Influence of stiffness constraints on optimal design of trusses using morphological indicators

摘要

Within the framework of sustainable development we strive for structures with a minimum volume of material. When we only consider criteria on resistance and buckling, Samyn and Latteur prove that even at the stage of conceptual design a clear hierarchy among the different truss typologies can be established. Up to now, stiffness constraints - such as the upper limit on static displacements - were not considered. However, an optimum obtained by minimising the volume, only considering the strength criterion, often results in solutions which violate the stiffness constraint(s). To avoid large displacements a stress level reduction can be imposed. However, this comes at the cost of a significant volume increase. With an optimisation process that involves the stiffness constraints at the stage of conceptual design, an optimum can be obtained without the necessity to alter the structure drastically afterwards, which partly annihilates the main objective of minimal use of material. This approach compares the different truss types on a new priority scale, generating new optima. This implicates a non-negligible change in the truss choice at conceptual design stage. The solutions are logically depended on the displacement criterions. This approach forms a first step to a new design philosophy that considers all the stiffness constraints (static displacements, resonance, local and global buckling) at conceptual design stage and is called design for stiffness.