INDIAN
STANDARDS ON EARTHQUAKE ENGINEERING
Bureau of Indian standards, the National Standard Body of India, is a Statutory Organization under the Bureau of Indian Standards Act 1986. One of the activity is formulation of Indian Standards on different subjects of Engineering through various Division Councils. The Civil Engineering Division Council is responsible for standardization in the field of Civil Engineering including Structural Engineering, Building materials and components, Planning Design, Construction and Maintenance of Civil Engineering Structures, Construction Practices, Safety in Building etc. These standards are evolved based on concensus principle through a net work of technical committee comprising representatives from Research and Development Organizations, Consumers, Industry, Testing Labs and Govt. Organizations etc.
The Civil Engineering Division Council is working towards to achieve the above goal through 34 Sectional Committees covering wide range of subjects and one of the Sectional Committee is Earthquake Engineering Sectional Committee, CED 39.
Bureau of Indian Standards has rendered invaluable services by producing large number of national standards, which are of direct relevance to the construction industry and some of them particular to the mitigation of disasters. A detail of Indian Standards in the area of mitigation of natural hazard of earthquake is given underneath.
Himalayan-Nagalushai
region, Indo-Gangetic plain, Western India and Cutch
and
It is to serve this purpose that standards have been formulated in the field of Design and Construction of Earthquake Resistant Structures and also in the field of measurement and tests connected therewith by the Earthquake Engineering Sectional Committee, CED 39. Following standards have been formulated under this Committee:
This standard deals with earthquake resistant design of structures and is applicable to buildings; elevated structures; bridges; dams etc. It also gives a map which divides the country into five seismic zones based on the seismic intensity.
IS 1893 was initially published
in 1962 as `Recommendations for Earthquake Resistant Design of Structures’ and
then revised in 1966. As a result of
additional seismic data collected in India and further knowledge and experience
gained the standard was revised in 1970, 1975 and then in 1984.
Consequent to the publication of this standard on account of earthquakes in various parts of the country including that in Uttar-Kashi, Latur and Bhuj and technological advancement in the field, the Sectional Committee decided to revise the standard into five parts which deals with different types of structures:
Part 1 : General provisions and Buildings
Part 2 : Liquid Retaining Tanks – Elevated and Ground
Supported
Part 3 : Bridges and Retaining Walls
Part 4 : Industrial Structures Including Stack Like Structures
Part 5 : Dams and Embankments
IS 1893(Part 1):2002 `Criteria for Earthquake Resistant Design of Structures : Part 1 General provisions and Buildings’
This standard contains provisions
that are general in nature and applicable to all structures. Also, it contains provisions that are
specific to buildings only. It
covers general principles and design criteria, combinations, design spectrum,
main attributes of buildings, dynamic analysis, apart from seismic zoning map
and seismic coefficients of important towns, map showing epicenters, map showing
tectonic features and lithological map of
Following are the major and
important modifications made in this revision:
a) The
seismic zone map is revised with only four zones, instead of five. Erstwhile Zone I has been merged to Zone II
and hence Zone I does not appear in the new zoning; only Zones II, III, IV and
V do. The killari
area has been included in Zone III and necessary modifications made, keeping in
view the probabilistic Hazard Evaluation.
The
b) This
revision adopts the procedure of first calculating the actual force that may be
experienced by the structure during the probable maximum earthquake, if it were
to remain elastic. Then the concept of
response reduction due to ductile deformation or frictional energy dissipation
in the cracks is brought into the code explicity, by
introducing the `response reduction factor’ in place of the earlier performance
factor.
c) The
values of seismic zone factors have been changed; these now reflect more
realistic values of effective peak ground acceleration considering Maximum
Considered Earthquake (MCE) and service life of structure in each seismic zone.
d) A
clause has been introduced to restrict the use of foundations vulnerable to
differential settlements in severe seismic zones.
Here it is worthwhile to mention
that it is not intended in this standard to lay down regulation so that no
structure shall suffer any damage during earthquake of all magnitudes. It has been endeavoured
to ensure that as far as, possible structures are able to respond, without
structural damage to shocks of moderate intensities and without total collapse
to shocks of heavy intensities.
IS 1893(Part 4):2005 `Criteria for Earthquake Resistant Design of Structures: Part 4 Industrial Structures Including Stack Like Structures
This standard deals with
earthquake resistant design of the industrial structures (plant and auxiliary
structures) including stack-like structures such as process industries, power plants,
textile industries, off-shore structures and marine/port/harbour
structures.
In addition to the
above, stack-like structures covered by this standard are such as transmission
and communication towers, chimneys and stack-like structures and silos
(including parabolic silos used for urea storage).
The characteristics
(intensity, duration, etc) of seismic ground vibrations expected at any
location depends upon the magnitude of earthquake, its depth of focus, distance
from the epicenter, characteristics of the path through which the seismic waves
travel, and the soil strata on which the structure stands.
The response of a
structure to ground vibrations is a function of the nature of foundations,
soil, materials, form, size and mode of construction of structures; and the
duration and characteristics of ground motion.
This standard specifies design forces for structures standing on rocks
or soils, which do not settle, liquify or slide due
to loss of strength during vibrations.
The design approach
adopted in this standard is to ensure that structures possess minimum strength
to withstand minor earthquakes (<DBE) which occur frequently, without
damage; resist moderate earthquakes (DBE) without significant structural damage
though some non-structural damage may occur; and withstand a major earthquake
(MCE) without collapse.
Formulation of revised codes for other parts of IS 1893 are in advance stages.
IS 4326:1993 Earthquake Resistant Design and
Construction of Buildings - Code of
Practice
This standard provides guidance
in selection of materials, special features of design and construction for
earthquake resistant buildings including masonry construction, timber
construction, prefabricated construction etc.
In this standard, it is intended to cover the specified features of
design and construction for earthquake resistance of buildings of conventional
types. The general principles to be
observed in the construction of such earthquake resistant buildings as
specified in this standard are Lightness, Continuity of Construction,
avoiding/reinforcing Projecting and suspended parts, Building configuration,
strength in various directions, stable foundations, Ductility of structure,
Connection to non-structural parts and fire safety of structures.
Special Construction Features
like Separation of Adjoining Structures, Crumple Section, Foundation
design, Roofs and Floors and Staircases have been elaborated in the
standard. It also covers the details
pertaining to the type of construction, masonry construction with rectangular
masonry units, masonry bearing walls, openings in bearing walls, seismic strengthening
arrangements, framing of thin load bearing walls, reinforcing details for
hollow block masonry, flooring/roofing with precast
components and timber construction.
IS
13827:1993 Improving
Earthquake Resistance of Earthen Buildings – Guidelines
The guidelines covered in this
standard deal with the design and construction aspects for improving earthquake
resistance of earthen houses, without the use of stabilizers such as lime,
cement, asphalt, etc.
The provisions of this standard
are applicable for seismic zones III, IV and V.
No special provisions are considered necessary in Zone II. However, considering inherently weak against
water and earthquake, earthen buildings should preferably be avoided in flood
prone, high rainfall areas and seismic zones IV and V.
It has been recommended that
such buildings should be light, single storeyed and
of simple rectangular plan. Qualitative
tests for the suitability of soil have been suggested.
Guidelines for Block or Adobe
Construction, Rammed earth construction, Seismic strengthening of bearing wall
buildings, Internal bracing in earthen houses and earthen constructions with
wood or cane structures have
heen elaborated in this standard.
IS 13828:1993 Improving Earthquake Resistance of Low
Strength Masonry Buildings – Guidelines
This standard covers the special
features of design and construction for improving earthquake resistance of
buildings of low-strength masonry.
The provisions of this standard
are applicable in all seismic zones. No
special provisions are considered necessary for buildings in seismic zone II if
cement-sand mortar not leaner than 1:6 is used in masonry and
through stones or bonding elements are used in stone walls.
The various provisions of IS
4326:1993 regarding general principles, special construction features, types of
construction, categories of buildings and masonry construction with rectangular
masonry buildings of low strength dealt with in this standard. There are however certain restrictions,
exceptions and additional details which are specifically included herein.
IS 13920:1993 Ductile Detailing of Reinforced
Concrete Structures Subjected to Seismic Forces – Code of Practice
This standard covers the
requirements for designing and detailing of monolithic reinforced concrete
buildings so as to give them adequate toughness and ductility to resist severe
earthquake shocks without collapse.
The provisions for reinforced
concrete construction given in this standard apply specifically to monolithic
reinforced concrete construction. Precast and/or prestressed
concrete members may be used only if they can provide the same level of
ductility as that of a monolithic reinforced concrete construction during or
after an earthquake.
Provisions on minimum and
maximum reinforcement have been elaborated which includes the requirements for
beams at longitudinal reinforcement in beams at joint face, splices and
anchorage requirements. Provisions have
been included for calculation of design shear force and for detailing of transverse
reinforcement in beams.
Material specifications are
indicated for lateral force resisting elements of frames. The provisions are also given for detailing
of reinforcement in the wall web, boundary elements, coupling beams, around
openings, at construction joints, and for the development, splicing and
anchorage of reinforcement.
IS 13935:1993 Repair and Seismic Strengthening of
Buildings – Guidelines
This standard covers the
selection of materials and techniques to be used for repair and seismic strengthening
of damaged buildings during earthquakes and retrofitting for upgrading of
seismic resistance of existing buildings.
The provisions of this standard
are applicable for buildings in seismic zones III to V of IS 1893:1984, which
are based on damaging seismic intensities VII and more on MSK Scales.
The buildings affected by
earthquake may suffer both non-structural and structural damages. This standard lays down guidelines for
non-structural/architectural as well as structural repairs, seismic strengthening
and seismic retrofitting of existing buildings.
Guidelines have been given for selection of materials for repair work
such as cement, steel, epoxy resins, epoxy mortar, quick setting cement mortar
and special techniques such as shotcrete, mechanical
anchorage etc. Seismic strengthening
techniques for the modification of roofs or floors, inserting new walls,
strengthening existing walls, masonry arches, random rubble masonry walls,
strengthening long walls, strengthening reinforced concrete members and
strengthening of foundations have been elaborated in detail.
IS 6922:1973 Criteria for Safety and Design of Structures
Subject to Underground Blasts
This standard deals with the
safety of structures during underground blasting and is applicable to normal
structures like buildings, elevated structures, bridges, retaining walls,
concrete and masonry dams constructed in materials like brickwork, stone
masonry and concrete.
As underground blasting
operations have become almost a must for excavation purposes, this standard
lays down criteria for safety of such structures from cracking and also
specifies the effective accelerations for their design in certain cases.
IS 4991:1968 Criteria for Blast Resistant Design of
Structures for Explosions Above Ground
This standard covers the
criteria for design of structures for blast effects of explosions above ground
excluding blast effects of nuclear explosions.
IS 4967:1968 Recommendations for Seismic
Instrumentation for
This standard covers
recommendations for instrumentation for investigation of seismicity,
study of microtremors and predominant period of a dam
site and permanent installation of instruments in the dam and appurtenant
structures and in surrounding areas.
These standards endeavour to provide a guideline in designing and repairing
of buildings under seismic forces.