Curved roof load calculations

I’ll look tomorrow. It’s been some time. They might be in Finnish only, with Finnish load requirements (we must prepare for a lot of wet snow, in some parts 2 m is not uncommon). Our structural wood members are made of local pine and spruce.
Edit: Here are tables for LVL beams, in English:

Glulam handbook(PDF):

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I use ForteWeb a lot. It’s produced by Weyerhaeuser mostly for it’s engineered wood products, which are the most common around here, but it also does commodity lumber available here. Other competing manufacturers have their own software as well. Outside the US market, I’m not sure how useful they are.

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As RTCool points out: straight beams and curved beams carry similar loads “in beam” if the ends of the curved beam are not constrained and/or the curvature ratio: height/span is very low: 1/20 etc. In my most recent designs I use parabolic arched columns to support a curved roof, but the height/span is approx 2/3 and I restrain the ends of the columns so the curved arch supports are mostly carrying the gravity snow loads in arch compression, which is very, very efficient. Wind side loads against my columns somewhat depend on “in beam” strength but they are less severe loads than snow loads for my structure. In my climate in the NW corner of the United States, snow loads in our mountains are significant: 120-lbs per square foot (with safety factor of 1.6 as is common in the ASCE building codes).

As mentioned in my first post above, I am not a structural engineer, so my opinions are only “amateur mixed with a bit of experience” and must be evaluated in that light. That said, I have spent the past 2 years working on residential home designs in an effort to devise more affordable structures, using materials more efficiently and even more important: reduce the time to manufacture and assemble the dwelling to the greatest extent possible. To that end, I will gladly spend more for a particular material choice, if in using it, time to construct is reduced even more.

SkyCiv FEA stress analysis tools have helped these efforts tremendously and given me some insight about various roof structures and the beams employed to support them. As others have mentioned: 9m is a serious span for a residential structure, but not as difficult if the loads your roof will see in the future are primarily wind loads (uplift is usually the worst case for nearly flat roofs) and not snow loading in your case. Perhaps in your location snow loads are non-existent or very modest. If this is the case my guess is your biggest roof loads as mentioned will likely be wind uplift. Depending on the shape of your house and the surrounding topography (high on a mountain escarpment ?, on a flat plain but with few trees to protect it ? …etc) wind uplift on a flat roof can generate loads (in imperial units) of 8 - 20 pounds/sqft acting upwards against gravity, depending on the calculated wind speed for your area in a gusting wind storm. -20psf may not sound like a lot but multiplied over the large surface area of your roof it generates substantial forces that work to rip the roof off your house. Your roof beams and all the parts of the roof that connect to them will need to resist this upward force in a wind storm. Normally your roof will work in the other direction to hold the weight of the roof and it’s materials from moving closer to the ground, but it is the unexpected forces, like wind uplift which must be thoroughly dealt with to keep the inhabitants inside the house safe.

Sometimes roof beams also need to resist what are called “moment forces”. These forces, for example, can act to push a wall over in an earthquake, but the roof beams working together with other structural members, add stability, shear resistance and what you might think of as torque resistance so that sideways forces to the house are resisted. Properly setup, SkyCiv can evaluate these forces against the house and the ability of the structural members to react safely.

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Yes, certainly it would be fine to message me directly. Unfortunately, I will have to ask other members what tools or procedures on this forum enable direct messaging.

Small world, in the late 1970’s when my mother studied for her Theology PhD in Boston and I visited her there from time to time, I would spend many happy hours in the Harvard and MIT architecture libraries researching various residential construction topics. Back then these libraries where “open stack” so members of the public could read there and at least photocopy the most relevant material, which I did copiously. My career diverged to computer control systems but architecture always fascinated me and I loved learning about many types of houses as you mention “Timber Frame” houses being one such.

It has always bothered me that during the past 100+ years, for all the incredibly talented architects and engineers throughout the world, none so far, that I am aware, have successfully solved the difficult problem of large scale affordable housing without the constraints imposed by “manufactured mobile homes” as they are known here in the United States. This has only gotten worse for the average family here and in many places in the world. Not having the talent possessed by these prior home designers, I attempt to contribute toward a solution using as much creative problem solving linked to my background in manufacturing (via my father the manufacturing engineer and my grandfather a very successful home builder/developer). We shall see… and it would be nice to have a patent too to carry on the family tradition.

Because my father co-founded an aerospace metal forming company in the early 1960’s here in Seattle, Washington State, based on his “axial load bulgeforming” patent I have always been comfortable working with metal lathes, milling machines … etc, which it seems you are experienced with as well and in the same informal “makers guild” as myself.

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Isn’t it a shame? Unfortunately, this system causes wasting forest, mine and energy resources to build weak structures. Ironically, in your country and most of Europe, this lunacy is being defended as ‘jobs for the citizens’, yet, kept alive by regularly taking in immigrants… In some cases, the same lunacy mandates borrowing for structures which will rot long before their mortgage is paid off…

Well, if problems are not solved nicely, they are solved awfully:

The best ever affordable housing was built in various countries in Europe (Sweden, Austria, Netherlands, Germany, for instance) by nonprofit organizations and communities in the time after WW I and before the Depression as just the kind of perimeter blocks like in your image, but three to four stories high (no elevators). Funny that the topic came up just after I watched a Swedish documentary series about the subject. This example from Helsinki, Finland.

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These look very nice… Not my favorite but nice. The ones in my picture are from St Petersburg Russia, they are awful…

18000 habitants and just one tennis court! (Yet they can still bring out the best tennis players of the world :stuck_out_tongue_closed_eyes:)

Yours look nice, except small windows. The sad thing about constructions in Northern countries is, buildings do not have enough light, since windows are kept small for energy preservation. Lack of sun contributes the darkness… Thanks to triple glazing and those low-e coatings, that is changing a little.

They are not so small as they look, especially in comparison to the very small rooms or kitchens they open into. I offered this only as an example. Not quite my style either.
Another way that was used was the one outlined by the garden city movement. Again, an example, some years earlier, from Helsinki, very simple wooden structures with small apartments:

I think affordable housing is a social, political and economic issue that cannot be solved by architects alone. There is currently no will.


here some examples in the Netherlands:

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Oops. I just realized that it is 40 years since I went to see those. (Amsterdam)

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Mike, I did not see it yet but I remember seeing that subject on TED Talks during my research:

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Anssi, here is what I like for a cold country, it is in Norway I guess:

It has ‘enough’ windows…))

I am uncertain if you want actual arched roof beams or just trying to accomplish a “look” similar to the photo provided.
Attached model has “standard” U.S. 3.5"x16" LVL w/2x6’s sistered to the LVL’s & beveled to match the radius for the sleepers to land flush.

Anyhow…just a suggestion and overhang at eave is left quite long and unresolved…built up studs for beam supports…etc

18mx7m_RadRoof_10_18_2021_V2015.skp (345.7 KB)

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Charlie, I wanted all. I like the look for sure but as far as I read, larger spans and more strength are possible with arched roofs so that is another reason. And I didn’t know that it was possible to create the arched look with straight elements, I am just learning it from you now.

Well, this is an option for sure…

Yeah…couple ways to “skin the cat”…attached find (2) additional options in that vein.
So just know what I have shared is a picture of a “bird”…it is up to others to make it fly. :slight_smile:

18mx7m_RadRoof_B_10_19_2021_V2015.skp (392.5 KB)

18mx7m_RadRoof_C_10_19_2021_V2015.skp (293.8 KB)

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Mark, I tried to send you a private message directly, but I don’t know if I succeeded or not. I did it by using the ‘message’ button which come out when I click your name to see your profile.

Hi - Architect here. Why do you need the long span? Assuming you have walls with glazing above which meets the roof then you do not want movement between them. Supporting the roof finish with rafters spanning front to back sitting on top of the curved beams is possible with them supported on each end bolted down to padstones, But it might be better to divide the span into three with two intermediate beams spanning front to back resting on stub columns bearing on the wall head. This would give you quite a saving in beam depth, which could then be made sectional thus making it easier to transport. It could also help by being more rigid and helping with wind load. Basically you don’t require a curved roof with a massive span when there is a shorter span available as a means of support. My advice would be to find a way to elegantly use it. It doesn’t matter where in the world your engineer is but you do need one. No sensible insurance company would cover this without proof of design competance. Good luck.

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Plusbyt, I am sorry for my late response, last week, I was far away from civilization, without any cellular signal.
About insurance coverage; before design competence of this roof and the rest of the structure, I think insurance companies will have a dozen other issues when considering to cover this house! Only if I can find some around! :laughing: :laughing: :laughing: :laughing:

Anyhow, yes, I think I found some engineer who can help me with the roof. I will take photos and detailed measurements to take to him. We also discussed possibility of him tutoring me basics of this subject, along with the basics of the software he uses.
Thank you very much for all the details. Yes, a long span is expensive and I will share your advices with him. I am hoping to post results after we move further.
Thanks a lot ! ))

Very sorry for such a late delayed reply. Just tonight I saw your email and have sent an email reply. We can proceed I hope in the next few days if my hectic schedule will allow. Many regards.

Upps, I was far away from civilization again, so I just saw yours now also…
Nope, there is no message in my inbox… Let me try to send you a message again…
I just did, now…