The poor durability performance of reinforced concrete structures is a major problem facing the construction industry throughout the world. It IS estimated that more than $200 billion will be required to repair and rehabilitate deteriorated concrete structures in the USA. Similarly, it is estimated that more than £2 billion will be needed to repair deteriorated concrete structures in the UK Also, considerable resources have to be diverted towards the repair of deteriorated concrete structures in the countries along the Arabian Gulf. Concrete deterioration, worldwide, is mainly attributed to reinforcement corrosion that is caused by chloride ions. However, the effect of other ions, particularly sulfates, on reinforcement corrosion has not been adequately studied. Reinforced concrete structures in marine environments and those built in ‘sabkha' soils are exposed to both chloride and sulfate salts The combined presence of these two ions may accelerate reinforcement corrosion. Cement chemistry may also Significantly influences the mechanisms of reinforcement corrosion. The quantity of C3A and the alkali content of cement effects its chloride-binding capacity. While considerable research has been conducted on the effect of C3A content of cement on its chloride-binding and reinforcement corrosion, meagre data exist on the effect of cement alkalinity on chloride-binding, while no study has been conducted to evaluate the effect of cement alkalinity on reinforcement corrosion.

The optimum design, with respect to cost, of reinforced concrete structures, satisfying Building Code Requirements (ACI 318-63), is investigated, using Box's Complex Method. Variables considered are: geometry, topology, member sizes and material properties. The optimum design, with respect to volume of single span, pin-connected, plane trusses, is investigated, using Box's Complex Method. Variables considered are: member sizes and nodal co-ordinates. The feasibility of the Complex Method is probed by checking the results, either by conducting exhaustive search or comparing them with solutions obtained with linear programming methods. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The investigation dealt mainly with the shear transfer capacity of a joint between a precast concrete column and a cast-in-place concrete beam. Four reinforced concrete frames, each consisting of two columns and two beams, were cast, assembled and tested in a special loading frame. To obtain a general pattern of failure mechanisms, a series of loads consisting of different ratios of moments, shears and axial forces were imposed on these frames. All recording of test data was done electronically in the form of punched tape to facilitate computer analysis. The investigation showed clearly that high values of shear transfer can be reached even under the most adverse load conditions. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The effects of the variability in strength and loading on the reliability of slender, reinforced concrete columns are investigated using the Monte Carlo simulation technique. The columns are considered to be axially loaded with equal end eccentricities and no lateral load. Variabilities in strength, axial load and eccentricity of axial loads are considered. A new procedure called the Implicit Uncorrelation Procedure has been developed to find the values of the failure function from the values of the basic variables named above. The allowable axial load at various eccentricity levels corresponding to a probability of failure of one in one hundred thousand has been found for three different cross sections. Seven different slenderness ratios are considered for each cross section. The results are compared with those obtained by following the code procedures outlined in CAN3-A23.3-M77 and CSA-A23.3 (1984). A change in the performance factor for moment magnification, ⌀m , (as given in CSA-A23.3 (1984)) is recommended in order to obtain a more accurate and consistent level of reliability in the design of slender reinforced concrete columns. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Under seismic excitation, the centre of stiffness of an eccentric structure is stationary as long as the structure remains elastic. Once yielding occurs, the centre of stiffness will begin to move away from its original position, as the torsional forces induced by the eccentricity cause uneven distribution of yielding among members. This movement of the centre of stiffness very often increases the eccentricity of the structure causing further damage. The purpose of this thesis is to determine the significance of this magnification of the initial eccentricity. A procedure for locating the centre of stiffness was developed and incorporated into a time-step dynamic analysis program code named DRAINTABS. Two models were chosen to describe the moment-rotation relationship of reinforced concrete members; the elasto-plastic model and the Takeda model. The former is a bilinear model whereas the latter takes into account the strength degradation of reinforced concrete members under cyclic loading. A number of reinforced concrete buildings were studied. It was found that the centre of stiffness did not always move towards the side of the structure which was more heavily loaded due to the torque induced by the eccenticity. Excursions in the other direction were possible when the translational motion was not in phase with the torsional motion at the instant of maximum excursion. Moreover, when the strength degrading characteristic of R/C members was modelled, the eccentricity of the structure increased gradually with increasing length of excitation. However, this increase was found to be small and therefore insignificant. The procedure for locating the centre of stiffness was also incorporated into another analysis program code named PITSA which utilizes the modified substitute structure method. The results obtained were compared to those obtained using DRAINTABS. Although PITSA has been proven to be a relatively inexpensive yet reliable alternative to a time step analysis, it failed to predict the maximum displacement of the centre of stiffness with any acceptable degree of accuracy. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The influence of reversed low cyclic loading on the bond behaviour of deformed bars in plain as well as steel-fiber-reinforced concrete has been studied experimentally and is discussed in this thesis. In total, ten specimens consisting of two plain concrete and eight steel-fiber reinforced specimens were tested to failure. The variables were the mix proportions, the size and shape of the steel fibers and the pattern of loading. The results indicate that the most important factor affecting bond or stress transfer is the peak stress reached in the previous cycle. It was observed that steel-fiber-reinforced concrete exhibits higher bond strength, improved stiffness and less bond-deterioration under reversed cyclic loading than plain concrete. It was also found that steel fibers make a definite contribution to crack control and better serviceability. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

D.Ing. (Civil Engineering) / Polypropylene (PP) fibre is one of the most widely used fibres for reinforcing concrete. Due to its unique material properties such as economic production cost, relatively high melting point and alkaline resistance, PP fibres in concrete are found to increase the toughness, provide restrained plastic and drying shrinkage cracking resistance, increase impact resistance and flexural loading capacity (especially during the post-crack stage) of concrete structures and components. The wettability of PP fibre surfaces is poor due to the hydrophobic surface nature of polypropylene. The bonding between the PP fibre and the concrete matrix is recognized as poor and currently the PP fibre / concrete interfacial bonding depends upon interlocking and keying (mechanical bonding). As the interfacial bond strength between the PP fibre and the concrete is much smaller than the tensile strength of PP fibre and concrete, in order to fully explore the reinforcing effect of PP fibres in concrete, further improvement of interfacial bonding is necessary. In this investigation, the research work was conducted on the surface oxyfluorinated PP fibre newly developed by the Atomic Energy Corporation of South Africa Limited. Examining the feasibility of using this fibre in concrete, as well as evaluating its superiority over unmodified PP fibres, is the key task of this investigation. This new type of oxyfluorinated PP fibre shows a large increase in interfacial bond strength compared to the unmodified PP fibres. The surface free energy concept and Lewis acid-base interfacial interaction theory were innovatively used to examine the interfacial bonding between the PP fibre and the concrete matrix. The purpose of this study was to develop the background of such oxyfluorinated PP fibres, to establish the mechanism of the increase in interfacial bonding and to investigate the basic properties of the concrete incorporating oxyfluorinated PP fibres. The experimental results on the properties of oxyfluorinated PP fibre reinforced concrete compared with those of unmodified PP fibre reinforced concrete and plain concrete are presented, with some field test results focused on the improvement in shrinkage cracking control capacity. It is concluded in this investigation that the surface oxyfluorinated PP fibres possess significantly increased PP fibre / concrete interfacial bonding due to the chemical bond arising from the acid base interfacial interaction and the intimate interfacial contact arising from the improved fibre surface wettability. When combining oxyfluorinated pp fibre with concrete, a general improvement in the physical and mechanical properties of fibrous concrete compared to that created with unmodified PP fibres, is obtained.

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