Indian Standards and Codes
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 Divisions 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 consensus principle through a net work of technical committee comprising representatives from Research and Development Organizations, Consumers, Industry, Testing Labs and Govt. Organizations etc.
EARTHQUAKE ENGINEERING SECTIONAL COMMITTEE
This Sectional Committee on Earthquake Engineering formulated by the Civil Engineering Division Council is working towards to achieve the above goal covering wide range of subjects and is engaged for the standardization work in the field of design and construction of earthquake resistant structures and in the field of measurements and tests connected herewith.
It has been a long felt need to rationalize the earthquake resistant design and construction of structures taking into account seismic data from studies of past earthquakes.
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, Civil Engineering Division Council (CED 39). Following standards have been formulated under this Committee:
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 India.
Following are the major and important modifications made in this revision:
· 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 Bellary isolated zone has been removed. The parts of eastern coast area have shown similar hazard to that of the killari area, the level of Zone II has been enhanced to Zone III and connected with Zone III of Godawari Graben area.
· 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 explicitly, by introducing the `response reduction factor’ in place of the earlier performance factor.
· 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.
· 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.
Earthquake Zones of India indicating 60 cities with population exceeding half a million
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 Zones I and 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 been 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 zones I and 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. Pre cast and/or pre stressed 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 River Valley Projects
This standard covers recommendations for instrumentation for investigation of seismicity, study of micro tremors and predominant period of a dam site and permanent installation of instruments in the dam and appurtenant structures and in surrounding areas.
BIS has also formulated a Handbook SP 22(S&T):1982 Explanatory Handbook on Codes for Earthquakes Engineering (IS 1893:1975 and IS 4326:1976).
These standards endeavor to provide a guideline in designing and repairing of buildings under seismic forces.