1,721,062 research outputs found
Seismic vulnerability assessment of masonry towers: advanced non linear dynamic modelling
No full textThe research work concerns the seismic vulnerability assessment of masonry bell towers in Italy, which is performed by comparing full non-linear dynamic analysis and non-linear static analysis. The seismic response of these structures involves a coupling between flexural and axial vibration modes, the presence of shear damage patterns, and high vibration modes causing the belfry collapse. The problem is simplified by using a plane 2D scheme. A specific Rigid Body and Spring Model is adopted to describe the in-plane dynamics including the main meso???scale damage mechanisms, by means of proper constitutive laws
Risposta sismica fuori del piano di facciate in muratura: confronto tra analisi dinamiche non-lineari e analisi pushover
No full textNell’ambito del tema della valutazione del rischio sismico degli edifici monumentali in muratura, si presenta una ricerca incentrata sull’analisi dei meccanismi di collasso fuori-piano. Due differenti metodologie di analisi sono applicate e confrontate. Da un lato si effettua un’analisi dinamica non-lineare completa (NLD) adottando un modello specifico a elementi rigidi e molle (RBSM – Rigid Body and Spring Model) in cui la progressione del danneggiamento è determinata dal meccanismo flessionale fuori-piano ed il comportamento costitutivo ciclico del materiale è definito attraverso una descrizione fenomenologica che include la dissipazione plastica e il degrado dei parametri meccanici. Dall’altro, con lo stesso modello RSBM, si effettua un’analisi statica non-lineare pushover (NSP) valutando la curva forza generalizzata-spostamento e lo spostamento limite ultimo, poi comparati con la domanda sismica espressa in termini di coordinate spettrali. Come caso di studio viene considerata la chiesa del Rosario a Guastalla, danneggiata dal terremoto dell’Emilia Romagna nel 1987, adottando accelerogrammi di diverso potenziale distruttivo e valutando la loro correlazione con i parametri rappresentativi del danno. Le due metodologie messe a confronto hanno mostrato una buona corrispondenza per quanto riguarda la valutazione della risposta nelle zone a bassa e media sismicità, con una tendenza delle NSP a sovrastimare il danno, specialmente per i livelli maggiori di azione sismica
Full dynamic and pushover analyses of out-of-plane masonry facades: application and comparisons by RBSM
No full textThe paper is focused on the analysis of out–of–plane mechanisms which actually represent the most recurrent collapse mode for the façade of buildings such as churches or basilicas. A full Nonlinear Dynamic (ND) modelling of the seismic response is performed by adopting a specific rigid body and spring model (RBSM), where damage is ascribed to the out-of-plane flexural behaviour. A phenomenological description of the cyclic response of the masonry material is provided in the definition of the constitutive prescriptions, including hysteretic and degrading material behaviour. Then, a comparison is made with a non linear static pushover (NSP) analysis, which is performed by means of the same specific RBSM under quasi-static loading, incrementally applied. The seismic response in terms of generalized force–displacement curve and the ultimate limit displacement capacity are evaluated, comparing them with the seismic displacement demand, expressed in terms of spectral coordinates. The two different approaches are compared by considering as a case study the church of Rosario, in Guastalla, which was damaged by Emilia Romagna Earthquake (1987). A number of analyses have been performed, investigating a variety of different aspects concerning the accelerogram records and their correlation with the damage indicators of the non-linear models
Out-of-plane seismic response of masonry façades: a comparison among full dynamic and pushover analyses
No full textThe paper is focused on the seismic risk assessment of monumental masonry buildings, and more specifically on the analysis of out–of–plane mechanisms which actually represent the most recurrent collapse mode for the fac ̧ade of buildings such as churches or basilicas. The full Nonlinear Dynamic (ND) modelling of the seismic response is performed by adopting a specific rigid body and spring model, RBSM, where damage is ascribed to the out-of-plane flexural behaviour. A phenomenological description of the cyclic response of the masonry material is provided in the definition of the constitutive prescriptions, including hysteretic and degrading material behaviour. Then, a comparison is made with a non linear static pushover (NSP) analysis , which is performed by means of the same specific RBSM under quasi-static loading, incrementally applied. The seismic response in terms of generalized force–displacement curve and the ultimate limit displacement capacity are evaluated, comparing them with the seismic displacement demand, expressed in terms of spectral coordinates. The two different approaches are compared by considering as a case study the church of Rosario, in Guastalla, which was damaged by Emilia Romagna Earthquake (1987). A number of analyses have been performed, investigating a variety of different aspects concerning the accelerogram records and their correlation with the damage indicators of the non-linear models
Non-linear dynamic analysis of masonry towers under natural accelerograms accounting for soil-structure interaction
No full textThe object of the paper is the influence of the soil-structure interaction on the dynamic response of masonry towers, for which a high level of stress is involved already in the static field. The relevant deformations and displacements at the base of the tower suggest that a significant volume of ground is engaged into the overall dynamic response, both as a participating mass and as a potential carrier of energy dissipation. In order to investigate this aspect and assess the sensitivity of the dynamic response of the soil-structure system to different soil characteristics, the non linear dynamic response of a case study is analysed, by including in
the model a significant volume of foundation soil and considering two different ground types. The numerical model is based on a specific Rigid Body and Springs approach, in which the structure is idealized as a mechanism made of rigid elements connected each to the other by axial and shear springs. The nonlinear behaviour is lumped into the springs assigning proper constitutive laws able to model the significant inelastic aspects of the constitutive behaviour and the meso-scale damage mechanisms with a moderate computational effort. Two types of foundation soil have been considered in order to perform the dynamical analysis accounting for
the soil-structure interaction: rock and deposits of compact gravel. For both models, non-linear dynamic analyses have been performed adopting natural records having different characteristics (with regard to the frequency content; distance from the epicentre and type of soil). Some interesting considerations are derived from this comparative study about a problem that is very actual for those who deal with non linear dynamics of structures, but yet is not much explored
SEISMIC VULNERABILITY ASSESSMENT OF MASONRY TOWERS: FULL NON-LINEAR DYNAMICS VS PUSHOVER ANALYSES
No full textThe paper concerns the seismic vulnerability assessment of masonry bell towers in Italy, which is performed by comparing full non-linear dynamic analysis and non-linear static analysis. An idealized case study is considered, in order to assess some basic and common
features of the seismic structural response and to appraise the performance of the proposed approach. The reference model is supposed to be structurally independent, i.e. with no adjacent interacting construction. The geometrical dimensions are chosen in order to represent an average north-Italian masonry bell tower, without the intent to cover all the possible situations. The seismic response of these structures involves a coupling between flexural and axial vibration modes, the presence of shear damage patterns, and high vibration modes causing the belfry collapse. The problem is simplified by using a plane 2D scheme. A specific Rigid Body and Spring Model is adopted to describe the in-plane dynamics. Constitutive laws were assigned following a simplified heuristic approach including the main meso–scale damage mechanisms: i) very low tensile strength; ii) significant post-elastic orthotropy plus texture effects; iii) different rules for post-elastic axial and shear damage; iv) different dependence of the shear strength on the vertical and horizontal axial stress component; v) hysteretic energy dissipation due to cyclic loading. Even using a quite coarse mesh, the model is capable to describe the higher vibration modes with a reasonable computational effort and using realistic accelerograms. Non linear static analysis was performed, by using the RBSM model, obtaining the capacity curve and assessing the seismic demand. A comparison between the two approaches is proposed, in order to appraise the difference in the results and to evaluate quality and significance of results in terms of operational drawbacks and reduction of computational times. Particular attention
is devoted to the fact that static non-linear analyses tends to neglect the damage effects induced by higher vibration modes, as well as the influence of the shear response on the global damage
Analisi sismica non lineare statica e dinamica di torri campanarie: applicazioni e confronti
No full textLa memoria riguarda la valutazione della vulnerabilità sismica dei campanili in muratura in Italia, che viene eseguita confrontando due metodi non lineari di analisi: analisi dinamica al passo e analisi pushover. Viene considerato un caso di studio ideale, al fine di confrontare la risposta strutturale prevista dai due metodi e valutarne le prestazioni. Il problema è semplificato, usando uno schema 2D piano, ed un modello specifico a masse rigide e molle per descrivere la dinamica nel piano. Le leggi costitutive sono state assegnate seguendo un approccio euristico semplificato, in cui sono contemplati i più significativi meccanismi di danno presenti alla meso-scala: i) resistenza a trazione molto bassa; ii) rilevante ortotropia ed effetti di tessitura in fase post-elastica; iii) diverse regole di danneggiamento assiale e a taglio; iv ) diversa resistenza a taglio a seconda della giacitura considerata (verticale o orizzontale); v) dissipazione isteretica dell’energia indotta dai carichi ciclici. Pur utilizzando una mesh abbastanza rada, il modello risulta
abbastanza ed efficiente, ed è in grado di cogliere anche gli effetti dei modi di vibrare superiori con un ragionevole sforzo computazionale. Analisi statiche non lineari sono state eseguite utilizzando il modello RBSM, ottenendo la curva di capacità e la valutazione della domanda sismica. Un confronto tra i due approcci, si propone, al fine di valutare la differenza di risultati (con particolare attenzione agli effetti danno indotto da modi di vibrazione più elevata) e di valutare la qualità e significatività dei risultati in termini di inconvenienti operativi e riduzione dei tempi di calcolo
Rischio sismico e strategie di mitigazione nei centri storici. Il caso di Laino Castello
No full text
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
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