Not available / text

This thesis addresses the topic of local bond behaviour in RC structures. The mechanism of bond refers to the composite action between deformed steel reinforcing bars and the surrounding concrete. Bond behaviour is an open research topic with a wide scope, particularly because bond it is such a fundamental concept to structural engineers. However, despite many bond-related research findings having wide applications, the primary contribution of this research is an experimental evaluation of the prominent features of local bond behaviour and the associated implications for the seismic performance of RC structures. The findings presented in this thesis attempt to address some structural engineering recommendations made by the Canterbury Earthquakes Royal Commission following the 2010-2011 Canterbury (New Zealand) earthquake sequence. A chapter of this thesis discusses the structural behaviour of flexure-dominated RC wall structures with an insufficient quantity of longitudinal reinforcement, among other in situ conditions, that causes material damage to predominantly occur at a single crack plane. In this particular case, the extent of concrete damage and bond deterioration adjacent to the crack plane will influence the ductility capacity that is effectively provided by the reinforcing steel. As a consequence of these in situ conditions, some lightly reinforced wall buildings in Christchurch lost their structural integrity due to brittle fracture of the longitudinal reinforcement. With these concerning post-earthquake observations in mind, there is the underlying intention that this thesis presents experimental evidence of bond behaviour that allows structural engineers to re-assess their confidence levels for the ability of lightly reinforced concrete structures to achieve the life-safety seismic performance objective the ultimate limit state. Three chapters of this thesis are devoted to the experimental work that was conducted as the main contribution of this research. Critical details of the experimental design, bond testing method and test programme are reported. The bond stress-slip relationship was studied through 75 bond pull-out tests. In order to measure the maximum local bond strength, all bond tests were carried out on deformed reinforcing bars that did not yield as the embedded bond length was relatively short. Bond test results have been presented in two separate chapters in which 48 monotonic bond tests and 27 cyclic bond tests are presented. Permutations of the experiments include the loading rate, cyclic loading history, concrete strength (25 to 70 MPa), concrete age, cover thickness, bar diameter (16 and 20 mm), embedded length, and position of the embedded bond region within the specimen (close or far away to the free surface). The parametric study showed that the concrete strength significantly influences the maximum bond strength and that it is reasonable to normalise the bond stress by the square-root of the concrete compressive strength, √(f'c). The generalised monotonic bond behaviour is described within. An important outcome of the research is that the measured bond strength and stiffness was higher than stated by the bond stress-slip relationship in the fib Model Code 2010. To account for these observed differences, an alternative model is proposed for the local monotonic bond stress-slip relationship. Cyclic bond tests showed a significant proportion of the total bond degradation occurs after the loading cycle in the peak bond strength range, which is when bond slip has exceeded 0.5 mm. Subsequent loading to constant slip values showed a linear relationship between the amount of bond strength degradation and the log of the number of cycles that were applied. To a greater extent, the cyclic bond deterioration depends on the bond slip range, regardless of whether the applied load cycling is half- or fully-reversed. The observed bond deterioration and hysteretic energy dissipated during cyclic loading was found to agree reasonably well between these cyclic tests with different loading protocols. The cyclic bond deterioration was also found to be reasonably consistent exponential damage models found in the literature. This research concluded that the deformed reinforcing bars used in NZ construction, embedded in moderate to high strength concrete, are able to develop high local bond stresses that are mobilised by a small amount of local bond slip. Although the relative rib geometry was not varied within this experimental programme, a general conclusion of this thesis is that deformed bars currently available in NZ have a relative rib bearing area that is comparatively higher than the test bars used in previous international research. From the parametric study it was found that the maximum monotonic bond strength is significant enhanced by dynamic loading rates. Experimental evidence of high bond strength and initial bond stiffness generally suggests that only a small amount of local bond slip that can occur when the deformed test bar was subjected to large tension forces. Minimal bond slip and bond damage limits the effective yielding length that is available for the reinforcing steel to distribute inelastic material strains. Consequently, the potential for brittle fracture of the reinforcement may be a more problematic and widespread issue than is apparent to structural engineers. This research has provided information that improve the reliability of engineering predictions (with respect to ductility capacity) of maximum crack widths and the extent of bond deterioration that might occur in RC structures during seismic actions.

This thesis concerns the development of alternate bars under steady state flows. The movable bed is flat at the beginning of the experiment; the bars reach their equilibrium or developed state at the time Td. The thesis has two objectives. The first is to introduce new equations for the geometric characteristics, namely height and length, of alternate bars at the fully developed stage, and to evaluate them against the existing equations. The second objective is to present the results of two series of experiments carried out to characterize the process of development of alternate bars and obtain estimates of their time of development. The data resulting from these experiments are intended as a foundation for future work towards the establishment of a predictive equation for the development time of alternate bars. The new equations for bar height and length rest on dimensional considerations and all the available data. Bars produced under rough turbulent and transitional flows are treated separately. The proposed equations are found to consistently give more accurate estimates of alternate bar dimensions than existing equations. The experiments to quantify the time of development of alternate bars are carried out in the 21 m long, 0.76 m wide sediment transport flume of the Queen’s Coastal Engineering Laboratory. In addition to providing estimates of the time of development of alternate bars, these experiments reveal aspects of the process of development of alternate bars that had not been reported previously. In particular, they show that, all other conditions being the same (including the sediment transport capacity of the initial flow), the more pronounced alternate bars formed under shallower flows develop faster than less pronounced bars formed under deeper flows. The findings of this study highlight the fact that the previously unexplained wide variation in alternate bar dimensions is related to the plotting position of the data point in the alternate bar existence region of Ahmari and da Silva (2011). This study also sheds light on the evolution and development of alternate bars, which establishes a strong foundation for future studies on the topic. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2014-03-30 16:27:07.025

Within the middle McMurray exposures along the Steepbank River (Steepbank River Outcrops 3 and 4), nine recognized facies can be divided into three genetically related groups: sand-dominated facies, inclined heterolithic stratification (IHS) facies and mixed heterolithic facies. Together, these facies are interpreted to represent a fluvially dominated, tidally influenced point bar that experienced strong seasonal variation in river discharge. Annual fluctuations between river-flood stage and low-flow stage are responsible for the deposition of fluvially dominated sand beds alternating with brackish, tidally influenced mud beds that cover the point-bar surface as members of the various IHS facies. The dichotomy of fluvially dominated sand deposition and brackish-water ichnology of the mud beds represents the annual migration in position of the tidal and salinity nodes caused by fluctuations in fluvial discharge. Recognition of metre-scale cycles (MSCs) of alternating sandier and muddier intervals within the IHS facies imply that decadal climate cycles, likely caused by fluctuations in ocean and/or solar dynamics, influenced point-bar deposition. These MSC packages are defined by an upward decrease in sand-bed thickness, an upward increase in mud-bed frequency, and an upward increase in bioturbation intensity, all occurring on a metre scale. MSCs are an important architectural element of these large-scale tidal-fluvial point bars because they are predictable, repeatable and continuous around the point bar. Analysis of paleocurrents relative to inclined-heterolithic-stratification bedding planes indicates that bend-flow modifications (BFMs) were effective in redistributing flow around the point bar. Furthermore, this suggests that Outcrop 3 is representative of an upstream-to-bend-apex transition within a large-scale point-bar planform. Recognition of multiple channels at Outcrop 4 was based on large-scale erosional truncation, IHS bed-orientation changes, large cumulative thicknesses of the middle McMurray, thick sand-package thicknesses, changes in relative scale of sedimentary structures, and the occurrence of large mud clasts. Similarities in depositional expression between channels suggest autogenic channel stacking (within-valley stacking), rather than the stacking of separate valleys. Finally, discordant paleocurrents within the basal sand-dominated facies are likely representative of amalgamated channel-bottom facies from several generations of channel. This suggests that only the upper intervals of basal sand-dominated facies are genetically linked to the overlying IHS facies. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2012-01-30 13:25:32.53

No description available.

No description available.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Reinforced concrete beam-column joints (BCJs) are commonly used in structures such as parking garages, multi-storey industrial buildings and road overpasses, which might be exposed to extreme weathering conditions and the application of de-icing salts. The use of the non-corrodible fiber-reinforced polymer (FRP) reinforcing bars in such structures is beneficial to overcome the steel-corrosion problems. However, FRP materials exhibit linear-elastic stress-strain characteristics up to failure, which raises concerns on their performance in BCJs where energy dissipation, through plastic behaviour, is required. The objective of this research project is to assess the seismic behaviour of concrete BCJs reinforced with FRP bars and stirrups. An experimental program was conducted at the University of Manitoba to participate in achieving this objective. Eight full-scale exterior T-shaped BCJs prototypes were constructed and tested under simulated seismic load conditions. The longitudinal and transversal reinforcement types and ratios for the beam and the columns were the main investigated parameters. The experimental results showed that the GFRP reinforced joints can successfully sustain a 4.0% drift ratio without any significant residual deformation. This indicates the feasibility of using GFRP bars and stirrups as reinforcement in the BCJs subjected to seismic-type loading. It was also concluded that, increasing the beam reinforcement ratio, while satisfying the strong column-weak beam concept, can enhance the ability of the joint to dissipate seismic energy. An analytical investigation was conducted through constructing a finite element model using ANSYS-software. The model was verified against the experimental results in this research. Then, a parametric study was performed on number of different parameters known to affect such joints including column axial load, concrete compressive strength, flexural strength ratio and joint transverse reinforcement. It was concluded that 70% of the column axial load capacity can be recommended as an upper limit to the applied axial loads on the column to avoid damage occurrence within the joint. It was also concluded that a minimum flexural strength ratio of 1.50 is recommended to ensure the strong-column weak-beam mechanism. In addition, a minimum joint transverse reinforcement ratio of 0.60% is recommended to insure that the failure will not occur in the joint zone.

Aramid fiber reinforced polymer (AFRP) composite materials show promise for prestressed concrete bridge applications. However, there are still some knowledge gaps due to lack of sufficient data to assess the long-term performance and therefore sustainability of beams prestressed with AFRP composite materials. The objective of this research is to effectively characterize the material properties based on the short-term and long-term characteristics of AFRP bars. Tensile, creep-rupture, and relaxation tests are experimentally conducted using AFRP bars to validate testing procedures and expand an existing limited database. Previous results from tensile tests show that the stress-strain behavior of Arapree® AFRP bars is linear until failure with tensile strength of approximately 210 ksi (1448 MPa) and strain of 2.1%. For the creep-rupture tests, three specimens are tested and monitored at four different load levels (50, 60, 75 and 85% of maximum tensile strength) throughout a period of 14 days (short-term evaluation) and 42 days (long-term evaluation). From these tests, it is expected that for a 100-year life span, 55% of the ultimate load, Fu, must be applied as an initial stress to obtain a long-term residual strength of 0.80 Fu. For the relaxation tests, six specimens at four different strain levels (50, 60, 75 and 85% of maximum tensile strain) are tested and monitored throughout a period of 14 days and 42 days. Relaxation loss profiles of the AFRP bars are developed based on the experimental data collected from prestressed AFRP bars, which have been less well understood given lack of sufficient experimental data. Overall, the results of this study provide more insight as to the reliability and potential long-term performance of AFRP bars embedded within prestressed bridge structures.

Reinforced concrete beam-column joints (BCJs) are commonly used in structures such as parking garages, multi-storey industrial buildings and road overpasses, which might be exposed to extreme weathering conditions and the application of de-icing salts. The use of the non-corrodible fiber-reinforced polymer (FRP) reinforcing bars in such structures is beneficial to overcome the steel-corrosion problems. However, FRP materials exhibit linear-elastic stress-strain characteristics up to failure, which raises concerns on their performance in BCJs where energy dissipation, through plastic behaviour, is required. The objective of this research project is to assess the seismic behaviour of concrete BCJs reinforced with FRP bars and stirrups. An experimental program was conducted at the University of Manitoba to participate in achieving this objective. Eight full-scale exterior T-shaped BCJs prototypes were constructed and tested under simulated seismic load conditions. The longitudinal and transversal reinforcement types and ratios for the beam and the columns were the main investigated parameters. The experimental results showed that the GFRP reinforced joints can successfully sustain a 4.0% drift ratio without any significant residual deformation. This indicates the feasibility of using GFRP bars and stirrups as reinforcement in the BCJs subjected to seismic-type loading. It was also concluded that, increasing the beam reinforcement ratio, while satisfying the strong column-weak beam concept, can enhance the ability of the joint to dissipate seismic energy. An analytical investigation was conducted through constructing a finite element model using ANSYS-software. The model was verified against the experimental results in this research. Then, a parametric study was performed on number of different parameters known to affect such joints including column axial load, concrete compressive strength, flexural strength ratio and joint transverse reinforcement. It was concluded that 70% of the column axial load capacity can be recommended as an upper limit to the applied axial loads on the column to avoid damage occurrence within the joint. It was also concluded that a minimum flexural strength ratio of 1.50 is recommended to ensure the strong-column weak-beam mechanism. In addition, a minimum joint transverse reinforcement ratio of 0.60% is recommended to insure that the failure will not occur in the joint zone.