Displacement-based assessment of the Gazi Hasan Pasha mosque in Kos island (GR) under the 2017 M6.6 earthquake and Eurocode 8, with proposals for upgrading

Abstract

On 21/7/2017 a M6.6 offshore earthquake shook the Greek island of Kos and the Turkish coastal city of Bodrum. The Gazi Hasan Pasha mosque, a 1786 structure, suffered very limited damage: the load-bearing walls have not shown cracks or extensive deformation; the minaret and few timber members at the roof and the floor suffered serious damage. Confirmation of the damage by the results of an analysis under the nearby recorded seismic loads validated both the model and the assumptions of the analysis. In the second step the seismic performance was assessed using seismic loads from the Greek National Annex to EN1998-1 and the effectiveness of strengthening measures to upgrade the monument was studied. The assessment was based on the Greek code for interventions to masonry structures (KADET) which employs performance-based criteria. The analyses show that the mosque with strengthening measures implemented after it was damaged by an earthquake in 1933, withstands the relative drifts caused by the 2017 event. The predicted damage concurs with the observed limited damage of the structure. Analysis using seismic loads from Eurocode 8 and the performance- and displacement-based criteria of the draft KADET led to the conclusion that the structure cannot withstand these loads and needs strengthening. Insertion of steel tendons at the crest of the most displaced wall attenuates but does not eliminate the damage; addition of further tendons at the level of the top of the ground story wall appears to be very effective in achieving Immediate Occupancy performance for most elements of the building.