Effects of surface topography on seismic response of reinforced concrete buildings

Abstract

Earthquakes are one of the most devastating and fatal natural disasters on Earth. In order to understand the complex structure of earthquakes and to construct safe and resilient cities, many fields, such as geophysicists, geotechnical engineers, civil engineers, and earthquake engineers, have put an excellent effort for hundreds of years. There are several parameters to determine the impacts of these devastating natural hazards on the environment and human-made structures. Some of the most prominent of these parameters are the distance to the fault, soil properties, interaction between the building and soil, and topographic characteristics of the land surface. Technological advancements and ensuring an appropriate engineering service led to construction activities in locations with different geographic aspects, such as highlands, hillsides, and valleys. However, these varieties influence the damage states of the buildings when excited to a ground motion. Istanbul is known as city of seven hills. One of the reasons for this discourse is that urbanisation took place on these seven hills during the Ottoman and Byzantine periods. Although it seemed a pulchritude from a historical perspective, it is expected that this geographical condition will have a crucial impact on earthquake-induced damages. It is evident that Istanbul is prone to strong earthquakes since it is close to the North Anatolian Fault Zone, and significantly destructive earthquakes (Mw > 7.0) occurred in the past. The motivation of this study is to investigate the impacts of surface topography on the seismic behavior of existing buildings. Hence, a representative ten-story building was selected regarding the building stock of Istanbul. The building has been constructed according to the Turkish Seismic Code 1997, and the structural system is RC shear walls. Then, the seismic performance of the structural model was evaluated, accounting for the topographic effects, and results were compared to analysis where these effects were neglected. The numerical model was conducted on OpenSees (Open System for Earthquake Engineering Simulation) software. Nonlinear fiber elements with distributed plasticity were used to model the RC shear walls, and the plastic hinges with lumped plasticity were preferred to model the beams. To ensure numerical accuracy, another model was created on the ETABS software. Comparisons showed that structural periods were consistent with each other. Firstly, static gravity and pushover analyses were conducted, then, nonlinear transient analyses were performed. Ground motions used in this study were modified to reflect topographic effects during the nonlinear transient analyses. In this scope, ground motions were chosen from a study where they were created artificially for more than 20000 different locations in the European region of Istanbul and 57 different scenarios considering and not considering the topographic effects. Since these simulations were location-based and included the topographic impact, they added significant value to the scope of this study. The analyses were limited to 11 locations and 7 scenarios, 154 ground motions in total, to investigate more general impacts of topographic effects. Consequently, the findings of the study revealed that surface topography has a great influence on the damage states and demands of the existing buildings. Most importantly, outcomes showed that topographic effects should be accounted for while preparing risk assessments of earthquake-prone cities such as Istanbul.