Light steel framed walls and floors

6.10

6.10.8Detailing of steel joist

Steel joists, fixings and connections shall be suitably detailed and provide satisfactory performance. Issues to be taken into account include:

  1. installation details
  2. support cleats
  3. prevention of roll.

Installation details

Joists should be:

  • spaced as shown in the design
  • accurately cut to length in the factory to ensure a tight fit
  • joined with the correct type, size and number of fixings.

Where light steel joists are supported by steel joists, cleats or web stiffeners should be used in accordance with the design.

Joists may be doubled up to support partitions or to form trimmers.

Ends of floor joists directly supported on walls should be stiffened. Continuous joists on load-bearing intermediate walls should be reinforced as required by the design.

Where joists overlap on load-bearing intermediate walls should be fixed together with bolts or screws. This is to prevent the floor decking being pushed up, or the ceiling being cracked, when the cantilevered part of the joist moves upwards.

Support cleats

Joist support cleats should:

  • be of the correct type
  • be fitted in the specified location
  • use fixings as specified in the design.

Where required, web stiffeners should be properly fitted.

Where joists are fitted directly to light steel wall studs, pre drilled holes should be correctly aligned before making the final connection.
Fixing holes should not be enlarged, and additional holes should not be cut without prior approval of the designer.

Prevention of roll

Bridging and blocking should be provided in accordance with the design to prevent roll.

Floors constructed using joists with an asymmetric web, e.g. of C or Sigma profile, can cause the floor to roll. To avoid roll, unless otherwise specified in the design, one of the following alternatives should be used where the span exceeds 3.5m for C joists, or 4.2m for Sigma joists:

  • A continuous line, or lines, of proprietary steel herringbone struts provided between the joists. The pairs of struts should have a physical gap between them so that they do not rub against each other at the cross-over point and create noise.
  • Solid blocking provided to every third pair of joists with ties between them.
  • Joists alternately reversed and tied together in pairs.
  • Joists alternately reversed and continuous ties (e.g. resilient bar) fixed to the joist flanges.

Where joists bear onto steelwork or are supported by cleats, blocking is not necessary adjacent to the supports.