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Timber Grid-shell Structures: form-finding, analysis and optimisation

D'Amico, Bernardino

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Abstract

This thesis aims to provide a set of tools for analysis and design of free-form timber grid-shells. It provides a brief introduction on the relationship between shape and structural behaviour of grid-shells, followed by an introduction to actively-bent structural systems. The design issues are then individuated and three main themes are defined, namely: Form-finding, Structural Analysis and Optimisation. The development and use of a numerical framework, based on a six Degree-of-Freedom (DoF) co-rotational beam-element in conjunction with the Dynamic Relaxation method, has formed the basis, on which a unified procedure for the Form-finding and Structural Analysis tasks are denied.
A two-step analysis procedure allows seeing a target shape for the grid-shell with the aid of a reference surface, whilst taking into account the effect of internal (bending) reactions on the final geometry. Coupling constraints are numerically simulated by development of a single-node cylindrical joint. An algorithm for grid cutting (mesh manipulation) is described, as well as a modified co-rotational beam-element, based on assumption of ‘equivalent’ bending stiffness. The modified formulation allows taking into account the change in stiffness of the double-layer members, when passing from the Form-finding to the analysis of the structure under working loads, by simply seeing a dimensionless parameter. A numerical framework for optimisation of the members’ cross-section is then introduced.
The optimisation problem is decomposed in two main sub-problems, to be separately solved by iterative techniques: the seeking of an ‘allowable’ thickness, for the laths under bending action, is pursued with a procedure based on Newton-Raphson method, whilst: a local-search approach is used to find (for a given load configuration) the optimal variation in thickness of the composite cross-section.
The proposed methods are validated by several numerical and full-size experimental test, as well as comparison with the corresponding analytical solution, where available.

Thesis Type Thesis
Deposit Date Apr 12, 2016
Peer Reviewed Not Peer Reviewed
Keywords Timber grid shells; free-form; structural behaviour; structural analysis; form-finding; optimisation;
Public URL http://researchrepository.napier.ac.uk/id/eprint/9833
Contract Date Apr 12, 2016
Award Date 2015-10

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