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

Inelastic behavior is inevitable in most structures subjected to strong earthquake forces. Any rational design procedure, therefore, should attempt to estimate the amount of inelastic behavior to be expected in each member of the structure. Methods of dynamic response analysis based on linear elastic assumptions can be carried out conveniently and economically. Such methods, however, can not provide any direct information on the inelastic behavior of the structure. On the other hand, time-step analysis programs can 'truly' simulate the non-linear behavior of the structure but are seldom used because of their cost and complexity. There is, therefore, a need for practical and efficient methods which can account for the inelastic behavior. Some methods for estimating the inelastic response and damage patterns of structures under ground motions are presented. One is the Modified Substitute Structure Method which is now revised so that the structure can be analysed for gravity loads prior to the seismic analysis. The other method which is proposed here uses a static analysis. The structure is first analysed for gravity loads and then lateral seismic forces (as given by the appropriate codes) are applied. The amplitude of the lateral forces is gradually increased, maintaining the specified pattern; a plastic hinge is placed where a member has yielded and the structure stiffness matrix revised each time. This process is continued until the structure has reached a predetermined displacement. At this point, the rotation of the plastic hinges is known and then the member curvature ductilities can be calculated. Thus, an idea is obtained, of the damage pattern in the structure. A computer program has also been written for analysing the structures by 'Freeman's Method' to predict the inelastic response of structures under severe ground motion. The method gives the overall inelastic response without predicting the pattern of local damage. These various methods are then compared by analyzing two idealized structures. A third, real structure, an office/residential building in downtown Vancouver is also analysed by these methods and the results compared with those obtained by a time-step analysis program DRAIN-2D. These methods appear to give good results and it is hoped that they will be found useful by practising engineers. A user's guide and the listing of these programs are included in the appendices. / 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.

The research on headed stud connections described in this dissertation forms a part of an overall objective of predicting the behaviour of precast concrete panel buildings under earthquake loads. Existing laboratory test data and current design procedures of headed stud connections are briefly reviewed. It is postulated that shear loads are transmitted via a connection to the surrounding concrete by three distinct mechanisms: 1. friction between faceplate and concrete 2. bearing of end of faceplate on concrete 3. interaction between studs and concrete Tests on laboratory models designed to isolate individual aspects of these mechanisms confirm that all three exist. Friction forces between faceplate and concrete are small in comparison with the remaining forces acting in a connection, particularly under cycled loading. Bearing of the end of the faceplate on concrete and interaction between studs and surrounding concrete are shown to be the main contributions to the total load carried by a connection. A simple analytical model is presented for the prediction of the ultimate shear load capacity of a connection and a computer algorithm is proposed for the prediction of the load versus deflection behaviour of a connection under both monotonic and cyclic conditions. Existence of the three mechanisms whereby a connection transfers applied shear forces to the surrounding concrete contradicts the shear friction equation which is currently used in the design of connections. The analytical equations developed in the investigation indicate that the strength of a connection is directly dependent upon the strength of the surrounding concrete, as opposed to the expression for shear friction, which does not contain concrete strength as a variable. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

No description available.

The growing demand to construct long, slender floors with minimum supports for aesthetic and economic reasons especially in modern building developments has resulted in increased floor slenderness leading to vibration problems. As a result, vibration serviceability has become the governing design criterion for many of these new civil engineering structures. It is known that long span, slender floors possess lower natural frequencies and reduced damping leading to vibration serviceability problems. As vibration serviceability becomes a major concern in the design of concrete floors, investigations of the beneficial effects of non-structural elements to the vibration serviceability of floors are becoming increasingly important. The vibration serviceability of long span, slender concrete floors may be improved through the installation of non-structural elements such as partition walls and raised access floors. Little research exists into the quantification of the effects of various types of partitions on the vibration serviceability of concrete floors that support them. There are no guidelines available to designers which take into account the effects of partitions in the design of concrete floors for vibration serviceability besides the different damping ratios that are recommended in different codes for bare floors as well as floors with half- or full-height partitions. Therefore a research project was initiated with the objectives of investigating the effects of non-structural partitions on the vibration serviceability of concrete floors as well as proposing guidelines on how to account for partitions in the design of concrete floors for vibration serviceability. The research project consisted of modal testing on a prestressed pre-tensioned concrete floor slab. The excitation of the floor was generated by an electrodynamic shaker and instrumented impulse hammer. The electrodynamic shaker excitation was used mainly to extract the natural frequencies and mode shapes of the test floor. The instrumented impulse hammer excitation was used mainly for damping studies. Force-balanced QA 700 accelerometers with a sensitivity of 8 V/g mounted to base plates were used to measure the responses of the test floor. The Data Physics Signal Calc Mobilyser was used to acquire the data from the accelerometers. A personal computer was used to store, analyse and present the data. The curve fitting method in Vibrant Technologies ME'Scope was used to estimate the natural frequencies and mode shapes of the test floor. Modal 1.20 by Brownjohn (2009) was used to estimate the damping ratios of the test floor. Modal 1.20 uses the logarithmic decrement method to estimate damping. The tests investigated the effects of partitions on the vibration serviceability of concrete floors.

In order to study the mechanical performance of dry-cast synthetic fiber reinforced concrete (SynFRC), samples of varying geometry, fiber content, and environmental exposure were developed and tested using the modified indirect tensile test. The samples created consisted of three different thicknesses (with two different geometries), and six different fiber contents that differed in either type, or quantity, of fibers. Throughout the duration of this research, procedures for inflicting detrimental materials into the concrete samples were employed at a number of different environments by implementing accelerated rates of deterioration using geometric adjustments, increased temperature exposure, wetting/drying cycles, and preparation techniques. The SynFRC samples studied were immersed in a wide range of environments including: the exposure of samples to high humidity and calcium hydroxide environments, which served at the control group, while the sea water, low pH, and barge conditioning environments were used to depict the real world environments similar to what would be experienced in the Florida ecosystem. As a result of this conditioning regime, the concrete was able to imitate the real-world effects that the environments would have inflicted if exposed for long durations after an exposure period of only 20-24 months. Having adequately conditioned the samples in their respective environments, they were then tested (and forensically investigated) using the modified indirect tensile testing method to gather data regarding each sample’s toughness and load handling capability. By analyzing the results from each sample, the toughness was calculated by taking the area under the force displacement curve. From these toughness readings it was found that possible degradation occurred between the fiber-matrix interface of some of the concrete samples conditioned in the Barge environment. From these specimens that were immersed in the barge environment, a handful of them exhibited multiple episodes of strain softening characteristics within their force displacement curves. In regard to the fibers used within the samples, the PVA fibers tended to pull off more while the Tuff Strand SF fibers had the highest tendency to break (despite some of the fibers showing similar pull off and breaking failure characteristics). When it comes to the overall thickness of the sample, there was clear correlation between the increase in size and the increase in sample toughness, however the degree to which it correlates varies from sample to sample. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

Bibliography: pages 71-74. / It has become necessary to determine the magnitude of creep, shrinkage, elastic and thermal deformations of concrete as these characteristics determine the loss of prestressing in prestressed concrete and affect the deflections with time of large concrete sections. Much of the literature available on this topic has conflicting conclusions. In this research, the effect of fly ash was first investigated with regard to general concrete properties such as bleeding, early set, workability, mortar excess and compressive strength. Classified Lethabo fly ash and local Western Cape materials were used for this work. With the increase in the percentage fly ash present in the concrete mix, the water requirement was reduced in order to get the same workability. This characteristic reduced the amount of water available for bleeding. For a given C/W ratio the inclusion of fly ash in a concrete mix had no effect on the mortar excess. The early setting time was retarded for mixes with increasing percentages of fly ash. Higher cementitious material to water ratios were required for concrete with classified Lethabo fly ash than Ordinary Portland Cement mixes, to obtain the same 28 day compressive strength. The fly ash mixes had higher strength developments with time i.e. they have lower early strengths and higher long term strengths than OPC mixes for the same 28 day compressive strengths. Having developed a wide range of concrete mixes, the main investigation was done on specific deformation properties of concrete such as the elasticity, shrinkage, creep and thermal movement. The effect of different wet curing durations and testing ages on these properties were investigated. The elastic modulus was determined by both static and dynamic test methods. A relationship was established between the two methods to estimate the static modulus from the dynamic modulus, which was quicker to perform. In this thesis, the elastic modulus was not affected by the presence of fly ash. The elastic properties of the fly ash mixes was found to be similar to that of the OPC mixes of the same compressive strength. Similarly, the drying shrinkage and thermal movement were not affected noticeably by the presence of fly ash. The volume of aggregate was not a variable as it did not change when fly ash was added to the mix. An attempt was made to develop a test to determine the plastic shrinkage of an unrestrained sample. The effect of fly ash on the plastic shrinkage was not investigated fully. For the creep of concrete, it was established that mixes containing fly ash have lower creep factors than OPC concretes, although no clear trends were apparent for increasing percentages of fly ash. The effect of fly ash in pump mixes was also investigated and the same trends were apparent, although in general, the pump mixes had higher creep factors than the normal mixes. The curing of concrete is critical if good quality concrete is to be obtained. For all deformation properties, the longer a specimen was wet cured, the lower were the deformations. With longer wet curing, a larger volume of hydrated gel developed which gave higher compressive strengths and more rigidity within the matrix. The conclusion reached in this thesis was that the presence of classified Lethabo fly ash did not noticeably affect the deformation properties of the concrete for equivalent compressive strengths. Where some effects were noticed, the fly ash concretes displayed somewhat lower deformations.