steel beam glued timber or log ??

[camaro1969]

The magnitudes used to assess various aspects of strength, bending resistance, and moment of inertia favor height over width. The amount of material in a log with a 30 cm diameter could suffice for a beam measuring 10x70 cm, which would have twice the bending resistance of the round log. When it comes to usage in horizontal structures, the log is probably not optimal. However, it is clear that a log used as a pillar has the advantage of not having a weaker buckling direction.

Of course, the bending resistance improves if you increase the height to 70 cm compared to 30...

but how does glulam, say 90x315, compare to a log with a diameter of 315?

 

[justusandersson]

Without having calculated it in detail, I would think that they are quite equivalent. The log has slightly better bending resistance and moment of inertia than the glulam, while the latter has about 20% better modulus of elasticity than normal construction timber (C24). An exact answer cannot be given without knowing the quality of the log.

 

[camaro1969]

sure, of course it depends on the log naturally...
but you can try to find one that's as nice and knot-free as possible, and then maybe adjust a bit regarding the thickness...
you can find one that's 40-50cm too...
and let the thick end remain as thick as it is naturally, it will be more stable...

this will probably be the cheapest option for me anyway.

wondering if I should cut the spruce at 6.5 meters... prop it up at each end and let it "hang" and dry for a year.

then its own weight should have done its job... and it will have its final shape before installation...

is there no "timber framing category" in this forum?

 

[Daniel 109]

Justusandersson: How does the moment of inertia come into play?

Since the tree has compensated for branches, they do not have as much significance for strength when it comes to round timber compared to sawn timber.

 

[holmberg87]

no, of course, it depends on the timber obviously...
but you can try to find one as nice and knot-free as possible, and then maybe account for the thickness...
you can find one that is 40-50cm as well...
and let the thicker end be as thick as it is naturally, it will be more stable...

this will probably be the cheapest option for me.

thinking about cutting the spruce at 6.5 meters... propping it up at each end and letting it "hang" and dry for about a year.

then the weight should have done its job... and it will have its final shape before installation...

isn't there a "log building category" in this forum?

Speaking of log building, you do have a neighbor who knows a bit.

 

[camaro1969]

Regarding timbering, you have a neighbor who knows a bit

yeah, I'll present the proposal to him when the opportunity arises

I think he'll think the timber log proposal is excellent...

 

[justusandersson]

The moment of inertia has no significance at all for the strength when it comes to a horizontal load-bearing structure. I just mentioned it in passing because it was previously discussed in comparison with logs with round cross-sections.

wondering if I should cut the spruce to 6.5 meters... prop it up at each end and let it "hang" and dry for a year.

I'm really not an expert on this. Spontaneously, I think it would be better to let it dry straight since you don't benefit from it sagging, but I'm not sure about that.

 

[camaro1969]

but do you think the strength is the same in a log with 315mm diameter as in a laminated wood beam with 315mm height?

it's the strength that's most important to me... deflection, etc. doesn't really matter...

I imagine it will sag under its own weight over time... so if you do this moment before installation, it should have taken its shape for all eternity? that's roughly the thought process anyway, though I'm not sure if it aligns with reality

 

[justusandersson]

but do you think the durability is the same in a log with 315mm dia as a glulam beam with 315mm height?

Yes, the bending strength in a horizontal position should be comparable.

 

[Daniel 109]

After reading up a bit, I realize that justus is talking about the moment of inertia for bending, which has nothing to do with the property moment of inertia. Hence my confusion. But surely the moment of inertia for bending should be relevant in this case? I need to read up a bit more.

 

[justusandersson]

I might have expressed myself a bit carelessly. I was referring to what I usually call the moment of inertia (b*h^3/12), often denoted as "I", which is used for horizontal structures to calculate deflection. The latter is important in many contexts, but not if you want to calculate the bending strength of something that is part of a roof structure if you can accept a certain deflection.

 

[Daniel 109]

Thank you for the clarification.