16 india should take seismic protection more seriously

8/12/2019 16 India Should Take Seismic Protection More Seriously

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India should take seismic protection more seriously

India's growing economic might is making many countries look at it with a sense of envy. This

newfound economic prosperity has also left India more vulnerable and susceptible to naturalcalamities. It is imperative that we start following the global best practices and stop living in a senseof denial.

India's growing economic might is making many countries look at it with a sense of envy. Thisnewfound economic prosperity has also left India more vulnerable and susceptible to naturalcalamities. It is imperative that we start following the global best practices and stop living in a senseof denial.

Two countries have learnt their lessons the hard way -- the US and Japan. The colossal damagecaused by the quakes of Northridge in 1994 and Kobe in 1995 forced the two governments to spend

millions on research. The research helped to reach a better understanding of how structures performin devastating scenarios. This led to classification of buildings depending on their performance. Nowthere exist internationally accepted documents issued by the two governments.

With the real estate boom having taken India by storm, it is imperative that everyone shouldunderstand the basics of seismic protection. Most neglect the subject as one that is a bit tootechnical for their liking; however, this should not be so.

Two questions that occur to an average educated person are: What are the different categories ofquake protection? What protection level is he achieving by following the Indian Seismic Code?

In today's world, simply stating that a building is earthquake resistant is meaningless. It does notportray anything about the building performance during an earthquake, its post-quake use and themagnitude and kind of damage that it will sustain.

It will come as a surprise that till date there is no definition in this country for what can be dubbedearthquake-resistant. Neither the national disaster management guidelines nor the Indian seismiccode has even attempted to address the issue. This has led the misuse of the term.

Internationally, earthquake protection is classified into four categories, each having a detaileddefinition. The categories are: operational, immediate occupancy, life-safety and collapseprevention.

'Operation' is the highest level and is adopted for important structures like hospitals, administrativecentres and essential infrastructure. Operational buildings are seldom more than 5 or 6 storey high.

The second level is 'immediate occupancy'. Buildings designed to these standards sustain minimalstructural damage even during a major earthquake. They are safe for occupation and for useimmediately after a major earthquake.

'Life-safety' buildings are those that are so designed that their primary aim is to save lives; the

building per se will sustain severe structural damage. After the earthquake the kind and level ofdamage that the columns suffer will determine if the building is repairable or will have to bedemolished and rebuilt.

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The lowest category 'collapse prevention' buildings are those that will sustain extensive structuraldamage. The damage will render the building unfit for use and will have to be immediately vacated,demolished and subsequently rebuilt.

In case the builder/developer has followed the Indian seismic building code to the fullest, thebuilding would achieve 'collapse prevention' level of safety. The term 'collapse prevention' isdisguised in our country by using alternative words: earthquake resistant.

The detailed definitions of various categories of protection are:

Operational Level: The lowest level of overall damage to the building (highest performance). Thestructure will retain nearly all of its pre-earthquake strength and stiffness. Expected damage includesminor cracking of facades, partitions and ceilings as well as structural elements. All mechanical,electrical, plumbing and other systems necessary for normal operation of the buildings are expected

to be functional, possibly from standby sources.

Negligible damage to non-structural components is expected. Under very low levels of earthquakeground motion, most buildings should be able to meet or exceed this performance level. Typically,however, it will not be economically practical to design for this level of performance under severelevels of ground shaking, except for buildings that house essential services.

Immediate Occupancy Level: Overall damage to the building is light. Damage to the structuralsystems is similar to the Operational Performance Level; however, somewhat more damage tonon-structural systems is expected. Non-structural components such as cladding and ceilings, and

mechanical and electrical components remain secured; however, repair and clean up may beneeded. It is expected that utilities necessary for normal function of all systems will not be available,although those necessary for life safety systems would be provided.

Many building owners may wish to achieve this level of performance when the building is subjectedto moderate levels of earthquake ground motion. In addition, some owners may desire suchperformance for very important buildings, under severe levels of earthquake ground shaking. Thislevel provides most of the protection obtained under the Operational Building Performance Level,without the associated cost of providing standby utilities and performing rigorous seismicqualification to validate equipment performance.

Life Safety Level: Structural and non-structural damage is significant. The building may lose asubstantial amount of its pre-earthquake lateral strength and stiffness, but the gravity-load bearingelements function. Out-of-plane wall failures and tipping of parapets are not expected, but there willbe some permanent drift and select elements of the lateral-force resisting system may havesubstantial cracking, spalling, yielding, and buckling.

Non-structural components are secured, but many architectural, mechanical and electrical systemsare damaged. The building may not be safe for continued occupancy until repairs are done. Repairof the structure is feasible but it may not be economically attractive to do so. This performance levelis generally the basis for the intent of code compliance.

Collapse Prevention Level or Near Collapse Level: The structure sustains severe damage. Thelateral-force resisting system loses most of its pre-earthquake strength and stiffness. Load-bearing

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columns and walls function, but the building is near collapse. Substantial degradation of structuralelements occurs, including extensive cracking and spalling of masonry and concrete elements, andbuckling and fracture of steel elements. Infills and unbraced parapets may fail and exits may be

blocked. The building has large permanent drifts.

Non-structural components experience substantial damage and may be falling hazards. The buildingis unsafe for occupancy. Repair and restoration is probably not practically achievable. This buildingperformance level has been selected as the basis for mandatory seismic rehabilitation ordinancesenacted by some municipalities, as it results in mitigation of the most severe life-safety hazards atrelatively low cost.

(Sandeep Donald Shah is a M.Sc. in Earthquake and Civil Engineering Dynamics from theUniversity of Sheffield, UK.)

Sandeep Donald Shah(Staff Writer, IANS)

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16 india should take seismic protection more seriously

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