Modelling force behaviour and contributions of metallic extrusion dampers for seismic energy dissipation. (2019)
Type of ContentTheses / Dissertations
Thesis DisciplineMechanical Engineering
Degree NameDoctor of Philosophy
PublisherUniversity of Canterbury
Supplemental energy dissipation devices are increasingly used to protect structures, limiting loads transferred to structures and absorbing significant response energy without sacrificial structural damage. HF2V, or high force to volume, devices are a successful form of relatively low-cost, robust supplemental dissipation devices. The displacement of the HF2V device bulged shaft plastically deforms a working material, dissipating significant energy.
HF2V devices are metallic extrusion dampers, currently designed using limited precision models, so there is variability in force prediction, which makes design difficult and time consuming. Furthermore, while a device force is predicted, the knowledge of the exact internal mechanisms occuring within these devices is lacking, limiting insight and predictive accuracy in device design. As a result, there is a need for significant analysis to develop and improve means of designing HF2V devices to deliver specific design required dissipation forces.
This thesis develops a first precision HF2V design model based on the sum of friction and extrusion forces modelled as a function of device dimensions. Specifically, the Area Ratio (AR), shaft Surface Area (SA), and Bulge Area (AB). Multiplicative coefficients for these terms in 14 linear and linear-quadratic models are calculated using regression analysis on data from 18 experimental devices with and without bulges. Pearson correlation coefficient values (R2) summarise model completeness and the error between experimental and model predicted force. Leave k=3 out validation for random and specific groups of devices assesses model robustness to the device data used to identify the model. The overall results provide a simple, generalisable model capturing all relevant mechanics for precise design of HF2V devices to a specific quasi-static force capacity, as well as a good starting point for more specific and detailed mechanics models.
Upper bound and lower bound analytical models are then derived by matching the HF2V device geometric parameters to direct and indirect extrusion design parameters from the metal forming industry. Six design based analytical models provide maximum and minimum loads produced in HF2V devices based on plasticity theorem, and results are compared to experimental device forces. The models exhibit an operational range for the devices within which the HF2V devices operate during plastic deformation. All the experimental device forces lie under the direct extrusion upper bound values and above the lower bound values. The indirect extrusion model forces broadly match the experimental HF2V device forces. A further method to achieve approximate HF2V device forces from these analytical boundary equations is developed using combinations of UB and LB force models. Device parameters directly influencing damper forces are identified through analysis, which is valuable for future HF2V design selection, and provide an accurate, and more complex analytical modelling approach from this thesis, as well as boundary limits useful in design.
Finally, a generic finite element model is developed using ABAQUS, to better understand force generation and aid in precision device design, thus speeding up the overall design and implementation process for uptake and use. The model is applied to experimental HF2V devices of various sizes. The highly nonlinear, large-deflection analysis is run using ABAQUS/Explicit with automatic increments to balance higher accuracy and computational time. The total force output is sum of the friction forces between the lead working material and the steel device components, due to the contact pressure forces acting between moving shaft and displaced lead. The results are accurate to ±20% for Typical and Large devices, yielding a third model, which also provides insight into internal device motion and strain in the working material, which has not previously been known.
Overall, three modelling approaches developed for lead extrusion dampers are presented in this thesis. The generalized and design based models can predict specific force capacities of the HF2V devices in the design stage and can serve as an optimization tool for design modifications. Design parameters affecting the device forces in the devices are identified and provide a guideline for future design of the devices.