Curved roof load calculations

SketchUp
1

Hi, I have a question about abilities of Sketchup.

I acquired a very old, single story stone house with a gable roof made of timber beams and red tiles. Beams are very old, there is insect damage and and the roof leaks… But foundation and the stone walls are in great shape. I want to crush the roof down and build a new one, but this time, a curved one, like the one in the picture I attached; curved, and made with metal sheets instead of tiles.

Curve 1

But since the house is in the in the middle of nowhere, it is impossible to find an architect or structural engineer around. Moreover, for the specific case of this house and its location, it is not feasible to hire one even if he accepts to prepare the project from his location. But I have access to CNC machines and high quality African lumber, glulam, and LVL, in a city 250 Km away, where I manufactured many kitchens, bathrooms and furniture with those resources.

Naturally, I had this idea of building the roof myself, with some affordable aid I can bring from that city (low cost labor and currency). I can obtain local live load data, and material specs & span tables etc. for the materials I listed above. And code compliance is not an issue I cannot handle here, once I have solid calculations to offer to officials. Actually, if I can make my case with a nicely done job and with proper calculations, they will even try to hire me for renewal of their leaking roofs as well! :stuck_out_tongue_closed_eyes:

Anyways, the question:
I was wondering if it is possible to make load bearing calculations of a curved roof with Sketchup and its plugins ?

Best regards,
JohnA
Edit: If not, would you recommend another solution?

2

I don’t believe there are any real load analysis extensions for SketchUp. Part of the problem is there’s no mating of objects in SketchUp.

1 Like
3

I would forget about the pitch when making the calculations, and dimension the members as if the roof was flat.

1 Like
4

One problem with answering your question is knowing the size of your proposed roof. If we are talking about something the size of the house in the picture, you may well use timber joists laid horizontally but they would need to be supported on structural beams at right angles to them. They could be Glulam beams or in radiused steel. But if the span is great, the Glulams would be pretty deep. I suspect you’re going to need a structural engineer but I don’t see why they could not assist even if they were a long way away - providing they are given all the info they need.

1 Like
5

I’m also not aware of any SU extensions for load calculations.
Aside from this, if you want to pursue the steel sheeting solution you suggest, you should consider the minimum pitch that is acceptable for the profile you choose; taking your reference picture as an example, that roof could be achieved with multiple sheets of 'secret-fix, or ‘zip-lock’ type of sheeting, pre-formed or formed on site to go from eaves to eaves in one piece. That depends of course where your house is located and if such a machine is available, and if not, you would need to increase the pitch and use 2 side pieces plus a ridge piece instead.

1 Like
6

This Previous Post may be of some help…

2 Likes
7

I have had great success for the past 2 years using the online stress analysis suite of tools: SkyCiv, from an Australian firm. SkyCiv uses a FEA (Finite Element Analysis) engine to perform very detailed structural analysis of a model you input in the S3D (SkyCiv Structural 3D) drawing workspace. Without the help of SkyCiv, my efforts to design more affordable housing options for my small startup company would be quite fruitless.

Support from the SkyCiv staff is exemplary using a real time texting window inside the app, however, I do not expect them to teach me how to use FEA generally, or how to define a stress analysis model, nor the myriad things a real structural engineer would know from college, only answer specific questions about the SkyCiv implementation of stress analysis in their tools.

I am a retired embedded computer systems designer (industrial metal forming machinery) from the late 1970’s, comfortable designing small architecture projects, but certainly NOT a trained architect, or a structural engineer. If I can teach myself to use SkyCiv productively to analyze my residential architecture structures then I believe anyone with a technical background such as yourself could do the same. That said, the learning curve was pretty steep, but worth it in my case. I think there is a SkyCiv feature to import STL models into the S3D drawing space to jumpstart your model structure’s outline, but I would not recommend using it initially. You should learn how to define your structure’s member elements: iBeams, columns, steel angles, wood members as S3D’s wireframe model. This wireframe can be converted into a rough 3D rendering to help us humans confirm it is placing the right kind of structural members where you want them …etc, but the wireframe model definition of your structure is what the FEA engine uses to do the analysis. After “solving” your model based on the load inputs: snow loads, wind, etc, you define, it will generate a nice series of stress diagrams for each structural element, and also a color coded 3D rendering of your structure to show you how much the structure is moving physically, what myriad stresses are happening inside the members and so forth.

I am using parabolic curved elements in my current design, but having an awful time getting Sketchup to curve my parts in my drawing, while SkyCiv has given me only a fraction of the grief Sketchup has to represent curved elements properly. I have tried to use the Flowify extension in my SU-2021-pro on a very powerful MacOS workstation, but it keeps crashing SU, which other extensions do not. Honestly, these problems with SU are so frustrating, I am happier to type in a long post to help you rather return to using SU to curve objects along a parabolic surface.

Hope your project goes well. I will make an effort to circle back here should you decide to try SkyCiv. They have a 7 day free trial period I think. My monthly “professional” subscription cost a reasonable $110 USD. For me the cost is a bargain given the answers it provides before I submit my design to our local professional structural engineer who has worked on other projects for my wife and I.

Good luck.

1 Like
8

DaveR, I am sorry to hear that. But thanks a lot for taking the time to write. :slightly_smiling_face:

9

Anssi, that is a brilliant idea actually. It may force me to pay more for beams, since a curved system can carry more load, and with trusses, even a lot more, I presume that less wood can be used for curved systems, compared to a straight ones. And they look a lot a lot cooler than hip or gable ones. Besides, I believe that with a curved system, sagging of the beams in time won’t be an issue either. So, your suggestion has a great value… I am working on it! THANKS!

10

Just don’t forget that everything about a curved roof is ultimately more expensive, from the bare structure to every other sub involved.

1 Like
11

Thank you very much for your answer. The building is simply rectangular, 18 meters x 7 meters. To make it look as good as the one in the picture I fell in love with, beams must cover the 18 meters distance, plus cantilever distance. Yes, gluelams will be deep, but they can be supported in the middle, 9 meters. Inner walls are negligible, we can change them. They can not be radiused steel because I cannot find it here, they should be imported, lots of complications, starting with hich cost and procedures. I am not in the US or EU. Yes an engineer would be very nice but as I mentioned above, even they can assist from way away, they will be a cost, and in this banana republic, this building in the middle of nowhere will never earn that money back, this is why I am trying to find a cheap solution.

12

Rodman, thanks a lot I will read it !

13

Phillip_H, thanks a lot for your valuable info. I will study those asap. Thanks!

14

Sonder, thanks! I will study the matter asap… Thanks…

15

It may be easy to say this from the comfort of a first world country, but what you write would worry the bejesus out of me! It looks like you aim to build a Glulam beam capable of supporting a domestic roof a staggering 9m without professional design input and justification! If that is the case, don’t ask me to visit.

A conventional European house rarely has a roof width greater than 7m and that is with a double pitch and (usually) tied rafter ends.

You’ll tell me next that you plan to make your own home-made Glulam beams from sheets of plywood and some woodworking glue, aren’t you? If so, I applaud your endeavour but worry for your sanity!

3 Likes
17

Simoncbevans, well, I agree with your concerns! You are right and this is why I am studying the matter to see how much of it I can handle… It will take time for me to learn enough, but well, in case you decide to visit me, this gives you time to start your shots since they are multiple, some of them takes a year to complete. Before you leave customs to go to the gates, will be asked to provide proofs of shots, for: measles, mumps, rubella, polio, hepatitis A & B, diphtheria, pertussis and tetanus! )))) See, you have some other issues you have to worry before a 9 meters curved arch)))

About building something from glulam beams and plywood and glue: Well, this house is stone, if I decide to do what you said, I would use CLT and marine quality plywood instead but never glues! Instead, I would use metal connectors! And I hate hammers and nails, they just destroy the product. I built many things and I do not own a hammer. But I can personally manufacture my own fastening components with a lathe machine… And I would use Inox 316 marine type fasteners, along with different metals and engineering plastics such as delrin and teflon, with lots of lubricant and torque adjustable wrenches to prevent galling… That is how I learned while I was working with a boat builder, he is exporting fantastic boats to Switzerland. And our boats are still in perfect shape, unlike many ‘code compliant’ houses in many first world countries. )))

18

What I meant was that at least in our parts, we have online calculators or tables for simple glulam or laminated veneer lumber beams. Required load is specified in local code. The difference in size between a flat roof and a slightly curved one would probably be measured in some millimeters. Trusses, then, are a different thing. We used to have standard drawings for in situ nailed trusses but nowadays nobody makes them by themselves.

2 Likes
19

This is correct. If both are simply continuous beams with three points of support, there’s no real difference. The curve only becomes more efficient if there is something to resolve outward thrust like abutments or a tie. A steel tie rod across the cord of the arc would make a difference.

1 Like
20

Mark, like all other messages I received, your answer is also very useful. It is also very comprehensive. Thank you very much! Tomorrow, I will visit their site and read all I see.

Another thing, while searching for business opportunities, I read reports presented to US Congress, and I regularly read reports of Harvard Dept of Housing Studies, and reports from many think tanks. Based on what I learned so far, I believe that subject you mentioned, ‘affordable housing’, has a huge potential in the US, due to multiple upcoming factors effective on that matter.

Furthermore, seeing the ‘quality and styles’ of some timber frame houses in the US, (I studied there), I am very curious about the vision of a computer systems designer on this subject.

I wish I had the chance to chat with you about this subject a little. So, may I message you directly?

22

Anssi, thanks a lot, I will do that ASAP.
In the meantime, I really appreciate if you can give me the names of the calculators you use, if they are online? Names are more than enough, I will search for them…