Rectangular hollow sections

Geometry and product identity

Under ANSI/AISC 360-22 §B4.2, HSS wall calculations use nominal wall for ASTM A1065/A1065M or A1085/A1085M and 0.93 × nominal for HSS to other standards approved under that specification. Keep the ordered nominal size, design basis and measured wall in separate fields. AISC design-wall rule

A rectangular hollow section (RHS) has a closed rectangular cross-section. The stock description needs outside height and width, wall thickness, corner geometry and length, together with material grade and product specification. Similar outer dimensions do not establish identical properties or an interchangeable manufacturing route.

Tata Steel's September 2020 structural-hollow-section overview distinguishes its cold-formed Hybox/Strongbox products to EN 10219 from its full-body-normalized hot-finished Celsius product to EN 10210. These are named product descriptions from that edition, not a claim that every tube with the same shape has the same treatment. Tata Steel structural hollow sections, manufacturing descriptions

Keep the physical geometry separate from steel identity, supplied condition and final application approval. RHS is not a pressure-pipe designation or a complete machine-frame specification. A finished structural assembly needs its own design, fabrication and inspection basis.

What to put on an order

A nominal wall value is not a promise of exactly uniform measured thickness. Outside dimensions also do not uniquely define an internal fit where corners, seam and dimensional tolerances matter. Obtain the actual section drawing and acceptance limits for inserts, telescoping members or closely fitted connections.

Define which side faces the applied load or a mating component. Rotating a nonsquare section exchanges its bending axes; an item description that drops orientation can remain ambiguous even when all three nominal dimensions are present.

A bounded material-property example

Tata's Celsius S355NLH Declaration of Performance, signed 24 July 2023, identifies EN 10210-1:2006 and gives thickness-dependent minimum yield strengths:

The declaration separately identifies dimensional/shape tolerances under EN 10210-2:2006 and an EN 10204 3.1 inspection document including specified full-length weld testing. These are the named product's declared provisions, not requirements proven for every RHS or for an uncertified piece of stock. Celsius S355NLH declaration, pp. 1–2

Preserve the full grade suffix and thickness basis. A grade's leading number alone is insufficient to choose a property row, and an incoming certificate does not establish the final weldment's toughness or fatigue performance.

Nominal wall and design wall are different fields

ANSI/AISC 360-22 §B4.2 requires a design wall thickness in calculations involving HSS walls. It uses nominal thickness for HSS produced to ASTM A1065/A1065M or A1085/A1085M, and 0.93 times nominal wall for HSS to other standards approved under that specification. The rule is part of that design framework; it is not a universal replacement for an actual thickness measurement or a European product tolerance. AISC 360-22, §B4.2

Steel Tube Institute's December 2022 presentation also cautions that the relevant AISC section-property tables already incorporate the reduction for A500. Check the table's material and wall basis before applying another reduction. STI, Unique Considerations, slide 16

Original geometry check

Assume an ideal sharp-cornered, uniformly thick section with height 100 mm, width 50 mm and wall 5 mm. Its rectangular inner envelope is 90 × 40 mm, giving metal area

A = 100 × 50 − 90 × 40 = 1400 mm².

The ideal second moments about centroidal axes are:

• Bending with 100 mm section depth: (50 × 100³ − 40 × 90³) / 12 = 1,736,667 mm⁴.
• Bending with 50 mm section depth: (100 × 50³ − 90 × 40³) / 12 = 561,667 mm⁴.

The ratio is approximately 3.09. This illustrates orientation sensitivity; it is not a catalogue section-property row. Real rounded corners, wall tolerances and the governing design-wall convention change the calculation. Use the producer's applicable geometry and properties for an actual section rather than assigning this ideal result to a nominal 100×50×5 product.

Connections and finished assembly

A closed section's gross properties do not establish connection resistance. Define how forces enter the walls through plates, bolts, welds or internal reinforcement. Assess local wall behavior, holes/slots, eccentricity, member stability and the actual support/restraint conditions under the adopted design rules. Two members sharing a nominal outside dimension may still require different connection details.

Plan cutting, welding and finishing as a sequence. Establish where straightness, twist, seam condition and finished dimensions are accepted after operations that can change them. Specify corrosion protection and internal-access requirements for the actual assembly, including the approved processing instructions where cavities are involved. The stock-form label supplies no universal welding procedure, span, load or service-life rating.

Source editions and release record

The Tata overview prints English Language 09/20 and copyright 2020; the cited Celsius declaration is dated July 2023. Their historical references are retained as written and do not establish current availability or a later standard edition. AISC's cited specification is dated August 1, 2022; STI's presentation is explicitly December 2022. Confirm contractual editions and product acceptance when ordering.

Retain producer, heat/lot, grade and product specification/edition, route/condition, complete geometry, certificate and fabrication/inspection record. See Stock forms and dimensions.