Thesis (MScEng (Civil Engineering))--Stellenbosch University, 2008. / Doubly symmetric I-section columns are often utilised in portal frame construction. The sheeting (or cladding) is carried by sheeting rails connected to the outer flange of these columns. Although it is common practice to include the sheeting rails in the longitudinal bracing system, by connecting the sheeting rail to the cross-bracing, designers must be wary because the connection between column and sheeting rail will not prevent twisting of the columns cross-section. It has been shown ([11], [12], [17]), that by including this eccentric restraint into the bracing of the column, that a torsional-flexural buckling mode of failure can occur when the column is subjected to axial load only. It was seen that this phenomenon is provided for in BS 5950 [18], but is not present in many other design codes of practice, in spite of this phenomenon being relatively well known. In some cases the compression resistance of a column can be significantly reduced when compared to that of a flexural buckled configuration. Previous work performed by Helwig and Yura [15] proposed specific column to sheeting rail connections which would allow for the sheeting rails to be used as elastic torsional braces and effectively rigid lateral braces. However, it is the objective of this investigation to determine if it is possible to include the eccentric sheeting rails into the bracing system, even when using a relatively simple cleat connection with only two bolts onto the sheeting rail. The objective of the research was investigated by conducting experimental tests coupled with a series of detailed finite element analyses. The purpose of the experimental set-up was to investigate the behaviour of a column laterally supported on one flange by a continuous sheeting rail and to compare it to the behaviour of a column laterally supported on both flanges by means of fly-braces (“kneebraces”). The behaviour of the columns, as determined by the experimental tests, was validated by the finite element analyses. The evident conclusion that can be drawn is that, for the case of a continuous sheeting rail, connected to column simply by two bolts and a cleat, that sufficient torsional restraint is provided to the column to prevent torsional-flexural buckling from being critical. This result is helpful, as it means that the buckling capacity of a column can be increased four-fold by enforcing the second flexural buckling mode instead of the first mode through utilising a continuous sheeting rail connected to a cross-bracing system as longitudinal bracing on the columns. This can be achieved without the need to provide any specific detailing to the column to sheeting rail connection. It is however, recommended that further experimental work be conducted on varying lengths of column in order to further validate the results of this work.

Avanços nas pesquisas em Veículos Agrícolas Autônomos (VAA\'s) e de Robôs Agrícolas Móveis (RAM\'s) têm sido conquistados nos últimos anos. Entretanto, um número limitado de trabalhos foca o desenvolvimento das estruturas destes veículos. O presente trabalho apresenta uma revisão de materiais encontrados na literatura e no mercado. Estudou-se modelagem cinemática de veículos autônomos que possuem configurações de suas estruturas projetadas para ter mobilidade melhorada. Estudaram-se estruturas mecânicas de máquinas que atuam em vários estádios de desenvolvimento de lavouras típicas brasileiras. Baseado no levantamento e esse estudo, foi projetado e construído um veículo com conceito modular e de pórtico para ser uma plataforma robótica no qual é utilizado para o sensoriamento em área agrícola. Uma modelagem cinemática simplificada do veículo foi realizada, fundamentada nos conceitos básicos de cinemáticas em robôs móveis. Por fim é apresentado o desenvolvimento da estrutura em pórtico do veículo. Pretende-se que o resultado auxilie no desenvolvimento de projeto de VAA\'s. / Advance on AAV (Autonomous Agriculture Vehicle) and MAR (Mobile Agriculture Robots) research are noticed in the recent years. However, a limited number of works focus in the structure development of such vehicles. This work introduces a review of the materials found in literature and market. Kinematics models of Autonomous Vehicles that have its structures designed to have mobility improved have been studied. It was studied mechanical structures of machines that act in various stages of typical brazilians crops. Based on this study and survey, a vehicle has been built with a modular concept and portal frame structure format to be used as a robotic platform in which it performs remote sensing in agricultural areas. A simplified Kinematic model have been done using basics concepts of mobile robots kinematics. At the end of this work is presented the portal frame structure development. The results obtained may assist in the design development of AAV\'s.

Avanços nas pesquisas em Veículos Agrícolas Autônomos (VAA\'s) e de Robôs Agrícolas Móveis (RAM\'s) têm sido conquistados nos últimos anos. Entretanto, um número limitado de trabalhos foca o desenvolvimento das estruturas destes veículos. O presente trabalho apresenta uma revisão de materiais encontrados na literatura e no mercado. Estudou-se modelagem cinemática de veículos autônomos que possuem configurações de suas estruturas projetadas para ter mobilidade melhorada. Estudaram-se estruturas mecânicas de máquinas que atuam em vários estádios de desenvolvimento de lavouras típicas brasileiras. Baseado no levantamento e esse estudo, foi projetado e construído um veículo com conceito modular e de pórtico para ser uma plataforma robótica no qual é utilizado para o sensoriamento em área agrícola. Uma modelagem cinemática simplificada do veículo foi realizada, fundamentada nos conceitos básicos de cinemáticas em robôs móveis. Por fim é apresentado o desenvolvimento da estrutura em pórtico do veículo. Pretende-se que o resultado auxilie no desenvolvimento de projeto de VAA\'s. / Advance on AAV (Autonomous Agriculture Vehicle) and MAR (Mobile Agriculture Robots) research are noticed in the recent years. However, a limited number of works focus in the structure development of such vehicles. This work introduces a review of the materials found in literature and market. Kinematics models of Autonomous Vehicles that have its structures designed to have mobility improved have been studied. It was studied mechanical structures of machines that act in various stages of typical brazilians crops. Based on this study and survey, a vehicle has been built with a modular concept and portal frame structure format to be used as a robotic platform in which it performs remote sensing in agricultural areas. A simplified Kinematic model have been done using basics concepts of mobile robots kinematics. At the end of this work is presented the portal frame structure development. The results obtained may assist in the design development of AAV\'s.