# Seismic Assessment and Strengthening of a Load-Bearing Masonry Structure Considering SSI Effects
## 2 Case Study
### Structural Description
#### 2.4.3 Second Floor  
At the second level, the timber floor was reinforced with metal IPE beams during the second construction phase, while an additional timber layer (floorboards) was installed during the third phase. The floor system comprises simply supported timber joists with a cross-section of 10 \(\times\) 10 cm, spaced at intervals of 40-50 cm. Floorboards and ceiling boards, each approximately 2.4 cm thick, are nailed above and below the joists, respectively. At the this level, the building features a distinctive hybrid system that combines stone masonry with integrated timber framing. This construction technique has been examined and thoroughly documented by [PERSON] (2001) in his study of the traditional settlement of Eressos in Lesvos [5]. The walls consist of 50 cm thick two-leaf masonry, reinforced on the inner face with a dense timber framework, locally known as \"friggia\". This system consists of vertical timber posts, typically with a cross-section of 10 \(\times\) 10 cm, spaced 40-100 cm apart depending on the wall configuration (Figure 7a). In areas requiring increased stiffness--such as between openings--horizontal members and diagonal braces of similar cross-section are installed. [PERSON] (2001) [5] (pp. 6-7) notes that vertical posts are generally aligned with the corners of openings, while horizontal ties correspond to lintels and sills. The timber framework is self-supporting and structurally capable of carrying roof loads independently of the masonry, while also connecting both wall faces transversely at openings [5] (p. 8). Figure 6: Structural features of the AML building: (**a**) Interior view of the external wall at the first level; (**b**) The two internal staircases of the building—a reinforced concrete staircase at the ground floor and a wooden staircase at the first floor. (Source: Digital Archive of the Ephorate of Antiquities of Lesvos, Hellenic Ministry of Culture and Sports; used with permission, Prot. No. 252765/16-06-2025). The interior walls of the second floor are of the baghdati type--timber framed partitions with a total thickness of 17 cm (Figure 7b). These lightweight walls complete the aforementioned timber frame system and contribute to the overall stiffness of the structure. The plaster used is of the same composition and strength as that of the first floor [27]. The building has a four-pitched timber roof of a distinctive structural configuration, covered with Roman-style clay tiles. Several additional timber members were added during the second, third, and fourth construction phases. However, the primary structural elements of the roof today include vertical posts, principle rafters and tie beams (14 \(\times\) 14 cm cross-section), along with diagonal braces (7 \(\times\) 14 cm cross-section). The structure is founded on stone foundation strips aligned with the ground-floor load-bearing masonry walls. These foundations reach a depth of 82 cm from the axis of the ground level floor and feature a cross-sectional widening of 20 cm on either side of the masonry in the final 60 cm of depth. As described in detail in this section, the building's structural system is of particular interest. It has a rigid base formed by load-bearing masonry with relatively small openings. The first floor is reinforced with arched spandrels to improve load distribution onto the piers surrounding the openings, while the second floor has two mechanisms for absorbing seismic forces: the stone masonry itself and the system of timber elements (timber wall frames, baghdati-type walls and timber flooring). These systems collectively facilitate the transfer of roof loads to the lower levels. In the event of masonry failure during an earthquake, the loads are transferred to the timber frame system. Table 1 depicts the repair methods of the structure under study. Figure 7: Structural features of the AML building at 2 nd level: (**a**) Interior view of the external wall; (**b**) Baghdati internal wall.