Ductility is a measure of the ability of a material, section, structural element or structural system to sustain deformations prior to collapse without substantial loss of resistance. The Australian design standard, AS 3600, imposes minimum ductility requirements on structural concrete members to try to prevent premature non-ductile failure and hence to ensure adequate strength and ductile-type collapse with large deflections. The requirements also enable members to resist imposed deformation due to differential settlement, time effects on the concrete and temperature effects, whilst ensuring sufficient carrying capacity and a safe design. Current AS 3600 requirements allow a limited increase or reduction in elastically determined bending moments in critical regions of indeterminate beams, accommodating their ability to redistribute moment from highly stressed regions to other parts of the beam. Design moment redistribution limits and ductility requirements in AS 3600 for bonded partially prestressed beams are a simple extension of the requirements for reinforced members. The possibility of premature non-ductile failure occurring by fracture of the reinforcement or prestressing steel in partially prestressed members has not adequately addressed. The aim of this research is to investigate the overload behaviour and deformation capacity of bonded post-tensioned beams. The current ductility requirements and design moment redistribution limits according to AS 3600 are tested to ensure designs are both safe and economical. A local flexural deformation model based on the discrete cracked block approach is developed to predict the deformation capacity of high moment regions. The model predicts behaviour from an initial uncracked state through progressive crack development into yielding and collapse. Local deformations are considered in the model using non-linear material laws and local slip behaviour between steel and concrete interfaces, with rigorous definition of compatibility in the compression and tension zones. The model overcomes limitations of past discrete cracked block models by ensuring compatibility of deformation, rather than strain compatibility. This improvement allows the modeling of members with multiple layers of tensile reinforcement and variable depth prestressing tendons having separate material and bond properties. An analysis method for simple and indeterminate reinforced and partially prestressed members was developed, based on the proposed deformation model. To account for the effect of shear in regions of high moment and shear present over the interior supports of a continuous beam, a modification to the treatment of local steel deformation in the flexural model, based on the truss analogy, was undertaken. Secondary reactions and moments due to prestress and continuity are also accounted for in the analysis. A comparison of past beam test data and predictions by the analysis shows the cracking pattern and deformation capacity at ultimate of flexural regions in reinforced and partially prestressed members to be predicted with high accuracy. The analysis method accurately predicts local steel behaviour over a cracked region and deformation capacity for a wide range of beams which fail either by fracture of steel or crushing of the concrete. A parametric study is used to investigate the influence of different parameters on the deformation capacity of a typical negative moment region in a continuous beam. The structural system consists of a bonded post-tensioned, partially prestressed band beam. The primary parameters investigated are the member height and span-to-depth ratio; relative quantity of reinforcing and prestressing steel; material properties and bond capacity of the steels; and lastly the compression zone properties. Results show that the effects of the various parameters on the overload behaviour of partially prestressed beams follow the same trends as reinforced beams. A new insight into the local steel behaviour between cracks is attained. The deformation behaviour displays different trends for parametric variations of the local bond capacity, bar diameter and crack spacing, when compared to past analytical predictions from comparable studies. The discrepancy in findings is traced back to the definition of the plastic rotation capacity and the sequencing of the yielding of the steels. Compared to the other local deformation models, the current model does not assume a linear distribution of strain at a crack. The current findings highlight an important difference between predicted behaviours from different deformation compatibility requirements in local deformation models which has not yet been discussed in the literature. The local deformation model evaluates the relationship between maximum steel strain at a crack and average steel deformation over a crack spacing for the entire loading history. The total steel percentage, hardening properties of the steel and concrete strength are shown by the model to have the greatest effect on these steel strain localisation factors. Section analysis, as currently used in design, can be improved with the proposed simplification of the relationships to identify and quantify the effects of steel fracture on deformation capacity and strength. The numerical effort required to simulate the overload behaviour of practical beam designs with multiple reinforcement elements and a prestressing tendon are currently too great to be used in an extensive numerical study. The numerically more efficient smeared block approach is shown to accurately predict the ultimate carrying capacity of prestressed beams failing by crushing of the concrete. Consequently, this method is adopted to study the allowable limits of moment redistribution in the present investigation, Simplified relationships of the steel strain localisation factors evaluated in the parametric study of deformation capacity is used to predict maximum steel strains and premature failure. The limits of moment redistribution in bonded, post-tensioned partially prestressed band beams are explored by comparing the design load and predicted carrying capacity, for different section ductilities and design moment redistribution. In addition, the effects of different concrete strengths, up to 85 MPa, along with as three reinforcing and prestressing steel ductilities are quantified and compared to current Australian and international design requirements. Limitations in the carrying capacity are investigated for different reinforcement and prestress uniform elongation capacities. More than one thousand beam simulations produce results showing that current design moment redistribution and ductility requirements in the Australian design code for concrete structures (AS 3600) are sufficient for normal strength concretes (less than 50 MPa). A suggestion for design moment redistribution limits, section ductility requirements and steel ductility limits is made for members constructed from higher strength concretes. A special high steel ductility class is proposed for both the reinforcement and prestressing steel to allow moment redistribution in higher strength concrete. No moment redistribution is proposed for members reinforced with low ductility (Class L) steel. An increase of the current elongation limit of Class L steel from 1.5 % to 2.5% is suggested to ensure strength and safety. An increase in the current ductility requirements from fsu/ fsy=1.03 and elongation equal to 1.5% to fsu/fsy=1.05 and 2.5% elongation for low ductility Class L steel is suggested to ensure strength and safety. / Thesis (Ph.D.)--Civil and Environmental Engineering, 2004.

Most materials including concrete have pre-existing flaws or defects. The fracture energy of concrete is a basic material property needed to understand fracture initiation and propagation in concrete. Whether fracture energy is size dependent or not is being discussed world over. Strictly the fracture energy if taken as a material property should be constant, and should be independent of the method of measurement, test methods, specimen shapes and sizes. A computational study on simulation of fracture in concrete using two dimensional lattice models is presented. A comparison is made with acoustic emission (AE) events with the number of fractured elements. A three-point bend specimen (TPB) is modeled using regular triangular lattice network. It was observed that the number of fractured elements increases near the peak load and beyond the peak load. AE events also increase rapidly beyond the peak load. Singular Fractal Functions (S.F.F) has been employed to interpret the size effect of quasi-brittle materials like concrete. The usual size dependent fracture energy of High Strength Concrete (HSC) beam is reported. The results are presented which are obtained directly from the experiments related to size effect in concrete carried out in the Structural engineering laboratory, Department of Civil engineering, IISc. Various fracture parameters studied in this experimental program are (a) Nominal strength N (b) Fracture energy, Gf (c)Fracture toughness, KIc, (c) Crack mouth opening displacement, CMOD (d) Size effect on the strength of concrete. Three-point-bend (TPB) specimen was chosen for the experimental study. Six different concrete mixes viz. A-mix, B-Mix, C-mix, D-Mix, E-mix, F-Mix were used. Acoustic Emission (AE) experiments are conducted to relate acoustic emission energy to fracture energy. It is interesting to note that both acoustic emission energy and fracture energy have similar characteristics. The advantage of the above relationship is that now it is possible to evaluate fracture energy by non-destructive testing methods. The b-value analysis of AE was carried out to study the damage in concrete structures. The Guttengberg-Richter relation for frequency versus magnitude can be applied to the AE method to study the scaling of the amplitude distribution of the acoustic emission waves generated during the cracking process in the test specimen at laboratory or in engineering structures. In the next part of this chapter b-value at various stages of damage of a reinforced concrete beam are obtained experimentally under typical cyclic loadings. The b-values at different levels of damage are tabulated. As fracture is size dependent, it may not be very useful unless its size dependency is eliminated. An effort is made to obtain size independent fracture energy by a hybrid technique.

An experimental and analytical study was conducted on a BT-63 prestressed concrete girder to investigate the thermal effects on the girder. A 2D finite element heat transfer analysis model was then developed which accounted for heat conduction, convection, radiation, and irradiation. The solar radiation was predicted using the location and geometry of the girder, variations in the solar position, and the shadow from the top flange on other girder surfaces. The girder temperatures obtained from the 2D heat transfer analysis matched well with the measurements. Using the temperatures from the 2D heat transfer analysis, a 3D solid finite element analysis was performed assuming the temperatures constant along the length of the girder. The maximum vertical displacement due to measured environmental conditions was found to be 0.29 inches and the maximum lateral displacement was found to be 0.57 inches. Using the proposed numerical approach, extremes in thermal effects including seasonal variations and bridge orientations were investigated around the United States to propose vertical and transverse thermal gradients which could then be used in the design of I-shaped prestressed concrete bridge girders. A simple beam model was developed to calculate the vertical and lateral thermal deformations which were shown to be within 6% of the 3D finite element analyses results. Finally, equations were developed to predict the maximum thermal vertical and lateral displacements for four AASHTO-PCI standard girders. To analyze the combined effects of thermal response, initial sweep, and bearing support slope on a 100-foot long BT-63 prestressed concrete girder, a 3D finite element sequential analysis procedure was developed which accounted for the changes in the geometry and stress state of the girder in each construction stage. The final construction stage then exposed the girder to thermal effects and performed a geometric nonlinear analysis which also considered the nonlinear behavior of the elastomeric bearing pads. This solution detected an instability under the following conditions: support slope of 5¡Æ and initial sweep of 4.5 inches.

Title page, abstract and table of contents only. The complete thesis in print form is available from the University of Adelaide Library. / The major contribution of this thesis is towards the shear capacity and shear failure mechanism of reinforced concrete beams with adhesively bonded transverse near surface mounted fiber reinforced plastic plates. In shear strengthening, there are two forms of plate debonding that interact with each other consisting of intermediate crack debonding that is governed by the axial forces in the plate are induced by shear deformations. This research considers both forms of debonding and in particularl their interaction. -- From abstract. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1283733 / Thesis (Ph.D.) -- University of Adelaide, School of Civil and Environmental Engineering, 2007

Title page, abstract and table of contents only. The complete thesis in print form is available from the University of Adelaide Library. / The major contribution of this thesis is towards the shear capacity and shear failure mechanism of reinforced concrete beams with adhesively bonded transverse near surface mounted fiber reinforced plastic plates. In shear strengthening, there are two forms of plate debonding that interact with each other consisting of intermediate crack debonding that is governed by the axial forces in the plate are induced by shear deformations. This research considers both forms of debonding and in particularl their interaction. -- From abstract. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1283733 / Thesis (Ph.D.) -- University of Adelaide, School of Civil and Environmental Engineering, 2007

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Call number: LD2668 .T4 1985 T33 / Master of Science

Στόχος της παρούσας διατριβής, είναι η κατά βάση πειραματική διερεύνηση της συμπεριφοράς διατάξεων ενίσχυσης πλακοδοκών Οπλισμένου Σκυροδέματος, έναντι τέμνουσας υπό ανακυκλιζόμενη φόρτιση, με χρήση πλεγμάτων συνεχών ινών άνθρακα δύο διευθύνσεων 0°/90°, σε ανόργανη μήτρα κονιάματος με βάση το τσιμέντο (Ινοπλέγματα Ανόργανης Μήτρας). Η τεχνική αυτή, αρχικά εφαρμόστηκε με την μορφή τρίπλευρου μανδύα ΙΑΜ μορφής U, με στόχο την διερεύνηση της αποτελεσματικότητας των ανοιχτών μανδυών ΙΑΜ στην αύξηση της ικανότητας ανάληψης τέμνουσας δύναμης, καθώς και του ρόλου του αριθμού των στρώσεων στην εν λόγω πιθανή αύξηση. Στην συνέχεια, στην προσπάθεια αντιμετώπισης των αδυναμιών των «ανοιχτών» μανδυών, δηλαδή της συνήθους τεχνικής ενίσχυσης δοκών σε τέμνουσα, εφαρμόστηκε ειδική διάταξη αγκύρωσης των άκρων του μανδύα, αποτελούμενη από καμπύλα μεταλλικά ελάσματα που συγκρατούσαν τον μανδύα και μετέφεραν τις δυνάμεις μέσω μηχανικών αγκυρίων στην μάζα της πλάκας σκυροδέματος της δοκού. Με βάση τα πειραματικά αποτελέσματα που εξήχθησαν, ήταν δυνατή η σύγκριση των παραπάνω διατάξεων ενίσχυσης και η εξαγωγή σημαντικών συμπερασμάτων για την πρωτοπόρα τεχνική ενίσχυσης σε τέμνουσα δύναμη πλακοδοκών οπλισμένου σκυροδέματος με χρήση Ινοπλεγμάτων Ανόργανης Μήτρας. Σχετικά με τη δομή της διατριβής, αυτή αποτελείται από έξι Κεφάλαια τα οποία με την σειρά τους διαχωρίζονται σε κατάλληλες ενότητες, υποενότητες και παραγράφους. Συνοπτικά περιγράφεται παρακάτω το περιεχόμενο κάθε Κεφαλαίου. Στο πρώτο Κεφάλαιο πραγματοποιείται μία εισαγωγή για την ανάγκη διατμητικής ενίσχυσης των κατασκευών από οπλισμένο σκυρόδεμα. Παρουσιάζεται η γενική κατεύθυνση των σύγχρονων Αντισεισμικών Κανονισμών, με στόχο την κατανόηση της συμπεριφοράς της κατασκευής και των μελών της κατά την σεισμική διέγερση και τους λόγους που οδηγούν στην ανάγκη διατμητικής ενίσχυσης των δοκών οπλισμένου σκυροδέματος. Εν συνεχεία, πραγματοποιείται μια παρουσίαση των συμβατικών τεχνικών διατμητικής ενίσχυσης πλακοδοκών οπλισμένου σκυροδέματος με την εξέλιξή τους, καθώς και τις αδυναμίες που προκύπτουν, με βάση γενικά κριτήρια που ορίζει ο Κανονισμός Επεμβάσεων, οδηγώντας στην ανάγκη αναζήτησης νέας τεχνικής. Τέλος,τίθεται το πρόβλημα που εξετάζεται στην παρούσα διατριβή, με ανάλογη παρουσίαση της γενικής ιδέας των νέων διατάξεων ενίσχυσης που εξετάζονται. Στο δεύτερο Κεφάλαιο πραγματοποιείται μία παρουσίαση των Ινοπλεγμάτων Ανόργανης Μήτρας. Παρουσιάζονται πληροφορίες για τις ίνες που απαρτίζουν τα πλέγματα, τους τύπους των πλεγμάτων σύνθετων υλικών, τους τύπους ανόργανης μήτρας και τη συνάφεια μεταξύ πλεγμάτων και μητρικού υλικού. Στην συνέχεια, γίνεται αναφορά στις εφαρμογές των στοιχείων από Ινοπλέγματα σε Ανόργανη Μήτρα στις νέες κατασκευές, ενώ ακολουθεί βιβλιογραφική ανασκόπηση για τον (περιορισμένο) αριθμό ερευνητικών εργασιών που αφορούν την εφαρμογή Ινοπλεγμάτων σε Ανόργανη Μήτρα στο πεδίο των ενισχύσεων των κατασκευών, διαπιστώνοντας παράλληλα ότι τα ΙΑΜ δεν έχουν εφαρμοστεί μέχρι σήμερα στη μορφή τρίπλευρου μανδύα για την διατμητική ενίσχυση πλακοδοκών οπλισμένου σκυροδέματος. Τέλος, στην βιβλιογραφική ανασκόπηση προστίθενται δύο ερευνητικές εργασίες που παρουσιάζουν τεχνικές αγκύρωσης των άκρων τρίπλευρων μανδυών ινοπλισμένων πολυμερών, παρόμοιες με αυτή που εφαρμόσαμε στην παρούσα διατριβή. Στο τρίτο Κεφάλαιο πραγματοποιείται λεπτομερής παρουσίαση της πειραματικής διαδικασίας που ακολουθήθηκε για την παρασκευή των δοκιμίων. Συγκεκριμένα, αρχικά παρουσιάζεται ο τρόπος που πραγματοποιήθηκε ο σχεδιασμός των δοκιμίων, οι οπλισμοί που προέκυψαν, η γεωμετρία τους και οι παράμετροι που καλούμαστε να διερευνήσουμε. Στην συνέχεια, περιγράφεται η διαδικασία κατασκευής των δοκιμίων, η διαδικασία ενίσχυσής τους και η πειραματική διάταξη που χρησιμοποιήθηκε, με τελική αναφορά στα χρησιμοποιούμενα υλικά και τις ιδιότητές τους. Στο τέταρτο Κεφάλαιο παρουσιάζονται όλα τα πειραματικά αποτελέσματα, με την μορφή διαγραμμάτων των πειραματικά μετρημένων μεγεθών, δηλαδή του φορτίου καταγραφής του εμβόλου και της σχετικής μετακίνησής του. Τα αποτελέσματα παρουσιάζονται αυτοτελώς για κάθε δοκίμιο, αλλά και συγκριτικά, ενώ ακολουθεί σχολιασμός και σύγκριση των αποτελεσμάτων.Τέλος, παρατίθενται τα διαγράμματα των πειραματικών μετρημένων μεγεθών των αισθητήρων, που είχαν επικολληθεί κάτω από το έμβολο, για λόγους πληρότητας και επιβεβαίωσης των αποτελεσμάτων του εμβόλου. Στο πέμπτο Κεφάλαιο, με τίτλο «Αποδοτικότητα διατάξεων ενίσχυσης», παρουσιάζεται αρχικά ο τρόπος ανάληψης τέμνουσας δύναμης από τα σύνθετα υλικά καιτο πρώτο προσομοίωμα που έχει προταθεί για τον υπολογισμό της συνεισφοράς των Ινοπλεγμάτων Ανόργανης Μήτρας στην ανάληψη τέμνουσας δύναμης. Ακολουθούν υπολογισμοί, μέσω των οποίων ποσοτικοποιείται η αποδοτικότητα κάθε διάταξης ενίσχυσης και επιχειρείται η κατανόηση των αδυναμιών που προκύπτουν από την εφαρμογή του προσομοιώματος . Τέλος, στο έκτο και τελευταίο Κεφάλαιο, πραγματοποιείται μία συνοπτική περίληψη του συνόλου της παρούσας διατριβής, με την παράθεση των βασικότερων συμπερασμάτων που προκύπτουν, ενώ γίνεται αναφορά σε προτάσεις για μελλοντική έρευνα, σχετικές με το αντικείμενο της παρούσας διατριβής. / --

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Civil Engineering / Master / Master of Philosophy