Seismic response evaluation of monuments based on ambient vibrations: the case studies of a Byzantine basilica and an Ottoman bath in Thessaloniki (Greece)

Abstract

The present work focuses on the seismic response and damage distribution studies on two Thessaloniki monuments with different structural systems. The first one is the Acheiropoietos basilica—a Byzantine monument included in the World Heritage List of UNESCO—with a flexible structural system consisted of internal colonnades and perimeter walls. The second one is the Bey hamam, an Ottoman bath with a stiff structural system. Its successive square or rectangular functional spaces are organized in such a way as to obtain both spatial and structural (bearing structure) autonomy; thick internal and external walls in two directions bear the domes directly or through single or double arches. Both monuments were subjected to the June 20, 1978 Thessaloniki earthquake ground motion (EQ) (M6.5) with significant damage which were accurately recorded and demonstrated in the Ephorate of Antiquities of Thessaloniki (EFAPOTH) archives. Sets of ambient vibration measurements were performed before any intervention work at the basilica. For the present study, similar measurements were performed at both monuments. Their eigen-properties were then calculated based on this data. Both monuments were modeled in details by finite element method; the analytical models were calibrated for the optimum approach of the eigen-properties resulted by the measurements. The main calibration parameter was the modulus of elasticity of the masonry walls. These calibrated models were also analytically subjected to the recorded acceleration time history of the Thessaloniki 1978 EQ. The findings of this work are related to the appropriately documented material properties and factors of these monuments that are unique. The result of this procedure was the calibration of reliable finite element models for response evaluation of the structures to potential ground motions in future earthquakes. These models were capable to quantitatively explain the damage patterns observed in the monuments. The monument with higher stiffness (Ottoman bath) exhibited damage concentrated to fewer elements than the more flexible monument (Byzantine basilica) where the damages were distributed to many structural elements.