hey fellas welcome back to part two of this series on how to design your own cabin today we're gonna
size the floor and wall framing we're gonna look at the footings and how we can brace the structure
and as i mentioned in part one if you haven't watched part one go back and watch it first
i'm using the tables from as1684 however if you have a preferred timber manufacturer
you can also use their tables for their specific products also a little advice for young engineers
if you're just starting out in the profession have these tables on hand so that you can
compare the results from the software you're using or any hand calculation you're doing
to the the values that these tables will give you and then avoid making mistakes so having said that
let's get started so we're going to start sizing fj1 which are the floor joists at the bathroom
there are no roof loads it's a continuous span and spaced at 450 millimeter centers
each span is 1800 but instead of using 90 by 35 which is what the table gives us i
will choose 90 by 45 just in case we use a heavier flooring material for the bathroom
so theoretically f2 should be the same size as fj1 but we're gonna upsize it so that we can
achieve a wet area set down so you want that um that's set down between the bathroom floor
and the the floor in the rest of the house obviously deck joists are single span 1300
which would give us 70 by 35 but since decks have higher live loads i will upsize that to 90 by 45
which also gives us a 50 millimeter step from the internal to the external
area so we've got the so the water doesn't get in if you have the step from the balcony to the house
and remember that every member exposed to the weather should be h3 treated and paint painted
or you can use a hardwood timber so next we're going to design the floor the floor beams
and deck beams starting from the intermediate fb1 it's a continuous span floor beam
1800 span floor load width is 1800 so we get that the fb1 is double 90 by 35
the perimeter fb1 i'm just naming the same because in the end i want to use the same size throughout
but we could get different results here the only difference from the perimeter one is that
they've got a load bearing wall with roof load on top so because you've got the external walls
on top of this perimeter beam the floor load width is 900 the roof load width is 1800
and it's a continuous span same deal we're going to get a double 90 by 45.
i'm assuming you guys know what the the
floor load width and roof load width means right the tributary sort of a tributary area
that db1 has a floor load width of 1800 divided by two plus 1300 divided by two equals 1550
um the the roof load width is 1800 plus 1300 divided by two
and that work that works out to be 2450
it's also a continuous span
so just looking at the table for continuous span roof load width we're going to get a
double 120 by 35 mgp 12. that could potentially be a single 190 by four by 35 for example
um and to make size uniform we're just gonna standardize everything i'm gonna make fb1 the
same size as db1 and don't forget that if the beam is exposed to the weather same deal h3
treated and painted or hot wood so next next we're going to design the studs in the wall framing
and we're going to look at the worst case scenario which is the front wall um
the front wall has a roof load width of 1800 plus 1300 divided by two the height of the studs are
2.4 meters they're spaced at every 450 centers and they've got noggins at 1.35 meters high
just drawing the noggins here that's where that's what noggins are they're sort of blockings
so looking at this table we've got rafter spaced at 900 centers we are using
metal sheet roof the studs are spaced at 450 centers and that gives us 70 by 35 studs
so stud 70 by 35 mgp 12 at 450 centers
now the top plates the top plate connects the rafters to the studs
and that's the location of the top plates
and following this table assuming we will have m12 rods tied down at 1200 centers
or it could it could also be at 1800 centers we get that the top plate is 70 by 35
mg p12 so it's the same size as this stud but the the top plate the top plates are laid flat
bottom bottom plate same procedure just go to the table we we're going
to get the same same size as well so bottom plates rafter space at 900 metal sheet roof
same same 70 by 35 mgp 12.
jamb studs they are the studs adjacent to openings and looking looking at the worst
case scenario l3 is three meters with a rough roof load width of 2450 that's the worst case
scenario we just just gonna do this one and you do the the other ones um looking at the table we
get that we need double 70 by 35 mgp 12. so every opening just double up the studs okay
now we're going to work out the racking force that the bracings need to resist we have already
determined the wind classification which is n2 we will determine the wind pressure the area of
elevation and the racking force in kilonewtons so the width of the cabin is 3.6 meters the brazing
walls need to resist the pressure on the upper half windward wall okay windward wall is the
wall that the wind is going to blow the wind is hitting that wall it means it's the windward wall
so the area of elevation is 3.6 meters times 1.2 meters equal to 4.32 meters squared
now the ultimate strength pressure which is the wind pressure that we're going to use can be found
on as4055 table 3.3 for any two at any position um we get we get a 0.86 kpa of pressure on the wall
if we multiply the area of elevation multiply an area by the pressure we get a force right
because it's meters squared times kilonewtons per meter squared cancel cancel we got kilonewtons
and that's the force that all um
ply bracings need to resist all the ply braces need to resist this force in that direction
now the same principle applies to the length of the cabin
we need to find the area of elevation of the upper half of the windward wall
um so the area of elevation is 1.2 meters times 11 meters so that's a tributary area tributary area
we get 13.2 13.2 times the pressure we're going to get a force in kilonewtons 11.35 kilonewtons
in the other direction so we've got 3.7 in one direction 11.35
in the other direction so let's assume that each ply has a capacity of 6 kilonewtons per meter
i'm going to start placing plies at every corner so 0.66 here 0.9 there and
what we're going to do we're going to call this direction a the direction from
um where the 3.7 kilonewtons is we're going to call it direction a we're just going to
add up all the the the ply bracing that we've got and multiply that by the capacity
of the ply brace and that will give us a total capacity bracing capacity
in that direction that's 24 kilonewtons that's way beyond 3.7 kilonewtons okay so we
we're covered we're easy easy same thing for the other direction i'm just going to play i place ply
bracings on the corners one in the middle in the kitchen here and i'm going to call it direction b
that that gives us pretty much same 25 kilonewtons which is way greater than 11.35
so let's have a look at the footings now we'll be using 350 millimeters diameter
bored piers with the minimum depth of 600 millimeters it's going to be 600
into the soil every timber post will be cast into the concrete and i'll show you the details later
so for the downward force the gravity loads each footing will have to support
a tributary tributary area of 1.8 meters times 1.8 meters that's equal to 3.24 meters squared
if we multiply this area by the dead load and then plus
the live load we're going to get the force that this bored pier needs to resist
the area the the area of the p is pi times 0.35 squared divided by four
and that's simple math right pressure
equals to force divided by area 6.5 divided by 0.0926 and we get a
we get a pressure we get the bearing capacity of the soil so
most natural soils can achieve 70 kpa so you will be fine if you put your board p in in the natural
soil so designing for lateral loads now pretty much the same same process area of elevation
but the footings and for the poles the area of elevation is going to be the whole wall
not only the upper half so you need to work out the area of the whole wall
so the area times the wind pressure we get a racking force
same thing okay 0.86 times 8.64 we get a force of 7.43 kilonewtons in the direction a
same calculation same calculations will apply to this side of the cabin the area of elevation is
11 times 2.4 meters remember it's the whole wall now it's not only the upper half wall
and wind pressure pressure times area gives us a force okay
and that's the racking force 0.8 0.86 times 26.4 we got we get the the force that
all or piers together will have to resist in the direction b
so the lateral capacitor of the pier and post can be found on table 8.10 of as1684
the height above the ground is 400 millimeter for 400 millimeters the pier depth will be
600 and the diameter 350. so this will result in a capacity of 4.2 kilonewtons
for each pier so hpa can resist 4.2 kilonewtons lateral loads
so we're going to work out the capacity in each direction which is the number of bears
times the capacity of each pier right and you will notice that we have way more resisting
force than we actually need 117 it's it's a lot that's the detail of the structure of your cabin
so if you're building it it should pretty much look like this detail or similar
you need m12 bolts to the post to the beams you need triple grips from the studs to the rafters
joists joists to to beams um your team reports will be cast into the concrete
you've got 600 your your um footing should be 600 deep into natural soil
and that's pretty much it you've got the the step from the outside to the inside looks it's
pretty easy and i hope you learned something with this video if you have any questions just drop a
comment below i'll be more than happy to answer your questions and i'll see you in the next video