ASTM A709 and AASHTO M270 Steels for Bridge Construction

The AASHTO Subcommittee on Bridges and Structures has adopted AASHTO M270-- Structural Steel for Bridges--as the preferred specification designation for bridge steels. AASHTO M270 is a direct adaptation of the ASTM A709 Specification. Bridge steel specifications and grade designations are shown in Table 10.2A of the AASHTO Standard Specification for Highway Bridges. AASHTO M270 (ASTM A709) now covers, in one document, all of the AASHTO prequalified bridge steels along with unique AASHTO requirements not contained in the previously used AASHTO or ASTM material specifications. For example, this specification includes easy-to-use tables containing AASHTO toughness requirements (Charpy V-Notch testing) for both fracture critical and non-fracture critical material.

The change to AASHTO M270 (ASTM A709) from previously used material specifications (e.g., AASHTO M183 or ASTM A36, etc.) was meant to simplify the ordering of steel for bridges. It also provides an efficient method of revising material specifications by consolidating bridge steels in one document instead of multiple documents. In addition, the previously used specifications did not include Charpy V-Notch toughness requirements for fracture critical members.

While the change to AASHTO M270 (ASTM A709) will simplify the specification of structural steel for bridges, some confusion always results during the learning period. This is apparent from the number of inquiries we have received regarding the use and specific requirements of AASHTO M270 or ASTM A709 steels.

History:
ASTM A709 was initially published in 1974; AASHTO M270 was first published in 1977 (Interim Specification-Materials). Since AASHTO prepares material specifications and revisions based on published ASTM specifications, there is always a delay pending the AASHTO approval.

The initial versions of these specifications could not be used by themselves without reference to other specifications such as AASHTO M183 (ASTM A36). AASHTO M223 (ASTM A572), etc. because complete chemical composition and mechanical property tables were not included. This situation existed until the mid-1980�s when ASTM A709 (and later AASHTO M270) were revised to stand alone with complete requirement tables--it was at this time that AASHTO Subcommittee on Bridges and Structures approved AASHTO M270 (ASTM A709) to be used in the Standard Specification for Highway Bridges. The previously used equivalent specifications are clearly shown as footnotes to Table 10.2A.

AASHTO M270 and ASTM A709 Grades and Equivalents:
A listing of the grades covered by the specifications along with their previous equivalents are shown in Table A.

AASHTO M270	Equiv. AASHTO Grade	ASTM A709 Grade	Equiv. ASTM Grade	Min Yield	Min. T.S.	Availability
AASHTO M270	Equiv. AASHTO Grade	ASTM A709 Grade	Equiv. ASTM Grade	Min Yield	Min. T.S.	Plates	Shapes
36	M183	36	A36	36	58	to 4" Incl.	All Groups
50	M223	50	A572	50	65	to 4" Incl	All Groups
50W	M222	50W	A588	50	70	to 4" Incl	All Groups
70W	M313	70W	A852	70	90	to 4" Incl	Not Appl.
100	M244	100	A514	100	110	to 2 1/2" Incl	Not Appl
				90	100	OV 2 1/2 to 4" incl.	Not Appl
100W	M244	100W	A514	100	110	to 2 1/2" Incl	Not Appl
				90	100	OV 2 1/2 to 4" incl	Not Appl

Chemistry Requirements:
AASHTO M270 and ASTM A709 now also specify the chemistry requirements for these grades.

Toughness Requirements for Bridges:
As previously indicated, AASHTO M270 and ASTM A709 contain easy-to-use tables listing Charpy V-Notch toughness requirements for both Fracture Critical and Non-Fracture Critical steel members. Standard AASHTO requirements are shown for all grades and all zones (1, 2 and 3).

Coding Procedure:
In addition to the desired ASTM A709 or AASHTO M270 grade, there are three suffix codes that enable the material requirements to be fully defined at the time of ordering.

Following the desired grade, the first suffix code is used to define the Atmospheric Corrosion Resistance requirements. No suffix code provides a level of atmospheric corrosion resistance typical of carbon steel without copper. If a weathering type steel is required for Grades 50, 70 or 100, the use of the suffix code "W" provides a level of atmospheric corrosion resistance approximately two times that of carbon steel with copper.

The next set of two suffix codes is for specifying Charpy V-Notch testing requirements. A "T" indicates a Non-Fracture Critical material, whereas an "F" indicates a Fracture Critical material. The "T" or "F" should then be followed by the appropriate AASHTO temperature zone, i.e. (1, 2 or 3). The Charpy V-Notch testing requirements are optional for A709 but mandatory for M270.

Grade

Atmospheric
Corrosion
Resistance

Charpy V-Notch
Testing Requirements

XXXX

Includes minimum yield point, except for Grade 100 or 100W over 2 1/2" to 4"

W if Weathering Steel; disregard if non-Weathering Steel

T or F

T= Non-Fracture Critical

F=Fracture Critical

1,2 or 3

AASHTO Temperature Zones

1 = 0�F and Above
2 = -1� F to -30�F
3 = -31�F to -60� F

Examples:
Conventional Designation	A709 or (M270) Designation
A588 or M222-Fracture Critical for Zone2	A709 Grade 50WF2 or (M270 Grade 50WF2)
A572 or M223-Non-Fracture Critical for Zone1	A709 Grade 50T1 or (M270 Grade 50T1)
A36 or M183-Non-Fracture Critical for Zone3	A709 Grade 36T3 or (M270 Grade 36T3)

Of course, the toughness requirements (foot-pounds, test temperature and testing frequency) can always be shown in detail if desired. However, it is always necessary to specify applicable toughness requirements or indicate that no toughness testing is required to avoid delays in the ordering and fabrication of steel for a bridge project.