Hello
I have a flat roof/terrace (4%) under design. While it is a garage roof, you can also use it as a terrace. The area is approximately 9.6 meters x 6 meters = just under 60 sqm.
I want to have rafters made of HEA beams mixed with pressure-treated lumber 45 x 145. All are securely anchored at both ends, and the span is 6 meters. I have assumed that HEA beams are much less expensive than laminated timber beams and save on ceiling height due to the greater strength of steel. 45 x 145 isn't particularly costly either.
I can no longer perform proper engineering calculations on this but have (as an old draftsman from the '70s) sketched this roughly and am looking for a skilled designer who could review:
With a spacing of 300cc over approximately 9600 meters, I have sketched with 31 rafters, i.e., 33 spacers of 300 mm.
The rafters alternately consist of lumber 45 x 145 and HEA 120 distributed with the main rule of 2 wood and one HEA. With a denser arrangement of HEA in the middle with every other being wood and every other being HEA (position 13 – position 18)
1 + 1 wood + 1 HEA will be in positions 1 -12 and 19 – 31, which gives 16 + 1 wood and 8 HEA.
In the middle, it becomes 1 wood + 1 HEA in positions 13-14, 15-16, 17-18, which results in 3 wood and 3 HEA.
A total of 20 wood and 11 HEA.
On the rafters, a metal roof, and on this, a joist and beams for UPM decking.
I have a flat roof/terrace (4%) under design. While it is a garage roof, you can also use it as a terrace. The area is approximately 9.6 meters x 6 meters = just under 60 sqm.
I want to have rafters made of HEA beams mixed with pressure-treated lumber 45 x 145. All are securely anchored at both ends, and the span is 6 meters. I have assumed that HEA beams are much less expensive than laminated timber beams and save on ceiling height due to the greater strength of steel. 45 x 145 isn't particularly costly either.
I can no longer perform proper engineering calculations on this but have (as an old draftsman from the '70s) sketched this roughly and am looking for a skilled designer who could review:
With a spacing of 300cc over approximately 9600 meters, I have sketched with 31 rafters, i.e., 33 spacers of 300 mm.
The rafters alternately consist of lumber 45 x 145 and HEA 120 distributed with the main rule of 2 wood and one HEA. With a denser arrangement of HEA in the middle with every other being wood and every other being HEA (position 13 – position 18)
1 + 1 wood + 1 HEA will be in positions 1 -12 and 19 – 31, which gives 16 + 1 wood and 8 HEA.
In the middle, it becomes 1 wood + 1 HEA in positions 13-14, 15-16, 17-18, which results in 3 wood and 3 HEA.
A total of 20 wood and 11 HEA.
On the rafters, a metal roof, and on this, a joist and beams for UPM decking.
Have I understood you correctly that every third beam should be an HEA 120 and the two in between 45x145 pressure-treated wood? When I make an estimate and calculate with 2 kN/m2 in live load/snow load and 0.5 kN/m2 in the self-weight of the wooden beams, not even a 45x220 is sufficient to meet a deflection requirement of 1/300, much less a modern flex requirement. HEA 120 probably holds up. But maybe I've misunderstood it all?
Hello!
Thank you so much for your response. My answer is:
Yes, but in the middle it's denser. It's every other HEÅ120 on positions 13 to 18.
Are you a structural engineer and can I hire your service? There’s no need for a drawing, just that the technical description is correct.
This really needs to be good. But do I have to have HEA 120 in all positions? I have ruled out glulam beams because it would cost 28—30,000 SEK at Beijers.
Thank you so much for your response. My answer is:
Yes, but in the middle it's denser. It's every other HEÅ120 on positions 13 to 18.
Are you a structural engineer and can I hire your service? There’s no need for a drawing, just that the technical description is correct.
This really needs to be good. But do I have to have HEA 120 in all positions? I have ruled out glulam beams because it would cost 28—30,000 SEK at Beijers.
But can't you go with only steel beams, but on cc600, or maybe cc900 instead?
Then it would be 17 steel beams and no wood. Or with cc900 11 beams.
Then it would be 17 steel beams and no wood. Or with cc900 11 beams.
But is 120 really enough for the steel beams? We have a 5m long HEA 180 in the intermediate floor in one place here in the house.
HiH hempularen said:
Your question can only be answered by the engineering. The only thing I can add is that maybe there are different conditions inside the floor of a house with greater loads compared to a deck?
Hi - I can't answer this but also assume that an HEA 120 or 140 outperforms other materials?Mikael_L said:
Sizing the roof so that it holds and does not sag too much is no problem to solve. However, there is a risk that it will sway when walking on the deck. Solving the swaying problem is a bit more complicated and will likely involve increased dimensions compared to just sizing so that they hold and do not sag too much.
Yes, you are probably right.B bossespecial said:
I have now had a structural engineer calculate this, and it has resulted in each of the positions having an HEB120. The sway and deflection will be minimal. It also withstands a minimum of 400 kg per square meter.
Hi see the answer below - with HEB120 at each position, this is more than sufficient.Y Yngve Levin said:
How close will the beams be placed and what were your plans for the rest of the roof construction?
As bossespecial points out, it is tricky to make it not too wobbly. As an alternative, I would suggest stronger and sparser steel beams as the primary support structure, possibly c/c 2400, and then wood perpendicular with c/c 600 as the secondary support structure. It's possible to recess the wood between the steel flanges to keep the height down. Assuming a snow load/useful load of 2 kN/m2 and a self-weight of 0.5 kN/m2 (estimates, must be verified), it might work with HEB 160 for the steel and 45x170 C24 for the wood. Just a thought.
The spacing should be 300 cc due to the specifications for the UPM-decking etc. on top. With a spacing of 300cc over approximately 9600 meters, there will be 31 truss positions, meaning 33 intervals of 300 mm with HEB 120 cc 300 at all positions and gable wall at both ends. Tongued and grooved boards on top of the joists, on top of which joists/regars are placed at the same spacing and positions as the trusses. Inside the H-beams, a 90 stud will be glued, which itself forms a recess for the longitudinal construction of the inner ceiling. This also braces against the shear forces. The project is not complete, but as far as HEB and UPM are concerned, it's more or less finalized now.B bossespecial said:
Hi - see my response below to bossespecial. It is anchored with a structural engineer. But with that said, maybe my current solution is not optimal. But for every 300cc, the UPM decks must have support all the way. UPmn is sort of on rails (the floor structure). I really appreciate your thoughts!J justusandersson said:
It's easy to lay the crosswise wooden beams at c/c 300 mm, even though it requires twice as many.