Posts Tagged engineering
Types of Seismic Waves
Posted by Architect in Earthquake Engineering on June 15, 2010
During fault ruptures which cause earthquakes, the sudden breakage and movement along the fault can release tremendous amount of energy. Some of this energy is used up in cracking and pulverizing the rock as the two blocks of rock separated by the fault grind past each other. Part of the energy, however, speeds through the rock as seismic waves. This waves can travel for and cause damage at great distances. Once they start, these waves continue through the earth until their energy is used up.
There are two basic types of seismic waves, and they travel at different speeds through earth. The faster p waves and the slower s waves.
Primary or push waves or P waves
Primary Waves
These are longitudinal in nature like sound waves. The velocity of P waves is highest about 5.4 km/s and depends on the density of the rock and resistance to compression. P waves can pass through liquids also.
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Building Stiffness and Flexibility | Earthquake Engineering
Posted by Architect in Earthquake Engineering on June 15, 2010
The taller a building, the longer its natural period tends to be. But the height of a building is also related to another important structural characteristic: the building flexibility. Taller buildings tend to be more flexible than short buildings. (Only consider a thin metal rod. If it is very short, it is difficulty to bend it in your hand. If the rod is somewhat longer, and of the same diameter, it becomes much easier to bend. Buildings behave similarly) we say that a short building is stiff, while a taller building is flexible. (Obviously, flexibility and stiffness are really just the two sides of the same coin. If something is stiff, it isn’t flexible and vice-versa).
Displacement of Building according to their Height & Stiffness
Inertial Forces in a Structure
Posted by Architect in Earthquake Engineering on June 15, 2010
An earthquake causes shaking of ground. So a building resting on it will experience motion at its base. From Newton’s first law of motion, even though the base of the building moves with the ground, the roof has a tendency to stay in its original position. But since the walls and columns are connected to it, they drag the roof along with them.
Inertial Forces in a Structure
This is much like the situation that you are faced with when the bus you are standing in suddenly starts, your feet move with the bus, but your upper body tends to stay back making you fall backwards!
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Horizontal and Vertical Shaking of a Structure
Posted by Architect in Earthquake Engineering on June 15, 2010
Earthquake cause shaking of ground in all three directions – along the two horizontal directions (X and Y, say), and the vertical direction (Z, say). Also during the earthquake, the ground shakes randomly back and forth (- and +) along each of this X, Y and Z directions.
Horizontal and Vertical Shaking
Flow of Inertia Forces to Foundations
Posted by Architect in Earthquake Engineering on June 15, 2010
Flow of Inertia Forces to Foundation
Under horizontal shaking of ground, horizontal inertia forces are generated at a level of the mass of the structure (usually situated at the floor levels). These lateral inertia forces are transferred by the floor slab to the walls or the columns, to the foundations, and finally to the soil system underneath. So, each of this structural elements (floor slabs, walls, columns, and foundations) and the connections between them must be designed to safely transfer these inertia forces through them.
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