The document summarizes how different buildings respond to ground shaking during an earthquake. Taller buildings typically have longer natural periods of vibration than shorter buildings. The period depends on factors like the building's height, mass, and flexibility. During an earthquake, the ground shaking contains a mixture of vibrational waves with different periods. A building will vibrate most strongly in response to ground motions that match its natural period.

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Figure 1: Free vibration response of a building:
the back-and-forth motion is periodic.
Roof
Displacement
Inverted Pendulum Model
Time
T
T
T
T
0
(a) Building pulled with a rope tied at its roof
(b) Oscillation of building on cutting the rope
Figure 2: Fundamental natural periods of
structures differ over a large range. The
natural period values are only indicative;
depending on actual properties of the structure,
natural period may vary considerably.
Adapted from: Newmark, (1970), Current trends in the Seismic
Analysis and Design of High Rise Structures, Chapter 16, in
Wiegel, (1970), Earthquake Engineering, Prentice Hall, USA.
Suspension Bridge: 6 sec
Large
Concrete Gravity Dam:
0.8 sec
Elevated Water Tank: 4 sec
Reinforced
Concrete
Chimney:
2 sec
Single Storey
Building:
0.05 sec
Low-rise
Building:
0.4 sec
15 Storey Building:
1 sec

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Figure 4: Different Buildings Respond Differently
to Same Ground Vibration.
Figure 3: Strong Earthquake Ground Motion is
transmitted by waves of different periods.
Earthquake Shaking
Time
Tshort
Short
Period
Wave
0
Time0
Tlong
Long
Period
Wave
Time0
Amplitude
Depth of Soil (m)
StructuralDamageIntensity(%)
50 100 150 200 250 300
10
20
30
40
50
0
0
10-14 Storey
Buildings
3-5 Storey
Buildings
Adaptedfrom:SeedandIdriss,(1982),Ground
MotionandSoilLiquefactionDuringEarthquakes,
EERI,USA.
(a) Buildings in a city lie on different soils
(b) Intensity of damage depends on thickness of
underlying soil layer: 1967 Caracas Earthquake