The UK Department of Transport (DoT) has recently encouraged the use of externally post-tensioned structures for bridge construction. This is due to the durability problems encountered with the conventional internally bonded post-tensioned structures. However, due to the lack of bond between the concrete and the external tendons, the ultimate strength of these structures cannot be determined by just performing a sectional analysis at the section of maximum moment. Although several recommendations have been made for the ultimate analysis of these structures, none were considered satisfactory here. Hence the purpose of this investigation is to study the flexural behaviour of these structures of all stages up to collapse, and to propose a practical methodology for estimating their ultimate strength. The study introduces eight non-linear analytical models developed for the prediction of the moment vs. deflection response of simply supported externally post-tensioned beams (with and without deviators located along their spans) up to ultimate. The models employ an iterative procedure that involves the application of loads to the structure in increments up to the collapse condition, where the curvature distribution predicted at each loading sequence is used to estimate the stress increase and variation in eccentricity in the external tendons. Second-order effects due to variation in eccentricity of external tendons and frictional behaviour of tendons at the deviators are both taken into account in these models. The eight models were then verified by comparing the results derived from them with reported experimental data, whereby good correlation was obtained. An extensive parametric study was subsequently conducted using the proposed models applied to the various parameters that influence the ultimate behaviour of externally prestressed structures Finally, the recommendations in the codes of practice for the ultimate design of these structures were also investigated here.

Thesis (Professional Degree)--University of Missouri, School of Mines and Metallurgy, 1932. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed July 15, 2010) Includes index (p. 29-31).

A detailed investigation was made to study the shear transfer between precast prestressed beams and in-situ concrete in a relatively new method of construction of continuous bridge decks where the ends of precast beams are connected to an integral in-situ crosshead away from the supports. Two series of tests were carried out. In the first series 1/3 scale models of the M. o. T, C&CA M-8 sections were used, and these were modified in the second series to study the effect of the beam's top flanges within the connection. One of the most important mechanisms of shear transfer proved to be the top flanges of the precast beam. For the precast beams with top flanges (first series), and with a 300mm beam embedment length, it was discovered that: a) The shear force is transferred from a small length at the end of the beam. b) The in-situ concrete nibs (concrete surrounding the web) can take this shear force without stirrups. c) There is no need either to project all the bars from the precast into the in-situ concrete or to prestress the connection transversely as a means of improving shear transfer. d) It was possible to transfer the whole shear force at the connection with a reduced embedment length of 100mm with nib stirrups. For the precast beam without top flanges, the transfer of the shear force at the connection required other improving details. In this respect transverse prestressing and web shear connectors were utilized effectively. The effect of projecting bars was also examined. In the general behaviour of composite continuous beams subjected to shear a detailed comparison was made between different Code predictions for the web cracking shear and web crushing strength. A mathematical model is also proposed to predict the stirrup stress according to shear span, effective depth and stirrup ratio when failure is controlled by web crushing. Stirrup stress measurement in the vicinity of continuous support made it possible to predict the enhanced shear strength and a design method is proposed for the continuous beams. A comparion is also made between different Code predictions in this respect. To obtain more information about the strength of web shear connectors used in the secod series, a separate dowel shear specimen was designed. Different interface conditions including bond, dowel bar size and strength and the effect of shrinkage were examined. A design method is proposed together with a comparison with different Code predictions.

This thesis deals with prefabricated composite bridges in general, and prefabricated concrete deck elements with dry joints in particular.As outlined in Paper I and Chapter 2 prefabrication has several advantages over in situ construction, and has hence been discussed for decades in the construction business. Further, the house building sector has taken large steps towards a more industrialized approach, in which prefabrication, lean thinking and Building Information Modelling (BIM) are all important components. Numerous studies have also examined the applicability of such an approach in the bridge sector, and several types of prefabrication techniques have been tested. Nevertheless, in many countries the bridge sector seems to lag far behind in the general shift towards more industrialized construction processes. One of the reasons for the relatively slow progress may be the fact that bridges are often unique objects with unique specifications and constraints. This hinders the standardisation that is often regarded as a key to industrialised construction.Chapter 2-3 and Paper I, presents evidence from a literature review together with information gathered from a Workshop, attended by bridge designers and researcher in Europe and the US, that prefabricated deck elements are still quite rarely used in bridge construction. Deck elements with dry transverse joints are even rarer. Few examples have been reported. In addition, the degree of prefabrication and the rate of progress towards more industrialised construction processes seem to vary substantially from one country to another.However, as described in Chapter 3 and Paper II, a prefabricated concrete deck element system with dry joints has been developed in Sweden for constructing composite bridges. The transverse joints are completely dry, and all forces are transferred by contact pressure between concrete surfaces. This implies that no tensional forces can be transferred over the transverse joints. Shear forces are transferred by overlapping concrete shear keys, designed as a series of male-female connections. The research presented in this thesis is focused on the structural behaviour of this deck element system. In order to investigate this, laboratory tests have been performed as well as field monitoring.Results of large-scale laboratory tests, presented in Chapter 4 and Paper V, show that a bridge of this type is less stiff than a similar bridge with an insitu cast deck slab. The concrete elements’ contributions to stiffness are negligible in sections with hogging moments, but make some contribution to global stiffness in sections with sagging moments. At moderate load levels, the interacting concrete area is much smaller than in a similar in-situ cast section. This is believed to be due to the combined effects of small gaps in the joints and continuous in-situ cast concrete in the injection channels.After the channels have been injected, existing gaps will be more or less permanent, since the in-situ cast concrete must be compressed up to a certain limit before the rest of the joint will be closed. Destructive testing showed that the differences in stiffness and stresses between a deck of this type and an in-situ cast bridge deck are much smaller in the ultimate limit state. In this case it could even be reasonable to design a cross-section according to Eurocodes, neglecting effects of the joints.As shown in Chapter 5 and Paper III, the overlapping shear keys are a critical detailing in this deck system. Therefore, they were tested in the laboratory to determine how they fail and evaluate their load capacity. The tests revealed two failure modes. The first is a rather ductile failure, activating the shear reinforcement. This was the expected failure mode for shear keys of this design. The second failure mode observed was a quite brittle failure in the concrete covering layer. It has only been observed in small-scale tests, and might be related to the test set-up. Nevertheless, overlapping of the rebars in the male-female shear key connection is strongly recommended to assure the robustness of shear transfer if failure occurs in the concrete covering layer.To complement the laboratory tests, a single span bridge was monitored in the field (Chapter 6 and Paper IV). The bridge was built in 2000, using the prefabricated deck system that this thesis is focusing on, and was tested in both 2001 and 2011. The tests, and subsequent Finite Element analyses, showed that under moderate loading the interacting concrete area is smaller than for a similar in-situ cast bridge. No significant long-term effects were observed, except that under eccentric loading the distribution of the deflection between the girders decreased slightly during the 10 years between tests. This indicates that the joint gaps may have narrowed and at least partly closed during this time.Chapter 7 summarises the research and presents recommendations for dealing with general issues related to the design and construction of a bridge of this type. The design methods are generally the same as for a conventional composite bridge with an in-situ cast deck slab. However, the Eurocodes require some modification for the design of prefabricated deck elements with dry joints, particularly regarding global analysis and the resistance of cross-sections. Finally, conclusions, a general discussion and suggestions for further research are presented in Chapter 8. / Denna avhandling behandlar ämnet prefabricerade samverkansbroar i allmänhet och prefabricerade betongelementfarbanor med torra fogar i synnerhetPrefabricering är ett ämne som har diskuterats i byggbranschen under de senaste decennierna. Husbyggnadsindustrin har gjort stora framsteg i riktning mot ett mer industriellt tänkande, i vilket prefabricering, Lean och BIM är viktiga pusselbitar. Även i brobranschen har mängder med forskningsprojekt utförts runt om i världen och flertalet olika prefabricering lösningar har testats genom åren. Trots detta så förefaller det så att brobranschen ligger lång efter i utvecklingen mot en mer industrialiserad byggprocess. Den långsamma utvecklingen kan till viss del förklaras av att varje bro ofta är ett unikt objekt med unika förutsättningar. Detta utgör ett hinder mot standardisering vilket ofta är beskrivet som nyckeln till industrialiserat byggande.En litteratur studie kompletterad med en Workshop, för insamling av information och erfarenheter från brokonstruktörer och forskare i Europa och USA, visar att prefabricerade farbaneelement fortfarande är ganska ovanliga på den globala byggmarknaden. Farbaneelement med torra fogar förefaller vara extremt ovanliga, enbart ett fåtal exempel har påträffats i litteraturstudien. Prefabriceringsnivån och utvecklingstakten mot ett mer industriellt byggande varierar mycket från ett land till ett annat. (Paper I och Kapitel 2-3)För samverkansbroar har ett prefabricerat farbanesystem med torra fogar mellan betongelementen utvecklats i Sverige. De tvärgående fogarna är helt torra och all kraft överförs genom kontakttryck mellan olika betongytor. Detta medför att inga dragkrafter alls kan överföras genom fogen. Tvärkrafterna överförs genom överlappande betongklackar som är utformade som en serie av hane-hona kopplingar. Forskningen som presenteras i denna avhandling är fokuserad på konstruktionens strukturella beteende. Detta beteende har undersökts via labbtester såväl som genom fältförsök. (Paper II och Kapitel 3)Storskaliga labbtester visar att en bro av denna typ är mindre styv än en liknande bro med en plastgjuten farbaneplatta. I områden med negativt böjmoment är betongelementens bidrag till styvheten försumbart. I områden med positivt böjmoment bidrar betongelementen till den globala styvheten. Vid måttlig belastning är dock den medverkande betongarean avsevärt mindre än i en motsvarande platsgjuten konstruktion. Detta orsakas förmodligen av de små glipor som finns i fogarna, i kombination med det faktum att de injekterade kanalerna är kontinuerliga över elementskarvarna. Detta medför att de initiala fogöppningarna mer eller mindre blir permanenta då kanalen injekteras, eftersom den injekterade betongen i kanalen måste tryckas samman till en viss gräns innan den resterande delen av fogen stängs. Förstörande provning visar dock att skillnaderna i spänningar och styvhet är avsevärt mindre i brottgränstillståndet. Det är därför rentav rimligt att utföra tvärsnittskontroller, i brottgränstillstånd, i enlighet med de regler som anges i Eurokoderna och därmed försumma de effekter som fogarna ger upphov till. (Paper V och Kapitel 4)De överlappande betongklackarna är en väsentlig detalj i det aktuella prefabriceringssystemet. Dessa klackar har därför testats i ett laboratorium för att för utreda hur de går i brott samt vilken last kapacitet som de har. Testerna resulterade i två olika typer av brott. Den första typen av brott aktiverade skjuvarmeringen, vilket resulterade i ett tämligen duktilt brott. Denna var även det förväntande brottscenariot och tämligen i linje med de dimensionerings metoder som föreslås för denna typ av betongklackar. Den andra typen av brott som observerades var ett tämligen sprött brott i betongens täckskikt. Denna typ av brott har enbart observerats i dessa labbtester och är möjligen relaterad till utformningen av testriggen. Det rekommenderas dock starkt att utforma armeringen i klackarna så att armeringsjärnen i hona-hane överföringen överlappar varandra. Detta för att säkerhetsställa en residualhållfasthet för skjuvöverföringen även efter ett eventuellt brott i betongens täckskikt i klackarna. (Paper III och Kapitel 5)Som ett komplement till labbtesterna har fältförsök utförs på en enspannsbro. Den aktuella bron byggdes år 2000 med den prefabriceringsteknik som denna avhandling behandlar och har instrumenterats såväl år 2001 som 2011. Även dessa tester och de efterföljande FE-analyserna visar att den medverkande betongarean, under måttlig belastning, är klart mindre än den medverkande arean för en platsgjuten betongfarbana. Inga väsentliga långtidseffekter har kunnat observeras. Enbart nedböjningsfördelningen mellan balkarna, vid excentrisk last, har minskat en del efter 10 år. Denna skillnad kan indikera att fog öppningarna var större år 2011, dessa kan åtminstone delvis ha stängts under den tid som förlöpt mellan testen. (Paper IV och Kapitel 6)Huvuddelen av denna avhandling avslutas med ett kapitel som summerar den utförda forskningen genom att presentera råd och förslag på hur det går att hantera generella konstruktions- och produktions-frågor för en bro av denna typ. Dimensioneringsmetoderna är i regel de samma som för en konventionell samverkansbro med platsgjuten farbana. För denna typ av prefabricerade farbaneelement finns det dock vissa områden där dimensioneringsreglerna i Eurokoderna bör modifieras eller rentav ändras. Systemanalys och tvärsnittskontroll är två av de dimensioneringssteg där reglerna i Eurokoderna bör modifieras en del. (Kapitel 7)

No description available.

The inverted-T bridge system is a rapid bridge construction technique that consists of precast inverted-T girders placed adjacent to one another and covered with a cast-in-place deck. This system was first implemented in the U.S. by the Minnesota Department of Transportation (Mn/DOT). This research focuses on improving the constructability of the Mn/DOT system while maintaining the system's structural performance characteristics. To accomplish this goal, five sub-assemblage specimens were cast and tested in the structures laboratory at Virginia Tech. These tests focused on identifying an improved precast girder geometry and transverse sub-assemblage connection for this system. From this study it was found that all of the proposed specimens behaved adequately at service load and strength. From these results, it is recommended to further evaluate a specimen with a tapered profile and no physical connection between precast girders for use in a Virginia Department of Transportation bridge near Richmond, VA. / Master of Science

Accelerated bridge construction methods are being progressively used to construct and replace bridges in North America. Unlike traditional bridge construction methods, accelerated bridge construction methods allow bridges to be built in a shortened period of time on the construction site. These methods reduce the road closure time and the traffic disruption that are associated with bridge construction. One of these methods is carried out by prefabricating the bridge elements offsite and then assembling them onsite in a time-efficient way to build the bridge. This construction method can be used to build steel-precast composite bridges, where steel plate girders are connected to full-depth precast concrete deck panels. For the expeditious construction of composite bridges, a proper shear connection detail is needed to develop composite action between the steel plate girders and the precast concrete deck panels. This research project investigated two types of shear connection that would accelerate the construction of steel-precast composite bridges. First, finite element analysis was used to study the behaviour of composite bridge girders with panel end connections. The girders were analyzed for their load-displacement behaviour, cross-sectional stress and strain profile, and connection force distributions. Secondly, experimental push tests were conducted to study the load-slip behaviour of bolted connections. The effects of steel-concrete interface condition, bolt diameter and bolt tension on the shear capacity of bolted connections were analyzed. Based on the finite element analysis results, it is concluded that the panel end connected girder exhibited strong composite action at service and ultimate load. The level of composite action decreased slightly when the panel end connection stiffness was reduced by a factor of ten. Based on the experimental results, it is concluded that the total shear capacity of the bolted connection is the sum of the friction resistance and the bolt dowel action resistance. The friction resistance of the connection depends on the interface condition and the bolt clamping force. An analytical model that can predict the ultimate shear capacity of bolted connections has been developed and recommended. The proposed model is shown to give reliable predictions of the experimental results. It should be noted that bolted connections exhibit good structural redundancy because the bolt fracture failures do not happen simultaneously.

A full-depth precast concrete deck system presents several safety, timeline, and cost benefits to the process of constructing a bridge, however the relevant professional codes do not provide dependable design models due to the limited amount of research conducted on the subject. One area lacking design direction is the development of a shear connection between the full-depth precast deck and a precast concrete girder via a pocket-haunch-connector system. Push-off tests are performed to investigate the effects of various pre- and post-installed shear connectors, haunch height, surface roughness, grouping effects, and grout composition as compared to cast-in-place specimens. The experimental results are presented along with a method for normalizing the variations of results by connection yield strength. This method is used to evaluate each connector type and connection parameter investigated. Ensuring sufficient shear reinforcement within the beam near the shear connector anchorage is found to be a vital aspect of holistic design. A simplified design procedure is outlined, the design connection forcedisplacement behavior is shown, and an example problem is solved. Recommendations for additions and modifications to current code and practice are prescribed.

Accelerated bridge construction methods are being progressively used to construct and replace bridges in North America. Unlike traditional bridge construction methods, accelerated bridge construction methods allow bridges to be built in a shortened period of time on the construction site. These methods reduce the road closure time and the traffic disruption that are associated with bridge construction. One of these methods is carried out by prefabricating the bridge elements offsite and then assembling them onsite in a time-efficient way to build the bridge. This construction method can be used to build steel-precast composite bridges, where steel plate girders are connected to full-depth precast concrete deck panels. For the expeditious construction of composite bridges, a proper shear connection detail is needed to develop composite action between the steel plate girders and the precast concrete deck panels. This research project investigated two types of shear connection that would accelerate the construction of steel-precast composite bridges. First, finite element analysis was used to study the behaviour of composite bridge girders with panel end connections. The girders were analyzed for their load-displacement behaviour, cross-sectional stress and strain profile, and connection force distributions. Secondly, experimental push tests were conducted to study the load-slip behaviour of bolted connections. The effects of steel-concrete interface condition, bolt diameter and bolt tension on the shear capacity of bolted connections were analyzed. Based on the finite element analysis results, it is concluded that the panel end connected girder exhibited strong composite action at service and ultimate load. The level of composite action decreased slightly when the panel end connection stiffness was reduced by a factor of ten. Based on the experimental results, it is concluded that the total shear capacity of the bolted connection is the sum of the friction resistance and the bolt dowel action resistance. The friction resistance of the connection depends on the interface condition and the bolt clamping force. An analytical model that can predict the ultimate shear capacity of bolted connections has been developed and recommended. The proposed model is shown to give reliable predictions of the experimental results. It should be noted that bolted connections exhibit good structural redundancy because the bolt fracture failures do not happen simultaneously.

Disturbance from engineering works is an increasing problem in terrestrial and marine ecosystems throughout the world. Many reported declines in population size, breeding success and body condition have been diagnosed as the result of anthropogenic disturbance, however little is known about the effect of long-term disturbance from large-scale engineering works. Understanding the mechanisms by which animals respond to anthropogenic activities is fundamental to explaining interactions, and resolving potential conflicts between humans and wildlife. This thesis focuses on the factors affecting the habitat use and foraging decisions in wintering shorebirds and wildfowl. The first half of this thesis considers the direct and indirect impacts on waterbirds of a major engineering project in central Scotland; construction of the new Clackmannanshire Bridge at Kincardine-on-Forth. For individual bird species in close proximity to the bridge site, round-the-clock construction work had consequences ranging from neutral to considerably negative. Cormorant Phalacrocorax carbo declined in the area, probably as a result of the disturbance of an important low tide roost. Redshank Tringa totanus, previously abundant in the prey-rich areas adjacent to the construction site, were displaced into poorer areas for most of the construction period; where they may also have suffered from increased interference competition and elevated risk from raptorial predators. Some positive effects of industrial development were also revealed; radio-transmitters combined with tilt-switch posture sensors indicate that Redshank were able to capitalise on the improved nocturnal visibility in areas around Grangemouth docks to assist with foraging and predator detection. Evidence is presented that birds switched foraging strategy (from sight to touch feeding) depending on ambient light levels; whereby artificial light was used in a similar manner to moonlight to assist with prey detection. Redshank also avoided riverine areas at night that were used frequently by day, probably in response to an elevated threat from nocturnal predators. As the predator landscape changes from day into night, birds adopt different strategies to minimise the risk from nocturnal predators. It is clearly important, therefore, that information on nocturnal distributions is available to inform decisions on site management, especially where anthropogenic activity continues throughout the diel cycle. Behavioural decisions were shown to vary widely within a species depending on individual state, metabolic demands and previous exposure to human disturbance. Prey resources were shown to change dramatically over the course of a winter. In response to this decline, the home range of Redshank contracted over a winter season. Similarly, animals responded less and took greater risks in response to experimental disturbance events later in the winter than earlier in the winter, and on days when the temperature was lower. This effect was strongest for individuals occupying heavily disturbed areas, which were possibly already compensating for lost feeding time and a negative energy balance. The results were consistent with the hypothesis that those individuals that respond most obviously to human disturbance were those least likely to suffer fitness consequences. This is the opposite from what is commonly assumed when behaviour is used as an index of disturbance impacts, most notably in the use of flush distance in the design of wildlife buffer zones. In conclusion, this study demonstrated various negative impacts of disturbance, including local displacement, due to construction activity on overwintering waterbirds. It also revealed two key, but poorly understood, phenomena relating to mechanisms for coping with anthropogenic disturbance: routine utilisation of artificial light to extend night-time feeding opportunities amongst Redshank and an adaptive flexibility in escape responses across a range of species under varying conditions of risk.