G'day welcome back to Buildsum this is presentation 17 on the timber frame code
And in this one we're going to look at the size of our struts, so
The rules
Well
There's two rules that look well three rules that look at struts 7.2.15 and
7.2.15.3, which looks at fan struts in particular
7.3.17 and
It's another miscellaneous member goes into Table 7.6 the actual size
So Rule 7.2.15 says that when necessary struts shall be provided to support roof members
Such as under purlins ridge boards and hip and valley rafters
Struts shall be supported off walls strutting beams combined hanging strutting beams or combined counter strutting beams
Struts shall not be supported on hanging or counter beams okay. They need to be a combined hanging or conterbeam
except as provided for in clause7.2.15.2, 7.2.15.3 and
7.2.15.4 struts. See how either be vertical or
perpendicular to the rafters or in an angle between vertical and perpendicular to the rafter
They shall be birds mouth or halved on to the under pills, so it just can't be butted up underneath them
7.2.15.3 covers fan struts a pair of fan struts
Fan or flying struts may be used in the same line as or perpendicular to the under purlin with their supports opposing each other
The pair of fan struts shall be at the same angle not greater than 45 degrees to the vertical
maximum fan strut length shall be 4.5m with maximum 3m spacing between the struts and the
under purlins connections
Rule 7.3.17 we've looked at before it refers to Table 7.6
To find out the sides of the struts, so if say at Table 7.6 if we go down here to
find the size of the roof struts
Sheet roof, which is what we're doing you can see that
We've got two choices
Struts up to
1500mm long for all stress grades or
Stuts 1500 to 2400 for all stress grades now if you look at our preliminary
Calculations we actually worked out that out
inclined strut
Our length would be 1.211m
and our fan strut length would be 1.713m
so we're actually both sides of the coin, so we'd be safer to use
70 x 70 as our strut for our
Inclined strut we could use 90 x 45 course for less than the 1500, but if we had to do a fan strap we'd
Be using 70 x 70 so we could use a combination of both
If you're doing a tiled roof you would have to come down here to the bottom roof struts tile roof and the same
Sort of thing you have to look at the length of your strut
And the size the stress grade of the timber you're going to use to work out what
what you're going to use and but basically
70 x 70 would cover
most
situations
Except if you're using very small stress grade timber like we are where you would have to use 90 x 75
That's for a tiled roof , thats not our situation, so we're going to use
70 x 70 to strut our Purlins
Okay, so there we go 70 x 70, and that's the strut size we need