H αύξηση των περιβαλλοντικών, αισθητικών και λειτουργικών απαιτήσεων που πρέπει να πληρούν οι σύγχρονες κατασκευές Πολιτικού Μηχανικού, σε συνδυασμό με την απαίτηση για συμπίεση του κόστους του κύκλου ζωής τους, οδηγούν στην ανάγκη για τη διερεύνηση της εφαρμογής νέων υλικών και μεθόδων που θα εφαρμοσθούν στη κατασκευή των δομικών έργων. Στην κατεύθυνση αυτή κινούνται οι μέθοδοι κατασκευής δομικών στοιχείων με τη χρήση παραμενόντων τύπων. Η παρούσα Διατριβή πραγματεύεται, τόσο σε αναλυτικό όσο και σε πειραματικό επίπεδο, το σχεδιασμό επίπεδων στοιχείων Ο/Σ που παρασκευάζονται έναντι παραμενόντων τύπων παρασκευασμένων από σύνθετα υλικά τσιμεντοειδούς μήτρας και οπλισμένων με πλέγματα μη μεταλλικών ινών (Ινοπλέγματα σε Ανόργανη Μήτρα-ΙΑΜ). Η Διατριβή αναπτύσσει την διαδικασία σχεδιασμού που προορισμός της είναι να ενσωματωθεί σε έναν αλγόριθμο βέλτιστου σχεδιασμού για την επίτευξη σχεδιαστικών λύσεων που θα αντιστοιχούν στο ελάχιστο κόστος κατασκευής για το σύμμεικτο στοιχείο. Η διαδικασία σχεδιασμού τροφοδοτείται από ένα εκτενές πρόγραμμα πειραματικών δοκιμών. / The continuously raising demands for cost effective and environmental friendly concrete structures which should fulfill also high aesthetic design criteria, lead the Engineers to explore new construction methods and materials. The application of semi-prefabrication techniques, involving the use of participating Stay-in-Place formwork elements seems to be an attractive solution. The present dissertation deals with the experimental and analytical investigation of one-way concrete slabs cast over Stay-In-Place formwork elements produced from cementitious composite materials reinforced with textile structures from non-metallic continuous fibers (Textile Reinforced Concrete). In this dissertation a design procedure for Composite Reinforced Concrete (RC)/TRC one-way slabs is developed. For the development of the design procedure the results from an extensive experimental investigation campaign were exploited. The campaign focused on the mechanical behavior of RC/TRC composite slabs under four point bending. Also tests on the formwork elements under four point bending tests were carried out. Ahead of the bending tests, uniaxial tension tests on dumbbell TRC specimens were conducted in order to characterize this composite material. Finally, the design procedure was integrated on a Genetic Algorithm in order to achieve minimum-cost design solutions.

The tradition of using naturally occurring plant fibers is still alive in Africa. In the Uíge province of northern Angola, bast fibers from Triumfetta cordifolia serve as the basis for everyday objects, such as baskets, mats, fishing nets, and traditional clothing. The fibers exhibit a Young’s modulus of 53.4 GPa and average tensile strength of 916.3 MPa, which are comparable to those of commercial kenaf fibers. These values indicate a high potential for use as a reinforcement in biocomposites. Based on this promising mechanical and physical profile of individual fibers, different biocomposites were produced with polylactide (PLA) as a matrix. The obtained composites were analyzed mechanically, physically, and visually. Unidirectionally arranged PLA/33% T. cordifolia composites with continuous fibers showed the highest Young’s modulus (10.79 GPa ± 1.52 GPa) and tensile strength (79.37 MPa ± 14.01 MPa). These composites were comparable to those of PLA/30% hemp composites (10.9 GPa and 82.9 MPa, respectively) and therefore have economic potential.

No description available.

Devido à fragilidade do concreto, o controle e combate da fissuração são de importância fundamental em estruturas de concreto armado. Uma maneira de melhorar as propriedades do concreto à tração é pelo emprego de fibras. A presente pesquisa é uma tentativa de fornecer diretrizes para o dimensionamento de estruturas de concreto armado com fibras, e armadura convencional sob condições de serviço. Apresenta-se inicialmente, um estudo do comportamento do material à tração. Um modelo probabilístico/micro-mecânico fundamentado na mecânica de fratura, e capaz de prever o comportamento pós-fissuração do compósito é apresentado. O modelo prevê a relação tensão-abertura de fissura do compósito levando em conta os seguintes micro-mecanismos: travejamento de agregado e fibras, a ruptura das fibras, os efeitos de: atrito local (snubbing effect), esmagamento da matriz, Cook-Gordon, e da pré-tração das fibras. Em nível estrutural, dois modelos macro-mecânicos são apresentados. O primeiro modelo tem premissa na teoria clássica de fissura, e o segundo na mecânica de dado. O primeiro modelo é ajustado para aplicação na previsão de espaçamento e aberturas de fissura em estruturas de concreto armado com fibras discretas e aleatoriamente dispostas. É demostrado que o modelo micro-mecânico pode alimentar perfeitamente o modelo macro-mecânico. Ensaios de tração com elementos de placas de argamassa com fibras armada com tela ou fios foram realizados. Os resultados teóricos previstos pelo modelo foram comparados com os obtidos do programa experimental, e mostram uma boa concordância, comprovando a validade do modelo apresentado. / Due to the brittleness of concrete, the control and prevention of cracking in reinforced concrete structures are of prime importance. One way of improving the tensile properties of concrete is by the addition of fibres. The present research is a trial to provide guidelines for the design of fibre reinforced concrete structures under service loads. First of all, a study of the tensile behaviour of the composite material is presented. A probabilistic/fracture mechanics based micromechanical model, capable of predicting the poscracking behaviour of the material is presented. The model predicts the tensile stress-crack width relationship, accounting for the following micromechanisms: fibre and aggregate bridging, fibre rupture, local snubbing, matrix spalling, the Cook-Gordon interface effect, and fibre prestressing. At the structural level, two macromechanical models are presented. One is founded on the classical theory of cracking, while the other, a shear lag model, is founded on the continuum damage mechanics. The first model is adjusted for application to the prevision of crack width and crack spacing in fibre reinforced concrete structures with short discrete and randomly dispersed fibres. It is shown that the micromechanical model fits very well in the macrostructural model. Tensile tests with mortar specimens reinforced with continuous steel wires or meshes and PVA or polypropylene fibres were carried out. The theoretical results predicted by the model were compared with results obtained from the experimental program, and show very good agreement, confirming the validity of the theoretical model.

Devido à fragilidade do concreto, o controle e combate da fissuração são de importância fundamental em estruturas de concreto armado. Uma maneira de melhorar as propriedades do concreto à tração é pelo emprego de fibras. A presente pesquisa é uma tentativa de fornecer diretrizes para o dimensionamento de estruturas de concreto armado com fibras, e armadura convencional sob condições de serviço. Apresenta-se inicialmente, um estudo do comportamento do material à tração. Um modelo probabilístico/micro-mecânico fundamentado na mecânica de fratura, e capaz de prever o comportamento pós-fissuração do compósito é apresentado. O modelo prevê a relação tensão-abertura de fissura do compósito levando em conta os seguintes micro-mecanismos: travejamento de agregado e fibras, a ruptura das fibras, os efeitos de: atrito local (snubbing effect), esmagamento da matriz, Cook-Gordon, e da pré-tração das fibras. Em nível estrutural, dois modelos macro-mecânicos são apresentados. O primeiro modelo tem premissa na teoria clássica de fissura, e o segundo na mecânica de dado. O primeiro modelo é ajustado para aplicação na previsão de espaçamento e aberturas de fissura em estruturas de concreto armado com fibras discretas e aleatoriamente dispostas. É demostrado que o modelo micro-mecânico pode alimentar perfeitamente o modelo macro-mecânico. Ensaios de tração com elementos de placas de argamassa com fibras armada com tela ou fios foram realizados. Os resultados teóricos previstos pelo modelo foram comparados com os obtidos do programa experimental, e mostram uma boa concordância, comprovando a validade do modelo apresentado. / Due to the brittleness of concrete, the control and prevention of cracking in reinforced concrete structures are of prime importance. One way of improving the tensile properties of concrete is by the addition of fibres. The present research is a trial to provide guidelines for the design of fibre reinforced concrete structures under service loads. First of all, a study of the tensile behaviour of the composite material is presented. A probabilistic/fracture mechanics based micromechanical model, capable of predicting the poscracking behaviour of the material is presented. The model predicts the tensile stress-crack width relationship, accounting for the following micromechanisms: fibre and aggregate bridging, fibre rupture, local snubbing, matrix spalling, the Cook-Gordon interface effect, and fibre prestressing. At the structural level, two macromechanical models are presented. One is founded on the classical theory of cracking, while the other, a shear lag model, is founded on the continuum damage mechanics. The first model is adjusted for application to the prevision of crack width and crack spacing in fibre reinforced concrete structures with short discrete and randomly dispersed fibres. It is shown that the micromechanical model fits very well in the macrostructural model. Tensile tests with mortar specimens reinforced with continuous steel wires or meshes and PVA or polypropylene fibres were carried out. The theoretical results predicted by the model were compared with results obtained from the experimental program, and show very good agreement, confirming the validity of the theoretical model.