This document discusses the earthquake design philosophy of making buildings resistant to earthquakes. It explains that earthquakes are divided into minor, moderate and strong shaking based on frequency and intensity. The goal of earthquake resistant design is to mitigate earthquake effects by designing structures to withstand smaller forces than actual earthquake forces. The document then outlines the expected damage to buildings under minor, moderate and strong shaking. It emphasizes designing key structural elements like beams and columns to be ductile to absorb energy and prevent collapse during earthquakes. Shear walls are also discussed as important seismic resistant elements.

1. Earth Resistant
Design Philosophy
Rishabh Lala
X Sem
Civil and Structural Engineering
Integrated PG Program
Rajiv Gandhi Proudyogiki Vishwavidyalaya

2. Earthquake Design Philosophy
• Shaking of earth is divided into 3 categories :
1. Minor Shaking  Assumed to occur Frequently
2. Moderate Shaking  Assumed to occur Occasionally
3. Strong Shaking  Assumed to occur Rarely
• Now, we know that, earthquake proof buildings are very expensive to
construct, as they require additional provisions. Therefore, earthquake
resistant design philosophy comes in existence. In this, we try to mitigate
the earthquake after effects and hence structures are designed for forces
much smaller than the actual earthquake forces.

3. Cases
• CASE 1 : UNDER MINOR BUT FREQUENT SHAKING :
Beams and columns or any other main member (like shear
walls) carries vertical and horizontal and horizontal forces
successfully, however buildings may suffer repairable
damage.
• CASE 2 : UNDER MODERATE BUT OCCASIONAL SHAKING :
a. Main members may undergo repairable damage
b. Other members may be replaced
• CASE 3: UNDER STRONG BUT REPAIRABLE SHAKING :
a. Main members may suffer severe and irreparable damage
but the building should not collapse

4. Purpose
• Building saves lives, even if building if it becomes dysfunctional
• Cracks in Building : does not mean that building is unsafe for use
• Economy of the construction project
• Key Strategy : Ductile Elements at key locations (load resisting
locations) of the structure, protects non-ductile elements from
getting over stressed. This inelastic response, tends to increase the
effective period of the structure, resulting in reduction in the
strength demand, to deal with wind and earthquake forces, as most
of the earthquake forces go in overcoming the damped structure
due to inelastic response.

5. Ductility
• Main elements of Earthquake Resistant Building should be designed with
property called Ductility
Example : Chalk on Breaking : gives a brittle Failure
While, Steel Pins on applying force : gives a ductile failure,
i.e. it bends
• Beams should be designed for such kind of ductility
• Ductility enables structures, which do not have adequate elastic strength to
survive ground motions, through its inelastic response, i.e. ability of the
structure to deform plastically without fracture.

6. Factors (ductility)
a.Architectural Plan :
a. Vertically and Horizontally symmetrical plan, improves ductility
b.Soft Storey :
a. Soft storeys reduce the overall ductility of the structure and should
be avoided, specially in the mid span of the vertical cantilever
(tower)
c.Weak Storey :
a. Aviod Weak Storey and provide strong diaphragm
d.Door Openings :
a. To be provided at atleast 0.6m away from the column edges.
e.Location of Water tanks :
a. Follow codal provisions, for determining water tank location and
swimming pool as it may affect the location of the center of mass
and the shear center

7. Increase ductility
a.Increase transverse shear reinforcement
b.Increase compressive strength of concrete
c.Increase percentage of compression steel
d.Increase percentage of tension steel

8. Shear Walls
• Provide large strength and stiffness to the structure in the
direction of their orientation, preventing it from lateral sways
during earthquakes, as they are good transmitters of
earthquake lateral forces that come along the direction of
their orientation.

9. Shear walls (Location)
• Hence, shear walls should be provided along both directions. Door
and window openings, may be provided in shear walls but their
openings should be limited so that they offer least interruption to
shear wall.
• Shear walls must be symmetrically located to avoid ill effects of
torsion and twists. Hence, shear walls are more effective, when they
are location in the exterior perimeters of the building and their
unsymmetrical location should be avoided.
• Shear walls are easy to construct as detailing is pretty straight
forward. Provisions from IS-13920 -1993, gives detailing concepts for
shear walls.