Pioneering projects

[vrvljs]

Hello, this is something a bit different and maybe not something for this forum but for anyone who is interested in helping I am very grateful.
So I have done some pioneering projects over the years with the scouts but never really studied the best way and the most structurally sound way of going about it (and there seems to be not a lot of people actually knowing how it works they seem to be all just putting thing together they have seen somewhere and making something new out of it and it does keep standing most of the time). I have tried and drawn some of the elementary pieces of a project like the 2 crossing diagonals with horizontal spars on long vertical spars (side of a tower for example) and some with spars joint lengthwise together and tried to figure out the best way of placing diagonals on it to minimize the stress on this rather weak joint. If someone would be interested in helping me with this I would be glad to hear I will attach a sketch with the rough idea for what it is that I would like to accomplish. (I have not studied anything in structural engineering or something similar only basic CAD software knowledge and some mechanics from school.)

Kind regards Jens

 

[phamENG]

vrvljs - as a once very active Boy Scout, I can certainly appreciate this. Almost killed a fellow scout when some ropes snapped while raising a too-heavy entrance gate while setting up for a summer camp one year.

However, I don't know that anyone has done any actual structural testing on your typical square lashing, etc. Likely too many variables to give accurate predictions. We typically like braces, beams, and columns to share a common working point through which all of there axes cross which, as you suggest, reduces the stresses in the joint. But with lashing spars together you have to offset the brace and the beam. You're best bet is typically to oversize the column a bit to take the small amount of moment that develops as a result.

I'd say, in general, the whole point of these projects is to not re-invent the wheel. The primary goal is to give the boys a chance to build something rather grand themselves using 'rudimentary' building materials. I would stick to the boiler plate structures and rules of thumb that have been published in the Handbook and the Pioneering Merit Badge book for decades. Now if the troop you're working with has exhausted all of those and is getting board with it or you're entering a competition and really want to push the limits, you're best bet is probably to find a local structural engineer with fond memories of their time in Scouting who would want to work on it...I have a feeling they'd jump at the opportunity if they have time.

 

[LittleInch]

Why not post the sketch or perhaps try in the Engineers with hobbies forum instead

https://www.eng-tips.com/threadminder.cfm?pid=1528

this one tends to be more about commercial and technical issues, not structures made by lashing bits of trees together...

There are some basics you can find such as what a 4 x 1 plank is a lot stronger when stressed in the 4 high mode than the 1 high mode.

And basic bracing / trusses and A frames. also things like putting reactions and loads onto beams not hanging loads off them.

but the quality and strength of the lashing is what limits you.

Having said that the chinese are pretty good at bamboo scaffolding. -

https://www.shutterstock.com/search/bamboo+scaffolding

Design manual

https://www.inbar.int/resources/inbar_publications/design-of-bamboo-scaffolds/

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[vrvljs]

Hello phamENG. Thanks for responding, ropes are indeed something to watch out for especialy in scouts where everthing is not load rated or has been used for many years already. Luckely ever since I replaced everthing with some decent synthetic ropes (its not like in the old days wich I am sad about but ist defently more durable)nothing has snapped yet. I am not realy looking for some detailed model of how much it could acutualy hold. I am looking more for some wisdom like what you mentioned of the common working point. And how these basic structures actualy work load wise how the cross in the structure helps with sideways forces. So i can place them in a spot that has the best use for it. The Handbook and the Pioneering Merit Badge book you mention those are things we do not have here everything is more mouth to mouth generation to generation if you still have those that could be useful. For the members we keep it to the basics this is more for leaders when we make some elaborate structures and towers wich the basic element are not enough.

I really appreciate you taking the time to answer.

 

[vrvljs]

Littleinch
Thanks for taking the time to answer. Indeed I will look to place this in the appropiate forum sorry for that.
Thanks for the links I will surely read them there seems to be some good information in them.


Kind regards Jens

 

[LittleInch]

I can only assume you know about this lot

https://scoutpioneering.com/tag/backwoods-engineering/

This seems to be what you're after?

https://scoutpioneering.com/2013/02/05/single-trestle-bridge/

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[rb1957]

yes thread may be better placed in our "engineers with hobbies" forum ?

another day in paradise, or is paradise one day closer ?

 

[phamENG]

Not sure I agree with the hobbies idea. This is somebody concerned about ensuring the safety of potentially a lot of kids using these temporary structures. Getting good advice from a structural engineer is probably wise. With that said, you should be aware, Jens, that we don't really give that kind of advice to non-engineers. This is supposed to be a professional forum for engineers to discuss technical topics with other engineers. Your issue just happens to bring up some very dear memories of my childhood.

Your profile suggests you're in Belgium. I would be surprised if you couldn't get your hands on the BSA handbook and merit badge books there. LittleInch's post is also a good one.

 

[kipfoot]

here's a troop with the pamphlet

https://www.troop109nj.com/merit-badge-library/

 

[vrvljs]

Hello all. Yes those sites are indeed helpful in the basic shapes , lashings and small projects. But most detailled texts stop at projects where the hight of the project is limited at the length of your spars. When round lashings are being used to make spars of 10+ meters ( where you do realy need some good support between them to keep them from colapsing.) not much info is available on the ideal placement of diagonals and horizontal lashing for support. Or even other supports for large towers that even tend to twist in a circular motion if made with only the 4 walls and no extra supports between poles diagonaly oppisite to eachother or between 2 walls.

 

[phamENG]

Trying to lash together 30ft poles is not a great idea. That was a surprising bright side to the bark beetle infestation we had - no shortage of dead 60ft poles with sound wood. We built some neat stuff out of those.

Like I said, stick to the typical, small projects unless you can find a local engineer with knowledge in the subject to help you.

 

[vrvljs]

Yes i am still looking for all books, sites and other media i can. From europe or american (harder to understand in english sometimes but also works) until now there is not much documentation on how to scale up these basic structures and most of these projects are made by just having a good idea of what you want starting from the bottom and as you build you put in the diagonals and other support you have planned and when it seems to be not enougt you look for a place to put something extra. This does work and is what I and most of the others i have asked do. But that is normaly not how towers are build by experts i think that seems like a lot of guessing and gut feeling for a engeneering project. Until now the projects under the 20m seem to hold with this method. But as they grow bigger the loads realy begin to add up when putting things that high. And the placelent and trying to reduce the stress on the weak lashings like the round lashings wich are plain and simple just 2 poles tied together to make a longer pole.

 

[vrvljs]

I think i will like you say try to get someone localy that has some understanding on this kind of construction or load distribution in general to explain it to me.

 

[epoxybot]

My thought off the bat was that lashings are serious business when it comes to sailing. Here's an interesting link.