D. Hareesh B. Anil Kumar A. Narendra Reddy V. Yaswanth
What is a Earthquake. An earthquake is also known as a quake, tremor, or
temblor An earth quake is the result of a sudden release of energy
in the Earth's crust that creates seismic waves In past century
11 Deadliest earth quakes effected in all
over the earth
What Causes Earthquakes? Long time ago, a large collection of material masses
coalesced to form the Earth Large amount of heat was generated by this fusion,
and slowly as the Earth cooled down, the heavier and denser materials sank to the centre and the lighter
ones rose to the top.
The Inner Core is solid and consists of heavy metals (e.g.,
nickel and iron), while the Crust consists of light materials (e.g., basalts and granites). The Outer Core is liquid in form and the Mantle has the
ability to flow. The differentiated Earth consists of the Inner Core , the
Outer Core ,the Mantle and the Crust.
Types of Earthquakes and Faults Most earthquakes in the world occur along the boundaries of the
tectonic plates and are called Interplate Earthquakes (e.g., 1897
Assam (India) earthquake). A number of earthquakes also occur within the plate itself away
from the plate boundaries these are called Intra-plate
Earthquakes. E.g: 1993 Latur (India) earthquake
In both types of earthquakes, the slip generated at the fault
during earthquakes is along both vertical and horizontal directions (called Dip Slip) and lateral directions (called Strike Slip), with one of them dominating sometimes.
For example, the energy released during the 2001 Bhuj
(India) earthquake is about 400 times (or more) that released by the 1945 Atom Bomb dropped on Hiroshima!!
Affects of earthquakes Shaking and ground rupture Landslides and avalanches Fires Soil liquefaction Tsunami
Floods Human impacts
How the ground shakes?...
Seismic Waves Large strain energy released during an earthquake travels
seismic waves in all directions through the Earths
layers, reflecting and refracting at each interface. These waves are of two types - (a)
(b) surface waves
Body waves consist of Primary Waves (P-waves) and
Secondary Waves (S-waves), and surface waves consist of Love waves and Rayleigh waves.
Under P-waves, material particles undergo extensional and
transmission, but under S-waves, oscillate at right angles to it
Love waves cause surface motions similar to that by S-
waves, but with no vertical component.
Rayleigh wave makes a material particle oscillate in an
elliptic path in the vertical plane.
Earthquake resistant structures In recent times, reinforced concrete buildings have become
common in India, particularly in towns and cities.
Reinforced concrete (or simply RC) consists of two primary
materials, namely concrete with reinforcing steel bars.
Earthquake resistant structures Earthquake-resistant
hazardous earthquake exposures at the sites of their
particular location The convective flows of Mantle material cause the Crust
and some portion of the Mantle, to slide on the molten outer core.
This sliding of Earths mass
takes place in pieces called Tectonic Plates.
These plates move in different directions and at different
speeds from those of the neighbouring ones.
Sometimes, the plate in the front is slower; then, the plate
behind it comes and collides (and mountains are formed).
On the other hand, sometimes two plates move away from
one another (and rifts are created).
In another case, two plates move side-by-side, along the
same direction or in opposite directions.
These three types of inter-plate interactions are the convergent, respectively. divergent andtransform boundaries
How do Earthquakes Affect Reinforced Concrete Buildings? Reinforced Concrete Buildings In recent times, reinforced concrete buildings have
become common in India, particularly in towns and cities. Reinforced concrete (or simply RC) consists of
two primary materials,1) concrete 2) reinforcing steel bars
ConcreteConcrete is made of sand, crushed stone (called aggregates) and cement, all mixed with pre-determined amount of water. Concrete can be molded into any
Reinforcing steel barssteel bars can be bent into many shapes. Thus, structures of complex shapes are possible with RC
A typical RC building is made of
Horizontal members :-(beams and slabs)vertical members :-(columns and walls)
And supported by foundations that rest on ground. The
system comprising of RC columns and connecting beams is
called a RC Frame.
The RC frame participates in resisting the earthquake
forces. Earthquake shaking generates inertia forces in the
building, which are proportional to the building mass. Since most of the building mass is present at floor
levels, earthquake-induced inertia forces primarily developat the floor levels.
These forces travel downwards - through slab and beams
to columns and walls, and then to the foundations from
where they are dispersed to the ground. As inertia forcesaccumulate downwards from the top of the building, the columns and walls at lower storeys experience higher earthquake-induced forces
Roles of Floor Slabs and Masonry Walls Floor slabs are horizontal plate-like
facilitate functional use of buildings. Usually, beams and slabs at one
storey level are cast
together. In residential multi-storey buildings, thickness of slabs is only about 110-150mm. When beams bend in the vertical direction during
earthquakes, these thin slabs bend along with them.
Masonry walls masonry walls are not connected to surrounding RC
columns and beams. When columns receive horizontal forces at floor levels,
they try to move in the horizontal direction, but masonry walls tend to resist this movement. Due to their heavy weight and thickness, these walls
attract rather large horizontal forces due to this these walls develop cracks
Strength Hierarchy For a building to remain safe during earthquake shaking,
columns (which receive forces from beams) should be stronger than beams, and foundations
(which receive forces from columns) should be stronger
than columns. Further, connections between beams & columns and columns & foundations should not fail so that beams can safely transfer force s to columns and columns to foundations. When this strategy is adopted in design, damage is likely to
occur first in beams if columns are made weaker, they suffer severe local
damage, at the top and bottom of a particular storey
How to Reduce Earthquake Effects on Buildings? Conventional seismic design attempts to make buildings
that do not collapse under strong earthquake shaking, but may sustain damage to non-structural elements (like glass facades) and to some structural members in the building.
Special techniques are required to design buildings such
that they remain practically undamaged even in a severe earthquake. Buildings with such improved seismic performance usually
cost more than normal buildings do. However,
Two basic technologies are used to protect buildings from
damaging earthquake effects.
Base Isolation Devices & Seismic Dampers.
The idea behind base isolation is to detach (isolate) the
building from the ground in such a way that earthquake
motions are not transmitted up through the building, or atleast greatly reduced. Seismic dampers are special devices introduced in the
building to absorb the energy provided by the ground motion to the building