## 5 Discussion  
The reliability of the presented results depends primarily on the accuracy of input data, such as variations of the material quality, assumptions related to structural detailing, as-built reinforcements, existing structural damage, soil conditions, etc. Exhaustive non-destructive experimental measurements were performed and the numerical models of various levels of complexity (from the simplest to the most complex ones) were created in order to achieve the best possible accuracy without performing destructive testing which would disrupt the functioning of the hospital. The main structural features of the building, quantitatively and qualitatively determining the structural performance during earthquakes, will be summarized in the following text, including general observations based on the performed analysis and presented results:  
* The structural system is mostly formed of RC (MB30) walls (25 cm), which continuously extend from the foundations to the roof. The building is irregular in height, especially at the transition from the second to third story above ground level. Analyses confirmed that the critical structural elements are mostly located on the third floor above ground level where the total cross-section area of walls (in plan) is much smaller than on the ground floor. Moreover, the area of walls is much smaller in the Y direction, so this represents the most detrimental earthquake direction. The frame system on the building perimeter contributes minimally with its stiffness to the overall structural load-bearing capacity to resist horizontal loads, but it is very important for transferring vertical loads. * The main deficiency of primary elements (walls, columns, beams and coupled beams) is their shear capacity. Analyses showed that shear reinforcement was insufficient in most of the elements, and could initiate brittle failure, which happened suddenly. Another problem is the boundary zones in walls, which are not confined by transversal reinforcement which is necessary for achieving ductility (at least before the redistribution of the force to adjoining elements). * The deficiency related to the lack of ductility is additionally emphasised by the use of smooth reinforcement bars (GA240) and questionable anchoring lengths and lap splices (with regard to modern seismic regulations). In some beams, longitudinal reinforcement ratios are very high, which significantly reduces their ductility. * Plan irregularity increases the torsional effects on the structural elements of the building perimeter at the south-west part. The reason is the relatively stiff north-east and central building parts (location of the stiffness centre is in the vicinity of the main staircase). Sensitivity to torsional vibrations may be observed in structural vibration modes, determined numerically and experimentally. The first vibration mode represents an almost regular translation in the Y direction, while the second mode comprises a significant torsional contribution to the translation  
Figure 26: Earthquake scenario for 475 y RP—EC8: (**a**) top displacements ux and uy (points 3 and 54 at story 9); (**b**) base shear in the X and Y directions; (**c**) shear forces in wall X1; (**d**) shear forces in wall X3; (**e**) time snapshots of failure mechanisms’ development at story 5.  
in the X direction. Due to torsion, columns located near the building perimeter may be damaged even for low intensity earthquakes. * Walls located at south and south-west part are significantly endangered due to insufficient transversal reinforcement and low ductility. Cracking and significant reduction of stiffness occurs very quickly followed by redistributions over by the adjoining walls. It should be pointed out that during cyclic loading the cracked wall does not return to its original position but remains damaged and maintains a reduced stiffness level. This process continues until a local mechanism is formed, which may lead to the local slab collapse which is confirmed by nonlinear analyses.