Analysis of international standards on concrete reinforcing steel bar Jorge Madias (1), Michael Wright (2), Gustavo Behr (3), Vanessa Valladares (3) (2) Modern Metal Consulting, Singapore (1) metallon, San Nicolas, Argentina (3) ADELCA, Aloag, Ecuador
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Analysis of international standards on concrete reinforcing steel bar
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Consulting & training company based in San Nicolas, Argentina
Modern Metal Consulting
Consulting & training company based in Singapore
ADELCA
Steel company with two plants in Ecuador
Aloag: EAF, LF, Billet caster, Rebar rolling mills
Milagro: New rebar & wire rod rolling mill recently started-up
Introduction
Standards usually reflect with a certain delay the advances of technology in product manufacturing and the growing requisites of the users
National, regional and international standards on steel reinforcing bar are analyzed
Rebar standards: low degree of globalization
Aim of the study 1) Verify trends in the quality constraints that may affect
the commercialization and application of rebar
2) Specifically, requisites related with seismic behavior and the influence of manufacturing processes (natural hardness, on-line quenching and tempering, micro-alloying)
Selected standards
Reasons for country / region selection Rebar exporting potential
High seismicity
High rebar production
Special features of the standard
In some countries, a single standard cover not only rebar but other long products for civil construction (generally round bars, but in some cases welded mesh, pre-stress concrete, etc.)
ASTM standards and their followers have usually two standards: one for reinforcing bar in general, and other for weldable rebar
Still there are in some countries standards for rebar produced by rolling rail or strip scrap (not taken into account in this study)
Selected standards
Country Standard Character Argentina IRAM-IAS U500-207 2004 Weldable
IRAM-IAS U500-528 2004 General Australia/N. Zealand AS/NZS 4671:11 General Brazil ABNT NBR7480 General Canada G30.18-09EN reaffirmed 2014 General Chile NCh 204 General China GB 1499.2 2007 General Colombia NTC 2289 2007 General Ecuador NTE INEN 102:2015 General
NTE INEN 2167:2017 Weldable Europe prEN 10080 2005 General Germany DIN 488.1 2009 Grades, properties, marking
DIN 488.2 2009 General DIN 488.6 2010 Conformity assessment
International ISO 6935-2 2015 Part 2 General Japan JIS G3112 2010 General Mexico NMX-C-407-ONNCCE-2001 General
NMX-B-457-Canacero-2013 Weldable Peru PNTP 341 031 2015 General
PNTP 339 186 2015 Weldable Spain UNE 36065 2011 High ductility UNE 36068 2011 Weldable Taiwan CNS 560 2005 General Turkey TS 708 2010 General United Kingdom BS 4429 2005 General USA ASTM A 615-14 General
ASTM A 706-14 Weldable Vietnam TCVN 1651-2 2008 General
Mechanical properties
Compared properties
Tensile and yield strength
Stress ageing ratio
Uniform elongation
Elongation to rupture
Yield strength
Present in all standards
Some standards define a minimal value, others both minimum and maximum
Lowest value 220 Mpa
Turkey, one grade
Maximum value 600 Mpa
ISO, one grade
Mechanical properties
Yield strength
Higher strength grades
0
100
200
300
400
500
600
700
Yie
ld s
tren
ggth
(M
Pa)
Mechanical properties
Yield strength Some Asian countries are
considering the introduction of 600 MPa minimum grade, as in ISO standard
Arguments favoring high strength rebar from the point of view of constructors Reducing rebar
congestion in anti seismic design, particularly in column-beam crossings
Reducing total steel mass needed for the overall construction.
Mechanical properties
Elongation Elongation to rupture is
preferred
But uniform elongation starts to make inroads Elongation measured for
the maximum load, more complex to measure (extensometer is required)
German standard changed to uniform elongation in 2009
China, Spain, Vietnam and some grades of the Turkish standard define minimum uniform elongations
Mechanical properties
Elongation
Elongation to rupture vs. yield strength
Mechanical properties
Elongation Uniform elongation
Australia / New Zealand standard: three ductility degrees low (an L is added to the bar
designation);
normal (an N is added to the bar designation)
high or seismic (an E is added to the bar designation).
Type E corresponds to 2 levels of minimum yield strength (300 and 500 MPa)
Very high uniform elongation is requested (15 and 10% respectively)
Tensile strength / yield strength ratio of at list 1.15
Important for New Zealand only
Mechanical properties
The question is “why is 5% elongation to rupture considered acceptable in higher yield strength rebar?” Experience suggests that the minimum acceptable elongation to
rupture (%) in rebar is dictated by what can reasonably be achieved in a high yield strength steel made with simple C-Mn metallurgy
But at what elongation to rupture would a metal be seen to be classed as “brittle”?
The reason for this question is that in a concrete-steel composite material, the concrete is a brittle material – if the steel is also brittle, then the entire structure can be classed as brittle. The ductile properties can only originate in the steel, so this property must be protected by Standards.
Mechanical properties
Tensile strength / yield strength ratio (strain hardening ratio)
High value for some grades and low value (or no value) for others
ISO, Australia/New Zealand, Brazil, USA, UK, Mexico, China, Turkey
Only high values
Argentina, Canada, Chile, Colombia, Ecuador, Peru, Spain, Japan
Highest ratio (>1.25)
ASTM A706, Argentina, Mexico NMX-B-457, Chile, Colombia, Ecuador, Peru (Taiwan, China just for some grades)
Bending and rebending Most standards: bending to 180º
Mandrel diameter function of bar diameter
Exception: Chile (90º bending)
Some standards prefer 90º bending only for the large diameter bars and/or the very high strength grades
Bending and rebending (with intermediate ageing) Spain, UK
Germany (for bars <40 mm)
Magnetized particles testing to assess if cracks are present after bending, common for other steel products, still not considered by rebar standards
Chemical analysis
Generally, just maximum content for some elements
Heat analysis and product analysis (usually 10% higher)
Brazil, Chile: no spec required
ASTM A615 and followers: only maximum P content
ASTM A 706 (weldable rebar) and followers: maximum values for C, Mn, P, S, Si and Ceq Same for high ductility / weldable rebar in other standards
ISO, European countries, China, Argentina: N2<0.012%, for some grades
European standard: Cu<0.80 %; Germany <0.60%
Canada: Mn, Si more restricted than usual for galvanized rebar
Internal specifications of steel plants are always more restrictive than those in the standards To make sure they obtain the required mechanical properties at
lower cost
To minimize surface and internal quality problems, as those related with high sulphur or high copper
Chemical analysis
Lowest P 0.035 ASTM (weldable rebar), Mexico, Colombia, Ecuador,
Peru
Lowest S 0,040% ISO (weldable grades), one of the Ecuador standards,
four Japanese grades, two weldable grades in Taiwan and Vietnam
Lowest C 0.22% Europe, Spain, Germany
Turkey, Argentina just for weldable rebar
Mn: <1.50 to <1.80, just some standards
Standards reflect with a long delay the advancement of steelmaking technology
Specs are relaxed; rejection is fairly uncommon
Exception: weldable / high ductility rebar C, Mn, residuals are to a certain extent under control
Trend to establish weldability / high ductility requirements
Special tests
Fatigue Not mentioned in ASTM standards and followers, and Chile, Taiwan, Turkey,
Vietnam
Required by Germany, UK. Spain for high ductility rebar
European standard: an option, but its application is very thoroughly detailed
Argentina, China, Australia / New Zealand: may be agreed between purchaser and manufacturer
Adherence Not mentioned in most standards
European standard Adherence given by the geometry of ribs, but that it can be verified by beam test or
pull test
UK: same, but beam test as the alternative testing tool
Australia / New Zealand Calculus for estimation of adherence in function of the surface of ribs
Pull test as an alternative
Fatigue Beam test Pull test
Non-standard regulations
Some governmental measures go beyond the standards regarding rebar specifications
Argentina, Ecuador: certification system for civil construction steel product In Europe this is included in the standards
Influence of the mechanism utilized by the manufacturer to achieve the required mechanical properties tends to be taken into account, as it influences behavior in use (corrosion, fire strength, seismic behavior) Department of Building and Housing of New Zealand issues Practice Advisory that
establish how to use the anti seismic grade rebar, taking into account if it was produced using microalloying or on-line quenching and tempering [36]. For example (MA means microalloyed and QT means on-line quenched and tempered) Cold re-bending/straightening Grade 500E MA and QT not permitted by NZS 3109.
Welding of Grade 500E QT is not permitted by NZS 3109.
Site welding of Grade 500E MA should be avoided.
Shop welding (but not tack welding) of Grade 500E MA is considered acceptable provided that evidence is presented that the procedures used do not affect compliance of the reinforcement with AS/NZS 4671
In certain countries, not only the producer name or logo must be rolled in the bar, but the name of the importing company, is such is the case Foreign manufacturers introducing rebar in Germany must roll in the rebar a
specific mark given by a local association
Conclusions
Trends Mechanical properties
Introduction of higher high yield grades, over 500 MPa, aiming to decrease bar congestion, particularly in column / beam crossings in high-rise buildings for seismic zones
Introduction of uniform elongation
Higher minimum elongation is high seismicity countries
Strain ageing ratio Consensus, for high seismicity countries, in >1.15 or higher
Bending European-influenced standards prefer bending and rebending.
Chemical analysis Low C and low Ceq for weldable / high ductilty grades
In some countries, particularly in Europe, only weldable / high ductility grades exist
Most critical chemistry requirements are low C (<0.22-<0.25%), and N2<120 ppm
Others Fatigue and adherence testing start to occur as a requisite in some European
standards
Grain size mentioned in the Chinese standard
Traceability more relevant, taking into account intervention of several manufacturers of different countries for a given product
Conclusions
Updating rebar standards Introduction of minimum uniform elongation, rather than elongation
to rupture, as a more fundamental requisite for seismic / high ductility purposes.
Introduction of magnetized particles testing to assess if cracks are present after bending
Maximum grain size should be considered for seismic / high ductility purposes
Lower phosphorus and sulphur contents.
As international trade of billets intended for rebar rolling becomes more important, traceability should be emphasized.
Request of conformity assessment by third parties
Hardening mechanism utilized by the manufacturer to obtain the properties becomes more important, as it influences performance (loss of properties, corrosion, seismic behavior, strength after fire)