The Ph.D. dissertation presents totally four non-destructive experimental procedures for the axial load evaluations in prismatic pre-stressed beams, regular space frames and generic space structures composed of slender beam-columns. The comparison between the design inner force and the experimental estimate can be used to obtain the structural safety assessment of the entire space frame system. Conversely, with regards to the pre-stress beams, the comparison between the design inner pre-stress force and the experimental estimate can be utilized to determine the pre-stress losses as, for example, in concrete bridge beams. The method proposed by Tullini (2013) and the simplified formula of the second-order displacements of Timoshenko and Gere (1961) and Bazant and Cedolin (1991) are able to estimate the axial forces, cited therein, making use of a set of displacements measured along the element spans and after applying a lateral force. A new static method was also developed to identify the compression axial forces of slender beams with known boundary conditions. In this case, one flexural displacement measured along the span subjected to a lateral force in enough. The phases of the three static tests do not involve the instrumentation of the beam-columns during the construction process, since the measurement devices must to be placed externally and at given cross sections of the element spans respectively. Additionally, the procedures make use of static parameters only and do not require any selection of the experimental data to be used in the identification algorithms. In fact, dynamic methods present in literature are particularly sensitive to experimental and model errors in which it is also difficult to select a-priori the best frequency that will estimate the axial loads. Different natural frequency values lead different accuracies in the axial load estimations. The extension of the simplified formula of the first natural frequency of Galef (1968), considered as non-destructive dynamic method, do not require any selection of the mode shape. Moreover, Southwell’s method is proposed as non-destructive technique for the experimental global buckling load evaluations of space frame systems. Experiments on some small-scale prototypes and on two post-tensioned beam specimens were developed to validate the procedures, that gave identification errors less than 10%. Finally, the displacements recorded by the innovative devices of “Fiber-Bragg-grating differential settlement measurement sensors” (FBG-DSM) have furnished very accurate measurements

La dissertazione di dottorato propone in totale quattro procedure sperimentali non distruttive per la stima dei carichi assiali in travi prismatiche precompresse, telai spaziali regolari e strutture spaziali generiche composte da elementi trave snelli. La comparazione tra la forza assiale considerata nel progetto e quella stimata sperimentalmente può essere utilizzata per verificare le condizioni di sicurezza strutturali dell’intero sistema strutturale spaziale. Diversamente, con riferimento alle travi precompresse, la comparazione tra la forza applicata in fase progettuale e quella stimata sperimentalmente può essere utilizzata per determinare le perdite di precompressione, come per esempio nelle travi in c.a.p. da ponte. Il metodo proposto da Tullini (2013) e la formula semplificata degli spostamenti del secondo ordine di Timoshenko e Gere (1961) e Bazant e Cedolin (1991) sono capaci di stimare le forze assiali, sopra citate, facendo uso di una serie di spostamenti misurati lungo le campate degli elementi dopo l’applicazione di un carico laterale. Un nuovo metodo statico è stato inoltre sviluppato per identificare le forze di compressione presenti in travi snelle con condizioni di vincolo note. In questo caso, uno spostamento flessionale misurato lungo la trave soggetta ad un carico laterale è sufficiente. Le fasi delle tre procedure statiche non prevedono la strumentazione dell’elemento trave durante il processo di costruzione, dato che i sistemi di misurazione devono essere posizionati esternamente ed in determinati punti delle campate. Differenti frequenze naturali forniscono diverse precisioni nelle stime dei carichi assiali. L’estensione della formula semplificata della prima frequenza naturale di Galef (1968), considerata come metodo dinamico non distruttivo, non richiede alcuna selezione della forma modale. Inoltre, il metodo di Southwell è stato proposto come metodo diagnostico per la determinazione sperimentale dei carichi critici globali di sistemi spaziali. Prove sperimentali su alcuni prototipi in piccola scala e su due travi (provini) in precompresso sono state sviluppate per la validazione delle procedure le quali, a loro volta, hanno fornito errori di identificazione minori del 10%. Infine, gli spostamenti misurati tramite i sensori innovativi denominati “Fiber-Bragg-grating differential settlement measurement sensors” (FBGDSM) hanno fornito misurazioni sperimentali molto precise.

Axial load identifications in space frame systems

BONOPERA, Marco
2016

Abstract

The Ph.D. dissertation presents totally four non-destructive experimental procedures for the axial load evaluations in prismatic pre-stressed beams, regular space frames and generic space structures composed of slender beam-columns. The comparison between the design inner force and the experimental estimate can be used to obtain the structural safety assessment of the entire space frame system. Conversely, with regards to the pre-stress beams, the comparison between the design inner pre-stress force and the experimental estimate can be utilized to determine the pre-stress losses as, for example, in concrete bridge beams. The method proposed by Tullini (2013) and the simplified formula of the second-order displacements of Timoshenko and Gere (1961) and Bazant and Cedolin (1991) are able to estimate the axial forces, cited therein, making use of a set of displacements measured along the element spans and after applying a lateral force. A new static method was also developed to identify the compression axial forces of slender beams with known boundary conditions. In this case, one flexural displacement measured along the span subjected to a lateral force in enough. The phases of the three static tests do not involve the instrumentation of the beam-columns during the construction process, since the measurement devices must to be placed externally and at given cross sections of the element spans respectively. Additionally, the procedures make use of static parameters only and do not require any selection of the experimental data to be used in the identification algorithms. In fact, dynamic methods present in literature are particularly sensitive to experimental and model errors in which it is also difficult to select a-priori the best frequency that will estimate the axial loads. Different natural frequency values lead different accuracies in the axial load estimations. The extension of the simplified formula of the first natural frequency of Galef (1968), considered as non-destructive dynamic method, do not require any selection of the mode shape. Moreover, Southwell’s method is proposed as non-destructive technique for the experimental global buckling load evaluations of space frame systems. Experiments on some small-scale prototypes and on two post-tensioned beam specimens were developed to validate the procedures, that gave identification errors less than 10%. Finally, the displacements recorded by the innovative devices of “Fiber-Bragg-grating differential settlement measurement sensors” (FBG-DSM) have furnished very accurate measurements
TULLINI, Nerio
TRILLO, Stefano
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/2403490
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