Designing Earthquake Resistant Buildings :
Tips and Tricks
Earthquakes are a dangerous phenomena. People are vulnerable to the destructive power of earthquakes. Earthquakes have unleashed their destructive power on humans time and time again. But today, with the advancement of construction technology, man has learnt to protect himseld from earthquakes.
What is an Earthquake?
An earthquake is a sudden, rapid shaking of the Earth caused by the breaking and shifting of rock beneath the Earth’s surface.
Ground shaking from earthquakes can collapse buildings and bridges; disrupt gas, electric, and phone services; and sometimes trigger landslides, avalanches, flash floods, fires, and huge, destructive ocean waves (tsunamis). Buildings with foundations resting on unconsolidated landfill and other unstable soil, and trailers and homes not tied to their foundations are at risk because they can be shaken off their mountings during an earthquake. When an earthquake occurs in a populated area, it may cause deaths and injuries and extensive property damage.
It is for this reason that it is often said,
“Earthquake don’t kill people, buildings do.”
Earthquake Resistant Building Design Philosophy
a) Under minor but frequent shaking, the main members of the buildings that carry vertical and horizontal forces should not be damaged; however buildings parts that do not carry load may sustain repairable damage.
b) Under moderate but occasional shaking, the main members may sustain repairable damage, while the other parts that do not carry load may sustain repairable damage.
c) Under strong but rare shaking, the main members may sustain severe damage, but the building should not collapse.
Protection from Earthquakes
There are various new techniques which help in reducing the impact of earthquake forces on buildings. Most of these techniques are expensive to implement.
Here is a list of Earthquake Resistant Techniques…
1. Base Isolation for Earthquake Resistance
The concept of base isolation is explained through an example building resting on frictionless rollers. When the ground shakes, the rollers freely roll, but the building above does not move. Thus, no force is transferred to the building due to the shaking of the ground; simply, the building does not experience the earthquake. Now, if the same building is rested on the flexible pads that offer resistance against lateral movements (fig 1b), then some effect of the ground shaking will be transferred to the building above. If the flexible pads are properly chosen, the forces induced by ground shaking can be a few times smaller than that experienced by the building built directly on ground, namely a fixed base building. The flexible pads are called base-isolators, whereas the structures protected by means of these devices are called base-isolated buildings.
2. Energy Dissipation Devices for Earthquake Resistance
Another approach for controlling seismic damage in buildings and improving their seismic performance is by installing Seismic Dampers in place of structural elements, such as diagonal braces. These dampers act like the hydraulic shock absorbers in cars – much of the sudden jerks are absorbed in the hydraulic fluids and only little is transmitted above to the chassis of the car. When seismic energy is transmitted through them, dampers absorb part of it, and thus damp the motion of the building.
3. Active Control Devices for Earthquake Resistance
The system consists of three basic elements:
a. Sensors to measure external excitation and/or structural response.
b. Computer hardware and software to compute control forces on the basis of observed excitation and/or structural response.
c. Actuators to provide the necessary control forces.
Thus in active system has to necessarily have an external energy input to drive the actuators. On the other hand passive systems do not required external energy and their efficiency depends on tunings of system to expected excitation and structural behavior. As a result, the passive systems are effective only for the modes of the vibrations for which these are tuned. Thus the advantage of an active system lies in its much wider range of applicability since the control forces are worked out on the basis of actual excitation and structural behavior. In the active system when only external excitation is measured system is said to be in open-looped. However when the structural response is used as input, the system is in closed loop control.
These techniques have been successfully employed in many projects across the world. They are most widely used in Japan. These techniques are also being used in earthquake prone areas of California, Indonesia and other such places.
You can find a detailed comparison report, information and case studies on Earthquake Resistant Buildings from www.architectjaved.com/earthquake_resistant_structures/
