PhD exam

Raluca defended successfully her PhD thesis "Seismic analysis and behaviour of reinforced concrete U-shaped walls". The members of his committee were Prof. S. Sritharan (University of Iowa State, US), Prof. B. Stojadinovic (ETHZ), Prof. A. Muttoni (EPFL), Prof. A. Nussbaumer (EPFL, exam president) and Katrin Beyer (PhD advisor). Raluca advanced the knowledge on the seismic response of U-shaped walls through an experimental and a numerical study. She tested two U-shaped walls that differed with regard to the axial load that was applied. It is only the fourth test series on the seismic response of U-shaped walls that has been carried out worldwide and the first to address loading in the diagonal direction. The three previous test series that were carried out on U-shaped walls subjected the walls to axial load ratios of 5% or less. Raluca’s tests extend this range therefore considerably and yield new insights into the behaviour of core walls in highrise buildings, where large axial load ratios are common. Furthermore, it led to shear stress ratios that are close to the stress limits given in the ACI code. These stress limits tend to drive the design of all core walls of highrise buildings that are currently constructed in California and Raluca’s tests are at present the only ones that investigated the core wall response close to these limits. In addition to the experimental study, Raluca investigated the response of U-shaped walls through detailed numerical shell element models and used these to develop new analytical formulations that can be used in early stages of the design procss. The main contributions concern the modification of effective stiffness estimates , yield displacement formulations that account further for shear deformations (which are particularly important for U-shaped walls), and plastic hinge lengths for different loading directions.