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Bridge & Structure
Modeling and Simulating Buildings of Cities for Urban Earthquake Disaster Mitigation using 3D GIS Data
Establishing models of buildings of a megacity is very important for disaster mitigation. A traditional approach employs manpower to collect data of huge amount of buildings and applies statistic-based analysis. This research work provides a new method of constructing structural models of buildings in a city using 3D GIS data.
The available GIS data, as shown in Figure 1, are a profile of a building in 2D and a height of this building. The profile of one building is given in a polygon with an outer loop and possible inner loops (holes). To build a simplest Single Degree-Of-Freedom (SDOF) structural model, a total mass and shear stiffness of a building need to be obtained (Figure 2). Natural periods, the most important dynamic feature of building structures, can be estimated using empirical equations with height and dimension of buildings. Original GIS data donft give the information of number of stories of buildings. As a building is designed according to engineering codes with predefined usages, number of stories can be obtained by a reasonable guess using the height and profile of this building. The mass density of each story can also be obtained using the same method. This way, the total mass of one building can be computed out. Stiffness can therefore be calculated using a basic equation of dynamic relation. A well-adopted simplified structural model for buildings is a Multi-Degree-Of-Freedom (MDOF) model, which has a condensed mass at each story of a building. Using superposition method a MDOF system can be condensed into a SDOF system by providing a mode shape related a natural frequency.
An implementation is given by constructing building models of an area in Bunkyo District of Tokyo using available GIS data (Figure 3). A 3D view of structure models constructed on a picked-up area is shown in Figure 4. Figure 5 illustrates a scenario under Takatori ground motions of the 1996 Kobe earthquake of the studied region by showing damage levels with the color and size of circles.
Figure 1: Structural information from GIS data
Figure 2: A simplified SDOF model
Figure 3: An area picked up in Bunkyo District of Tokyo
Figure 4: A 3D view of structural models