# Seismic Assessment and Strengthening of a Load-Bearing Masonry Structure Considering SSI Effects
## 1 Introduction  
Although relatively rare, destructive earthquakes can cause extensive damage or even lead to the partial or total collapse of historical load-bearing masonry buildings that have not been retrofitted in accordance with modern seismic codes. These structures typically exhibit inherent structural weaknesses, such as inadequate connections between individual load-bearing components and the low mechanical strength of materials, which render them particularly vulnerable to seismic forces. Failure mechanisms--such as in-plane and out-of-plane bending of masonry walls, leading to wall overturning, disaggregation and/or collapse of external wall corners [1]--have been repeatedly observed in recent major earthquakes, including those in Lesbos (2017) [2] and Turkey (2023) [3, 4], thus confirming the need for further investigation into the seismic performance of such structures. To this end, this paper examines the Archaeological Museum of Lemnos--a three-storey load-bearing stone masonry building with a timber-tiled roof, located in the island's capital,Myrina. The structure features a regular floor plan and a distinctive composite system of timber-framed load-bearing masonry. Analogous construction typologies are found in the traditional architecture of various regions, including Lesvos [5], Lefkada [6], Turkey [4], the Himalayas [7], Chile [8], and Portugal (Pombalino System) [9]. Generally, in timber-framed load-bearing masonry buildings, the timber framing functions as a secondary seismic response mechanism (substructure). Whether implemented as floor-level ties, reinforcement at critical masonry points (e.g., around openings), or as a timber space truss embedded within the masonry--often in combination with internal timber-framed partition walls (bagdadi)--this system enhances the compressive strength of the masonry (by up to 20%), prevents vertical cracking, and reduces overall cracking (by up to 50%) [10]. It also increases the shear capacity and deformability of the masonry prior to failure [10]. Notably, despite the large deformations they may undergo, such structures have demonstrated the ability to withstand major seismic events [7]. In addition, timber-framed interior partition walls contribute--among other things--to increasing the stiffness and overall strength of the structure. It should be noted that significant interventions have been carried out on the building under study, including the addition of reinforced concrete (RC) elements (an RC slab at the first-floor level and a bond beam at the roof level), which have altered its original structural system at the diaphragm levels [11]. Regarding the seismicity of the broader study area--the northeastern Aegean Sea, where the western end of the North Anatolian Fault extends--significant earthquakes have been recorded, including the Agios Efstratios event on 20 February 1968 (Mw 7.0-7.4) and the Lemnos earthquake on 24 May 2014 (Mw 6.9). However, seismic acceleration data are only available for the latter, with a recorded peak ground acceleration (PGA) of 0.11 g [12]. According to a seismic hazard assessment study for the North Aegean region [13], PGAs of up to 0.3 g are estimated in areas near Lemnos under earthquake scenarios with magnitudes of Mw 7.0 or higher. Notably, during the 12 June 2017 earthquake on the neighboring island of Lesvos, accelerations reached values as high as 0.2 g--approaching the design PGA value specified by the Eurocode 8 response spectrum for the broader region [2]. To assess the seismic response of the AML to strong ground motions, three major seismic events were selected: the Northridge earthquake (Pacific Palisades--Sunset station, Los Angeles, CA, USA, 1994, Mw = 6.7) [14]; the Kahramanmaras earthquake (Turkey, 2023, Mw = 7.7) [15]; and the Kocaeli earthquake (Duzce station, Turkey, 1999, Mw = 7.51) [14]. To adapt these seismic records to the target spectrum calculated for the AML, the procedure outlined in EC8 was followed.