An interdisciplinary investigation of the seismic performance of a historic tower in Istanbul during the 1999 Kocaeli earthquake

This paper investigates the effects of soil-structure interaction and site amplification on the seismic response of one of the towers of the Theodosian walls of Constantinople during the Kocaeli earthquake in 1999, that largely damaged it. The interacting system is first analysed in the frequency domain by the well-known replacement oscillator model, turning out that the effect of soil-structure interaction could be relevant. The complete system is then examined by the direct approach considering non linearity of the behaviour of both the structure and the soil. The failure mechanism detected from where stress and plasticization concentrate into the masonry panels is consistent with the out-of-plane mechanism of one of the tower facades triggered by the reference earthquake. The focus was then set on the effectiveness of some retrofitting interventions, including the lateral disconnection of the embedded sides of the tower from the surrounding soil, the soil treatment by grouted columns and the classical technique for masonry rehabilitation. Even though the latter choice is the most common one, retrofitting interventions concentrated into the soil could be effective as well. Their use should be properly considered when the scope of the intervention is the preservation of cultural heritage.