# Vulnerability and Seismic Exposure of Residential Building Stock in the Historic Center of Alcamo
## 3 Exposure of the Historic Center of Alcamo  
Figure 2 shows the plan of the historic center of Alcamo, coinciding with areas A1 and A2 of the current general master plan (PRG). The historic center is an area of about 509,000 m\({}^{2}\). To assess the seismic vulnerability, the area was divided into two compartments:  
* Compartment C01, originated in the 14 th century, called \"Historic center: the walled city\", coinciding with area A1 of the PRG. The compartment has an extension of 109,280 m\({}^{2}\) and it contains about 640 building units and a population of about 1300 residents;
* Compartment C02, originated in the 16 th century, called \"Historic center: the ancient quarters\", coinciding with area A2 of the PRG. It is an area of about 398,700 m\({}^{2}\) and contains about 2465 building units, with a population of about 5700 residents. According to the classification presented in the CARTIS sheet [36], three types of masonry buildings and two types of reinforced concrete buildings were initially identified in Compartment C01. The characteristics of the masonry typologies according to the CARTIS sheet classification criteria, summarized in Figure 3, and the acronyms that identify the typologies are as follows:  
* MUR1: included units built before the 1920s, characterized by irregular vertical masonry elements, rough stone with a haphazard texture, without recourse (A2.1), with lime mortar, predominantly 2 or 3 stories, average floor height of less than 3.50 m, average area between 60 and 110 m\({}^{2}\), predominantly irregular configurations in plan, and average irregular configuration in elevation. The average wall thickness of the ground floor was about 50 cm and the average prevailing wall spacing was 3.0 m. The prevailing type of floor slab (90%) was constituted by single plank wood, forming a deformable diaphragm, while the remainder (10%), following renovations, was made of reinforced concrete with prefabricated joists and cast-in-place slab. The stairs, made of stone, were generally made with cantilevered steps or rarely with ramped vulting. The roofs were wooden, lightweight, with predominantly single pitch (70%), while the remainder show sloping pitches. Buildings were characterized by a lack of adequate buttresses between orthogonal walls and a presence of lintels with reduced flexural rigidity. Sometimes, there were localized reductions in the wall section due to the presence of flues, cavities, or niches. Numerous constructions of this type present irregular forometry with respect to the outer wall box. The roof was usually not adequately connected to the walls. The foundations were superficial and continuous, made of rubble stone. Almost all of these buildings were in aggregate and a high number of buildings were in connection and shared, with the adjacent units, the end-bearing vertical structures. Vulnerability was often increased by location in aggregate, with the floors staggered with respect to the adjoining buildings. Few buildings of this typology have been affected by local interventions, which, in any case, have only resulted in modest seismic improvement. Figure 2: Compartment divisions of the historic center of Alcamo. The second typology, identified by the acronym MUR2, was built between the early 1920s and 1960. The masonry of the vertical elements was made of pseudo-regular rough-hewn stone without recourses (B2.1). The typology included 2 or 3 floors. Many of the typological-structural characteristics coincided with those of the previous typology. There was a prevalent average spacing of the masonry walls that reached 4 m, a stronger connection between the orthogonal wall and a stringer connection of the roof to the external walls. The stairs were usually made of reinforced concrete ramped slab. The foundations were superficial and continuous, made of rubble stone or squared blocks. Finally, the MUR3 typology was the most recent, built until the late 1970s. This typology was made of masonry classifiable as regular squared stone without recourses (C1.1).