3.1 Design codes in Albania
Historic development and the extent of enforcement of Albanian building codes in practice and the construction typologies addressed by these codes are strongly related to political and economic setting in the country during different time periods. A timeline of Albanian design codes, major earthquakes, and construction typologies characteristic for different time periods is presented in Fig. 2.
The first seismic provisions were published in 1952 (Council of Ministers 1952), and they were incrementally improved in the 1963 seismic design code (Ministry of construction 1963), which included provisions for buildings and other types of structures (Baballëku and Myftaraga 2020). According to the code seismic action was considered by taking into account dynamic properties of the structures and elastic response spectra. The first design code for RC structures in Albania was issued in 1960 (KTP-NB 60 1960). Subsequent revisions of the Albanian design codes (KTP) and construction codes (KTZ) were issued in 1978 and 1979, but the updated versions did not bring significant improvements in the seismic safety compared with the 1963 seismic code. The 1978 seismic design code (KTP-N.2-78 1978) was mostly focused on masonry structures and general aspects, such as the seismic action, structural regularity, seismic gaps and other general rules. Although masonry was the predominant construction technology before 1989, RC technology was also used for construction of important public facilities such as hospitals and university buildings. Seismic design of RC structures according to the code was largely based on force-based design approach and detailing of RC structures was not adequately addressed by the code, hence the seismic safety of these buildings was at risk due to a lack of proper detailing for ductility and large inelastic demands. The code was amended in 1982, based on the lessons learned from the 1979 Montenegro earthquake (Stermasi et al. 1980).
The 1989 seismic design code KTP-N.2-89 (1989) brought significant advancements compared to previous code editions and was in line with other international seismic design codes at the time. The code included reinforcement detailing rules for critical regions of RC members, design provisions for masonry infills in RC framed structures, and advanced methods of seismic analysis. Reinforcement detailing requirements for RC frames illustrated in Fig. 3 were prescribed depending on the seismic intensity at the construction site, with more stringent requirements for sites located at higher seismic intensities. For example, maximum spacing of longitudinal bars enclosed by hoops was limited to 30 cm for seismic intensity up to VIII and 20 cm for intensity above VIII per MSK-1964 scale. Critical regions in which denser transversal reinforcement was required were prescribed for both beams and columns (see Fig. 3 for intensity above VIII). The length of the critical region was required to be twice the depth of the beam for beams (for all seismic intensities), whereas for columns the length depended on the clear height, the size of the column and the seismic intensity (for intensity above VIII, see Fig. 3).
Several limitations of the code have become apparent over time, including the lack of explicit treatment of damage limitation, serviceability criteria, and incomplete provisions for ductile detailing of RC members. It is important to mention that KTP-N.2-89 (1989) was the official seismic design code in Albania at the time of the November 26, 2019 earthquake.
The fall of communism in Albania occurred in 1990, shortly after the 1989 seismic design code was released. This period was also characterized by a shift towards RC as the preferred construction technology and a rapid urbanisation of Tirana and Durrës, largest cities in the country. Unfortunately, a significant increase in informal construction practices also took place during the same period (Chryssy and Augustinius 2010).
After 1990 structural engineers in Albania started to apply codes from neighbouring countries and, more recently, the Eurocodes, however the application of international codes was done on a voluntary basis - either proposed by design engineers or requested by investors of important projects. As of this writing the Eurocodes have the status of National Standards, but their implementation is still optional.
3.2 Construction practices
This section presents an overview of RC construction technology in Albania, with the focus on cast-in-place RC technology, which has been discussed in four distinct time periods: i) before 1960, ii) from 1960-1990, iii) from 1990-2000, and iv) 2000-present.
Prior to 1960s masonry was the prevalent construction technology in Albania, and its applications ranged from low-rise dwellings to major heritage structures, such as fortresses. It was a common practice to use different masonry elements (units) in a building, for example to construct stone masonry walls at the ground floor level and other materials (adobe, clay bricks, timber) at the upper floor. During that period majority of Albanian population occupied rural areas of the country. RC construction technology in Albania started after 1920, mostly through involvement of Italian companies, and was limited to bridges and public facilities. The first cement manufacturing plant in the country, with 12,000 tons annual capacity, was constructed in Shkodra in 1927.
Due to increased housing demand after World War II, large-scale construction of multi-family (apartment) buildings started in urban areas of Albania. These buildings were mostly constructed using unreinforced masonry (URM) technology. In the period from 1945-1960 some public facilities (hospitals, schools, etc.) were constructed using a mixed structural system, consisting of exterior loadbearing URM walls and interior RC columns, which were mostly intended to sustain the effect of gravity loading.
The period from 1960-1990 was characterized by wider use of RC construction technology, mostly for public facilities (schools, hospitals, etc.) and multi-family residential buildings (usually 5-6 storeys high). Majority of residential RC buildings were constructed using prefabricated construction technology (Guri et al. 2021), while cast-in-place RC technology was more often used for construction of public facilities which were characterized by larger open spaces. During that period standardized designs were prepared by a few specialized government design institutes, while local design offices were responsible for developing designs for building interventions, which were mostly related to foundations and depended on local site conditions.
Limited use of cast-in place RC frame system has been influenced by several factors, including limited capability to produce good quality in-situ concrete, hence concrete need to be transported from a plant to the construction site. Also, steel reinforcement was partially locally available and considerable amount had to be imported at a higher cost. RC buildings constructed during that period were regular in plan and elevation. Building blocks were separated by means of construction joints, but the size of such joints was determined without seismic considerations. Although the codes as early as in 1978 required the consideration of plastic behavior of RC frames under seismic loading through the development of plastic hinges, they did not contain sufficient provisions to ensure an adequate fulfilment of this requirement. Reinforcement detailing provisions for RC columns and beams were limited, but included a provision for closer tie spacing in columns within the spliced region of longitudinal reinforcement. Prefabricated concrete hollow core slabs were commonly used for construction of suspended floor slabs, and RC columns were supported by pad footings connected by RC tie-beams. In the 1980s some RC buildings, particularly public facilities, were constructed using a dual system, consisting of RC frames and masonry shear walls in elevator cores and exterior walls, although seismic design of dual systems was not covered by the codes. Masonry units used for construction of infill and partition walls were solid clay bricks, but in 1980s silicate bricks emerged as a common type of masonry units and perforated bricks started to be used for infill walls. Some RC buildings of the 1980s vintage were constructed using a hybrid structural system, with RC frames at the ground floor level which was used for service purposes, while upper floors were constructed using URM walls which were in some cases confined with vertical and RC horizontal elements like a confined masonry system. This hybrid system was characterized by a soft storey irregularity, and these buildings experienced extensive damage or even collapse in the 2019 earthquakes, as discussed later in the paper. In general, quality of construction materials (concrete and masonry) appears to have deteriorated over time, particularly in the 1980s.
Major political changes that took place in Albania in the 1990s also affected the construction sector. Rapid and uncontrolled construction activities, particularly in urban and suburban areas, resulted in substandard construction quality and many buildings were not designed or constructed in compliance with the KTP-N.2-89 code (1989). These buildings were characterized by design flaws (e.g., soft storey irregularity) and substandard quality of building materials, particularly concrete. After the construction was completed, in some cases inappropriate interventions were made, such as perforations in existing walls and vertical extensions. By and large, these buildings showed poor performance in the November 2019 earthquake - an example is “Këneta”, a marsh area populated by RC buildings of the 1990s vintage near Durrës.
In the early 2000s construction of high-rise RC buildings became more prominent in urban areas. These buildings were characterized by services at the lower 1 or 2 floors and residential area at the upper floors. This period was characterized by a continuous improvement in the field of construction (both design and execution). The adoption of European standards (Eurocodes) and their implementation on some projects has had a positive influence on the quality of design and construction materials. The most common structural systems were RC frames with masonry infills and a dual RC system, which consists of frames and shear walls. However, even in these modern buildings, implementation of seismic design criteria is not adequate in some cases, mostly due to a lack of control within the construction industry and a lack of necessary reviews pertaining to structural design. Common deficiencies observed in these buildings include structural irregularities (both in plan and elevation); frequent use of shallow floor beams in RC frame systems without an adequate accompanying lateral load resisting system, and “heavy” masonry infill walls at upper floors.