Cold-formed steel members
Light gauge cold-formed steel members as used in light steel framing, flooring , roofing or cladding applications are usually specified in accordance with the manufacturer’s safe load tables or similar technical data. The member capacities used in the load tables may be obtained by calculation to the appropriate British Standard or Eurocode, derived directly from test results, or calculated using a design model which has itself been derived from physical tests. Since for purlins, cladding rails and similar applications, the capacities of the members are rarely checked by the specifying structural engineer, it is essential to have confidence in the published data.
Steel decking
Cold rolled steel deck is used as a permanent, structural formwork in composite floor construction. Design properties have to be established for the behaviour at the construction stage, when the decking supports the weight of the wet concrete and construction loads, and at the normal stage, when it acts compositely with the concrete as tensile reinforcement. All of these design values are generally determined from testing, although the Standards allow for the bare steel properties to be determined by calculation. The test methods are described in the structural design standards such as BS EN 1993-1-3 and BS EN 1994-1-1. When determining design values by tests, a formal statistical analysis of the results in accordance with BS EN 1990 (typically) is required to determine the characteristic values, which are usually available from the manufacturer either explicitly, as load-span tables or in design software.
Steel cladding
Cold formed steel cladding sheets are used to form a weathertight building envelope for a wide range of building applications. Typically, the steel sheets form the inner and outer layers of a ‘built-up’ system, with a layer of insulation in between. They are designed to span between purlins (typically 1.8m span) and must be capable of resisting snow loading, access loads and wind suction. Unlike decking, the design resistances used in the published load tables are usually generated by calculation to BS 5950-6 or EN 1993-1-3. Similar calculation procedures are given in EN 1999-1-4 for aluminium cladding products.
Existing technical data
Where a manufacturer already has published load tables, SCI will assess the tables and the technical data behind them, permitting the ‘SCI Assessed’ mark to be displayed on the manufacturer’s technical literature or website. Depending on the origin of the load tables, the assessment procedure may involve checking calculations to BS 5950-5, BS 5950-6, EN 1993-1-3 or BS EN 1994-1-1, reviewing test results and associated test procedures, performing statistical analyses on test results and design models or a combination of these activities.
The following information is required from the product supplier:
1. Scope of applications.
2. Support and restraint conditions (use of sag rods, cleat details etc.).
3. Material grade(s) and gauge(s).
4. Section dimensions
5. Spanning condition – single, double, sleeved etc.
6. Technical information to be assessed usually in the form of load tables to BS 5950-5, BS 5950-6, EN 1993-1-3 or BS EN 1994-1-1.
7. Any relevant supporting calculations, design models or details of computer software used to generate the load tables, together with assumptions and limitations.
8. Any test results used to derive the load capacities or used in support of design models, together with the associated test procedures.
The assessment of the data will be performed for a one-off fee, dependent on the quantity of data to be assessed and the nature of the assessment (e.g. whether it involves test results, hand calculations, computer software etc.). In addition to technical assessment, the SCI will also review the technical literature to which the ‘SCI Assessed’ logo is to be attached in order to verify that the use of the logo is compatible with the scope of the assessment. There will also be a small administrative fee to be charged at the time of the initial assessment and annually thereafter.
New technical data
Where a manufacturer does not already have load tables or similar technical information or where there is a desire to expand or replace the existing information (e.g. to update the tables in line with the Eurocodes), the SCI can produce the load tables for the manufacturer through its light gauge steel specialist consultancy service. In this case, the technical assessment of the data will be performed as part of the SCI’s normal checking procedures and the resulting technical information will automatically qualify for the ‘SCI Assessed’ mark, subject to the payment of the annual administrative fee.
Results
The results of the testing, analysis and claculation, and the load span tables and design properties will be recorded in a SCI Report.