Design of a 14-storey reinforced building according to TBDY-2018, considering structure-pile-soil interaction

Piled foundations have emerged as a precaution against horizontal and vertical loads for buildings constructed on soft soils with insufficient bearing capacity. In Turkey, prior to the implementation of the Turkish Building Earthquake Code (TBDY-2018), the design of piled buildings was generally based on limiting their settlements under vertical loads. However, TBDY-2018 made it mandatory to consider the interaction between the structure, piles, and soil under earthquake effects. In this thesis, the design of a 14-story reinforced concrete building, founded on a type-ZE soft soil, with a structural system composed of shear walls and frames, 2 basements, ground floor, and 11 above-ground floors, was performed while taking into account the structure-pile-soil interaction. Initially, by neglecting the structure-soil interaction, the building's base was modeled as a fixed support, and its design was conducted based on its resistance. After determining the cross-sectional dimensions and reinforcement details, a nonlinear model of the building was established, and eight time-domain nonlinear analyses (ZTA) were performed considering four selected strong ground motion records to assess the building's performance. The evaluation involved the maximum absolute values of internal forces, displacements, and storey drift ratios over time for each ZTA. Subsequently, by considering the average, average±standard deviation, minimum, and maximum values from the eight analyses, a comprehensive performance assessment was conducted. The evaluated quantities included storey shear forces, relative storey displacements, storey drifts, steel and confined concrete strain in the basement walls, and plastic rotation values along the height of the structure for a selected column and beam section. Additionally, the average storey displacements, relative storey drift ratios, and storey shear forces obtained from ZTA analyses were compared with those obtained using the modal combination method. The results indicated that the average values obtained from the design based on resistance were in good agreement with the design results based on deformation. The structure-soil-pile interaction was considered using the subsystem approach for the building under earthquake effects. In this context, Method III specified in TBDY-2018 was employed. Initially, a kinematic interaction model was developed, considering only the piles, massless rigid foundation, and basement walls. The interaction between pile elements and the soil was considered through p-y, t-z, and Q-z springs, while the behavior between the basement walls and the soil was indirectly taken into account through p-y springs. Losses due to group effects in the piles were approximately calculated using empirical relationships. For the main rock layer characterized as ZB, 11 earthquake records were selected and modified using the SeismoMatch program to match the elastic acceleration spectrum defined in TBDY-2018. One-dimensional free-field soil response analyses were conducted using the DeepSoil program, considering the soil layers. Elastic acceleration spectra were derived at the base of the structure for each record, and their averages were used to obtain the design spectrum based on inertial interaction. However, due to the ZE soil class resulting in small spectrum ordinates from the behavior analyses, the design spectrum compatible with the ZE soil class was adopted. From the free-field vibration analyses, maximum displacement envelopes along the piles were obtained for each earthquake record, and incremental static analysis was performed to achieve the target displacements at the base of the building. For the inertial interaction, masses of the basement floors and foundation were considered in the model, and interaction springs were defined at a designated node at the center of gravity of the foundation plan for two horizontal axes and the rotational degree of freedom about these axes. Inertial interaction was realized according to the modal combination method, and the reduced pile internal forces arising from this interaction were calculated. The sum of the absolute values of the forces obtained from kinematic and inertial interactions was considered as the design forces for the piles, and pile reinforcements were determined.