Performance evaluation of a RC building with A1 and A3 plan irregularities designed according to TBDY-2018

Earthquake is a natural event that threatens humanity in our country as well as all over the world. Although precautions are being taken against this disaster with the developing technology, it is important to design an earthquake-resistant structure to ensure life safety. In this context, earthquake regulations have been established, including specific rules and guidelines for the implementation principles of earthquake-resistant building design. Within the scope of the thesis, the Turkish Building Earthquake Code-2018 (TBEC-2018), which entered into force in our country as of January 1, 2019, was taken as a basis. In general, strength-based design principles built on linear-elastic analysis are used in building design. On the other hand, deformation-based design, which reflects the real behavior of the buildings and where nonlinear analysis methods are used, is important in order to determine the performance levels of the buildings under seismic loads. In TBEC-2018, deformation-based design has been made mandatory for important buildings such as high-rise buildings, seismic isolated buildings, which require the estimation of the actual building behavior under earthquake ground motion. In such buildings, strength-based design has been adopted as a preliminary design method. Within this scope, in the thesis study, performance evaluation of a 10-storey reinforced concrete building consisting of shear walls and frames with A1-torsion irregularity and A3-re-entrant corner irregularity designed in accordance with strength-based design principles of TBEC-2018 is done. Therefore, deformation-based design is completed. In the thesis study, first of all, within the scope of strength-based design, a three-dimensional (3D) numerical model rely on the linear-elastic behavior of the building was created in the ETABS program. Columns and beams are modeled as frame elements, shear walls and floors are modeled as shell elements. The effective section stiffness factors used in the linear-elastic analysis are assigned to the related sections. According to the load acceptance criteria specified in TS498, loads were assigned to the floors and beams. Free vibration analysis (modal analysis) of building was performed by considering the floor masses calculated by the program. The dominant vibration periods, mode shapes and mass participation ratios in the X, Y and torsional directions of the building were determined. Equivalent earthquake load method was applied, taking into account the elastic acceleration spectrum and storey masses defined in TBEC-2018, as well as additional eccentricity effects. Eight different combinations were created by taking into account the eccentricity effects and the directions of earthquake ground motions in the X and Y directions, and controls for irregularity, storey drifts, second order effects and overturning moment were made. It has been determined that there are A1 torsional irregularities and A3 re-entrant corner irregularities in the plan. Since the overturning moment controls could not be achieved, the building behavior coefficient (R) was corrected. The eccentricity effects were increased by the ratio of the torsional irregularity coefficient and the equivalent earthquake load method was applied to the building again. Considering the simultaneous effect of the X and Y components of the earthquake, the dimensions and reinforcement ratio of columns, beams and shear walls were determined according to the most unfavorable situations arising from a total of 65 load combinations including the design combination of vertical loads only. Since the mass participation ratios of the free vibration modes of the building could not provide sufficient participation in the X, Y and torsional directions, the mode superposition method was also applied to the building. The design was carried out with also by load combinations created for mode superposition method and strength-based design was finalized. Within the scope of deformation-based design, the numerical model rely on the non-linear behavior of the building was created with the ETABS program. In order to take into account the material nonlinearity, the concentrated plasticity model in beams and columns, while, distributed plasticity model was used in shear walls. M3 moment hinge are assigned to the ends of the beams, the P-M2-M3 hinge which can take into account the biaxial bending and normal force interaction was assigned to columns, and fibers in which nonlinear concrete and reinforcing steel stress-strain relations can be defined, were assigned to shear walls along the critical wall height. XTRACT program is used to create moment-curvature relations of column and beam sections. By idealizing the moment-curvature relations as bi-linear, the plastic rotation values were calculated for the effective section stiffnesses and the Collapse Prevention (CP) and Life Safety (LS) performance limits, which will be the basis for the non-linear analysis. The axial load to be considered when creating the moment-curvature relations in columns is determined by nonlinear vertical load analysis. Parabolic hardening reinforcement steel and Mander confined-unconfined concrete models assigned to the fibers used in the shear walls elements are taken from TBEC-2018. Due to the low mass participation ratios in the X and Y directions, the single-mode pushover analysis method was not applied to the building; Nonlinear Time History Analysis (NTHA) method was applied. The horizontal earthquake acceleration records to be used in the analysis corresponding to the design earthquake ground motion level were selected from the real earthquake records in the Pacific Earthquake Engineering Research Center (PEER) database, according to the earthquake magnitude, the source mechanism, local site class and the distance to the fault that. The simple scaling method in TBEC-2018 was performed by the PEER database. In this context, earthquake selection was done by the following rule: the average elastic spectrum calculated from the 11 acceleration spectrum ordinates after taking the square root of the sum of the squares of X and Y components of each earthquake pair should be greater than 1.3 times of the design basis elastic spectrum acceleration ordinates. Nonlinear vertical load analysis is defined as the initial step of nonlinear time history analysis. Based on the deformation and stiffness conditions resulting from this analysis, both components of the ground motion were simultaneously applied to the building by using pre-determined scale factor. As a result, eleven ground motion acceleration pairs were affected on the building by changing their directions, and 22 nonlinear time history analysis was performed in total. In order to determine the performance of the new building under earthquake ground motion, the averages of the largest values of the time series results of demand parameters obtained from the NTHA were taken into account. For some demand parameters, the values calculated from NTHA analysis were compared with the results obtained from the mode superposition method. As a result of the calculations, although a certain amount of damage was allowed in the strength-based design in accordance with TBEC-2018, approximately 85% of the elements working as columns and beams remained in the Limited Damage Zone despite the A1 and A3 type irregularities. It has been determined that the plasticization of the shear wall elements is limited at the ground floor level and the deformations are below the damage limit value of the regulation for all earthquakes. Compared to the results obtained by the Mode Combination Method, it was observed that the peak displacements are increased by 70% on average in both directions in the nonlinear analysis, the relative storey drift values are below the regulation limit values for both methods, and the nonlinear analysis results of the base story shear forces are approximately 3 times higher. As a whole, it can be said that the building was designed according to the TBEC-2018 guidelines, and that it was at the level of controlled damage performance under the design earthquake ground level DD-2, but it has a very safe performance due to the fact that there are very few elements in the significant damage zone. Especially considering that the shear walls remain at a limited damage performance level, it becomes possible to use lower reinforcement ratios in the design of the shear wall.