Kinky structures

Currie, NGR

Abstract

Rotational springs are not widely used in structural engineering other than within undergraduate texts to aid with the understanding of strut buckling or other similar theoretical exercises.
The inclusion of rotational springs can significantly alter the behaviour of a structure, bringing several potential benefits if inserted strategically. For instance, allowing a frame to be delivered to site as a single deployable piece, where the rotational springs introduce an element of temporary stability during erection; by ensuring hinges form in specific locations during extreme loading events, creating reliable load paths whilst retaining structural integrity; or by limiting the axial force in specific elements, forcing an element to buckle at specific loads.
Currently, there is a significant gap in the existing research with regards the analysis and behaviour of structures that have springs distributed through the frame. The inclusion of springs within structural frames will typically encourage gross, yet controlled and predictable displacements that are challenging to analyse. Equally, deployable structures require an element of instability to deploy. With most research focusing on the packed and deployed states of these structures, there is still considerable research to be done on the structural performance of the intermediate stages of deployment.
Several forms of deployable structure, such as cable-chain arches for example, are vulnerable and unstable during their intermediate deployment phase and it is proposed that the integration of rotational springs in these types of structure could help control the deployment and maintain stability from a packed shape into the final in-service form as well as preventing phenomenon such as snap-through buckling under large loads.
Original work within this thesis creates several repeatable and reliable methods for undertaking buckling analysis of sprung chains to determine an initial balanced equilibrium form to which in-service loadings can then be applied as well as determining the post-buckled behaviour for sprung structures.
The application of numerical analysis methods is demonstrated as giving reliable results for single and multiple degrees of freedom systems, but due to the potential for incompatibilities between the stiffnesses of the rotational springs and beam elements there are issues associated with ill-conditioning and methods have been established to identify and mitigate these effects.
Alternative structural forms, beyond simple arches, have also been developed through seeking inspiration from the higher buckling modes. Shapes resembling these higher modes have been generated through the careful manipulation of spring stiffnesses (mobilising linear and non-linear springs) combined with the introduction of initial geometrical imperfections allowing the structures to adopt alternative stable states in direct response to specific loading conditions.
The analysis methods contained within this thesis are currently more advanced than the manufacturing techniques required to realise these designs in the real world. Although, flexible springs are already being cut into stiff plywood panels using living hinges and multi-material 3D printing is commonplace within the maker community, but these techniques have not yet progressed through to the scale and consistency needed to fabricate a large structural element.
However, as these manufacturing techniques mature, the work presented within this thesis will provide a solid base from which the effective analysis of multi-stiffness structures will be possible.

Citation

Currie, N. Kinky structures. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Nov 10, 2020
• Publicly Available Date: Nov 10, 2020
• Award Date: Apr 1, 2020