|M.Sc Student||Vilnay Margalite|
|Subject||Using Shape Memory Alloys for Seismic Upgrading|
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Robert Levy|
|Full Thesis text|
Protection of structures from seismic risk is one of the principal challenges in structural engineering. This has led to many innovative concepts of structural protection. One is passive energy dissipation, the basic role of which is to absorb a portion of the input energy thereby minimising possible structural damage. Although research is still in early stages Shape-Memory-Alloys’ (SMAs) properties seem to make them ideal for use in such innovative applications. SMAs are metal alloys which can sustain large strains (up to 15%) with no residual deformation after unloading. These alloys exhibit re-centring properties and high fatigue resistance and therefore are particularly attractive for applications in seismic design.
This work studies the advantages of seismic upgrading using super-elastic SMAs. Two main structural types were chosen; frames (modern) and masonry (historic) structures.
Both steel and reinforced-concrete frames were considered. The frames were modelled using the Abaqus software code. Geometric and material nonlinear behaviour was taken into account. Seismic analysis was performed using the explicit solution algorithm. The SMA retrofit alternative was compared to a conventional steel one. The brace cross sections were optimally obtained using the fully-stressed-design procedure. Calculated SMA cross section areas were lower than those of steel. Additionally, the results presented an overall reduction in inter-storey drift values for SMA braces, no residual displacements due to the re-centring capability and faster vibrational decay. The conventional steel braces underwent yielding and buckling, resulting in permanent story drifts and less effective seismic vibration control.
The second structural type considered was masonry. Three structures were investigated; an arch, a barrel vault and a groin vault. The structures were modelled in Abaqus using the discrete-element-method which is an achievement on its own. Moreover it was shown that finite-elements representing reinforcement can be embedded into the discrete-element-method leading to imperative results. Nonlinear material and geometric seismic analysis was performed using the explicit solution algorithm. A retrofit scheme was chosen and implemented using both steel and SMA. The behaviour of the structures was compared during different seismic intensities. Comparisons between steel and SMA reinforcing schemes show that SMA effectiveness increases with seismic intensity. In high excitations the steel reinforcement attains irreversible plastic strains that lead to collapse whereas SMAs exhibit better overall behaviour and are an improved method of reinforcement.
Overall, the super elastic SMA retrofitting proved to be an adequate solution for the protection of both modern and historical structures from seismic hazards.