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Keywords: static shape control, prestress control, displacement control, actuator placement, force method.

Summary

There are applications of structural engineering where tolerances of structural shape and internal forces, under changing service conditions, are not only important but actually impinge on the structure's serviceability limit state. Such structures could be supporting sensitive and demanding scientific or communications equipment. These structures are typically pin-jointed assemblies, since length actuations can be more readily incorporated to bring about the shape and/or bar force changes.

A direct method for controlling nodal displacements, internal bar forces, and simultaneously both nodal displacements and internal bar forces, of a prestressable pin-jointed assembly under load, is presented in this paper. The method is based on the force method of structural analysis, and revolves around the solution to a matrix equation of the form: d=Ye_o+d_P, where Y is a lengthy but straightforward expression involving the compatibility and flexibility matrices, and the states of selfstress, d_P is the vector of nodal displacements of the structure due only to the load, and d is the desired resultant nodal displacements which can be obtained when elongation actuation e_o is applied. The problem then is typically that of looking for a suitable e_o to apply that takes the structural displacement from d_P to d in at least some of the components, without incurring additional bar force violations.

The paper discusses the method to identify which are the most effective bars for actuation (i.e. what should e_o be) so that the desired structural shape can be obtained, without incurring violation in bar forces, through both a minimal number of actuators and minimum actuation in those actuators. The method can also be used for adjustment of bar forces to either reduce instances of high forces or increase low forces, for example in a cable nearing slack.

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 88 PROCEEDINGS OF THE NINTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY Edited by: B.H.V. Topping and M. Papadrakakis Paper 162 Displacement and Force Control in Pin-Jointed Assemblies A.S.K. Kwan Cardiff School of Engineering, Cardiff University, United Kingdom doi:10.4203/ccp.88.162 purchase the full-text of this paper Full Bibliographic Reference for this paper A.S.K. Kwan, "Displacement and Force Control in Pin-Jointed Assemblies", in B.H.V. Topping, M. Papadrakakis, (Editors), "Proceedings of the Ninth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 162, 2008. doi:10.4203/ccp.88.162 Keywords: static shape control, prestress control, displacement control, actuator placement, force method. Summary There are applications of structural engineering where tolerances of structural shape and internal forces, under changing service conditions, are not only important but actually impinge on the structure's serviceability limit state. Such structures could be supporting sensitive and demanding scientific or communications equipment. These structures are typically pin-jointed assemblies, since length actuations can be more readily incorporated to bring about the shape and/or bar force changes. A direct method for controlling nodal displacements, internal bar forces, and simultaneously both nodal displacements and internal bar forces, of a prestressable pin-jointed assembly under load, is presented in this paper. The method is based on the force method of structural analysis, and revolves around the solution to a matrix equation of the form: d=Ye_o+d_P, where Y is a lengthy but straightforward expression involving the compatibility and flexibility matrices, and the states of selfstress, d_P is the vector of nodal displacements of the structure due only to the load, and d is the desired resultant nodal displacements which can be obtained when elongation actuation e_o is applied. The problem then is typically that of looking for a suitable e_o to apply that takes the structural displacement from d_P to d in at least some of the components, without incurring additional bar force violations. The paper discusses the method to identify which are the most effective bars for actuation (i.e. what should e_o be) so that the desired structural shape can be obtained, without incurring violation in bar forces, through both a minimal number of actuators and minimum actuation in those actuators. The method can also be used for adjustment of bar forces to either reduce instances of high forces or increase low forces, for example in a cable nearing slack. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £145 +P&P)
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