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Comments On Proposed Draft for ESR

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INDIAN ASSOCIATION OF STRUCTURAL ENGINEERS
( Gujarat State Centre )
CENTER  FOR ENVIRONMENTAL PLANNING AND TECHNOLOGY
UNIVERSITY ROAD,  NAVARANGPURA,  AHMEDABAD - 380 009.
 Web :  www.iaseguj.org ,  e-mail: secy(--nospam--at)iaseguj.org
_______________________________________________________________

Date : 2nd March, 2005


Dear Sir,


Sub : Comments On Proposed Draft Provisions For Seismic Design Of Elevated
Tanks supported on R.C. shafts

This has reference to the proposed draft code for seismic analysis & design
of E.S.R.. The same may be downloaded by going to : www.nicee.org. It has
been observed that response reduction factor for tank supported on the shaft
is reduced to 1.5. This leads to increase in earthquake force in the water
tanks by almost 3 times than as calculated by IS:1893-1984. This is the
opinion of the authors of the code that water tanks supported on the shaft
do not perform well during earthquake as compared to that supported on
beam - column staging.

The meeting was organised by Indian Association of Structural Engineers
(Gujarat State Centre) for discussions on the above mentioned subject on
25-09-04. Based on the meeting, a report was prepared and the same was
submitted to concerned authorities.

The report may be downloaded by going to :
http://www.iaseguj.org/forum/Files/viewthread.php?tid=109&page=1#pid160

____________________________________________________________________________


Concerned Authorities have raised following queries :

a) The number of failures of Shaft supported tanks over the years even in
non-seismic conditions appears to be a point of concern for many. As per
information received from Water Tank expert Mr. L K Jain of Nagpur,
Maharashtra PWD discourages/disallows construction of new Shaft supported
tanks.

b) The collapse of a new shaft supported water tank last year at Bhuj
compounds our concerns regarding such tanks. We seek your opinion with facts
and figures, if any such study has been done on the apparently large rate of

fialures of Shaft supported Tanks.

c) The report of Dr Durgesh Rai in the "Earthquake Spectra" volume for Bhuj
Earthquake (Suppl A to Vol 18 -Chapter 15) gives very alarming facts and
figures about the behaviour of elevated shaft supported tanks in Bhuj
earthquake. Kindly opine on the report.

d) We draw your attention to the paper "Review of Code Provisions on Design
Seismic Forces for Liquid Storage Tanks" by Dr O R Jaiswal and others in the
IITK-GSDMA codes project which is available on www.nicee.org  website. As
per the study while Indian  Building response reduction factors as per IS
1893-2002 (and subsequently design forces) are comparable to Int'l codes,
our Tank design forces are far lower than those of all International codes
including the IBC, NZSEE, FEMA, Eurocode etc. We need to address this
inequality.

e) It is not very clear what would be the increase in cost for increase of
seismic forces. Is it possible for IASE Guj to take this up as an exercise
and send us these figures for our review? It would help the stakeholders to
determine the cost-benefit ratio in building safer tanks.

____________________________________________________________________________


 If you have any suggestions / contribution to make, kindly send us the same
as early as possible at : Iaseforum(--nospam--at)iaseguj.org


Regards,

Bhavin Shah
Hon. Secretary
Indian Association of Structural Engineers, Gujarat State Centre


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