Selective Weakening Techniques for RC Walls
Principal Researcher: Assoc. Prof. Stefano Pampanin
Staff involved: Professor Des Bull
Students involved: Matthew Ireland, Kam Weng Yuen
Current seismic retrofit strategies generally focus on increasing strength, stiffness or upgrading characteristics of a structure. A typical drawback is that the upgraded behaviour could result in an increased demand on the structure. Previous research has focused on developing retrofit solutions that involve a selective upgrade of single properties (i.e. strength, stiffness & ductility) of the behaviour.
A selective weakening approach strategy has been proposed by the researcher as a counter-intuitive but rational seismic retrofit strategy with large potentiality and a wide range of applications (walls, b-c joints, columns and diaphragm systems).
Matthew Ireland has performed a series of tests on a benchmark specimen and two retrofit solutions, plus carrying out some numerical analyses on prototype buildings. These results will be presented at the NZSEE conference in Palmerston North in 2007.
A selective weakening intervention is performed with the aim of improving the inelastic mechanism (i.e. from shear to flexure) by selectively reducing the strength/stiffness of specific members within the structural system. This in turn can result in a reduced demand on the structural member. A rocking behaviour with all the recognized advantages will thus be enforced to occur. Additional unbonded post-tensioning can be added to provide further re-centering while controlling the level of overturning moment to desired limit and protect the foundation. Once weakening has been achieved the designer can use the wide range of available techniques and materials (e.g. supplemental damping or dissipation devices, FRP) to ensure that adequate characteristics of the weakened member are realized and an alternative and safer load path can develop. Flag-shape systems (i.e. re-centering and dissipating can thus be obtained as best means for a performance based seismic retrofit strategy) Basic principles of capacity design as well as advanced performance-based criteria should be satisfied.
