Investigation of the changed post-strengthening structural performance characteristics of existing reinforced concrete school buildings

In Turkey, which is located in an active seismic zone and has structural deficiencies in its building stock, severe earthquakes have resulted in significant loss of life and property, especially due to inadequate structural features. In Turkey, where a significant portion of the building stock is reinforced concrete, the same problem is encountered not only in residential buildings but also in public buildings, which have high social priorities and must be urgently used after disasters. The rapid and effective strengthening of some public buildings, which did not receive adequate engineering services during their construction, is a very important issue from this perspective. Although the type of strengthening depends on structural characteristics, it is evident that structural performance will change in different ways for each strengthening scenario. During the design phase, predicting these changes accurately and selecting strengthening methods that will increase the building's performance most effectively and, correspondingly, have low costs is an important engineering problem. In this study, a series of analyses have been performed on three different school building models (with 8, 14, and 22 classrooms) known to have inadequate earthquake performance. After evaluating the current conditions of the buildings with available site data according to TBDY 2018, their inadequate performance characteristics have been improved using different strengthening strategies (addition of shear walls, jacketing of columns, addition of shear walls + jacketing of columns). The STA4CAD program have been used for modeling. In the parametric content of the study, the cities where the buildings are located, AFAD, and the Turkey Earthquake Hazard Map Interactive Web Application were used to select the maximum ground acceleration (PGA) values for the building coordinates. In this study, Ankara/Çankaya with a PGA value of 0.295 m/s² and Sakarya/Adapazarı with a PGA value of 0.995 m/s² were chosen. The local soil classes (ZC, ZD, and ZE) of the existing buildings, the reinforcement classes (S220, S420), and the variability of the concrete strengths of the buildings (10, 15, and 20 MPa) have been considered. Evaluations have been based on 22 x 33 x 4 (432) building models according to these variables. The evaluations indicate that the shear wall addition + jacketing -type strengthening method has the most significant effect on the structural period. Consequently, spectral displacement demands decrease considerably with this type of strengthening. However, the over strength factor and reinforcement costs are noticeably higher compared to other strengthening methods. The absence of a over strength factor target in TBDY 2018 for reinforced buildings is seen as a major deficiency, which should be considered in future regulations.