1,720,984 research outputs found
A novel approach to improve accuracy in seismic fragility analysis: The modified intensity measure method
No full textSeismic fragilities, i.e., probabilities that structural systems exceed specified limit states, are used in Performance-Based Earthquake Engineering to characterize structural behavior during seismic events. Generally, seismic fragilities are constructed from structural responses to scaled accelerograms described by single/multiple ordinates of the pseudo-acceleration response spectrum, peak ground acceleration or other intensity measures. Recently, it was shown that the resulting fragilities provide limited if any information on the structural seismic performance if the dependence between intensity measures and demand parameters is weak. Yet, the method is used in Performance-Based Earthquake Engineering since the statistical uncertainty caused by the limited numbers of recorded ground accelerations is overcome by scaling these records. This study develops a method for estimating the fragility of linear systems for cases in which intensity measures and demand parameters are weakly correlated, i.e., situations in which the current methodology is inaccurate. The method is based on a linear transformation of samples of a given intensity measure which is designed to improve the correlation between demand and intensity parameters. The effectiveness of the proposed method for linear system is demonstrated by an elementary oscillator, a multi-degree of freedom system and a real complex multi-degree of freedom structural system
Experimental characterization of natural fibre–soil interaction: lessons for earthen construction
No full textEarthen construction materials are the subject of renewed interest due to the rising alarm about environmental pollution from the construction industry. Current research efforts are focused on improving the mechanical properties of earthen materials to make them modern and competitive. To increase strength and improve ductility fibres can be added to the soil mixture and if natural fibres are used one achieves stabilisation in an environmentally friendly way. Several previous studies have dealt with the behaviour of this composite material at a macroscopic level and on the general interaction between fibres and soil, but there is little published research on the interfacial mechanical interaction between natural fibre reinforcement and a soil matrix which is key to the former. This paper attempts to fill this gap by presenting and discussing laboratory results from a large campaign of pull-out tests conducted on composite earthen samples. The variables investigated here are the nature of the fibres (i.e. single or collections twisted together) and the use of fibre treatments such as PVA glue and baking soda. In the study both fibre–soil failure and soil-soil failure are investigated and the results lead to conclusions as to appropriate use of fibres to reinforce earthen construction materials
A novel hemp-fiber bio-composite material for strengthening of arched structures: Experimental investigation
No full textFiber reinforced composites represent an alternative to traditional techniques for strengthening and retrofitting masonry structures. Within the growing environmental awareness, the development of composite materials to replace conventional synthetic fibers and polymeric matrices has become a crucial issue. In this paper, a novel sustainable composite material consisting in hemp fibers and a natural matrix made of a mix of ground clay bricks and organic binder is proposed. Experimental tests are carried out in order to estimate the mechanical characteristics of the single composite components. The structural performance of polycentric masonry arches strengthened at the extrados first with only natural matrix and then with the bio-composite material (i.e. hemp fibers and biodegradable matrix) is investigated. Single point vertical load tests and tilt tests are carried out in order to assess the effectiveness of the strengthening by comparing the results with those obtained with unstrengthened masonry arches
Confined vs. unreinforced masonry: Construction and shaking table tests of two-storey buildings
No full textConfined masonry (CM) is a simple, convenient and effective building construction technology in seismic areas. Although a large background of experimental testing aimed to study the behavior of CM walls to vertical and in-plane lateral loads is available in literature, only a few experimental studies about the CM buildings behavior to seismic loads have been carried out. In this work, the results of a series of shaking-table tests carried out on two-storey unreinforced (URM) and confined masonry (CM) buildings are presented. Two structural systems with the same geometry were built and tested on a shaking table, in order to compare the dynamic response of the two different construction systems. The structures were subjected to seismic accelerations of increasing intensity yielding performance states ranging from minor damage to near collapse. The paper describes both the dynamic response using intensity measures, drift and acceleration profiles, and the observed damage evolution. The obtained results highlight the better performance of CM vs URM to withstand dynamic loads and provide crucial information to be used for numerical models calibration and response estimation
An integrated approach for the numerical modeling of severely damaged historic structures: Application to a masonry bridge
No full textThis paper presents an integrated approach that combines advanced survey procedures, such as close range photogrammetry based on high resolution images provided by Unmanned Aerial Vehicles, and Ambient Vibration Tests to develop accurate Finite Element models of severely damaged historic masonry structures. The proposed methodology is applied to a masonry arch bridge located in Todi, Central Italy, characterized by severe damage conditions involving diffuse material degradation and structural damages. Two numerical models are developed starting from the digital geometric survey: the first accurately describes the irregular actual geometry due to damage; the second regularizes the boundary surfaces as standard procedure in common practice when detailed survey is not available. The crucial role of the geometric irregularities given by the severe damage state on the dynamic properties of the masonry bridge is demonstrated by comparing the modal parameters of the two models. Furthermore, sensitivity analysis is carried out in order to assess the combined effect of different mechanical characteristics and geometric configurations on the modal properties and to select suitable updating parameters. The overall methodology is completed by a final model updating procedure targeting the experimental modal parameters estimated from Ambient Vibration Tests
Approximate Bayesian Computation for structural identification of ancient tie-rods using noisy modal data
No full textMasonry arches and vaults are common historic structural elements that frequently experience asymmetric loading due to seismic action or abutment settlements. Over the past few decades, numerous studies have sought to enhance our understanding of the structural behavior of these elements for the purpose of preventive conservation. The assessment of the structural performance of existing constructions typically relies on effective numerical models guided by a set of unknown input parameters, including geometry, mechanical characteristics, physical properties, and boundary conditions. These parameters can be estimated through deterministic optimization functions aimed at minimizing the discrepancy between the output of a numerical model and the measured dynamic and/or static structural response. However, deterministic approaches overlook uncertainties associated with both input parameters and measurements. In this context, the Bayesian approach proves valuable for estimating unknown numerical model parameters and their associated uncertainties (posterior distributions). This involves updating prior knowledge of model parameters (prior distributions) based on current measurements and explicitly considering all sources of uncertainties affecting observed quantities through likelihood functions. However, two significant challenges arise: the likelihood function may be unknown or too complex to evaluate, and the computational costs for approximating the posterior distribution can be prohibitive. This study addresses these challenges by employing Approximate Bayesian Computation (ABC) to handle the intractable likelihood function. Additionally, the computational burden is mitigated through the use of accurate surrogate models such as Polynomial Chaos Expansions (PCE) and Artificial Neural Networks (ANN). The research focuses on setting up numerical models for simple structural systems (tie-rods) and inferring unknown input parameters, such as mechanical properties and boundary conditions, through Bayesian updating based on observed structural responses (modal data, strains, displacements). The main novelties of this research regard, on the one hand, the proposal of a methodology for obtaining a reliable estimate of the axial force in ancient tie-rods accounting for different sources of uncertainty and, on the other hand, the application of ABC to obtain the structural identification inverse problem solution
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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