d single crystal. The Hall anomaly and the first-order vortex-lattice melting transition are observed simultaneously. Changes in the dynamic behavior of the vortex solid and liquid are correlated with features of the Hall conductivity sxy. With the magnetic field oriented at an angle from the twin-boundaries, the Hall conductivity sharply decreases toward large negative values at the vortex-lattice melting transition.Comment: 6 pages, 2 figures included, Postscript, to appear in Phys. Rev. Let

Extreme events driven glassy behaviour in granular media

Motivated by recent experiments on the approach to jamming of a weakly forced granular medium using an immersed torsion oscillator [Nature 413 (2001) 407], we propose a simple model which relates the microscopic dynamics to macroscopic rearrangements and accounts for the following experimental facts: (1) the control parameter is the spatial amplitude of the perturbation and not its reduced peak acceleration; (2) a Vogel-Fulcher-Tammann-like form for the relaxation time. The model draws a parallel between macroscopic rearrangements in the system and extreme events whose probability of occurrence (and thus the typical relaxation time) is estimated using extreme-value statistics. The range of validity of this description in terms of the control parameter is discussed as well as the existence of other regimes.Comment: 7 pages, to appear in Europhys. Let

Correlations between eigenvalues of large random matrices with independent entries

We derive the connected correlation functions for eigenvalues of large Hermitian random matrices with independently distributed elements using both a diagrammatic and a renormalization group (RG) inspired approach. With the diagrammatic method we obtain a general form for the one, two and three-point connected Green function for this class of ensembles when matrix elements are identically distributed, and then discuss the derivation of higher order functions by the same approach. Using the RG approach we re-derive the one and two-point Green functions and show they are unchanged by choosing certain ensembles with non-identically distributed elements. Throughout, we compare the Green functions we obtain to those from the class of ensembles with unitary invariant distributions and discuss universality in both ensemble classes.Comment: 23 pages, RevTex, hard figures available from [email protected]

Renormalizing Rectangles and Other Topics in Random Matrix Theory

We consider random Hermitian matrices made of complex or real $M\times N$ rectangular blocks, where the blocks are drawn from various ensembles. These matrices have $N$ pairs of opposite real nonvanishing eigenvalues, as well as $M-N$ zero eigenvalues (for $M>N$.) These zero eigenvalues are ``kinematical" in the sense that they are independent of randomness. We study the eigenvalue distribution of these matrices to leading order in the large $N,M$ limit, in which the ``rectangularity" $r={M\over N}$ is held fixed. We apply a variety of methods in our study. We study Gaussian ensembles by a simple diagrammatic method, by the Dyson gas approach, and by a generalization of the Kazakov method. These methods make use of the invariance of such ensembles under the action of symmetry groups. The more complicated Wigner ensemble, which does not enjoy such symmetry properties, is studied by large $N$ renormalization techniques. In addition to the kinematical $\delta$-function spike in the eigenvalue density which corresponds to zero eigenvalues, we find for both types of ensembles that if $|r-1|$ is held fixed as $N\rightarrow\infty$, the $N$ non-zero eigenvalues give rise to two separated lobes that are located symmetrically with respect to the origin. This separation arises because the non-zero eigenvalues are repelled macroscopically from the origin. Finally, we study the oscillatory behavior of the eigenvalue distribution near the endpoints of the lobes, a behavior governed by Airy functions. As $r\rightarrow 1$ the lobes come closer, and the Airy oscillatory behavior near the endpoints that are close to zero breaks down. We interpret this breakdown as a signal that $r\rightarrow 1$ drives a cross over to the oscillation governed by Bessel functions near the origin for matrices made of square blocks.Comment: LateX, 34 pages, 3 ps figure

Influence of wall-to-floor connections and pounding on pre- and post-diction simulations of a masonry building aggregate tested on a shaking table

This paper presents numerical simulations within the frame of the project SERA-AIMS (Seismic Testing of Adjacent Interacting Masonry Structures). The study includes blind pre-diction and post-diction stages. The former was developed before performing the shaking table tests at the laboratory facilities of LNEC (Lisbon), while the latter was carried out once the test results were known. For both, three-dimensional finite element models were prepared following a macro-modelling approach. The structure consisted of a half-scaled masonry aggregate composed by two units with different floor levels. Material properties used for the pre-diction model were based on preliminary tests previously provided to the participants. The masonry constitutive model used for the pre-diction study reproduced classical stress-strain envelope, whereas a more refined model was adopted for the post-diction. After eigenvalue analysis, incremental nonlinear time history analysis was performed under a unique sequence based on the given load protocol to account for damage accumulation. In the post-diction, the numerical model was calibrated on the data recorded during the shaking table tests and nonlinear dynamic analysis repeated under the recorded accelerogram sequence. The interaction between the two units was simulated through interface elements. Moreover, the timber floors were accounted following different strategies: not modelling or considering nonlinear wall-to-floor connections. Advantages and disadvantages are then analysed, comparing the pre-diction and post-diction results with the experimental data. Numerical results differ from the experimental outcomes regarding displacements and interface pounding, although a clear improvement is visible in the post-diction model

Simulation of blind pre-diction and post-diction shaking table tests on a masonry building aggregate using a continuum modelling approach

Masonry buildings of historical centres are usually organized within aggregates, whose structural performance against seismic actions is challenging to predict and constitutes still an open issue. The SERA-AIMS (Seismic Testing of Adjacent Interacting Masonry Structures) project was developed to provide additional experimental data by testing a half-scale, two-unit stone masonry aggregate subjected to two horizontal components of dynamic excitation. In this context, this paper investigates the reliability of the modelling approach and the assumptions adopted to generate a three-dimensional continuum finite element model. The work involves two stages, namely a blind pre-diction and a post-diction phase, and proposes a series of simulation analyses including a strategy to shorten the actual records and save computation costs. The study was performed to investigate the extent of uncertainty in modelling for such masonry aggregates in relation to the experimental outcomes. Pre-diction results were proven to be not accurate in terms of predicted displacements and damage patterns. The upgrades introduced for the post-diction analyses, including the calibration of the elastic modulus and the introduction of a non-linear interface between the two units, allowed to improve the outcomes, with reasonable results in terms of predicted base shear force, displacements along Y-direction and damage pattern for the non-linear stage. The overall approach showed to be appropriate for the structural analysis of existing masonry aggregates, but the accurate modelling of this type of structure remains challenging due to the high level of uncertainties