2.2.3. Previous Earthquakes in Albania

As we can see from the graphic below, there are deficiencies for KTP spectre in confront with EC-8 spectre for periods lower than 2.2 sec. With this spectre, have been designed the buildings in the period 79-90. This spectre, officially is still in use nowadays, but in practice the design engineer use the EC-8 one,

2.2.3. Previous Earthquakes in Albania Earthquake of 15 April 1979 Among the most damaging seismic events in Albania was the earthquake of April 15, 1979. According to (Pistoli, 1982), among various engineering works in our country, the earthquake also hit new buildings with masonry or reinforced concrete structure constructed in accordance with the design codes in force at the time (KTP-63). This includes 5-storey masonry buildings, which according to KTP- 63 should not show problems. The three-storey buildings have suffered corner damage. These effects are displayed on the upper floors where the displacements of the walls are greater where the compression that could serve as opposition is at a lower value. From the overall conclusions of the ‘79 earthquake the damage is thought to have been caused also from the wrong use of soft storeys (RC structure at the base and masonry at the height), use of lime mortar, buildings with a height/length ratio of less than 1.5 as well as the lack of RC belts in some cases.

Earthquake of November 26 An earthquake of magnitude Mw 6.4, with focal depth of 20 km, struck northwest Albania The November 26 earthquake’s epicenter was north of the city of Durrës, although the macro-seismic effects were most extensive in the Shijak municipality that is situated about 10 km east of Durrës. The earthquake claimed 51 lives and resulted in at least 913 injuries (including 255 individuals hurt in the earthquake's aftershocks) (The World Bank GPURL D-RAS Team, 2019). The fatalities were mostly caused by the collapse of ten buildings in Durrs and Thuman (both in the Kruj municipality) (figure 2-7). The November 26 earthquake was also preceded on September 21 at 16:04 hrs local time by magnitude Mw 5.6 earthquake, with focal depth of 10 km, that occurred 5 km north of Durrës city injuring 108 people and causing damage to more than 2,000 buildings and 47 educational facilities, including considerable damage in the capital city of Tirana (and in the port city of Durrës). These earthquakes are significant as it increased the vulnerability of buildings and of communities. The housing industry sustained the most severe damage. 18% of all housing units in the impacted area were predicted to require reconstruction or restoration (Marinković, et al., 2021).

Figure 2-7 The main shock's modeled seismic intensity distribution. As per the EMS-98 scale, the darkest red corresponds to intensity VII (extremely severe), whereas the yellow and orange tints correlate to VI and VII (strong and very strong, respectively) (Source: World Bank Report, 2019)

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Damage statistics in table 2-2 relate to single-family houses, apartment blocks that contain usually more than ten housing units, as well as non-residential buildings.

Table 2-2 Building damage statistics from three municipalities in the epicentral region (Source: World Bank Report, 2019)

Ins pe c te d

D urre s M. K ruja M. Shija k M. Combine d 2112 2499 1670 6281 Sa f e 1369 1533 346 3247 U ninha bita ble 651 921 900 2472 D e molition 93 45 424 562 D e molis he d 34 12 0 46

Sa f e 64. 80% 61. 20% 20. 70% 51. 70% U ninha bita ble 30. 80% 36. 90% 53. 90% 39. 40% D e molition 4. 40% 1. 80% 25. 40% 8. 90%

As these datasets do not include the number of “undamaged” buildings, it is difficult to draw definite conclusions; however, it can be seen that among the assessed buildings, those that were built prior to 1992 suffered more damage than those built in or after 1992 (43.6% of the pre-1992 buildings were classed as red or yellow as opposed to 28.4% of the post-1991 buildings). Damage was most extensive among the low-rise buildings that were assessed (70.2% were classed as red or yellow), and least extensive among the high-rise (6 or more floors) buildings (22% were classed as red or yellow). Some of the reason is that the low-rise buildings are old unreinforced masonry houses made of adobe or clay brick, whereas the tall buildings are virtually exclusively reinforced concrete buildings built after 1991 (table 2-3). The mid-rise buildings (3 to 5 floors), on the other hand, consist of a mixture of structural types (brick masonry, structural masonry, reinforced concrete) and were built across both examined periods of construction.

Table 2-3 Tirana Municipality building damage statistics analysis (by period of construction, number of floors, type of structure and 3- colour damage levels). (Source: World Bank Report, 2019)

Building Cha ra c te ristic s Sa fe Re vie w Eva c ua te pre -1992 56.30% 23. 60% 20. 00% pos t-1991 71.60% 15. 30% 13. 10% U nc la ss if ie d 47.00% 16. 60% 36. 50%

1-2 floors 3-5 floors 6+ floor s U nc la ss if ie d 29.80% 22. 10% 48. 00% 60.60% 23. 40% 16. 10% 78.00% 14. 00% 8. 10% 66.30% 12. 50% 21. 20%

A dobe w a lls

17.40% 17. 40% 65. 20% Br ic k Ma sonry 56.10% 20. 90% 23. 00% Conc re te B loc k Ma sonry 9. 10% 9. 10% 81. 80% P r e fa bric a te d 86.20% 10. 30% 3. 40% Re inforc e d Conc re te 71.70% 16. 00% 12. 30% Struc tur a l Ma s onry 62.80% 21. 80% 15. 40% U nc la ss if ie d 4. 00% 36. 00% 60. 00% TO TA L 60.60% 19. 20% 20. 20%

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• In terms of the impact on the built environment, the primary shock caused damage to buildings in Durrës, Tirana, and a number of other settlements in the surrounding area. • The affected area's primary building types include unreinforced masonry structures and reinforced concrete (RC) structures with infill baked clay and/or concrete walls. Additionally, mixed kinds were seen. The majority of current structures were built in accordance with the KTPs – Albanian Technical Codes, which were first issued and implemented in 1963 and were last modified in 1989. • The unreinforced structures with load-bearing masonry walls were the most severely damaged by the earthquake for a variety of reasons, including their age, poor quality of construction, poor workmanship, human intervention, the time period's design code - assuming it had been implemented - an absence of maintenance and poor repair following earlier devastating seismic events. This type of structure received both nonstructural and structural damage, including the partial or complete collapse of load-bearing masonry walls. Dominant types of buildings Masonry buildings with and concrete floor slabs are primarily composed of thick, heavy unreinforced masonry (URM) formed of solid clay bricks that provides structural support for the entire construction, including the horizontal concrete slab, which may be reinforced concrete. A significant characteristic of this type of structure, not only in Albania but also around the world, is the lack of concrete columns and beams. The solid brick walls are the only and the main load bearing elements of the structure. This masonry type is unreinforced and thus it presents brittle - non-ductile behavior. Due to the construction material (solid clay bricks), they also present small stiffness resulting in good performance and flexibility during an earthquake up to a certain limit. Once this limit is exceeded, the damage is instantaneous in this case, the earthquake shaking and displacement did not exceed this limit and these structures remained intact by the earthquake (Lekkas, Mavroulis, Papa, & Carydis, 2019).

Figure 2-8 Dominant types of buildings (source (Lekkas, Mavroulis, Papa, & Carydis, 2019)) A very positive characteristic in this type of buildings is that the best possible continuity between the soil and the construction is achieved, in terms of material and stiffness. These elements appear to have a positive effect on the antiseismic performance, particularly with respect to the vertical component of the earthquake ground motion. Taking into account these elements, this building type excel in antiseismic performance. Unreinforced masonry (URM) construction should not be used today. They do not present good performance during earthquakes. It is significant to mention that the majority of fatalities induced by earthquakes around the world have attributed to collapse of unreinforced masonry buildings. They are heavy brittle structures, which usually suffer heavy structural damage.

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Figure 2-9 Structural damage (source (Lekkas, Mavroulis, Papa, & Carydis, 2019)) Heavy structural damage to masonry buildings with concrete floor slab in Thumanë town are presented. Damage comprised detachment of large pieces of plaster from the brick walls, cracks in brick walls and partial collapse of the building. The floor slabs were composed of simply supported prefabricated reinforced concrete hollow core strap slabs. The concrete strap slabs are not transversally connected to each other neither to the load bearing system. In this way, the diaphragmatic function of the floors, which is beneficial for the earthquake safety of the structure, is totally missing. Also, below, are presented in the same graph the sprectre of September earthquake, November earthquake with two spectres from two codes, KTP and EC-8. As we can see, the spectral acceleration of the September earthquake, is higher than the KTP-spectre (which the buildings was design with) for periods 0.2-0.3sec. The September earthquake caused structural damages in the buildings with these fundamental periods (URM type, the case of building in fig 2-9). When the November earthquake occurred, the building was damaged and therefore its shear capacity of bearing walls was reduced, and didn’t withstand the last quake (although the November earthquake spectre is lower than the KTP one). If the building would have been designed with EC-8 spectre, it would had withstood both earthquakes with light and non-structural damages.

Figure 2-10 Comparison of the two latest earthquake spectre with the two design codes used in Albania Conclusions • The major structures in the affected area include (a) load-bearing solid brick walls with concrete floor slabs, (b) precast concrete panel structures, and (c) reinforced concrete frame structures with infill and partition walls. The bulk of these structures are characterized by the presence of precast concrete floor slabs with widths ranging from 0.7 to 1.0 m and no connections between them.

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