Structural Steel – Don’t be Caught Out

We should like to bring to your attention a product known within the steel market as ‘Strongbox 235’. Strongbox is a cold formed square hollow section manufactured for the general engineering market to suit a requirement for low-grade ‘box’ use in non-structural applications. This product does not undergo the rigorous testing to ensure structural capability.

The British Standard for design of structural steelwork BS5950 does not permit the use of any structural member of steel less than grade 275. Despite looking the same as fully compliant cold-formed sections, there is a different manufacturing process and hence the only mechanical property guaranteed is its minimum yield strength.
The Steel Construction Institute Advisory Desk notes”…..it’s strongly recommended that Strongbox 235 section should not be used in structural applications; in particular where design must comply with building regulations and/or design codes”

Here at Pearson Knight we continue to deliver the highest standard of product and service by only using certified products and we are able to provide relevant documentation on every project.

We would happily discuss the findings with you, and answer any questions you may have.

SCI ADVISORY DESK

AD 271 Strongbox® 235 Hollow Sections and Structural Applications

Although the issues relating to specifying Hot Finished (BS EN 10210) and Cold Formed (BSEN 10219) structural hollow sections have been addressed in AD 259 we continue to receive questions in this area; in particular, concerning the use of Strongbox® 235 in structural applications.

Strongbox® 235 is the brand name of a range of cold-formed hollow sections manufactured by Corus Tubes for the general engineering market requiring a low-grade ‘box’. It is strongly recommended that this range of hollow sections should not be used in structural applications.Corus Tubes do however manufacture two alternative ranges of hollow sections for the structural sector, Hybox® and Celsius® 355.

Since Strongbox® 235 is intended for the general engineering market it is not manufactured to a particular product standard and hence the only mechanical property guaranteed is its minimum yield strength ReH of 235 N/mm2. None of the other mechanical properties required of a structural steel are guaranteed; namely, minimum tensile strength Rm, Charpy Impact properties at specified test temperatures and minimum percentage elongation requirements. Further, hollow sections in the Strongbox® 235 range are supplied with a Test report type 2.2 (not subject to ‘specific’ inspection and test requirements) and hence do not conform to
clause 2.1.3 of BS 5950-2: 2001. This clause requires that all steel used in structural applications in buildings must be subjected to ‘specific’ inspection and testing requirements, which is satisfied by a 3.1.B Inspection certificate. Reference should be made to the product standards for structural steels, BS EN 10021 and BS EN 10204 for an understanding of ‘specific’ and ‘non-specific’ inspection and testing requirements at manufacture as well as
the accompanying certificates and reports.

In addition, Strongbox® 235 hollow sections are manufactured to the dimensional tolerances of BS EN 10219 with the exception of the weight tolerance. The lack of a weight tolerance means that the section properties of the Strongbox® 235 hollow section range are smaller than the section properties of Cold Formed hollow sections, which fully conform to BS EN10219. Corus Tubes do provide tables of section properties for Strongbox®235 for situations where ‘designs’ are not intended to comply with the building regulations and / or design codes.

In view of the above it is strongly recommended that Strongbox® 235 hollow sections should not be used in structural applications; in particular, where designs must comply with the building regulations and / or design codes.

The two fully compliant ranges of hollow sections manufactured by Corus Tubes for use in
structural applications are:

Cold Formed Sections to BS EN 10219 S355J2H: Brand name – Hybox®
Hot Finished Sections to BS EN 10210 S355J2H: Brand name – Celsius® 355

Contact:
Thomas Cosgrove, SCI. Tel : 01344 623345, E-mail : t.cosgrove@steel-sci.com or
Eddie Hole, Corus Tubes, Tel : 01536 402121, E-mail eddie.hole@corusgroup.com