From: "Drew A. Norman, SE" <DNorman(--nospam--at)dnormanse.com>
Date: Wed, 18 Apr 2001 09:46:48 -0700
While we don't directly control elongation, we do worry about overstrength
(which typically translates into reduced elongation in the test specimen)
and require minimum ductility by calling for tensile strength at least 125%
of yield. Here are City of Los Angeles special requirements as they
translate into general notes my office uses on structural design drawings
for all projects in areas of seismic risk:
2. ALL REINFORCING STEEL SHALL MEET THE FOLLOWING SPECIAL DUCTILITY
a. ACTUAL TENSILE YIELD STRENGTH SHALL BE NO MORE THAN THIRTY PERCENT
(30%) GREATER THAN SPECIFIED.
b. ACTUAL ULTIMATE TENSILE STRENGTH SHALL BE NO LESS THAN ONE HUNDRED AND
TWENTY-FIVE PERCENT (125%) OF ACTUAL TENSILE YIELD STRENGTH.
STEEL CERTIFIED AS ASTM A706 PER UBC STANDARD 26-4 MAY BE ASSUMED TO COMPLY
WITH THESE REQUIREMENTS. OTHER GRADES AND TYPES OF STEEL SHALL BE DELIVERED
TO THE SITE WITH EITHER MILL CERTIFICATION OR REPORTS OF INDEPENDENT
LABORATORY TESTS VERIFYING COMPLIANCE. SUCH CERTIFICATION OR TESTING SHALL
BE AT THE CONTRACTOR'S EXPENSE.
3. REINFORCEMENT DELIVERED TO THE SITE SHALL BE ACCOMPANIED BY APPROPRIATE
TESTING REPORTS AND CERTIFICATION, INCLUDING EVIDENCE OF CONFORMANCE WITH
SPECIAL DUCTILITY REQUIREMENTS SPECIFIED ABOVE.
4. LACK OF CERTIFICATION OR INADEQUATE CERTIFICATION SHALL BE SUFFICIENT
CAUSE FOR REJECTION OF MATERIAL. UNCERTIFIED OR INADEQUATELY CERTIFIED
MATERIAL SHALL NOT BE STORED AT THE SITE OR USED IN THE WORK AND IF
DELIVERED TO THE SITE SHALL BE IMMEDIATELY REMOVED.
5. SUBJECT TO <my firm's> WRITTEN APPROVAL, REINFORCEMENT NOT MEETING THE
SPECIAL DUCTILITY REQUIREMENTS SPECIFIED ABOVE (NOTE 2) MAY BE PERMITTED IN
LOCATIONS NOT SUBJECT TO YIELDING UNDER SEISMIC LOAD.
Hope that helps.
Drew A. Norman, S.E.
Drew A. Norman and Associates
----- Original Message -----
From: "Prakash C. Chowdhury" <pcchowdhury(--nospam--at)yahoo.com>
Sent: Wednesday, April 18, 2001 6:57 AM
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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