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The meaning, science and cost of retrofitting

Mayura Janwalka explains what it takes to retrofit a building — make it resistant to tremors.

Written by MAYURA JANWALKAR | Published: May 4, 2015 12:17 am
nepal earthquake, retrofitting, retrofit building, building retrofit, earthquake resistant building, earthquake proof building, earthquake prone buildings, earthquake safe buildings, indian express explained, explained, indian express Leaning buildings in Kathmandu last week. Base isolation, or strengthening a building’s base in such a way that it takes the bulk of its load, is a retrofitting technique that makes structures more resistant to tremors. (Source: AP photo)

It’s a word heard often in times of earthquakes. The Indian Express explains what it takes to retrofit a building — make it resistant to tremors

What does retrofitting of buildings mean?
In general, to retrofit is to add a component (to any piece of machinery or a existing structure) which wasn’t there originally, in order to rectify a deficiency. Earthquake engineers explain that the word, used in the context of making buildings earthquake-resistant, means strengthening of buildings already constructed. Old buildings may not have been built keeping earthquake resistance parameters in mind, even though that may not necessarily make them unsafe. Parameters for earthquake-resistant construction are laid down in the Indian Standards Code of 2002. The code has been periodically updated; the last revision came in 2009, experts say.

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Who can do the work of retrofitting of buildings?
The job entails studying a building’s design and assessing its construction material by conducting non-destructive or radiological tests, for which structural engineers with knowledge of earthquake engineering are ideal. The Delhi government will soon publish a list of 200 structural engineers registered with various civic agencies. Delhi lies in seismic zone 4, and is at risk of an earthquake of severe intensity.

Does retrofitting require a building to be evacuated?
That depends on the extent of the work required in a building. If the building is up to four storeys high, and the work is done in phases, evacuation may not be necessary. It would be like shutting down a room in a flat while it is being painted or renovated. However, evacuation would be necessary in precarious buildings. And if the building is too dangerous, the answer sometimes might be demolition, not retrofitting, say engineers.

What is the ‘base isolation system’ in retrofitting?
To make a building earthquake-resistant, its base is strengthened in such a way that during an earthquake, the building’s load is borne by the base alone, and the upper storeys do not experience much quaking. The part of the base that is above the ground is cut and rested on bearings, exactly like how a jack is used to lift a car to change a wheel. The bearings are a combination of roller bearings and elastomer bearings — which, to extend the analogy of the car, act like shock absorbers. Just like one may not feel bumps on the road in an expensive car with effective shock absorbers, similarly, higher floors of a building retrofitted by base isolation may not feel any shaking in the event of an earthquake.

How long does it take to retrofit a building?
The time required to retrofit a building would depend on the material used to construct the building. Engineers say that symmetrical structures in the shape of a square, circle or rectangle are less vulnerable during an earthquake, and are easier to retrofit. Buildings erected on stilts are prone to collapsing, and hence retrofitting them would involve laying sheer walls or steel bars to support the structure. Some experts say that the time required for retrofitting can be roughly calculated on the basis of the number of rooms in the structure. It should ideally not take more than two days per room.

How much does it cost to retrofit?
The cost of a building under construction increases by about 10 per cent roughly to make it earthquake resistant, say engineers. However, retrofitting an existing structure may cost roughly 15-20 per cent of the total cost of the structure.

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  1. Manish Garg
    May 3, 2016 at 2:44 pm
    base isolation system similiar to putting shock absorber, base of building absorbs tremors
    1. Bhavadasan Veemboor Kadalayil
      May 4, 2015 at 9:20 am
      QUOTE: “means strengthening of buildings already constructed.” UNQUOTE: A building already constructed cannot be strengthened. QUOTE: “and the upper storeys do not experience much quaking.” UNQUOTE: When the foundation shakes either in vertical or horizontal direction, the upper story also shakes. While designing, depending on the Zone, intensity of EQ a horizontal load is applied on superstructure in addition to wind load. QUOTE: “The part of the base that is above the ground is cut and rested on bearings.” UNQUOTE: I have heard and designed bridges and Marine structures resting on roller bearing and neoprene bering. Never heard about bearing for buildings. The failure of structure may be due to failure of superstructure or foundation. 01) Superstructure Failure: Failure of column or beam. Normally columns are designed to axial load only (Short/long) and not designed subject to axial load bending. Making such design, the cost will be prohibitive. 02) Foundation Failure: Foundation failure is least when the strata is rocky. In sandy soil due to liquefaction of sand the failure will be sudden. In clayey soil failure could be due to unequal settlement. Deep foundation (pile) if designed for axial load and bending can withstand. (prohibitive cost)
      1. R
        Raman Dogra
        May 12, 2015 at 7:47 am
        Base Isolation is one of the effective technology to make a building earthquake resistant. At least important buildings like Hospitals Communication Control rooms etc can be base isolated so that they works when they most needed after a disaster. My company Dynamic Isolation System is active in India and working on few projects
        1. N
          May 5, 2015 at 5:29 am
          Pl wake up Bhavadasan. Base isolation is a old hat. Every structural engineer worth his salt should be knowing that. Normally Chief Engineers are good at procedures, modalities and adjustments. They may not know much of Engineering! You seem to be one such.
          1. Y
            May 4, 2015 at 9:40 am
            It should have been "supporting" not "strengthening", I guess.
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