Reinforced concrete structures deteriorate throughout their lifetime. This is particularly apparent in structures subjected to aggressive environments, which results in corrosion of reinforcing steel. Designers make allowances for accelerated deterioration in these environments in an attempt to ensure the durability of the structure. To combat corrosion, improved concrete characteristics and additional concrete cover are used to increase the protection provided by concrete to reinforcing. In spite of these measures, cracking of structures in service and from natural hazards can limit the effectiveness that these measures provide. Ultimately, this results in structures suffering from corrosion, which affects their strength, stiffness, and ductility. While strength reduction can be associated directly with a reduction in bar area, impacts on stiffness and ductility are associated with more complex mechanisms, one of which is bond deterioration. A key assumption in reinforced concrete design is that there is perfect bonding between steel reinforcing and surrounding concrete to allow for strain compatibility to be assumed. Perfect bond does not exist and diminished bond performance due to corrosion deterioration further violates this assumption, the effects of which are not fully understood. This thesis investigates the effects of bond deterioration due to corrosion on the seismic performance of reinforced concrete structures. 60 monotonic and cyclic pull-out tests were undertaken on corroded reinforced concrete specimens, with corrosion levels ranging from 0% to 25% reinforcing mass loss. Additional tests were also conducted on specimens with variations in the amount of confining steel to simulate losses in confinement associated with corrosion of confining steel. Experimental results were used to develop corrosion and confinement dependent cyclic bond-slip model. The proposed bond-slip model was then used to modelling pull-out of reinforcing bars detailed in accordance with New Zealand design standard NZS3101. Analyses were performed at a range of corrosion levels, levels of confinement, and uncorroded bond strengths. These showed that pull-out of reinforcement occurred at as little as 8% corrosion in low strength, unconfined conditions. Multi-spring modelling of standard reinforced concrete columns, representing a bridge pier to foundation connection, was performed at the full range of deterioration with allowance for bond slippage. These analyses showed significant reductions in stiffness occurring with increased corrosion levels as well as reduced ductility and possible pull-out of reinforcement.

Self-compacting concrete (SCC) was first developed in Japan about two decades ago. Since then, it has been offered as a solution to various challenges inherently associated with traditional concrete construction; i.e. quality and speed of construction, impact of unskilled labour force and noise pollution etc. SCC flows into a uniform level under its own weight and fills in all recesses and corners of the formwork even in highly congested reinforcement areas. In recent years the interest in using SCC in structural members has increased manifold; therefore many researchers have started investigating its characteristics. Nevertheless, before this special concrete is widely accepted and globally used in structures, its structural performance under different conditions should be investigated. This research focuses on investigating the behaviour of high strength self-compacting concrete (HSSCC) in reinforced concrete (RC) structures through a systematic approach in order to bridge part of an existing gap in the available literature. The dissertation is comprised of four main stages; namely, mix design development and mechanical properties of HSSCC, bond performance of deformed bars in HSSCC, experimental investigation on interior RC beam-column joints (BCJs) cast with HSSCC under reversed cyclic excitations, and finally finite element (FE) modelling and analysis of interior BCJs. First, a HSSCC mix proportion yielding compressive strength greater than 100 MPa was developed in the laboratory using locally available materials in New Zealand. Two benchmark concrete mixes of conventionally-vibrated high-strength concrete (CVHSC) and normal-strength conventionally vibrated concrete (CVC) were also designed for comparison purposes. Material characteristics (such as compressive, splitting tensile and flexural strengths as well as modulus of elasticity, shrinkage and microstructural properties) of all mixes were evaluated. It was found that, once the lower quality of material in normal strength concrete is offset by achieving a denser mix in high-strength concrete, mechanical properties of HSSCC are equivalent to or higher than those in CVHSC. Given that the performance of RC structures (and in specific BCJs) is highly dependent on bond between reinforcement and concrete, understanding the bond behaviour in HSSCC was an imperative link between the first and third phases of this research. Therefore, the second phase focused on scrutinizing bond properties of deformed bars in HSSCC using monotonic pull-out and innovative cyclic beam tests. Processing of the pull-out results revealed that a shorter development length may be utilized in HSSCC. In addition, the grade (or ductility) of reinforcing steel was found to substantially influence the post-yield bond performance. Important modifications to the bond model used in the CEB-FIP model code and Maekawa’s bond-slip-strain relationship were suggested from the results of this phase. An innovative cyclic beam specimen and test setup were also designed such that a more realistic bond performance could be observed in the laboratory tests compared to that in real RC structures. Deleterious impact of cyclic loading and buckling of reinforcement on bond performance were investigated using this testing protocol. The third phase of this research focused on the design, fabrication and testing of seven full-size BCJs. BCJs are one of the most critical parts in RC frame structures and their response substantially affects the overall behaviour of the structure. In seismically active regions like New Zealand, the criticality of BCJs is exacerbated with the complexities involved in seismic resistance. The already congested intersection of RC beam and column looks more like a solid steel connection after consideration of earthquake requirements, and placement of concrete becomes problematic in such areas. At the same time, in many of the high-rise structures, normal strength concrete does not meet the capacity requirements; this requires the usage of high-strength concrete. Therefore, once the seismic performance of HSSCC is guaranteed, it can possibly be a solution to both the capacity and compaction problems. Variables such as axial load, concrete type, steel grade, casting direction, and joint shear reinforcement were considered variable in the experimental investigations. It was found that HSSCC has similar seismic performance to that of CVHSC and it can also be incorporated in the joint area of CVC for an enhanced performance. Finally, DIANA (a nonlinear FE program) was used to simulate the experimental results obtained in the third phase of this research. All BCJs were successfully modelled using their relevant attributes (such as the mechanical properties of HSSCC, steel stress-strain response, test setup and loading protocol) and nonlinear FE analyses (FEA) were performed on each model. FE results were compared to those obtained in the laboratory which showed a reasonable agreement between the two. The capabilities of the FEA were scrutinized with respect to the hysteresis loops, energy dissipation, joint shear deformations, stress development in the concrete and steel, and drift components. Integrating the results of all stages of this research provided better understanding of the performance of HSSCC both at the material and structural levels. Not only were none of the seismically important features compromised by using HSSCC in BCJs, but also many other associated benefits were added to their performance. Therefore, HSSCC can be confidently implemented in design of RC structures even in seismically active regions of the world.

Four full-size statically indeterminate reinforced concrete frames with two symmetrical bays were tested to obtain sufficient data to evaluate the adequacy of the current ACI-ASCE Committee 352 design recommendations, as well as to determine whether a relaxation of some of the limits in these guidelines can be justified. Each specimen contained three 8.5-foot-long columns, connected at mid-height by two 9-foot-long beams. Initially, a constant axial load was applied to each column. The specimens were then subjected to a displacement-controlled loading schedule to simulate the type of displacements a frame may experience during a severe earthquake. In designing the specimens, the latest recommendations of the ACI-ASCE Committee 352 and the ACI building code ACI 318-83 were satisfied except for the following modifications: (1) the flexural strength ratio (M(R)) in the second specimen was reduced from 1.4 to 1.2, (2) the shear-stress factors (γ) in the joints of the third specimen were increased from 12 and 15 to 15 and 20 for the exterior and interior joints respectively, and (3) the number of the transverse reinforcements inside the right exterior joint in the fourth specimen was reduced from 4 to 2 sets of hoops. The conclusion inferred from the results indicate that for drift levels within the elastic range, the elongations and the rotations of the beam regions near the faces of the columns, in addition to the joint shear strains, were not affected by the design values for the primary variables in the last three specimens. For larger excursions into the inelastic range, the relaxation of the current Committee 352 design recommendations in the last three specimens not only showed a significant effect in reducing the elongations and the rotations of the beams, or in increasing the joint shear strains but led to lower energy dissipation of the specimens. Consequently, the current design guidelines by the ACI-ASCE Committee 352 yield statically indeterminate frames which exhibit sufficient ductility.

No description available.

Experimental research was conducted to investigate the influence of axial load and prestress on the shear strength of web-shear critical reinforced concrete elements. The ability of two design codes, the ACI code and the CSA code, to accurately predict the shear strength of web-shear critical reinforced concrete elements was investigated through two sets of experiments performed for this thesis, the panel tests and the beam tests. The experimental results indicated that the CSA code provided better predictions for the shear strength of web-shear critical reinforced concrete members subjected to combined axial force and shear force than the ACI code. A total of six panels, reinforced almost identically, were tested under different combinations of uni-axial stress and shear stress. In addition to the panel tests, a total of eleven I-shaped beams, with the same web thickness, were tested under different combinations of axial force and shear force. The parameters for these beams were the amount of longitudinal reinforcement, the amount of transverse reinforcement, and the thickness of the flanges. The beams were simply supported, but the loading geometry was specially designed to simulate the loading conditions in continuous beams near points of inflection. The experimental results from the panel tests and the beam tests followed a similar trend of variations. Both the inclined cracking strength and the ultimate shear strength were increased by compression and were reduced by tension. The specimens subjected to very high compression failed explosively without developing many cracks. The inclined cracking strength could be predicted with good accuracy if the influence of the co-existing compression on the cracking strength of the concrete and the non-uniform distribution of the stresses over the depth of the cross-section were considered. The strength predictions using the ACI code for these tests were neither accurate nor consistent. The ACI code was unconservative for members subjected to compression and was excessively conservative for members subjected to tension. In contrast, the strength predictions using the CSA code for these tests were generally conservative and consistent. The CSA code accurately predicted the response of specimens subjected to compression and was somewhat conservative in predicting the shear strength of specimens subjected to tension.

Reinforced Concrete (RC) bridge piers, RC columns along exterior of buildings or those located in parking garages are designed to support large compressive axial loads but are vulnerable to transverse out-of-plane loadings, such as those arising from impacts or explosions. To address a lack of understanding regarding blast and impact response of RC members and the need for retrofit techniques to address deficiencies in existing structures, a multi-disciplinary team including various institutes of the National Research Council and the University of Ottawa has initiated work towards developing a fibre reinforced polymer composite protection system for RC columns subjected to extreme shocks. This thesis will focus on the impact program of the aforementioned project. An extensive literature review was conducted to gain a better understanding of: impact loading and associated dynamic effects; experimental testing of RC members subjected to impact; experimental testing of axially loaded members; and retrofit methods for the protection of RC under impact loading. Five half-scale RC columns were constructed and tested using a drop-weight impact machine and two additional specimens were tested under static loading. Deflections, strain distributions within the columns, impact loads and reaction loads were measured during the testing of the built RC members. Comparisons of experimental datum were established between members with differing levels of axial load and between a retrofitted and a non-retrofitted member. Single-degree-of-freedom analysis was used to obtain the predicted response of certain columns under impact loading allowing for comparisons with experimental data.

The topic of structural damage caused by fires following an earthquake (FFE) has been discussed extensively by many researchers for over a decade in order to bring the two fields closer together in the context of performance based structural engineering. Edinburgh University, Heriot-Watt University, Indian Institute of Technology Roorkee (IIT Roorkee) and Indian Institute of Science initiated a collaboration to study this problem under a UK-India Engineering Research Initiative (UKIERI) funded project. The first construction of a single-storey reinforced concrete frame at IIT Roorkee was completed in summer 2011; this is known as the Roorkee Frame Test 1 throughout this thesis. This thesis presents the modelling of the Roorkee Frame Test 1 using the finite element method and assesses the capability of the numerical methodologies for analysing these two sequential events. Both two and three dimensional finite element models were developed. Beam and shell elements were chosen for the numerical modelling, which was carried out using the general purpose finite element package ABAQUS (version 6.8). The variation in material properties caused by these two types of loading, including strength and stiffness degradation, compressive hardening, tension stiffening, and thermal properties, is implemented in the numerical modelling. Constitutive material calculations are in accordance with EC4 Part 1.1, and all loading is according to IS 1893:2002 Part 1 (Indian Standard). The time-temperature curve used in the analysis is based on data from the test carried out. The behaviour of the Roorkee Frame Test 1 when subjected to monotonic, cyclic lateral loading followed by fire is presented. The capacity of the frame when subjected to lateral loading is examined using a static non-linear pushover method. Incremental lateral loading is applied in a displacement-controlled manner to induce simulated seismic damage in the frame. The capacity curve, hysteresis loops and residual displacements are presented, discussed and compared with the test results. The heat transfer analysis using three dimensional solid elements was also compared against temperature distributions recorded during the Roorkee frame fire test. Based on the smoke layer theory, two emissivity values were defined. In this study, the suitability of numerical modelling using ABAQUS to capture the behaviour of Roorkee frame test is examined. The results from this study show that the 3D ABAQUS model predicted more reliable hysteresis curves compared to the 2D ABAQUS model, but both models estimated the lateral load capacity well. However neither model was able to simulate the pinching effect clearly visible in the hysteresis curves from the test. This was due to noninclusion of the bond slip effect between reinforcing bars and concrete. The residual displacement obtained at the end of the cyclic lateral loading analysis from the 2D ABAQUS model is higher than that seen in the test. However, the result in the 3D ABAQUS model matched the trend obtained in the test. The both columns appear to stiffen under the heating and the residual displacement seems to recover slightly. Lateral displacements, obtained in the thermo-mechanical analysis of the numerical models, show that thermal expansion brings the frame back towards its initial position. Finally, correlation studies between analytical and experimental results are conducted with the objective to establish the validity of the proposed model and identify the significance of various effects on the local and global response of fire resistance earthquake damaged of reinforced concrete frames. These studies show that the effect of tension stiffening and bond-slip are very important and should always be included in finite element models of the response of reinforced concrete frame with the smeared crack model when subjected to lateral and thermal loading. The behaviour of reinforced concrete frames exposed to fire is usually described in terms of the concept of the fire resistance which defined in terms of displacement limit. This study shows the global displacement of the frame subjected to fire recover slightly due to the thermal expansion during the heating.

It is crucial for a building to maintain structural stability when subjected to multiple and sequential extreme loads. Safety and economic considerations dictate that structures are built to resist extreme events, such as a earthquakes, impacts, blasts or fires, without collapse and to provide adequate time for evacuation of the occupants. However, during such events, some structural damage may be permissible. Design codes do not account for the scenario where two extreme events occur consecutively on a structure nor do they address the situation of the structure having some initial damage prior to being subjected to a fire load. This work begins by detailing the major inconsistancies between designing reinforced concrete structures for extreme mechanical loads and designing for fire. The material behaviour and traits of the constitutive parts (i.e. the concrete and the steel), including post yielding behaviour, thermal relationships and their interaction with each other are all explored in detail. Comprehensive experimental and numerical investigations are undertaken to determine whether, and to what extent, phenomena such as tensile cracking and loss of the concrete cover affect the local and global fire resistance of a member or structure. The thermal propagation through tensile cracks in reinforced concrete beams is examined experimentally. A comparison is made between the rate of thermal propagation through beams that are undamaged and beams that have significant tensile cracking. The results show that, although small differences occur, there is no significant change in the rate of thermal propagation through the specimens. Consequently, it is concluded that the effects of tensile cracking on the thermal propagation through concrete can be ignored in structural analyses. Significantly this means that analyses of heated concrete structures which are cracked can be carried out with heat-transfer and mechanical analyses being conducted sequentially, as is currently normal and fully-coupled thermo-mechanical analyses are not required. The loss of concrete cover and the impact on the thermal performance is examined numerically. A comparison is made of the thermal propagation, beam deflections and column rotations between structures that are undamaged and structures that have partial cover loss in a variety of locations and magnitudes. Results show that any loss of cover can lead to unsymmetrical heating, causing larger deflections in both vertical and horizontal directions, which can result in a more critical scenario. It is concluded that the effect of cover loss on the thermal performance of the structure is extremely significant. A new approach to numerically simulating the loss of cover by mechanical means from a member is developed. This new approach provides the user with an extremely flexible yet robust method for simulating this loss of cover. The application of this method is then carried out to show its effectiveness. A large experimental study carried out at the Indian Institute of Technology, Roorkee and separately numerically modelled at the University of Edinburgh. Unfortunately, due to unforseen circumstances, the experimental data available is limited at this time and as a result the validation of the numerical simulation is limited. Through these investigations it is clear that it is necessary to develop a method in enhance the stability and integrity of the concrete when subjected to the scenario of a fire following another mechanically extreme event. Therefore, finally a method is proposed and experimentally investigated into the use of fibres to increase the post crushing cohesiveness of the concrete when subjected to thermal loads. Results show that the fibrous members display an increased thermal resistance by retaining their concrete cover through an enhanced post crushing cohesion. From this investigation, it is concluded that the use of fibrous concrete is extremely beneficial for the application of enhancing the performance under extreme sequential mechanical and thermal loading.

Master of Science / Department of Architectural Engineering and Construction Science / Kimberly W. Kramer / This report offers a parametric study analyzing the vertical reinforcement for slender reinforced concrete walls (tilt-up panels) subject to 90 miles per hour (mph), 110 mph, 130 mph, and 150 mph three-second gust wind speeds. Wall panel heights of 32 feet (ft) and 40 ft are considered for one-story warehouse structures. First, solid tilt-up panels serve as the base design used in the comparison process. Next, square openings of 4 ft, 8 ft, 12 ft, and 16 ft centered in the wall panel, are analyzed. A total of 32 tilt-up panel designs are conducted, establishing the most economical design by the least amount of reinforcement and concrete used. In addition to lateral wind pressures, the gravity loads acting on the load bearing tilt-up panel are dead load, roof live load, and snow load. All loads for this report are determined based on a typical 24 ft by 24 ft bay. The procedure to design the tilt-up panels is the Alternative Design of Slender Walls outlined in the American Concrete Institute standard ACI 318-08 Building Code Requirements for Structural Concrete and Commentary Section 14.8 In general, an increase in panel height, lateral wind pressure, and/or panel openings, requires an increase in reinforcement to meet strength and serviceability. Typical vertical reinforcement in tilt-up panels is #4, #5, and #6 size reinforcement bars. A double-mat reinforcement scheme is utilized when the section requires an increase in reinforcement provided by use of a single-layer of reinforcement. A thicker tilt-up panel may be needed to ensure tension-controlled behavior. Panel thicknesses of 7.25 inches (in), 9.25 in, and 11.25 in are considered in design.

Call number: LD2668 .T4 1986 M34 / Master of Science / Civil Engineering