Hybrid passive seismic mitigation devices for low-damage structures.
Thesis DisciplineMechanical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Earthquake ground motions impose a significant risk of damage on structures which can result in post-event repair and downtime costs, potential demolition and, in extreme cases, loss of life. These consequences can put an economic burden on communities following a large earthquake. Therefore, development of low-damage structures using repeatable, low cost, and effective supplemental dissipation to preserve life safety and improve resilience is crucial.
This thesis investigates the design, development, and experimental validation of two types of novel hybrid self-centring dissipation devices for low-damage structures. The elements used to create the hybrid devices consist of a friction ring-spring (RS), a high-force-to-volume (HF2V) lead extrusion damper, and a viscous damper (VD). These hybrid devices can be used as alternate means of dissipating energy to develop and design low-damage structures. The devices investigated within this thesis are relatively compact and are therefore appropriate for structural applications in a wide range of architectural spaces. Therefore, the development of these devices is a step towards developing a wider range of low-damage structural design methods, reducing the adverse impacts of earthquake ground motions on communities.
Nonlinear spectral analyses of elastoplastic structures with supplemental hybrid dissipaters are presented to provide an indication of their performance as a function of the balance of hybrid elements used. Hybrid combinations of ring-springs and HF2V devices and a hybrid combination of viscous dampers and ring-springs is used in these analyses. The results indicate hybrid devices can offer significant reductions in peak drift owing to the dissipative behaviour of their constitutive elements, which also leads to lower residual drifts. Residual drifts are further improved by the re-centring capability of the ring-spring. These benefits come at a cost of increased base shear demand of the structures with supplemental hybrid damping, arising as a result of the reaction loads from the added device forces. The overall results illustrate the trade-off of dissipation and re-centring goals when hybrid devices are used.
Experimental validation analyses are done using a prototype hybrid RS+VD device. The hybrid device combines rate-dependent dissipation of a viscous damper with the rate-independent dissipation and re-centring restoring force of a ring-spring in a parallel configuration. Proof-of-concept validation tests use sinusoidal displacement inputs across a comprehensive matrix of amplitudes and frequencies, and two ring-spring pre-loads to generate force-displacement graphs for the hybrid device and enable comparison with the behaviour of individual components. The results offer a range of new, easily implemented options for energy dissipation in developing low-damage structures, which can also provide necessary re-centring capability within the same package. The overall method is readily generalised for a wide range of hybrid device force capacities and design requirements.
Overall, this thesis develops a hybrid re-centring damping device through simulation, prototype development and experimental validation where the presented methods are generalisable to other similar hybrid devices. The main outcomes include providing simultaneous, repeatable supplemental dissipation using hybrid damping devices where the damping and re-centring components are readily customisable. The hybrid devices presented are entirely generalisable for both new designs and retrofit of existing structures.