Seismic Design Values For Buildings Crack In The

Yes a chalk breaks easily On the contrary, a steel pin allows it to be bent back-and-forth.

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Relatively speaking, minor shaking occurs frequently, moderate shaking occasionally and strong shaking rarely.

For instance, on average annually about 800 earthquakes of magnitude 5.0-5.9 occur in the world while the number is only about 18 for magnitude range 7.0-7.9.

So, should we design and construct a building to resist that rare earthquake shaking that may come only once in 500 years or even once in 2000 years at the chosen project site, even though the life of the building itself may be only 50 or 100 years Since it costs money to provide additional earthquake safety in buildings, a conflict arises: Should we do away with the design of buildings for earthquake effects Or should we design the buildings to be earthquake proof wherein there is no damage during the strong but rare earthquake shaking Clearly, the former approach can lead to a major disaster, and the second approach is too expensive.

Hence, the design philosophy should lie somewhere in between these two extremes.

Instead, the engineering intention is to make buildings earthquake-resistant; such buildings resist the effects of ground shaking, although they may get damaged severely but would not collapse during the strong earthquake.

Thus, safety of people and contents is assured in earthquake-resistant buildings, and thereby a disaster is avoided.

This is a major objective of seismic design codes throughout the world.

And, after moderate shaking, the building will be operational once the repair and strengthening of the damaged main members is completed.

But, after a strong earthquake, the building may become dysfunctional for further use, but will stand so that people can be evacuated and property recovered.

For example, important buildings, like hospitals and fire stations, play a critical role in post-earthquake activities and must remain functional immediately after the earthquake.

These structures must sustain very little damage and should be designed for a higher level of earthquake protection.

Collapse of dams during earthquakes can cause flooding in the downstream reaches, which itself can be a secondary disaster.

Therefore, dams (and similarly, nuclear power plants) should be designed for still higher level of earthquake motion.

Seismic Design Values For Buildings Crack In The

Contrary to the common thinking that any crack in the building after an earthquake means the building is unsafe for habitation, engineers designing earthquake-resistant buildings recognize that some damage is unavoidable.

Different types of damage (mainly visualized though cracks; especially so in concrete and masonry buildings) occur in buildings during earthquakes.

Some of these cracks are acceptable (in terms of both their size and location ), while others are not.

In general, qualified technical professionals are knowledgeable of the causes and severity of damage in earthquake-resistant buildings.

This approach of earthquake-resistant design is much like the use of electrical fuses in houses: to protect the entire electrical wiring and appliances in the house, you sacrifice some small parts of the electrical circuit, called fuses; these fuses are easily replaced after the electrical over-current.

Likewise, to save the building from collapsing, you need to allow some pre-determined parts to undergo the acceptable type and level of damage.

To do this, let us first understand how different materials behave.

Consider white chalk used to write on blackboards and steel pins with solid heads used to hold sheets of paper together.