Hi,
I hope someone kind with a minute to spare can answer the following regarding roof construction:
-4 glued laminated beams with dimensions 66x315 mm, length 4.5m with CC 120cm,
Snow load 3.0 and the roof's own weight 0.4
As seen in the simple attached sketch, it's a "double-sided dormer/extension." I have planned for 4 glued laminated beams to constitute the roof construction. Thus, it is the deflection that must be checked.
The support beams/hammer beams can be considered rigid, and we don't need to account for them.
PS. regarding the sketch, you can see in the lower corner that I plan to splice construction timber to achieve a roof pitch of around 5 degrees from the ridge. The additional strength that the "saddle block wedges" might contribute to can be disregarded.
SO, are 4 66x315 mm glued laminated beams sufficient?
I hope someone kind with a minute to spare can answer the following regarding roof construction:
-4 glued laminated beams with dimensions 66x315 mm, length 4.5m with CC 120cm,
Snow load 3.0 and the roof's own weight 0.4
As seen in the simple attached sketch, it's a "double-sided dormer/extension." I have planned for 4 glued laminated beams to constitute the roof construction. Thus, it is the deflection that must be checked.
The support beams/hammer beams can be considered rigid, and we don't need to account for them.
PS. regarding the sketch, you can see in the lower corner that I plan to splice construction timber to achieve a roof pitch of around 5 degrees from the ridge. The additional strength that the "saddle block wedges" might contribute to can be disregarded.
SO, are 4 66x315 mm glued laminated beams sufficient?
Do you still have load-bearing capacity in the ridge or not?
Sounds more than fine, 4.5m works with 45x220. But if you want to maintain cc1200, glulam sounds good.
Deflection less than L/300 is likely good sizing.
v=5 q l^4 / 384 E I =
5 * 3400 *1.2 * 4.5^4 / (384 10 000 * bh^3/12) = 0.0126m
L/300 = 0.015m
A quick gut feeling says it's fine.
Sounds more than fine, 4.5m works with 45x220. But if you want to maintain cc1200, glulam sounds good.
Deflection less than L/300 is likely good sizing.
v=5 q l^4 / 384 E I =
5 * 3400 *1.2 * 4.5^4 / (384 10 000 * bh^3/12) = 0.0126m
L/300 = 0.015m
A quick gut feeling says it's fine.
Hi, thanks for the quick response!
The thing is that the old ridge will completely disappear and be replaced by the dormer's "flat roof," so there's no support left from it.
I hadn't even thought that it might be enough for deflection with regular structural timber like 45x220, but maybe it is? Provided you place them at 60 cm centers, of course.
You seem to have calculated Deflection L/300 to about 15 mm then, what is that calculation and formula above?
Hmm, what would be suitable wall studs and header beams? Maybe a standing wall stud 145x45 against the facade and a crossed 45x45 inwards, i.e., a 195 mm insulated wall. Would a standing 145x45 as a load-bearing beam suffice, or should one use a lying header beam like double 145x45?
The thing is that the old ridge will completely disappear and be replaced by the dormer's "flat roof," so there's no support left from it.
I hadn't even thought that it might be enough for deflection with regular structural timber like 45x220, but maybe it is? Provided you place them at 60 cm centers, of course.
You seem to have calculated Deflection L/300 to about 15 mm then, what is that calculation and formula above?
Hmm, what would be suitable wall studs and header beams? Maybe a standing wall stud 145x45 against the facade and a crossed 45x45 inwards, i.e., a 195 mm insulated wall. Would a standing 145x45 as a load-bearing beam suffice, or should one use a lying header beam like double 145x45?
L/300 is the maximum value for deflection that the eye accepts before it becomes noticeable.
Aesthetics often take precedence over actual durability in wood.
The formula above v=5ql^4/385IE is the deflection under distributed load.
Regarding walls, it depends greatly on the windows. If you can't laterally brace studs against buckling because there are many windows, more robust ones are required. If you have a stud under each glulam beam and can laterally brace them, 145 is sufficient.
45x220 is a bit weak even at cc600. If there's space, it's convenient to use glulam as it becomes easier to support it in the wall.
Aesthetics often take precedence over actual durability in wood.
The formula above v=5ql^4/385IE is the deflection under distributed load.
Regarding walls, it depends greatly on the windows. If you can't laterally brace studs against buckling because there are many windows, more robust ones are required. If you have a stud under each glulam beam and can laterally brace them, 145 is sufficient.
45x220 is a bit weak even at cc600. If there's space, it's convenient to use glulam as it becomes easier to support it in the wall.