Design, testing and simulation of grip ‘n’ grab ratcheting, tension-only devices for seismic energy dissipation systems.
Thesis DisciplineMechanical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This thesis details the development of a ratcheting, tension-only mechanism for use with seismic energy dissipation systems, known as the Grip 'n' Grab (GNG). The development is taken from initial design concepts through to construction and testing of two prototype devices, as well as development of a material model algorithm to simulate the hysteretic response of the devices, and a finite element flexible rocking system model to assess the behaviour of a controlled rocking system instrumented with the GNG device. The GNG devices developed use single direction engagement to provide resistance to system displacements while allowing for re-centring and closure of rocking joints. Concerns around buckling and residual compressive forces in the dissipater, which can exist in traditional tension-compression solutions are ameliorated. The ratcheting mechanism reduces the take-up prior to engagement on cycles after previous engagement of the dissipater element has occurred, increasing resistance to displacement and improving energy dissipation capability.
The completed schedule of monotonic compressive and cyclic experiments, with 14 yielding steel dissipaters, has provided insight into operational issues and design considerations. Careful detailed design was used in both prototypes to ensure a low-cost and easy to machine device, to increase likelihood of uptake. The results of the testing of the two prototype devices, and the subsequent numerical analyses, show the potential of the GnG concept to be a favourable option in supplementary damping and bracing systems. Robust, repeatable operation of both prototype mechanisms, with redundancy in engagement, was observed, with negligible compressive forces recorded. The GNG ratcheting, tension-only devices developed provide a unique solution which can be implemented with a range of energy dissipation mechanisms as desired. The ratcheting mechanism itself is generalisable and could be attached to the dissipater element through a range of interfaces, depending on what is required for a given application.
The GNG material model algorithm developed allowed for the device behaviour to be simulated in numerical analysis, providing a basis for the inclusion of a GNG device within a structural design. The finite element controlled rocking system model also developed in this thesis was used to simulate the behaviour of a rocking frame and provide insight into GNG behaviour in a rocking structure and the impact on the overall behaviour of the controlled rocking system. Multiple parameter studies were conducted involving over 18000 individual time-history analyses looking at the response of a range of structures to a ULS seismic event based in the Wellington region. The study of rocking system response and demand in the GNG devices completed in this thesis provides a tentative guide for implementation and required capacity in deployment.