## 5 Discussion
The gradual cracking and decrease in stiffness of elements may be noticed on the pushover curve of the structure. * The distribution of the RC partition walls (7 or 10 cm thick) is not regular in terms of height. These elements participate in structural responses for small amplitude excitations, but for high amplitude excitations it may be expected that their discrete connections will fail and walls may lose their stability. Although discrete anchorages to the floor system were defined by the original design, it was detected by visual inspection that these connections were not adequately built in. * Due to the existing nuclear shelter, basement stories are much stiffer than those above ground level, so they are not significantly affected by seismic loads. On the basis of the presented results of detailed numerical analysis, an engineering assessment of the expected performance of the building due to different earthquake scenarios is as follows:  
* The 95 year return period earthquakes may cause local damage to the columns, but significant damage of the structural walls is not expected. Moreover, the damage in coupled beams, and the cracking and spalling of some non-structural elements, especially of partition walls, may be expected, which pose a potential danger for occupants. However, with regard to valid (modern) regulations [43], this earthquake intensity level corresponds to the limit state (LS) of damage limitation in which the structure should only be lightly damaged and would not need any repair measures, which could be significantly exceeded for this structure. According to the performed analyses, the LS of damage limitation is expected to be reached for a PGA of 0.08 g (not shown in the results). It should be pointed out that an earthquake of this return period roughly (according to the response of the structure) corresponds to the limit state to which the structure was designed in 1980, so it can be concluded that the structure meets the requirements according to which it was designed. As mentioned before, the results obtained using records simulated for a deterministic earthquake scenario are less unfavorable than the results obtained by artificial records matched to the prescribed response spectrum. * The 225 year return period earthquakes may significantly affect the structural load-bearing capacity. The most vulnerable locations are the north facade wall with openings and the south-west area of the third story above ground level (marked as story five in figures). Local failures may also occur in the frame systems near edges of the structure. Generally, it can be said that structure is in the limit state of significant damage (SD). * The 475 year return period earthquakes may induce failures of the main structural elements and the load-bearing capacity of the system may significantly be degraded. Failure mechanisms can be formed which can occur relatively fast and without significant plastic deformations. It should be emphasised that a global collapse of the structure at a large scale would probably not happen because a large number of plastic hinges should form and a great amount of energy dissipation (damping) will occur. This is the advantage of such a highly statically indeterminate system--and therefore, a globally very robust one--especially during cyclic loading. Regarding the modern seismic regulations, this earthquake intensity level corresponds to the limit state of significant damage (SD). For this state, it should be expected that structure has some residual lateral strength and vertical elements that are still capable of sustaining vertical loads after an earthquake, but the structure is likely to be uneconomic to repair. However, it is not to be expected that this structure can satisfy these demands. The analysis for the 2475 year return period has shown that this level of earthquake intensity is too high for this building, so the results are not presented herein.