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RE: ductility requirements for rebars

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I can only speak for the bridges in the western US.  The rebar is ASTM A706
which has elongations of 10-14% based on bar size, and is also used because
it is more weldable than other rebar types (even though we don't let them
weld it in critical locations).  I'd say proper detailing is more important
than the rebar ductility.



-----Original Message-----
From: Prakash C. Chowdhury [mailto:pcchowdhury(--nospam--at)yahoo.com]
Sent: April 18, 2001 6:57 AM
To: seaint(--nospam--at)seaint.org
Cc: SpragueHO(--nospam--at)bv.com
Subject: ductility requirements for rebars


This query may be too basic for members but I am not a civil engineer and
am more concerned here with requirements for material specifications.

Steel rebar specs around the world specify widely varying requirements 
for rebar 'elongation %'. One reason is that the steels vary from the 
high-carbon steels in some ASTM specs to more ductile low-alloy steels.
As for service requirements, the steel may not be normally required to
sustain a strain more than the 3 to 4% that the concrete can take. But
what is the situation when designing for earthquake resistance ? Is it 
sufficient to rely on detailing for ductile design or is there a minimum
elongation % mandated for the steel rebar ?

When the CEB Model Code was being formulated in Europe in the 80's, there
was a proposal to test the steel so that it undergoes 3 strain reversals
(in the plastic region) but it may have been dropped because of the
difficulty of regular testing for such low-cycle fatigue.

I will welcome any responses off-list if they are considered of marginal
interest to list members. Thanks in advance.


=====
Prakash C.Chowdhury, B.Sc(Surrey), Ph.D.(N'cle),
Regional Resident Representative, Torsteel Research Foundation in
India,H-1A, Hauz Khas,New Delhi - 110 016, INDIA. 
E-Mail : pcchowdhury(--nospam--at)yahoo.com

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