Most models developed for hydraulic fracturing in unconsolidated sands are based on Linear Elastic Fracture Mechanics (LEFM) and tensile fracture (Mode I fracture). However, in unconsolidated sand formations the field data shows that LEFM based models cannot properly predict the fracture behavior. Hydraulic fracture lab experiments in a true triaxial setup which was made as a part of this study are designed to investigate the failure mechanism around the crack tip in unconsolidated sands and effects of fluid rheology, leak off, and stress state are investigated. The results show that two mechanisms of tensile and shear failure are involved in fracture propagation in unconsolidated sands and depending on the fracturing fluid rheology and stress state of the formation one or both of them can happen at the crack tip. Several experiments with different fracturing fluids, rates, and different stress boundary conditions are categorized into two major categories based on whether we have a fracture or not. A subsequent categorization is used to categorize the fractured cases into Tensile Failure, Shear Failure and Mixed Failure categories. First the experimental observations are presented and subsequently observations are analyzed and compared in order to explain the observations and conclusions. ;Tensile failure category is happening in medium viscosity fracturing fluids in the order of 20,000 cP viscosity at unit 1/s shear rate. Shear failure category is mostly taking place in low viscosity fluids (200 cP viscosity at unit 1/s shear rate). Mixed mode fracturing is happening in high viscosity fluids (70,000 cP viscosity at unit 1/s shear rate) with high stress anisotropy. However, the same fluid will give a No Fracture result in the case of isotropic or near isotropic stress state. It is shown that higher stress anisotropy increases the tendency of shear failure and at the same time, the resulting fracture will propagate in a preferential direction. However, tilting and branching might happen due to high stress anisotropy which is more pronounced in case of thicker fluids. It was also observed that in case of vaseline injection, stress anisotropy decreases treatment breakdown pressure. / text

No description available.

No description available.

The large majority of New Zealand's road network is constructed from thin surfaced unbound flexible pavements where a granular layer provides the main structural strength of the pavement. The current New Zealand empirical design theory states that permanent deformation should largely be attributed to the subgrade and that shape loss in the granular layers is simply a consequence of a previously deformed subgrade. However, recent research and field trials have indicated that basecourse shear strains may be a large contributor to rutting in unbound granular layers. The purpose of this investigation was to determine whether the shear strains induced under heavy vehicle loads can be accurately measured using in-situ induction coils and whether the shear strains are related to permanent pavement deformation. In this investigation a rosette configuration of free floating induction coils was designed to measure principal basecourse shear strains. The principal strains were then used to construct Mohr's circle of strain in order to calculate the maximum shear strain occurring in the granular layer. The rosettes were installed in two full scale test pavements at the Canterbury Accelerated Pavement Testing Indoor Facility (CAPTIF). The pavements were loaded with an 8 tonne dual wheel axle load for 1 million and 600,000 load applications respectively and strain and rut depth testing occurred periodically throughout the test life. The research showed that the rosette coil arrangement was a feasible and accurate device for measuring in-situ shear strains in granular pavement layers. Finite element modelling confirmed the accuracy of the system. The results from the two CAPTIF pavements showed that there was a strong linear relationship between the magnitude of the basecourse shear strain and the rut depth at the end of the post construction compaction period. The investigation also showed that shear strain magnitudes in the region of 5000µƐ result in rapid shear failure in the granular layer. In addition, after the post construction compaction period had finished, the rate of change of shear strain was proportional to the rate of change of rut development. The results indicated that there was approximately a 4:1 ratio between the rate of change in rut depth and the rate of change in shear strain after the initial post construction period. Investigations into the effect of load magnitude on the magnitude of the basecourse shear strain showed that a linear relationship existed between the two parameters. Further to this, load location testing revealed that for a dual wheel configuration, 50mm of lateral wheel variation either side of a point of interest was the maximum allowable movement that would result in similar strain measurements. The research highlighted the dominance of the longitudinal tensile strain and shear strain over the vertical compressive strain within granular layers. As a result, these pavement responses should be considered in further granular pavement research in addition to the commonly used vertical compressive strains.

Recent studies showed the need for timber connections with high fire performance. Connections of members in timber structures commonly comprise steel connectors, such as dowels, screws, nails and toothed plates. However, multiple studies have shown that the presence of exposed metal in timber connections leads to a poor performance under fire conditions. Replacing metallic fasteners with non-metallic fasteners potentially enhances the fire performance of timber connections. Previous studies showed that Glass Fibre Reinforced Polymer (GFRP) dowels can be a viable replacement for steel dowels and that Densified Veneer Wood functions well as a flitch plate material. However, as the resin matrix of GFRP dowels is viscoelastic, connection creep, which is not studied before, can be of concern. Also no research has been carried out on the fire performance of these connections. Therefore, a study of the creep behaviour and the fire performance of non-metallic timber connections comprising GFRP dowels and a Densified Veneer Wood flitch plate was performed, as is discussed in this thesis. Predictive models were proposed to determine the connection slip and load bearing capacity at ambient and elevated temperatures and in a fire. The material properties and heat transfer properties required for these models were determined experimentally and predictions of these models were experimentally validated. Furthermore, an adjustment of the predictive model of connection slip at ambient temperature allowed approximating the creep of the connection. The material properties, required for the creep model, were determined experimentally and predictions of the model were compared to results of longterm connection tests. The study confirmed that timber members jointed with non-metallic connectors have a significantly improved fire performance to timber joints using metallic connections. Models developed and proposed to predict fire performance gave accurate predictions of time to failure. It was concluded that non-metallic connections showed more creep per load per connector, than metallic connections. However, the ratio between initial deflection and creep (relative creep) and the ratio between load level and creep were shown to be similar for metallic and non-metallic connections.

Ziel des Folgeantrages war die Entwicklung der photogrammetrischen Messtechnik zur onlinefähigen Anwendung bei In-situ-Belastungsversuchen. Dies wurde mit den in Kapitel 3 beschriebenen Ansätzen erfolgreich umgesetzt. Die gewählte künstliche Texturierung der Bauteiloberflächen stellte sich als sehr geeignet heraus, um bereits kleinste Strukturveränderungen beobachten und visualisieren zu können. Durch die Verwendung einer Industriekamera konnte die onlinefähige Bildanalyse und simultane Darstellung der Ergebnisse auf dem Bildschirm umgesetzt werden. Durch die Verwendung von Dreiecken und der Ermittlung der Hauptverzerrung jedes dieser Dreiecke wurden Bereiche hoher lokaler Dehnungen (Rissentwicklung) frühzeitig detektiert. Diese frühe und automatisierte Erkennung der Rissentwicklung ermöglicht und verbessert die Beurteilung des Tragzustandes des zu untersuchenden Bauteils erheblich. Für die Beurteilung des Tragverhaltens von Stahlbetonbauteilen ohne oder mit zu geringer Bügelbewehrung wurden neben der Photogrammetrie die Schallemissionsanalyse, herkömmliche Verformungsmesstechniken und abschnittsweise Verformungsmessungen mit Neigungssensoren durchgeführt. Es zeigte sich, dass gerade die Kombination dieser Messverfahren zu einer erheblichen Verbesserung der Information über den Tragzustand des untersuchten Bauteils führte.

Railways are one of the largest transportation networks in the world that play an important role in the mass transportation of both the passengers and freight. The speed of trains and as well as the axial load carrying capacity have been increasing significantly during the past few decades to keep in pace with the population and economy growth and to compete with other modes of transportation such as the road, air and water transportation system. Billions of dollars are spent annually for maintenance of rail tracks in the world. The efficient and optimum use of these funds is a challenging task that demands innovative and cutting edge technologies in railway engineering. The railway subgrade is an important part of railway foundation and should be capable of providing a suitable base supporting the ballast and subballast to accommodate the stresses due to traffic loads without failure or excessive deformation. The progressive shear failure is a well-known and age old challenging problem for railways over the world for centuries. The subgrade of railway track which typically constitutes of fine-grained material tends to fail through the accumulation of soil movements up- and sideward developing a path for the least resistance along which progressive shear failure occurs under repeated train-induced loads and due to the effects of climate factors. To-date, limited number of studies have addressed failure mechanism associated with the progressive shear failure, especially using the mechanics of unsaturated soils. In this thesis, a novel and first of its kind, Visual Basic program developed in AutoCAD environment based on Mohr-Coulomb failure criteria and unsaturated soil mechanics theory. This program is capable of taking account of the influence of matric suction and simulate progressive shear failure in the subgrade under moving train. Simulation results suggest several parameters that include stress distribution, matric suction, cohesion, coefficient of lateral earth pressure at rest, and coefficient of residual friction as well as the angle of internal friction have a significant effect on the progressive shear failure and the shape of failure planes in the subgrade. The progressive shear failure in subgrade can be reduced by increasing matric suction, cohesion, coefficient of lateral earth pressure at rest, and coefficient of residual friction as well as the angle of internal friction, and optimizing combination of these parameters. The simulation results suggest the progressive shear failure can be well simulated with the Mohr-Coulomb failure criteria. Several suggestions are made for railway subgrade construction and maintenance based on the results of this study.

No description available.

Impulsive loads have been observed to cause brittle shear failure in reinforced concrete elements designed for ductile failure modes under static loads. Brittle failure modes exhibit poorer energy absorption capabilities compared to ductile flexural failure modes due to their limited deformation capacity, leading to premature failure. The discrepancy between the responses under static and extreme dynamic loads arises from inertia and wave propagation effects, which tend to increase as the load duration decreases relative to the fundamental period of the element.   This thesis investigated the occurrence of shear failures in reinforced concrete elements subjected to impulsive loads, both experimentally and numerically, and evaluated to what extent current analysis methods for impulse-loaded structures can predict shear failure. Furthermore, the study examined the influence of crucial parameters on the energy absorption capacity during flexural failure modes when shear failure was inhibited.   The results demonstrated that shear-plug damage, prevalent during impact loads, may lead to premature shear failure during sequential impact testing. This occurred for a statically flexure-critical beam with a significantly larger static flexural-shear capacity relative to its flexural capacity. Similar conclusions applied to the residual static capacity after an initial impact introduced shear-plug damage. These findings indicate potentially severe consequences of shear-plug damage, which should be considered when assessing structures damaged by impact loads.   The energy absorption capacity of reinforced concrete elements is closely related to the plastic work capacity of the reinforcement. The experimental study showed how the plastic work capacity varied with reinforcement properties, concrete properties, and impact velocity using static and dynamic four-point flexural tests. The results revealed that the reinforcement type, specifically whether the steel is mild or stiff, governs the strain distribution during static and low-velocity impact testing. Generally, stiff steels result in strain localization before rupturing, indicating a lower plastic work capacity. Factors such as stress and strain capacity also proved significant. However, as the impact velocity increased, wave propagation effects governed strain distribution rather than reinforcement type.    Numerical studies comparing results with outcomes using proposed design methods indicated agreement for support reactions used to verify the shear capacity in the later stages of the response. However, this agreement decreased in the initial stages of the response. This may be because the dynamic equilibrium method only considers a global response, while the local response due to wave propagation is influential in the initial stages of the response. Today, resources such as Biggs [8] and the Swedish Fortifications Agency [86] recommend using two stages of the response to determine the internal forces; an elastic global response and a later elastoplastic global response. From the observations in the papers, it is suggested to add a third initial stage of the response considering wave propagation effects. However, it is deemed that this response stage only has a significant effect for high-intensity blast loads with short rise times relative to the shear wave velocity. / Impulsiva laster har i litteraturen visats leda till spröda skjuvbrott for armerade betongelement designade for mjuka brott under statiska laster. Spröda brottmoder påvisar sämre energiupptagande förmågor jämfört med mjuka böjbrott på grund av dess lägre deformationskapacitet, vilket resulterar i tidigt brott. Skillnaden i respons under statisk och dynamisk belastning kommer från tröghetskrafter och vågutbredningseffekter, där effekten av båda ökar med en minskande lastvaraktighet i relation till fundamentala perioden av elementet.   Det här arbetet undersöker förekomsten av skjuvbrott under impulsiva laster experimentellt och med numeriska analyser. Hur väl befintliga beräkningsmetoder kan förutspå skjuvbrott utvärderas aven. Dessutom studeras effekten av viktiga parametrar på den energiupptagande förmågan när skjuvbrott hämmas.   Resultaten påvisade att skjuv-plugg-skada, allmänt förekommande under stötbelastning, kan leda till tidigt skjuvbrott under sekventiell stötbelastning. Detta förekom for en statiskt böj-kritisk balk med en markant högre skjuvkapacitet relativt till dess böjkapacitet. Liknande slutsatser kunde dras vid provning av den statiska residualhållfastheten efter att ett initiellt fallviktsförsök introducerade skjuv-plugg-skada. Dessa resultat indikerar potentiellt allvarliga konsekvenser av skjuv-plugg-skada, vilket bör beaktas vid bedömning av element skadade från stötbelastning.   Den energiupptagande förmågan hos armerade betongelement är nära relaterat till det plastiska arbetet som armeringen kan utföra. Den experimentella studien visade hur kapaciteten for plastiskt arbete hos armeringen berodde på armeringsegenskaperna, betongegenskaperna samt anslagshastigheten hos massan vid statisk och dynamisk fyrpunktsbelastning. Resultaten visade att armeringstypen, mer specifikt ifall stålet var mjukt eller styvt, styrde töjningslokaliseringen under statisk belastning samt dynamisk belastning med låg anslagshastighet. Generellt sett resulterade styvare stål i töjningslokalisering när stålet slets av, vilket ledde till en mindre kapacitet for plastiskt arbete hos armeringsstången. Faktorer som töjnings- och spänningskapaciteten visades även vara betydande. Däremot indikerade resultaten att allt eftersom anslagshastigheten ökade så var vågutbredningseffekter det som bestämde grad av töjningslokalisering, och inte styvheten hos stålet.   Numeriska studier där resultat jämfördes mot resultat från rekommenderade designmetoder indikerade överenskommelse för stödreaktioner som används för att verifiera skjuvkapaciteten i ett senare skede av responsen. Däremot så var överenskommelsen sämre i ett tidigare skede av responsen. Detta kan möjligen förklaras av att den dynamiska jämviktsmodellen endast tar hänsyn till den globala responsen, medans lokal respons från vågutbredning är dominerande tidigt. Idag använder referenser som Biggs [8] och Fortifikationsverket [86] två stadium av responsen for att bestämma interna krafter; ett globalt elastiskt stadie och ett globalt elasiskt-plastiskt stadie. Från observationer i artiklarna så rekommenderas det att ett tredje initiellt stadie som beaktar vågutbredningseffekter bör inkluderas. Detta stadie anses dock bara visa markant effekt for intensiva stötvågsbelastningar med kort stegtid relativt till skjuvvågshastigheten i materialet. / <p>QC 230828</p>

This paper presents test results and code predictions of four continuously and two simply supported concrete slabs reinforced with basalt fibre reinforced polymer (BFRP) bars. One continuously supported steel reinforced concrete slab was also tested for comparison purposes. All slabs tested were 500 mm in width and 150 mm in depth. The simply supported slabs had a span of 2000 mm, whereas the continuous slabs had two equal spans, each of 2000 mm. Different combinations of under and over BFRP reinforcement at the top and bottom layers of slabs were investigated. The continuously supported BFRP reinforced concrete slabs exhibited larger deflections and wider cracks than the counterpart reinforced with steel. Furthermore, the over reinforced BFRP reinforced concrete slab at the top and bottom layers showed the highest load capacity and the least deflection of all BFRP slabs tested. All continuous BFRP reinforced concrete slabs failed owing to combined shear and flexure at the middle support region. ISIS-M03-07 and CSA S806-06 design guidelines reasonably predicted the deflection of the BFRP slabs tested. However, ACI 440-1R-06 underestimated the BFRP slab deflections and overestimated the moment capacities at mid-span and over support sections.