Choosing a front girder for the balcony - glulam or steel?

[Kobolt]

Hello,
I am planning to build a balcony according to the picture below.
I have been looking for alternatives for the front beam, leaning towards glulam or possibly a steel beam.

I want to keep the height of the beam down so as not to obstruct the view from inside the house, around 300 is the limit. The span is about 4.5m, so my knowledge tells me that a 115x315 would be insufficient. If anyone is experienced in calculating balconies (snow zone 2), please feel free to share what needs to be considered.

(The beam is placed 3m from the wall, the total roof area is 3.5x5m, the area for the balcony decking itself is 2.7x3.8)

Also looking at HEA beams but am unsure about the suitable dimension and how best to attach them to posts and floor joists, etc. I have seen variations with wooden beams that push against the web of the steel beam but I would like them to be securely attached and not just resting.

Any suggestions on dimensions or other tips??... PS. I do not want a third post in the middle

Thankful for any responses I can get.

 

[huggan]

Snow zone 2 corresponds to 200 kg/sqm, a normal wooden floor corresponds to 200kg/sqm. Since the terrace is not used in the winter, you don't need to significantly increase the load capacity.

What type of roof construction will you have?

If I calculate with a heavy roof, self-weight of 90kg/sqm, snow zone 2, and your spans, you can manage with a 66*315 glulam beam; if you use 115*315, you know it will hold.

 

[Kobolt]

Hello and thanks for your response, huggan. I'm happy to go with glulam...
but according to EKS on boverket.se, balconies are dimensioned according to 3.5kN/sqm but point load at 2kN.
I've tried calculating with 3.5+self-weight 2kN/sqm and then I need to go up to at least height 115*370mm to avoid a deflection greater than 25mm. (I've calculated an approximate load of 52kN evenly distributed over the length of the beam).

Please tell me I'm wrong. :eek:

For the roof, I'm planning to cover it with sheet metal and then a simple decking on the sheet metal with a railing.
/Kobolt

 

[huggan]

What do you mean by point load 2kN? And considering self-weight 2 kN is very high.

How did you determine that the load becomes 52 kN? Sounds like a lot.

The slope is 4 degrees? Roof overhang?

 

[huggan]

90*315 can handle 52 kN, however, 66*315 cannot. Distributed load, that is.

 

[larsbj]

The point load of cobalt should be considered in design, but in the Eurocode, it states distributed or point load so they do not need to be combined.

 

[larsbj]

What I think you are forgetting is that all the loads you mention are characteristic values that need to be accounted for when calculating the beam, and even the bending resistance of the glulam should be designed based on load duration and climate class.

If you are to design the above as a balcony, a glulam beam 140x315 is required. Alternatively, HEA160.

But I think it is incorrect reasoning since the balcony values are intended for cantilever constructions, so it's probably values for a regular floor that are reasonable to use.

This would mean that 90x315 is a sufficient dimension for a glulam beam. Alternatively, HEA140.

I have calculated the actual self-weights to 2.4 KN/m beam, approximately 0.7 KN/m2.
Used safety class 2
Medium load duration
And climate class 2
Calculated in the ultimate limit state with the Eurocode formulas B1a and B2a.

 

[Kobolt]

Thank you for the wise words. I probably interpreted everything very conservatively and took a too high value for the self-weight on the floor structure.

What do you think the deflection would be, larsbj? I got more than 25mm with the 315 beam. What can be acceptable?

 

[larsbj]

With 90x 315 I get 27 mm. But that's when you have 3000 kg of load in the form of snow or furniture and people, so it probably won't happen very often So, a maximum of 35 people at the balcony party.

 

[Kobolt]

Then it will probably be a 90x315 or 115, so there's a bit of margin if I need to make any cutouts.
Thanks for the great answers from both of you. I have learned quite well how glulam is dimensioned and can avoid the steel beam.

 

[mani33]

I am trying to size a front beam for my balcony as I am replacing all the wood because it is rotten. Then I will build a sunroom under the balcony, which means I want to remove the middle post; today there are three posts. The glulam beam then needs to be six meters long and will support a balcony that is about 140 cm deep.

What dimension will I actually need for the front beam? I live in snow zone 2.5. I plan to attach it to the existing beam in the wall.