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VERMICULUX® - Design consideration
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Specifications of
steelwork section factor
The Hp/A (Heated perimeter/Area) is a method of
measurement of the rate at which a steel section will heat
up when exposed to fire.
The higher its value, the greater the thickness of fire
protection material is required.
Hp/A(m-1) =
Rectangular perimeter of
exposed steelwork (m)
/ Cross-sectional area of the steel section (m-2)
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Calculation of Hp/A factors
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Find the actual depth (D) and width (B) in metres of
the steel section from supplier’s literature, or site
measurements.
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Refer to TABLE 1 for the extent of exposure, and
calculate Hp.
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Find the cross-sectional area (A) in square metres of
the section from supplier’s literature, or site
measurements. For partial exposed members the A
value is still the total cross-sectional area.
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Divide Hp by A to give Hp/A in m-1.
Please refer to the
VERMICULUX®
brochure for Hp/A values.
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For partially exposed members, the A value is still the total cross-sectional area.
An example for a universal beam, exposed on 3 sides:
| Serial size |
= |
475mm x 152mm x 82kg/m |
| Actual size (D x B) |
= |
465.1mm x 153.5mm |
| Hp (2D + B) |
= |
(2 x 465.1)mm + 153.5mm =
1083.7mm = 1.0837m |
| A |
= |
104.5cm2 = 0.01045m2 |
| Hp/A |
= |
1.0837m / 0.01045m2 = 103.7m-1 = 104m-1 |
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