summer is coming and you've been engaged to design an outdoor area
with a classy pergola and a high-end deck
in today's video we're going to learn what to consider if you're thinking of
designing timber structures for external use i'll
quickly cover some essential concepts that engineers
builders and architects should be aware of when
designing or building these structures i'll show
you how i would design a deck beam and the
difference from a normal floor beam protected from
the weather hi i'm Gabriel i'm a qualified civil
engineer practicing structural engineering in
queensland australia and today we're going to learn together
a little bit about timber structures first things first
let's talk about durability the natural durability rating of a timber species
determines the natural resistance to insect attack
and decay so my question is will the timber perform well over a
specified period of time
you are now looking at as1684.2 timber framing code appendix b
this image gives general guidance on the natural durability class
or level of preservative treatment required to give an
acceptable service life for various applications
and today we're going to focus on this application here
which is above ground exposed to weather in simple words any element on this
region needs to be above ground durability
class 1 timber or above ground durability class 2 3
4 timber with preservative treated h3 class 1 highly durable
class 2 durable class 3 moderately durable and class 4
non-durable from class 2 to 4 the timber needs to be H3 treated
h gives the standard levels of hazard scroll down to table b1 the term
h3 indicates the level to which the timber has been treated
so h3 is suitable for use outdoors above ground if your timber has been
treated to h3 it should be marked on the timber or
certified by some documentation from the supplier
okay so now that you know what type of timber we're working with
let's have a look at the design opening up a hyne design if you don't
know this software i'll put the website on the description
you can download it for free however if you're
not an engineer the software limits your access to some
tools on the initial screen it's the project
data with wind loads snow loads in case you
in case it knows where you live and dead loads on my complex design
tab remember if you're not an engineer the simple design tab will be activated
for you i'm going to choose bearers and beams
bearer trimmer and this little window pops up
asking for span length and whether the beam will be exposed or not
together so my span will be 3 meters and since
it's a deck beam it will be exposed to sun and rain
it displays the length of the tag beam from support to support i'll choose
a type of floor for dead loads live load will be 2 kpa for balcony
my floor load width is let's say 2 meters for those who don't know
floor load width is the contributor width of floor that imparts load to the
beam i'll show you an example if you go back
if you go back to as1684 in this image page 25
the bearer b will take half of x plus half of y
so floor load width is x plus y divided by two the floor dynamics will
perform a dynamic check to as1720
i'm gonna clear settings and choose the type of timber i want
i'm gonna choose a lgl which is a lumber glue
laminated which is an alternative for lvl laminated veneer
lumber i'm also picking a kiln dried hardwood f-27
i'll click design and before we go over the results
you can see that my lgl requires a h3 treatment nonetheless my hardwood
doesn't i particularly chose f 27 hardwood
because most of them are class 1 durability
therefore no treatment is necessary but be aware that some f 27 hardwood
maybe cost 2 or 3 and does require treatment for instance
carrying is a hardwood if we scroll down you can find stress grade f 27
season and then season seasoning if you don't know is the process of
drying timber which is often performed in
kilns so unseasoned timber may present a greater moisture content um
and if we look up Keruing on as5604
it is class three therefore needs h3 treatment
okay so going back to hein all results are a 240 by 45 lgl
or a 240 by 35 kiln dried hardwood f 27.
i'll choose a minimum weight of 45 because it's easier to nail and is more
stable it's just a personal preference or dynamic
deflections is 0.9 the maximum value
is 2.0 if it goes over 2.0 the floor will bounce i personally keep it
under 1.5 now if we design the same floor beam for
an interior use h3 treatment will not be necessary
let's make a quick comparison my lgl is deflecting 7.1 mil whereas the
h3 treated lgl is deflecting 9.4 mil this difference is due to the creep
factor j2 which is larger for h3 treated beam
if you don't remember creep is the increase in deformation
following prolonged loading it happens in concrete mainstream and also in
timber
okay cool if you have um if you have any questions on how to use the software or
you want more videos only just drop a comment below and i'll
i'll review it and finally to wrap this video up
a few comments that may be interesting for architects
most timbers leaches red brown during heavy rain periods
so be aware of that to not mess up your beautiful design
and also architects need to plan for the best
orientation for example the worst weather comes from
north northwest and is very harsh whereas
easterly or southerly locations get little uv
exposure therefore timber color will not be consistent
because of because because your house faces different directions and
some face will get more sun exposure than others
and finally a good ventilation under the deck will help to keep it
healthy so hopefully this video gave you a pretty good idea of how you should go
about when working with timber for outdoors areas and