Fire Resistance

Fire Resistance:

Introduction:

This paper discusses fire resistance test for beams and columns as described in the British standards EN 1365. for both cases the fire resistance of specimen is tested in a furnace where load is added and the specimen heated, temperatures are recorded during heating and as the specimen deforms this indicates the strength of the specimen, the following is a discussion on how the test should be undertaken for both column and beam.

Requirements:

These standards of testing the fire resistance of a specimen are provided in the British standard EN 1365 part 3, according to this standards general requirements that are provided in EN

1363-1 and EN 1363-2 must be followed, according to EN 1365-3 testing for fire resistance of specimen involves heath hazards where toxic gases may be emitted and also disposal of residual may cause health hazards.

Safety precautions:

–  EN 1363-3 provides safety          precautions and what should be done to avoid health risks

–  Adequate training should be provided         to the technicians

–  The instructions provided in the       standards must be followed at all times by the

Fire Resistance

technicians

Beams:

The main aim of this test is to check the integrity of a beam that will be constructed to support a floor or roof

The associated construction:

The associated construction is the construction that represents the load on the beam under normal circumstances example roof or floor; the following are the conditions of this construction:

–  It should be constructed in discrete          sections

– It should contain discontinuous reinforcements

– Made or aerated concrete slab

Fire Resistance

–  Density should be 450 – 850 kegs per          meter cubed

– Maximum width should be 600mm

– Thickness should be 175 – 125 mm

Fire protection material:

Specimens are sometimes sealed with fire protection materials; if these materials are applied then they must be applied on the entire length of the specimen

Where a void or hole is created in the beam the hole should not extend outside the furnace

Gaps that may exist between the furnace wall and associated construction shall be sealed

– Mineral wool should be 90 mm to 110 mm thick and density should 90 to 150 kg per meter cubed

–  Finally the specimen should be       mounted horizontally

Fire Resistance

The load (associated construction);

–  The load should match the expected          load that the beam is expected to bear in practice

–  The load which is the associated          construction should be placed uniformly on the beam

and should cover at      least 500 mm on the span.

Temperature:

Thermocouples or plate thermometers will be used to measure temperature, in this case there should be at least two thermocouples for every meter of the specimen.

They should be placed 100 mm below the surface below of the beam and 100mm from each end of the beam

When the beam is 500m thick or greater then they will be placed on the side (mid height) of the beam and not the lower side

If the specimen is made from inert material such as steel and aluminium then their properties are known and the temperatures can assist in detecting failure

Deflection:

The beam is expected to deform as temperature increases, zero deformation however should be recorded as the nature of the axis before the test

Fire Resistance

The performance of beam will be judged with reference to loading capacity

Reporting:

Reports regarding such test should specify that EN 1365-3 standards were used.

Factors that may affect the fire resistance of beam include:

–  The Cross sectional area of the beam

The diagram below shows the standard procedure of testing the fire resistance of a beam

Columns:

Specimen:

Fire Resistance

The section that is exposed to heat should be at least 3 meters long

The specimen may be placed in the furnace whereby one end may be pin jointed and the other restrained or both ends restrained

The ends of the specimen must be sealed with mineral wool to prevent gas losses

The load applied to the specimen must be parallel to the axis of the specimen.

If joints are incorporated then they will be placed at mid height and coated with fire protective material

The specimen shall be placed vertically

End conditions:

End conditions are that if one end is pin jointed then the end will comprise of a cylindrical rolled, hinges must be accurately located on the axis of the column, if the ends are restrained then they must be fully restrained.

Report:

Fire Resistance

Reports regarding such test should specify that EN 1365-3 standards were used.

The test applied to:

Columns that are fully exposed to fire on three sides and the test will depend on end conditions; small amounts of friction that may emerge at the ends will considerable increase the load bearing capacity of the test specimen.

Temperature:

Temperature will be measured using thermocouples or plate thermometers, these devices will be placed ¼, ½ and ¾ of the length on the exposed part of the column

Thermometers should be at least placed 50 to 150 mm from the column facing the column. Also if column is made of composite material example steel and concrete then temperature for individual components is important

Behaviour after heating:

The specimen is expected to deform, and therefore zero deformation sill be measured before the beginning of the test and deformation will be measured using a dial gauge.

Fire Resistance

This will result due to a number of factors, one is because the moisture is lost and the specimen shrinks, loss of moisture will result into a decline in the cross sectional area and therefore loss of strength.

For materials such as steel columns, they will expand and will contract as the column deflects. Steel tubes filed with concrete will expand and still be able to hold the concrete inside, however further heating will result into deformation, steel tubes filled with timber then the initially there will be no change but further heating deformation will occur.

The diagram below demonstrates the fire resistance test for a column:

REFERENCE:

British Standards: EN 1365, fire resistance of load bearing elements, part 3 and part 4