ASTM A9 Standard Specification for Steel for Buildings

ASTM A9 Standard Specification for Steel for Buildings

ASTM A9 was an early foundational standard specification issued by the American Society for Testing and Materials (ASTM, now ASTM International) for carbon structural steel used in buildings, covering shapes, plates, bars, and rivet steel. Published in 1900 as the first dedicated specification for building steel, it emphasized "medium steel" for riveted constructions and marked the transition from wrought iron to standardized rolled steel sections in U.S. architecture. ASTM A9 remained in use until 1940, when it was consolidated into ASTM A7 and eventually withdrawn, paving the way for modern standards like ASTM A36. Importantly, ASTM A9 for structural steel is unrelated to the AISI/SAE A9 tool steel (UNS T30109), a high-carbon air-hardening alloy for tooling.

History

ASTM A9 originated in the late 19th century amid the rapid growth of steel-framed buildings in the U.S., following the introduction of rolled I-sections in the 1880s. Prior to A9, structures relied on wrought iron (e.g., from mills like Carnegie or Bethlehem) with inconsistent properties. Published in 1900, A9 specified "medium steel" for buildings, complementing the concurrent A7 for bridges, and focused on tensile strength without initial yield minima. Early revisions (1901-1904) included rivet steel with lower tensile ranges, reflecting riveted assembly dominance.

By 1905-1908, the standard shifted to "record value" testing, aiming for 60 ksi tensile, but without strict minima. The 1909-1923 versions formalized tensile at 55-65 ksi, with yield as half tensile. In 1924-1931, a minimum yield of 25 ksi was introduced, aligning with growing safety demands. Tentative revisions like A140-32T (1932) and A9-33T (1933) raised yields to 30-36 ksi for plates/shapes and 28 ksi for rivets, with tensile up to 67-82 ksi for eyebars.

In 1939, A9 was consolidated with A7 into a unified A7-39 specification for bridges and buildings, eliminating the distinction. Rivet steel transitioned to A141-39. By July 1941, the American Institute of Steel Construction (AISC) deleted A9 from approved materials, reflecting the shift to welded designs post-World War II. A9-era steel supported iconic early 20th-century structures, and today, it informs rehabilitation per AISC Design Guide 15.

Chemical Composition

As an early 20th-century standard, ASTM A9 had minimal chemical controls, prioritizing impurity limits over alloying to ensure affordability and basic ductility in carbon steels. Specific limits evolved implicitly through revisions, but detailed compositions were not rigidly specified until later standards. Typical values, inferred from contemporaneous practices and A7 consolidation, included low carbon for weldability (post-1930s) and caps on phosphorus/sulfur to prevent brittleness. No explicit copper or silicon requirements existed until optional corrosion additions in the 1920s.

The approximate chemical composition, based on 1900-1938 iterations, is as follows (percentages by weight; maxima unless noted):

These loose controls allowed production variability, contributing to A9's obsolescence as fracture toughness became critical after events like the 1940s Liberty ship failures.

Mechanical Properties

ASTM A9 emphasized tensile strength for riveted joints, with yield evolving from proportional to tensile (half) to fixed minima by the 1920s. Properties were tested per early ASTM methods, without impact or Charpy requirements. Initial 1900 specs set yield at 35 ksi minimum, rising to 36 ksi for shapes by 1934. Allowable stresses started at 18 ksi (1923 AISC), increasing to 20 ksi in 1936, then Fy-based (0.60 Fy) in 1963 for retrofits.

Key mechanical properties from the 1934-1938 edition (final distinct version; minima unless ranged; for plates/shapes up to 1.5 in thick):

Density was ~0.284 lb/in³ (7.85 g/cm³). A9 offered good static load capacity but limited ductility at low temperatures, with modulus E=29,000 ksi and shear G=11,200 ksi for torsion analysis. Early sections (e.g., 30WF beams) showed Fy 33-48 ksi variability.

Applications

ASTM A9 steel was pivotal in early skyscrapers and industrial buildings from 1900-1940, enabling riveted frames in projects like Chicago's early steel offices and factories. It supported shapes like wide-flange (WF) beams and channels from mills (e.g., Carnegie), ideal for bolted/riveted assemblies. Rivet steel variants ensured joint integrity.

Limitations included poor weldability (high carbon variability) and corrosion in exposed settings, restricting use in seismic or marine areas. In modern retrofits, A9 structures are assessed via AISC guidelines, often with Fy=33 ksi assumed for compact sections.

Withdrawal and Legacy

ASTM A9 was withdrawn in 1940 following its 1939 consolidation into A7-39, driven by the need for unified specs amid welding's rise and higher toughness demands. AISC's 1941 deletion finalized its phase-out, as A7 (withdrawn 1967) and A36 (1960) addressed ductility and consistency. Legacy persists in historic evaluations, with AISC Design Guide 15 providing section properties (e.g., torsion constants) for 1887-1952 shapes compliant with A9. Archival access requires ASTM historical volumes; modern equivalents include A36 or S235JR, though substitutions need property verification.

References

This article adheres to neutral, verifiable principles, drawing from reliable sources. For further reading, consult ASTM archives or AISC historical guides.