Effects of building collapse direction and bridge functionality on road networks following an earthquake

Istanbul is one the most important megacities in the world with a population approaching 15 million in the world. Migration from all over Turkey to Istanbul is still ongoing because, Istanbul is the industrial, commercial, cultural and educational centre of Turkey. However, those migrations caused unplanned construction and these led to the formation of vulnerable and undocumented building stock in Istanbul. Besides this, Istanbul is located in one of the most active seismic zones in the world. Many scientific studies estimate that Istanbul is expecting a major earthquake and the possible damage to the structures will be extensive. The occurrence of earthquakes cannot be prevented by human efforts. If an earthquake were to occur in a populated area, especially one covered with vulnerable building stock such as the city of Istanbul, it could cause a serious impact on human life. Besides this, if the road's functionality decreases due to damage to the transportation structures, the level of damage gets even higher and earthquake impacts may not be managed properly. Therefore, road network also plays an important role in activities of search and rescue, evacuation, firefighting operations and medical services after an earthquake. This study aims to estimate road functionality in Istanbul following the potential Istanbul Earthquake by taking into account the direction of the collapsed buildings and damaged transporation structures. One of the major disadvantages of Istanbul case is the lack of knowledge about the absolute number of buildings and the ages of those buildings. The various instances of earthquake loss asssessment software require the age, the construction type and the height of the buildings to estimate the possible damage of a scenario earthquake. The accuracy of such an estimation also depends on the reliability of the input data. To make a reliable earthquake damage estimation, a building database containing at least the; building age, construction type, and number of floors is required in most of the earthquake loss assessment software. For this reason, the first part of this study aims to create a recent and accurate building data of Istanbul including the occupacy classes, construction types, the number of floors and the most important one of all, their age. Firstly, in order to create the recent building dataset of Istanbul, the structure data and the building data were separated from each other. The building dataset was then classified but this data set did not include the building age. This is why the building age data was determined for every single building in Istanbul, according to structural codes for the earthquake zones by using aerial and satellite images of Istanbul. The classification should be based on the regulations in order to minimise the age classes and maximise their accuracy. First, building regulations in Turkey came into force in 1940 in order to determine the essential conditions for the realisation of functional, safe and disaster-resistant building design in Turkey. The last updated building code regulations in Turkey came into force in 2007. It was also important to investigate the proper building detection method for the aim of this study and it was determined as the manual digitisation. In this study, the buildings of Istanbul and their age are determined for every single building, by digitising the selected aerial photos (1966, 1982), orthophoto mosaics (1996, 2013) and satellite images (2004, 2007) of Istanbul based on the official structural codes in Turkey. Thus, first the exact number and location of buildings in Istanbul, rather than the structures and the age of every single building were determined and the recent building data consisted of occupacy classes, construction types, the number of floors and building age were produced in GIS. The results were also validated with two separate studies of Istanbul for different periods of times. In this way, the earthquake damage analysis for the Istanbul buildings can be run for the real building data of Istanbul with any earthquake loss assessment software. The second part of this study presents a building damage analysis for every single building in Istanbul, based on updated building data. The building damage analysis was made using the scenario based deterministic earthquake hazard maps of PGA and 0,2 second Sa demand types by using HAZTURK software. Results from the damage analysis for Istanbul were also presented for districts and sub-districts, in order to compare with other studies. The third part of this study is to determine the building collapse direction and the debris area radius in order to reveal road blockages in Istanbul. The building collapse direction estimation method generated is based on the collapsed buildings data during the 1999 Kocaeli Earthquake by using 1994 and 1999 Gölcük aerial photos, before and after the earthquake. Based on the method developed, if roadside buildings collapsed during the earthquake, then the scattered parts of the buildings could cause roads to lose their functionality. After the determination of the collapse directions of the buildings, the roads still functioning were also revealed during emergency operations. Defining the collapse direction of buildings has helped us to define which roads would be open after an earthquake. Routes are important for defining evacuation or escape roads, while emergency transportation roads, and roads are urgently needed for emergency use. This is hence the first study on this subject both in the national and international literature. It is not only collapsed buildings but also transportation structures that damage that effect the functionality of the road network. For this reason, in the fourth part of this study, we will estimate transportation structures' (bridge, viaducts, tunnels, overpasses, etc.) damage analysis according to PGA demand type by using HAZTURK software. Functionalities are then determined for a certain time period. It is also very important to reveal the functionality of transportation structures based on potential Istanbul earthquake, because they have critical importance during the post-earthquake response and long-term recovery phases of the disaster management. A complete understanding of the earthquake impact on the transportation structures with damage possibility, post-earthquake functionality and retrofitted damage possibility analysis, is a very important input for the decision makers in order to mitigate, prepare for, respond to, and recover from the potential impact on the potential Istanbul earthquake. At the end of the study, we have estimated building collapse directions, building debris areas, and transportation structures' damages and then performedan overall evaluation to reveal road functionality in Istanbul following an earthquake scenario. The results and the proposed methods in this study represent very important contributions that could be used as base data for decision makers to develop important strategies for risk reduction. That is, they could be used to prevent a hazard from becoming a disaster, to mitigate possible risks and to transform urban areas based on the earthquake risk.