Deciphering ASTM Standards for Structural Steel W-Shapes

[View within mini-mill melt shop where recycled steel is prepared for processing into new steel]

A recent article on this site, Structural Steel Materials Standards, described recommended ASTM standards for specifying various structural steel shapes and components. For those not regularly involved in the reading and writing of specifications, deciphering the meaning and significance of ASTM standards can be a challenge. As a way of introduction, the following provides some explanation regarding ASTM standards commonly applied to structural W-shapes.

Material Properties
One of the important functions of specifying steel standards is to define the material properties of the steel used on a project. The following table summarizes some commonly used designations for structural steel and several properties of the steel specified. As can be seen from the table, by specifying an ASTM designation (and in some cases also a Grade), minimum structural properties of the steel are established:

ASTM Designation	Minimum Yield Stress (ksi)	Minimum Tensile Stress (ksi)
A36	36	58-80
A572 Grade 50	50	65
A572 Grade 60	60	75
A572 Grade 65	65	80
A992	50-65	65

Other materials properties not shown in the above table may also influence the choice of steel type. For example, even though A992 steel and A572 Grade 50 steel appear comparable in the chart above, the relatively newer A992 designation is preferred for other aspects of its material definition.

Method of Manufacture and Cost
Differences in ASTM structural steel standards also reflect changes in steel manufacturing processes. For many decades, structural steel was manufactured mostly from raw materials and was formulated to meet the requirements of ASTM A36. Higher-strength steel was only specified where the need for its superior structural properties justified the significant additional cost associated with such material.

Today, most structural steel is manufactured in so-called mini-mills. By relying on scrap steel as the primary raw ingredient for manufacturing new steel, these newer mills are able to produce higher strength alloys such as ASTM A572 or A992 at lower cost than traditionally manufactured A36 steel. Consequently high-strength steel is now routinely specified for structural W-shapes.

How Are Standards Created and Enforced?
ASTM standards are developed through a consensus process involving industry stakeholders such as producers, consumers, users, government bodies, and researchers. ASTM itself is a not-for-profit organization. It has no enforcement mandate, and the standards it publishes are strictly voluntary.

ASTM standards may become defacto standards when they are adopted by the trade association that represents a particular industry. For example, in the case of the structural steel standards dicussed in this article, definitive recommendations for their use are found in the American Institute of Steel Construction's (AISC) LRFD Manual of Steel Construction (3rd Edition).

ASTM standards may change from voluntary to required when they are adopted by reference in building codes or other regulations. For example, the 2003 International Building Code makes AISC's design standards mandatory in paragraph 2205.1 General, which reads in part:

The design, fabrication and erection of structural steel for buildings and structures shall be in accordance with either the AISC-LRFD, AISC 335, or AISC-HSS...

In this way, ASTM standards that are part of the referenced AISC standards become mandated through the building code. (In other cases, the building code may directly reference ASTM standards themselves, rather than indirectly referencing them through other publications as in this example.)