Experimental and analytical investigation of the behaviour of interfaces between high injectability hydraulic grouts and stone or brick substrates

552 σ.Το αντικείμενο της παρούσας Διατριβής εντάσσεται στο επιστημονικό πεδίο της δομητικής αποκατάστασης ιστορικών τοιχοποιιών με ενέματα. Ειδικότερα, η Διατριβή επικεντρώνεται στην πειραματική διερεύνηση του μηχανισμού συνάφειας σε διεπιφάνειες μεταξύ δομικών λίθων και υδραυλικών ενεμάτων με μέτρια και χαμηλά μηχανικά χαρακτηριστικά. Από την συστηματική μελέτη του μηχανισμού συνάφειας, η οποία περιλαμβάνει α) την μελέτη της μικροδομής των διεπιφανειών, β) μηχανικές δοκιμές και γ) την συσχέτιση των αποτελεσμάτων των σημείων α και β, τεκμηριώνεται ότι ο μηχανισμός συνάφειας -για τα εν λόγω υλικά- είναι μηχανικής φύσης. Επί πλέον, αξιολογείται η επίδραση των ιδιοτήτων του υποβάθρου και των ενεμάτων στην συνάφεια και αποδεικνύεται ότι ενέματα με μέτρια και χαμηλά μηχανικά χαρακτηριστικά είναι ανταγωνιστικά σε όρους συνάφειας με άλλα ισχυρότερα ενέματα. Με βάση τα πειραματικά αποτελέσματα, διατυπώνεται τοπικός καταστατικός νόμος για την περιγραφή της συμπεριφοράς των διεπιφανειών έναντι διάτμησης και καταστρώνονται εμπειρικές σχέσεις για την πρόβλεψη της επιστρατευομένης διατμητικής αντίστασης κατά μήκος μιας διεπιφάνειας ενέματος/υποβάθρου, καθώς και της ολίσθησης και του ανοίγματος ρωγμής για τις οποίες αυτή η αντίσταση ενεργοποιείται. Τα παραπάνω στοιχεία αξιοποιούνται στο Αναλυτικό Μέρος της Διατριβής, στο οποίο κατασκευάζονται δύο προσομοιώματα για την περιγραφή των μηχανικών χαρακτηριστικών της διεπιφανειακής ζώνης. Η συμπεριφορά των διεπιφανειών αναπαράγεται επαρκώς και με τις δυο προσομοιώσεις. Τέλος, ένα εκ των προσομοιωμάτων διεπιφάνειας εισάγεται σε ένα απλό αναλυτικό προσομοίωμα στοιχείου τοιχοποιίας και αποτιμάται η συνεισφορά των ενεμάτων στην μηχανική απόκριση των ενισχυμένων με ενέματα τοιχοποιιών.The objective of the Doctoral Dissertation is placed among the field of structural rehabilitation of historic masonries with the grouting technique. Within the Thesis the bond mechanism of interfaces between masonry units and medium or low mechanical properties hydraulic grouts is experimentally investigated. Based on an extended systematic study (with more than 700 tests), which comprises a) microstructural study of the interfaces b) mechanical tests and c) correlation of the results of points a and b, it is proved that the bond mechanism is mechanical in nature for the materials considered. Furthermore, the results allow for the effect of properties of both substrate and grout on bond to be evaluated. The main finding of the experimental campaign is that grouts with medium and low mechanical properties are competitive in terms of bond strength with stronger grouts. Based on the experimental results, local constitutive laws describing the behaviour of grout-to-masonry unit interfaces under shear are formulated. The proposed local constitutive laws are used to predict the shear stress-horizontal displacement and horizontal displacement-crack opening response of such interfaces, as well as to determine the values of the ultimate shear bond strength and the corresponding slip values. Moreover, the grout-to-in-situ material interfaces are simulated by means of Finite Elements Analysis using a 2D model. Two different models are applied for the description of mechanical characteristics of the interfaces. Both models are applied, after calibration, to reproduce the experimental results. In general, the experimental curves are adequately simulated by the proposed models. Finally, the abovementioned models are tuned to a simple analytical model of three-leaf masonry element with the purpose to estimate the contribution of grout interfaces to the mechanical behaviour of masonry walls.Χρυσή-Ελπίδα Ν. Αδάμ

Soft computing-based models for the prediction of masonry compressive strength

Masonry is a building material that has been used in the last 10.000 years and remains competitive today for the building industry. The compressive strength of masonry is used in modern design not only for gravitational and lateral loading, but also for quality control of materials and execution. Given the large variations of geometry of units and joint thickness, materials and building practices, it is not feasible to test all possible combinations. Many researchers tried to provide relations to estimate the compressive strength of masonry from the constituents, which remains a challenge. Similarly, modern design codes provide lower bound solutions, which have been demonstrated to be weakly correlated to observed test results in many cases. The present paper adopts soft-computing techniques to address this problem and a dataset with 401 specimens is considered. The obtained results allow to identify the most relevant parameters affecting masonry compressive strength, areas in which more experimental research is needed and expressions providing better estimates when compared to formulas existing in codes or literature.publishe

Soft computing-based models for the prediction of masonry compressive strength

Masonry is a building material that has been used in the last 10.000 years and remains competitive today for the building industry. The compressive strength of masonry is used in modern design not only for gravitational and lateral loading, but also for quality control of materials and execution. Given the large variations of geometry of units and joint thickness, materials and building practices, it is not feasible to test all possible combinations. Many researchers tried to provide relations to estimate the compressive strength of masonry from the constit-uents, which remains a challenge. Similarly, modern design codes provide lower bound solutions, which have been demonstrated to be weakly correlated to observed test results in many cases. The present paper adopts soft-computing techniques to address this problem and a dataset with 401 specimens is considered. The obtained results allow to identify the most relevant parameters affecting masonry compressive strength, areas in which more experimental research is needed and expressions providing better estimates when compared to formulas existing in codes or literature.MU - Malayer University(undefined