Steel Frame Construction in UK Buildings

What This Requirement Covers

Steel frame construction is widely used in commercial buildings, multi-storey residential developments, and industrial structures. The structural design of steel frame buildings in the UK must comply with BS EN 1993 (Eurocode 3: Design of Steel Structures) and the UK National Annex.

Key Requirements

Design Standards

1. Primary structural steelwork must be designed to BS EN 1993-1-1 (General rules and rules for buildings)
2. Connection design follows BS EN 1993-1-8 (Design of joints)
3. Fire design follows BS EN 1993-1-2 (Structural fire design)
4. Steel grades commonly used: S275 and S355 (yield strength in N/mm²)

Fire Protection

1. Unprotected structural steel loses strength rapidly in fire, reaching critical temperature at approximately 550 degrees Celsius
2. Fire protection is required where the steel frame forms part of a fire-resisting element:

- Intumescent coatings: Applied to steelwork; expand in fire to form an insulating layer - Board encasement: Fire-rated boards (plasterboard, calcium silicate) fixed around steel members - Concrete encasement: Steel sections encased in concrete - Spray-applied protection: Cementitious or fibre-based coatings sprayed onto steelwork

1. The required fire resistance period depends on the building type and height (30, 60, 90, or 120 minutes)

Connections

1. Simple connections (flexible end plates, web cleats): Transfer shear forces only; used in braced frames
2. Moment connections (extended end plates, haunched connections): Transfer both shear and bending moment; used in portal frames and unbraced frames
3. All connections must be designed by a qualified structural engineer and detailed on the fabrication drawings

Corrosion Protection

1. Structural steelwork must be protected against corrosion, particularly in exposed or humid environments
2. Common systems: hot-dip galvanising, paint systems (primer + intermediate + topcoat), or metallic spray coatings
3. The specification depends on the environmental category and the required design life

Practical Compliance Tips

1. Appoint a structural engineer experienced in steel design from the outset
2. Coordinate the steel frame design with the fire engineer to determine fire protection requirements early
3. Specify the fire protection system at design stage; different systems have different thickness requirements and programme implications
4. Ensure the steelwork fabricator works to a quality management system (CE marking under BS EN 1090 is a legal requirement)
5. Inspect fire protection application thoroughly; inadequate thickness or missed areas are common defects
6. Plan for the interface between steelwork and other construction (masonry, cladding, services); early coordination avoids delays
7. Retain all design calculations, fabrication drawings, and test certificates for the building file