Earthquake resilience of Pol houses in Ahmedabad
2.1.2 Ground shaking effect on buildings • • •
Resultant earthquake force Seismic waves Inertia force direction Building mass
Figure 6 Inertia force action during earthquake, Source – Author
How much will be the damage in the structure? Will there be loss of lives due to the collapse? Will the building completely collapse? Or there will be partial damages that can be repaired later? The answer to all these questions lies in the structure of the building and how that structure will perform during the earthquake. Though the damages majorly depend on the intensity4, duration, and frequency5 content of the ground motion, type of soil, and other geologic conditions, the building design and quality of construction play a major role in the degree of damages and loss of lives. During an event of an earthquake when the earth vibrates, all the buildings on the ground surface will respond differently. (IAEE, 2004) The seismic loads are difficult to determine due to the random nature of earthquake motions, however by understanding the structural behavior, the building designs can be formulated and studied to reduce the damages.
Following are the ground shaking effects on buildings (IAEE, 2004):
i.
Inertia Force – Every built structure on the ground has its mass, when the ground shakes and the base of the building moves towards the right there is a tendency of the building to move towards left, this resistance is termed as inertia force. During an earthquake, the ground shakes in all directions and the inertia force acts in all the directions.
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Intensity - The intensity is a number (written as a Roman numeral) describing the severity of an earthquake in terms of its effects on the earth's surface and on humans and their structures. Several scales exist, but the ones most commonly used is the Modified Mercalli scale. (U.S. Geological Survey, 1879 ) 5 Frequency content – The physical signal (earthquake) which is decomposed into a number of discrete frequencies, or a spectrum of frequencies over a continuous range. The frequency content of ground motions seems to be the most important parameter to explain the structural damage experienced during strong earthquakes. The frequency content of ground motions can be characterized using various stochastic and/or deterministic indicators. (Pavel, 2012)
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