ASSOCIATIONS
Not all products are equal
We look at the risks associated with accepting alternative
products to those you have specified.
By Dennis White, director at SAMCRA | Photos by Pixabay
When it comes to metal cladding one size does not fit all regarding wind loading.
F
ollowing on our recent article titled
‘Are you getting what you specified?’
published in the 2016 Steel
Construction Journal, the question arises as
to how you evaluate tendered alternatives.
When it comes to cladding it is vitally
important that the performance of entire
cladding system (sheets, method of
attachment and ancillary items) is evaluated.
The foremost criteria that influence
performance are:
• Structural properties
• Waterproofing capabilities
• Installation
• Durability
• Maintenance
Structural properties
By far the greatest component is the
geometry of the profile (±80%) with the
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MARCH 2018
RESIDENTIAL // COMMERCIAL // INDUSTRIAL
combination of size (particularly the depth)
and spacing of the ribs having the most
influence. Thickness and strength of the
base material contribute the balance.
Cladding must resist both gravitational
(downward) and wind (invariably upward)
forces. Under upward loading a cladding
system is only as good as the resistance
provided by the anchors (fasteners,
clips, cleats) that attach it to the
supporting structure.
A little-known fact is that most span
tables are based on the gravitational
loading requirements only. Resistance to
uplift from wind action, if indicated at all, is
generally quoted as a nominal uniformly
distributed load independent of span.
Some tables contain notes and reduction
factors relating to location and size of a
building, others do not differentiate. It must
be remembered that when it comes to
metal cladding one size does not fit all
regarding wind loading. Even if the
geometry, base metal and anchor
mechanism appear to be the same it is
necessary to check the wind load
capabilities of a cladding system.
Another factor to consider is
manufacturing tolerances for the base
metal. Locally produced coil is
manufactured within a tolerance of
±0.02mm whereas imported coil, depending
on the country of origin, could have a
tolerance of ±0.05mm. it is also important
to establish if the quoted thickness is TCT
(total coated thickness) or BMT (base metal
thickness, such as thickness of steel core
excluding coatings).
Waterproofing capabilities
Water carrying capacity and the method of
sealing the junction between profiled