Dynamical analysis and optimisation of statically determinate strusses at conceptual design stage

Thomas Vandenbergh, Benjamin Verbeeck, Willy De Wilde

Research output: Chapter in Book/Report/Conference proceedingConference paper

Abstract

Within the framework of sustainable development we strive for constructions with a minimum volume of material. When we only consider criteria on resistance and buckling, it is shown that even at the stage of conceptual design a clear hierarchy among the different truss topologies can be established with Morphological Indicators (MI). MI are dimensionless numbers that represent a characteristic performance of a structure (e.g. volume) and depend only on a small number of variables (in its most simple formulation only the slenderness of the structure). We define the slenderness as L/H, L being the horizontal and H the vertical dimension of the rectangle, which inscribes the structure. This allows us to compare the efficiency of structures objectively, with only a reduced number of variables to consider. The problem is formulated as follows: given a load case (e.g. distributed load), structural typology and geometry (e.g. Warren truss) and supports (e.g. hinge and roller), we seek the slenderness that minimises a MI (e.g. volume indicator). Up to now, dynamic effects -such as resonance- were not considered when designing constructions with MI. However, an optimum obtained by minimising the volume, and only considering strength performance, often results in solutions with a problematic dynamic behaviour. To avoid resonance the stiffness and/or the damping charac-teristics must be modified in order to shift the eigenfrequencies outside the range of possible excitation frequencies. This yields a volume increase, additional equipment and as a consequence a cost raise. With an optimisation process that considers dynamic behaviour at the stage of conceptual design, an optimum can be obtained without the necessity to alter the (strength-optimised) construction drastically afterwards. In this study the undamped solutions for statically determinate trusses are analysed.
Taking stiffness into account compares the different truss types on a new priority scale, gen-erating new optima. This implicates a significant change in the truss choice at conceptual de-sign stage. The solutions depend logically on the forbidden frequency range(s).
This approach forms a first step to a design philosophy that considers all the stiffness con-straints at conceptual design stage and is called design for stiffness.
Original languageEnglish
Title of host publicationProc. of the ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, Rethymno, Creta, Greece, 13-16 June
EditorsM. Papadrakakis, D.c. Charmpis, N.d. Lagaros, Y. Tsompanakis
Pages253
Number of pages1
Publication statusPublished - 13 Jun 2007
EventFinds and Results from the Swedish Cyprus Expedition: A Gender Perspective at the Medelhavsmuseet - Stockholm, Sweden
Duration: 21 Sep 200925 Sep 2009

Publication series

NameProc. of the ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, Rethymno, Creta, Greece, 13-16 June

Conference

ConferenceFinds and Results from the Swedish Cyprus Expedition: A Gender Perspective at the Medelhavsmuseet
Country/TerritorySweden
CityStockholm
Period21/09/0925/09/09

Bibliographical note

M. Papadrakakis, D.C. Charmpis, N.D. Lagaros, Y. Tsompanakis

Keywords

  • conceptual design
  • Optimisation
  • Morphological indicators

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