8/12/2019 000 the Single Factor That Will Contribute Thousands of Deaths in a Quake

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The Single Factor that will contribute Thousands of Deaths in the event of a Quake

By

Sandeep Donald Shah

Last two years has seen an increased number of conferences and workshops on

earthquake risk mitigation and this has resulted in valued interaction amongst members of

the scientific/engineering community specializing in earthquake related issues. Most of

these formal gatherings have aimed at better understanding of earthquake effects on the

 built environment and the mitigation techniques that need to be adopted.

The engineering fraternity has been unanimous in identifying the building category which

is considered the most vulnerable amongst all of the engineered buildings in our country

today - !uildings on "tilts#. $ simpler e%planation would be buildings that have an open

ground floor area and which on most occasions are used as car park.

&onstructing multi storey buildings with open ground floor is a common practice in all

cities as the ground floor car park area is not counted in the building '$(/'") by the

municipality while sanctioning the plans.

)f not all ma*ority of the buildings on stilts will collapse in the event of a ma*or quake

whether it is zone +, or . To make matters worse all of these buildings are multi storey

and hence the casualty rate would be much higher when compared to a low rise building.

The fatal casualties due to collapse of this single building type would be in thousands.

hat happened to buildings in $hmedabad when an earthquake struck !hu* is a live

testimony.

0ne may ask is the 1overnment aware of this grave problem and if so what#s it doing

about it2 3owever the answer is not as simple as even though the 1overnment is fully

conversant with the problem the 'rankenstein has become so large that most feel it is an

issue easier brushed under the carpet rather than have to deal with it.

The irony of the matter is that even though we are not ready to deal with this issue which

has the potential of becoming a nightmare *ust yet, with each passing day it keeps getting

 bigger as more of the similar unsafe building stock is getting added to our cities.

The problem isn#t insurmountable if one has the resolve and approaches it in a systematicand time bound manner. To start with the 1overnment will have to generate awareness

amongst the masses through print and electronic media that all buildings on stilts be

 prima-fascia considered unsafe until a safety certificate is issued by a structural

consultant. )n most )ndian cities multistory buildings are constructed and continue to be

constructed on 4 to 56 inch thick columns which are highly inadequate even by 7one +

standards. These buildings will come crashing down in the event of a ma*or quake.

The 1overnment should then ensure that the owners/occupants are guided to having a

structural audit done for their building so as to positively identify those at risk that will

need structural retrofit to upgrade. )ndia has many thousands of structural engineers who

can help in this gigantic task8 a public-private partnership model may also prove to be

highly successful with tiny cells of individual consultants working on single building.

8/12/2019 000 the Single Factor That Will Contribute Thousands of Deaths in a Quake

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The guidelines for creating the computer model of the building will need attention and

guidance for e%ample using cracked section properties i.e. reducing the moment of inertia

of structural sections by half, limiting the inter-story drifts to 69 of the story height forLife "afety# protection and limiting the inter-storey drifts in the stilt floor to a value

much less than 69, using appropriate spectrum/ spectrum compatible time-histories etc.

'undamentally a structural engineer would face two issues, first to ensure that the

 building structure behaves as a moment frame during seismic loading, if not than retrofit

to provide ductility and introduce new structural members to complete the load paths

would have to be undertaken. The second issue which is slightly more comple% is that of

modulating the structural response so that the building can withstand a ma*or earthquake

without collapse. 'or this the engineers modulates and optimizes the three fundamental

 properties that govern the structural response i.e. mass, stiffness and damping.

Most buildings in our cities and especially the one#s on stilts are stiffness deficient.

Lateral stiffness which is required to resists the earthquake forces is contributed by

columns and shear walls. )ncase a building is found to be stiffness deficient this can be

easily compensated by going in for concrete *acketing/ additional columns/shear walls.

&are has to be taken that *acketing is done all the way down to the foundation. Though a

minimum stiffness criterion is to be met, care must be taken not to make the building over

stiff as then it will attract higher earthquake forces which may prove detrimental and can

even be the cause of building failure.

1reat care has to be taken even when deciding on the shear walls, a few (&& walls will

definitely be beneficial in controlling deflections however having e%cess of them will prove detrimental as not only will shear walls attract higher earthquake forces, each of

them will also contribute towards building eccentricity which enhances the torsional

 building response, resulting in increased inter-story drifts and hence the enhanced

structural damage. This enhanced damage can also lead to building collapse.

!ased on the computer analysis the engineer can recommend a retrofit methodology

which can then be handed over to the owners of the building for implementation. 0nce

this process is completed the responsibility of making the building safe should rest with

the owners. $s an incentive the 1overnment can evaluate the possibility of ta% incentives

on the amount spent on retrofit.

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