Investigati̇on of the behavior of prefabricated reinforced concrete buildings with different interstory layouts

Precast reinforced concrete structures are widely adopted in modern construction, offering improved quality control along with significant advantages in terms of cost efficiency, construction time, and environmental sustainability. In Turkey, these systems are predominantly used in industrial buildings, where mezzanine floors are often required to accommodate offices, storage areas, or technical spaces. Following the February 2023 Kahramanmaraş earthquakes, it was observed that in buildings with partial mezzanine floors, damage was concentrated primarily in the columns located outside the mezzanine zone. This revealed a notable gap in both knowledge and practical experience regarding the design of such buildings. The present thesis investigates the seismic performance of three two-story precast reinforced concrete buildings with varying mezzanine layouts, providing a comparative evaluation of how mezzanine configuration influences structural behavior. The buildings analyzed in this study are typical two-story industrial structures. Each building has a single 20 m span in the short direction and ten spans of 8 m in the long direction, making the total length 80 m. In the first building, the mezzanine covers half of the building's length (20x40 m). In the second, it covers the entire floor area (20x80 m). In the third, it covers half of the building's width (10x80 m). For all buildings, the clear column height is 8 m, and the mezzanine height is 4 m. The mezzanine joints use wet connections (MAB3), which are common in precast structures, while the roof joints use pin connections (MFB1). The design of the buildings was completed using SAP2000 according to the Turkish Building Earthquake Code (TBDY, 2018). Since two different connection types were used on the mezzanine and roof floors, the response modification factor (R) and overstrength factor (D) for the lower floor were calculated by considering the differing building response coefficients. The equivalent lateral force method was applied to account for earthquake effects in both directions. Additional eccentricity effects were included in the model as equivalent floor torsional moments specified in TBDY-2018, and eight different earthquake load combinations were generated. After the linear earthquake analyses, irregularity checks were performed on the buildings. The reinforced concrete design of the frame elements was carried out using a strength-based design approach. Based on the linear analysis results, the three buildings were compared in terms of interstory drifts, story shear forces, column dimensions, and reinforcement ratios. When comparing buildings with partial mezzanines (Building 1 and Building 3) to Building 2, which lacks a partial mezzanine, a noticeable increase was observed in both interstory drifts and longitudinal reinforcement ratios in the buildings with partial mezzanines. A numerical model of the designed building, including its nonlinear behavior, was developed. For the columns, a fiber section model with distributed plasticity was applied, considering both confined and unconfined concrete properties. For the beams, a lumped plasticity model was used. In the nonlinear time-history analyses, eleven earthquake record sets were scaled to match the acceleration spectrum corresponding to the DD-2 earthquake level. Another important aim of this thesis is to verify the accuracy of the different R and D factors used in strength-based design by applying the Incremental Dynamic Analysis (IDA) method. For this purpose, 11 earthquake record pairs were selected in accordance with TBDY-2018, and nonlinear time-history analyses were carried out for 10 different earthquake intensity levels. The scaling factor was chosen to increase in steps of 0.2g, ranging from 0.2g to 2.0g. Additionally, fragility curves were generated based on the results of the IDA. These curves probabilistically show how the buildings respond to increasing earthquake intensities and indicate the likely damage at each ground acceleration level. Damage limits were defined according to TBDY 2018 for the performance levels of Immediate Occupancy (IO), Life Safety (LS), and Collapse Prevention (CP) performance levels, and fragility curves were created based on these levels. Evaluation of the IDA results indicates that the R and D factors calculated for the lower floors of the buildings are similar to those used in strength-based design. This suggests that the coefficients provided in TBDY-2018 are appropriate. To prevent the adverse effects observed in buildings with partial mezzanes, it is recommended to either avoid partial mezzane construction or, if such a layout is necessary, to separate the building into two parts using seismic joints.