Academic literature on the topic 'Space frame structures'

Space structures are inevitable while covering large spans. Space structures are skeletal structures, which are lighter for the same stiffness when compared with RCC roofs. Till now, space structures, like any other metal structures have been designed assuming the joints as rigid, although there have been several publications about semi rigid joints. Of course, the publications mostly deal with 2D structures and there are very few reports on 3D structures. Space structures, by their nature fall into the latter category. The joints in a space structure are popularly called as "nodes". Generally, nodes, which ensure concentricity of member axes, are either solid or hollow. These are either cast or forged. There are other proprietary types, which do not come under the above classification, and have not been considered in this thesis. Hollow nodes are obviously more economical than solid nodes, but also more flexible. While it is prudent to prefer hollow nodes, it is equally necessary to assess their flexibility, because of its influence on the behaviour of the structure. The hollow spherical node is very popular because of its simplicity and adaptability to various forms of space frames. Double layer grids, which are the most popular forms for roofing applications, are being increasingly implemented. While the hollow spherical node is well suited for double layer grids, an evolutionary development has been what is called as the hollow octahedral node (this node is simply referred to as the 'Octa ' node in this thesis). Chapter 1 introduces space frames and double layer grids in particular, with the advantages of using double-layer grids. Jointing systems available around the world are briefed and the node connector used in the present study is introduced with a brief write-up on its advantages and disadvantages. This chapter also explores the available literature and, the scope and objectives of the thesis are mentioned. Chapter 2 introduces 3D finite element models of the hollow spherical and octahedral nodes. The stiffness matrixes of these nodes have been derived by conducting analyses on the computer for six sizes each of the Octa and spherical nodes. Using the stiffness matrix of the node, a new method of incorporating this into the regular analysis of a space truss has been developed. The new method proposed yields realistic values for the forces in the members and takes into account the elastic deflections in the node under the action of member forces. Implementation of the proposed method has been carried out by writing a custom program using state-of-the-art object oriented programming techniques. A sample problem has been analyzed using this program to demonstrate the effect of including joint flexibility. The effect of flexibility of nodes on the effective length of compression members in double-layer grids has been evaluated. The effect of compliance on the dynamic characteristics of a space frame has also been evaluated for the sample space frame with flexible joints. The analysis program has been modified to evaluate the natural frequencies of the system using rigid or flexible nodes. The study of the Octanode and spherical node under the action of uniaxial compression and tension dominates the contents of Chapter 3. The two types of nodes have been analyzed using commercially available finite element software considering material nonlinearity. The stress patterns from the analyses have been examined thoroughly. Two consistent methods for fixing the load at yield in both uniaxial compression and tension have been proposed using the load-displacement curve. Yield loads for all the nodes have been evaluated using both the methods and the results agree well between the two methods. Three material yield values have been selected for each of the node size for evaluating the yield values viz. 240,320 and 415 MPa. The members of a double layer grid are connected to the nodes by bolts and holes are drilled in the nodes for this purpose. The bolthole patterns differ between two popular types of double-layer grids. Both these bolthole patterns have been modeled separately in the above exercise and the results for these two have been shown to be approximately the same. The effect of varying diameters of the boltholes on the response of the nodes has been examined. Relationships between the yield load, diameter, thickness and material yield have been developed using the method of least squares. The differences in the behaviour of the nodes under uniaxial compression and tension have been discussed. Ramberg Osgood type of relationships have been worked out for all the load-displacement curves obtained from the analyses. The simulation of non-linear behaviour of nodes with cracks with plastic crack closing forces have been carried out with useful insights into the behaviour of the two types of nodes in uniaxial compression and tension. Chapter 4 is devoted largely for studying the two types of nodes under the influence of biaxial load combinations. The combinations studied are dual compression, dual tension and compression-tension. In all cases equal loads are applied along two orthogonal; directions in the horizontal plane. Stress patterns have been examined for each type of load combination and yield values for each case have been obtained using one of the methods proposed in chapter 3. These have been compared with the corresponding uniaxial values in both compression and tension. Some useful inferences have been possible by studying the behaviour of the nodes under the various biaxial load combinations. In each case, relationships between the biaxial yield load, uniaxial yield load, diameter of node, thickness of node and material yield of node have been obtained using the method of least squares. The nodes have been analyzed under some selected Multi-axial loading and combinations of load which cause yield based on the second method proposed in Chapter 3 have been obtained and tabulated. However, a proper and thorough study of the nodes under multi-axial loading proved to be beyond the scope of this thesis. Chapter 5 contains the contributions made towards developing new methods and algorithms for obtaining the several results of chapters 2, 3 and 4, using object oriented programming (OOP) techniques. The contributions have been in Object Pascal, the underlying language of Delphi, a popular RAD tool developed by Borland/Inprise of USA. Several new modules have been developed to reliably handle the large amounts of data generated by the hundreds of analyses detailed in chapters 2,3 and 4. The ease with which new methods were possible to be incorporated into existing software using OOP has been demonstrated, with source code examples. Comparisons with other types of tools available and die advantages of using OOP have also been demonstrated using the experience during the preparation of this thesis. A strong case for OOP as an indispensable tool for the researcher has been made. Chapter 6: Several important conclusions and suggestions for future work have been made. Appendix 1 contains a brief note on the Method of Least Squares. Appendix 2 contains a small write-up on Delphi and OOP. Concepts of OOP have been briefly described and comparisons between three popular OOP languages have been attempted. A brief description of the features in Delphi's Object Pascal has also been provided. Appendix 3 contains the listing of Unit Arrays, which is a general purpose unit developed to make handling of large arrays easy. Several matrix calculations have been implemented which make the unit extremely useful for programmers. Appendix 4 contains the full listing of program FormK, which has been developed for chapter 2 to derive the fall stiffness matrix of a space frame node. The program picks up results from several analyses, forms a few columns of the stiffness matrix and then fills up the rest using the cyclic symmetry present in the space frame node. This program is given in full, with the intention that other researchers may find it useful to use it as-is or use after making small alterations to suit their circumstances. OOP is known for fast, reliable and easy ways of implementing modifications to existing code. Appendix 5 provides the full listing of the Object Pascal program for extracting Eigenvalues of a space truss with rigid joints or flexible joints. The incorporation of flexibility of the joints proposed in chapter 2 has been implemented. Descriptions of the program's implementations have been provided in chapter 5. Bibliography contains the alphabetical list of references.

Space structures are inevitable while covering large spans. Space structures are skeletal structures, which are lighter for the same stiffness when compared with RCC roofs. Till now, space structures, like any other metal structures have been designed assuming the joints as rigid, although there have been several publications about semi rigid joints. Of course, the publications mostly deal with 2D structures and there are very few reports on 3D structures. Space structures, by their nature fall into the latter category. The joints in a space structure are popularly called as "nodes". Generally, nodes, which ensure concentricity of member axes, are either solid or hollow. These are either cast or forged. There are other proprietary types, which do not come under the above classification, and have not been considered in this thesis. Hollow nodes are obviously more economical than solid nodes, but also more flexible. While it is prudent to prefer hollow nodes, it is equally necessary to assess their flexibility, because of its influence on the behaviour of the structure. The hollow spherical node is very popular because of its simplicity and adaptability to various forms of space frames. Double layer grids, which are the most popular forms for roofing applications, are being increasingly implemented. While the hollow spherical node is well suited for double layer grids, an evolutionary development has been what is called as the hollow octahedral node (this node is simply referred to as the 'Octa ' node in this thesis). Chapter 1 introduces space frames and double layer grids in particular, with the advantages of using double-layer grids. Jointing systems available around the world are briefed and the node connector used in the present study is introduced with a brief write-up on its advantages and disadvantages. This chapter also explores the available literature and, the scope and objectives of the thesis are mentioned. Chapter 2 introduces 3D finite element models of the hollow spherical and octahedral nodes. The stiffness matrixes of these nodes have been derived by conducting analyses on the computer for six sizes each of the Octa and spherical nodes. Using the stiffness matrix of the node, a new method of incorporating this into the regular analysis of a space truss has been developed. The new method proposed yields realistic values for the forces in the members and takes into account the elastic deflections in the node under the action of member forces. Implementation of the proposed method has been carried out by writing a custom program using state-of-the-art object oriented programming techniques. A sample problem has been analyzed using this program to demonstrate the effect of including joint flexibility. The effect of flexibility of nodes on the effective length of compression members in double-layer grids has been evaluated. The effect of compliance on the dynamic characteristics of a space frame has also been evaluated for the sample space frame with flexible joints. The analysis program has been modified to evaluate the natural frequencies of the system using rigid or flexible nodes. The study of the Octanode and spherical node under the action of uniaxial compression and tension dominates the contents of Chapter 3. The two types of nodes have been analyzed using commercially available finite element software considering material nonlinearity. The stress patterns from the analyses have been examined thoroughly. Two consistent methods for fixing the load at yield in both uniaxial compression and tension have been proposed using the load-displacement curve. Yield loads for all the nodes have been evaluated using both the methods and the results agree well between the two methods. Three material yield values have been selected for each of the node size for evaluating the yield values viz. 240,320 and 415 MPa. The members of a double layer grid are connected to the nodes by bolts and holes are drilled in the nodes for this purpose. The bolthole patterns differ between two popular types of double-layer grids. Both these bolthole patterns have been modeled separately in the above exercise and the results for these two have been shown to be approximately the same. The effect of varying diameters of the boltholes on the response of the nodes has been examined. Relationships between the yield load, diameter, thickness and material yield have been developed using the method of least squares. The differences in the behaviour of the nodes under uniaxial compression and tension have been discussed. Ramberg Osgood type of relationships have been worked out for all the load-displacement curves obtained from the analyses. The simulation of non-linear behaviour of nodes with cracks with plastic crack closing forces have been carried out with useful insights into the behaviour of the two types of nodes in uniaxial compression and tension. Chapter 4 is devoted largely for studying the two types of nodes under the influence of biaxial load combinations. The combinations studied are dual compression, dual tension and compression-tension. In all cases equal loads are applied along two orthogonal; directions in the horizontal plane. Stress patterns have been examined for each type of load combination and yield values for each case have been obtained using one of the methods proposed in chapter 3. These have been compared with the corresponding uniaxial values in both compression and tension. Some useful inferences have been possible by studying the behaviour of the nodes under the various biaxial load combinations. In each case, relationships between the biaxial yield load, uniaxial yield load, diameter of node, thickness of node and material yield of node have been obtained using the method of least squares. The nodes have been analyzed under some selected Multi-axial loading and combinations of load which cause yield based on the second method proposed in Chapter 3 have been obtained and tabulated. However, a proper and thorough study of the nodes under multi-axial loading proved to be beyond the scope of this thesis. Chapter 5 contains the contributions made towards developing new methods and algorithms for obtaining the several results of chapters 2, 3 and 4, using object oriented programming (OOP) techniques. The contributions have been in Object Pascal, the underlying language of Delphi, a popular RAD tool developed by Borland/Inprise of USA. Several new modules have been developed to reliably handle the large amounts of data generated by the hundreds of analyses detailed in chapters 2,3 and 4. The ease with which new methods were possible to be incorporated into existing software using OOP has been demonstrated, with source code examples. Comparisons with other types of tools available and die advantages of using OOP have also been demonstrated using the experience during the preparation of this thesis. A strong case for OOP as an indispensable tool for the researcher has been made. Chapter 6: Several important conclusions and suggestions for future work have been made. Appendix 1 contains a brief note on the Method of Least Squares. Appendix 2 contains a small write-up on Delphi and OOP. Concepts of OOP have been briefly described and comparisons between three popular OOP languages have been attempted. A brief description of the features in Delphi's Object Pascal has also been provided. Appendix 3 contains the listing of Unit Arrays, which is a general purpose unit developed to make handling of large arrays easy. Several matrix calculations have been implemented which make the unit extremely useful for programmers. Appendix 4 contains the full listing of program FormK, which has been developed for chapter 2 to derive the fall stiffness matrix of a space frame node. The program picks up results from several analyses, forms a few columns of the stiffness matrix and then fills up the rest using the cyclic symmetry present in the space frame node. This program is given in full, with the intention that other researchers may find it useful to use it as-is or use after making small alterations to suit their circumstances. OOP is known for fast, reliable and easy ways of implementing modifications to existing code. Appendix 5 provides the full listing of the Object Pascal program for extracting Eigenvalues of a space truss with rigid joints or flexible joints. The incorporation of flexibility of the joints proposed in chapter 2 has been implemented. Descriptions of the program's implementations have been provided in chapter 5. Bibliography contains the alphabetical list of references.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2017.<br>The aim of this thesis is to investigate the applications of multifunctional compos- ite (MFC) technology to nano-satellite structures and to produce a working concept design, which can be implemented on future Cube-Satellites (CubeSats). MFC tech- nologies can be used to optimise the performance of the satellite structure in terms of mass, volume and the protection it provides. The optimisation of the structure will allow further room for other sub-systems to be expanded and greater payload allowance. An extensive literature view of existing applications of MFC materials has been conducted, along with the analysis of a MFC CubeSat structural design account- ing for the environmental conditions in space and well-known design practices used in the space industry. Numerical analysis data has been supported by empirical analysis that was done where possible on the concept material and structure. The ndings indicate that the MFC technology shows an improvement over the conventional alu- minium structures that are currently being used. Improvements in rigidity, mass and internal volume were observed. Additional functions that the MFC structure o ers include electrical circuitry and connections through the material itself, as well as an increase electromagnetic shielding capability through the use of carbon- bre composite materials. Empirical data collected on the MFC samples also show good support for the numerical analysis results. The main conclusion to be drawn from this work is that multifunctional composite materials can indeed be used for nano-satellite structures and in the same light, can be tailor-made to the speci c mission requirements of the satellite. The technology is in its infancy still and has vast room for improvement and technological development beyond this work and well into the future. Further improvements and additional functions can be added through the inclusion of various other materials.

The displacement method of the finite element is adopted. Both the updated Lagrangian formulation and total Lagrangian formulation of a three-dimensional beam element is employed for large displacement and large rotation, but small strain analysis. A beam-column element or finite element can be used to model geometrically nonlinear behavior of space frames. The two element models are compared on the basis of their efficiency, accuracy, economy and limitations. An iterative approach, either Newton-Raphson iteration or modified Riks/Wempner iteration, is employed to trace the nonlinear equilibrium path. The latter can be used to perform postbuckling analysis.<br>Ph. D.

Recent demands in large space structure technology have suggested the use of active control actuators integral to a structures' construction. The concept of a 3-D (triangular cross-sectioned) active truss is presented. The linear equations of motion for one plane of the truss are derived. A model for a generic flexible beam is then appended to the planar truss model. A linear time-invariant optimal control law is found, followed by a presentation of an experimental planar truss built to test the concept. Physical parameters are then substituted into the dynamic model and several sets of control gains are found. The "Kalman'' gains are applied to the experimental structure. Experimental results are compared to expected theoretical results with good (30%) correlation. Conclusions are drawn and suggestions are made for further research.<br>Master of Science