Hello

[saveasteading]

3 hours ago, SteamyTea said:

This changes the bending moment of the structure.

It makes it effectively into  a beam with extremely wide flanges.

A steel column or  beam works by having one flange in tension and the other in compression.  Keeping them apart is a steel spacer or web. The same logic applies with engineered joists.  But in a SIPS panel  it is a continuous block of glue separating the 2 flanges made of plywood. In a normal timber framed structure the outer face is of osb fixed onto timber studs, effectively making a lot of T beams., and for even greater strength an inner timber sheet could b added.

[SteamyTea]

2 hours ago, saveasteading said:

and for even greater strength an inner timber sheet could b added.

It improves the buckling/warping resistance and racking strength. 

[Gus Potter]

On 22/04/2024 at 20:10, SteamyTea said:

Maybe @Gus Potter can comment more as I am very rusty on my structural engineering terms these days (took me decades to work out what a 'moment' was).

Simplistically a bending moment is a turning (rotational) force. If you want to take the wheel nut off your car you get the spanner out and apply a force to the end. Say 25kg (you are partly in a bad mood). 25kg = about 0.25 kN kilo Newtons ( a bag of cement weight wise) which is the units that Engineers use unless in the US say where they have pounds lb.

 

Ok, say your spanner is a short one.. 0.25m long.  The turning force on the nut is 0.25 (kN) * 0.25m = 0.0625 kNm. This turning force is called a bending moment when we look at say a beam.. torsion when we are trying to take a wheel nut off. Now if you double the length of your spanner to say 0.5m now you have a turning force of 0.25(kN) * 0.5m = 0.125 kNm or you only need to apply 12.5kg to the end of the spanner to get the same effect cf the shorter spanner.

 

If we have a beam over say a set of bifold doors the beam is much longer than a spanner and the loads are much larger. The maginitudes of the rotational force (moment) increase a lot. We can calculate the moment at a point along the length of a beam and then convert that into the stress that the beam material is experiencing and check to see if the beam is ok. For comparison a 254 x 102mm Universal steel beam that is fully restrained to prevent it twisting might be able to resist 70.0 kNm or so bending (moment) force.

 

 

 

 

 

 

 

 

[Gus Potter]

On 22/04/2024 at 20:10, SteamyTea said:

SIPs is a bit different in that it is a monocoque construction,

Now that is a cracking word "monocoque"!

 

In summary though monocoque is a bit of a genreric term. In the early days it was used to decribe a modern method of construction where basically the ceilings were laid down with shear studs "thingies" on top and later a top layer added to make a permenant load bearing structure.

 

Now we think of SIPS in a different way.. but they tend to need reinforced internally to carry vertical structural loads. This is where problems can arise as if you don't get the loads from above lining up with the reinforced bits in the SIPS you are in trouble.

 

 

[Gus Potter]

On 22/04/2024 at 15:24, Graham Walker said:

Hi, I’ve been a member for a while but have been mostly sitting, getting frustrated, waiting for our planning decision. 2 weeks ago we finally got our approval for a strawbale house in the village of Minard, in Argyll and Bute. Now we’re moving into the building warrant stage and at least this time, we’re prepared for a wait - our planning took ten months after being told ten weeks.

Ok to finish. Cracking part of the world. Keep posting about your bale house as very interested. Would love to have sight of your warrant drawings to see how you are dealing with the loadings, movement etc. wishful thinking...

 

Fundamentally though if you keep the straw dry, well ventilated and the perimeter drainage around the house clear it should last a lifetime or more. If you go and plant loads of trees close to the house then it won't last so long.

 

Are you local to the area and know the climate well? Lastly.. depending on where you are there may be a bit of salt from the sea in the air.. make sure you specify the right fixings. I have family that live on the islands and it can play havoc with fixings etc if you use the wrong ones.