Ductility has become a fundamental characteristic in structural design/analysis, a healthy and in some case necessary property, so much that also in actual Normative ductile requirements/recommendations are given. However, its definition is often not clear and sometimes controversial, as much at conceptual/qualitative level that at numerical/quantitative one. Firstly a bibliographic research is needed, differentiating among the different existing levels: material, sections and members of structures (the ones related to the interfaces and to the elements have been not deepened in this study); for each one firstly the characteristic diagram are identified. Then the experimental results, the theoretical proposal and the Normative indications are reported; finally, a collection of the most important variables influencing in ductility estimation is given. Then, as proposal for the actual Normative, a quantitative estimation of ductility parameter is done: the definition sought must be useful in the practice, coherent with the convention adopted and valid for every level; its meaning is explained through examples at each one of the three levels considered. Moreover, for each one of the levels analysed, an in-depth analysis is performed on some of the key points arisen from the previous study. At material level, steel ultimate strains have been investigated, since there is a lack of clearness on the topic, reflected also in the Normative. For the sections, the study of the moment – curvature diagram is deepened: three different approaches are illustrated (simplified, discrete and continuous), underlining their key points, for the case of constant applied axial load. The case of constant imposed eccentricity is shown, explaining its interest/utility and the difference with the previous case; then, the moment – curvature diagram corresponding to every M – N load path is introduced. At structural level, the topic of structural redistribution is analysed: firstly two basic procedures of non-linear analysis are explained, then a proposal for a simplified method of estimation is given; lastly a brief mention on the geometric criteria for reinforcement dimensioning is introduced.
La duttilità è diventata una caratteristica fondamentale nel progetto/analisi strutturale, una proprietà benefica e in alcuni casi necessaria, tanto che nella Normativa vigente vengono forniti requisiti/raccomandazioni di duttilità. Tuttavia, la sua definizione è spesso non chiara e a volte addirittura controversa, tanto a livello concettuale/ qualitativo come a livello numerico/quantitativo. Pertanto innanzitutto si rende necessaria una ricerca bibliografica, differenziando tra i diversi livelli esistenti: materiale, sezioni e membri di strutture (gli aspetti riguardanti interfaccia ed elementi strutturali non sono stati approfonditi in questo studio); per ciascuno di questi livelli vengono identificati i diagrammi caratteristici. Si riportano quindi i risultati sperimentali, le proposte teoriche e le indicazioni della Normativa; infine, viene riportato un elenco delle variabili con maggiore influenza nella stima della duttilità. In seguito, come proposta per l’attuale Normativa, viene fatta una stima quantitativa del parametro della duttilità: la definizione cercata deve essere utile nella pratica, coerente con la convenzione utilizzata e valida ad ogni livello; il suo significato viene spiegato attraverso esempi a ciascuno dei tre livelli considerati. Inoltre, per ciascun livello analizzato, viene sviluppato uno studio di approfondimento riguardo ad alcuni punti chiavi emersi nel precedente studio. A livello di materiale, si sono investigate le deformazioni ultime dell’acciaio, dal momento che c’è una mancanza di chiarezza in merito, come emerge anche nella Normativa. Per le sezioni, si approfondisce lo studio del diagramma momento – curvatura: vengono illustrati tre diversi approcci (semplificato, discreto e continuo), sottolineandone gli aspetti critici, nel caso di azione assiale applicata costante. Viene poi mostrato il caso di eccentricità imposta costante, spiegando il suo interesse/utilità e le differenze con il caso precedente; in seguito si introduce il diagramma momento – curvatura corrispondente a un percorso di carico M – N qualsiasi. A livello di struttura, viene affrontato il tema delle redistribuzioni strutturali: dapprima vengono spiegate due procedimenti basici dell’analisi non-lineare, in seguito viene riportata una proposta per un metodo semplificato per stimare tali redistribuzioni; da ultimo vengono introdotto con un breve accenno i criteri di dimensionamento geometrico per la disposizione dell’armatura.
Study on ductility of materials, sections and members of structures
DELL'ORTO, ANDREA
2013/2014
Abstract
Ductility has become a fundamental characteristic in structural design/analysis, a healthy and in some case necessary property, so much that also in actual Normative ductile requirements/recommendations are given. However, its definition is often not clear and sometimes controversial, as much at conceptual/qualitative level that at numerical/quantitative one. Firstly a bibliographic research is needed, differentiating among the different existing levels: material, sections and members of structures (the ones related to the interfaces and to the elements have been not deepened in this study); for each one firstly the characteristic diagram are identified. Then the experimental results, the theoretical proposal and the Normative indications are reported; finally, a collection of the most important variables influencing in ductility estimation is given. Then, as proposal for the actual Normative, a quantitative estimation of ductility parameter is done: the definition sought must be useful in the practice, coherent with the convention adopted and valid for every level; its meaning is explained through examples at each one of the three levels considered. Moreover, for each one of the levels analysed, an in-depth analysis is performed on some of the key points arisen from the previous study. At material level, steel ultimate strains have been investigated, since there is a lack of clearness on the topic, reflected also in the Normative. For the sections, the study of the moment – curvature diagram is deepened: three different approaches are illustrated (simplified, discrete and continuous), underlining their key points, for the case of constant applied axial load. The case of constant imposed eccentricity is shown, explaining its interest/utility and the difference with the previous case; then, the moment – curvature diagram corresponding to every M – N load path is introduced. At structural level, the topic of structural redistribution is analysed: firstly two basic procedures of non-linear analysis are explained, then a proposal for a simplified method of estimation is given; lastly a brief mention on the geometric criteria for reinforcement dimensioning is introduced.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/100321