Bayesian Optimised Collection Strategies for Fatigue Testing : Constant Life Testing

This paper presents a statistical framework enabling optimal sampling and robust analysis of fatigue data. We create protocols using Bayesian maximum entropy sampling, which build on the staircase and step methods, removing the requirement of prior knowledge of the fatigue strength distribution for data collection. Results show improved sampling efficiency and parameter estimation over the conventional approaches. Statistical methods for distinguishing between distribution types highlight the role of the protocol in model distinction. Experimental validation of the above work is performed, showing the applicability of the methods in laboratory testing.Comment: 25 pages, 12 figures + 1 SI figur

Fast fatigue method for self-compacting recycled aggregate concrete characterization

ABSTRACT: Designing or analysing the influence of fatigue on concrete structures is becoming increasingly important for a number of structural elements. For this reason, it is necessary to define a method capable of determining the concrete´s fatigue limit in the most economical, fast and efficient way. The aim of this study is to compare and correlate different methods found in the literature in order to reduce the number and duration of the tests required to determine the fatigue limit. This reduction will consequently reduce the economic costs of determining the fatigue limit. For these proposes three different types of self-compacting recycled concrete was used. A linear correlation was found between the analysed methods, which means that the methods are capable of providing similar results and that the results obtained by the economical procedure must be selected. This work opens the door to define an optimal procedure in the process of concrete fatigue characterization, which is capable of yielding results up to five times faster and more economical than with other methodologies, so that resources are not wasted.The authors would like to thank the Spanish Ministry of Economy and Competitiveness of Spain for financing the project MAT2014-57544-R

Effect of Steel Fibre Reinforcement on Flexural Fatigue Behaviour of Notched Structural Concrete

ABSTARCT: One of the biggest challenges in facilitating the installation of concrete is the development of fibre-reinforced concrete. Although nowadays fibre reinforced concrete is relatively common, it is still necessary to deepen in the study on its behaviour, especially regarding its fatigue behaviour. This paper proposes a new methodology to analyse the bending fatigue behaviour of notched test specimens. From these tests, it was possible to verify that, despite carrying out the tests with load control, the presence of fibres extends the fatigue life of the concrete after cracking. This effect is of great importance since during the extra lifetime with the cracked concrete, the damage to the concrete will be evident and the corresponding maintenance measures can be carried out. Regarding the analysis of the results, in addition to obtaining a traditional S-N curve, two new criteria have been applied, namely energy and notch growth. From these two new approaches, it was possible to determine critical energy values that can be used as predictive indicators of the collapse of the element. Moreover, from the notch growth analysis, it was possible to determine crack growth rate as a function of the stress conditions for the concrete and the specific geometry. From the comparison among the results obtained from the different tests, a limit cracking index of 0.05 mm can be defined

Impact of workspace change on organisational outcomes

Masters Research ReportWorldwide, organisational workspaces are changing dramatically, due to the social, legal and economic pressures. Organisational workspaces must support the rapid technological enhancements, the balance of privacy and collaboration as well as the dynamic organisational changes. This dynamic change in organisations is essential because maintaining and operating a building is less costly than employing people, and spending money on enhancing and improving the physical workspace may in turn increase productivity. Therefore it is critical to understand the manner in which the design of an office workspace impacts on employees perceived productivity, job satisfaction and well-being from moving from a conventional building (time 1) to a green building (time 2). This study firstly investigated whether there was a change in workspace aspects, perceived productivity, job satisfaction, and well-being of employees from time 1 to time 2. Secondly it investigated whether there was a relationship between workspace aspects impacting on perceived productivity, job satisfaction and well-being. This was achieved by sampling employees from the Ernst & Young building who were first situated in the Wanderers building and then moved to a green building in Sandton. This study adopted a mixed method approach in which questionnaires were sent out at time 1 and time 2, followed by conducting one-on-one interviews with participants. The data were compared over two time frames, which were 8 months apart. The results indicated improved workspace aspects, a slight increase in psychological well-being and job satisfaction, and a decrease in perceived productivity, and physical well-being from time 1 to time 2. However, it was found that workspace aspects have a relationship with psychological well-being and job satisfaction. Therefore understanding these results is essential, as it will aid in creating effective and well-used workspace for the future

Quality Measurements on Quantised Meshes

In computer graphics, triangle mesh has emerged as the ubiquitous shape rep- resentation for 3D modelling and visualisation applications. Triangle meshes, often undergo compression by specialised algorithms for the purposes of storage and trans- mission. During the compression processes, the coordinates of the vertices of the triangle meshes are quantised using fixed-point arithmetic. Potentially, that can alter the visual quality of the 3D model. Indeed, if the number of bits per vertex coordinate is too low, the mesh will be deemed by the user as visually too coarse as quantisation artifacts will become perceptible. Therefore, there is the need for the development of quality metrics that will enable us to predict the visual appearance of a triangle mesh at a given level of vertex coordinate quantisation

Resonance Fatigue Behaviour of Concretes with Recycled Cement and Aggregate

ABSTRACT: The huge increase in production of construction and demolition waste (CDW) worldwide is leading to the valorisation of as recycled aggregates. One of the most promising alternatives is its use as a recycled aggregate in the manufacture of structural concrete, which motivates the study of the dynamic behaviour of these materials in order to ensure their suitability for use in elements subjected to dynamic loads. This work evaluated the resonant compressive fatigue behaviour of structural concretes with 25% or 50% recycled mixed aggregates, either individually or in combination with 25% recycled cement of clay-based materials both from CDW. All mixes were subjected to compressive fatigue tests using the accelerated Locati method. Regarding the fatigue limit, the results showed that for all mixes, it was between 30% and 45% of the compressive strength. In addition, a correlation was also found between the resonance frequency of the test and the deformation suffered by the specimen. This correlation enabled the estimation of the fatigue limit through a more stable parameter than the strain measured by strain gauges, namely, the resonance frequency. In addition, it was found that the resonance frequency of the test changed as the specimen damage increased. This observation enabled the estimation of the fatigue limit through a more stable parameter than the strain measured by strain gauges, namely, the resonance frequency.This research was funded by the Spanish Ministry of Science and Innovation within the framework of the project BIA 2013-48876-C3-2-R

Analysis of in-situ and long-term critical loads of steel fibre-reinforced concrete in wind turbine towers

La presente Tesis tiene como objetivo generar conocimiento sobre aspectos críticos asociados al hormigón reforzado con macrofibras metálicas en su aplicación a torres de aerogeneradores. Por un lado, se analiza la influencia del método de hormigonado en la disposición de las fibras, relacionada a su vez con su resistencia, con el objetivo de seleccionar la forma idónea de puesta en obra que optimice las propiedades del material según la dirección de las fuerzas más críticas soportadas por la estructura en sí. Por otro lado, las torres eólicas están sometidas a distintos esfuerzos críticos, entre los que destacan la flexión, fluencia y fatiga, por lo que es de vital importancia ahondar en el comportamiento del hormigón bajo estos esfuerzos, con el fin de que éste sea aceptado y empleado, además de ayudar a optimizar los diseños. Por ello, se estudia el comportamiento a fluencia del hormigón reforzado con fibras de acero, analizando su evolución dependiendo de la edad y magnitud de carga, así como su comportamiento bajo esfuerzos de fatiga a flexión, analizando distintas cargas y frecuencias.The objective of this Thesis is to generate knowledge on critical aspects associated with concrete reinforced with metallic macro-fibers in its application to wind turbine towers. On the one hand, it analyzes the influence of the method of pouring on the arrangement of the fibers, related in turn to their resistance, with the aim of selecting the ideal way of placing the concrete that optimizes the properties of the material according to the direction of the most critical forces supported by the structure itself. On the other hand, wind towers are subjected to different critical stresses, including bending, creep and fatigue, so it is of vital importance to delve into the behavior of concrete under these stresses, in order for it to be accepted and used, as well as to help optimize the designs. Therefore, the creep behavior of concrete reinforced with steel fibers is studied, analyzing its evolution depending on age and load magnitude, as well as its behavior under flexural fatigue stresses, analyzing different loads and frequencies.Ministerio de Economía, Industria y Competitividad: financiación del proyecto S2C – “Desarrollo de un nuevo concepto de torre de hormigón in situ de gran altura para aerogeneradores de gran potencia”, dentro de la convocatoria Retos-Colaboración 201