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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.

On May 13, 2008, the Faculty of Architecture Building, or ‘Bouwkunde’, at the Delft University of Technology, Netherlands suffered a fire that resulted in the collapse of the northwest wing of the 13 story building. No one was injured but the building was a complete loss. Collapse of concrete buildings in fire is rare; this report aims to provide a preliminary evaluation of the structure and point to key areas that may be of interest to future analyses and investigations. To this end, a large database of information was collected, including original and renovation construction documents, original structural calculations, and over 3000 photographs of the structure during and after the fire. This data has been organized and reviewed to provide a clearer understanding of the building and fire. Preliminary models of the fire are developed and applied to selected structural elements in the FOA to the temperature distributions within the members. Also provided is an overview of available methods for calculating the ultimate strength of reinforced concrete members at elevated temperatures and a computer application, UT Fire: Reinforced Concrete Analysis, which can be used to estimate member capacities through a given fire event, based on their internal temperature distributions. / text

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The proposed study explores the feasibility of detecting and quantifying corrosion and delamination (physical separation) at the interface between reinforcing steel bars and concrete using ultrasonic guided waves. The problem of corrosion of the reinforcing steel in structures has increased significantly in recent years. The emergence of this type of concrete deterioration, which was first observed in marine structures and chemical manufacturing plants, coincided with the increased applications of deicing salts (sodium and calcium chlorides) to roads and bridges during winter months in those states where ice and snow are of major concern. Concrete is strengthened by the inclusion of the reinforcement steel such as deformed or corrugated steel bars. Bonding between the two materials plays a vital role in maximizing performance capacity of the structural members. Durability of the structure is of concern when it is exposed to aggressive environments. Corrosion of reinforcing steel has led to premature deterioration of many concrete members before their design life is attained. It is therefore, important to be able to detect and measure the level of corrosion in reinforcing steel or delamination at the interface. The development and implementation of damage detection strategies, and the continuous health assessment of concrete structures then become a matter of utmost importance. The ultimate goal of this research is to develop a nondestructive testing technique to quantify the amount of corrosion in the reinforcing steel. The guided mechanical wave approach has been explored towards the development of such methodology. The use of an embedded ultrasonic network for monitoring corrosion in real structures is feasible due to its simplicity. The ultrasonic waves, specifically cylindrical guided waves can propagate a long distance along the reinforcing steel bars and are found to be sensitive to the interface conditions between steel bars and concrete. Ultrasonic transducers are used to launch and detect cylindrical guided waves along the steel bar.In this dissertation, in-situ corrosion monitoring technique for reinforced concrete is developed based on two methods - 1) variation of signal strength and 2) the time-of-flight (TOF) variations as the corroded member is loaded transversely. This is the first attempt ever to monitor corrosion inside concrete by measuring the change in the time of flight of guided waves along reinforcing bars as the concrete beam is subjected to bending. Advantages of corrosion monitoring by TOF change are discussed in the dissertation.

This research quantifies the seismic vulnerability of older reinforced concrete frame structures located in Mid-America. After designing a representative three-story gravity load designed reinforced concrete frame structure, a nonlinear analytical representation was used evaluate inter-story drift demands from simulated earthquake time histories that were representative for the region. Limit state story drift capacities were identified for FEMA 273 guidelines, nonlinear pushover analyses, and incremental dynamic analyses. Integrating these two quantities allowed for the creation of fragility curves which relates the probability of exceeding a particular limit state given an imposed spectral acceleration at the fundamental building period. These curves were then used to evaluate the seismic vulnerability of the representatively designed structure. The structure as originally designed was found to be inadequate to resist large lateral loading that would be typical for the Memphis area. So structural retrofit performed by increasing the column-to-beam strength ratio was evaluated by increasing the strength of the column members in the analytical model. The first retrofit raised the column-to-beam strength ratio to 1.2, which is currently required by the ACI code provisions. The second retrofit raised the column-to-beam strength ratio to 1.8, as suggested in previous studies. The story capacity, demand, and fragility curves were once again created for these retrofitted structures. Comparison of these fragility curves is discussed in relation to the retrofit strategy of column strengthening for older reinforced concrete frame structures in Mid-America.

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A non-linear finite element computer program capable of predicting the complete response of two-dimensional reinforced concrete members was developed. This tool which accounts for the stress strain characteristics of cracked concrete was used to predict the responses of a number of members containing discontinuities. These members included corbels, dapped end beams, beams with web holes, and deep beams. The results of tests performed by the author as well as tests performed by other researchers were compared with the non-linear predictions. In addition, simple strut and tie models suitable for designing regions near discontinuities were developed. The predictions obtained by these models were compared with the non-linear finite element predictions and with the test results.

In prestressed precast segmental concrete bridges, conventional longitudinal reinforcement serves only as shrinkage crack controllers. The presence of this reinforcement, however, has restricted the ability to reduce the cross-section of the segments when high strength concrete is used because of the minimum dimensions required to accomodate the reinforcement. Research on fibre reinforced concrete (FRC) indicated that the addition of steel fibres to concrete significantly improved the tensile behaviour and the crack control characteristics of the concrete. This research investigates the feasibility of fibres to replace the conventional shrinkage reinforcement, allowing for the design of thinner and lighter structures with comparable or better crack control characteristics. Extensive work was conducted to investigate the effectiveness of hooked-end steel fibres to control cracks. Seven types of material tests were performed: uniaxial tension test, cylinder compression test, modulus of rupture test, splitting test, free and autogenous shrinkage test, and restrained shrinkage test. In addition, ten 890×890×70 mm concrete panels were tested under in-plane pure-shear loading using the Panel Element Tester. The parameters of study were the fibre volume content (0.5%, 1.0%, and 1.5%), the concrete compressive strength (50 and 80 MPa), and the fibre geometry and tensile strength. In addition to the experimental study, a model was developed to investigate the behaviour of a 1D restrained FRC member subjected to shrinkage. The experimental results indicated that the addition of fibres significantly improved the behaviour of the concrete, particularly the crack control characteristics, the post-peak compressive response, the post-cracking tensile response, the toughness, and the ductility of the concrete. The results also indicated that steel fibres were as effective as conventional reinforcement in controlling shrinkage cracking, provided that sufficient fibre volume content was added to the concrete. For example, in order to achieve a maximum crack width of 0.35 mm, a minimum fibre content of 0.9% and 1.1% should be provided for 50 MPa FRC containing high aspect ratio fibres and low aspect ratio fibres, respectively. In addition, the results indicated the importance of fibre content and fibre aspect ratio on the effectiveness of fibre reinforcement.

In prestressed precast segmental concrete bridges, conventional longitudinal reinforcement serves only as shrinkage crack controllers. The presence of this reinforcement, however, has restricted the ability to reduce the cross-section of the segments when high strength concrete is used because of the minimum dimensions required to accomodate the reinforcement. Research on fibre reinforced concrete (FRC) indicated that the addition of steel fibres to concrete significantly improved the tensile behaviour and the crack control characteristics of the concrete. This research investigates the feasibility of fibres to replace the conventional shrinkage reinforcement, allowing for the design of thinner and lighter structures with comparable or better crack control characteristics. Extensive work was conducted to investigate the effectiveness of hooked-end steel fibres to control cracks. Seven types of material tests were performed: uniaxial tension test, cylinder compression test, modulus of rupture test, splitting test, free and autogenous shrinkage test, and restrained shrinkage test. In addition, ten 890×890×70 mm concrete panels were tested under in-plane pure-shear loading using the Panel Element Tester. The parameters of study were the fibre volume content (0.5%, 1.0%, and 1.5%), the concrete compressive strength (50 and 80 MPa), and the fibre geometry and tensile strength. In addition to the experimental study, a model was developed to investigate the behaviour of a 1D restrained FRC member subjected to shrinkage. The experimental results indicated that the addition of fibres significantly improved the behaviour of the concrete, particularly the crack control characteristics, the post-peak compressive response, the post-cracking tensile response, the toughness, and the ductility of the concrete. The results also indicated that steel fibres were as effective as conventional reinforcement in controlling shrinkage cracking, provided that sufficient fibre volume content was added to the concrete. For example, in order to achieve a maximum crack width of 0.35 mm, a minimum fibre content of 0.9% and 1.1% should be provided for 50 MPa FRC containing high aspect ratio fibres and low aspect ratio fibres, respectively. In addition, the results indicated the importance of fibre content and fibre aspect ratio on the effectiveness of fibre reinforcement.