Dissertations / Theses on the topic 'Plates (Engineering) Cracking Testing'

A solution procedure based on the finite strip method is presented herein, for the analysis of plate systems exhibiting geometric and material non-linearities. Special emphasis is given to the particular problem of rectangular plates with stiffeners running in a direction parallel to one side of the plate. The finite strip method is selected for the analysis as the geometry of the problem is well suited for the application of this method and also as the problem is too complicated to solve analytically. Large deflection effects are included in the present study, by taking first, order non-linearities in strain-displacement relations into account. Material non-linearities are handled by following von-Mises yield criterion and associated flow rule. A bi-linear stress-strain relationship is assumed for the plate material, if tested under uniaxial conditions. Numerical integration of virtual work equations is performed by employing Gauss quadrature. The number of integration points required in a given direction is determined either by observing the individual terms to be integrated or by previous experience. The final set of non-linear equations is solved via a Newton-Raphson iterative scheme, starting with the linear solution. Numerical investigations are carried out by applying the finite strip computer programme to analyse uniformly loaded rectangular and I beams with both simply supported and clamped ends. Displacements, stresses and moments along the beam are compared with analytical solutions in linear analyses and with finite element solutions in non-linear analyses. Investigations are also extended to determine the response of laterally loaded square plates with simply supported and clamped boundaries. Finally, a uniformly loaded stiffened panel is analysed and the results are compared with finite element results. It was revealed that a single mode in the strip direction was sufficient to yield engineering accuracy for design purposes, with most problems.
Applied Science, Faculty of
Civil Engineering, Department of
Graduate

Steel plates are widely used in a variety of civil engineering applications for load bearing structural components, due to their favourable strength to weight ratio. Many of these plates have openings that are commonly used for reducing weight, access for utilities or for inspection in shipping and offshore installations. However the influence of these openings to the structural component’s robustness and resilience against blast loading is relatively unknown, with limited research conducted in this subject to date. Due to the high costs associated with offshore facilities they are typically very congested. This coupled with the producing, processing, storing and transporting of hydrocarbon materials means that explosions and subsequent fires are major hazards with severe consequences. In the event of an explosion, the blast load will initially impact the secondary structure (large spanning plated sections) and then transfer through to the primary structure, highlighting their critical consideration in safety assessments. Plated structures are also known to cause confinement, which in turn will results in higher overpressures, making the consequences of an event more severe. The aim of this research was to investigate the combined influence that openings have on the overpressure and the structural response of thin ductile plates subjected to extreme dynamic transverse loads. This was achieved by conducting a set of well-defined experiments investigating the response of 1/8 scale (0.5 m square) mild steel plates with openings subjected to pulse pressure loading. Six central (scaled) openings were considered; circular (50, 75 and 100 mm) and extended circular (50 by 75, 75 by 100 and 100 by 125 mm) representative of typical offshore and shipping applications. Each plate design was assessed with two boundary conditions (restrained and non-restrained) and two nominal loading conditions. The boundary conditions adopted in this study allowed the response to be bounded, and enabled them to be practicably modelled in FEA-analyses and in the simplified analytical approaches. A pulse pressure test facility was used to generate nominal pulse pressure loads (25 and 50 psi) applied over a time (100 to 200+ ms load duration) representative of extreme explosion loading conditions offshore. All plates exhibited a mode I type failure (large inelastic deformation) highlighting the large reserve strength in such members. The work has shown that the inclusion of an opening (<5% of the exposed panel area) does not significantly degrade the structural resistance when damage is restricted to large inelastic deformation. The reduction in stiffness due to the hole is compensated by the reduced area to which the load is applied. The data generated in the laboratory tests was used to develop and validate finite element models. In general, excellent correlation was observed between the experimental failure modes and the permanent displacements, within an average difference of 12% and 15% for the restrained and non-restrained plates respectively. The finite element models also provided a useful insight into the various failure processes and transient behaviour which could not be observed experimentally. A simplified analytical model was developed to predict the response of the plates and was validated against the experimental data. The results for the permanent displacements compared favourably with the restrained plates at the two nominal pressures (6.5% at 25 psi and 7% at 50 psi), but correlated less well with the non- restrained ones (10% at 25 psi and 3% at 50 psi). Correct definition of support conditions along with a detailed description of the development of plasticity, as shown in the finite element models was fundamental in accurately predicting response of the non-restrained plates. The simplified techniques developed are cost effective compared with more sophisticated finite element methods making them suitable for preliminary engineering design studies. Ultimately this study provides evidence to suggest that small (circular or extended circular) openings positioned away from areas of high stress, could be used as a passive system to mitigate the influences of an explosion event offshore. This has many benefits in the form of reducing weight, reducing confinement (thus lowering overpressures) and reducing the loading applied to these members, and subsequently reducing the loading transferred through to the primary structure.

Non metallic bearing plates have been identified as the weakest component in GRP rockbolting systems used in UK coal mines. A literature review revealed a shortage of information on the design of rockbolting components, particularly the design of the non metallic bearing plates. Over twenty parameters concerning the design and testing of non metallic rockbolt bearing plates have been investigated using Finite Element Analysis and laboratory testing. The parameters included bearing plate depth, central hole diameter, external diameter, material, coned angle for both solid and webbed bearing plates. The designs have been evaluated by comparing the load/plate volume to consider the efficient use of the material. The experiments were designed using Taguchi and one factor at a time methodologies. Interactions between some parameters have been investigated. Reasons for the observed effect of parameters have been suggested. A modification of the BS 7861 test is proposed which more closely simulates the colliery failure mechanism and hence gives a better measure of a bearing plate's suitability for use in a coal mine. The modified test uses a 100 mm hole in the steel support plate as specified by American Standard F432 for steel rockbolt bearing plates, not the 55 mm hole as specified by BS 7861.Optimum values for important parameters have been determined for a 100 mm hole in the steel support plate as proposed in this research and for the 55 mm hole diameter specified by BS 7861. The results produced can be used to design a bearing plate for use in a coal mine with optimum depth and coned angle.

The incremental structural analysis program NISA83 was used to investigate various parameters affecting the ultimate capacity of square plates with circular perforations subjected to uniform shear stress. Both nonlinear material properties and nonlinear geometry were taken into account in determining the ultimate in-plane capacities and buckling capacities of perforated shear plates. The parameters investigated during this study were the hole size for a concentric location, and the hole location for a constant ratio of hole diameter to plate width of 0.2. In addition various doubler plates were studied to determine the most effective shape to restore a shear plate to its original ultimate in-plane capacity. For the first two parameters, the analysis was separated into three parts. The ultimate in-plane capacity, elastic buckling capacity and the ultimate elastic-plastic buckling capacity was determined for each combination of the two parameters. These were used to identify the importance of both elastic buckling and nonlinear material contribute to the reduced ultimate plate capacities. The results from plates with a concentrically located hole of varying size showed excellent correlation with other published experimental and analytical results for both the in-plane capacity and the 3-dimensional buckling capacities. Variation of the center location of a hole of a standard size provided some significant results. Little change was found in the ultimate in-plane capacity for all hole locations. On the other hand, the elastic buckling capacity was raised by 50% after moving the hole from the plate tension diagonal to the compression diagonal. Finally, from the ultimate elastic-plastic' buckling capacity results it was concluded that the concentric provides lower bound capacity for all other hole locations. The in-plane analysis of the optimum doubler plate size showed wide and thin plates to be more effective than narrow and thick plates. A doubler plate with the same thickness as the plate and twice the diameter of the hole is recommended to restore the perforated plate to its original in-plane capacity. In order to aid in the tedious task of checking the input data and to provide a convenient way of displaying the result, a full graphic post-processor was developed as part of this thesis. The program NISPLOT used color graphics available at the UBC Civil Engineering lab to process the output from NISA83. It was written in FORTRAN 77, utilizing subroutines from a commercial graphics package, DI3000, to obtain device independent graphics. NISPLOT generated plots of the nodes and element mesh for each data check. When a complete analysis was carried out by NISA83, nodes, element mesh, deflected shape, and color stress fill plots were generated.
Applied Science, Faculty of
Civil Engineering, Department of
Graduate

The recording head industry is one of the dominant users of advanced ceramics such as alumina, silicon nitride, silicon carbide and AlTiC. The high hardness of these materials makes diamond the optimal abrasive for machining. One challenge when manufacturing recording heads for rigid disk drives is to generate surfaces that are both planar and smooth. Flatness tolerances are in the range of a few tens of nanometers to a few hundred nanometers per millimeter of length [1]. Roughness tolerances are in the range of a few nanometers to the subnanometer range [1]. Fixed-abrasive lapping, sometimes called nanogrinding, is a common method of machining used on ceramics. Fixed-abrasive lapping is generally a two-body abrasive process, with the abrasive grain fixed in the lapping plate that produces an extremely smooth surface due to the controlled depth of cut. The process of fabricating a quality fixed-abrasive lapping plate is a lengthy and sometimes demanding process. The goals of this research are to investigate the current fabrication process for improvements in surface texture quality, charging time and waste reduction of abrasive as well as the development of methods and equipment capable of estimating the lapping qualities of the plate during it?s fabrication process. The improvement of this process will reduce plate fabrication time and improve lapping performance. Current processes used to fabricate a plate can require 2 hours or more, and often the lapping quality of the plate is unknown until it is used. The research started by analyzing the current process used. The surface texture and charging quality were analyzed by quantifying characteristics such as surface roughness, kurtosis, bearing ratio and diamond concentration. The new process developed at the Precision Engineering Center changed the surface texture from scratches of random geometry to a continuous spiral groove cut by a diamond turning machine. This texture not only has better reproducibility than the random scratches, but the geometry of the individual features can be better controlled. The charging mechanism was also changed from a large charging ring that was half the diameter of the lapping plate to a small rolling cylinder. The cylinder creates higher pressures and the ability to follow the profile of the plate. These changes created a shorter charging time, higher charging quality and reduced abrasive waste during the charging process. A tribometer was developed to test the charging quality of the plate during the charging process. It took advantage of the changing friction coefficient on the surface of the plate with charging time. The mechanism constructed and tested did not perform as designed, but can be used as a prototype for future developments. The use of other equipment for charging verification utilizing friction or other aspects of the charging process is viable.

Results of an experimental and analytical study of the nonlinear response and failure characteristics of internally pressurized 4- to 16-ply-thick graphite-epoxy cylindrical panels are presented. Specimens with clamped boundaries simulating the skin between two frames and two stringers of a typical transport fuselage were tested to failure. Failure results of aluminum specimens are compared with the graphite-epoxy test results. The specimens failed at their edges where the local bending gradients and interlaminar stresses are maximum. STAGS nonlinear two-dimensional shell analysis computer code results are used to identify regions of the panels where the response is independent of the axial coordinate. A geometrically nonlinear one-dimensional cylindrical panel analysis was derived and used to determine panel response and interlaminar stresses. Inclusion of the geometric nonlinearity was essential for accurate prediction of panel response. Measurements of panel radius and edge circumferential displacements associated with specimen slipping were also required in the one-dimensional analysis for good correlation between analytical and experimental results. Some panels failed with significant damage in the form of tensile fiber breaks and ply delaminations preceding the ultimate pressure. Other panels failed suddenly without any apparent damage preceding the ultimate pressure. The failure usually occurred along one edge of the panel leaving the other edge intact. The damage on the panel surfaces and through-the-thickness were examined to determine the failure characteristics of the panels. Various failure criteria were applied to the stresses predicted from the one-dimensional analysis. The maximum stress failure criterion applied to the predicted tensile stress in the fiber direction agreed best with the experimentally determined first damage pressures. Results indicate that all panels tested would support applied internal pressures well above fuselage proof pressures.
Ph. D.

This research consists of experimental load tests and numerical simulations of structural steel connections with various filler materials to study the effect of non-steel fillers on the connection strength. Non-steel fillers are used in the steel connections to provide thermal insulation by reducing thermal bridging. Eight specimens having steel and polypropylene filler plates of various thicknesses were tested in the laboratory. The collected data were compared to a Finite Element Analysis (FEA) using ABAQUS to validate the numerical results. After validation, three parametric studies were conducted using ABAQUS to provide insight into general behavior of connections with a variety of fillers that could be used as thermal breaks. In addition, an extreme case of having air gaps instead of alternative fillers was also considered. The Research Council on Structural Connections (RCSC 2014) suggests a reduction in the bolt shear strength when undeveloped fillers with a thickness of more than 0.25 inch are used while using any non-steel material is prohibited due the limited research available. Most research studies have investigated the mechanical behavior of thermal breaks in either end-plate moment connections or slip-critical connections. No data is available for thermal breaks in bearing-type connections up to failure. This research aims to study the effects of filler material properties such as modulus of elasticity and strength on bolt strength, as well as investigate whether the current equation in RCSC 2014 is applicable for alternative filler materials like polypropylene that has less than 0.5% of the steel modulus of elasticity and less than 10% of steel strength.

Thesis (MScEng)-- Stellenbosch University, 2013.
ENGLISH ABSTRACT: Macro synthetic fibre reinforced concrete (SynFRC) is a relatively new concrete for the purpose of being used in structural elements which only require minimum reinforcement and are supported continuously by sub-layers. One structural element that is of particular interest is slabs-on-grade which is supported by a subgrade/sub-base and requires minimum reinforcement to control the shrinkage strains which may result in cracking. The aim of this project is to investigate the potential use of macro SynFRC in the application of controlling drying shrinkage cracking (DSC) in concrete slabs-on-grade. The focus is on the use of concrete slabs-on-grade that is intended for industrial floors. The SynFRC material parameters of interest were characterised first with the aid of various experimental tests. These are: flexural tests, compression tests, friction tests between the SynFRC and wooden surfaces used for full scale testing, and the shrinkage of the concrete. Next the post-cracking tensile behaviour of the SynFRC was determined by way of an inverse analysis. These tensile responses were subsequently used to perform a series of different finite element analyses. These analyses were performed on specific slabs-on-grade to determine the effects of the added tensile behaviour of the SynFRC on the DSC. The results obtained concerned: the spacing of cracks, the maximum and average crack width, and the difference in crack width between the normal concrete (NC) and the SynFRC. These changes take place in accordance to the concrete age. From the analyses it was determined that the addition of fibres gives the concrete a ductility that allows the concrete to crack more than NC, yet does not allow the cracks to propagate. This applies to low fibre contents of less than 0.4% by volume and a slab thickness of 200mm, as well as to fibre contents that have Re,3 values of 0.51 and higher. Moreover, it results in improvements seen when adding fibres if the friction is sticky, meaning when the maximum friction between the slab and the subgrade is reached with a very small amount of movement. With a stickier friction though smaller crack widths occur within both the NC and the SynFRC.
AFRIKAANSE OPSOMMING: Makro sintetiese vesel versterkte beton (SynFRC) is 'n relatiewe nuwe beton. Dit het ten doel om gebruik te word in strukturele elemente wat minimale versterking benodig en wat deurlopend deur sublae ondersteun word. Een spesifieke strukturele element van belang is grondvloere wat deur 'n sublaag ondersteun word en wat minimale ondersteuning benodig om die krimping vervorming te beheer wat moontlike krake kan veroorsaak. Die doel van die projek was om die potensiële gebruik van makro sintetiese vesels te ondersoek tydens die beheer van die uitdroog krimp kraking van 'n beton grondvloer. Die fokus was op die gebruik van betonvloere vir fabrieksdoeleindes. Die eienskappe van SynFRC materiale is vooraf vasgestel vir die doel van verskeie eksperimentele toetse. Hierdie toetse sluit in buigbaarheidstoetse, druktoetse, krimping van beton en toets van wrywing tussen die SynFRC en hout oppervlaktes wat gebruik is vir volskaalse toets. Die trek gedrag van SynFRC na kraking is vasgestel deur inverse analise. Hierdie trek gedrag is dan gebruik om 'n reeks eindige element analises uit te voer. Hierdie analises is uitgevoer op spesifieke grondvloere om die effek te bepaal van verhoogde trek gedrag van SynFRC op die uitdroog krimp kraking. Volgens die uitslae sodoende verkry was die kraakspasiëring, die maksimum en gemiddelde kraakwydte en die verskil in die kraakwydte tussen normale beton en die SynFRC as ‘n funksie van beton oudedom. Vanuit die analises het dit duidelik geblyk dat die byvoeging van vesels die beton se smeebaarheid verhoog het en dit het tot gevolg gehad dat die beton meer krake vorm, maar dat die krake nie vergroot nie. Dit is waargeneem by 'n lae vesel inhoud van minder as 0.4% per volume en 'n betonblad met 'n dikte van 200mm. Dit is ook waargeneem by 'n hoër vesel volume wat Re,3 waardes van 0.51 en hoër het. Kleiner kraakwydte is waargeneem waar vesel volume verhoog is indien die wrywing hoër is, bedoelende dat die maksimum wrywing tussen die betonblad en die sublaag bereik is met baie min beweging. Daar het wel kleiner kraakwydtes in beide die normale beton en die SynFRC voorgekom waar daar hoër wrywing was.

A mixed method of approximation based on Reissner's variational principle is developed for the linear analysis of interlaminar stresses in laminated composites, with special interest in laminates that contain terminated internal plies (dropped-ply laminates). Two models are derived, one for problems of generalized plane deformation and the other for the axisymmetric response of shells of revolution. A layerwise approach is taken in which the stress field is assumed with an explicit dependence on the thickness coordinate in each layer. The dependence of the stress field on the thickness coordinate is determined such that the three-dimensional equilibrium equations are satisfied by the approximation. The solution domain is reduced to one dimension by integration through the thickness. Continuity of tractions and displacements between layers is imposed. The governing two-point boundary value problem is composed of a system of both differential and algebraic equations (DAEs) and their associated boundary conditions. Careful evaluation of the system of DAEs was required to arrive at a form that allowed application of a one-step finite difference approximation. A two-stage Gauss implicit Runge-Kutta finite difference scheme was used for the solution because of its relatively high degree of accuracy. Patch tests of the two models revealed problems with solution accuracy for the axisymmetric model of a cylindrical shell loaded by internal pressure. Parametric studies of dropped-ply laminate characteristics and their influence on the interlaminar stresses were performed using the generalized plane deformation model Eccentricity of the middle surface of the laminate through the ply drop-off was found to have a minimal effect on the interlaminar stresses under longitudinal compression, transverse tension, and in-plane shear. A second study found the stiffness change across the ply termination to have a much greater influence on the interlaminar stresses. Correlations between the stiffness ratio of the thick to the thin sections of the laminates and the magnitude of a parameter based on a quadratic delamination criterion were found to be surprisingly good for longitudinal compression and in-plane shear loadings. For laminates with very stiff terminated plies loaded in longitudinal compression, inclusion of a short insert of softer composite material at the end of the dropped plies was found to significantly reduce the interlaminar stresses produced.
Ph. D.

The ability to predict failure of laminated composites in compression has been doggedly pursued by researchers for many years. Most have, to a limited extent, been able to predict failure for a narrow range of laminates. No means, as yet, exist for predicting the strength of generic laminates under various load conditions. Of primary concern has been the need to establish the mode at failure in compression. Even this has been known to vary for fiber and matrix dominated laminates. This study has been carried out to analyze the failure of specimens with a hole made of laminates with various quasi-isotropic stacking sequences. Different stacking sequences are achieved by rotating a [±45/90/0]s stacking sequence laminate as a whole with respect to the loading axis of the specimens. Two- and three-dimensional finite element models, using commercial packages, were generated to evaluate the stresses in the region of the hole. Two different compressive failure prediction techniques based on distinctly different failure modes have been used. The validity of these techniques was measured against experimental data of quasi-isotropic specimens tested. To investigate the applicability of the failure criteria for different laminated composite plates, analyses were repeated for specimens with different stacking sequences resulting from the rotation of the laminate. The study shows the need for the use of three-dimensional analysis of the stress state in the vicinity of the hole in order to be able to accurately predict failure. It also shows that no one mode of failure is responsible for limiting the strength for all laminate orientations but rather the mode changes with change in stacking sequence. The failure of the laminate with a hole was seen to be very sensitive to the stacking sequence. Experimental data presented also shows that the peak strength obtainable from the laminate analyzed, [±45/90/0]s, is going to be in the off-axis configuration rather than on-axis placement of the stacking sequence with respect to the loading direction.
Master of Science

This investigation was aimed at understanding the global and local strain and deflection responses of stiffened skins. Global deformations of the stiffened skins, under load, produce high local stresses in the interface region between the stiffener and skin. Test panels were designed to study the stiffener and skin interactions using parameters typical of stiffened skins for aircraft fuselages. A total of six panels were tested. Two skin laminates, both 0.04 in. thick, and three stiffener configurations were studied. The panels, having clamped edge boundary conditions, were subjected to pressure loads of up to 14.5-14.8 psi. Out-of-plane deflections and longitudinal and transverse strains were measured in several locations. The deflection responses showed a strongly nonlinear behavior at pressure loads of less than 5 psi. In addition relatively severe gradients of both longitudinal and transverse strains were measured in the interface region of the stiffener and skin. Finite element models incorporating geometric nonlinearities were made of four of the panels. Results of these models substantiated the overall findings of the experimental measurements.
Master of Science
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Low temperature cracking is a major distress in asphalt pavements. Several test configurations have been introduced to characterize the fracture properties of hot mix (HMA); however, most are considered to be research tools due to the complexity of the test methods or equipment. This dissertation describes the development of the indirect ring tension (IRT) fracture test for HMA, which was designed to be an effective and user-friendly test that could be deployed at the Department of Transportation level. The primary advantages of this innovative and yet practical test include: relatively large fracture surface test zone, simplicity of the specimen geometry, widespread availability of the required test equipment, and ability to test laboratory compacted specimens as well as field cores. Numerical modeling was utilized to calibrate the stress intensity factor formula of the IRT fracture test for various specimen dimensions. The results of this extensive analysis were encapsulated in a single equation. To develop the test procedure, a laboratory study was conducted to determine the optimal test parameters for HMA material. An experimental plan was then developed to evaluate the capability of the test in capturing the variations in the mix properties, asphalt pavement density, asphalt material aging, and test temperature. Five plant-produced HMA mixtures were used in this extensive study, and the results revealed that the IRT fracture test is highly repeatable, and capable of capturing the variations in the fracture properties of HMA. Furthermore, an analytical model was developed based on the viscoelastic properties of HMA to estimate the maximum allowable crack size for the pavements in the experimental study. This analysis indicated that the low-temperature cracking potential of the asphalt mixtures is highly sensitive to the fracture toughness and brittleness of the HMA material. Additionally, the IRT fracture test data seemed to correlate well with the data from the distress survey which was conducted on the pavements after five years of service. The maximum allowable crack size analysis revealed that a significant improvement could be realized in terms of the pavements performance if the HMA were to be compacted to a higher density. Finally, the IRT fracture test data were compared to the results of the disk-shaped compact [DC(t)] test. The results of the two tests showed a strong correlation; however, the IRT test seemed to be more repeatable.

Civil Engineering
M.S.C.E.
There is growing appreciation and research regarding geophysical methods to evaluate near surface soil properties in geotechnical engineering. Geophysical methods are generally non-destructive test (NDT) methods that do not necessitate traditional sampling of soils. Instead, they rely on application of input signals and deduction of soil properties from the measured response of the domain. Geophysical methods include various seismic, magnetic and nuclear techniques applied at the surface and/or subsurface within boreholes. Surface seismic methods, which include Multichannel Analysis of Surface Waves (MASW), are increasing in usage for geotechnical engineering purposes to evaluate stiffness properties of soils. MASW typically involves using a hammer to impact a base plate (also referred to as a striker plate) to transmit surface waves into the ground. These waves propagate through the underlying soils at a site and are received by an array of geophones placed on the ground surface. The manner in which the waves propagate is primarily influenced by soil stiffness, particularly against shear. Therefore, the signals recorded during an MASW survey can be analyzed to estimate the shear stiffness of the soils at a site, a parameter that is extremely important for seismic-related engineering purposes (e.g., site amplification, liquefaction, etc.). Aluminum plates are routinely used in a large number of MASW studies as a striker plate to couple the energy from a sledgehammer blow to the underlying soil layers. Various researchers have postulated that the material make-up of the striker plate has an effect on the frequency of the generated waves and, for that matter, the depth achieved with a typical MASW survey. For example, a less stiff material such as ultra-high-molecular-weight (UHMW) polyethylene is often recommended to increase low frequency energy of the input surface wave relative to aluminum. However, very limited research work has been performed in this area to systematically ascertain the effects of modifications to the striker plate material. Due to the limited direct research related to striker plates, MASW was utilized in this study to measure the dispersion curve resulting from MASW at various sites in the Philadelphia metropolitan area. Different striker plate configurations were used during testing to systematically quantify their effects on typical MASW results. The proposed striker base plate configurations included a one (1.0) inch thick aluminum plate, a one (1.0) inch thick aluminum plate over additional rubber mats of varying thickness, and multiple ultra-high-molecular-weight (UHMW) polyethylene plates of various thicknesses. The purpose of this testing was to examine the performance of each configuration, particularly at the low frequency range of the dispersion results. Also efforts were made to qualitatively access the durability of the configurations with respect to long term exposure to impact load.
Temple University--Theses

Thesis (MScEng)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: This research investigates the flexibility and the performance properties of bitumen stabilised materials under the influence of mix variables. The laboratory testing consisted of two main phases. During the first phase (mix design), the strength and the flexibility of the mixes were assessed through ITS (Indirect Tensile Strength), UCS (Unconfined Compressive Strength), displacement at break, strain at break and fracture energy. The second phase consisted of a series of triaxial tests done to assess the performance properties (shear strength: cohesion and angle of internal friction; and stiffness: resilient modulus) of the mixes. The mineral aggregates used in this study were milled from different locations of the R35, near Bethal. This was a blend of granular material (dolerite, from various locations of the existing base and subbase layer of the R35) and Reclaimed Asphalt (RA) milled from the existing surfacing. During the mix design phase, two types of bituminous binders were used (bitumen emulsion and foamed bitumen) at bitumen content ranges of 2%, 2.4% and 2.8% each. Two types of active filler were used separately and in combination at a proportion of 1% and 2%. Finally, specimens were tested in wet and dry conditions for each mix combination. During the triaxial testing phase, only the optimum bitumen content of 2.4% was used, both for bitumen emulsion and foamed bitumen, with only cement as active filler in a proportion 1% and 2%. The specimens were tested at different ranges of densities and saturation levels. The flexibility of the mix was assessed through the fracture energy, the strain and the displacement at break parameters. An analysis of variance (ANOVA) was conducted on the data to assess the significance of experimental variables on this property. This property was found to be very sensitive to bitumen and cement content added to the mix. When assessing the combined effect and the significance of the variables on the flexibility of the mixes, it was found that fracture energy is mostly influenced by the cement content, followed by the bitumen content, then the type of treatment and finally the testing condition. However, the level of significance was not in the same order for the other two parameters (displacement and strain at break). It was also found that the combined effect of some independent variables (cement content + testing condition, type of treatment + cement content + bitumen content) had a significant effect on the fracture energy and the strain at break respectively. From the ITS and UCS tests, an increase in strength was noticed with the increase of cement content. On the other hand, the increase in bitumen content led to a decrease in strength of the material. The statistical analysis on the ITS and UCS values show that the independent variable with the most significant effect on the ITS is the cement content, followed by the testing conditions, then the bitumen content and finally the type of treatment. The combined effect of cement content + bitumen content was found to be significant both for ITS and UCS. In the second phase triaxial tests were performed in order to evaluate the performance properties of the mixes. It was found that the increase of the active filler content significantly improves the shear strength of the material. It was also found that at a fixed cement content, specimens tested at low density and/or high level of saturation show low shear strength. The Mr-θ model was used to model the resilient modulus of the mixes and the model coefficients used to evaluate the effect of experimental variables on the resilient modulus. It was found that the resilient modulus of the mixes increases as the bulk stress increases. This confirms the stress dependent behaviour of bitumen stabilised materials. The analysis show that increasing the percentage of active fillers content results in a significant increase in the resilient modulus values. An increase in relative density also resulted in an increase in the resilient modulus of the mixes, while the opposite effect was observed with the increased of the saturation level. Besides the engineering properties and the mechanical test parameters, other parameters such as the Tensile Strength Ratio (TSR) was calculated in order to evaluate the moisture sensitivity of the mixes. Weakening due to moisture was found to be more predominant in the mixes with less active filler. In addition, bitumen emulsion mixes were found to have a better resistance to moisture weakening effects compared to foamed bitumen. In addition, a comparison between the rapid curing and the accelerated curing was done. Higher ITS and UCS results were obtained for specimens cured using long term curing compared to specimens cured using the accelerated curing method. In conclusion, flexibility is an important property of bitumen road construction material (bitumen stabilised material include) however, it is not an easy property to measure. Although, displacement/strain at break and fracture energy from ITS and UCS were able to give us some indications on the main factors governing the flexibility of bitumen stabilised materials (the bitumen and active filler content), more accurate and adequate tests are required to evaluate the parameter.
AFRIKAANSE OPSOMMING: Die buigsaamheid en gedragseienskappe van bitumen gestabiliseerde materiale was getoets om sodoende die invloed van verskeie mengselveranderlikes te evalueer. Die ondersoek het uit twee fases bestaan. Tydens die eerste fase (mengfase) is die sterkte en buigsaamheid deur middel van indirekte treksterkte toetse (ITS), onbegrensde druksterkte toetse (UCS), verplasing – en vervorming by breekpunt sowel as breek-energie toetse gedoen en ondersoek. Die tweede fase het bestaan uit ʼn reeks drie-assige triaksiaal toetse. Triaksiaaltoetse is uitgevoer om die gedragseienskappe soos die skuifsterkte, kohesie, hoek van interne wrywing, styfheid en weerstand modulus te ondersoek. Die gemaalde mineraal-aggregaat wat in hierdie ondersoek gebruik is, was verkry op verskeie areas van die R35, geleë naby Bethal. Die materiaal is ʼn mengsel van granulêre materiaal (van die bestaande kroonlaag en stutlaag van die pad) en herwonne asfalt (RA). Tydens die mengontwerp fase is twee tipes bitumen gebruik naamlik bitumenemulsie en skuimbitumen in hoeveelhede van 2%, 2.4% en 2.8%. Twee tipes aktiewe vulstof (hoeveelhede van onderskeidelik 1% en 2%) was saam met elk van die verskeie bitumen-hoeveelhede gebruik. Proefstukke van elk van hierdie mengsel kombinasies is onder beide nat en droë kondisies getoets. Tydens die tweede fase, is slegs die optimum binder inhoud (2.4%) gebruik vir beide emulsie- en skuimbitumen, gekombineer met 1% en 2% aktiewe vulstof. Proefstukke was getoets by ʼn reeks van verskillende digthede en versadigingvlakke. Die buigsaamheid was ondersoek deur middel van breek-energie, vervorming en die verplasing by breekpunt. ʼn Analise van variasie (ANOVA) is uitgevoer op die toetsdata om sodoende die te evalueer of die veranderlikes beduidend is ten opsigte van buigsaamheid. Daar is gevind dat die buigsaamheideienskap sensitief is vir beide bitumen en sement inhoud. Met assessering van die gekombineerde effek en betekenis van die veranderlikes op die buigsaamheid van die mengsels, is daar gevind dat die hoogste beduidende veranderlike t.o.v breek-energie die sement inhoud is, gevolg deur die bitumeninhoud, tipe behandeling en laastens die toetskondisie. Die orde van belangrikheid verskil vir die ander twee parameters (verplasing en vervorming by breekpunt). Daar is ook gevind dat die gekombineerde effek van sommige veranderlikes (sement inhoud en toets kondisie, tipe behandeling en sement inhoud tesame met bitumen inhoud) ook beduidend was t.o.v breek-energie en vervorming by breekpunt. Vanuit die ITS en UCS toetse was daar ʼn toename in sterkte waargeneem soos die sementinhoud toeneem. Aan die anderkant, het ʼn toename in bitumeninhoud ‘n afname in sterkte veroorsaak. Die statistiese analise van ITS en UCS resultate, toon dat die grootste beduidende onafhanklike t.o.v ITS waardes ook die sement inhoud was, gevolg deur toets kondisies die grootste effek, bitumen inhoud en die tipe behandeling. Die gekombineerde effek van sementinhoud en bitumeninhoud, was betekenisvol vir beide ITS en UCS. Drie-assige triaksiaaltoetse was uitgevoer om die gedragseienskappe van die mengsels te evalueer. Daar is gevind dat die toename in sement inhoud, die skuif sterkte van die materiaal grootliks verbeter. By ʼn konstante sementinhoud, wys toetsresultate van proefstukke wat getoets is by lae digthede en hoë vlakke van versadiging, lae skuif sterkte. Die Mr – θ model was gebruik om die veerkragsmodulus van die mengsels te moduleer en die modelkoëffisiënte is gebruik om die effek van eksperimentele veranderlikes op die weerstand modulus te evalueer. Met toename in die omhullende spanning is ‘n toename in die veerkragsmodulus waargeneem, wat bevestig dat die gedrag van bitumen gestabiliseerde materiale spannings afhanklik is. ʼn Toename in die sement en relatiewe digtheid het ʼn merkwaardige toename in die veerkragsmodulus tot gevolg gehad, terwyl die teenoorgestelde waargeneem is met toename in versadigingsvlakke. Buiten die ingenieurseienskap en meganiese toetsfaktore, is ander faktore (soos die trekspanning verhouding) bereken om die vogsensitiwiteit van die mengsels te evalueer. Mengsels met laer sement inhoud het groter verswakking ervaar met blootstelling aan water. Bitumenemulsie proefstukke toon beter weerstand teen water as skuimbitumen. Vergelyking tussen versnelde en korttermyn nabehandelingsprosedure van proefstukke, toon hoër ITS en UCS waardes vir die versnelde nabehandelingsprosedure prosedure. Buigsaamheid is ‘n belangrike eienskap van bitumen in padkonstruksie materiale (insluitend bitumen gestabiliseerde materiale), maar word moeilik gemeet. Alhoewel verplasing/vervorming by breekpunt en breek energie, bepaal vanaf ITS en UCS, ‘n indikasie toon van die hooffaktore (binder en sement) wat buigsaamheid van bitumen gestabiliseerde materiaal beïnvloed, word meer akkurate toetse benodig om die eienskap te ondersoek.

This research evaluated the feasibility of the empirical design method for reinforced concrete bridge decks for the Florida Department of Transportation [FDOT]. There are currently three methods used for deck design: empirical method, traditional method and finite element method. This research investigated and compared the steel reinforcement ratios and the stress developed in the reinforcing steel for the three different methods of deck design. This study included analysis of 15 bridge models that met the FDOT standards. The main beams were designed and load rated using commercial software to obtain live load deflections. The bridges were checked to verify that they met the empirical method conditions based on the FDOT Structures Design Guidelines – January 2009. The reinforced concrete decks were designed using the traditional design method. Then the bridges were analyzed using three-dimensional linear finite element models with moving live loads. The reinforced concrete decks were designed using dead load moment, live load moment, and future wearing surface moment obtained from the finite element models. The required reinforcing steel ratio obtained from the finite element method was compared to the required reinforcing steel ratio obtained from traditional design method and the empirical design method. Based on the type of beams, deck thicknesses, method of analysis, and other assumptions used in this study, in most cases the required reinforcing steel obtained from the finite element design is closer to that obtained from the empirical design method than that obtained from the traditional design method. It is recommended that the reinforcing steel ratio obtained from the empirical design method be used with increased deck thicknesses to control cracking in the bridge decks interior bays.

Thesis (MEng)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Flexible pavement designers have a choice of two wearing course: either asphalt concrete or surfacing seals. The latter have been widely used by several countries as their preferred wearing course over other methods, especially countries with a limited number of average inhabitants per square kilometre. Moreover, the surfacing seals were identified as an efficient cost effective road preventive maintenance technique. Surfacing seals in New Zealand, South Africa and Australia cover about 65%, 80% and 90% of their surfaced road networks respectively. The preference of surfacing seals is due to their competitive initial cost and ease of construction. In South Africa, the life expectancy of surfacing seals varies between 8 and 12 years with an average of 10 years. This has not been the case in a number of surfacing seals constructed in winter, especially when the night recorded temperature is below 10oC. The dominant failure mechanism is ravelling (chip loss) soon after construction due to traffic loading. This chip loss is linked to the poor adhesion bond development rate in the bitumen-aggregate system during winter adverse conditions. In order to address the issue of premature chip loss the need for the development of a robust adhesion test method was identified. For that purpose, recently, researchers in the bitumen industry developed the Bitumen Bond Strength test method. This method was used in this study. This study intends to contribute to the understanding of binder-aggregate adhesion bond development for winter surfacing seals using the BBS test. Binder type, precoat type and conditioning, aggregate type and curing time are amongst the factors influencing winter seals adhesion bond performance. An experimental matrix involving three types of binder, two types of aggregate, four different precoating fluids, two precoat conditionings and two binder-curing times were then developed and investigated. Winter weather parameters affecting adhesion properties were also taken into consideration during the course of the investigation. Throughout the test, the procedure described in AASHTO TP 91-11 was followed. However, in order to enhance the control of the binder application temperature, a new method for hot applied binder sample preparation was developed as part of this study. The findings show that there is a significant difference between adhesion properties of the hot applied binders (70/100 and S-E1) and the emulsion (SC-E1). In most of the cases, the hot applied binders performed better than the emulsion. The failure mode observed was found to be linked to the condition of the precoating. The influence of the precoat type and conditioning, and effect of binder curing time were significantly highlighted. The use of a dry precoat benefited the adhesion bond strength up to around 50% relatively to the corresponding non-precoated combination. However, a decrement in the bond strength due to precoating of up to 28.7% was also observed. A statistical analysis using ANOVA did not illustrate any statistical significant effect of the aggregate type. The interaction effects analysis using ANOVA revealed the aggregate type interacting with precoat type to be the most influential interaction at level two. The precoat conditioning implication to the adhesion development rate, which influences the time for opening to traffic after construction, was illustrated. Insightful aspects on the compatibility between the binder type and precoat type and conditioning during the aggregate precoating practices and on the time for opening to traffic are highlighted. Finally, the repeatability analysis proved the BBS test to be a repeatable testing method with caution. Recommendations for further studies that could support the conclusions drawn in this study were provided.
AFRIKAANSE OPSOMMING: Buigbare plaveiselontwerpers het 'n keuse van twee deklae: óf Asfalt of oppervlak seëls. Laasgenoemde word algemeen gebruik deur verskeie lande as hul voorkeur deklaag, veral die lande met beperkte aantal gemiddelde inwoners per vierkante kilometer. Verder, is die seëls geïdentifiseer as 'n doeltreffende koste-effektiewe deklaag tegniek. Oppervlakseëls in Nieu-Seeland, Suid-Afrika en Australië dek ongeveer 65%, 80% en 90% van hul padnetwerke onderskeidelik. Die seëls se voorkeur is te danke aan hul mededingende aanvanklike koste en eenvoudige vorm van die konstruksie. In Suid-Afrika wissel die seël se lewensverwagting tussen 8 en 12 jaar met 'n gemiddeld van 10 jaar. Dit is egter nie die geval van 'n aantal seëls wat in die winter gebou word nie, veral wanneer die aangetekende nagtemperatuur onder 10o C daal nie. Die dominante swigtingsmeganisme is stroping (klipverlies) kort na konstruksie. Hierdie klipverlies is gekoppel aan die power kleef-ontwikkeling van bitumen gedurende die winter. Ten einde die probleem van voortydige klipverlies aan te spreek het die behoefte vir die ontwikkeling van 'n robuuste toetsmetode ontstaan. Om hierdie rede het navorsers onlangs in die bitumenbedryf die “BBS toetsmetode” ontwikkel en is dié toetsmetode in hierdie studie gebruik. Hierdie studie beoog om by te dra tot die begrip van bindmiddel-klip kleefontwikkeling vir die winter seëls dmv die BBS toets. Die faktore, insluitend maar nie beperk tot bindmiddeltipe, voorafdekking (“PRECOAT”) -tipe en kondisionering, aggregaattipe en kuurtyd beïnvloed winter seëls se kleefeienskappe. 'n Eksperimentele matriks met drie tipes bindmiddels, twee tipes aggregate, vier verskillende voorafdekking-vloeistowwe, twee voorafdekking kondisionering en twee bindmiddel kuurtye is toe ontwikkel en ondersoek. Winter weer parameters wat kleefeienskappe beïnvloed is ook in ag geneem tydens die verloop van die ondersoek. Regdeur die studie is die prosedure AASHTO TP 91-11 gevolg, maar ten einde die beheer van die bindmiddel spuittemperatuur te verbeter, is ‘n nuwe metode vir warmspuit-bindmonsters voorbereiding ontwikkel as deel van hierdie studie. Die bevindinge toon dat daar 'n beduidende verskil tussen die kleefeienskappe van die warm aangewende bindmiddels (70/100 en S-E1) en die emulsie (SC-E1) is. In die meeste van die gevalle het die warmspuit-bindmiddels beter as emulsie gevaar. Daar is gevind dat die swigtingsmeganisme verbind word met die toestand van die voorafdekking. Die invloed van voorafdekkingtipe, kondisionering, en die effek van bindmiddelkuurtyd is duidelik uitgelig. Die gebruik van droë voorafdekking het die kleefkrag tot sowat 50% verhoog relatief tot die ooreenstemmende onbedekte klipkombinasie. Daar is egter ook ‘n verlaging van die kleefkrag weens voorafdekking gevind van tot so hoog soos 28,7 persent. Die statistiese ontleding met behulp van ANOVA het geen statisties beduidende effek van die verksillende aggregaattipe te vore gebring nie. Die interaksie-effek analise, met behulp van ANOVA, het wel die interaksie met voorafdekkingtipe met aggregaat die mees invloedryke bevestig. Die voorafdekking kondisioneering het ver rykende kleefkrag implikasies bloot gelê, wat die tyd vir die opening van die verkeer na konstruksie beïnvloed. Insigwekkende aspekte oor die versoenbaarheid tussen die bindmiddeltipe, voorafdekkingtipe, kondisionering, voorafdekkingpraktyk en tyd tot opening vir verkeer word uitgelig. Ten slotte, die herhaalbaarheidsanalise het die BBS toets as 'n herhaalbare toetsmetode met omsigtigheid bewys. Daar is aanbevelings tot verdere studies, wat uit die gevolgtrekking gekom het, gemaak.

X-Ray Diffraction Contrast Tomography (DCT) is a recently developed, non-destructive synchrotron imaging technique which characterizes microstructure and grain orientation in polycrystalline materials in three dimensions (3D). By combining it with propagation based phase contrast tomography (PCT) it is for the first lime possible to observe in situ the 3D propagation behavior of short fatigue cracks (SFCs) within a set of fully characterized grains (orientation and shape). The combined approach, termed 3D X-ray Tomography of short cracks and Microstructure (3DXTSM), has been developed on the metastable beta titanium alloy "Beta21S". A large part of this work deals with the development of the 3DXTSM methodology. In the combined dataset, each point on the 3D fracture surface can be associated with a multidimensional data structure containing variables describing the grain orientation, the local fracture surface normal and the propagation history. The method uses a surface mesh composed of triangles that describes the crack (in other words: the fracture surface) in the last propagation state measured. Grain orientations, crack fronts, local growth rates and grain boundaries can be visualized by assigning colors to this mesh. The data structure can be interrogated in a number of different ways. Tools for extracting pole figures and pole density distribution functions have been implemented. An algorithm was developed that is capable of measuring the 3D local growth rate of a crack containing branches. The accuracy of the grain boundaries as reconstructed with OCT was evaluated and the elastic constants of Beta21S were determined.

With increasing number of structures reaching their designed life or capacities everyday, retrofitting has become an important area in civil engineering. A popular method of strengthening and stiffening reinforced concrete ( RC ) beams is by adhesively bonding steel or FRP plates to the external surfaces. This technique has been proven to be efficient, inexpensive, unobtrusive and can be applied while the structure is in use. However, it has been found that adhesively bonded plates are prone to premature debonding prior to reaching their designed capacities, which restricts the use of existing design rules and guidelines for retrofitting RC beams using this relatively new form of structure. There are various forms of debonding including : plate end ( PE ) debonding ; critical diagonal crack ( CDC ) debonding ; and intermediate crack ( IC ) debonding. IC debonding is an especially important mechanism as it will occur at plated hinges of continuous members, and unlike other premature debonding mechanisms, IC debonding is very difficult to prevent. This debonding mechanism is associated with the formation of flexural or flexural - shear cracks in the vicinity of the plates, which causes slip to occur at the plate / concrete as well as the bar / concrete interfaces. Most research to date has been focusing on the bond - slip relationship at the plate / concrete interface, while little attention has been given to the IC debonding behaviour of flexural members. To allow safe and effective use of plated structures, it is necessary to model the debonding behaviours at the plate / concrete interface as premature debonding will affect both the strength and ductility of the members, and hence the ability of continuous structures to redistribute moment. Despite the importance of moment redistribution, very limited research has been carried out on the moment redistribution of continuous plated members. Since IC debonding is likely to occur at plated hinges of continuous members hence affecting the ductility of the hinges, the existing approaches for determining moment redistribution of reinforced concrete beams cannot be applied to plated members. In this research a numerical model based on discrete cracking and partial interaction theory has been developed which models the IC debonding of plated beams, taking into account the slips at all interfaces. This model will allow a better understanding of the IC debonding behaviour of plated members, and also from the model, the rotation capacity of both plated and unplated hinges in continuous reinforced concrete beams can be determined. Mathematical models and design rules have been developed for analysing critical diagonal crack debonding, which is dependent on the IC debonding behaviour of the plated members. Moment redistribution of beams with externally bonded and near surface mounted plates is studied through a series of tests and a mathematical model based on variation in flexural rigidity is proposed. Through the tests carried out on continuous plated beams, much moment redistribution is evident as oppose to that suggested by the existing design guidelines for plated members, where no moment redistribution is allowed for members plated with FRP. From the models proposed for IC and CDC debonding in this research, together with the existing PE debonding models available, all debonding mechanisms can now be modelled. Furthermore from the research on continuous plated beams, moment redistribution of plated beams can be analysed, allowing safe, effective and economic use of this retrofitting technique. This thesis is presented in the form of a collection of journal papers published or submitted for publication as a result of the research performed by the author. A selection of ten publications have been included in the following context, together with literature reviews performed on the related areas of studies, as well as further discussions on the papers, which consist of any additional information or work that was carried out in this research but not presented in the papers.
Thesis (Ph.D.)--School of Civil and Environmental Engineering, 2006.

With increasing number of structures reaching their designed life or capacities everyday, retrofitting has become an important area in civil engineering. A popular method of strengthening and stiffening reinforced concrete ( RC ) beams is by adhesively bonding steel or FRP plates to the external surfaces. This technique has been proven to be efficient, inexpensive, unobtrusive and can be applied while the structure is in use. However, it has been found that adhesively bonded plates are prone to premature debonding prior to reaching their designed capacities, which restricts the use of existing design rules and guidelines for retrofitting RC beams using this relatively new form of structure. There are various forms of debonding including : plate end ( PE ) debonding ; critical diagonal crack ( CDC ) debonding ; and intermediate crack ( IC ) debonding. IC debonding is an especially important mechanism as it will occur at plated hinges of continuous members, and unlike other premature debonding mechanisms, IC debonding is very difficult to prevent. This debonding mechanism is associated with the formation of flexural or flexural - shear cracks in the vicinity of the plates, which causes slip to occur at the plate / concrete as well as the bar / concrete interfaces. Most research to date has been focusing on the bond - slip relationship at the plate / concrete interface, while little attention has been given to the IC debonding behaviour of flexural members. To allow safe and effective use of plated structures, it is necessary to model the debonding behaviours at the plate / concrete interface as premature debonding will affect both the strength and ductility of the members, and hence the ability of continuous structures to redistribute moment. Despite the importance of moment redistribution, very limited research has been carried out on the moment redistribution of continuous plated members. Since IC debonding is likely to occur at plated hinges of continuous members hence affecting the ductility of the hinges, the existing approaches for determining moment redistribution of reinforced concrete beams cannot be applied to plated members. In this research a numerical model based on discrete cracking and partial interaction theory has been developed which models the IC debonding of plated beams, taking into account the slips at all interfaces. This model will allow a better understanding of the IC debonding behaviour of plated members, and also from the model, the rotation capacity of both plated and unplated hinges in continuous reinforced concrete beams can be determined. Mathematical models and design rules have been developed for analysing critical diagonal crack debonding, which is dependent on the IC debonding behaviour of the plated members. Moment redistribution of beams with externally bonded and near surface mounted plates is studied through a series of tests and a mathematical model based on variation in flexural rigidity is proposed. Through the tests carried out on continuous plated beams, much moment redistribution is evident as oppose to that suggested by the existing design guidelines for plated members, where no moment redistribution is allowed for members plated with FRP. From the models proposed for IC and CDC debonding in this research, together with the existing PE debonding models available, all debonding mechanisms can now be modelled. Furthermore from the research on continuous plated beams, moment redistribution of plated beams can be analysed, allowing safe, effective and economic use of this retrofitting technique. This thesis is presented in the form of a collection of journal papers published or submitted for publication as a result of the research performed by the author. A selection of ten publications have been included in the following context, together with literature reviews performed on the related areas of studies, as well as further discussions on the papers, which consist of any additional information or work that was carried out in this research but not presented in the papers.
Thesis (Ph.D.)--School of Civil and Environmental Engineering, 2006.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfiment of the requirements for the degree of Master or Science in Engineering. Johannesburg, 1993.
The stress concentration factors around rectangular holes in carbon-fibre reinforced epoxy plates, subject uniaxial loads, were investigated experimentally and theoretically. To obtain theoretical solutions, two approaches were adopted; the finite element method and the theory of elasticity using the method of complex variable functions. Reflective photoelasticity was used as the experimental method. The determination of the stress concentration factor around a rectangular hole in a glass-fibrereinforced plate was attempted using transmissive photoelasticity, but no meaningful results were obtained. [Abbreviated Abstract. Open document to view full version}
MT2017

"June 2002"
Includes bibliographical references (leaves 349-374)
xxxix, 416 leaves : ill., plates ; 30 cm.
Thesis (Ph.D.)--University of Adelaide, Dept. of Civil and Environmental Engineering, 2002

Concrete structures can often be modeled as plates, for example, bridges, tunnel walls and pipes. Near-surface damage in concrete structures mostly takes the form of cracking. Surface-breaking cracks affect concrete properties and structural integrity; therefore, the nondestructive evaluation of crack depth is important for structural monitoring, strengthening and rehabilitation. On the other hand, material damping is a fundamental parameter for the dynamic analysis of material specimens and structures. Monitoring damping changes is useful for the assessment of material conditions and structural deterioration. The main objective of this research is to develop new methodologies for depth evaluation of surface-breaking cracks and the evaluation of damping in concrete plates. Nondestructive techniques based on wave propagation are useful because they are non-intrusive, efficient and cost effective. Previous studies for the depth evaluation of surface-breaking cracks in concrete have used diffracted compressional waves (P-waves). However, surface waves exhibit better properties for the characterization of near surface defects, because (a) surface waves dominate the surface response, they carry 67% of the wave propagation energy, and present lower geometrical attenuation because the propagating wave front is cylindrical; and (b) the penetration depth of Rayleigh waves (R-waves) depends on their frequency. Most of the R-wave energy concentrates at a depth of one-third of their wavelengths. The transmission of R-waves through a surface-breaking crack depends on the crack depth; this depth sensitivity is the basis for the so-called Fourier transmission coefficient (FTC) method. R-waves only exist in a half-space (one traction-free surface); whereas in the case of a plate (two traction-free surfaces), Lamb modes are generated. Fundamental Lamb modes behave like R-waves at high frequencies, because their wavelengths are small relative to the plate thickness. Lamb modes are not considered in the standard FTC method, and the FTC method is also affected by the selected spacing between receivers. The FTC calculation requires the use of an explicit time window for the identification of the arrival of surface waves, and the selection of a reliable frequency range. This research presents theoretical, numerical and experimental results. Theoretical aspects of Lamb modes are discussed, and a theoretical transfer function is derived, which can be used to study changes of Lamb modes in the time and frequency domains as a function of distance. The maximum amplitude of the wavelet transform varies with distance because of the dispersion of Lamb modes and the participation of higher Lamb modes in the response. Numerical simulations are conducted to study the wave propagation of Lamb modes through a surface-breaking crack with different depths. The surface response is found to be dominated by the fundamental Lamb mode. Using the 2D Fourier transform, the incident, transmitted and reflected fundamental Lamb modes are extracted. A transmission ratio between the transmitted and incident modes is calculated, which is sensitive to crack depths (d) normalized to the wavelength (λ) in a range (d / λ) = 0.1 to 1/3. A new wavelet transmission coefficient (WTC) method for the depth evaluation of surface-breaking cracks in concrete is proposed to overcome the main limitations of the FTC method. The WTC method gives a global coefficient that is correlated with the crack depth, which does not require time windowing and the pre-selection of a frequency bandwidth. To reduce the effects of wave reflections, which are present in the FTC method because of the non-equal spacing configuration, a new equal spacing configuration is used in the WTC method. The effects of Lamb mode dispersion are also reduced. In laboratory tests, an ultrasonic transmitter with central frequency at 50kHz is used as a source; the 50kHz frequency is appropriate for the concrete plate tested (thickness 80mm), because the fundamental Lamb modes have converged to the Rayleigh wave mode. The new method has also been used in-situ at Hanson Pipe and Precast Inc., Cambridge, Ontario, Canada, and it shows potential for practical applications. In general, the evaluation of material damping is more difficult than the measurement of wave velocity; the dynamic response and attenuation of structural vibrations are predominantly controlled by damping, and the damping is typically evaluated using the modal analysis technique, which requires considerable efforts. The existing methods based on surface waves, use the Fourier transform to measure material damping; however, an explicit time window is required for the spectral ratio method to extract the arrival of surface wave; in addition, a slope of the spectral ratio varies for different frequency ranges, and thus a reliable frequency range needs to be determined. This research uses the wavelet transform to measure material damping in plates, where neither an explicit time window nor the pre-selection of a frequency bandwidth are required. The measured material damping represents an average damping for a frequency range determined by source. Both numerical and experimental results show good agreement and the potential for practical applications.

Design of commercial aircraft structure, composed of composite material, requires the prediction of failure loads given large scale damage. In particular, a fuselage of graphite/epoxy lamination was analyzed for damage tolerance given a standard large crack that severed both skin and internal structure. Upon loading, a zone of damage is known to develop in front of a crack-tip in composite laminates; and, its material behavior within the damage zone is characterized as strain softening. This investigation sought to develop a computational model that simulates progressive damage growth and predicts failure of complex laminated shell structures subject to combined tensile and flexural load conditions. This was accomplished by assuming a macroscopic definition of orthotropic damage that is allowed to vary linearly through the shell thickness. It was further proposed that nonlocal plate strain and curvature act to force damage growth according to a set of uniaxial criteria. Damage induced strain softening is exhibited by degradation of laminate stiffness. An expression for the damage reduced laminated plate stiffness was derived which assumed the familiar laminated plate [AM] stiffness matrix format. The model was implemented in a finite element shell program for simulation of fracture and evaluation of damage tolerance. Laminates were characterized for damage resistance according to material parameters defining nonlocal strain and the damage growth criteria. These parameters were selected using an inverse method to correlate simulation with uniaxial strength and fracture test results. A novel combined tension-plus-flexure fracture test was developed to facilitate this effort. Analysis was performed on a section of pressurized composite fuselage containing a large crack. Good agreement was found between calculations and test results.
Graduation date: 1998

Indiana University-Purdue University Indianapolis (IUPUI)
This thesis proposes an automated grid-based alignment system utilizing lasers and an array of light-detecting photodiodes. The intent is to create an inexpensive and scalable alignment system for pick-and-place robotic systems. The system utilizes the transformation matrix, geometry, and trigonometry to determine the movements to align the robot with a grid-based array of photodiodes. The alignment system consists of a sending unit utilizing lasers, a receiving module consisting of photodiodes, a data acquisition unit, a computer-based control system, and the robot being aligned. The control system computes the robot movements needed to position the lasers based on the laser positions detected by the photodiodes. A transformation matrix converts movements from the coordinate system of the grid formed by the photodiodes to the coordinate system of the robot. The photodiode grid can detect a single laser spot and move it to any part of the grid, or it can detect up to four laser spots and use their relative positions to determine rotational misalignment of the robot. Testing the alignment consists of detecting the position of a single laser at individual points in a distinct pattern on the grid array of photodiodes, and running the entire alignment process multiple times starting with different misalignment cases. The first test provides a measure of the position detection accuracy of the system, while the second test demonstrates the alignment accuracy and repeatability of the system. The system detects the position of a single laser or multiple lasers by using a method similar to a center-of-gravity calculation. The intensity of each photodiode is multiplied by the X-position of that photodiode. The summed result from each photodiode intensity and position product is divided by the summed value of all of the photodiode intensities to get the X-position of the laser. The same thing is done with the Y-values to get the Y-position of the laser. Results show that with this method the system can read a single laser position value with a resolution of 0.1mm, and with a maximum X-error of 2.9mm and Y-error of 2.0mm. It takes approximately 1.5 seconds to process the reading. The alignment procedure calculates the initial misalignment between the robot and the grid of photodiodes by moving the robot to two distinct points along the robot’s X-axis so that only one laser is over the grid. Using these two detected points, a movement trajectory is generated to move that laser to the X = 0, Y = 0 position on the grid. In the process, this moves the other three lasers over the grid, allowing the system to detect the positions of four lasers and uses the positions to determine the rotational and translational offset needed to align the lasers to the grid of photodiodes. This step is run in a feedback loop to update the adjustment until it is within a permissible error value. The desired result for the complete alignment is a robot manipulator positioning within ±0.5mm along the X and Y-axes. The system shows a maximum error of 0.2mm in the X-direction and 0.5mm in the Y-direction with a run-time of approximately 4 to 5 minutes per alignment. If the permissible error value of the final alignment is tripled the alignment time goes down to 1 to 1.5 minutes and the maximum error goes up to 1.4mm in both the X and Y-directions. The run time of the alignment decreases because the system runs fewer alignment iterations.

Adjacent precast, prestressed box beam bridges have a history of poor performance and have been observed to exhibit common types of deterioration including longitudinal cracking, concrete spalling, and deterioration of the concrete top flange. The nature of these types of deterioration leads to uncertainty of the extent and effect of deterioration on structural behavior. Due to limitations in previous research and understanding of the strength of deteriorated box beam bridges, conservative assumptions are being made for the assessment and load rating of these bridges. Furthermore, the design of new box beam bridges, which can offer an efficient and economical solution, is often discouraged due to poor past performance. Therefore, the objective of this research is to develop improved recommendations for the inspection, load rating, and design of adjacent box beam bridges. Through a series of bridge inspections, deteriorated box beams were identified and acquired for experimental testing. The extent of corrosion was determined through visual inspection, non-destructive evaluation, and destructive evaluation. Non-destructive tests (NDT) included the use of connectionless electrical pulse response analysis (CEPRA), ground penetrating radar (GPR), and half-cell potentials. The deteriorated capacity was determined through structural testing, and an analysis procedure was developed to estimate deteriorated behavior. A rehabilitation procedure was also developed to restore load transfer of adjacent beams in cases where shear key failures are suspected. Based on the understanding of deterioration developed through study of deteriorated adjacent box beam bridges, improved inspection and load rating procedure are provided along with design recommendations for the next generation of box beam bridges.