Krstulovic–Opara and Nau 2003
The authors perform a numerical study on the response of structures with self-actuating fuses. HPFRC is used in conjunction with SMAs in zones of beams with high forces in improve the performance of these regions.
System Concept
In HPFRCs, fibers are inserted into the concrete mix. This results in the concrete being able to hold tensile stresses, as well as strain hardening after the first cracks appear. SMAs are metals with the characteristic property that they return to their original shape after inelastic deformations through either an increase in temperature provided by a small electric current, or a super-elastic response, in which removal of stress causes the deformation to be recovered.
In both cases, SMAs are able to absorb significant amounts of energy and exhibit self-centering characteristics. This study combines the properties of HPFRCs and SMAs at the ends of beams to create a much more ductile zone where there is a high combination of shear and flexure. HPFRCs and SMAs in this zone or more free to deform than traditional concrete, resulting in ductile beam ends and the dissipation of energy. SMAs are longitudinally pre-stressed, giving them the propensity to return to their original positions. The nature of SMAs (phase changes that occur) allow them to adjust their response to higher capacities as required.
Analytical Study, Results, and Discussion
An analytical study was performed on 5-story reinforced concrete structures with the HPFRC and SMA fuse system and without the system. It was observed that under seismic loading, the fuses were able to absorb the high seismic energy that could not be dissipated by the building without the HPFRC and SMA fuse system. Only the building with the system was deemed repairable after high earthquake loading.
It can be concluded that a self-actuating fuse system has potential for increasing the ductility of buildings under seismic loading, but further research is required in this area of nontraditional building construction. Experimental results still need to verify the effectiveness of the system.
Reference
Krstulovic–Opara, N. & Nau J. "Self–Actuating SMA–HPFRC Fuses for Auto–Adaptive Composite Structures." Computer-Aided Civil & Infrastructure Engineering, 18.1, pp. 78-94.