Thesis (Ph. D.)--Universiteit Utrecht, 2001. / Includes bibliographical references (p. 163-171). "Publications: " p. 174.

Understanding specific pathways for sand transport in the lower reaches of large rivers, particularly the Mississippi, is the key to addressing multiple significant geologic problems and for environmental restoration efforts. Field studies were performed in the Mississippi River 75-100 km upstream of the Gulf of Mexico outlet in April 2010 (water discharge: 23,000 m³ s⁻¹), May 2010 (18,500-20,500 m³ s⁻¹), and March 2011 (27,000 m³ s⁻¹) to examine sediment transport phenomena in the river channel. Methods comprised multibeam sonar bathymetric surveys, acoustic Doppler current profiler measurements of current velocity and acoustic backscatter, point-integrated isokinetic suspended sediment sampling, and channel-bed grab sampling. Channel morphology surveys revealed a 30-60 m deep thalweg, alternating between banks every 2-3 km, opposite bedform-covered lateral sand bars. Dune sizes nearest the thalweg ranged from 7 m wavelength and 0.3 m height to over 100 m wavelength and 2.3 m height as a function of water discharge, with decreasing dune sizes towards shallow water. Material comprising the dunes was well-sorted, 125-500 [mu]m sand. Bedload transport rates increased exponentially with water discharge in April 2010 and March 2011 comparable to previous studies in this reach, though rates in May 2011 were well below predicted values for a site (Myrtle Grove) immediately downriver of a sand-mining project. Average water velocities ranged from 1.3 m s⁻¹ in May 2010 to 2 m s⁻¹ in March 2011. Skin-friction shear stress increased with water discharge, but varied over an order of magnitude at all measured discharges. Suspended sand concentration and grain size increased with proximity to the bed during all study periods, and was most pronounced in March 2011. Suspended sand concentrations were greatest over the center of lateral bars, and lowest in the thalweg, indicating that sand transport downstream occurs primarily over lateral sand bars where there is a combination of high shear stress and available bed material. Total bed-material discharge increased exponentially with water discharge. Bedform-induced turbulence may be responsible for the bed material suspension. These results are relevant to coastal restoration efforts by river diversion which seek to distribute sand from the upper water column to deltaic interdistributary wetlands. / text

Continuous beams represent main structural elements in most reinforced concrete (RC) structures such as parking garages and overpass bridges. Deterioration of such structures due to corrosion of steel reinforcement is common in North America. To overcome the corrosion problems, the use of fiber-reinforced polymer (FRP) bars and stirrups becomes a viable alternative to steel reinforcement. However, to date, the shear behaviour of FRP-RC continuous beams has not been explored yet. As such, the objective of this study is to investigate the shear behaviour of such beams. In this study, twenty four full-scale continuous concrete beams were constructed and tested. The test beams had rectangular cross section with 200-mm width and a height of 300, 550 or 850 mm and were continuous over two equal spans. The main investigated parameters were concrete strength, type and ratio of longitudinal reinforcement, type and ratio of transverse reinforcement and beam effective depth. Moreover, a 3-D nonlinear finite element model (FEM) was constructed to simulate the behaviour of FRP-RC continuous beams. The model was verified against the experimental results and validated against test results from previous studies. Then, the verified/validated model was used to conduct a parametric study to investigate the effect of a wide range of the parameters on the shear behaviour of GFRP-RC beams. The experimental and FEM results showed that shear-critical GFRP-RC continuous beams exhibited moment redistribution. Also, it was observed that increasing the concrete strength and the longitudinal reinforcement ratio increased the shear strength significantly. Moreover, the presence of GFRP stirrups significantly enhanced the shear strength of the tested beams. Regarding the size effect, test results showed that there was adverse or no size effect on the shear strength of GFRP-RC continuous beams when they failed in the interior shear span while beams failed in the exterior shear span exhibited clear size effect. Furthermore, a comparison between the test results and the provisions of the available models and FRP standards and design guidelines in North America revealed that these design provisions can be safely applied to continuous beams. / February 2016

M. Tech. Business Administration / The important role that Small, Micro and Medium Enterprises (SMMEs) play in creating jobs and income generation cannot be overemphasised. While the contribution of small businesses to the economic development is acknowledged, small businesses are faced with many obstacles that limit their growth and/or survival and most of them ultimately close down. This study examined the problems and challenges faced by shebeens and taverns in Soshanguve Township. These problems and challenges were attributed to the following factors; capital, managerial skills and experience, government support, legislation and regulations, competition with big businesses, criminal activities and entrepreneurial capabilities.

Το οπλισμένο σκυρόδεμα αποτελεί στις μέρες μας το πιο διαδεδομένο υλικό για την κατασκευή του φέροντος οργανισμού κτιριακών κατασκευών. Παρά την εξαιρετική επίδοση του οπλισμένου σκυροδέματος ως φέροντος υλικού, διαπιστώθηκε ότι στη διάρκεια ζωής των κατασκευών από οπλισμένο σκυρόδεμα, η οποία συχνά ξεπερνά τα 100 χρόνια, παρατηρείται μια βαθμιαία συσσώρευση βλάβης, ένας από τους κύριους παράγοντες της οποίας εντοπίζεται στη διάβρωση του σιδηροπλισμού. Tα τελευταία χρόνια το πρόβλημα της υποβάθμισης της φέρουσας ικανότητας του οπλισμού σκυροδέματος λόγω βλάβης διάβρωσης έχει προσελκύσει το ενδιαφέρον αρκετών ερευνητών παγκοσμίως. Όμως, μέχρι σήμερα ούτε η τεχνολογική σημασία της υποβάθμισης αυτής μπορεί να εκτιμηθεί ικανοποιητικά, κυρίως λόγω της έλλειψης σχετικών συστηματικών μελετών αλλά και επαρκών πειραματικών δεδομένων, ούτε οι φυσικοί μηχανισμοί που συμβάλλουν στην παρατηρούμενη υποβάθμιση των μηχανικών ιδιοτήτων έχουν γίνει πλήρως κατανοητοί. Κατά την εκπόνηση της παρούσας διδακτορικής διατριβής πραγματοποιήθηκε μια συστηματική μελέτη της μηχανικής συμπεριφοράς χαλύβων οπλισμού σκυροδέματος διαβρωμένων τόσο στο φυσικό τους περιβάλλον εντός του σκυροδέματος όσο και σε συνθήκες εργαστηριακής επιταχυμένης διάβρωσης. Με βάση τη σύγκριση της απώλειας μάζας σε συνάρτηση με το χρόνο έκθεσης στο διαβρωτικό μέσο που καταμετρήθηκε στο εργαστήριο, με την απώλεια μάζας δειγμάτων υλικού τα οποία είχαν διαβρωθεί φυσικά σε κατασκευές, κατέστη δυνατή η εξαγωγή ενός εμπειρικού συντελεστή επιτάχυνσης της βλάβης διάβρωσης όταν το υλικό διαβρώνεται με τη μέθοδο της αλατονέφωσης σε σχέση με τη βλάβη φυσικής διάβρωσης. Κατά την παρούσα εργασία εξετάστηκαν οι χάλυβες S400 και S500s, οι οποίοι χρησιμοποιήθηκαν ευρύτατα για κατασκευές του φέροντος οργανισμού κτιρίων στην Ελλάδα κατά το πρόσφατο παρελθόν, καθώς και ο χάλυβας B500c ο οποίος από τα τέλη του 2006 χρησιμοποιείται στην Ελλάδα σχεδόν αποκλειστικά. Για την εξασφάλιση μια επαρκούς πειραματικής βάσης, πραγματοποιήθηκαν περισσότερες από 500 δοκιμές εφελκυσμού σε διαβρωμένα και μη διαβρωμένα δοκίμια. Οι μηχανικές δοκιμές εφελκυσμού έδειξαν ότι οι ιδιότητες αντοχής του διαβρωμένου υλικού παρουσιάζουν μικρή μόνο υποβάθμιση. Παρά ταύτα, η μείωση της διατομής των ράβδων του σιδηροπλισμού λόγω βλάβης διάβρωσης οδηγεί σε αύξηση των εφαρμοζόμενων τάσεων, αφού το βάρος των δομικών στοιχείων των κατασκευών προφανώς δεν μεταβάλλεται. Αυτό έχει ως συνέπεια τη σημαντική μείωση των συντελεστών ασφαλείας. Αντίθετα με τις ιδιότητες αντοχής, παρατηρήθηκε μια σημαντική μείωση στην παραμόρφωση θραύσης του διαβρωμένου υλικού. Η παραμόρφωση θραύσης και η ειδική ενέργεια παραμόρφωσης είναι κρίσιμες τεχνολογικές ιδιότητες σε συνθήκες σεισμού. Για την κατανόηση των φυσικών μηχανισμών που συμβάλλουν στην παρατηρούμενη υποβάθμιση των μηχανικών ιδιοτήτων, διεξήχθη εκτενής μεταλλογραφική μελέτη καθώς και μελέτη των επιφανειών θραύσης του διαβρωμένου υλικού. Παρατηρήθηκε ότι η διάβρωση είναι ομοιόμορφη, ενώ κατά το μήκος των δοκιμίων εντοπίστηκαν περιοχές με εντονότερη και άλλες με λιγότερο έντονη διάβρωση. Επιπλέον, η ανάλυση των επιφανειών θραύσης έδειξε πλήρως όλκιμη συμπεριφορά θραύσης των δοκιμίων ακόμη και στο έντονα διαβρωμένο υλικό. Επομένως, μπορεί να εξαχθεί το συμπέρασμα ότι η υποβάθμιση των μηχανικών ιδιοτήτων εφελκυσμού του χάλυβα οπλισμού οφείλεται κυρίως στην ανομοιομορφία που παρουσιάζει η διατομή του σιδηροπλισμού κατά μήκος των ράβδων του υλικού λόγω της βλάβης διάβρωσης, με συνέπεια αφενός την τοπική συγκέντρωση τάσεων και αφετέρου την καταπίεση της ομοιόμορφης παραμόρφωσης κατά τον εφελκυσμό του υλικού. Τέλος, στην εργασία αυτή παρουσιάζεται μια μέθοδος με την οποία προσομοιώνεται η βλάβη λόγω διάβρωσης με μια τεχνητή εγκοπή. Η μέθοδος αυτή στηρίζεται στις παραδοχές ότι η ολκιμότητα του υλικού παραμένει αμετάβλητη λόγω της διάβρωσης και η παρατηρούμενη μείωση στην παραμόρφωση θραύσης οφείλεται στην καταπίεση της ομοιόμορφης παραμόρφωσης λόγω των εγκοπών που προκαλεί η διάβρωση στο υλικό οι οποίες διευκολύνουν τη δημιουργία του λαιμού. Επίσης γίνεται η παραδοχή ότι η παρατηρούμενη μείωση των ιδιοτήτων αντοχής οφείλεται στη συγκέντρωση τάσεων που προκαλούν οι εγκοπές αυτές. Δοκιμές εφελκυσμού σε δοκίμια με εγκοπές γνωστής γεωμετρίας έδειξαν ότι η μέθοδος αυτή μπορεί να χρησιμοποιηθεί με ικανοποιητική ακρίβεια για τον υπολογισμό των ιδιοτήτων εφελκυσμού του υλικού χωρίς την ανάγκη πραγματοποίησης μηχανικών δοκιμών. / Reinforced concrete is currently the most common material used for the construction of the load bearing elements of structures. Although this composite material performs exceptionally well, it has been noted that during the life span of reinforced concrete structures, which often exceeds 100 years, a gradual damage accumulation takes place. One of the most influential factors of this damage has been attributed to the corrosion of steel reinforcement. Recently, the degradation of the load bearing ability of steel reinforcement has been an issue under research by several researchers worldwide. Yet to date, the technological importance of this degradation caused by corrosion damage cannot be assessed to a satisfactory degree, mainly due to the lack of relevant experimental studies. Similarly, the physical mechanisms which contribute to the degradation have not been totally resolved. In the framework of the current PhD thesis, a systematic study of the mechanical behaviour of concrete reinforcing steel bars, corroded both in their natural environment (embedded in concrete) and by means of laboratory accelerated corrosion, was performed. By comparing the mass loss as a function of time recorded during the laboratory corrosion tests with the respective mass loss recorded from naturally corroded samples, an empirical acceleration factor was derived for laboratory corrosion damage compared to natural corrosion damage. Reinforcing steel grades S400* and S500s*, which have been used in the recent past for the reinforcement of concrete structures in Greece, as well as steel grade B500c**, which from the end of 2006 is used almost exclusively, were tested. To obtain a sufficient experimental database more than 500 tensile tests on corroded and non-corroded samples were performed. The tensile tests performed have shown only a slight degradation of the strength properties of the corroded steel bars. However, the reduction of the cross sectional area of the corroded bars lead to an increase of the applied stress, as the loads applied to which steel bars in structures are constant over time. This leads to a significant reduction of the safety factors applied during design. On the contrary, a significant reduction of the material’s ductility properties was recorded. Elongation to failure and strain energy density are crucial properties in the case of alternating loading during earthquakes. In order to understand the physical mechanisms which contribute to the recorded degradation of the mechanical properties, an extensive metallographic investigation as well as an investigation of the fracture surfaces of corroded material was performed. From this investigation it was concluded that corrosion damage is uniform without pitting, while along the bars’ length areas more severe corrosion damage was noted. Furthermore, the investigation of the fracture surfaces showed ductile fracture characteristics even of the most severely corroded specimens. It can therefore be concluded that the degradation of the tensile properties of corroded material is caused mainly by the non-uniformity of the corrosion damage and therefore of the cross sectional area along the longitudinal axis of the bars. This leads to a local stress concentration as well as to the depression of the uniform elongation during the tensile testing of the material. Finally, in the current PhD thesis a method by which corrosion damage can be simulated by a fictitious notch is suggested. This method is based on the assumptions that the ductility of the material remains unaffected by corrosion and the recorded reduction of the ductility properties is attributed to the depression of the uniform elongation caused by notches which are formed on the bars due to corrosion exposure and facilitate necking. In addition, the recorded reduction of the strength properties is attributed to the stress concentration caused by these notches. Tensile tests performed on specimens with artificial notches of known geometry have shown that the suggested method can be used to assess to a satisfactory degree the tensile properties of steel reinforcing bars without the need to perform tensile tests. * Names according to the Hellenic regulations. These steel grades are similar to the StIIIs and StIVs steel grades of the DIN regulations respectively. ** Name according to the Hellenic regulations. It is similar to StIV steel grade but with higher ductility requirements compared to S500s.

Sukamas javų kombaino kūlimo būgnas sukuria oro srautą tarpe tarp būgno ir pobūgnio. Dalis oro nukreipiama pro pobūgnio ardelius. Darbe atlikti oro srauto greičio tarpe tarp kūlimo būgno ir pobūgnio bei pobūgnio ardeliuose tyrimai. Laboratoriniai tyrimai atlikti stacionariu tangentiniu vienbūgniu kūlimo stendu, kurį sudarė 0,6 m skersmens ir 1,2 m pločio aštuonių spragilų tangentinis kūlimo būgnas, kurį 146º kampu gaubė ardelinis pobūgnis. Pateiktos oro srauto greičio tarpe tarp būgno ir pobūgnio bei pobūgnio ardeliuose priklausomybės nuo technologinių ir konstrukcinių kūlimo būgno parametrų. Laboratoriniais tyrimais nustatyta, jog kūlimo būgno konstrukciniai ir technologiniai parametrai sąlygoja būgno sukuriamą oro srautą. Oro srauto greitis didėja pobūgnio galo link. Būgną sukant 350 min-1 dažniu (spragilų linijinis greitis vs=11 m s-1), greičių skirtumas pirmojoje ir trečiojoje pobūgnio dalyse siekia 1 m s-1, o padidinus sukimosi dažnį iki 750 min-1 – apie 3 m s-1. Didinant kūlimo būgno sukimosi dažnį nuo 350 min-1 iki 750 min-1 oro srauto judėjimo greitis tarpe tarp būgno ir pobūgnio bei pobūgnio ardeliuose didėja, tačiau spragilų greičio nepasiekia. Būgno tarpspragiliuose pritvirtinus 8 balastus, oro srauto greitis tarpe tarp būgno ir pobūgnio sumažėjo 10%, o tarpspragilius uždengus dangalais – 37% lyginant su įprastos tarpspragilių konstrukcijos būgnu. Pobūgnio ardeliuose oro srauto greitis atitinkamai sumažėjo 9% ir 33%. Tolimesniais eksperimentiniais tyrimais... [toliau žr. visą tekstą] / The rotation of combine harvester threshing cylinder creates an air flow within threshing crescent, part of which is directed through the openings in the concave. The present work gives the air flow velocity trials within threshing crescent. Experimental studies were carried out with a stationary tangential threshing cylinder stand which consisted of 0.6 m diameter and 1.2 m wide eight rasp bars tangential threshing cylinder which is surrounded by concave with 146º. Air velocity was measured at 56 locations, distributed dependent on construction of concave. The air velocity was measured using a hot wire anemometer unit. The output data was recorded on PC using 10 bit ADC converter. Nine levels of cylinder peripheral speed (from 11.0 ms-1 to 23.6 ms-1) at cylinder-concave clearances of: 36 mm at front, 32 mm in middle, and 20 mm at rear part of concave were used in this experiment. The results of the experiment show that there were significant differences of air velocity among cylinder peripheral speeds and locations. The air velocity increased with increased cylinder peripheral speed and towards the rear of the concave. Air flow velocity within threshing crescent dependence on technological and constructional parameters of the threshing cylinder is presented. Threshing cylinder with mounted 8 ballast and cylinder with covered space between rasp bars creates an air flow, whom velocity was respectively 10% and 37% lower compared with the standard cylinder construction. Air... [to full text]

No description available.

This thesis concerns the occurrence of the large-scale bed and plan forms known as alternate bars and meandering, and the internal structures of the flow associated with their formation. The work is to be viewed as an extension of previous work by da Silva (1991), Yalin (1992), and Yalin and da Silva (2001). As a first step in this work, the criteria for occurrence of alternate bars and meandering of Yalin and da Silva (2001) is re-considered in view of additional field and laboratory data from the recent literature and data resulting from two series of experimental runs carried out in two sediment transport flumes. This leads to a number of modifications of the boundary-lines in the related existence-region diagram of Yalin and da Silva. The size of the largest horizontal coherent structures (HCS’s) of an alternate bar inducing flow was then investigated experimentally on the basis of three series of flow velocity measurements. These were carried out in a 21m-long, 1m-wide straight channel, conveying a 4cm-deep flow. The bed consisted of a silica sand having a grain size of 2mm; its surface was flat. The measurements were carried out using a Sontek 2D Micro ADV. The horizontal burst length was found to be between five and seven times the flow width. The effect of the HCS’s on the mean flow was also investigated. A slight internal meandering of the flow caused by the superimposition of burst-sequences on the mean flow was clearly detectable. Finally, with the aid of three new series of measurements in the same channel, an attempt was made to penetrate the dynamics and life-cycle of the HCS’s. For this purpose, quadrant analysis was used; the cross-sectional distribution of relevant statistical turbulence-related parameters was investigated; and cross-correlations of flow velocity along the flow depth and across the channel were performed. The analysis indicates that the HCS’s originate near the channel banks, with the location of ejections and sweeps being anti-symmetrically arranged with regard to the channel centreline, and then evolve so as to occupy the entire depth of the water and the entire width of the channel. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2010-03-09 10:20:53.596

The non-corrodible nature of FRP bars along with their high strength, light weight and ease of installation made it attractive as reinforcement especially for structures exposed to aggressive environment. In addition, the transparency of FRP bars to magnetic and electrical fields makes them an ideal alternative to traditional steel reinforcement in applications sensitive to electromagnetic fields such as magnetic resonance imaging (MRI) units. Continuous concrete beams are commonly-used elements in structures such as parking garages and overpasses, which might be exposed to extreme weather conditions and the application of de-icing salts. In such structures, using the non-corrodible FRP bars is a viable alternative to avoid steel-corrosion problems. However, the linear-elastic behaviour of FRP materials makes the ability of continuous beams to redistribute loads and moments questionable. The objective of this research project is to investigate the flexural behaviour of continuous concrete beams reinforced with FRP and their capability of moment redistribution. An experimental program was conducted at the University of Manitoba to realize the research objectives. Ten full-scale continuous concrete beams were constructed and tested to failure in the laboratory. The specimens had a rectangular cross-section of 200×300 mm and continuous over two spans of 2,800 mm each. The main investigated parameters were the amount and material of longitudinal reinforcement, the amount and material of transverse reinforcement and the spacing of used stirrups. The experimental results showed that moment redistribution in FRP-reinforced continuous concrete beams is possible if the reinforcement configuration is chosen properly, and is improved by increasing the amount of transverse reinforcement. A finite element investigation was conducted using ANSYS-software. A 3-D model was created to simulate the behaviour of continuous beams reinforced with FRP. The model was verified against the experimental results obtained from the present study. This verified model was used to investigate the effect of the concrete compressive strength, longitudinal reinforcement ratio, midspan-to-middle support reinforcement ratio and the amount of transverse reinforcement on the behaviour of FRP-reinforced beams. The analytical results of this parametric investigation along with the experimental results were used to propose an allowable limit for moment redistribution in FRP-reinforced continuous concrete beams.

This paper describes a study designed to determine average labor and machine times required to implement erosion control and revegetation best management practices (BMPs) for skid trails in Kentucky. Labor and machine activities were recorded for 14,400 feet of skid trail on 10 nonindustrial private logging sites. Water bar construction and reshaping activities such as filling ruts and berm removal were filmed continuously with a video camera and then analyzed using time-motion study techniques. Labor activities for revegetation such as seeding and application of fertilizer were also timed. The average total machine time for retirement activities per 1000 feet was 51 minutes for sites using dozers and 52 minutes for sites using skidders. The average water bar construction time using a bulldozer was 1.5 minutes (n=112) while the average construction time using a skidder was 3.5 minutes (n = 21). The average amount of labor time required to seed 1000 feet of skid trail was 23 minutes (n = 5). Three methods of water bar construction were observed and analyzed to identify differences among them. While there were significant differences among the three methods, the data suggest that skid trail percent slope may have the greatest effect on water bar construction times.