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Seismic Forces

The document discusses the seismic effects on structures during earthquakes, highlighting the role of inertia forces and the motion of buildings. It emphasizes the importance of wall and column resilience to withstand inertia forces and prevent structural failure. Additionally, it notes that while vertical shaking is less critical, horizontal shaking poses significant design challenges for buildings.

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sraddhasreekkutty
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50 views6 pages

Seismic Forces

The document discusses the seismic effects on structures during earthquakes, highlighting the role of inertia forces and the motion of buildings. It emphasizes the importance of wall and column resilience to withstand inertia forces and prevent structural failure. Additionally, it notes that while vertical shaking is less critical, horizontal shaking poses significant design challenges for buildings.

Uploaded by

sraddhasreekkutty
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Seismic Effects on Structures

Earthquake Tip 5

Alok Satheesh K, 8705


1. Earthquake-Induced Motion
• Earthquakes cause ground shaking, leading to motion at a building's base.
• Roof of the building tends to remain in its original position due to inertia.

• Walls and columns drag the roof along, causing different motions between
the roof and ground.

• Inertia: tendency to resist changes in motion, similar to when a bus starts


suddenly.
2. Inertia Forces in Structures
• Inertia Force: When ground moves, the building is 'thrown' backward.

• The roof experiences an inertia force (FI = M * a) opposite to acceleration.


• Larger mass results in higher inertia force.
• Lighter buildings perform better during earthquakes.
3. Effect of Deformations in Structures
• Inertia forces from the roof are transferred to the ground via columns.

• Columns resist deformation and try to return to a straight vertical position.


• Horizontal displacement generates internal forces known as stiffness forces.
• Stiffer columns generate larger forces.
4. Horizontal and Vertical Shaking
• Earthquakes cause ground shaking in three directions: X, Y (horizontal) and
Z (vertical).

• Structures are primarily designed to carry gravity loads.


• Vertical shaking is usually not critical due to design safety factors.
• Horizontal shaking can be problematic and requires additional design
considerations.

5. Flow of Inertia Forces to Foundations


• Horizontal shaking generates inertia forces at floor levels.
• Forces are transferred from floor slabs to walls/columns, then to
foundations.
6. Structural Element Vulnerability: Walls
• Walls/columns are crucial for transferring inertia forces.
• Walls, often made of brittle materials like masonry, are vulnerable to failure
• Historical evidence shows failure of masonry walls during past earthquakes.
• Design and construction must focus on improving wall resilience.

7. Structural Element Vulnerability: Columns


• Poorly designed/constructed reinforced concrete columns are prone to
failure
• Column failure can lead to disastrous building collapses.
• Proper design and construction of columns are essential for earthquake
safety.

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