There are approximately 6000 Gulfport-type wood structures used to support 1600 km of 230 kV electrical transmission lines in Ontario. An unexpected structural failure caused by wood deterioration has been recognized as a major risk to the safety of these transmission lines. Since the reliability of the electricity transmission and distribution lines is extremely important to the electrical industry and other users of electricity, failure of these structures can result in devastating incidents. Due to the remote location of the transmission network and the requirement to keep the power lines in continuous service, replacement of the Gulfport structures has proved to be very difficult and expensive. This research program investigated the use of Glass Fibre Reinforced Polymer (GFRP) wrap as a light weight and durable strengthening system that can be applied to the existing structures without any interruptions in the functionality of the transmission lines. A total of three control specimens and three strengthened samples were tested in Phase I of the experimental program, which was designed as a feasibility study. It was concluded that the average strength of strengthened samples was 42% higher than the average strength of the control samples, and was greater than the end of life (EOL) threshold of 30 MPa for the cross arms. Therefore, the proposed strengthening system was concluded to be an effective solution for strengthening the deteriorated cross arms of the Gulfport structures. Taguchi methods and Analysis of Variation (ANOVA) were employed in Phase II to optimize the proposed strengthening system. The optimal configuration was determined to be the application of the filler material, non-sanded surface, and the shorter width of wrap (width of 0.6 m). The mean strength of the optimal configuration was estimated to be 52 MPa with a 95% confidence interval of: 38.7 MPa < True Mean < 65.3 MPa. Phase III confirmed the estimated mean and the confidence interval for the optimal configuration in Phase II. The strengthening system changed the failure mode from combined shear-flexure failure to pure flexure and resulted in more consistent strength and stiffness values. The strain values of the GFRP wrap showed that a single layer of wrap was sufficient for the confinement purposes.

There are approximately 6000 Gulfport-type wood structures used to support 1600 km of 230 kV electrical transmission lines in Ontario. An unexpected structural failure caused by wood deterioration has been recognized as a major risk to the safety of these transmission lines. Since the reliability of the electricity transmission and distribution lines is extremely important to the electrical industry and other users of electricity, failure of these structures can result in devastating incidents. Due to the remote location of the transmission network and the requirement to keep the power lines in continuous service, replacement of the Gulfport structures has proved to be very difficult and expensive. This research program investigated the use of Glass Fibre Reinforced Polymer (GFRP) wrap as a light weight and durable strengthening system that can be applied to the existing structures without any interruptions in the functionality of the transmission lines. A total of three control specimens and three strengthened samples were tested in Phase I of the experimental program, which was designed as a feasibility study. It was concluded that the average strength of strengthened samples was 42% higher than the average strength of the control samples, and was greater than the end of life (EOL) threshold of 30 MPa for the cross arms. Therefore, the proposed strengthening system was concluded to be an effective solution for strengthening the deteriorated cross arms of the Gulfport structures. Taguchi methods and Analysis of Variation (ANOVA) were employed in Phase II to optimize the proposed strengthening system. The optimal configuration was determined to be the application of the filler material, non-sanded surface, and the shorter width of wrap (width of 0.6 m). The mean strength of the optimal configuration was estimated to be 52 MPa with a 95% confidence interval of: 38.7 MPa < True Mean < 65.3 MPa. Phase III confirmed the estimated mean and the confidence interval for the optimal configuration in Phase II. The strengthening system changed the failure mode from combined shear-flexure failure to pure flexure and resulted in more consistent strength and stiffness values. The strain values of the GFRP wrap showed that a single layer of wrap was sufficient for the confinement purposes.

Nach zwölf Jahren endete am 30.6.2011 die Förderung des Sonderforschungsbereiches 528 durch die Deutsche Forschungsgemeinschaft (DFG). Der Abschlussbericht fasst die zentralen Ergebnisse des Sonderforschungsbereiches auf dem Gebiet der Verstärkung und Instandsetzung mit textilbewehrtem Beton über die gesamte Laufzeit des SFBs zusammen. Dazu berichten die einzelnen Teilprojekte über ihre aktuellen Erkenntnisse aus der letzten Förderperiode.

Structures in high seismic risk areas may be susceptible to severe damage in a major earthquake. Structures designed to meet older code requirements may be at even greater risk. When these structures are evaluated with respect to current code criteria, it is observed that they lack of lateral strength and/or ductility. Since safety and economic considerations are major problems, these structures become viable candidates for retrofit and seismic strengthening. For the variety of structures and possible deficiencies that arise, several retrofitting techniques can be considered. Diagonal bracing system is one of the retrofitting techniques and it provides an excellent approach for strengthening and stiffening existing building for lateral forces. Also, another potential advantage of this system is the comparatively small increase in mass associated with the retrofitting scheme since this is a great problem for several retrofitting techniques. In this study, the use of steel bracing for the strengthening of low, intermediate, and relatively high rise reinforced concrete frames are investigated analytically. The ultimate lateral load capacities of the strengthened frames are determined by a load controlled push-over analysis. The post-tensioning effect of preloading is also investigated.

Seismic resistance of many buildings in Turkey is insufficient. Strengthening using R/C infills requires huge construction work. Feasible, easy strengthening techniques are being studied in Structural Mechanics Laboratory of METU. In this project, it was aimed to develop an economical strengthening method. This method is based on addition of steel fibers and/or PP fibers in mortar and application of mortar on masonry wall. Project was sponsored by the Scientific and Technical Research Council of Turkey (T&Uuml / BiTAK). Physical properties of cement, aggregate, and mortar used in tests were determined by material tests. After performing flexural strength and compressive strength tests, optimum mortar was obtained. R/C frames strengthened by applying the mortar to brick infilled walls were tested under reversed cyclic loads. Before the frame tests, two series of panel tests were performed to correctly model strengthened infill walls and to gather information about behavior of walls under load. Totally 10 frame tests were done. 4 tests were done as reference tests, and other 6 were done as strengthened frame tests. In the analytical part of study, the plastered hollow brick infill wall strengthened by FRM was modeled as two separate compression struts. First strut was used to model the plastered hollow brick infill wall. Second strut was used to model the FRM. This technique is effective in improving seismic behavior by increasing strength, initial stiffness, energy dissipation, and ductility. Moreover, the method provides strengthening of the buildings without evacuating the structure.

An innovative strengthening technique is applied for the first time in this study to provide flexural strengthening in two-way reinforced concrete (RC) slabs supported on edge beams. The technique comprises external bonding of textiles on the tension face of RC slabs through the use of polymer-modified cement- based mortars. The textiles used in the experimental campaign comprised fabric meshes made of long stitch-bonded fibre rovings in two orthogonal directions. The specimens measured 2 x 2 m in plan and were supported on hinges at the corners. Three RC slabs strengthened by textile reinforced mortar (TRM) overlays and one control specimen were tested to failure. One specimen received one layer of carbon fibre textile, another one received two, whereas the third specimen was strengthened with three layers of glass fibre textile having the same axial rigidity (in both directions) with the single-layered carbon fibre textile. All specimens failed due to flexural punching. The load-carrying capacity of the strengthened slabs was increased by 26%, 53%, and 20% over that of the control specimen for slabs with one (carbon), two (carbon) and three (glass) textile layers, respectively. The strengthened slabs showed an increase in stiffness and energy absorption. The experimental results are compared with theoretical predictions based on existing models specifically developed for two-way slabs and the performance of the latter is evaluated. Based on the findings of this work the authors conclude that TRM overlays comprise a very promising solution for the strengthening of two-way RC slabs.

<p>Materials to be used in thermal power plants have to resist creep deformation for time periods up to 30 years. The role of alloying elements for creep strength of 9-12% Cr steels is analysed. The creep strength in these steels relies on minor additions of alloying elements. Precipitates give rise to the main strengthening and remaining elements produce solid solution hardening. Nucleation, growth and coarsening of particles are predicted by thermodynamic modelling. Phase fractions and size distributions of M₂₃C₆ carbides, MX carbonitrides and Laves phase are presented. The size distributions are needed in order to determine the particle hardening during creep. At elevated temperatures the climb mobility is so high that the dislocations can climb across particles instead of passing by making Orowan loops.</p><p>By solving Fick's second law the concentration profile around a moving dislocation can be determined. The results show an accumulation of solutes around the dislocation that slows down dislocation movement. When Laves phase grows a decrease in creep strength is observed due to a larger loss in solid solution hardening than strength increase by particle hardening. Solid solution hardening also gives an explanation of the low dislocation climb mobility in 9-12% Cr steels.</p><p>Three different dislocation types are distinguished, free dislocations, immobile dislocation and immobile boundary dislocations. This distinction between types of dislocations is essential in understanding the decreasing creep with strain during primary creep. The empirical relation with subgrain size inversely proportional to stress has been possible to predict. The total creep strength can be predicted by adding the contribution from individual mechanisms.</p>

This thesis describes part of the work associated with Project 0-6719 sponsored by the Texas Department of Transportation (TxDOT). The primary objective of the project is to examine the feasibility of strengthening older continuous multi-span steel girder bridges through the use of post-installed shear connectors. Bridges potentially eligible for retrofit have noncomposite floor systems, where the concrete slab is not attached to the steel girders with shear connectors. Many of these bridges were designed in the 1950's and 1960's for loads smaller than the standard design loads used today. A secondary objective of the project, and the main focus of this thesis, is to examine the design of post-installed shear connectors for fatigue. Of particular interest in this study is the adhesive anchor, given its convenient installation procedure but relatively poor fatigue performance in previous tests. The objectives of this thesis were to quantify the fatigue strength of the adhesive anchor, as well as quantify the shear force and slip demands on adhesive anchors in realistic bridge conditions. In regards to the first objective, twenty-six direct shear fatigue tests were performed on adhesive anchors. Each test was conducted on a single adhesive anchor in order to capture its individual cyclic load-slip behavior. Results indicate that adhesive anchors have considerably higher fatigue strength than conventional welded shear studs, making partial composite design feasible in the strengthening of older steel bridges. In regards to the second objective, analytical and computational studies were conducted on composite beams with adhesive anchors. Results show that the shear force and slip demands are typically smaller than the endurance limits determined from direct-shear testing. This suggests that fatigue failure of adhesive anchors under service loads may not be a primary concern. Based on the results, preliminary recommendations for the design of adhesive anchors for fatigue are provided. / text

Στην παρούσα εργασία εξετάζεται η μοντελοποίηση στοιχείων από οπλισμένο σκυρόδεμα και συγκεκριμένα υποστυλώματα μονολιθικά αλλά και ενισχυμένα με την μέθοδο των πεπερασμένων στοιχείων. Τα δοκίμια τα οποία εξετάζονται έχουν υποβληθεί σε ανακυκλιζόμενη φόρτιση στο Εργαστήριο Κατασκευών του Τμήματος Πολιτικών Μηχανικών του Πανεπιστημίου Πατρών και τα αποτελέσματα των πειραματικών δοκιμών χρησιμοποιούνται για τον έλεγχο της αξιοπιστίας των αναλύσεων. Τα μοντέλα που κατασκευάστηκαν έχουν την δυνατότητα να λαμβάνουν υπόψιν την σχετική ολίσθηση μεταξύ του χάλυβα οπλισμού και του σκυροδέματος και επομένως και την εξόλκευση των ράβδων οπλισμού από το πέδιλο. Ωστόσο στα ενισχυμένα δοκίμια εξετάζονται διαφορετικοί τρόποι μοντελοποίησης της διεπιφάνειας μεταξύ παλαιού και νέου σκυροδέματος. Στο πρώτο κεφάλαιο της εργασίας παρουσιάζονται ορισμένα γενικά θεωρητικά θέματα σχετικά με τις ενισχύσεις και επισκευές στοιχείων από οπλισμένο σκυρόδεμα και κυρίως υποστυλωμάτων. Στο δεύτερο κεφάλαιο αναφέρονται λίγα πράγματα για την μέθοδο των πεπερασμένων στοιχείων και στην συνέχεια γίνεται μια σύντομη περιγραφή του προγράμματος πεπερασμένων στοιχείων ANSYS και των δυνατοτήτων που έχει. Στο τρίτο κεφάλαιο υπάρχει λεπτομερής περιγραφή των παραδοχών καθώς και των στοιχείων που χρησιμοποιούνται για την μοντελοποίηση στοιχείων από οπλισμένο σκυρόδεμα. Στο τέταρτο κεφάλαιο πραγματοποιείται μία βιβλιογραφική ανασκόπηση με σκοπό την τεκμηρίωση παραδοχών που χρησιμοποιούνται για την καλύτερη πρόβλεψη της συμπεριφοράς στοιχείων από οπλισμένο σκυρόδεμα. Στο πέμπτο κεφάλαιο παρουσιάζονται δύο αναλυτικές προσεγγίσεις του φαινομένου της εξόλκευσης των ράβδων οπλισμού από το πέδιλο. Η περιγραφή των πειραματικών δοκιμών που πραγματοποιήθηκαν στο Εργαστήριο Κατασκευών του Τμήματος Πολιτικών Μηχανικών του Πανεπιστημίου Πατρών, τα αποτελέσματα των οποίων χρησιμοποιούνται, για τον έλεγχο της αξιοπιστίας των αναλύσεων, πραγματοποιείται στο κεφάλαιο έξι. Στο έβδομο κεφάλαιο παρουσιάζονται τα αποτελέσματα των αναλύσεων που πραγματοποιήθηκαν για τρία μονολιθικά δοκίμια. Επιπλέον εξετάζεται και ένας εναλλακτικός απλοποιητικός τρόπος μοντελοποίησης με τον οποίο θεωρείται πλήρης συνάφεια χάλυβα – σκυροδέματος. Χρησιμοποιώντας την παραδοχή αυτή, αγνοείται το φαινόμενο της εξόλκευσης των ράβδων από το πέδιλο. Για το λόγο αυτό πραγματοποιείται και μια αναλυτική προσέγγιση της πρόσθετης μετατόπισης λόγω της εξόλκευσης και προκύπτουν τα τελικά αποτελέσματα τα οποία είναι αντίστοιχα με αυτά στα οποία γίνεται θεώρηση σχετικής ολίσθησης χάλυβα – σκυροδέματος. Στο όγδοο κεφάλαιο εξετάζονται πέντε ενισχυμένα δοκίμια. Παρουσιάζονται τρεις διαφορετικοί τρόποι μοντελοποίησης της διεπιφάνειας μεταξύ παλαιού – νέου σκυροδέματος γίνονται, ενώ προσομοιώνεται και η δράση βλήτρου κάνοντας χρήση ειδικών πολυγραμμικών ελατηρίων. Στην συνέχεια παρουσιάζονται τέσσερις διαφορετικού τρόποι για την έμμεση προσομοίωση της επίδρασης της ανακύκλισης στην συμπεριφορά της διεπιφάνειας. Επιπλέον εξετάζεται και η επίδραση της ανακυκλιζόμενης φόρτισης στην δράση του βλήτρου. Τα αποτελέσματα συγκρίνονται τόσο με τα αντίστοιχα πειραματικά όσο και με αυτά στα οποία αγνοείται η επίδραση της ανακύκλισης. Τέλος στο ένατο κεφάλαιο παρουσιάζονται τα τελικά συμπεράσματα που προέκυψαν καθώς και οι προτάσεις για μελλοντική έρευνα. Τα συμπεράσματα που προέκυψαν από την παρούσα εργασία είναι αρχικά, ότι η επιδραση του φαινομένου της εξόλκευσης στην συμπεριφορά των υποστυλωμάτων είναι αρκετά σημαντική. Ωστόσο τα αποτελέσματα που προέκυψαν από την ανάλυση που συμπεριλάμβανε το φαινόμενο αυτό καθώς και τα αντίστοιχα που προέκυψαν από τον συνδυασμό της απλοποιητικής ανάλυσης (πλήρη συνάφεια χάλυβα – σκυροδέματος) σε συνδυασμό με την αναλυτική μέθοδο είναι αρκετά ικανοποιητικά και προσεγγίζουν σχετικά καλά την περιβάλλουσα που προκύπτει από τα πειραματικά αποτελέσματα. Από τα αποτελέσματα που προέκυψαν για τα ενισχυμένα δοκίμια φαίνεται η επίδραση των χαρακτηριστικών της διεπιφάνειας στην συμπεριφορά των ενισχυμένων στοιχείων καθώς και η συμβολή των βλήτρων τόσο στην γενικότερη συμπεριφορά όσο και στην μείωση της ολίσθησης στην διεπιφάνεια. Ωστόσο σύμφωνα με τα αποτελέσματα η επίδραση της ανακύκλισης της φόρτισης είναι αρκετά σημαντική και επηρεάζει την συμπεριφορά του στοιχείου. / This thesis examines the simulation of reinforced concrete elements. In particular, the finite element method is used to investigate the behaviour of monolithic and strengthened columns that were tested under cyclic loading in the Structural Laboratory of the Department of Civil Engineering at the University of Patras. The reliability of the analytical models is examined by comparing experimental and numerical results. The numerical models created included modelling the sliding between the reinforcing steel and the concrete, the consequence of bar elongation and the total extension of a reinforcing bar at a particular point in relation to the surrounding concrete. Therefore, for strengthened specimens, different ways of modelling the interface between old and new concrete are examined. The first chapter presents some theoretical models for the strengthening and repair of reinforced concrete elements with particular reference to reinforced concrete columns. A brief review of the finite element method and the finite element program ANSYS is presented in the second chapter. The third chapter presents a detailed description of the basic assumptions and the elements that were used to model reinforced concrete members. A literature review is presented in the fourth chapter in order to explain assumptions and to describe the elements that were used for the models. Two analytical approaches for the phenomenon of bar elongation are presented in the fifth chapter. A description of the experimental tests performed in the Structural Laboratory of the Department of Civil Engineering at the University of Patras and the experimental results that were used to examine the reliability of the numerical results is presented in chapter six. In the seventh chapter, the results of the analysis of three monolithic specimens are presented. In this way, a simplified method is examined by considering a perfect bond between the steel and the concrete. By using this assumption, the phenomenon of bar elongation is neglected. In addition, an analytical approach for the supplementary deflection due to bar elongation is presented and the total result, including the supplement deflection, is similar to that using the assumption of relative slip between the steel and the concrete. Five strengthened columns are investigated in the eighth chapter. Three different methods of modelling the interface between the old and the new concrete are proposed and the presence of dowels is simulated by using special multi-linear springs. Therefore, four different processes for the simulation of the effect of cyclic loading on the behaviour at the interface are proposed. Furthermore, the effect of cyclic loading on the behaviour of dowels is examined. The results are compared to the relevant experimental results and to results where the effects of cyclic loading are neglected. Finally, the ninth chapter presents results and recommendations for further research. One conclusion that arises from this thesis is that the effect of bar elongation on the behaviour of reinforced concrete columns is quite significant. It was found that the results from the analysis that took into account bar elongation due to relative slippage and the analysis using the simplified method (perfect bond between steel and concrete) in combination with the supplementary deflection due to the bar elongation calculated using analytical methods are similar to the experimental results. Using the results of the strengthened specimens that have been presented, the effect of the properties at the interface and the contribution of the dowels on the behaviour of the strengthened specimens and in the reduction of sliding on the interface can been noted. However, according to the results, it must be stressed that the effects of cyclic loading are significant and affects the behaviour of the model.

Μια από τις πολλές δομικές εφαρμογές των συνθέτων υλικών, είτε αυτά έχουν την μορφή ινοπλισμένων πολυμερών είτε την μορφή ινοπλισμένων κονιαμάτων, είναι και η ενίσχυση τοιχοποιίας, φέρουσας ή μη. Τα σύνθετα υλικά είναι δυνατό να δώσουν λύση σε προβλήματα στατικής επάρκειας και αναβάθμιση στάθμης επιτελεστικότητας κτηρίων σύμφωνα με τους Ευρωκώδικες. Ο στόχος της συγκεκριμένης μεταπτυχιακής διατριβής είναι: i. Να μελετηθούν οι τρόποι με τους οποίους είναι δυνατόν να ενισχυθεί μια τοιχοποιία από οπτοπλινθοδομή και να πραγματοποιηθούν πειραματικές δοκιμές, (για να καταστεί με αυτό τον τρόπο δυνατή η σύγκριση των θεωρητικών με τα πειραματικά δεδομένα). ii. Η κατασκευή αντιπροσωπευτικών δοκιμίων που να εξετάζουν και να απεικονίζουν την πλειονότητα των δομημάτων και τελικά η πειραματική επεξεργασία τους. iii. Η επιλογή των κατάλληλων υλικών με τα οποία είναι δυνατή η αποτελεσματική και πρακτική η ενίσχυση της τοιχοποιίας. iv. Η μελέτη του τρόπου με τον οποίο αλληλεμπλέκονται τα σύνθετα υλικά με την τοιχοποιία και η τελική αστοχία της τελευταίας, με στόχο την απόκτηση μεγαλύτερης αντοχής και πλαστιμότητας. v. Η σύγκριση των τρόπων ενίσχυσης με ανόργανη (τσιμεντοκονίαμα) και οργανική (εποξειδική ρητίνη) μήτρα και ανθρακονήματα. vi. Η εφαρμογή και εκτίμηση της αποτελεσματικότητας της ενίσχυσης με ράβδους ινών άνθρακα σε βαθιά αρμολογημένο τοίχο με την βοήθεια εποξειδικού τσιμεντοκονιάματος. vii. Η εκτίμηση κατά πόσο με την βοήθεια ενίσχυσης φέρουσας οπτοπλινθοδομής με σύνθετα υλικά είναι δυνατή η κάλυψη των σύγχρονων αντισεισμικών απαιτήσεων. / One of the many uses of composite materials, either in the form of fiber reinforced plastics "FRP" either in the form of fiber reinforced mortars, is the structural reinforcement of masonry. The composite materials are capable to provide a structural upgrade to a building so that it meats the contemporary eurocode demands. The goal of this master thesis is: 1. to study the possible ways of brick masonry reinforcement and perform experimental studies (so that it become possible to compare the theoretical with the experimental data) 2. the construction of representative experimental specimens that examine end picture the majority of civil masonry constructions end finally the experimental elaboration of these specimens. 3. The selection of the suitable material with witch it is possible end practical the reinforcement of the masonry. 4. The study of the ways that composite materials collaborate with the brick masonry up to the point of destruction end finding a way that the reinforced specimens would have more strength end ductility than the unreinforced ones. 5. The comparison end effectiveness of the specimens reinforced with inorganic matrix (cement mortar) versus the ones reinforced with organic matrix (epoxy resin) end carbon fibers. 6. The application end estimation of the effectiveness of carbon fiber bar reinforcement that is applied near the surface in the bed joints of the masonry specimens with the help of epoxy resin cement mortar. 7. To estimate if it is possible with the help of composite materials to reinforce masonry so that it meats contemporary antiseismic construction demands.