What is the Property Wet weight per area and Dry weight per area reported when using profiled metal decking?
Environment
Not environment-specific
Question
When defining a slab, the Properties window provides a Wet weight per area and Dry weight per area property value. When using a profiled metal deck these values do not match the value in published tables. Why is this?
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Answer
The slab weight per area and the dry weight per area property values are not used for profiled metal decking where the true profile shape is considered. They are included to consider solid slabs such as precast.
Calculation of wet/dry weight per area
The wet and dry weight per area is calculated using a simple cubiod using Density x slab depth x gravitational acceleration . These values are not used for profiled metal decking and are only used for solid slabs.
Wet weight per area = 2600 kg/m3 x 150mm x 9.805 / 1000 = 3.825 kN/m2
Dry weight per area = 2500 kg/m3 x 150mm x 9.805 / 1000 = 3.677 kN/m2
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We will prove these values are not used when the deck is defined as profiled metal decking, by means of a simple example.
Example
Using a simple 6x4m model with a 150mm thick slab utlising a profiled Kingspan Multideck 60-v2 profile.
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If we review the slab self weight decomposed loads applied to the beam this will confirm the dry weight per unit area is not utilised.
UDL applied to each beam = 6.0 kN/m
UDL if dry weight per unit area was used would have been = 3.677 x 4m / 2 = 7.354kN/m
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Or looked at another way in terms of support reactions
Reaction if dry weight per unit area was used = 3.677 x 4 m / 2 x 6 m / 2 = 22.062 kN
Actual Reaction = 17.9 kN
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The above example verifies that the wet weight per area and dry weight per area, are not utilised when profiled metal decking is assigned. The true shape of the profiled metal decking is taken into consideration in the calculation.
Enhancement
From Tekla Structural Designer 2017 Service Pack 1 (17.0.1.x), these wet weight per unit area and dry weight per unit area values have been hidden from the Property Window when the deck is defined as composite slab with profiled metal decking to avoid possible confusion.
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