Advanced Construction Technology

By Professor Chris Gorse & Ian Dickinson – licensed under the Creative Commons Attribution – Non-Commercial – Share Alike License

http://creativecommons.org/licenses/by-nc-sa/2.5/

Steel frame: Fire Protection

Chris Gorse and Ian Dickinson

These slides should be read in conjunction with Emmitt, S. and Gorse, C. (2010) Barry’s Advanced Construction

of Buildings. Oxford, Blackwell Publishing

Fire protection

• Steel rapidly loses strength in a fire and needs protection from heat.

• 550oC is normally considered a critical temperature in building fires as carbon steel will lose 50% of its strength at this temperature.

• Low carbon steel actually melts at a considerably higher temperature - around 1464oC, high carbon steels melt at slightly lower temperatures 1353oC.

Properties of steel in a fire(Source fireengineering.corus.garnerdigital.com)

• “For hot rolled structural steel the yield strength reduces as the temperature increases dropping to about 60% of its ambient temperature strength at around 400°C and approximately 10% at 800°C. However the stress at 2% strain (normally reached when a steel floor beam attains its permitted limit of deflection) initially increases with increasing temperature reaching a peak value at around 250°C.

High strength bolts (Source fireengineering.corus.garnerdigital.com)

• High strength bolts achieve much of their strength by a quenching and temper process.

• The bolts are quenched at temperatures from around 850°C creating an extremely hard but brittle structure.

• The bolts are then tempered between 475°C to 600°C to restore some ductility, but this does result in a measured loss in strength.

• If these temperatures are exceeded during a fire the bolts will over temper resulting in a sharp drop in strength.

Main types of fire protection

• Boarded protection e.g. plasterboard, vermiculite boards, calcium silicate boards, mineral fibre boards.

• Spray on fire protection e.g. vermiculite cement, mineral fibre, magnesium oxychloride

• Painted or sprayed coatings: Intumescent coatings, these are generally water or solvent based and are applied in thicknesses of 0.2 to 5mm.

• There are epoxy type resins that can be used in hostile environments and these may be up to 12mm thick.

• Traditional materials such as block, brick, concrete and timber can be used

• Tubular steel filled with water can also offer some protection. The mass of water absorbs the heat and for a time disperses it through the column.

Incombustible board protection

Boarded fire protection

Board protection

All joints sealed

Intumescent paint (swelling paint)

Intumescent paint